CA1207639A - Low alloy steel plate and process for production therefor - Google Patents
Low alloy steel plate and process for production thereforInfo
- Publication number
- CA1207639A CA1207639A CA000449354A CA449354A CA1207639A CA 1207639 A CA1207639 A CA 1207639A CA 000449354 A CA000449354 A CA 000449354A CA 449354 A CA449354 A CA 449354A CA 1207639 A CA1207639 A CA 1207639A
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- CA
- Canada
- Prior art keywords
- steel
- thickness
- low alloy
- hot
- copper
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
-
- 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
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
-
- 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
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/02—Hardening by precipitation
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
LOW ALLOY STEEL PLATE AND
PROCESS FOR PRODUCTION THEREOF
ABSTRACT OF THE DISCLOSURE
Low alloy steel shape of at least 4.8 mm thickness is produced by providing a steel consisting essentially of from about 0.02% to 0.07% carbon, 1.2% to 2.0%
manganese, 0.020% maximum sulfur, up to 0.5% silicon, 0.1% to 0.4% molybdenum, 0.01% to 0.1% columbium, about 0.01% to 0.10% acid soluble aluminum, about 0.8% to 2.0%
copper, about 0.4% to 2.0% nickel, residual chromium, and balance iron; hot reducing the steel to a desired final thickness with a total reduction in thickness of at least 30% while within the temperature range of about 760° to 927°C whereby to avoid substantial recrystallization of austenite and to obtain a predominant heavily deformed austenite phase; and cooling at a rate which transforms the austenite phase to a predominantly fine acicular ferrite and lower-bainite phase. The steel may also be precipitation hardened, or may be hot reduced either by the above-described controlled hot reduction or by conventional hot reduction, austenitized, quenched, and precipitation hardened. The product has high strength, improved low temperature toughness and excellent weldability.
PROCESS FOR PRODUCTION THEREOF
ABSTRACT OF THE DISCLOSURE
Low alloy steel shape of at least 4.8 mm thickness is produced by providing a steel consisting essentially of from about 0.02% to 0.07% carbon, 1.2% to 2.0%
manganese, 0.020% maximum sulfur, up to 0.5% silicon, 0.1% to 0.4% molybdenum, 0.01% to 0.1% columbium, about 0.01% to 0.10% acid soluble aluminum, about 0.8% to 2.0%
copper, about 0.4% to 2.0% nickel, residual chromium, and balance iron; hot reducing the steel to a desired final thickness with a total reduction in thickness of at least 30% while within the temperature range of about 760° to 927°C whereby to avoid substantial recrystallization of austenite and to obtain a predominant heavily deformed austenite phase; and cooling at a rate which transforms the austenite phase to a predominantly fine acicular ferrite and lower-bainite phase. The steel may also be precipitation hardened, or may be hot reduced either by the above-described controlled hot reduction or by conventional hot reduction, austenitized, quenched, and precipitation hardened. The product has high strength, improved low temperature toughness and excellent weldability.
Description
~2~D7~3~
LOW ALLOY STEEL PI.ATE AND
PROCESS FOR PRODUCTION THEREOF
This inven~ion relates to a low alloy steel shape of at least 3/16 inch (4.8 mm) thickness having improved yield strength, toughness and excellent weld-ability, and to a novel process for the production thereof.
The steel shape of the invention ~ay be produced, from a castiny or previously rolled slab as a starting material, in the :Eorm of plate, bar, tube and structural shape, as hot reduced, hot reduced and precipitation hardened, or hot reduced, austeniti~ed, quenched and precipitation hardened products. Al~hough not so limited, the invention has particular utility in the production of plate of at least 3/16 inch thickness which retains yood tou~hness in the heat afected zone of weldments made by any of the usual welding processesO
Steel plate hot rolled in accordance with the process of the invention exhibits a yield strength of at least 80 ksi (56 kg/mm2)at room temperature and a Charpy V-notch impact strength of at least 20 ft-lbs (27 Joules) in the longitudinal direction at -S0F (-46CC). Wh~n hot rolled in accordance with the proce~s of the invention and precipitation hardenQd, steel plate e~hibits a yield strength of at least 85 ksi (60 kg/mm2)at room t~npera-ture and a Charpy V-notch impact strength o at least 20 ft-lbs (27 Joules) l~ngitudinal at -50F (-46C~. When hot rolled in conventional manner, austenitized, quenched and precipitation hardened, the steel plate of the invention has a yield strength of at least 80 k~i ~56 kg/mm2) at room temperature and a Charpy V-notch impact strength of at least 50 ft-lbs (68 Joules) longitudinal at 80E' (-62C)-~,V~;
~, ~D7~3~
1 British Patent 1,436,846, published May 26, 1976, discloses a steel alleged to exhibit good weldability and high strength containing from 0.4 to 0.8~ nickel, 0.7 to 1~1% copper, 0.01 to 0.09~ carbon, 0.02 to 0.1~ niobium, 1.1 to 1.65~ manganese, 0 to 0.5% chromium, 0 to 0.6%
silicon, 0 to 0.5~ molybdenum, 0 to 0.01% boron, 0 to 0.08% aluminum, 0 to 0.1% total of at least one of zir-conium, magnesium, c~lcium, and rare earth me~als, and balance iron except for impurities. Exemplary steels are stated to have a yiel.d strength of at least 450 MN/m~
(65 ksi) and a toughness level such that the 70 J transi-tion temperature is below 10C when the hot rolled plate is finished at a temperature up to 1050C. Hot rolling finishing temperatures ranged from 950 to 1050C in the specific examples.
ASTM A710 Grade B steel is based on United States Patent 3,132,025, issued to Hurley May 5, 1964, which discloses a low alloy structural steel alleged to exhibit in the hot rolled condition an excellent combination of metallurgical properties. The steel contains up to 0.08 carbon, about 0.2 to 0.75% manganese, up to 0.35~
silicon, about 1 to 1.7~ copper, about 0.7 to 1.6%
nickel, about 0.01 to 0.16~ columbium (niobium) and balance essentially iron. Up to 0.1% aluminum may also be present. The steel is stated to exhibit a yield strength of at least 70 Xsi at room temperature, a Charpy V-notch impact strength of at ~east 15 ft-lbs at -50F
and a reduction of area of at least 60~. The steel is processea by heating above about 2000F, hot rolled and finished at about 1650F. A precipitation hardening treatment can also be applied by heatlng between about 850 and 1150 DF for about 1 hr.
United States Patent 3,945,8S8, issued March 23, 1976 to Matsubara et al, discloses a low alloy steel alleged to have high notch toughness at low temperature, ~2d~7~3~
1 comprising 0.02 to 0.10% carbon, 1.20 to 1.80% manganese, less than 0.015% sulfur, 0.05 to 0.50% chromiurn, 0.01 to 0.10~ niobium, 0.10 to 0.50% ~ilicon, less than 0.030%
phosphorus, 0.05 to 0.50% nickel, 0.05 to 0.50% copper and balance iron and unavoidable impurities. A rare earth metal or alloy may be added within the range of 0.01 to 0.20%. The steel i5 hot rolled with a reduction in thickness of from 30 to 80~ at a tempera~ure below 950C (1742F). This is alleged to result in improved notch toughness.
