CN102753719A - High strength steel sheet having excellent brittle crack resistance and method for manufacturing same - Google Patents

High strength steel sheet having excellent brittle crack resistance and method for manufacturing same Download PDF

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CN102753719A
CN102753719A CN2010800638629A CN201080063862A CN102753719A CN 102753719 A CN102753719 A CN 102753719A CN 2010800638629 A CN2010800638629 A CN 2010800638629A CN 201080063862 A CN201080063862 A CN 201080063862A CN 102753719 A CN102753719 A CN 102753719A
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steel plate
fragility
plate
ctod
high tensile
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CN102753719B (en
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金相镐
房基铉
徐仁植
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Posco Holdings Co ltd
Posco Holdings Inc
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Posco Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • B21B3/02—Rolling special iron alloys, e.g. stainless steel
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2201/00—Treatment for obtaining particular effects
    • C21D2201/05—Grain orientation
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

Provided is a steel plate having excellent resistance to brittle crack initiation in a parent material zone and a weld heat affected zone. More particularly, the present invention relates to a high-strength steel sheet having excellent resistance to brittle crack initiation which includes 0.02 wt% to 0.06 wt% of carbon (C), 0.1 wt% or less of silicon (Si), 1.5 wt% to 2.0 wt% of manganese (Mn), 0.012 wt% or less of phosphorous (P), 0.003 wt% or less of sulfur (S), 0.5 wt% to 1.5 wt% of nickel (Ni), 0.003 wt% to 0.015 wt% of aluminum (Al), 0.005 wt% to 0.02 wt% of titanium (Ti), 0.005 wt% to 0.015 wt% of niobium (Nb), 0.002 wt% to 0.006 wt% of nitrogen (N), and iron (Fe) as well as unavoidable impurities as a remainder, and has a value of C+0.5Si-0.1Ni+6Al+3Nb of 0.1% or less, and a method of manufacturing the high-strength steel sheet.

Description

High tensile steel plate and method of manufacture thereof with good resistance to brittle fracture
Technical field
The present invention relates to be used for the high tensile steel plate of offshore structures and building structure; More specifically; Relate to at mother metal and welded heat affecting zone (Heat Affected Zone; HAZ) fragility open split (brittle crack initiation) have good resistivity high tensile steel plate, with and method of manufacture.
Background technology
To the quick growth of energy requirement, setting about the exploitation to the petroleum resources in extremely cold zone, particularly Karafuto and the Arctic Ocean according to emerging economy center such as the nations of China and India, these zones since low income before do not developing.
In order to ensure the safety of buildings, the steel that in the buildings in extremely cold zone, use need have high low temperature resistant fragility and open and split characteristic.Main use crack tip opening displacement (Crack Tip Opening Displacement, CTOD) test is opened the method for splitting characteristic as the low temperature resistant fragility of assessment based on fracture mechanics.
Up to the present, CTOD tests the fragility that mainly is used for assessing welded heat affecting zone and opens the resistivity of splitting.Differently, be to test therewith with shock test replaced C TOD for the mother metal district.Yet; Because consider the iceberg collision; Have the above high-strength steel plate of 50mm and on the offshore structures that is built in like extremely cold zones such as Karafuto and the Arctic Ocean, be widely used, in addition, the fatigue crack that embrittlement maybe be under special conditions originating from welding region by fatigue crack (fatigue crack) is along the direction that applies cyclic stress and generation after propagating into the mother metal district; For mother metal district and welded heat affecting zone, have high-caliber anti-fragility and open that to split characteristic be essential.
Open the steel plate that splits characteristic about having good low temperature resistant fragility, its correlation technique is described below.
The open text of korean patent application discloses a kind of method that prevents that brittle rupture (brittle fracture) produces in the welded heat affecting zone for 2002-0028203 number, and it is through adding near the grain coarsening that magnesium (Mg) produces the welded bonds (Fusion Line) when suppressing to weld.Yet this patent only guarantees for the preventing of the brittle rupture under temperature more than-10 ℃, therefore can not guarantee for as the resistivity of brittle rupture under-40 ℃ of low temperature.
