SI20278A - Ultra-high strenght steels with excellent cryogenic temperature toughness - Google Patents

Abstract

An ultra-high strength, weldable, low alloy steel, containing less than 9 wt.% nickel, with excellent cryogenic temperature toughness in the base plate and in the heat affected zone (HAZ) when welded, having a tensile strength greater than 830 MPa (120 ksi) and a microstructure comprising predominantly fine-grained lath martensite and/or fine-grained lower bainite, is prepared by heating a steel slab comprising iron and some or all of the additives carbon, manganese, nickel, nitrogen, copper, chromium, molybdenum, silicon, niobium, vanadium, titanium, aluminum, and boron; reducing the slab to form plate in one or more passes in a temperature range in which austenite recrystallizes; finish rolling the plate in one or more passes in a temperature range below the austenite recrystallization temperature and above the Ar3 transformation temperature; quenching the finish rolled plate (10''') to at a suitable Quench Stop temperature; stopping the quenching; and tempering the plate (10''') at a suitable temperature for a period of time sufficient to cause precipitation of hardening particles.

Description

PODROČJE IZUMAFIELD OF THE INVENTION

Predloženi izum se nanaša na nizko legirane jeklene plošče z ultra visokimi trdnostmi, ki se dajo variti, z odlično žilavostjo pri kriogenih temperaturah tako v matični plošči kot tudi v coni, prizadeti s toploto (HAZ) pri varjenju. Nadalje se predloženi izum nanaša na postopek za pripravo takih jeklenih plošč.The present invention relates to low-alloy, weldable ultra-high strength steel plates with excellent toughness at cryogenic temperatures both in the motherboard and in the heat affected zone (HAZ) during welding. The present invention further relates to a process for preparing such steel plates.

OZADJE IZUMABACKGROUND OF THE INVENTION

V naslednjem opisu so definirani različni izrazi. Za pomoč je tik pred zahtevki slovar izrazov.The following description defines different terms. For help, just before the requests is a dictionary of terms.

Pogosto je potrebno skladiščiti in transportirati hlapne tekočine pod tlakom pri kriogenih temperaturah, t.j. pri temperaturah pod okoli -40 °C. Npr. obstaja potreba po posodah za skladiščenje in transportiranje utekočinjenega naravnega plina pod tlakom (PLNG) pri tlaku v širokem območju okoli 1035 kPa do okoli 7590 kPa in pri temperaturi v območju okoli -123 °C do okoli -62 °C. Obstaja tudi potreba po posodah za varno in ekonomično skladiščenje in transportiranje drugih hlapnih tekočin z visokim parnim tlakom, kot so metan, etan in propan, pri kriogenih temperaturah. Za take posode, ki naj bi jih konstruirali iz varjenega jekla, mora imeti jeklo primemo trdnost, da zdrži tlak tekočine, in primemo žilavost za preprečevanje iniciacije preloma, t.j. odpovedi, pri pogojih obratovanja tako pri matičnem jeklu kot tudi pri HAZ.It is often necessary to store and transport volatile pressurized liquids at cryogenic temperatures, i.e. at temperatures below -40 ° C. E.g. there is a need for containers for the storage and transport of liquefied natural gas under pressure (PLNG) at pressures in the wide range of about 1035 kPa to about 7590 kPa and at temperatures in the range of -123 ° C to about -62 ° C. There is also a need for vessels for the safe and economical storage and transportation of other volatile liquids with high vapor pressure, such as methane, ethane and propane, at cryogenic temperatures. For such vessels to be constructed of welded steel, the steel must have a strength to withstand the fluid pressure and a toughness to prevent fracture initiation, i.e. failures under operating conditions for both parent steel and HAZ.

Temperatura prehoda od kovnega do krhkega (DBTT) opisuje oba režima prelomov v konstrukcijskih jeklih. Pri temperaturah pod DBTT večkrat pride do odpovedi v jeklu zaradi nizko energijskega razkolnega (krhkega) preloma, medtem ko pri temperaturah nad DBTT večkrat pride do odpovedi v jeklu zaradi visoko energijskega kovnega preloma. Varjena jekla, uporabljena pri konstrukciji skladiščnih in transportnih posod za preje omenjene kriogene temperaturne aplikacije in za druga opravila pod obremenitvijo pri kriogenih temperaturah, morajo imeti DBTT precej pod temperaturo opravila tako pri matičnem jeklu kot tudi pri HAZ, da se izognemo odpovedi zaradi nizko energijskega razkolnega preloma.The transition temperature from forged to brittle (DBTT) describes the two fracture modes in structural steels. At temperatures below DBTT, steel failure is repeatedly caused by a low-energy fracture (brittle) break, while at temperatures above DBTT, steel failure is repeatedly caused by a high-energy fracture. Welded steels used in the construction of storage and transport containers for yarns of said cryogenic temperature application and for other cryogenic temperatures under load must have DBTT well below the temperature of the parent steel as well as HAZ to avoid failure due to low energy split fracture.

Jekla, ki vsebujejo nikelj, običajno uporabljana za konstrukcijske uporabe pri kriogenih temperaturah, npr. jekla z vsebnostmi niklja nad okoli 3 mas.%, imajo nizke DBTT, imajo pa tudi relativno nizke natezne trdnosti. Tipično imajo tržno dostopna jekla s 3,5 mas.% Ni, 5,5 mas.% Ni oz. 9 mas.% Ni DBTT okoli -100 °C, -155 °C oz. -175 °C in natezne trdnosti do okoli 485 MPa, 620 MPa oz. 830 MPa. Da bi dosegli te kombinacije trdnosti in žilavosti, ta jekla na splošno podvržejo dragi predelavi, npr. dvojni žarilni obdelavi. V primeru aplikacij pri kriogenih temperaturah industrija sedaj uporablja ta komercialna jekla, ki vsebujejo nikelj, zaradi njihove dobre žilavosti pri nizkih temperaturah, vendar mora obiti njihove relativno nizke natezne trdnosti. Za to so na splošno potrebne izredne debeline jekel za aplikacije pri kriogenih temperaturah pod obremenitvijo. Tako je uporaba teh jekel, ki vsebujejo nikelj, pri aplikacijah pri kriogenih temperaturah pod obremenitvijo navadno draga zaradi visoke cene jekla v kombinaciji z zahtevanimi debelinami jekla.Nickel-containing steels commonly used for structural applications at cryogenic temperatures, e.g. steels with nickel contents above about 3% by weight, have low DBTTs and also have relatively low tensile strengths. Typically, commercially available steels with 3.5 wt.% Ni, 5.5 wt.% Or. 9 wt% no DBTT around -100 ° C, -155 ° C, or. -175 ° C and tensile strengths of up to about 485 MPa, 620 MPa, respectively. 830 MPa. In order to achieve these combinations of strength and toughness, these steels generally undergo expensive processing, e.g. double annealing processing. In the case of cryogenic temperature applications, the industry now uses these commercial nickel-containing steels because of their good toughness at low temperatures, but must bypass their relatively low tensile strengths. This generally requires extraordinary thicknesses of steel for applications at cryogenic temperatures under load. Thus, the use of these nickel-containing steels for applications at cryogenic temperatures under load is usually costly due to the high cost of steel combined with the required thicknesses of steel.

Po drugi strani mnoga tržno dostopna uveljavljena nizko legirana jekla z malo in srednje veliko ogljika z visokimi trdnostmi (HSLA jekla), npr. jekla AISI 4320 ali 4330, potencialno nudijo boljše natezne trdnosti (npr. večje kot okoli 830 MPa) in nizko ceno, imajo pa relativno visoke DBTT na splošno, zlasti pa v coni, prizadeti z varilno toploto (HAZ). Na splošno je pri teh jeklih tendenca, da se varivost in nizko temperaturna žilavost zmanjšujeta, ko se povečuje natezna trdnost. Zaradi tega razloga se sedaj tržno dostopna uveljavljena HSLA jekla na splošno ne upoštevajo za aplikacije pri kriogenih temperaturah. Visoka DBTT od HAZ pri teh jeklih je na splošno zaradi tvorbe neželenih mikrostruktur, ki izvirajo iz varilnih termičnih ciklov v interkritično ponovno segretih HAZ grobe zmavosti, t.j. HAZ, ki so segrete na temperaturo od okoli Aci transformacijske temperature do okoli AC3 transformacijske temperature (glej slovar za definiciji Ac_t in Ac₃ transformacijskih temperatur). DBTT se znatno povečuje z naraščajočo velikostjo zrn in mikrostrukturnimi sestavinami, ki povzročajo krhkost, kot so otočki martenzita - avstenita (MA), v HAZ. Npr. DBTT za HAZ v uveljavljenem HSLA jeklu za XI00 cevovode za prenos olja in plina je nad okoli -50 °C.On the other hand, many commercially available low and medium carbon high strength (HSLA) steels, e.g. AISI 4320 or 4330 steels, potentially offering better tensile strengths (e.g. greater than about 830 MPa) and low cost, but have relatively high DBTTs in general, and especially in the weld zone (HAZ). Generally, for these steels, the tendency for weldability and low temperature toughness to decrease as the tensile strength increases. For this reason, commercially available established HSLA steels are generally not considered for applications at cryogenic temperatures. The high DBTT of HAZ in these steels is generally due to the formation of unwanted microstructures arising from welding thermal cycles in intercritically reheated HAZ coarse particles, i.e. HAZ, which are heated to a temperature from about Aci transformation temperature to about AC3 transformation temperature (see glossary for definitions of Ac _t and Ac ₃ transformation temperatures). DBTT increases significantly with increasing grain size and fragility-causing microstructural components, such as islets of martensite - austenite (MA), in HAZ. E.g. DBTT for HAZ in established HSLA steel for XI00 oil and gas transmission pipelines is above -50 ° C.

Obstajajo znatne pobude v sektorjih energijskega shranjevanja in transporta za razvoj novih jekel, ki združujejo lastnosti nizko temperaturne žilavosti zgoraj omenjenih tržnih jekel, ki vsebujejo nikelj, z lastnostmi visoke trdnosti in nizke cene HSLA jekel, obenem pa je tudi zagotovljena odlična varivost in želena primernost .debelega preseka, t.j. v bistvu enakomerna mikrostruktura in lastnosti (npr. trdnost in žilavost) pri debelinah nad okoli 2,5 cm.There are significant initiatives in the energy storage and transport sectors for the development of new steels that combine the low-temperature toughness properties of the above-mentioned nickel-containing market steels with the high strength properties and low cost of HSLA steels, while ensuring excellent weldability and desired suitability. thick cross section, i essentially a uniform microstructure and properties (eg strength and toughness) at thicknesses above about 2.5 cm.

Pri ne-kriogenih aplikacijah je večina tržno dosegljivih, uveljavljenih HSLA jekel z malo in srednje veliko ogljika zaradi svoje relativno nizke žilavosti pri visokih trdnostih zasnovana bodisi z delčkom njihovih trdnosti ali po drugi strani predelana do nižjih trdnosti za doseganje primerne žilavosti. Pri konstrukcijskih aplikacijah vodijo ti pristopi do povečane debeline preseka in zato do višjih mas komponent in končno višje cene, kot če bi lahko v celoti uporabili potencial visoke trdnosti HSLA jekel. Pri nekaterih kritičnih aplikacijah, kot so visoko učinkovita gonila, uporabljajo jekla, ki vsebujejo nad okoli 3 mas.% Ni (kot AISI 48ΧΧ, SAE 93ΧΧ itd.) za vzdrževanje zadostne žilavosti. Ta pristop vodi do bistvenega povečanja stroškov, da bi dosegli izredno trdnost HSLA jekel. Dodaten problem, ki ga srečajo pri uporabi standardnih tržnih HSLA jekel, je razpokanje zaradi vodika v HAZ, zlasti kadar uporabljajo varjenje z nizkim vnosom toplote.For non-cryogenic applications, most commercially available, low- and medium-carbon HSLA steels are designed, due to their relatively low toughness at high strengths, either with a fraction of their strengths or, on the other hand, processed to lower strengths to achieve adequate toughness. For structural applications, these approaches lead to increased cross-section thickness and therefore to higher component masses and ultimately higher cost than if the high strength potential of HSLA steels could be fully utilized. For some critical applications, such as high efficiency gearboxes, steels containing more than about 3% by weight (such as AISI 48ΧΧ, SAE 93ΧΧ, etc.) are used to maintain sufficient toughness. This approach leads to a significant increase in costs to achieve the exceptional strength of HSLA steels. An additional problem encountered with the use of standard market HSLA steels is the cracking due to hydrogen in HAZ, especially when using welding with low heat input.

Obstajajo znatne ekonomske pobude in določena konstrukcijska potreba po povečanju žilavosti ob visokih in ultra visokih trdnostih pri nizko legiranih jeklih, z nizkimi stroški. Zlasti gre za potrebo po jeklu z zmerno ceno, ki ima ultra visoko trdnost, npr. natezno trdnost nad 830 MPa, in odlično žilavost pri kriogenih temperaturah, npr. DBTT pod okoli -73 °C, oboje v matični plošči in v HAZ, za uporabo pri tržnih aplikacijah pri kriogeni temperaturi.There is considerable economic incentive and a certain structural need to increase the toughness at high and ultra high strengths of low alloy steels at low cost. In particular, there is a need for a moderately priced steel having ultra high strength, e.g. A tensile strength exceeding 830 MPa and an excellent toughness at cryogenic temperatures, e.g. DBTT below about -73 ° C, both in motherboard and HAZ, for use in commercial applications at cryogenic temperature.