United States Patent 3,955,971, issued May 11, 1976 to Reisdorf, discloses a low alloy structural steel having good low temperature properties, such as a mi~imum yield strength of at least 60 ksi and good impact toughness down to temperatures as low as -80F. The steel comprises 0.06 to 0.12% carbon, 0.20 to 1~00%
manganese, 0.020% maximum phosphorus, 00015% m~iml7m sulfur, 0.15 to 0.40% silicon, 0.75 to 1.50% nickel, 0.50 to 1.25% chromium, 0.15 to 0.40% molybdenum, 0.010 to 0.060% aluminum, 0.75% maximum copper with copper plus chromium being 1.50~ maximum, and balance iron and conventional impurities. In the processing of exsmplary 1 and 2 inch thick plates, samples were austenitized at 1650CF, water quenched, and then tempered at 1150, 1200 and 1250F.
Other prior art or which applicant is aware includes United States Patents 3,692,514, 3,841,866; 3,849,209 and 4,008,103, and Canadian Patent 988,751.
ASTM alloy A710, Grade A, has an analysis, in weight percent, of 0.07% m;7~iml7m carbon, 0.40 to 0.70% manga-nese, 00025% maximum phosphorus~ 0.025~ maximum sulur, 0.40~ m~;mllm silicon, 0.70 to 1~00% nickel, 0.60 to 0.90~ chromium, 0.15 to 0.25% molybdenum, 1.00 to 1.30%
copper, 0.02% minimum columbium, and balance iron. This composition is based on the above-mentioned U.S. Pa~ent 3,692,51~.
1 Despite the numerous prior art developments in -the field o~ low alloy steel plate for structural purposes, there is still a need for such a steel in plate form, particularly in thicknesses of 3/16 to 2" (4.8 to Sl mm), which consistently exhibits a yield strength of at least 80 ksi at room temperature, a Charpy V-notch impact strength of at least 20 ft-lbs (longitudinal) and at least 15 ft-lbs (transverse) at -50F in the hot rolled condition, a yield strength of at least 85 ksi and a Charpy V-notch impact streng~h of at least 20 -Et-lbs (longitudinal) and at least 15 ft-lbs (transverse) at -50F in the rolled and precipitation hardened condition;
and a yield strength of at least 80 ksi and a Charpy V-notch impact strength of at least 50 ft-lbs (longitudinal) and at least 35 ft-lbs t47 Joules) (transverse~ at -80F in the quenched and precipitation hardened condition, together with excellent weldability, particularly retention of toughness in the heat affected zone of a weldment made by any of the usual welding processesO
It is an object of the invention to pro~ide a process for producing low alloy steel plate by coR~rolled hot rolling, which plate will possess adequate mechanical and metallurgical properties for most applications in the as-hot rolled condition.
It is a another object of the invention to provide a process for producing low alloy steel plate of at least 3/16 inch thickness by controlled hot rolling and precipitation h~rdening which has the novel combination o properties described above.
It is a further object of the invention to provide a process for producing low alloy steel plate in the quenched and precipitation hardened condi~ion which exhibits improved strength and low temperature toughness.
3~
1 It is another object of the present invention to provide low alloy steel plate of at least 3/16 inch -thickness having the abov~ described combination of properties not now available in ths prior art.
According to the invention there is provided a process for producing a low alloy steel shape of at least 3/16 inch (4.8 mm3 thickness exhibiting a yield strength of at least 80 ksi (56 kg/mm2) at room temperature and a Charpy V-notch impact strength (longitudinal) of at least 10 20 ft-lbs (27 Joules) at -50F (-46C) in the hot reduced condition together with excellent weldability including retained toughness in the heat affected ~one of a weldment, characterized by the steps of providing a steel starting material consisting essentially of, in weight 15 percentS from about 0~02% to 0.07~ carbon, 1.2~ to 2.0 manganese, 0.020% ma~imum sulfur, up to 0.5% silicon, 0.1% to 0.4% molybdenum, 0.01% to 0.1% columbium, about 0.01~ to 0.10~ acid soluble aluminum, about 0.8% to ~.0%
copper, about 0.4% to 2.0% nickel, resi.dual chromium, and ~ balance iron except for incidental impurities; hot reducing sa.id starting material to a desired final thickness with a total reduction in thickness of at least 30~ while within the temperature range of about 1400 to 1700F (760 to 927~C) whereby to a~oid substantial recrystallization of austenite and to obtain a predominant heavily deformed austenite phase; and cooling at a rate which transforms ~aid austenite phase to a predominantly fine acicular ferrite and lower-bainite phase.
The invention further provides a process for pro~
ducing a low alloy steel plate as set forth hereinabove, and including the further step of precipitation hardening the hot reduced shape by heating within the range between about 900F (482C) and the ACl point, whereby to obtain a shape having a yield strength of at least 85 ksi (60 kg/mm2~ at room temperature and a Charpy V-notch impact 763~39 1 strength (longitudinal) of at least 20 ft-lbs (27 Joules) at ~50F (-46C).
In a further embodiment of the invention there is provided a process for producing a low alloy steel shape of at least 3/16 inch (4.8 mm~ thickness exhibitlng a yield ~trength of at least 80 ksi (56 kg/mm2) at room temperature anc a Charpy V-Notch impact strength (longitudinal) of at least 50 ft-lbs (68 Joule~) a~ -80F
(-62C3in the austenitized, quenched and precipitation 0 hardened condition together with excellent weldability including re~ainea toughness in the heat affected zone of a weldment, characterized by the steps of providing a steel starting material conqisting essentially of, in weight percent, rom about 0.0~ to 0.07~ carbon, 1.2% to 15 2.0~ manganese, 0.020% maximum sulfur, up to 0.5%
silicon, 0.1% to 0.4% molybdenum, 0.01~ to 0.1%
columbium, about 0.01~ to 0.10~ acid soluble aluminum, about 0.8~ to 2.0~ copper, about 0.4% to 2.0~ nickel, residual chromium, and balance iron except for incidental impurities; hot reducing said starting material to a desired final thickness, cooling to a temperature a-t which the steel transfor~s to ferrite; reheatin~ the hot reduced shape to a temperature of about 1600 to 1800~F
(871 to 982C) and within the austeni7.ation range whereby to transform said errite to austenite;
quenching at a rate which transforms substantially all said austenite to predominantly fine acicular ferrite and low~r-bainite and which avoids substantial precipitation of copper-rich particles; and precipitation hardening by 30 heatin~ within the range between about 900F (482C) and the ACl point.
The invention further provides a low alloy steel Qhape of at least 3/16 inch (4.8 mm) thickness exhibiting a yield strength of at least 80 ksi (56 kg/mm2) at room temperature and a Charpy V-notch impact strength (longi-tudinal) of at least 20 ft-lbs (27 Joules) at -50F
6~
1 (-46C)in the hot reduced condition~ together with excel-lent weldability including retained toughness in -the heat affected zone of a weldment, characterizPd by a predomi-nantly acicular ferrite and lower bainite microstructure, said steel consisting essentially of, in weight percent, from about 0.02% to 0.07% carbon, 1.2% to 2.0% manganese, 0.020~ maximum sulfur, up to 0.5% silicon, 0.1% to 0.4%
molybdenum, 0.01% to 0.10% columbium, about 0.01~ to 0.10% acid soluble aluminum, about 0.8~ to 200% copper, about 0.4% to 2.0% nickel, residual chromium, and balance iron except for incidental impurities.