Equally; The open text of korean patent application discloses a kind of technology 2008-0067957 number; Specific as follows: prevent sharply to reduce through the qualification that aluminium (Al) or niobium (Nb) is lower than preset limit value in the toughness that welded heat affecting zone takes place, and through using toughness to welded heat affecting zone to influence less manganese (Mn) even guarantee that under-40 ℃ low temperature fragility to welded heat affecting zone opens ripper resistivity is arranged.Yet, this patent not to the fragility in the mother metal district that differs from welded heat affecting zone open split how to guarantee resistivity method describe.
Simultaneously; The fragility that the open text of korean patent application discloses mother metal district and welded heat affecting zone under a kind of right-40 ℃ of low temperature for 2006-0090287 number open ripper have good resistivity the method for manufacture of steel; As a technology guaranteeing the steel plate physical properties; It suppresses the formation on martensite island through reducing carbon (C) content, and has utilized the deposit sclerosis that produces owing to the formed copper of Cu (Cu) deposition of adding more than 0.8%.Yet, because, carrying out controlled rolling therein in order to obtain the Cu deposition under the state of heavy addition Cu, this patent needs extra ageing treatment afterwards with the acceleration cooling, therefore may cause the loaded down with trivial details and manufacturing cost raising of manufacturing processed.
Summary of the invention
The problem that invention will solve
One aspect of the present invention provides a kind of to have good anti-fragility and opens and split characteristic, can suppress at low temperatures that the fragility in mother metal district and welded heat affecting zone (HAZ) opens the high tensile steel plate that splits and have the above ys of 420MPa, and the method for making this high tensile steel plate.
The scheme of dealing with problems
One aspect of the present invention provides to have good anti-fragility and opens the high tensile steel plate that splits characteristic, and it comprises: the C of 0.02wt%-0.06wt% (carbon); Si (silicon) below the 0.1wt%; The Mn of 1.5wt%-2.0wt% (manganese); P (phosphorus) below the 0.012wt%; S (sulphur) below the 0.003wt%; The Ni of 0.5wt%-1.5wt% (nickel); The Al of 0.003wt%-0.015wt% (aluminium); The Ti of 0.005wt%-0.02wt% (titanium); The Nb of 0.005wt%-0.015wt% (niobium); The N of 0.002wt%-0.006wt% (nitrogen); With the Fe (iron) and the unavoidable impurities of surplus, wherein, the value of C+0.5Si-0.1Ni+6Al+3Nb is below 0.1wt%.
Another aspect of the present invention provides to make has the method that good anti-fragility opens the high tensile steel plate that splits characteristic, and it comprises: the plate slab that satisfies above-mentioned compositing range at 1000 ℃ of-1100 ℃ of scope internal heating; Under temperature more than 950 ℃, the slab of said heating is carried out roughing with the accumulative total draft more than 40% (cumulative reduction rate); In 700-800 ℃ of scope, carry out finish rolling after the roughing; And the steel plate behind the cold rolling.
The invention effect
One aspect of the present invention; Can provide have the above ys of 420MPa, simultaneously the fragility of the mother metal under the low temperature of right-60 ℃ and-40 ℃ and welded heat affecting zone open ripper have good resistivity high tensile steel plate, and the method for making said high tensile steel plate.Above-mentioned Plate Steel can be used for offshore structures, building structure, boats and ships and the oil tanker etc. that move at extreme environment.
Description of drawings
Fig. 1 representes the chart according to the crack tip opening displacement of the welded heat affecting zone of C+0.5Si-0.1Ni+6Al+3Nb numerical value (CTOD) test-results.
Fig. 2 representes the chart according to the CTOD test-results in the mother metal district of effective size of grain (effective grain size).
Embodiment
Below, the present invention is specified.