Torej so primarni predmeti predloženega izuma izboljšati uveljavljeno tehnologijo nizko legiranih jekel z visokimi trdnostmi za uporabnost pri kriogenih temperaturah na treh ključnih področjih: (i) znižanje DBTT na pod okoli -73°C v matičnem jeklu in v varilni HAZ, (ii) doseganje natezne trdnosti nad 830 MPa in (iii) zagotavljanje izredne varivosti. Drugi predmeti predloženega izuma so, da pridemo do preje omenjenih HSLA jekel z bistveno enakomernimi mikrostrukturami po vsej debelini in lastnostmi pri debelinah nad okoli 2,5 cm, za to pa uporabimo sedanje tržno dostopne procesne tehnike, tako da je uporaba teh jekel pri komercialnih postopkih pri kriogenih temperaturah ekonomsko izvedljiva.Therefore, the primary objects of the present invention are to improve the established technology of low-alloy steels with high strengths for serviceability at cryogenic temperatures in three key areas: (i) lowering DBTT to below -73 ° C in parent steel and welding HAZ, (ii) achieving tensile strengths exceeding 830 MPa and (iii) providing exceptional weldability. It is a further object of the present invention to provide yarns of the aforementioned HSLA steels with substantially uniform microstructures throughout their thickness and properties at thicknesses above about 2.5 cm, using current commercially available process techniques such that the use of these steels is commercially available at cryogenic temperatures economically feasible.

POVZETEK IZUMASUMMARY OF THE INVENTION

V skladu z zgoraj navedenimi predmeti v smislu predloženega izuma gre za procesno metodologijo, pri kateri nizko legiran jekleni slab želene kemije ponovno segrejemo do primerne temperature, nato vroče valjamo, da nastane jeklena plošča, in hitro ohladimo na koncu vročega valjanja z gašenjem s primemo tekočino, kot vodo, do primerne temperature po ustavitvi gašenja (QST), da pretvorimo mikrostrukturo jekla v prednostno pretežno fino zmav letvast martenzit, fino zmav nižji bainit ali njihove zmesi, ter nato s popuščanjem v primernem temperaturnem območju, da dobimo mikrostrukturo v popuščenem jeklu, ki prednostno obsega pretežno popuščen fino zmav letvast martenzit, popuščen fino zmav nižji bainit ali njihove zmesi ali bolj prednostno obsega v bistvu 100% popuščenega fino zmavega letvastega martenita. Gašenje, kot se uporablja pri opisu predloženega izuma, se nanaša na pospešeno hlajenje na katerikoli način, pri Čemer uporabimo tekočino, izbrano zaradi njene tendence, da poveča hitrost hlajenja jekla, v nasprotju z zračnim hlajenjem jekla, do sobne temperature. Pri eni izvedbi v smislu predloženega izuma jekleno ploščo zračno ohladimo do sobne temperature po tem, ko smo ustavili gašenje, in pred popuščanjem.According to the foregoing objects of the present invention, it is a process methodology in which the low-alloy steel of poor chemistry of the desired chemistry is re-heated to a suitable temperature, then hot-rolled to form a steel plate, and rapidly cooled at the end of the hot-rolling quench with the applied liquid , as water, to a suitable quenching temperature (QST) to convert the microstructure of the steel into a preferred predominantly fine lath martensite, fine lime lower bainite or mixtures thereof, and then by yielding in a suitable temperature range to obtain a microstructure in the lowered steel, which preferably comprises a predominantly yielded finite dragon molded martensite, a finely loosened finer dragon bainite or mixtures thereof, or more preferably comprises substantially 100% rebounded finely dragged molded martensite. Quenching, as used in the description of the present invention, refers to accelerated cooling in any way, using a fluid selected because of its tendency to increase the rate of cooling of steel, as opposed to air cooling of steel, to room temperature. In one embodiment of the present invention, the steel plate is air-cooled to room temperature after stopping the quenching and before quenching.

Tudi v skladu z zgoraj navedenimi predmeti predloženega izuma so jekla, predelana v skladu s predloženim izumom, zlasti primerna za mnoge aplikacije pri kriogenih temperaturah v tem, da imajo jekla naslednje karakteristike, prednostno za debeline jeklene plošče okoli 2,5 cm in več: (i) DBTT pod okoli -73°C v osnovnem jeklu in v varilni HAZ, (ii) natezno trdnost nad 830 MPa, prednostno nad okoli 860 MPa in bolj prednostno nad okoli 900 MPa, (iii) izredno varivost, (iv) v bistvu po vsej debelini enakomerno mikrostrukturo in lastnosti ter (v) izboljšano žilavost v primerjavi s standardnimi tržno dostopnimi HSLA jekli. Ta jekla imajo lahko natezno trdnost nad okoli 930 MPa ali nad okoli 965 MPa ali nad okoli 1000 MPa.Also, in accordance with the foregoing objects of the present invention, the steels processed according to the present invention are particularly suitable for many applications at cryogenic temperatures in that the steels have the following characteristics, preferably for steel plate thicknesses of about 2.5 cm or more: ( i) DBTT below about -73 ° C in base steel and in welding HAZ, (ii) tensile strength above 830 MPa, preferably above about 860 MPa and more preferably above about 900 MPa, (iii) extremely weldable, (iv) essentially uniform microstructure and properties throughout the thickness and (v) improved toughness compared to standard commercially available HSLA steels. These steels may have a tensile strength of about 930 MPa or above about 965 MPa or above about 1000 MPa.

OPIS RISBDESCRIPTION OF THE DRAWINGS

Prednosti predloženega izuma bomo bolje razumeli ob sklicevanju' na naslednji podroben opis in priložene risbe, kjer je sl. 1A shematski prikaz velikosti zm austenita v jeklenem slabu po ponovnem segrevanju v smislu predloženega izuma;The advantages of the present invention will be better understood by reference to the following detailed description and the accompanying drawings, in which: FIG. 1A is a schematic view of the size of austenite in steel poor after reheating according to the present invention;

sl. IB shematski prikaz predhodne velikosti zm austenita (glej slovar) v jeklenem slabu po vročem valjanju v temperaturnem območju, v katerem austenit rekristalizira, vendar pred vročim valjanjem v temperaturnem območju, v katerem austenit ne rekristalizira, v skladu s predloženim izumom; in sl. IC shematski prikaz podaljšane ploske strukture zm v austenitu, z zelo fino efektivno velikostjo zm v smeri po debelini, jeklene plošče po dokončanju TMCP v smislu predloženega izuma.FIG. IB is a schematic illustration of a previous size of austenite (see glossary) in steel bad after hot rolling in a temperature range in which austenite recrystallizes but before hot rolling in a temperature range in which austenite does not recrystallize, in accordance with the present invention; and FIG. IC schematic illustration of an extended planar structure of the zm in austenite, with a very fine effective size of the zm in the thickness direction, of the steel plate after completion of the TMCP of the present invention.

Čeprav bomo predloženi izum opisali v zvezi z njegovimi prednostnimi izvedbami, se razume, da izum nanje ni omejen. Nasprotno, mišljeno je, da izum pokriva vse alternative, modifikacije in ekvivalente, ki so lahko vključeni v duha in obseg izuma, kot je definirano s priloženimi zahtevki.Although the present invention will be described with reference to its preferred embodiments, it is understood that the invention is not limited thereto. On the contrary, it is intended that the invention covers all alternatives, modifications and equivalents that may be included in the spirit and scope of the invention as defined by the appended claims.

PODROBEN OPIS IZUMADETAILED DESCRIPTION OF THE INVENTION

Predloženi izum se nanaša na razvoj novih HSLA jekel, ki izpolnjujejo zgoraj opisane izzive. Izum temelji na novi kombinaciji kemije jekla in predelave, da zagotovimo tako intrinzično kot tudi mikrostruktumo žilavost, da znižamo DBTT kot tudi da povečamo žilavost pri visokih nateznih trdnostih. Intrinzično žilavost dosežemo z razumnim ravnotežjem kritičnih legimih elementov v jeklu, kot je podrobno opisano v tem opisu. Mikrostruktuma žilavost je posledica tega, da dosežemo zelo fmo efektivno velikost zrn kot tudi da proizvedemo fmo zmave martenzitne in/ali nižje bainitne letve, ki nastopajo v finih paketih s povprečno dimenzijo, ki je mnogo finejša kot predhodno zrno austenita. Poleg tega pri predloženem izumu uporabimo disperzij sko ojačanje iz finih bakrovih oborin in mešanih karbidov in/ali karbonitridov, da optimiramo trdnost in žilavost med popuščanjem martenzitne/bainitne strukture.The present invention relates to the development of new HSLA steels that meet the challenges described above. The invention is based on a new combination of steel chemistry and processing to provide both intrinsic and microstructural toughness, to reduce DBTT and to increase toughness at high tensile strengths. Intrinsic toughness is achieved by a reasonable balance of critical alloy elements in steel, as detailed in this description. The microstructural toughness is the result of achieving a very fmo effective grain size, as well as producing fmo kites of martensite and / or lower bainite slats, which appear in fine packages with an average dimension much finer than the previous austenite grain. In addition, dispersive reinforcement from fine copper precipitates and mixed carbides and / or carbonitrides is used in the present invention to optimize strength and toughness during loosening of the martensite / bainite structure.

V skladu s prejšnjim gre za postopek za pripravo jeklene plošče z mikrostrukturo, ki obsega pretežno popuščen fino zmav letvast martenzit, popuščen fino zmav nižji bainit ali njihove zmesi, označen s tem, da obsega naslednje stopnje: (a) segrevanja jeklenega slaba do temperature ponovnega segrevanja, ki je zadosti visoka, da (i) se v bistvu homogenizira jekleni slab, (ii) se raztopijo v bistvu vsi karbidi in karbonitridi nioba in vanadija v jeklenem slabu in da (iii) se dobijo fina začetna austenitna zrna v jeklenem slabu; (b) reduciranja jeklenega slaba, da nastane jeklena plošča v enem ali več prehodih vročega valjanja v prvem temperaturnem območju, v katerem austenit rekristalizira; (c) nadaljnjega reduciranja jeklene plošče v enem ali več prehodih vročega valjanja v drugem temperaturnem območju pod okoli T_nr temperaturo in nad okoli Ar₃ transformacijsko temperaturo; (d) gašenja jeklene plošče pri hitrosti hlajenja od okoli 10°C na sekundo do okoli 40°C na sekundo do temperature po ustavitvi gašenja pod okoli M_s transformacijsko temperaturo plus 200°C; (e) ustavitve gašenja; in (f) popuščanja jeklene plošče pri temperaturi popuščanja od okoli 400°C do okoli Aci transformacijske temperature, prednostno do, vendar ne vključno, Acj transformacijske temperature, v časovnem obdobju, ki zadostuje, da pride do obarjanja delcev za kaljenje, t.j. enega ali več izmed ε-bakra, Mo₂C ali karbidov in karbonitridov nioba in vanadija. Časovno obdobje, ki zadostuje, da pride do obarjanja delcev za kaljenje, je odvisno primarno od debeline jeklene plošče, kemije jeklene plošče in temperature popuščanja ter ga lahko določi strokovnjak. (Glej slovar za definicije pretežno, delci za kaljenje, T_nr temperatura, Ar₃, M_s in Aci transformacijske temperature ter Mo₂C.)According to the foregoing, it is a process for the preparation of a microstructure steel plate comprising a substantially yielded finite dragon molded martensite, a loose finite dragon lower bainite, or mixtures thereof, characterized in that it comprises the following steps: (a) heating the steel poor to the reflux temperature heating sufficiently high to (i) substantially homogenize the steel slab, (ii) dissolve substantially all the carbides and carbonitrids of niobe and vanadium in the steel slab and (iii) produce fine initial austenitic grains in the steel slab; (b) reducing the steel slab to produce a steel plate in one or more hot rolling passes in the first temperature range in which the austenite recrystallizes; (c) further reducing the steel plate in one or more hot rolling passages in another temperature range below about T _nr temperature and above about Ar ₃ transformation temperature; (d) quenching the steel plate at a cooling rate of from about 10 ° C per second to about 40 ° C per second to the temperature after stopping the quenching below about M _{with a} transformation temperature plus 200 ° C; (e) shutdowns; and (f) failure of the steel plate at a failure temperature of from about 400 ° C to about Aci transformation temperature, preferably up to, but not including, Acj transformation temperature, for a period sufficient to cause precipitation of the quenching particles, i.e. one or more of ε-copper, Mo ₂ C or carbides and carbonitrides of niobe and vanadium. The time period sufficient to cause precipitation of the quenching particles depends primarily on the thickness of the steel plate, the steel plate chemistry and the failure temperature and can be determined by one skilled in the art. (See dictionary for definitions predominantly, quenching particles, T _nr temperature, Ar ₃ , M _s and Aci transformation temperatures, and Mo ₂ C.)