When in the precipitation hardened condition, the low alloy steel shape defined above exhibits a yield strength of at least 85 ksi (60 kg/mm2) at room temperature and a Charpy V-notch impact strength (longitudinal) of at least 20 ft-lbs at -50F (-46C).
When austenitized, quenched and precipitation hardened, the low alloy steel shape of the invention as defined above exhibits a yield strength of at least 80 ksi (56 kg/mm2 at room temperature and a Charpy V-notch impac-t s-trength (longitudinal) of at least 50 ft-lbs at -80F (-62C)-Reference is made to the accompanying drawing wherein~
Fig. 1 is a graphic comparison of tensile properties vs. plate thickness o a steel of the invention with ASTM
A710 Grade A and a similar s-teel containing substan-tially no molybdenum, Fig. 2 is a graphic comparison o ductile-to-brittle transition temperature vs. plate thickness o a s~eel o the invention with ASTM A710 Grade A and a ~imilar steel containing substarltially no molybdenum, Figs. 3 and 4 are photomicrographs at 200 x of hot rolled plates of the steel of the invention, Fig. 5 is a photomicrograph at 200 x of hot rolled 3~
1 ASTM A710 Grade A; and Fig. 6 is a photomicrograph at 200 x of hot rolled steel of the invention.
A preferred composition of the steel of the invention consists essentially of, in weight percent, from about 0.03~ to 0.05~ carbon, about 1.3% to 1.65~
manganese, about 0.010% maximum sulfwr, about 0.15~ to 0~40~ si]icon, about 0.15~ to 0.30~ molybdenum, about 0~02% to 0.05% columbium, about 0.02~ to 0006% acid soluble aluminum, about 100% to 1~3% copper, about 0.7 to 1.0% nickal, less than 0.25~ chromium, and balance iron ex~ept for incidental impurities.
Carbon is essential for its contribution to strength and a minimum of about 0.02% is needed for this purpose.
However, carbon in excess of 0.07% results in a clecrPase in toughness and drastic impairment of weldability.
Since the steel plate in final form is predominantly fine acicular ferrite and lower-bainite, carbon in excess o 0.07~ would result in excessive amounts of pearlite, coarse upper-bainite, and small regions of a high carbon austenite + martensite constituent. These phases are considered to reduce toughness without any substantial strengthening. Best results are obtained within a carbon range of about 0.03% to 0.05~.
Manganese i5 required at a minimum of 1.2% in order to pr~vide strength and toughness. More than 200% manga-nese can produce segregation during casting and can form martensite during welding. Manganese additives with low carbon content are also relatively expensive, and higher concentrations result in accelerated erosion of refractories durlng melting. A range of 1.2% to 2.C%
manganese 's thus considered essential, pre~erably about 1.3% to 1.65%.
Sulfur, commonly occurring as an impurity, must be restricted to a maximum of 0.020~ in order to minimize t;3~
1 sulfide inclusion "stringers" in the hot rolled plate which would adversely affect the ductility and toughness of the steel in the long transverse and short transverse directions. Preferably, sulfur is restricted to a maximum of 0.01~
Silicon is added for deoxidation and provides some additional strength to the steel. However, silicon should be restricted to a maximum of 0.5~ since amounts in excess o this value are detrimental to toughness and welding properties.
Molybdenum is added conventionally in order to strengthen and harden steel, and it has the same function in the steel of the present invention. However, the principal and essential reason for addition of molybdenum within the limits of 0.1~ to 0.4% and preferably between about 0015% and 0.30%, is because of its apparent interaction with columbium to control the transformation of austenite to ferrite during cooling after hot xolling or during subsequent reheating and quenching. It helps to achieve a sub~tantially unrecrystallized austenite during lcw temperature hot rolling. When molybdenum is present within the specified range, columbium is more efective in retarding the recrystallization of austenite. Zirconium, vanadium and titanium do not ~ufficiently retard austenite recrystallization, ~ither with or without molybdenum, and hence these alloying elements are not equivalent to columbium in the steel of the present invention. A maximum of 0.4% molybdenum should be observed since amounts in excess of this would cause martensite duriny welding, which is brittl~ and hence unacceptable. Larger molybdenum additions also raise the cost without additional strength or toughness improvements~
At least 0.01% columbium must be added in order to effect retardation of austenite recrystallization. For l any columbium level, less than about 0.1~ molybdenum will not produce sufficient retardation except in very thin plates. Since the present invention is directed to shapes having thicknesses greater than about 3/16 inch, a columbium range of 0.01% to 0.1~, preferably about 0.02%
to about 0.05%, in combination with 0.1% to 0.4% molyb-denum, is necessary. Columbium le~els above about 0.1%
become difficult to dissol~e prior to rolling, and in such cases these additions will not give the required retardation in austenite recystallization while deforming at least 30% in the 1400 to 1700F range. Also, higher columbium levels raise costs, cause toughness losses and promote cracking in welds.
Aluminum is required for grain size control during processing, and at least about 0.01% in acid soluble form is needed for this purpose. Grain coarsening is detrimental to toughness and strength. Aluminum is also effective in combining with residual nitrogen which may be present, but a maximum of O.lOg acid soluble aluminum should be observed since excessive amounts adversely affect ductility.
Copper i3 essential as a precipitation hardening element, and a minimum of about 0.8% is necessary for this purpose. Amounts in excess of 2.0% copper are expensive, and preferably copper range~ between about l.0~ and 1~3~. Copper within this range also helps to obtain the required acicular errite and lower-baini~e microstructure during cooling after hot rolling or quenching after austenitizing.
~ickel is present within the range of about 0~4% to
LOW ALLOY STEEL PI.ATE AND
PROCESS FOR PRODUCTION THEREOF
This inven~ion relates to a low alloy steel shape of at least 3/16 inch (4.8 mm) thickness having improved yield strength, toughness and excellent weld-ability, and to a novel process for the production thereof.