The inventor recognizes that the martensite island structure that results from welded heat affecting zone is the reason that produces embrittlement in the welded heat affecting zone at low temperatures.Particularly; Even also may in like the test of the crack tip opening displacement (CTOD) under-40 ℃ the low temperature, cause brittle rupture because very small amount of martensite island is present in the welded heat affecting zone; Therefore the inventor recognizes that the inhibition on martensite island is very important, and deep research has been carried out in the generation of the martensite island structure that suppresses welded heat affecting zone.
In addition; As the result that the reason that in the Plate Steel mother metal of the above thickness of 50mm, produces embrittlement is studied; The inventor has found that also brittle rupture mainly occurs in the plate center on the steel plate thickness direction; And embrittlement originates from coarse relatively crystal grain place in the plate center crystal grain on the thickness direction on microtexture, and as the result that the method that suppresses embrittlement is furtherd investigate, the inventor has accomplished the present invention simultaneously.
Below, to of the present invention with part by weight (hereinafter, wt%) meter compositional range specify.
Carbon (C): 0.02%-0.06%
, be necessary that therefore the content of the restriction C of elder generation suppresses the formation on martensite island because thereby C constitutes to betide the important alloying element that welded heat affecting zone causes the martensite island of brittle rupture.If the content of C is higher than 0.06%, then owing to the martensite island fully not being suppressed and can not realizing the object of the invention.Therefore, the upper limit of C preferably defines 0.06%.Yet,, therefore preferably its lower limit is limited to 0.02% if the content of C is crossed the low intensity that is difficult to guarantee steel plate.
Silicon (Si): (do not comprise 0%) below 0.1%
Si improves necessary element in the deoxidation of tensile strength and steel in mother metal district; Yet; By not changing austenite cooling and when forming final structure through Thermal Cycle is formed; Si prevents not change austenite and resolves into ferritic and cementite, thereby promotes the formation on martensite island, has therefore significantly reduced CTOD toughness in welding heat affected zone.Therefore, the addition of Si preferably defines below 0.1%.
Manganese (Mn): 1.5%-2.0%
Because Mn is a useful element of guaranteeing intensity, must add Mn more than 1.5% to guarantee the intensity of steel plate.Yet; If the addition of Mn is too much; Then promote on thickness direction formation, and promoted the formation on the martensite island in being formed with the part of center segregation partly, so it has significantly worsened the CTOD characteristic in welding heat affected zone at the center segregation at plate center.Therefore the upper limit of Mn preferably defines 2.0%.
Phosphorus (P): below 0.012%, sulphur (S): below 0.003%
Because P and S are the elements that produces embrittlement of grain boundaries (grain boundary embrittlement) in the welded heat affecting zone, be necessary the content of P and S minimized.Yet it is inconvenient in steelmaking process, P and S being reduced to very low level, and therefore the content with P is limited to below 0.012%, and the content of S is limited to below 0.003%.
Nickel (Ni): 0.5%-1.5%
Ni can improve hardening capacity and promote the formation on martensite island.But comparison therewith, the toughness strengthening effect of the matrix that is brought is more outstanding, and therefore differently with other alloying element, Ni can have the effect of raising to the toughness in welding heat-affected zone.In addition, the tough property improvement effect of the matrix that is caused by Ni also can be presented in the mother metal district, also is effective for the toughness of strengthening the mother metal district therefore.In addition, in order to ensure required armor plate strength among the present invention under the extremely limited state of the content of C and Si, Ni need add the content more than 0.5%.Yet if add excessive N i, the effect that substrate tissue toughness strengthens will reach capacity, and therefore preferably its upper limit will be limited to 1.5%.
Aluminium (Al): 0.003%-0.015%
Similar with Si, Al is through preventing in the Thermal Cycle process to form the element that ferritic and cementite impel the martensite island to form by unconverted austenite.Surpass 0.015% content if Al adds, then significantly reduce the toughness of welded heat affecting zone, therefore preferably its upper limit is limited to 0.015%.Yet Al is unusual effective elements for the deoxidation of steel.If be limited to the content of Al under the state below 0.1% in the present invention at Si content low too, the deoxidation of steel can not fully realize, so the spatter property of steel possibly significantly worsen.Therefore, Al preferably adds the content more than 0.003%.