Za zagotovitev žilavosti pri sobni in kriogenih temperaturah imajo jekla v smislu predloženega izuma prednostno mikrostrukturo, ki obsega pretežno popuščeni fino zmav nižji bainit, popuščeni fino zmav letvast martenzit ali njihove zmesi. Prednostno je, da se v bistvu minimizira nastanek sestavin, ki povzročajo krhkost, kot je gornji bainit, dvojčeni martenzit in MA. Kot se uporablja pri opisu predloženega izuma in v zahtevkih, pomeni pretežno vsaj okoli 50 vol.%. Bolj prednostno obsega mikrostruktura vsaj okoli 60 vol.% do okoli 80 vol.% popuščenega fino zmavega nižjega bainita, popuščenega fino zmavega letvastega martenzita ali njihovih zmesi. Celo bolj prednostno obsega mikrostruktura vsaj 90 vol.% popuščenega fino zmavega nižjega bainita, popuščenega fino zmavega letvastega martenzita ali njihvoih zmesi. Najbolj prednostno obsega mikrostruktura v bistvu 100% popuščenega fino zmavega letvastega martenzita.In order to provide toughness at room and cryogenic temperatures, steels according to the present invention have a preferred microstructure comprising a predominantly yielded finer dragon lower bainite, loose finite dragon molded martensite or mixtures thereof. It is advantageous to substantially minimize the formation of fragility-causing components such as upper bainite, twin martensite and MA. As used in the description of the present invention and in the claims, it is preferably at least about 50% vol. More preferably, the microstructure comprises at least about 60% by volume to about 80% by volume of the finely divided lower bainite, the finely divided molded martensite or mixtures thereof. Even more preferably, the microstructures comprise at least 90% by volume of the reduced finely baked lower bainite, the finely molded lath martensite or mixtures thereof. Most preferably, the microstructure consists essentially of 100% loose finely stripped molded martensite.

Jekleni slab, predelan v smislu predloženega izuma, izdelamo na običajen način in v eni izvedbi obsega železo in naslednje legime elemente, prednostno v masnih območjih, navedenih v naslednji tabeli I:Weak steel processed according to the present invention is manufactured in the usual manner and in one embodiment comprises iron and the following legime elements, preferably in the mass ranges listed in the following Table I:

Tabela ITable I

Legirni elementAlloy element

Območje (mas.%) ogljik (C) mangan (Mn) nikelj (Ni) baker (Cu) molibden (Mo) niob (Nb) titan (Ti) aluminij (Al) dušik (N)Range (wt.%) Carbon (C) manganese (Mn) nickel (Ni) copper (Cu) molybdenum (Mo) niob (Nb) titanium (Ti) aluminum (Al) nitrogen (N)

0,04 - 0,12, bolj prednostno 0,04 - 0,07 0,5 - 2,5, bolj prednostno 1,0 - 1,8 1,0 - 3,0, bolj prednostno 1,5 - 2,5 0,1 -1,5, bolj prednostno 0,5 - 1,0 0,1 - 0,8, bolj prednostno 0,2 - 0,5 0,02 - 0,1, bolj prednostno 0,03 - 0,05 0,008 - 0,03, bolj prednostno 0,01 - 0,02 0,001 - 0,05, bolj prednostno 0,005 - 0,03 0,002 - 0,005, bolj prednostno 0,002 - 0,0030.04 - 0.12, more preferably 0.04 - 0.07 0.5 - 2.5, more preferably 1.0 - 1.8 1.0 - 3.0, more preferably 1.5 - 2, 5 0.1 -1.5, more preferably 0.5 - 1.0 0.1 - 0.8, more preferably 0.2 - 0.5 0.02 - 0.1, more preferably 0.03 - 0 , 05 0.008 - 0.03, more preferably 0.01 - 0.02 0.001 - 0.05, more preferably 0.005 - 0.03 0.002 - 0.005, more preferably 0.002 - 0.003

Jeklu včasih dodamo vanadij (V), prednostno do okoli 0,10 mas.%, bolj prednostno okoli 0,02 mas.% do okoli 0,05 mas.%.Vanadium (V) is sometimes added to the steel, preferably up to about 0.10 wt%, more preferably about 0.02 wt% to about 0.05 wt%.

Jeklu včasih dodamo krom (Cr), prednostno do okoli 1,0 mas.%, bolj prednostno okoli 0,2 mas.% do okoli 0,6 mas.%.Chromium (Cr) is sometimes added to the steel, preferably up to about 1.0 wt%, more preferably about 0.2 wt% to about 0.6 wt%.

Jeklu včasih dodamo silicij (Si), prednostno do okoli 0,5 mas.%, bolj prednostno okoli 0,01 mas.% do okoli 0,5 mas.%, in celo bolj prednostno okoli 0,05 mas.% do okoli 0,1 mas.%.Silicon (Si) is sometimes added to the steel, preferably up to about 0.5 wt%, more preferably about 0.01 wt% to about 0.5 wt%, and even more preferably about 0.05 wt% to about 0 , 1 wt.%.

Jeklu včasih dodamo bor (B), prednostno do okoli 0,0020 mas.%, bolj prednostno okoli 0,0006 mas.% do okoli 0,0010 mas.%.Steel (B) is sometimes added to the steel, preferably up to about 0.0020% by weight, more preferably about 0.0006% to about 0.0010% by weight.

Jeklo prednostno vsebuje vsaj okoli 1 mas.% niklja. Vsebnost niklja v jeklu lahko povečamo nad okoli 3 mas.%, če želimo povečati učinek po varjenju. Za vsak 1 mas.% dodatka niklja se pričakuje, da bo znižal DBTT jekla za okoli 10°C. Vsebnost niklja je prednostno pod 9 mas.%, bolj prednostno pod okoli 6 mas.%. Vsebnost niklja prednostno minimiziramo, da minimiziramo ceno jekla. Če vsebnost niklja povečamo nad okoli 3 mas.%, lahko vsebnost mangana zmanjšamo pod okoli 0,5 mas.% do 0,0 mas.%.The steel preferably contains at least about 1% by weight of nickel. The nickel content of steel can be increased above about 3 wt% to increase the effect after welding. Each 1% by weight of nickel additive is expected to reduce the DBTT of steel by about 10 ° C. The nickel content is preferably below 9% by weight, more preferably below about 6% by weight. Nickel content is preferably minimized to minimize the price of steel. If the nickel content is increased above about 3 wt%, the manganese content can be reduced below about 0.5 wt% to 0.0 wt%.

Poleg tega v jeklu prednostno bistveno minimiziramo preostanke. Vsebnost fosforja (P) je prednostno pod okoli 0,01 mas.%. Vsebnost žvepla (S) je prednostno pod okoli 0,004 mas.%. Vsebnost kisika (O) je prednostno pod okoli 0,002 mas.%.In addition, steel is preferably substantially minimized in residues. The phosphorus (P) content is preferably below about 0.01% by weight. The sulfur content (S) is preferably below about 0.004% by weight. The oxygen (O) content is preferably below about 0.002% by weight.

Predelava jeklenega slaba (1) Znižanje DBTTPoor steel processing (1) DBTT reduction

Doseženje nizke DBTT, t.j. pod okoli -73°C, je ključni izziv v razvoju novih HSLA jekel za aplikacije pri kriogenih temperaturah. Tehničen izziv je, da vzdržujemo/povečamo trdnost pri sedanji HSLA tehnologiji ob znižanju DBTT, zlasti v HAZ. Pri predloženem izumu izrabimo kombinacijo legiranja in predelave, da spremenimo tako intrinzične kot tudi mikrostruktume prispevke k porušitveni odpornosti tako, da proizvedemo nizko legirano jeklo z odličnimi lastnostmi pri kriogenih temperaturah v matični plošči in v HAZ, kot je opisano v nadaljevanju.Achieving low DBTT, i.e. below -73 ° C, a key challenge is the development of new HSLA steels for applications at cryogenic temperatures. The technical challenge is to maintain / increase strength with current HSLA technology while reducing DBTT, especially in HAZ. In the present invention, a combination of alloying and processing is used to modify both the intrinsic and microstructural contributions to the tensile strength by producing low alloy steel with excellent cryogenic temperature properties in the motherboard and in HAZ, as described below.

Pri predloženem izumu izrabimo mikrostruktumo žilavost za znižanje DBTT osnovnega jekla. Ključna komponenta te mikrostruktume žilavosti obstoji iz udrobnjenja predhodne velikosti zrn austenita in modificiranja morfologije zm, cilj vsega tega pa je povečanje medploskovne površine velikokotnih meja na enotski volumen v jekleni plošči. Kot strokovnjaki vedo, pomeni zrno, kot se tukaj uporablja, posamezen kristal v polikristalnem materialu in pomeni meja zrna, kot se tukaj uporablja, ozko cono v kovini, ki ustreza prehodu iz ene kristalografske orientacije v drugo in tako loči eno zrno od drugega. Kot se tukaj uporablja, je velikokotna meja zrna meja zrna, ki loči dve sosednji zrni, katerih kristalografski orientaciji se razlikujeta za več kot okoli 8°. Tudi kot se tukaj uporablja, je velikokotna meja meja, ki se efektivno obnaša kot velikokotna meja zrna, t.j. meja, ki teži k temu, da spelje vstran razširjajočo se razpoko ali prelom in tako povzroči zakrivljenost na poti preloma.In the present invention, microstructural toughness is used to reduce the DBTT of base steel. A key component of this toughness microstructure consists of the fragmentation of the previous austenite grain size and modification of the morphology of the zm, the aim of which is to increase the interplanar surface of the wide-angle boundaries to a single volume in the steel plate. As is well known in the art, a grain as used herein is a single crystal in a polycrystalline material, and the grain boundary as used here means a narrow zone in metal corresponding to a transition from one crystallographic orientation to another, thus separating one grain from another. As used herein, a large-angle grain boundary is a grain boundary separating two adjacent grains whose crystallographic orientations differ by more than about 8 °. Also, as used here, the large-angle boundary is a boundary that effectively behaves as a large-angle grain boundary, i.e. a boundary that tends to cause a widening fissure or fracture to the side, causing curvature along the fracture path.

Prispevek termo-mehaničnega kontroliranega valjanja (TMCP) k celotni medploskovni površini velikokotnih meja na enotski volumen, Sv, je definiran z naslednjo enačbo:The contribution of thermo-mechanical controlled rolling (TMCP) to the total interplanar surface of large-angle boundaries per unit volume, Sv, is defined by the following equation:

Sv = l^l + J?+l^+0,63(r-30) kjer je d povprečna velikost austenitnih zm v vroče valjani jekleni plošči pred valjanjem v temperaturnem območju, v katerem austenit ne rekristalizira (predhodna velikost zm austenita);Sv = l ^ l + J? + L ^ + 0.63 (r-30) where d is the average size of austenitic zm in a hot-rolled steel plate before rolling in a temperature range in which austenite does not recrystallize (previous size of austenite);

R je redukcijsko razmerje (originalna debelina jeklenega slaba/končna debelina jeklene plošče); in rje odstotna redukcija v debelini jekla zaradi vročega valjanja v temperaturnem območju, v katerem austenit ne rekristalizira.R is the reduction ratio (original thickness of steel poor / final thickness of steel plate); and rust percentage reduction in the thickness of the steel due to hot rolling in a temperature range in which the austenite does not recrystallize.