The steel shape of the invention ~ay be produced, from a castiny or previously rolled slab as a starting material, in the :Eorm of plate, bar, tube and structural shape, as hot reduced, hot reduced and precipitation hardened, or hot reduced, austeniti~ed, quenched and precipitation hardened products. Al~hough not so limited, the invention has particular utility in the production of plate of at least 3/16 inch thickness which retains yood tou~hness in the heat afected zone of weldments made by any of the usual welding processesO
Steel plate hot rolled in accordance with the process of the invention exhibits a yield strength of at least 80 ksi (56 kg/mm2)at room temperature and a Charpy V-notch impact strength of at least 20 ft-lbs (27 Joules) in the longitudinal direction at -S0F (-46CC). Wh~n hot rolled in accordance with the proce~s of the invention and precipitation hardenQd, steel plate e~hibits a yield strength of at least 85 ksi (60 kg/mm2)at room t~npera-ture and a Charpy V-notch impact strength o at least 20 ft-lbs (27 Joules) l~ngitudinal at -50F (-46C~. When hot rolled in conventional manner, austenitized, quenched and precipitation hardened, the steel plate of the invention has a yield strength of at least 80 k~i ~56 kg/mm2) at room temperature and a Charpy V-notch impact strength of at least 50 ft-lbs (68 Joules) longitudinal at 80E' (-62C)-~,V~;
~, ~D7~3~
1 British Patent 1,436,846, published May 26, 1976, discloses a steel alleged to exhibit good weldability and high strength containing from 0.4 to 0.8~ nickel, 0.7 to 1~1% copper, 0.01 to 0.09~ carbon, 0.02 to 0.1~ niobium, 1.1 to 1.65~ manganese, 0 to 0.5% chromium, 0 to 0.6%
silicon, 0 to 0.5~ molybdenum, 0 to 0.01% boron, 0 to 0.08% aluminum, 0 to 0.1% total of at least one of zir-conium, magnesium, c~lcium, and rare earth me~als, and balance iron except for impurities. Exemplary steels are stated to have a yiel.d strength of at least 450 MN/m~
(65 ksi) and a toughness level such that the 70 J transi-tion temperature is below 10C when the hot rolled plate is finished at a temperature up to 1050C. Hot rolling finishing temperatures ranged from 950 to 1050C in the specific examples.
ASTM A710 Grade B steel is based on United States Patent 3,132,025, issued to Hurley May 5, 1964, which discloses a low alloy structural steel alleged to exhibit in the hot rolled condition an excellent combination of metallurgical properties. The steel contains up to 0.08 carbon, about 0.2 to 0.75% manganese, up to 0.35~
silicon, about 1 to 1.7~ copper, about 0.7 to 1.6%
nickel, about 0.01 to 0.16~ columbium (niobium) and balance essentially iron. Up to 0.1% aluminum may also be present. The steel is stated to exhibit a yield strength of at least 70 Xsi at room temperature, a Charpy V-notch impact strength of at ~east 15 ft-lbs at -50F
and a reduction of area of at least 60~. The steel is processea by heating above about 2000F, hot rolled and finished at about 1650F. A precipitation hardening treatment can also be applied by heatlng between about 850 and 1150 DF for about 1 hr.
United States Patent 3,945,8S8, issued March 23, 1976 to Matsubara et al, discloses a low alloy steel alleged to have high notch toughness at low temperature, ~2d~7~3~
1 comprising 0.02 to 0.10% carbon, 1.20 to 1.80% manganese, less than 0.015% sulfur, 0.05 to 0.50% chromiurn, 0.01 to 0.10~ niobium, 0.10 to 0.50% ~ilicon, less than 0.030%
phosphorus, 0.05 to 0.50% nickel, 0.05 to 0.50% copper and balance iron and unavoidable impurities. A rare earth metal or alloy may be added within the range of 0.01 to 0.20%. The steel i5 hot rolled with a reduction in thickness of from 30 to 80~ at a tempera~ure below 950C (1742F). This is alleged to result in improved notch toughness.
United States Patent 3,955,971, issued May 11, 1976 to Reisdorf, discloses a low alloy structural steel having good low temperature properties, such as a mi~imum yield strength of at least 60 ksi and good impact toughness down to temperatures as low as -80F. The steel comprises 0.06 to 0.12% carbon, 0.20 to 1~00%
manganese, 0.020% maximum phosphorus, 00015% m~iml7m sulfur, 0.15 to 0.40% silicon, 0.75 to 1.50% nickel, 0.50 to 1.25% chromium, 0.15 to 0.40% molybdenum, 0.010 to 0.060% aluminum, 0.75% maximum copper with copper plus chromium being 1.50~ maximum, and balance iron and conventional impurities. In the processing of exsmplary 1 and 2 inch thick plates, samples were austenitized at 1650CF, water quenched, and then tempered at 1150, 1200 and 1250F.
Other prior art or which applicant is aware includes United States Patents 3,692,514, 3,841,866; 3,849,209 and 4,008,103, and Canadian Patent 988,751.
ASTM alloy A710, Grade A, has an analysis, in weight percent, of 0.07% m;7~iml7m carbon, 0.40 to 0.70% manga-nese, 00025% maximum phosphorus~ 0.025~ maximum sulur, 0.40~ m~;mllm silicon, 0.70 to 1~00% nickel, 0.60 to 0.90~ chromium, 0.15 to 0.25% molybdenum, 1.00 to 1.30%
copper, 0.02% minimum columbium, and balance iron. This composition is based on the above-mentioned U.S. Pa~ent 3,692,51~.
1 Despite the numerous prior art developments in -the field o~ low alloy steel plate for structural purposes, there is still a need for such a steel in plate form, particularly in thicknesses of 3/16 to 2" (4.8 to Sl mm), which consistently exhibits a yield strength of at least 80 ksi at room temperature, a Charpy V-notch impact strength of at least 20 ft-lbs (longitudinal) and at least 15 ft-lbs (transverse) at -50F in the hot rolled condition, a yield strength of at least 85 ksi and a Charpy V-notch impact streng~h of at least 20 -Et-lbs (longitudinal) and at least 15 ft-lbs (transverse) at -50F in the rolled and precipitation hardened condition;
and a yield strength of at least 80 ksi and a Charpy V-notch impact strength of at least 50 ft-lbs (longitudinal) and at least 35 ft-lbs t47 Joules) (transverse~ at -80F in the quenched and precipitation hardened condition, together with excellent weldability, particularly retention of toughness in the heat affected zone of a weldment made by any of the usual welding processesO
It is an object of the invention to pro~ide a process for producing low alloy steel plate by coR~rolled hot rolling, which plate will possess adequate mechanical and metallurgical properties for most applications in the as-hot rolled condition.
It is a another object of the invention to provide a process for producing low alloy steel plate of at least 3/16 inch thickness by controlled hot rolling and precipitation h~rdening which has the novel combination o properties described above.
It is a further object of the invention to provide a process for producing low alloy steel plate in the quenched and precipitation hardened condi~ion which exhibits improved strength and low temperature toughness.
3~
1 It is another object of the present invention to provide low alloy steel plate of at least 3/16 inch -thickness having the abov~ described combination of properties not now available in ths prior art.
According to the invention there is provided a process for producing a low alloy steel shape of at least 3/16 inch (4.8 mm3 thickness exhibiting a yield strength of at least 80 ksi (56 kg/mm2) at room temperature and a Charpy V-notch impact strength (longitudinal) of at least 10 20 ft-lbs (27 Joules) at -50F (-46C) in the hot reduced condition together with excellent weldability including retained toughness in the heat affected ~one of a weldment, characterized by the steps of providing a steel starting material consisting essentially of, in weight 15 percentS from about 0~02% to 0.07~ carbon, 1.2~ to 2.0 manganese, 0.020% ma~imum sulfur, up to 0.5% silicon, 0.1% to 0.4% molybdenum, 0.01% to 0.1% columbium, about 0.01~ to 0.10~ acid soluble aluminum, about 0.8% to ~.0%
copper, about 0.4% to 2.0% nickel, resi.dual chromium, and ~ balance iron except for incidental impurities; hot reducing sa.id starting material to a desired final thickness with a total reduction in thickness of at least 30~ while within the temperature range of about 1400 to 1700F (760 to 927~C) whereby to a~oid substantial recrystallization of austenite and to obtain a predominant heavily deformed austenite phase; and cooling at a rate which transforms ~aid austenite phase to a predominantly fine acicular ferrite and lower-bainite phase.