Titanium (Ti): 0.005%-0.02%
Ti forms tiny nitride through combined nitrogen (N) and prevents the grain coarsening near the generation of weld-fusion line place, has therefore improved the toughness of welded heat affecting zone.If the content of Ti is low excessively, then because the inadequate formation of Ti nitride possibly can't prevent the grain coarsening near the weld-fusion line place.Therefore, Ti preferably adds the amount more than 0.005%.Yet; If Ti adds with the content above 0.02%, when forming the Ti nitride, also form the Ti carbide, and the hardness of mother metal district and welded heat affecting zone possibly improve owing to the precipitation hardening effect of Ti carbide; Therefore, fragility opens the possibility of splitting can increase.Therefore, its upper limit preferably defines 0.02%.
Niobium (Nb): 0.005%-0.015%
Nb be when adding, reduce to the resistivity of the brittle rupture of welded heat affecting zone alloying element.Yet Nb helps refined structure very much in controlled rolling-accelerating cooling process, thus Nb be improve to the resistivity of the brittle rupture in mother metal district important element.Particularly, in the Plate Steel of the above thickness of 50mm, the effective size of grain below the 30 μ m required for the present invention is difficult to obtain, even carried out controlled rolling-accelerating cooling process, carries out structure refinement only if add Nb simultaneously.Therefore, Nb preferably adds 0.005% above content and guarantees the resistivity of wanting to the brittle rupture in mother metal district required for the present invention.Yet when Nb adds when excessive, to such an extent as to possibly promote the generation on martensite island to worsen the toughness of welded heat affecting zone, therefore, its upper limit preferably defines 0.015%.
Nitrogen (N): 0.002%-0.006%
N combines Ti to form the TiN particle, has therefore prevented the grain coarsening near weld-fusion line.The content that therefore, possibly comprise more than 0.002% obtains above-mentioned effect.Yet as N during by excessive interpolation, the toughness of mother metal district and welded heat affecting zone maybe be owing to do not worsen with the Ti bonded N atom that dissociates.Therefore, the upper limit of N preferably defines 0.006%.
In the present invention, can guarantee enough physical propertiess through above-mentioned basal component.Yet, can add the characteristic that copper (Cu) further improves steel plate.The content of Cu can be below 0.35%.Cu can guarantee armor plate strength and the toughness of welded heat affecting zone is damaged less relatively alloying element.Yet armor plate strength excessively improves when the excessive interpolation of Cu, therefore, can not in the mother metal district, obtain stable CTOD toughness, and the Cu crackle possibly begin to occur in the surface of slab and steel plate.Therefore, the upper limit of Cu preferably defines 0.35%.
Fe and unavoidable impurities are as surplus and involved.
In the present invention, the value of the C+0.5Si-0.1Ni+6Al+3Nb in component is preferably below 0.1%.
To influencing after alloying element that welded heat affecting zone martensite island produces done further investigation, the inventor obtain a kind of hot input range be 0.8kJ/mm-4.5kJ/mm low-in the condition of heat input welding under with the minimized method of generation on the martensite island of welded heat affecting zone.
In order to infer the mutual relationship between alloying element and the welded heat affecting zone based on above-mentioned result of study; The inventor has carried out the welded heat affecting zone simulated experiment; It is used for simulating critical hot again coarse-grain (intercritically reheated coarse grained) district, and this district is as a zone that in welded heat affecting zone, forms a large amount of martensite islands and known.
Simulation to critical hot coarse grain zone again is under such mode, to carry out: the small samples with 10mm thickness, 10mm width and 60mm length is heated to 1400 ℃ temperature; Cool off in 800 ℃-500 ℃ TR with the rate of cooling of 20 ℃/s then; And critical heat again, afterwards with the cooling of the rate of cooling of 20 ℃/s in the TR of maximum heating temperature to 500 ℃.Introduce fatigue crack to be up to 50% of heat affected zone analog sample width, under-40 ℃, carry out the CTOD test then.Infer the relation between the CTOD toughness of alloying element and welded heat affecting zone from the result of test, and its result is presented among Fig. 1.