Znano je, da ko se Sv jekla povečuje, se DBTT zmanjšuje zaradi speljave razpoke vstran in spremljajoče zakrivljenosti na poti razpoke pri velikokotnih mejah. V tržni TMCP praksi je vrednost R fiksirana za dano debelino plošče in je gornja meja za vrednost r tipično 75. Pri danih fiksiranih vrednostih za R in r lahko Sv bistveno povečamo samo z zmanjšanjem d, kot je razvidno iz gornje enačbe. Za zmanjšanje d v jeklih v smislu predloženega izuma uporabimo Ti-Nb mikrolegiranje v kombinaciji z optimirano TMCP prakso. Za enako celotno količino redukcije med vročim valjanjem/deformacijo bomo jeklo z začetno finejšo povprečno velikostjo zrn austenita dobili v finejši gotovi povprečni velikosti zrn austenita. Zato pri predloženem izumu količino Ti-Nb dodatkov optimiramo za prakso z nizkim ponovnim segrevanjem ob nastanku želene inhibicije rasti zrn austenita med TMCP. Glede na sl. 1A uporabimo relativno nizko temperaturo ponovnega segrevanja, prednostno med okoli 955°C in okoli 1065°C, da dobimo v začetku povprečno velikost D' zrn austenita pod okoli 120 pm v ponovno segretem jeklenem slabu 10' pred vročo deformacijo. S predelavo v smislu predloženega izuma se izognemo prekomerni rasti zrn austenita, ki je posledica uporabe višjih temperatur ponovnega segrevanja, t.j. nad okoli 1095°C pri običajni TMCP. Za pospeševanje z dinamično rekristalizacijo povzročenega udrobnjenja zrn uporabimo velike redukcije na prehod, nad okoli 10%, med vročim valjanjem v temperaturnem območju, v katerem rekristalizira austenit. Če se sedaj sklicujemo na sl. IB, zagotavlja predelava v smislu predloženega izuma povprečno predhodno velikost D zrn austenita (t.j. d) pod okoli 30 pm, prednostno pod okoli 20 pm in celo bolj prednostno pod okoli 10 pm, v jeklenem slabu 10 po vročem valjanju (deformaciji) v temperaturnem območju, v katerem austenit rekristalizira, vendar pred vročim valjanjem v temperaturnem območju, v katerem austenit ne rekristalizira. Polega tega, da dosežemo učinkovito redukcijo velikosti zrn v smeri po debelini, izvedemo velike redukcije, prednostno nad okoli 70% kumulativno, v temperaturnem območju po okoli T_nr temperaturo, vendar nad okoli Ar₃ transformacijsko temperaturo. Če se sedaj sklicujemo na sl. 1C, vodi TMCP v smislu predloženega izuma do nastanka podaljšane ploske strukture zrn v austenitu v dovršilno valjani jekleni ploščiIt is known that as the Sv of steel increases, the DBTT decreases due to the propagation of the crack sideways and the accompanying curvature along the crack path at wide-angle boundaries. In market TMCP practice, the value of R is fixed for a given plate thickness and the upper limit for the value of r is typically 75. For given fixed values for R and r, Sv can be significantly increased only by decreasing d, as shown in the above equation. To reduce the two steels of the present invention, Ti-Nb microalloying is used in combination with optimized TMCP practice. For the same total amount of reduction during hot rolling / deformation, steel with an initial finer average austenite grain size will be obtained in a finer finished average austenite grain size. Therefore, in the present invention, the amount of Ti-Nb additives is optimized for low reheat practices to produce the desired inhibition of austenite grain growth during TMCP. According to FIG. 1A, a relatively low reheat temperature, preferably between about 955 ° C and about 1065 ° C, is used to obtain an average size of D 'grains of austenite below about 120 pm in the initially heated steel poor 10' initially before hot deformation. The processing of the present invention avoids the overgrowth of austenite grains resulting from the use of higher reheating temperatures, i.e. above about 1095 ° C at conventional TMCP. To accelerate the dynamic recrystallization of grain fragmentation induced, large reductions per pass, above about 10%, are used during hot rolling in the temperature range in which the austenite recrystallizes. Referring now to FIG. IB, the processing of the present invention provides average pre-size D grains of austenite (ie d) below about 30 pm, preferably below about 20 pm, and even more preferably below about 10 pm, in steel of less than 10 after hot rolling (deformation) in the temperature range in which the austenite recrystallizes but before hot rolling in a temperature range in which the austenite does not recrystallize. In order to achieve an effective reduction in grain size in the thickness direction, large reductions are made, preferably above about 70% cumulatively, in the temperature range after about T _nr temperature, but above about Ar ₃ transformation temperature. Referring now to FIG. 1C, leads TMCP according to the present invention to the formation of an extended flat grain structure in austenite in a finely rolled steel plate

10' z zelo fino efektivno velikostjo D' zrn v smeri po debelini, npr. efektivno velikost D' zrn pod okoli 10 pm, prednostno pod okoli 8 pm in celo bolj prednostno pod okoli 5 pm, pri čemer se poveča medploskovna površina velikokotnih meja, npr. 11, na enotski volumen v jekleni plošči 10', kot bodo razumeli strokovnjaki.10 'with a very fine effective grain size D' in the thickness direction, e.g. effective size D 'of the grains below about 10 pm, preferably below about 8 pm and even more preferably below about 5 pm, increasing the interfacial area of the wide-angle boundaries, e.g. 11, per unit volume in steel plate 10 ', as will be understood by those skilled in the art.

Nekoliko bolj podrobno pripravimo jeklo v smislu predloženega izuma s tvorjenjem slaba z želeno sestavo, kot je tukaj opisano; s segrevanjem slaba na temperaturo od okoli 955°C do okoli 1065°C; z vročim valjanjem slaba, da se tvori jeklena plošča v enem ali več prehodih, kar zagotavlja okoli 30% do okoli 70% redukcijo v prvem temperaturnem območju, v katerem austenit rekristalizira, to je nad okoli T_nr temperaturo, in z nadaljnjim vročim valjanjem jeklene plošče v enem ali več prehodih, kar zagotavlja okoli 40% do okoli 80% redukcijo v drugem temperaturnem območju pod okoli T_nr temperaturo in nad okoli Ar₃ transformacijsko temperaturo. Vroče valjano jekleno ploščo nato pogasimo pri hitrosti hlajenja okoli 10°C na sekundo do okoli 40°C na sekundo do primerne QST pod okoli M_s transformacijsko temperaturo plus 200°C, takrat pa z gašenjem končamo. Pri eni izvedbi v smislu izuma nato jekleno ploščo zračno ohladimo do sobne temperature. To predelavo uporabimo za pripravo mikrostrukture, ki prednostno obsega pretežno fino zmav letvast martenzit, fino zmav nižji bainit ali njihove zmesi ali bolj prednostno obsega v bistvu 100% fino zmavega letvastega martenzita.The steel of the present invention is further prepared in more detail by forming a slab having the desired composition as described herein; by heating to a temperature of about 955 ° C to about 1065 ° C; hot-rolled is poor to form a steel plate in one or more passes, providing about 30% to about 70% reduction in the first temperature range in which austenite recrystallizes, i.e. above about T _nr temperature, and with further hot-rolling of the steel plates in one or more passages, providing about 40% to about 80% reduction in the second temperature range below about T _nr temperature and above about Ar ₃ transformation temperature. The hot rolled steel plate is then quenched at a cooling rate of about 10 ° C per second to about 40 ° C per second to a suitable QST below about M _{with a} transformation temperature plus 200 ° C and then quenched. In one embodiment of the invention, the steel plate is then air-cooled to room temperature. This processing is used to prepare a microstructure which preferably comprises a predominantly fine lath martensite slurry, a lower bainite slurry or mixtures thereof, or more preferably comprising substantially 100% fine lime martensite.

Tako direktno gašen martenzit v jeklih v smislu predloženega izuma ima visoko trdnost, njegovo žilavost pa lahko izboljšamo s popuščanjem pri primerni temperaturi od nad okoli 400°C do okoli Aci transformacijske temperature. Popuščanje jekla v tem temperaturnem območju tudi vodi do zmanjšanja napetosti pri gašenju, kar po drugi strani vodi do povečane žilavosti. Čeprav popuščanje lahko poveča žilavost jekla, normalno vodi do znatne izgube trdnosti. Pri predloženem izumu se običajna izguba trdnosti zaradi popuščanja kompenzira z uvedbo obarjalnega disperzij skega kaljenja. Disperzijsko kaljenje iz finih bakrovih oborin ter mešanih karbidov in/ali karbonitridov uporabljamo za optimiranje trdnosti in žilavosti med popuščanjem martenzitne strukture. Enkratna kemija jekel v smislu predloženega izuma omogoča popuščanje v širokem območju od okoli 400°C do okoli 650°C brez znatne izgube trdnosti zaradi gašenja. Jekleno ploščo prednostno popuščamo pri temperaturi popuščanja od nad okoli 400°C do pod Aci transformacijsko temperaturo v časovnem obdobju, ki zadostuje, da pride do obarjanja delcev za kaljenje (kot je tukaj definirano). Ta predelava olajša pretvorbo mikrostrukture jeklene plošče v pretežno popuščen fino zmav letvast martenzit, popuščen fino zmav nižji bainit ali njihove zmesi. Spet je časovno obdobje, ki zadostuje, da pride do obarjanja delcev za kaljenje, odvisno primarno od debeline jeklene plošče, kemije jeklene plošče in temperature popuščanja ter ga lahko strokovnjak določi.Thus, the directly quenched martensite in the steels of the present invention has high strength, and its toughness can be improved by loosening at a suitable temperature from above about 400 ° C to about Aci transformation temperature. Loosening the steel in this temperature range also leads to a decrease in the quenching stress, which in turn leads to increased toughness. Although loosening can increase the toughness of steel, it normally leads to a significant loss of strength. In the present invention, the conventional loss of strength due to failure is compensated for by the introduction of precipitation dispersive tempering. Dispersion hardening from fine copper precipitates and mixed carbides and / or carbonitrides is used to optimize strength and toughness during loosening of the martensitic structure. The one-time steel chemistry of the present invention allows for loosening in a wide range of from about 400 ° C to about 650 ° C without significant loss of quenching strength. The steel plate is preferably loosened at a freezing temperature from above about 400 ° C to below Aci transformation temperature over a period sufficient to cause precipitation of the quenching particles (as defined herein). This processing facilitates the transformation of the microstructure of the steel plate into a predominantly yielded finite dragon molded martensite, loose finite dragon lower bainite or mixtures thereof. Again, a period of time sufficient to cause precipitation of the quenching particles depends primarily on the thickness of the steel plate, the steel plate chemistry and the failure temperature and can be determined by one skilled in the art.

Kot bodo razumeli strokovnjaki, se odstotna redukcija v debelini, kot.se tukaj uporablja, nanaša na odstotno redukcijo v debelini jeklenega slaba ali plošče pred navedeno redukcijo. Le za namene razlage in ne da bi pri tem omejevali izum, lahko jekleni slab z debelino okob 25,4 cm reduciramo za okoli 50% (50% redukcija) v prvem temperaturnem območju na debelino okoli 12,7 cm, nato reduciramo okoli 80% (80% redukcija) v drugem temperaturnem območju na debelino okoli 2,5 cm. Kot se tukaj uporablja, pomeni slab kos jekla kakršnihkoli dimenzij.As will be understood by those skilled in the art, the percentage reduction in thickness, as used herein, refers to the percentage reduction in the thickness of a steel slab or slab prior to said reduction. For the purposes of interpretation only and without limiting the invention, a steel slab with an oak thickness of 25.4 cm can be reduced by about 50% (50% reduction) in the first temperature range to a thickness of about 12.7 cm, then reduced by about 80% (80% reduction) in the second temperature range to a thickness of about 2.5 cm. As used here, it means a bad piece of steel of any size.

Jekleni slab prednostno segrevamo s primernim načinom za zviševanje temperature v bistvu celotnega slaba, prednostno celotnega slaba, na želeno temperaturo ponovnega segrevanja, npr. z namestitvijo slaba v peč za določen čas. Specifično temperaturo ponovnega segrevanja, ki jo je treba uporabiti za katerokoli sestavo jekla v območju v smislu predloženega izuma, lahko zlahka določi strokovnjak bodisi s poskusom bodisi z izračunom ob uporabi primernih modelov. Poleg tega lahko temperaturo peči in čas ponovnega segrevanja, potreben za zviševanje temperature v bistvu celotnega slaba, prednostno celotnega slaba, na želeno temperaturo ponovnega segrevanja zlahka določi strokovnjak z ozirom na standardne industrijske publikacije.Preferably, the steel slab is heated by a suitable method for raising the temperature of substantially the entire slab, preferably the total slab, to the desired reheating temperature, e.g. by installing the bad in the furnace for a limited time. The specific reheating temperature to be used for any steel composition in the range of the present invention can be readily determined by one of skill in the art, either by experiment or by calculation using suitable models. In addition, the furnace temperature and reheat time required to raise the temperature of substantially the whole of the poor, preferably the total, of the poor may be readily determined by one skilled in the art with regard to standard industry publications, at the desired reheating temperature.

Razen temperature ponovnega segrevanja, ki se nanaša na v bistvu celoten slab, so sledeče temperature, navedene pri opisu postopka predelave v smislu predloženega izuma, temperature, merjene na površini jekla. Površinsko temperaturo jekla lahko merimo z uporabo npr. optičnega pirometra ali s katerokoli drugo pripravo, primemo za merjenje površinske temperature jekla. Tukaj navedene hitrosti hlajenja so tiste v sredini ali bistveno v sredini debeline plošče; in temperatura po ustavitvi gašenja (QST) je najvišja ali v bistvu najvišja temperatura, dosežena na površini plošče po ustavitvi gašenja zaradi toplote, ki se prenese iz sredinske debeline plošče. Npr. med procesiranjem eksperimentalnih toplot sestavka za jeklo v smislu predloženega izuma namestimo termoelement v sredini ali v bistvu v sredini debeline jeklene plošče za merjenje središčne temperature, površinsko temperaturo pa merimo z uporabo optičnega pirometra. Korelacijo med središčno temperaturo in površinsko temperaturo razvijemo za uporabo med sledečo predelavo istega ali v bistvu istega sestavka za jeklo, tako da lahko središčno temperaturo določimo preko direktnega merjenja površinske temperature. Tudi potrebno temperaturo in pretočno hitrost tekočine za gašenje, da dosežemo želeno pospešeno hitrost hlajenja, lahko določi strokovnjak z ozirom na standardne industrijske publikacije.In addition to the reheat temperature, which relates to substantially the whole of the poor, the following temperatures indicated in the description of the processing process of the present invention are those measured on the surface of the steel. The surface temperature of the steel can be measured using e.g. optical pyrometer or any other device used to measure the surface temperature of steel. The cooling rates listed here are those in the middle or substantially in the middle of the plate thickness; and the post-quenching temperature (QST) is the highest or essentially the highest temperature reached on the surface of the board after quenching due to heat transferred from the center thickness of the panel. E.g. while processing the experimental heat of the steel composition according to the present invention, a thermocouple is placed in the center or substantially in the middle of the thickness of the steel plate to measure the center temperature, and the surface temperature is measured using an optical pyrometer. The correlation between the center temperature and the surface temperature is developed for use during the subsequent processing of the same or substantially the same steel composition, so that the center temperature can be determined by directly measuring the surface temperature. The required temperature and flow rate of the extinguishing fluid to achieve the desired accelerated cooling rate may also be determined by one skilled in the art with respect to standard industry publications.