The invention further provides a process for pro~
ducing a low alloy steel plate as set forth hereinabove, and including the further step of precipitation hardening the hot reduced shape by heating within the range between about 900F (482C) and the ACl point, whereby to obtain a shape having a yield strength of at least 85 ksi (60 kg/mm2~ at room temperature and a Charpy V-notch impact 763~39 1 strength (longitudinal) of at least 20 ft-lbs (27 Joules) at ~50F (-46C).
In a further embodiment of the invention there is provided a process for producing a low alloy steel shape of at least 3/16 inch (4.8 mm~ thickness exhibitlng a yield ~trength of at least 80 ksi (56 kg/mm2) at room temperature anc a Charpy V-Notch impact strength (longitudinal) of at least 50 ft-lbs (68 Joule~) a~ -80F
(-62C3in the austenitized, quenched and precipitation 0 hardened condition together with excellent weldability including re~ainea toughness in the heat affected zone of a weldment, characterized by the steps of providing a steel starting material conqisting essentially of, in weight percent, rom about 0.0~ to 0.07~ carbon, 1.2% to 15 2.0~ manganese, 0.020% maximum sulfur, up to 0.5%
silicon, 0.1% to 0.4% molybdenum, 0.01~ to 0.1%
columbium, about 0.01~ to 0.10~ acid soluble aluminum, about 0.8~ to 2.0~ copper, about 0.4% to 2.0~ nickel, residual chromium, and balance iron except for incidental impurities; hot reducing said starting material to a desired final thickness, cooling to a temperature a-t which the steel transfor~s to ferrite; reheatin~ the hot reduced shape to a temperature of about 1600 to 1800~F
(871 to 982C) and within the austeni7.ation range whereby to transform said errite to austenite;
quenching at a rate which transforms substantially all said austenite to predominantly fine acicular ferrite and low~r-bainite and which avoids substantial precipitation of copper-rich particles; and precipitation hardening by 30 heatin~ within the range between about 900F (482C) and the ACl point.
The invention further provides a low alloy steel Qhape of at least 3/16 inch (4.8 mm) thickness exhibiting a yield strength of at least 80 ksi (56 kg/mm2) at room temperature and a Charpy V-notch impact strength (longi-tudinal) of at least 20 ft-lbs (27 Joules) at -50F
6~
1 (-46C)in the hot reduced condition~ together with excel-lent weldability including retained toughness in -the heat affected zone of a weldment, characterizPd by a predomi-nantly acicular ferrite and lower bainite microstructure, said steel consisting essentially of, in weight percent, from about 0.02% to 0.07% carbon, 1.2% to 2.0% manganese, 0.020~ maximum sulfur, up to 0.5% silicon, 0.1% to 0.4%
molybdenum, 0.01% to 0.10% columbium, about 0.01~ to 0.10% acid soluble aluminum, about 0.8~ to 200% copper, about 0.4% to 2.0% nickel, residual chromium, and balance iron except for incidental impurities.
When in the precipitation hardened condition, the low alloy steel shape defined above exhibits a yield strength of at least 85 ksi (60 kg/mm2) at room temperature and a Charpy V-notch impact strength (longitudinal) of at least 20 ft-lbs at -50F (-46C).
When austenitized, quenched and precipitation hardened, the low alloy steel shape of the invention as defined above exhibits a yield strength of at least 80 ksi (56 kg/mm2 at room temperature and a Charpy V-notch impac-t s-trength (longitudinal) of at least 50 ft-lbs at -80F (-62C)-Reference is made to the accompanying drawing wherein~
Fig. 1 is a graphic comparison of tensile properties vs. plate thickness o a steel of the invention with ASTM
A710 Grade A and a similar s-teel containing substan-tially no molybdenum, Fig. 2 is a graphic comparison o ductile-to-brittle transition temperature vs. plate thickness o a s~eel o the invention with ASTM A710 Grade A and a ~imilar steel containing substarltially no molybdenum, Figs. 3 and 4 are photomicrographs at 200 x of hot rolled plates of the steel of the invention, Fig. 5 is a photomicrograph at 200 x of hot rolled 3~
1 ASTM A710 Grade A; and Fig. 6 is a photomicrograph at 200 x of hot rolled steel of the invention.
A preferred composition of the steel of the invention consists essentially of, in weight percent, from about 0.03~ to 0.05~ carbon, about 1.3% to 1.65~
manganese, about 0.010% maximum sulfwr, about 0.15~ to 0~40~ si]icon, about 0.15~ to 0.30~ molybdenum, about 0~02% to 0.05% columbium, about 0.02~ to 0006% acid soluble aluminum, about 100% to 1~3% copper, about 0.7 to 1.0% nickal, less than 0.25~ chromium, and balance iron ex~ept for incidental impurities.
Carbon is essential for its contribution to strength and a minimum of about 0.02% is needed for this purpose.
However, carbon in excess of 0.07% results in a clecrPase in toughness and drastic impairment of weldability.
Since the steel plate in final form is predominantly fine acicular ferrite and lower-bainite, carbon in excess o 0.07~ would result in excessive amounts of pearlite, coarse upper-bainite, and small regions of a high carbon austenite + martensite constituent. These phases are considered to reduce toughness without any substantial strengthening. Best results are obtained within a carbon range of about 0.03% to 0.05~.
Manganese i5 required at a minimum of 1.2% in order to pr~vide strength and toughness. More than 200% manga-nese can produce segregation during casting and can form martensite during welding. Manganese additives with low carbon content are also relatively expensive, and higher concentrations result in accelerated erosion of refractories durlng melting. A range of 1.2% to 2.C%
manganese 's thus considered essential, pre~erably about 1.3% to 1.65%.
Sulfur, commonly occurring as an impurity, must be restricted to a maximum of 0.020~ in order to minimize t;3~
1 sulfide inclusion "stringers" in the hot rolled plate which would adversely affect the ductility and toughness of the steel in the long transverse and short transverse directions. Preferably, sulfur is restricted to a maximum of 0.01~
Silicon is added for deoxidation and provides some additional strength to the steel. However, silicon should be restricted to a maximum of 0.5~ since amounts in excess o this value are detrimental to toughness and welding properties.