Fig. 1 illustrates the relation between the critical CTOD trial value under the value of C+0.5Si-0.1Ni+6Al+3Nb and from the analog sample of heat affected zone, obtain-40 ℃.Can know that the value of C+0.5Si-0.1Ni+6Al+3Nb is low more, the CTOD threshold value of the welded heat affecting zone under-40 ℃ is high more.If the value of C+0.5Si-0.1Ni+6Al+3Nb is higher than 0.2%, then brittle rupture all takes place in all samples.According to Fig. 1, can know that the value of C+0.5Si-0.1Ni+6Al+3Nb must be below 0.1% so that reach more than the 0.25mm in the CTOD of-40 ℃ of measurements threshold value.
In formula C+0.5Si-0.1Ni+6Al+3Nb, promoted fragility in the welded heat affecting zone to open when adding C, Si, Al and Nb alloying element and split, but only had Ni that adverse effect is arranged.To the explanation of its reason is that substrate tissue toughness's stiffening effect of Ni likens that to reduce the flexible effect more obvious through increasing the martensite island in welded heat affecting zone for hardening element to.
In steel plate of the present invention; In having minimum 5000 above crystal grain---plate center that said crystal grain is defined in the steel plate thickness direction through EBSD figure (Electro Back-Scattered Pattern, EBSP) the grain orientation mistake measured of method is the above borders of 15 degree---the average circular equivalent diameter of the crystal grain of preceding 5% size is preferably in below the 30 μ m.In the present invention, the plate center on the thickness direction be defined as be located on the thickness direction apart from steel plate thickness 1/2 place ± 1mm in.
Usually, be used for the measurement of granularity based on the image analysis method of optical microscope image.Yet, in said image analysis method, have only when microtexture is made up of polygonal ferrite and perlite, can analyze relatively accurately it; Because the grain boundary is unsharp in having the microtexture that pin type ferritic or its be mixed with bainite, possibly be unusual difficulty therefore to the accurate measurement of granularity.
Therefore, the inventor adopts the EBSP method based on the Kikuchi pattern, its objective is the granularity of measuring thickness direction upper plate center more accurately.The EBSP method has the advantage that the microtexture of not receiving can be carried out quantitative analysis to the intergranular misorientation with influencing.When through this method definition crystal grain, have the above border of measuring the intergranular misorientation of 15 degree and be defined as the wide-angle grain boundary.
Size-grade distribution and CTOD characteristic through the plate center on the thickness direction that will utilize the acquisition of EBSP method compare; Can find; Anti-fragility opens that to split characteristic be to confirm by having the crystal grain that belongs to before whole size-grade distribution 5% size, rather than is confirmed by the crystal grain of the size of the whole crystal grain that are defined as the wide-angle grain boundary.To that is to say, in order improving mother metal district fragility to be opened the resistivity of splitting, some coarse grains that suppress the microtexture at the plate center on the thickness direction are very important.
In the present invention; Have in the minimum 5000 above particles that are defined as border (wide-angle grain boundary) of the above grain orientation mistake of 15 degree through of the plate center measurement of EBSP method at the steel plate thickness direction; Have the average circular equivalent diameter of the crystal grain (effectively crystal grain) of preceding 5% size, be defined as effective size of grain.
In order to infer the effective size of grain that defines among the present invention and to the correlationship between the resistivity of the brittle rupture in the mother metal district; Through changing heating and rolling condition, prepare sample with multiple granularity by the slab that consists of 0.05C-0.04Si-1.62Mn-0.95Ni, and through utilizing sample under all temps, to carry out the critical CTOD transition temperature that CTOD has obtained 0.25mm after testing.Transition temperature when here, the critical CTOD transition temperature of the 0.25mm critical CTOD value representing to measure is for 0.25mm.Show in Fig. 2 from the effective size of grain of each sample and the mutual relationship between the critical CTOD transition temperature of 0.25mm.