Za katerikoli sestavek za jeklo v obsegu predloženega izuma je temperatura, ki definira mejo med rekristalizacijskim območjem in ne-rekristalizacijskim območjem, T_nr temperatura, odvisna od kemije jekla, zlasti koncentracije ogljika in koncentracije nioba, od temperature ponovnega segrevanja pred valjanjem in od količine redukcije, podane v prehodih valjanja. Strokovnjaki lahko določijo to temperaturo za posamezno jeklo v smislu predloženega izuma bodisi s poskusom ali z modelnim izračunom. Podobno lahko tukaj navedene Aci, Ar₃ in M_s transformacijske temperature strokovnjaki določijo za katerokoli jeklo v smislu predloženega izuma bodisi s poskusom ali z modelnim izračunom.For any steel composition within the scope of the present invention, the temperature defining the boundary between the recrystallization zone and the non-recrystallization zone is T _nr temperature depending on the chemistry of the steel, in particular carbon concentration and niobe concentration, the reheat temperature before rolling and the amount of reduction given in rolling passages. Those skilled in the art can determine this temperature for a particular steel of the present invention, either by trial or by model calculation. Similarly, the Acl, Ar ₃ and M _s transformation temperatures experts determined for any steel according to this invention either by experiment or by model calculation.

Čeprav so zgoraj opisani mikrostruktumi pristopi koristni za znižanje DBTT v matični jekleni plošči, niso popolnoma učinkoviti za vzdrževanje zadostno nizke DBTT v grobo zmavih območjih varilne HAZ. Tako gre pri predloženem izumu za postopek za vzdrževanje zadosti nizke DBTT v grobo zmavih območjih varilne HAZ z uporabo intrinzičnih učinkov legimih elementov, kot je opisano v nadaljevanju.Although the microstructural approaches described above are useful for reducing DBTT in the motherboard, they are not fully effective for maintaining sufficiently low DBTT in coarse-grained areas of welding HAZ. Thus, the present invention is a process for maintaining sufficiently low DBTT in coarse-grained areas of welding HAZ using the intrinsic effects of the leg elements, as described below.

Vodilna feritna jekla za kriogene temperature so na splošno na osnovi prostorsko centrirane kubične (BCC) kristalne mreže. Čeprav ta kristalni sistem nudi potencial za zagotavljanje visokih trdnosti ob nizki ceni, ima obnašanje strmega prehoda od kovnega do krhkega preloma, ko se temperatura znižuje. To lahko v osnovi pripišemo močni senzibilnosti kritične razločitvene strižne napetosti (CRSS) (kot je tukaj definirano) na temperaturo v BCC sistemih, kjer CRSS strmo narašča z zmanjševanjem temperature in s tem postanejo strižni procesi in posledično kovni prelom bolj težki. Po drugi strani je kritična napetost za procese krhkega preloma, kot je razkol, manj občutljiva za temperaturo. Zato, ko se temperatura znižuje, postane razkol prednosten prelomni način, ki vodi do nastopa nizko energijskega krhkega preloma. CRSS je intrinzična lastnost jekla in je občutljiva na lahkoto, s katero lahko dislokacije prečno drsijo pri deformaciji; t.j. jeklo, pri katerem je prečno* drsenje lažje, bo tudi imelo nizko CRSS in zato nizko DBTT. Za nekatere ploskovno centrirane kubične (FCC) stabilizatorje, kot Ni, je znano, da pospešujejo prečno drsenje, medtem ko BCC stabilizimi legimi elementi, kot Si, Al, MO, Nb in V, odvračajo prečno drsenje. Pri predloženem izumu prednostno optimiramo vsebnost FCC stabilizimih legimih elementov, kot Ni in Cu, pri čemer upoštevamo razmisleke o stroških in ugoden učinek za znižanje DBTT, z Ni legiranjem prednostno vsaj okoli 1,0 mas.% in bolj prednostno vsaj okoli 1,5 mas.%; in vsebnost BCC stabilizimih legimih elementov v jeklu bistveno minimiziramo.The leading ferrite steels for cryogenic temperatures are generally based on a space-centered cubic (BCC) crystal network. Although this crystalline system offers the potential to provide high strengths at low cost, it has the behavior of a steep transition from forged to brittle when the temperature drops. This can basically be attributed to the strong sensitivity of critical resolving shear stress (CRSS) (as defined here) to temperature in BCC systems, where CRSS increases sharply with decreasing temperature, making shear processes and, consequently, fracturing more difficult. On the other hand, the critical stress for brittle fracture processes such as a rift is less sensitive to temperature. Therefore, as the temperature decreases, the split becomes the preferred fracture mode leading to the occurrence of a low-energy brittle fracture. CRSS is an intrinsic property of steel and is sensitive to the ease with which dislocations can slip transversely in deformation; i.e. steel that makes cross * gliding easier will also have low CRSS and therefore low DBTT. Some plane-centered cubic (FCC) stabilizers, such as Ni, are known to accelerate transverse sliding, while BCC stabilized alloy elements such as Si, Al, MO, Nb, and V discourage transverse sliding. In the present invention, it is preferable to optimize the FCC content of stabilizable alloys such as Ni and Cu, taking into account cost considerations and a favorable effect for reducing DBTT, with Ni alloying preferably at least about 1.0 wt.% And more preferably at least about 1.5 wt. .%; and the BCC content of the stabilizable alloy elements in steel is significantly minimized.

Kot rezultat intrinzične in mikrostruktume žilavosti, ki izvira iz enkratne kombinacije kemije in predelave za jekla v smislu predloženega izuma, imajo jekla odlično žilavost pri kriogenih temperaturah tako v matični plošči kot tudi v HAZ po varjenju. DBTT tako v matični plošči kot tudi v HAZ po varjenju teh jekel so pod okoli -73°C in so lahko pod okoli -107°C.As a result of the intrinsic and microstructure of toughness, which comes from a unique combination of chemistry and processing for steels according to the present invention, steels have excellent toughness at cryogenic temperatures both in the motherboard and in the HAZ after welding. DBTTs both in the motherboard and in the HAZ after welding these steels are below about -73 ° C and may be below about -107 ° C.

(2) Natezna trdnost nad 830 MPa ter enakomernost po debelini mikrostrukture in lastnosti(2) Tensile strength exceeding 830 MPa and uniformity in microstructure thickness and properties

Na splošno se pri popuščanju navadna ogljikova in nizko legirana martenzitna jekla brez močnih karbidnih tvorcev zmehčajo ali izgubijo svojo trdnost pri popuščanju, pri čemer je stopnja te izgube trdnosti funkcija specifične kemije jekla ter temperature popuščanja in trajanja popuščanja. Pri jeklih v smislu predloženega izuma se izguba trdnosti med popuščanjem znatno izboljša s finim obarjanjem delcev za kaljenje.In general, ordinary carbon and low alloyed martensitic steels without strong carbide formers soften or lose their tensile strength upon failure, with the degree of this tensile strength being a function of the specific chemistry of the steel and the temperature of the failure and the duration of the failure. In the steels of the present invention, the loss of strength during failure is significantly improved by the fine precipitation of the quenching particles.

Enkratna kemija jekel v smislu predloženega izuma omogoča popuščanje v širokem območju od okoli 400°C do okoli 650°C brez znatne izgube trdnosti pri gašenju. V tem širokem območju popuščanja pride do ojačitve zaradi obarjanja delcev za kaljenje, ki nastopi ali ima pik pri različnih temperautmih režimih; t.j. v tem širokem območju pride do zadostnega obarjanja delcev za kaljenje, da zagotovimo kumulativno trdnost, ki je ustrezna, da kompenzira izgubo trdnosti, ki je normalno povezana s popuščanjem. Prednostna je predelovalna fleksibilnost, ki jo zagotovi sposobnost popuščanja v tem širokem območju.The one-time steel chemistry of the present invention allows for loosening in a wide range of from about 400 ° C to about 650 ° C without significant loss of quenching strength. In this wide failure zone, reinforcement is caused by precipitation of the quenching particles, which occurs or has peaks under different tempera- ture regimes; i.e. sufficient precipitation of the quenching particles occurs over this wide range to provide a cumulative strength that is adequate to compensate for the loss of strength normally associated with failure. Manufacturing flexibility, which is provided by the ability to yield in this wide area, is preferred.

Pri predloženem izumu dosežemo želeno trdnost pri relativno nizki vsebnosti ogljika s spremljajočimi prednostmi v varivosti in odlični žilavosti tako v matičnem jeklu kot tudi v HAZ. Minimalno okoli 0,04 mas.% C je prednostno v celotni zlitini za doseganje natezne trdnosti nad 830 MPa.In the present invention, the desired strength is achieved at a relatively low carbon content with the accompanying advantages in weldability and excellent toughness in both parent steel and HAZ. A minimum of about 0.04% by weight of C is preferably throughout the alloy to achieve a tensile strength above 830 MPa.

Čeprav so legimi elementi, različni od C, v jeklih v smislu predloženega izuma v bistvu nepomembni, kar se tiče maksimalne dosegljive trdnosti v jeklu, so ti elementi zaželeni, da se zagotovi zahtevana enakomernost mikrostrukture in trdnosti po debelini za debelino plošče nad okoli 2,5 cm in za območje hitrosti hlajenja, želenih za fleksibilnost predelave. To je pomembno, ker je dejanska hitrost hlajenja v srednjem preseku debele plošče manjša kot na površini. Mikrostruktura površine in centra je lahko tako čisto različna, razen če je jeklo tako zasnovano, da je izločena njegova senzibilnost za razliko v hitrosti hlajenja med površino in centrom plošče. V tem pogledu so posebno učinkoviti Mn in Mo legimi dodatki, zlasti kombinirani dodatki Mo in B. Pri predloženem izumu te dodatke optimiramo glede kaljivosti, varivosti, nizke DBTT in stroškovno. Kot je navedeno preje v tem opisu, je s stališča znižanja DBTT bistveno, da se celotni BCC legimi dodatki držijo pri minimumu. Postavljene so prednostne kemijske tarče in območja za izpolnitev teh in drugih zahtev v smislu predloženega izuma.Although non-C alloy elements are substantially unimportant in the steel of the present invention as far as the maximum achievable strength in steel is concerned, these elements are desirable in order to provide the required uniformity of microstructure and thickness in thickness for a plate thickness above about 2, 5 cm and for the cooling rate range desired for processing flexibility. This is important because the actual cooling velocity in the middle section of the thick plate is less than on the surface. The microstructure of the surface and center may be so different, unless the steel is so designed that its sensitivity is eliminated for the difference in cooling rate between the surface and the center of the plate. In this respect, Mn and Mo are legally effective additives, in particular the combined Mo and B additives. In the present invention, these additives are optimized for hardness, weldability, low DBTT and cost. As stated in the present description, from the point of view of reducing DBTT, it is essential that all BCC legume additives be kept to a minimum. Priority chemical targets and areas are set to meet these and other requirements of the present invention.

(3) Izvrstna varivost za varjenje z nizkim vnosom toplote(3) Excellent weldability for welding with low heat input

Jekla v smislu predloženega izuma so zasnovana za izvrstno varivost. Najbolj zaskrbljujoče je, zlasti pri varjenju z nizkim vnosom toplote, razpokanje v hladnem ali razpokanje zaradi vodika v grobo zmavi HAZ. Ugotovili smo, da je za jekla v smislu predloženega izuma občutljivost za razpokanje v hladnem kritično prizadeta z vsebnostjo ogljika in tipom HAZ mikrostrukture in ne s trdoto in ekvivalentom ogljika, za katera se je smatralo v stanju tehnike, da sta kritična parametra. Da bi se izognili razpokanju v hladnem, kadar naj bi jeklo varili ob pogojih varjenja brez predhodnega segrevanja ali z nizkim predhodnim segrevanjem (pod okoli 100°C), je prednostna gornja meja za dodatek ogljika okoli 0,1 mas.%. Kot se tukaj uporablja, ne da bi predloženi izum kakorkoli omejevab, pomeni varjenje z nizkim vnosom, toplote valjenje z ločnimi energijami do okoh 2,5 kJ/mm.The steels of the present invention are designed for excellent weldability. Most worrying, especially when welding with low heat input, is cracking in the cold or cracking due to hydrogen in the coarse HAZ. It has been found that for the steels of the present invention, the cold cracking sensitivity is critically affected by the carbon content and type of HAZ microstructure and not by the hardness and carbon equivalent, which were considered to be critical parameters in the prior art. In order to avoid cracking in cold when welding steel under conditions of welding without preheating or with low preheating (below about 100 ° C), a carbon limit of about 0.1% by weight is preferred. As used herein, without limiting the present invention, it means low-input welding, heat-rolling with separate energies up to about 2.5 kJ / mm.

Nižje bainitne ali avtopopuščene letvaste martenzitne mikrostrukture imajo izvrstno odpornost proti razpokanju v hladnem. Drugi legimi elementi v jeklih v smislu predloženega izuma so skrbno uravnoteženi, sorazmerno z zahtevami za kaljivost in trdnost, da zagotovimo nastanek teh želenih mikrostruktur v grobo zmavi HAZ.Lower bainitic or self-permeable molded martensitic microstructures have excellent cold cracking resistance. The other alloy elements in the steel of the present invention are carefully balanced, in proportion to the requirements for hardness and strength, to ensure the formation of these desired microstructures in the coarse HAZ.