Molybdenum is added conventionally in order to strengthen and harden steel, and it has the same function in the steel of the present invention. However, the principal and essential reason for addition of molybdenum within the limits of 0.1~ to 0.4% and preferably between about 0015% and 0.30%, is because of its apparent interaction with columbium to control the transformation of austenite to ferrite during cooling after hot xolling or during subsequent reheating and quenching. It helps to achieve a sub~tantially unrecrystallized austenite during lcw temperature hot rolling. When molybdenum is present within the specified range, columbium is more efective in retarding the recrystallization of austenite. Zirconium, vanadium and titanium do not ~ufficiently retard austenite recrystallization, ~ither with or without molybdenum, and hence these alloying elements are not equivalent to columbium in the steel of the present invention. A maximum of 0.4% molybdenum should be observed since amounts in excess of this would cause martensite duriny welding, which is brittl~ and hence unacceptable. Larger molybdenum additions also raise the cost without additional strength or toughness improvements~
At least 0.01% columbium must be added in order to effect retardation of austenite recrystallization. For l any columbium level, less than about 0.1~ molybdenum will not produce sufficient retardation except in very thin plates. Since the present invention is directed to shapes having thicknesses greater than about 3/16 inch, a columbium range of 0.01% to 0.1~, preferably about 0.02%
to about 0.05%, in combination with 0.1% to 0.4% molyb-denum, is necessary. Columbium le~els above about 0.1%
become difficult to dissol~e prior to rolling, and in such cases these additions will not give the required retardation in austenite recystallization while deforming at least 30% in the 1400 to 1700F range. Also, higher columbium levels raise costs, cause toughness losses and promote cracking in welds.
Aluminum is required for grain size control during processing, and at least about 0.01% in acid soluble form is needed for this purpose. Grain coarsening is detrimental to toughness and strength. Aluminum is also effective in combining with residual nitrogen which may be present, but a maximum of O.lOg acid soluble aluminum should be observed since excessive amounts adversely affect ductility.
Copper i3 essential as a precipitation hardening element, and a minimum of about 0.8% is necessary for this purpose. Amounts in excess of 2.0% copper are expensive, and preferably copper range~ between about l.0~ and 1~3~. Copper within this range also helps to obtain the required acicular errite and lower-baini~e microstructure during cooling after hot rolling or quenching after austenitizing.
~ickel is present within the range of about 0~4% to
2.0~ in order to avoid hot shortness during hot rolling.
Since nickel is expensive, it is restricted to a ma~imum of 2~0%, preferably 1.0%, and amounts in excess of ~he broad m~; mllm can cause welding problems.
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1 The manganese and copper ranyes of the present steel are higher than those normally used for low alloy plate steels. These higher ranges increase the strength and toughness of the steel, and manganese is further believed 5 to function in a manner similar to that of molybdenum in making columbium more effective in retarding the recrystallization of austeniteO Manganese also helps to promote the formation of fine acicular ferrite and lower-bainite.
Chromium is restricted to residual amounts ~about 0.25% maximum~ since chromium in combina-tion with relatively high manganese causes forma-tion of upper-bainite in the microstructure, which is highly detrimental to toughness. The use of chromium in prior art plate steels resulted in the sacrifice of toughness in order to obta.in higher strengthn In the steel of the present invention this problem is avoided. Chromium additions also cause martensite to forrn in welds, causirlg lower toughness and making hydrogen cracking more 20 pO9 sible.
The importance of retarding austenite recrystal-lization during the latter stages of hot rolling is to obtain a predominantly heavily deformed austenite phase.
A total reduction in thickness of at least 30~ while within the temperature range of about 1400 to 1700F has been found to be necessary to accomplish this. The reductiorl in thickness may be done in one or several passes. Preferably the total reduction in thickness is at least 50% within 2 preferred temperature range of 1400 to 1600~F. No ferrite is formed intentionally during hot rolling in the controlled process o~ the present invention~ At higher rolling temperatures, or in steels not containiny the critical columbiurn, molybdenum and manganese additions, deformed grains immediately 3S recrystallize during hot rolling after each rolling pass :~2~ ;3~
1 into undeformed or stress-free new grains, but in the present invention substantial recrystallization does not occur because of the composition of the steel. Hence, at the completion of hot rolling the austenite grains are highly deformed. During cooling after completion of hot rolling the deformed austenite structure transforms to errite in the usual manner, but the ferrite is predominantly fine grained and acicular rather than polygonal. The high strength and toughness of the present steel ls attributed to the predominantly acicular ferrite and lower-bainite microstructure.
When producing the quenched and precipitation hardened steel plate of the present invent.ion, it is not essential to control the hot rolling in such manner that a reduction in thickness of at least 30% is effected while within the temperature range of about 1400 to 1730F where austenite xecrystyallization is ret~rded by the columbium, molybdenum and manganese additions.
However, controlled hot rolling may be used. The further steps after conventional hot rolling include reheating the hot rolled plate to a temperature within the austenization range, namely ~bout 1500 to 1800~F and preferably within the range of about 1~50 to 17003F
(899 to 927C). After txansformation of substantially all the ferrite phase to austenite the steel is quenched rapidly to transform austenite back to substantially all fine acicular ferrite and lower-bainite and at a rate sufficient to retain most of the copper in solid solution. The quench medium for this step should be
Since nickel is expensive, it is restricted to a ma~imum of 2~0%, preferably 1.0%, and amounts in excess of ~he broad m~; mllm can cause welding problems.
~7~
1 The manganese and copper ranyes of the present steel are higher than those normally used for low alloy plate steels. These higher ranges increase the strength and toughness of the steel, and manganese is further believed 5 to function in a manner similar to that of molybdenum in making columbium more effective in retarding the recrystallization of austeniteO Manganese also helps to promote the formation of fine acicular ferrite and lower-bainite.
Chromium is restricted to residual amounts ~about 0.25% maximum~ since chromium in combina-tion with relatively high manganese causes forma-tion of upper-bainite in the microstructure, which is highly detrimental to toughness. The use of chromium in prior art plate steels resulted in the sacrifice of toughness in order to obta.in higher strengthn In the steel of the present invention this problem is avoided. Chromium additions also cause martensite to forrn in welds, causirlg lower toughness and making hydrogen cracking more 20 pO9 sible.
The importance of retarding austenite recrystal-lization during the latter stages of hot rolling is to obtain a predominantly heavily deformed austenite phase.
A total reduction in thickness of at least 30~ while within the temperature range of about 1400 to 1700F has been found to be necessary to accomplish this. The reductiorl in thickness may be done in one or several passes. Preferably the total reduction in thickness is at least 50% within 2 preferred temperature range of 1400 to 1600~F. No ferrite is formed intentionally during hot rolling in the controlled process o~ the present invention~ At higher rolling temperatures, or in steels not containiny the critical columbiurn, molybdenum and manganese additions, deformed grains immediately 3S recrystallize during hot rolling after each rolling pass :~2~ ;3~
1 into undeformed or stress-free new grains, but in the present invention substantial recrystallization does not occur because of the composition of the steel. Hence, at the completion of hot rolling the austenite grains are highly deformed. During cooling after completion of hot rolling the deformed austenite structure transforms to errite in the usual manner, but the ferrite is predominantly fine grained and acicular rather than polygonal. The high strength and toughness of the present steel ls attributed to the predominantly acicular ferrite and lower-bainite microstructure.
When producing the quenched and precipitation hardened steel plate of the present invent.ion, it is not essential to control the hot rolling in such manner that a reduction in thickness of at least 30% is effected while within the temperature range of about 1400 to 1730F where austenite xecrystyallization is ret~rded by the columbium, molybdenum and manganese additions.