Can know that by Fig. 2 when the effective size of grain that defines among the present invention is 30 μ m when following, can obtain-60 ℃ of lower critical CTOD minimum value is the steel plate more than the 0.25mm.When effective particle diameter during greater than 30 μ m, the critical CTOD value in-60 ℃ steel plate mother metal district becomes below the 0.25mm, therefore, possibly can't reach target of the present invention.
In addition, the basic microtexture at thickness direction upper plate center preferably comprises ferritic, bainite or they is not contained martensitic composite structure here.Reason is, to such an extent as to even since martensitic hardness too high have under the fine-grained situation as-60 ℃ extremely low temperature under also causing the phenomenon of advancing by leaps and bounds (pop-in phenomenon) easily, thereby can't guarantee target CTOD threshold value.
That is to say; In the steel plate of the present invention; Because the mother metal district CTOD threshold value at-60 ℃ is more than the 0.25mm; And the welded heat affecting zone in-40 ℃ welding process (HAZ) CTOD threshold value is more than the 0.25mm, so also the same with the welded heat affecting zone characteristic that obtains good anti-low-temperature embrittleness in mother metal district.
Specify in the face of method of manufacture of the present invention down.
The plate slab that satisfies said composition heats in 1000 ℃-1100 ℃ TR.
Said slab preferably uses the slab of continuous casting.Because casting process have than ingot iron process faster molten steel solidification speed with solidify after rate of cooling, can obtain meticulousr TiN particle in the material, therefore can improve the resistivity of splitting is opened in mother metal district and welded heat affecting zone fragility.
The Heating temperature of slab is the important factor that influences the final structure granularity.When the Heating temperature of slab is higher than 1100 ℃, can not fully refinement final structure, and make the TIN particle in the structure become coarse and reduce the toughness in welding heat affected zone.Therefore, its upper limit preferably defines at 1100 ℃.On the contrary, when the Heating temperature of slab was lower than 1000 ℃, alloying element possibly dissolve insufficient, and abundant rolling on recrystallization temperature possibly be difficult.Therefore, the heating of slab can be carried out under the temperature more than 1000 ℃.
Behind the heating slab, under the temperature more than 950 ℃, carry out roughing with the accumulation draft more than 40%.Austenite particulate recrystallization occurs in the temperature more than 950 ℃ actively, so granularity can reduce.In addition, having the reason of accumulating draft more than 40% is to be lower than at 40% o'clock at the accumulation draft may in final structure, produce mixing crystal grain (mixed grain) because the recrystallization generation of austenite crystal is insufficient.
Finish rolling can be carried out in 700 ℃-800 ℃ TR.When final rolling temperature is higher than 800 ℃, fragility is opened the resistivity of splitting to accomplish insufficient assurance that can not get owing to the structure refinement at thickness direction upper plate center.Final rolling temperature is low more, and the structure at thickness direction upper plate center may be meticulous more.Yet, when final rolling temperature is too low, cause rolling yield too low so possibly be difficult in industry and go up to use.Therefore, its lower limit preferably defines at 700 ℃.
In addition, finish rolling is preferably in accumulation draft situation about being at least more than 40% to be got off to carry out, with further refinement final structure.
Cooling is carried out after said controlled rolling, and here, rate of cooling and cooling termination temperature are preferably respectively in the scope of 3 ℃/s-20 ℃/s and 350 ℃-550 ℃.Split because when intensity excessively is higher than target value, can promote fragility to open, it is very important therefore not having too high intensity.Viewpoint like this, rate of cooling and cooling termination temperature can be respectively with more than 350 ℃ below the 20 ℃/s.Yet because target strength of the present invention can not obtain when cooling is insufficient, rate of cooling and cooling termination temperature can be respectively that 3 ℃/s is above with below 550 ℃ for this reason.
Embodiment
Specify in the face of embodiment of the present invention down.Yet the present invention is not limited to following embodiment.
(embodiment)
In 300 tons of electric furnaces, prepare molten steel according to the component shown in the table 1, and prepare the slab of 300mm through continuous cast method.As shown in table 2, the slab of preparation heats and carries out roughing and finish rolling thus, and prepares steel through final acceleration cooling.