Vloga legirnih elementov v jeklenem slabuThe role of alloying elements in steel slab

Vloga različnih legirnih elementov in prednostne meje njihovih koncentracij za predloženi izum so podane spodaj:The role of the various alloying elements and the preferred concentration limits for the present invention are given below:

Ogljik (C) je eden od najbolj učinkovitih ojačevalnih elementov v jeklu. Se tudi kombinira z močnimi tvorci karbidov v jeklu, kot so Ti, Nb, V in Mo, da zagotovimo inhibiranje rasti zrn in ojačitev obarjanja med popuščanjem. Ogljik tudi poveča kaljivost, t.j. sposobnost tvorbe trsih in močnejših mikrostruktur v jeklu med hlajenjem. Če je vsebnost ogljika manj kot okoli 0,04 mas.%, ne zadostuje za sproženje želenega ojačenja, namreč nad 830 MPa natezne trdnosti, v jeklu. Če je vsebnost ogljika nad okoli 0,12 mas.%, je jeklo občutljivo za razpokanje v hladnem med varjenjem in žilavost se zmanjša v jekleni plošči in njeni HAZ pri varjenju. Vsebnost ogljika v območju okoli 0,04 mas.% do okoli 0,12 mas.% je prednostna, da dosežemo želeno trdnost in HAZ mikrostrukture, namreč avtopopuščen letvasti martenzit in nižji bainit. Celo bolj prednostno je gornja meja za vsebnost ogljika okoli 0,07 mas.%.Carbon (C) is one of the most effective reinforcing elements in steel. It is also combined with strong carbide makers in steel such as Ti, Nb, V and Mo to provide inhibition of grain growth and reinforcement of precipitation during failure. Carbon also increases germination, i.e. the ability to form canes and stronger microstructures in steel during cooling. If the carbon content is less than about 0.04% by weight, it is not sufficient to trigger the desired reinforcement, namely above 830 MPa of tensile strength, in the steel. If the carbon content is above about 0.12% by weight, the steel is susceptible to cracking in the cold during welding and the toughness is reduced in the steel plate and its HAZ during welding. Carbon content in the range of about 0.04 wt% to about 0.12 wt% is preferred in order to achieve the desired strength and HAZ of the microstructures, namely the self-leveled lath martensite and lower bainite. Even more preferably, the upper limit for carbon content is about 0.07% by weight.

Mangan (Mn) ie ojačevalec osnovne mase v jeklih in tudi močno prispeva h kaljivosti. Minimalna količina 0,5 mas. % Mn je prednostna, da dosežemo želeno visoko trdnost v debelini plošče, ki presega okoli 2,5 cm, minimalno najmanj okoli 1,0 mas.% Mn pa je celo bolj prednostno. Vendar lahko preveč Mn škoduje žilavosti, tako da je pri predloženem izuma prednostna gornja meja okoli 2,5 mas. % Mn. Ta gornja meja je tudi prednostna, da bistveno minimiziramo sredinsko izcejanje, ki navadno nastopa v visokih Mn in kontinuimo litih jeklih, in spremljajočo neenakomernost po debelini v mikrostrukturi in lastnostih. Bolj prednostno je gornja meja za vsebnost Mn okoli 1,8 vManganese (Mn) is a base weight enhancer in steels and also contributes greatly to hardening. Minimum amount of 0.5 wt. % Mn is preferred to achieve the desired high strength in slab thickness exceeding about 2.5 cm, and a minimum of at least about 1.0 wt% Mn is even more preferred. However, too much Mn can be detrimental to toughness, so that the upper limit of about 2.5 wt. % Mn. This upper limit is also advantageous in order to substantially minimize the mean shear, which typically occurs in high Mn and continuous cast steels, and the accompanying thickness unevenness in microstructure and properties. More preferably, the upper limit for Mn content is about 1.8 v

mas.%. Ce se vsebnost niklja poveča nad okoli 3 mas.%, lahko želeno visoko trdnost dosežemo brez dodatka mangana. Zato je v širokem smislu prednostno do okoli 2,5 mas.% mangana.wt.%. If the nickel content increases above about 3% by weight, the desired high strength can be achieved without the addition of manganese. Therefore, up to about 2.5% by weight of manganese is preferred in the broad sense.

Silicij (Si) lahko dodamo jeklu za deoksidacijske namene in za ta namen je prednostno minimalno okoli 0,01 mas.%. Vendar je Si močan BCC stabilizator ter tako dvigne DBTT in ima tudi škodljiv učinek na žilavost. Zato je, kadar dodamo Si, prednostna gornja meja okoli 0,5 mas.% Si. Bolj prednostno je, kadar dodamo Si, gornja meja za vsebnost Si okoli 0,1 mas.%. Silicij ni vedno potreben za deoksidacijo, ker lahko aluminij ali titan izvajata isto funkcijo.Silicon (Si) can be added to steel for deoxidation purposes, and a minimum of about 0.01% by weight is preferred for this purpose. However, Si is a powerful BCC stabilizer, thus raising DBTT and also having a detrimental effect on toughness. Therefore, when Si is added, an upper limit of about 0.5 wt% Si is preferred. More preferably, when Si is added, the upper limit for Si content is about 0.1% by weight. Silicon is not always required for deoxidation because aluminum or titanium can perform the same function.

Niob (Nb) dodamo za pospeševanje udrobnjenja zm valjane mikrostrukture jekla, kar izboljša tako trdnost kot tudi žilavost. Obarjanje niobovega karbida in karbonitrida med vročim valjanjem služi za zadrževanje rekristalizacije in za inhibiranje rasti zm, pri čemer zagotovi sredstvo za udrobnjenje zm austenita. Tudi obarjanje niobovih karbidov in karbonitridov med popuščanjem zagotavlja želeno sekundarno kaljenje, da se kompenzira izguba trdnosti, ki jo normalno opazimo pri jeklu, kadar ga popuščamo nad okoli 500°C. Za to je prednostno vsaj okoli 0,02 mas.% Nb, celo bolj prednostno pa je vsaj okoli 0,03 mas.% Nb. Vendar je Nb močan BCC stabilizator in tako dvigne DBTT. Preveč Nb je lahko škodljivo za varivost in HAZ žilavost, tako da je prednostno maksimalno okoli 0,1 mas.%. Bolj prednostno je gornja meja za vsebnost Nb okoli 0,05 mas.%.Niob (Nb) is added to accelerate the grinding of the ground microstructure of the steel, which improves both its strength and toughness. The precipitation of niobe carbide and carbonitride during hot rolling serves to retain recrystallization and to inhibit the growth of zm, providing a means of crushing zm austenite. Also, precipitation of niob carbides and carbonitrides during failure provides the desired secondary tempering to compensate for the loss of strength normally observed in steel when released above about 500 ° C. Preferably at least about 0.02 wt% Nb is preferred, and at least about 0.03 wt% Nb is even more preferred. However, Nb is a powerful BCC stabilizer, thus raising DBTT. Too much Nb can be detrimental to weldability and HAZ toughness, with a maximum of about 0.1% by weight preferably. More preferably, the upper limit for the Nb content is about 0.05% by weight.

Vanadij (V) včasih dodamo, da dosežemo obarjalno ojačitev s tvorbo finih delcev karbidov in karbonitridov vanadija v jeklu pri popuščanju in v njegovi HAZ pri hlajenju po varjenju. Kadar je raztopljen v austenitu, ima V močan ugoden učinek na kaljivost. Kadar V dodamo jeklom v smislu predloženega izuma, je prednostno vsaj okoli 0,02 mas.% V. Vendar bo prebiten V pripomogel k povzročitvi razpokanja v hladnem pri varjenju in tudi poslabšal žilavost osnovnega jekla in njegove HAZ. Dodatek V je zato prednostno omejen na maksimalno okoli 0,1 mas.% in celo bolj prednostno je omejen na maksimalno okoli 0,05 mas.%.Vanadium (V) is sometimes added to achieve precipitating reinforcement by forming fine particles of vanadium carbides and carbonitrides in steel upon failure and in its HAZ upon cooling after welding. When dissolved in austenite, V has a strong beneficial effect on hardening. When V is added to the steels of the present invention, at least about 0.02 wt% is preferred. However, excess V will help to cause cold cracking during welding and also impair the toughness of the base steel and its HAZ. Appendix V is therefore preferably limited to a maximum of about 0.1% by weight and even more preferably limited to a maximum of about 0.05% by weight.

Titan (Ti) je, kadar ga dodamo v majhni količini, učinkovit pri tvorbi finih delcev titanovega nitrida (TiN), ki udrobnijo velikost zm tako v valjani strukturi kot tudi v HAZ jekla. Tako se žilavost jekla izboljša. Ti dodamo v taki količini, da je masno razmerje Ti/N prednostno okoli 3,4. Ti je močan BCC stabilizator in tako dvigne DBTT. Prebiten Ti navadno poslabša žilavost jekla s tvorbo bolj grobih delcev TiN ali titanovega karbida (TiC). Vsebnost Ti pod okoli 0,008 mas.% na splošno ne more zagotoviti zadosti fine velikosti zm ali blokira N v jeklu kot TiN, več kot okoli 0,03 mas.% pa lahko povzroči poslabšanje žilavosti. Bolj prednostno vsebuje jeklo vsaj okoli 0,01 mas.% Ti in ne več kot okoli 0,02 mas.% Ti.Titanium (Ti), when added in a small amount, is effective in the formation of fine titanium nitride (TiN) particles, which fragment the size of the zm in both the rolled structure and the HAZ of steel. This improves the toughness of the steel. These are added in such an amount that the Ti / N weight ratio is preferably about 3.4. Ti is a powerful BCC stabilizer, raising DBTT. Excessive Ti usually exacerbates the toughness of steel by forming coarser TiN or titanium carbide (TiC) particles. A Ti content of about 0.008% by weight generally cannot provide a sufficiently fine size of zm or blocks N in steel as TiN, and more than about 0.03% by weight can lead to a deterioration in toughness. More preferably, the steel contains at least about 0.01 wt% Ti and not more than about 0.02 wt% Ti.

Aluminij (Al) dodamo jeklom v smislu predloženega izuma za deoksidacijske namene. Za ta namen je prednostno vsaj okoli 0,001 mas.% Al, celo bolj prednostno pa je vsaj okoli 0,005 mas.% Al. Al tudi blokira dušik, raztopljen v HAZ. Vendar je Al močan BCC stabilizator in tako dvigne DBTT. Če je vsebnost Al previsoka, t.j. nad okoli 0,05 mas.%, obstaja težnja po tvorbi vključkov tipa aluminijevega oksida (AI2O3), kar je navadno škodljivo za žilavost jekla in njegove HAZ. Celo bolj prednostno je gornja meja za vsebnost Al okoli 0,03 mas.%.Aluminum (Al) is added to the steels of the present invention for deoxidation purposes. For this purpose at least about 0.001 wt.% Al is preferred, and even more preferably at least about 0.005 wt.% Al. Al also blocks nitrogen dissolved in HAZ. However, Al is a powerful BCC stabilizer, thus raising DBTT. If the Al content is too high, i.e. above 0.05% by weight, there is a tendency to form aluminum oxide (AI2O3) type inclusions, which is usually detrimental to the toughness of steel and its HAZ. Even more preferably, the upper limit for Al content is about 0.03% by weight.

Molibden (Mo) zviša kaljivost jekla pri direktnem gašenju, zlasti v kombinaciji z borom in niobom. Mo je tudi zaželen za pospeševanje sekundarnega kaljenja med popuščanjem jekla s tem, da zagotovi fine Mo₂C karbide. Prednostno je vsaj okoli 0,1 mas.% Mo, celo bolj prednostno pa je vsaj okoli 0,2 mas.% Mo. Vendar je Mo močan BCC stabilizator in tako dvigne DBTT. Prebiten Mo pripomore k nastanku razpokanja v hladnem pri varjenju in tudi navadno poslabša žilavost jekla in HAZ, tako da je prednostno maksimalno okoli 0,8 mas.% Mo, celo bolj prednostno pa je maksimalno okoli 0,5 mas.% Mo.Molybdenum (Mo) increases the hardness of steel during direct quenching, especially in combination with boron and niob. Mo is also desirable to accelerate secondary tempering during steel failure by providing fine Mo ₂ C carbides. Preferably at least about 0.1 wt% Mo is preferably, and even more preferably at least about 0.2 wt% Mo. However, Mo is a powerful BCC stabilizer, thus raising DBTT. Excessive Mo contributes to the formation of cracking in the cold during welding and also usually worsens the toughness of the steel and HAZ, so that a maximum of about 0.8 wt% Mo is preferably, and even more preferably a maximum of about 0.5 wt% Mo.