However, controlled hot rolling may be used. The further steps after conventional hot rolling include reheating the hot rolled plate to a temperature within the austenization range, namely ~bout 1500 to 1800~F and preferably within the range of about 1~50 to 17003F
(899 to 927C). After txansformation of substantially all the ferrite phase to austenite the steel is quenched rapidly to transform austenite back to substantially all fine acicular ferrite and lower-bainite and at a rate sufficient to retain most of the copper in solid solution. The quench medium for this step should be
3~ water since media such as oil, salt or forced air pxobably would not provide a cooling rate suficient to prevent precipitation of the copper as fine particles, except in thinner plate up to about 3/B inch (9.5 mm~
thicXness.
1 The precipitation hardening step involves heating within the range between about 900F and the ACl point.
At temperatures below about 900F, copper will not precipitate within a reasonable time period, and any small amount of martensite which forms will not be adequately tempered. On the other hand, if heated to above the A~l temperature, i.e. about 1300F, some austenite will again form which can transform to embrittling martensite upon subse~uent air coolingO It is also necessary to avoid precipitation of copper during a preceding quenching step since such premature preci~
pitation would result in no contribution to strength.
This is the reason or requiring a quench rate sufficiently rapid to retain the copper in solid solution. Preferably the precipitation hardening temperature range is between about 1000 and 1200F (538 and 649C).
Wh~n producing low alloy steel plate in the as hot rolled condition in accordance with the controlled hot rolling process of the present invention a yield strength of at least ao ksi at room temperature iB obtained without the necessity for precipitation hardening or other streng~lening step as is presently required for ASTM A710 Grade A Class 1 alloy steel~. This provides reduction in processing costs, and improved surface since less scale is produced. Better flatness is also obtained, particularly in wide, relatively thin plate within the range of 3/15 to 3/8 thickness. At the same time good toughness in both the longitudinal and trans-verse directions is achieved.
Re~erring to Figs. 1 and 2 of the drawing, t0nsileand toughness properties are plotted for steels which have been subjected to the controlled hot rolling process of the present invention and precipitation hardenedO It is evident from Fig. 1 that a steel oE the invention 7~3~
1 exhibits substantially higher tensile and yield strengths than A5TM A710 Grade A and a steel otherwise within the ranges of the present steel except for omission of molyb-denum. Similarly, Fig. 2 discloses a ductile-to-brittl~
transition ~emperature for the steel og the invention substantially superior to that of ASTM A710 Grade A and comparable to that of the steel otherwise within the ranges of the present invention except for omission of molybdenum.
After preliminary laboratory tests, which are not reported herein, a series of production trials was con-ducted. As summarized in Table I, Heat A was prepared with all essential elements within the preferred ranges of the steel of the invention. Slabs from this heat were hot rolled to plate o varying thicknesses using both conventional hot rolling and the controlled hot rollincJ
process of the present invention~ The slab reheating temperature or hot rolling was within the range of 2250~
to 2350F (1232 to 1288~C). Controlled rolling in these trials involved 65~ to 70~ reduction in thickness at temperatures between 1500 and 1700F. Hot roll finish temperatures were between about 1450 and 1500F.
Conventional hot rolling involved only small reductions below 1700F and finish temperatures at about 1600F.
Samples of all thicknesses were further subjected to precipitation hardening after hot rolling at a temperature o 1100F (593C) for a period of one hour, followed by air cooling.
As shown in Table I, in the as-rolled condition, samples which were subjected to the controlled hot rolling process of the invention showed a slight superiority in yield and tensile strength over samples subjected to conventional hot rolling. Of greater si~nificance was the dramatic superiority in -toughness in the as-rolled condltion exhibited by all sample~
~ 36~
1 subjected to the controlled hot rolling process of the invention.
The precipitation hardened samples exhibited a signi-ficant increasé in yield and tensile strength as compared to the same samples in the as-rolled condition, and samples subjected to the controlled hot rolling process of the invention were sligthly superior in yield strength as compared to precipitation hardened samples subjected to conventional hot rolling. Again the toughness of samples in the precipitation hardened condition subjected to controlled hot rolling showed a marked superiority over samples which were subjected to conventional hot rolling prior to precipitation hardening.
For purpose 5 of direct comparison, 9 amples of Heat A
were subjected to the same tests as Heat B of ASTM A710 Grade A steel, analyzing, in weight percent, 0.035%
carbon, 0.44% manganese, 0.010% phosphorus, O.Ol5~
sulfur, 0.28% silicon, 0.68~ chromium, 0.89~ nickel, 0.21~ molybdenum, 1.16~ copper, 0,044% aluminum, 0.~45%
columbium, and balance essentially iron. Samples of both heats were hot rolled in accordance with the controlled rolling process of the present invention to plates of 1/2 inch (12.~ mm) thickness, and a sample of each steel was al50 subjected to precipitation hardening at llOO~F
~593C) for one hour. In other respects preparation was the same as reported above.
The comparative transverse tensile properties and longitudinal and transverse toughness values are set forth in Table II. It is apparent that the yield strength of Heat A in the as-control rolled condition was substantially equivalent to that of Heat B in the pre-cipitaton hardened condition. In the precipitation hardened condition the yield strength of Heat A was substantially higher than ~hat of Heat B. The toughness of the steel of the invention in the longitudinal ~2~3~
1 direction was substantially higher in the as-control rolled condition than that of Heat B in the precipitation hardened condition.
Additional heats of steels in accordance with the invention were prepared, and the composi~ions thereof are set forth in Table III.
Samples of steels from Heats C and D in Table III
and of Heat A were subjected to both conventional and controlled hot rolling, austenitizing, quenching and precipitation hardeningO Plates of varying thickness were produced for testing. The austenitizing was effected by reheating to a temperature of about 1650F
(gO0C~, holding for about 30 to 75 minutes and qu~nching - in water. Precipitation hardening was effected either at 1200F or 1100F for 30 minutes, followed by air cool.ing.
Tensile and toughness properties of these speci.mens are set forth in Tab].e IV, rom which it will be noted that a yield strength in excess of 90 ksi was obtained at least for plate thicknesses up to and including one inchO For the thicker plates wherein the yield strength ranged between 86.4 and 88.3 ksi, sornewhat hiyher yi.eld strengths could undoubtedly be obtained by precip~t.ation hardening at 1000F (538C).
It will be evident that outstanding toughness was achieved in the longitudinal direction for all specimens regardless of whether the hot rolling w~s conventional or conducted in accordanc~ with the controlled hot rolling process of the present invention. Transverse toug~ness ~alues were also generally e~cellent and well above the aim of 35 ft-lbs at -80F.
Referring next to Figs~ 3 and 4, microstructures are shown of specimens taken from the steel of Heat A at the mid thickness of 3/4 inch ~19 mm) thick plates~ Fig. 3 illustrates the recrystallized grain structure obtained in the as~rolled condition when subjected to conventional 63~
1 hot rolling. Fig. 4 shows the deformed grain structure obtained by the controlled hot rolling process of the present invention, which is predominantly fine grained and acicular ferrite.