EBSD figure (EBSP) equipment that is installed on sem (SEM) can be used to measure the effective size of grain of prepared steel plate.Used enlargement ratio is in 300 times-500 times scope, and step-length is 0.75 μ m, observes at the thickness direction of rolling xsect and the plate center on the thickness direction.In order to obtain significant data value, the minimum 5000 above crystal grain that are defined as border have been comprised with the above grain orientation mistake of 15 degree.Through using the software that to analyze the misorientation of measuring by the EBSP method, calculate defined effective size of grain among the present invention.Tension test is carried out through the sample of collecting the steel plate for preparing through the condition shown in the table 1 and 2, and carries out the CTOD test with the resistivity of assessment to the brittle rupture in mother metal district.After collecting sample with the mode that becomes the length direction of sample at 1/4 place of the steel plate thickness on distance surface, perpendicular to the direction of rolling direction, sample machine is machined for the clavate sample of tension test.CTOD sample evidence BS7448 standards is helped thick sample, and the length direction of sample is perpendicular to rolling direction.Behind the making of electrodischarge machining(E.D.M.) in CTOD sample groove, produce fatigue crack until 50% specimen width, CTOD test afterwards under-60 ℃ temperature, each sample is carried out three times and each sample is assessed with its minimum value.
Split characteristic for the anti-fragility of the welded heat affecting zone of assessing made Plate Steel opens, assess according to APIRP 2Z standard.Make according to API RP 2Z standard and singly to burst at the seams, and be respectively under 0.8kJ/mm and the 4.5kJ/mm the welding heat input of medicine core welding arc weldering (Flux Cored Arc Welding) and submerged arc welding (Submerged Arc Welding) and weld.According to the BS7448 standard, in the mother metal district, thick sample is helped in welded sample processing, and fatigue crack is incorporated in the coarse grain zone near weld-fusion line.CTOD test afterwards under-40 ℃, each sample is carried out three times and each sample is assessed with its minimum value.
Table 3 is represented steel plate ys and the tensile strength through the tension test acquisition, and the mother metal districts that under-60 ℃ and-40 ℃, assess respectively and the CTOD threshold value of welding region.Wherein, each the CTOD threshold value shown in the table 3 is minimum in three trial values, and CTOD-60 is illustrated in the CTOD trial value of-60 ℃ mother metal district assessment, and CTOD-40 is illustrated in the CTOD trial value of-40 ℃ welded heat affecting zone assessment.
[table 1]
Figure BDA00002010892800101
Figure BDA00002010892800111
[table 2]
Figure BDA00002010892800112
Figure BDA00002010892800121
[table 3]
Figure BDA00002010892800131
In the invention example 1-16 of correspondence composition of the present invention and method of manufacture institute; The effective size of grain that the present invention confirms is below the 30 μ m; The CTOD threshold value in-60 ℃ of mother metal districts that assess down is more than the 0.25mm; And the CTOD minimum value of the welded heat affecting zone under-40 ℃ also is more than the 0.25mm under the heating initial conditions in low, therefore, can obtain extraordinary anti-fragility and open fragility.
On the contrary, in comparative example 1, the CTOD value of welded heat affecting zone is not higher than 0.25mm, is because the value of C+0.5Si-0.1Ni+6Al+3Nb has exceeded 0.1%.The value of discontented unabridged version scope of invention of Si in comparative example 2 and Al and C+0.5Si-0.1Ni+6Al+3Nb is also up to 0.199%, and therefore, the CTOD characteristic of-40 ℃ welded heat affecting zone is non-constant.
In comparative example 3, the value that Nb has broken away from the scope of the invention and C+0.5Si-0.1Ni+6Al+3Nb also is more than 0.1%.In comparative example 4, the value of C+0.5Si-0.1Ni+6Al+3Nb is below 0.1%, and it has reached target of the present invention.Yet, because that the content of C is higher than the toughness of scope thereby welded heat affecting zone of the present invention's definition is not enough.In comparative example 5, because the deficiency of Ni content, armor plate strength is not enough, and the toughness of mother metal district and welded heat affecting zone is all not enough.