Krom (Cr) navadno poveča kaljivost jekla pri direktnem gašenju. Izboljša tudi korozijsko odpornost in odpornost proti razpokanju zaradi vodika (HIC). Podobno kot Mo prebiten Cr navadno povzroči razpokanje v hladnem pri varjenjih in. navadno poslabša žilavost jekla in njegove HAZ, tako da je pri dodatku Cr prednostno maksimalno okoli 1 mas.% Cr. Bolj prednostno je pri dodatku Cr vsebnost Cr okoli 0,2 mas.% do okoli 0,6 mas.%.Chromium (Cr) usually increases the hardness of steel during direct quenching. It also improves corrosion and hydrogen cracking (HIC) resistance. Similar to Mo, excess Cr usually causes cold cracking in welding and. it usually exacerbates the toughness of the steel and its HAZ so that a maximum of about 1 wt% Cr is preferred with the addition of Cr. More preferably, the Cr content is about 0.2 wt% to about 0.6 wt% in the Cr addition.

Nikelj (Ni) je pomemeben legimi dodatek jeklom v smislu predloženega izuma, da dobimo želeno DBTT, zlasti v HAZ. Je eden najmočnejših FCC stabilizatorjev v jeklu. Dodatek Ni jeklu poveča prečno drsenje in s tem znižuje DBTT. Čeprav ne do enake stopnje kot dodatki Mn in Mo, dodatek Ni jeklu tudi pospešuje kaljivost in zato enakomernost po debelini v mikrostrukturi in lastnostih v debelih presekih (t.j. debelejših kot okoli 2,5 cm). Za doseganje želene DBTT v varilni HAZ je minimalna vsebnost Ni prednostno okoli 1,0 mas.%, bolj prednostno okoli 1,5 mas.%. Ker je Ni drag legimi element, je vsebnost Ni v jeklu prednostno pod okoli 3,0 mas.%, bolj prednostno pod okoli 2,5 mas.%, bolj prednostno pod okoli 2,0 mas.% in celo bolj prednostno pod okoli 1,8 mas.%, da bistveno minimiziramo ceno jekla.Nickel (Ni) is a significant addition to steels of the present invention to obtain the desired DBTT, especially in HAZ. It is one of the most powerful FCC stabilizers in steel. The addition of Ni to steel increases cross-slip, thereby lowering DBTT. Although not to the same extent as the Mn and Mo additives, the Ni steel addition also accelerates the hardening and therefore the uniformity in thickness in the microstructure and properties in thick sections (i.e., thicker than about 2.5 cm). To achieve the desired DBTT in welding HAZ, the minimum content of Ni is preferably about 1.0 wt.%, More preferably about 1.5 wt.%. As Ni is an expensive element, the Ni content in steel is preferably below about 3.0 wt%, more preferably below about 2.5 wt%, more preferably below about 2.0 wt% and even more preferably below about 1 , 8 wt.% To substantially minimize the price of steel.

Baker (Cu) je koristen legimi dodatek, da zagotovimo kaljenje med popuščanjem preko ε-bakrovega obarjanja. Za ta namen prednostno dodamo vsaj okoli 0,1 mas.%, bolj prednostno vsaj okoli 0,5 mas.% Cu. Cu je tudi FCC stabilizator v jeklu in lahko prispeva k znižanju DBTT v majhnih količinah. Cu je tudi ugoden za korozijsko in HIC odpornost. Pri višjih količinah Cu povzroči prekomerno obarjalno kaljenje ter lahko zniža žilavost in dvigne DBTT tako v matični plošči kot tudi v HAZ. Višji Cu lahko tudi povzroči nastanek krhkosti med litjem slaba in vročim valjanjem, ki zahteva so-dodatke Ni za ublažitev. Zaradi gornjih razlogov je prednostna gomja meja okoliCopper (Cu) is a useful alloy additive to provide quenching during cracking via ε-copper precipitation. For this purpose, at least about 0.1 wt%, more preferably at least about 0.5 wt% Cu, is preferably added. Cu is also an FCC stabilizer in steel and can contribute to the reduction of DBTT in small quantities. Cu is also favorable for corrosion and HIC resistance. At higher amounts of Cu, it causes excessive precipitation hardening and can reduce toughness and raise DBTT in both the motherboard and HAZ. Higher Cu can also cause brittleness between casting poor and hot rolling, which requires Ni co-additives to alleviate. For the above reasons, a bunch of borders around are preferred

1,5 mas.% Cu, celo bolj prednostna pa je gomja meja okoli 1,0 mas.%.1.5 wt.% Cu, and even more preferred is a bumpy limit of about 1.0 wt.

Bor (B) lahko v majhnih količinah znatno poveča kaljivost jekla in pospeši tvorbo jeklenih mikrostruktur letvastega martenzita, nižjega bainita in ferita s preprečevanjem tvorbe gornjega bainita tako v matični plošči kot tudi v grobo zmavi HAZ. Za ta namen je na splošno potrebno vsaj okoli 0,0004 mas.% B. Kadar dodamo bor jeklom v smislu predloženega izuma, je prednostno od okoli 0,0006 mas.% do okoli 0,0020 mas.%, celo bolj prednostna pa je gomja meja okoli 0,0010 mas.%. Vendar ni nujno, da je bor dodatek, če drugo legiranje v jeklu zagotovi primemo kaljivost in želeno mikrostrukturo.Boron (B) can significantly increase the hardening of steel in small amounts and accelerate the formation of steel microstructures of molded martensite, lower bainite and ferrite by preventing the formation of upper bainite in both the motherboard and the rough HAZ dragon. For this purpose, at least about 0.0004% by weight is generally required. When boron is added to the steels of the present invention, it is preferably from about 0.0006% to about 0.0020% by weight, and even more preferred is the tuber boundary is about 0.0010% by weight. However, boron does not have to be an additive if the second alloying in the steel provides a firm germination and desired microstructure.

Ta kombinacija lastnosti jekel v smislu predloženega izuma zagotavlja stroškovno ugodno tehnologijo za določene operacije pri kriogenih temperaturah, npr. skladiščenje in transport naravnega plina pri nizkih temperaturah. Ta nova jekla lahko zagotovijo znatne prihranke pri ceni materiala za uporabe pri kriogenih temperaturah glede na uveljavljena tržna jekla, ki na splošno zahtevajo mnogo višje vsebnosti niklja (do okoli 9 mas.%) in imajo mnogo nižje trdnosti (pod okoli 830 MPa). Kemija in zasnova mikrostrukture se uporabljata za znižanje DBTT in zagotavljata enakomerne mehanske lastnosti po debelini za debeline presekov nad okoli 2,5 cm. Ta nova jekla imajo prednostno vsebnosti niklja pod okoli 3 mas.%, natezno trdnost nad 830 MPa, prednostno nad okoli 860 MPa in bolj prednostno nad okoli 900 MPa, temperature prehoda od kovnega do krhkega (DBTT) pod okoli -73°C in nudijo odlično žilavost pri DBTT. Ta nova jekla imajo lahko natezno trdnost nad okoli 930 MPa ali nad okoli 965 MPa ali nad okoli 1000 MPa. Vsebnost niklja v teh jeklih lahko povečamo nad okoli 3 mas.%, če je želeno, da izboljšamo obnašanje po varjenju. Za vsak 1 mas.% dodatka niklja pričakujemo, da zmanjša DBTT jekla za okoli 10°C. Vsebnost niklja je prednostno pod 9 mas.%, bolj prednostno pod okoli 6 mas.%. Vsebnost niklja prednostno minimiziramo, da minimiziramo ceno jekla.This combination of steel properties of the present invention provides cost-effective technology for certain operations at cryogenic temperatures, e.g. storage and transportation of natural gas at low temperatures. These new steels can provide significant cost savings for cryogenic temperature material applications relative to established market steels, which generally require much higher nickel content (up to about 9% by weight) and have much lower strengths (below about 830 MPa). The chemistry and design of the microstructure are used to reduce DBTT and provide uniform mechanical properties across the thickness for cross-section thicknesses above about 2.5 cm. These new steels preferably have nickel contents below about 3% by weight, a tensile strength above 830 MPa, preferably above about 860 MPa and more preferably above about 900 MPa, transition temperatures from forged to brittle (DBTT) below about -73 ° C and provide excellent toughness at DBTT. These new steels may have a tensile strength of about 930 MPa or above about 965 MPa or above about 1000 MPa. The nickel content of these steels can be increased above about 3% by weight if it is desired to improve the welding behavior. For every 1 wt% nickel additive, we expect it to reduce DBTT steels by about 10 ° C. The nickel content is preferably below 9% by weight, more preferably below about 6% by weight. Nickel content is preferably minimized to minimize the price of steel.

Čeprav smo gornji izum opisali z eno ali več prednostnimi izvedbami, je treba razumeti, da lahko naredimo druge modifikacije, ne da bi se oddaljili od obsega izuma, ki je naveden v sledečih zahtevkih.Although the above invention has been described by one or more preferred embodiments, it should be understood that other modifications can be made without departing from the scope of the invention set forth in the following claims.

Slovar izrazov Glossary Aci transformacijska temperatura: Aci Transformation Temperature: temperatura, pri kateri se začne austenit tvoriti med segrevanjem; the temperature at which austenite begins to form during heating; Ac₃ transformacijska temperatura:Ac ₃ transformation temperature: temperatura, pri kateri se transformacija ferita v austenit konča med segrevanjem; the temperature at which the transformation of ferrite to austenite ends during heating; A1₂O₃: Ar₃ transformacijska temperatura:A1 ₂ O ₃ : Ar ₃ transformation temperature: aluminijev oksid; temperatura, pri kateri se začne austenit pretvarjati v ferit med hlajenjem; aluminum oxide; the temperature at which austenite begins to convert to ferrite during cooling; BCC: CRSS (kritična razločitvena napetost): BCC: CRSS (critical resolution voltage): prostorsko centriran kubičen; strižna intrinzična lastnost jekla, občutljiva na lahkoto, s katero lahko dislokacije prečno drsijo pri deformaciji, t.j. jeklo, pri katerem je prečno drsenje lažje, bo tudi imelo nizko CRSS in zato nizko DBTT; space-centered cubic; shear intrinsic property of steel sensitive to the ease with which dislocations can slip transversely in deformation, i.e. steel that makes cross-slip easier, will also have low CRSS and therefore low DBTT;

DBTT (temperatura prehoda od kovnega opisuje oba režima prelomov vDBTT (the transition temperature from the forging describes both break modes in

do krhkega): to fragile): konstrukcijskih jeklih; pri temperaturah pod DBTT večkrat pride do odpovedi zaradi nizko energijskega razkolnega (krhkega) preloma, medtem ko pri temperaturah nad DBTT večkrat pride do odpovedi zaradi visoko energijskega kovnega preloma; structural steels; at temperatures below DBTT, failure is repeatedly caused by a low-energy (brittle) fracture, while at temperatures above DBTT, failure is repeatedly caused by a high-energy forging; delci za kaljenje quenching particles eden ali več od ε-bakra, Mo₂C alione or more of ε-copper, Mo ₂ C or FCC: FCC: karbidov in karbonitridov nioba in vanadija; ploskovno centriran kubičen; niobe carbides and carbonitrides and vanadium; flat centered cubic; gašenje: extinguishing: kot se uporablja pri opisu predloženega izuma, pospešeno hlajenje na katerikoli način, pri čemer uporabimo tekočino, izbrano zaradi njene tendence, da poveča hitrost hlajenja jekla, v nasprotju z as used in the description of the present invention, accelerated cooling in any way, using a fluid selected because of its tendency to increase the cooling rate of steel, as opposed to

zračnim hlajenjem; air-cooled; HAZ: HAZ: cona, prizadeta s toploto; zone affected by heat; HIC: HIC: razpokanje zaradi vodika; hydrogen cracking; HSLA: HSLA: nizko legiran z visokimi trdnostmi; low alloy with high strengths; hitrost hlajenja: cooling speed: hitrost hlajenja v sredini ali v bistvu v sredini debeline plošče; cooling rate in the middle or basically in the middle of the plate thickness; interkritično ponovno segreto: intercritically reheated: segreto (ali ponovno segreto) na temperaturo od okoli Aci transformacijske temperature do okoli Ac₃ transformacijskeheated (or reheated) to a temperature of from about Aci transform temperature to about Ac ₃ transform kriogena temperatura: MA: cryogenic temperature: MA: temperature; katerakoli temperatura pod okoli -40°C; martenzit-austenit; temperature; any temperature below about -40 ° C; martensite-austenite; M_s transformacijska temperatura:M _s transformation temperature: temperatura, pri kateri se začne med hlajenjem transformacija austenita v martenzit; the temperature at which the transformation of austenite into martensite; meja zrna: grain boundary: ozka cona v kovini, ki ustreza prehodu iz a narrow zone in the metal corresponding to the transition from Mo₂C natezna trdnost:Mo ₂ C tensile strength: ene kristalografske orientacije v drugo, pri čemer loči eno zrno od drugega; oblika molibdenovega karbida; pri nateznem testiranju razmerje maksimalne obremenitve proti originalni one crystallographic orientation to another, at separating one grain from another; molybdenum carbide form; in tensile testing the ratio of maximum load to original nizko legirano jeklo: low alloy steel: površini prečnega preseka; jeklo, ki vsebuje železo in pod okoli 10 mas.% skupnih legimih dodatkov; cross-sectional area; steel containing iron and less than about 10% by weight of total alloys; predhodna velikost zrn austenita: previous austenite grain size: povprečna velikost austenitnih zrn v vroče valjani jekleni plošči pred valjanjem v temperaturnem območju, v katerem austenit ne rekristalizira; the average size of austenitic grains in hot-rolled steel plate before rolling in a temperature range in which austenite does not recrystallize; pretežno: predominantly: kot se uporablja pri opisu predloženega izuma, pomeni vsaj okoli 50 vol.%; as used in the description of the present invention means at least about 50% by volume; Sv: Sv: celotna medploskovna površina velikokotnih meja na enotski volumen v the entire interplanar surface large - angle boundaries per unit volume v

slab:weak:

TiC:TiC:

TiN:TiN:

TMCP:TMCP:

T_nr temperatura:T _nr temperature:

temperatura po ustavitvi gašenja (QST) varjenje z nizkim vnosom toplote:after quenching temperature (QST) welding with low heat input:

velikokotna meja:large-angle boundary:

velikokotna meja zrna:large grain boundary:

zrno:grain:

jekleni plošči;steel plates;

kos jekla kakršnihkoli dimenzij; titanov karbid; titanov nitrid;a piece of steel of any size; titanium carbide; titanium nitride;

termo-mehanična kontrolirana predelava z valjanjem;thermo-mechanical controlled processing by rolling;

temperatura, pod katero austenit ne rekristalizira;a temperature below which austenite does not recrystallize;

najvišja ali v bistvu najvišja temperatura, dosežena na površini plošče po.ustavitvi gašenja zaradi toplote, ki se prenese iz sredinske debeline plošče;the maximum or substantially the highest temperature reached on the surface of the plate after the stopping of the quenching due to heat transferred from the center thickness of the plate;

varjenje z ločnimi energijami do okoli 2,5 kJ/mm;welding with separate energies up to about 2.5 kJ / mm;

meja, ki se efektivno obnaša kot velikokotna meja zrna, t.j. teži k temu, da spelje vstran razširjajočo se razpoko ali prelom in tako povzroči zakrivljenost na poti preloma;a boundary that effectively behaves as a large-angle grain boundary, i.e. tends to drive away a widening crack or fracture, thus causing curvature along the fracture path;

meja zrna, ki loči dve sosednji zrni, katerih kristalografski orientaciji se razlikujeta za več kot okoli 8°; in posamezen kristal v polikristalnem materialu.grain boundary separating two adjacent grains whose crystallographic orientations differ by more than about 8 °; and single crystal in polycrystalline material.

ZaFor

ExxonMobil Upstream Research Company: PA^TF^^T'¹*' Γ’ΒΑΡίΝΑ: <Ι·ΟΛ.ExxonMobil Upstream Research Company: PA ^T F ^ ^T ' ¹ *'Γ'ΒΑΡίΝΑ:<Ι · ΟΛ.

Claims (17)

PATENTNI ZAHTEVKIPATENT APPLICATIONS 1. Postopek za pripravo jeklene plošče, ki ima DBTT pod okoli -73 °C tako v jekleni plošči kot tudi v njeni HAZ, natezno trdnost nad 830 MPa in mikrostrukturo, ki obsega pretežno popuščen fino zmav letvast martenzit, popuščen fino zmav nižji bainit ali njihove zmesi, označen s tem, da obsega naslednje stopnje:A process for the preparation of a steel plate having a DBTT below about -73 ° C in both the steel plate and its HAZ, a tensile strength exceeding 830 MPa and a microstructure comprising a predominantly yielded finite lath martensite, loosened finer bainite or mixtures thereof, characterized in that it comprises the following stages: (a) segrevanje jeklenega slaba do temperature ponovnega segrevanja, (i) ki je zadosti visoka, da se v bistvu homogenizira jekleni slab ter se raztopijo v bistvu vsi karbidi in karbonitridi nioba in vanadija v jeklenem slabu, in (ii) dovolj nizka, da se dobijo fina začetna austenitna zrna z velikostjo zm pod okoli 120 pm v jeklenem slabu;(a) heating the steel poor to the temperature of reheating, (i) high enough to substantially homogenize the steel poor and dissolve essentially all the carbides and carbonitrides of niobe and vanadium in the steel poor, and (ii) low enough that a fine initial austenitic grain having a grain size of less than about 120 µm in a steel slab is obtained; (b) reduciranje jeklenega slaba, da nastane jeklena plošča v enem ali več prehodih vročega valjanja v prvem temperaturnem območju, v katerem austenit rekristalizira;(b) reducing the steel slab to produce a steel plate in one or more hot rolling passes in the first temperature range in which the austenite recrystallizes; (c) nadaljnje reduciranje jeklene plošče v enem ali več prehodih vročega valjanja v drugem temperaturnem območju pod okoli T_nr temperaturo in nad okoli Ar₃ transformacijsko temperaturo;(c) further reducing the steel plate in one or more hot rolling passages in another temperature range below about T _nr temperature and above about Ar ₃ transformation temperature; (d) gašenje jeklene plošče pri hitrosti hlajenja od okoli 10°C na sekundo do okoli 40°C na sekundo do temperature po ustavitvi gašenja pod okoli M_s transformacijsko temperaturo plus 200°C;(d) quenching the steel plate at a cooling rate of from about 10 ° C per second to about 40 ° C per second to the temperature after quenching below M _{with a} transformation temperature plus 200 ° C; (e) ustavitev gašenja; in (f) popuščanje jeklene plošče pri temperaturi popuščanja od okoli 400°C do okoli Aci transformacijske temperature v Časovnem obdobju, ki zadostuje, da pride do obarjanja delcev za kaljenje, da olajšamo pretvorbo mikrostrukture jeklene plošče v pretežno popuščen fino zmavi letvasti martenzit, popuščen fino zmavi nižji bainit ali njihove zmesi.(e) stopping firefighting; and (f) failure of the steel plate at a temperature of about 400 ° C to about Aci transformation temperature over a period sufficient to cause precipitation of the quenching particles to facilitate the transformation of the steel plate microstructure into a substantially indented finely slagged molded martensite finely bind lower bainite or mixtures thereof. 2. Postopek po zahtevku 1, označen s tem, da je temperatura ponovnega segrevanja stopnje (a) med okoli 955°C in okoli 1065°C.Process according to claim 1, characterized in that the reheating temperature of step (a) is between about 955 ° C and about 1065 ° C. 3. Postopek po zahtevku 1, označen s tem, da pride do redukcije v debelini jeklenega slaba okoli 30% do okoli 70% v stopnji (b).Method according to claim 1, characterized in that the reduction in the thickness of the steel slab is about 30% to about 70% in step (b). 4. Postopek po zahtevku 1, označen s tem, da pride do redukcije v debelini jeklene plošče okoli 40% do okoli 80% v stopnji (c).Process according to claim 1, characterized in that the reduction in the thickness of the steel plate is about 40% to about 80% in step (c). 5. Postopek po zahtevku 1, označen s tem, da nadalje obsega stopnjo, pri kateri pustimo jekleno ploščo, da se zračno ohladi do sobne temperature s temperature po ustavitvi gašenja pred popuščanjem jeklene plošče v stopnji (f).5. The method of claim 1, further comprising the step of allowing the steel plate to cool to room temperature from the temperature after quenching before the steel plate is released in step (f). 6. Postopek po zahtevku 1, označen s tem, da jekleni slab stopnje (a) obsega železo in naslednje legime elemente v navedenih mas. odstotkih:A method according to claim 1, characterized in that the low grade steel (a) comprises iron and the following legime elements in said masses. percent: okoli 0,04% do okoli 0,12% C, vsaj okoli 1% Ni do pod okoli 9% Ni, okoli 0,1% do okoli 1,0% Cu, okoli 0,1% do okoli 0,8% Mo, okoli 0,02% do okoli 0,1% Nb, okoli 0,008% do okoli 0,03% Ti, okoli 0,001% do okoli 0,05% Al in okoli 0,002% do okoli 0,005% N.about 0.04% to about 0.12% C, at least about 1% Ni to below about 9% Ni, about 0.1% to about 1.0% Cu, about 0.1% to about 0.8% Mo , about 0.02% to about 0.1% Nb, about 0.008% to about 0.03% Ti, about 0.001% to about 0.05% Al, and about 0.002% to about 0.005% N. 7. Postopek po zahtevku 6, označen s tem, da jekleni slab obsega pod okoli 6 mas.% Ni.Method according to claim 6, characterized in that the steel poorly comprises less than about 6 wt% Ni. 8. Postopek po zahtevku 6, označen s tem, da jekleni slab obsega pod okoli 3 mas.% Ni in dodatno obsega okoli 0,5 mas.% do okoli 2,5 mas.% Mn.A method according to claim 6, characterized in that the steel poorly comprises less than about 3 wt% Ni and additionally comprises about 0.5 wt% to about 2.5 wt% Mn. 9. Postopek po zahtevku 6, označen s tem, da jekleni slab nadalje obsega vsaj en dodatek, izbran iz skupine ki obstoji iz (i) do okoli 1,0 mas.% Cr, (ii) do okoli 0,5 mas.% Si, (iii) do okoli 0,1 mas.% V in (iv) do okoli 2,5 mas.% Mn.A method according to claim 6, characterized in that the steel slab further comprises at least one additive selected from the group consisting of (i) up to about 1.0 wt% Cr, (ii) up to about 0.5 wt% Si, (iii) up to about 0.1 wt% V and (iv) up to about 2.5 wt% Mn. 10. Postopek po zahtevku 6, označen s tem, da jekleni slab nadalje obsega okoli 0,0004 mas.% do okoli 0,0020 mas.% B.A method according to claim 6, characterized in that the steel slab further comprises from about 0.0004% by weight to about 0.0020% by weight B. 11. Postopek po zahtevku 1, označen s tem, da jeklena plošča obsega v bistvu 100% popuščenega fino zmavega letvastega martenzita po popuščanju v stopnji (f).A method according to claim 1, characterized in that the steel plate comprises substantially 100% of the reduced finely slatted molded martensite after the failure in step (f). 12. Jeklena plošča, ki ima DBTT pod okoli -73°C tako v jekleni plošči kot tudi v njeni HAZ, natezno trdnost nad 830 MPa in mikrostrukturo, ki obsega pretežno popušČen fino zmav letvast martenzit, popuščen fino zmav nižji bainit ali njihove zmesi, pri čemer jekleno ploščo proizvedemo iz ponovno segretega jeklenega slaba, ki obsega železo in naslednje legime elemente v navedenih mas. odstotkih:12. A steel plate having a DBTT below about -73 ° C in both the steel plate and its HAZ, having a tensile strength exceeding 830 MPa and a microstructure comprising a substantially indented fine lath martensite, lax finite bainite or mixtures thereof, whereby the steel plate is produced from a reheated steel slab comprising iron and the following legime elements in said masses. percent: okoli 0,04% do okoli 0,12% C, vsaj okoli 1% Ni do pod okoli 9% Ni, okoli 0,1% do okoli 1,0% Cu, okoli 0,1% do okoli 0,8% Mo, okoli 0,02% do okoli 0,1% Nb, okoli 0,008% do okoli 0,03% Ti, okoli 0,001% do okoli 0,05% Al in okoli 0,002% do okoli 0,005% N.about 0.04% to about 0.12% C, at least about 1% Ni to below about 9% Ni, about 0.1% to about 1.0% Cu, about 0.1% to about 0.8% Mo , about 0.02% to about 0.1% Nb, about 0.008% to about 0.03% Ti, about 0.001% to about 0.05% Al, and about 0.002% to about 0.005% N. 13. Jeklena plošča po zahtevku 12, označena s tem, da jekleni slab obsega pod okoli 6 mas.% Ni.A steel plate according to claim 12, characterized in that the steel sheet has a low content of less than about 6% by weight. 14. Jeklena plošča po zahtevku 12, označena s tem, da jekleni slab obsega pod okoli 3 mas.% Ni in dodatno obsega okoli 0,5 mas.% do okoli 2,5 mas.% Mn.Steel plate according to claim 12, characterized in that the steel sheet has a low content of less than about 3 wt% Ni and additionally comprises about 0.5 wt% to about 2.5 wt% Mn. 15. Jeklena plošča po zahtevku 12, označena s tem, da nadalje obsega vsaj en dodatek, izbran iz skupine ki obstoji iz (i) do okoli 1,0 mas.% Cr, (ii) do okoli 0,5 mas.% Si, (iii) do okoli 0,1 mas.% V in (iv) do okoli 2,5 mas.% Mn.Steel plate according to claim 12, characterized in that it further comprises at least one additive selected from the group consisting of (i) up to about 1.0 wt% Cr, (ii) up to about 0.5 wt% Si , (iii) up to about 0.1 wt% V and (iv) up to about 2.5 wt% Mn. 16. Jeklena plošča po zahtevku 12, označena s tem, da nadalje obsega okoli 0,0004 mas.% do okoli 0,0020 mas.% B.Steel plate according to claim 12, characterized in that it further comprises about 0.0004% by weight to about 0.0020% by weight B. 17. Postopek za doseženje DBTT pod okoli -73°C v HAZ jeklene plošče, označen s tem, da dodamo vsaj okoli 1,0 mas.% Ni in vsaj okoli 0,1 mas.% Cu ter dodatno dodatek BCC stabilizimih elementov.17. A process for achieving DBTT below about -73 [deg.] C. in HAZ steel plates, characterized in that at least about 1.0 wt% Ni and at least about 0.1 wt% Cu are added and the addition of BCC stabilizers is added.