About comparative example 6-8, alloy compositions belongs to the scope of the invention, and the value of C+0.5Si-0.1Ni+6Al+3Nb is below 0.1%, and therefore, the toughness of welded heat affecting zone is not very poor.Yet because required for the present invention creating conditions do not satisfied, effective size of grain is more than the 30 μ m.In addition, in comparative example 7, intensity does not reach level of the present invention yet.In comparative example 9, the toughness of welded heat affecting zone worsens owing to the value of C+0.5Si-0.1Ni+6Al+3Nb has exceeded 0.1%, and causes the ys of steel plate not reach 420MPa owing to the rate of cooling in creating conditions is insufficient.

Claims (9)

1. have good anti-fragility and open the high tensile steel plate that splits characteristic, comprise:
The C of 0.02wt%-0.06wt%,
Si below the 0.1wt%,
The Mn of 1.5wt%-2.0wt%,
P below the 0.012wt%,
S below the 0.003wt%,
The Ni of 0.5wt%-1.5wt%,
The Al of 0.003wt%-0.015wt%,
The Ti of 0.005wt%-0.02wt%,
The Nb of 0.005wt%-0.015wt%,
The N of 0.002wt%-0.006wt% and
As the Fe and the unavoidable impurities of surplus,
Wherein, the value of C+0.5Si-0.1Ni+6Al+3Nb is below the 0.1wt%.
2. the good anti-fragility that has of claim 1 opens the high tensile steel plate that splits characteristic, and its light plate also comprises the Cu below the 0.35wt%.
3. the good anti-fragility that has of claim 1 opens the high tensile steel plate that splits characteristic; Wherein, the average circular equivalent diameter of the crystal grain of the size of---it is the border more than 15 degree that said crystal grain is defined as the grain orientation mistake of measuring at the plate center of steel plate thickness direction through the EBSD drawing method---preceding 5% is below the 30 μ m in having minimum 5000 above crystal grain.
4. the good anti-fragility that has of claim 3 opens the high tensile steel plate that splits characteristic, and wherein, the structure that is arranged in the plate center of steel plate thickness direction comprises any of ferritic, bainite and its composite structure.
5. the good anti-fragility that has of claim 1 opens the high tensile steel plate that splits characteristic; Wherein, CTOD threshold value in the steel plate mother metal district under-60 ℃ is more than the 0.25mm, and the CTOD threshold value in the welded heat affecting zone under-40 ℃ (HAZ) is more than the 0.25mm.
6. a manufacturing has the method that good anti-fragility opens the high tensile steel plate that splits characteristic, comprising:
At 1000 ℃ of-1100 ℃ of a kind of plate slabs of TR internal heating; Said plate slab comprise Ti, the 0.005wt%-0.015wt% of Al, the 0.005wt%-0.02wt% of Ni, the 0.003wt%-0.015wt% of Mn, the P below the 0.012wt%, the S below the 0.003wt%, the 0.5wt%-1.5wt% of Si below the C, 0.1wt% of 0.02wt%-0.06wt%, 1.5wt%-2.0wt% Nb, 0.002wt%-0.006wt% N and as the Fe and the unavoidable impurities of surplus, and have the value of the C+0.5Si-0.1Ni+6Al+3Nb below 0.1%;
With the accumulation draft more than 40% at the plate slab that is heated of the temperature roughing more than 950 ℃,
After the roughing, in 700 ℃-800 ℃ TR, carry out finish rolling; And
The steel plate that cooling is rolled.
7. the method for claim 6, wherein, plate slab also comprises the Cu below the 0.35wt%.
8. the steel plate of claim 6, wherein, finish rolling is carried out with the accumulation draft more than 40%.
9. the method for claim 6, wherein, rate of cooling in process of cooling and cooling termination temperature are respectively in 3 ℃/s-20 ℃/s and 350 ℃ of-550 ℃ of scopes.
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