Fig. 5 illustrates the grain structure of an ~STM
A710 Grade A steel (Heat B3 after hot rolling in accord ance with the controlled hot rolling process of the present invention, with the specimen being taken at the mid thickness position of 1/2 inch plate. The micro-structure comprises polygonal ferrite, pearlite and bainite which resulted from recrystalliYed austenite before transformation.
Fig. 6 illustrates the microstructure of the steel of the invention (Heat No. A), taken at the mid thickness position of 1/2 inch plate when subjected to the con~
trolled hot rolling process of the present invention.
The microstructure is a very fine acicular errite with some lower-bainite obtained by transformation from an austenite phase which had not completely recrystallized.
In Figs. 3 and 4 the same ~teel was subjected to different hot rolling conditions, and the marked dif-ference in microstructures shows the criticality of the controlled hot rolling process of the invention when practiced on a steel of the specified composition in the a8-rolled condition. In Figs~ 5 and 6, different steels were subjected to the identical controlled hot rolling process of the invention, and the steel of the present invention transformed to a very fine acicular ferrite microstructure, whereas the conventional prior art steel transformed to a poly~onal ferrite, pearlite and bainite microstructure, thus il~ustrating the critieality of the composition of the present steel.
It is thus evident that the present invention in-volves criticality with respect to composition regardless of the condition of the final product. It is further 3~
1~
1 evident that the controlled hot rolling process of the invention is critical for production of as-rolled and as rolled and precipitation hardened plates having the desired combination of properties. For the production of austenitized, quenched and precipitation hardened shapes, ~he hot rolling process is not critical.
, .
TA B L E
TT,~ A~D~u~
~h c~l C~r~itisn, wt.~
Hea~ C Mn P S Si_ Cr Ni Mo Cu Al Cb A 0.04 1.45 Q.014 0.007 0.30 0.06 0.96 0.20 1.14 Q.036 0.041 As-Rolled As-Rolled ~ 1100F P~.
~long. ~ ElongO
~hi~kn~ in in inc~ R~l 1 i n~ ksiU3'S ~ ksi 8 " ~ , ksi UIY;, ksi 2 " % RA
3/8Conventional 87.6 103.0 18 53 ND* 117.8 33 57 3/8Fresent In~ention B6.2 106.0 14 49 104.9 114.8 29 46 1/2 " " 81.9 105.4 13.5 55 107.5 116.2 ~1 57 3/4Conv~n~i~n~l 82.1 102.9 18 54 103c7 117.8 42 52 3/4Present Invention 83.5 104.4 18 51 99.9 107.9 46 58 3~4ConvPn~i~n~l 83.3 104.6 18 60 97.9 113.4 40 55 ~ ~-3j4Present In~ention 84.2 105.3 18 50 98.1 110.4 39 51 * ~D = nct detPrmin~
~B
Charpy V-~ctch Impact Energy at -5QF
Thickness Energy, f~-Ib - As rolled* Energy, t-lb - As-Rollad ~ llOO~F PH*
inch ~lling SperimPn Lcngitud~nal ~1~ ~vtlse Sp~im~n Lcngi~ud~nal ~1~ ~vt~se 3/8 Conv~tjnn~ 3/4-size 31 19 3~4-size 26 19 3/8 Present Inve~tion " 65 38 " 55 3~
1/2 " " Full-size 78 46 Full-siz2 45 23 3~4 C~nt i~ 6 10 ' 14 iO
3/4 Pres~nt Invention " 37 43 " 67 32 ~f4 C~l1V~ L I f~ial 18 ~5 26 75 3/4 Present Invention " 69 50 " 76 31 -- * Average of three rqrli~te tes~s TA B LE I I
v~se Tensile Prc~ties - 12.5 ~n Pla~es Rolled Acc~rdirlg to Pre~ent Invention Heat Test Co~ditic:YnYS, ksi UIS, ksi % Eiong. in 8" ~ Elong. in 2"
A As-RDlled 81.9 105.4 13.5 ND
As--Rolle~ ~ 1100F E~ 1~7.5 116.2 ~D 41 B As-R~lled + 1100F ~ 83.3 98.8 ND 31 MD = Not De~in~
Langitudin~l and 'r~dl~v~,s~ Cha~ ~7~1O~h I~pact Energ~ at -50F
Fnergys ft-lb*
He~,t Test CarlditionSp~i~PnL~ngitudinal Transve~se N ~
A As-Rolled Full-size 78 46 C--`
" As-Rolle~ + 1100F PH " " 45 23 B As-R~lled + 1100F P~ " " 56 ~D
*2~verage o three replicate ,,~ ng for E~ea~ A and cw~ fi~ Heat !3 lot Det~rm;ned ~ A B I. 1~ I 3[ I
Heat C Mn P S Si ~ ~ FD Cu Al Cb C O.C6 1.4(~ 0.01~) O.(~t)4 0.24 0.0~3 0.85 0.18 1.1~ 0.050 0.1~44 D 0.05 1.42 0.010 0.005 0.30 0.23 0.87 0.17 1.13 0.033 0.()5t) TA B LE I V
% Elong.
Plate in He2t Thi l~kni~sF~ h Rl~l l i n~~L~ ~i_uL esy~ urs, ksi 2 " %RA
A 3/8 C~nvPnti~ l 1200F ~D 46.0 44 58 3/8 Present Inventi~ " 98.3 104.7 31 65 " 1/~ " " " 98.3 1040~ 36 63 3/4 Corn~.-n~ n~l ~t 88.1 98.6 48 65 3/4 Present Irlventian " S4.7 101.8 38 47 C 1 ConvPnti~n~l 1100F 95.9 101.4 24 69 A 1 1/4 " 1200F 88.3 96.7 55 63 D 1--1/4 " 1100F 87.0 98.0 25 67 " 2 " " 86~4 98.9 25 72 ~D = Not De~rmi nf~
Charpy V ~ . I~ct Ener~y at -80F G
Pltat~3 Ener~, ft-lb* r Heat ~ h Rt ll;n~ T~tl.~es Sp~;~nLc)ngitudir~
A 3/8 Conv~n~ l 1200F 3/4-size 42 35 3/8 P~eserlt Invention " " " 97 58 1/2 " " " Full-size 129 62 3/4 Co~Iv~n~ t- 1.07 81 3/4 Present I~lventitn " " " 90 61 C 1 Co~v~ n~l llOOF 1- ~, 119 98 A 1-1/4 ll 1200F '~ c~ 112 79 3 1-1/4 " 1100F " " 106 68 " 2 " " '~ " 42 60 ~e of t~ree rep~ieate ~est~ 3~ ot Detf~TinG~1
thicXness.
1 The precipitation hardening step involves heating within the range between about 900F and the ACl point.
At temperatures below about 900F, copper will not precipitate within a reasonable time period, and any small amount of martensite which forms will not be adequately tempered. On the other hand, if heated to above the A~l temperature, i.e. about 1300F, some austenite will again form which can transform to embrittling martensite upon subse~uent air coolingO It is also necessary to avoid precipitation of copper during a preceding quenching step since such premature preci~
pitation would result in no contribution to strength.
This is the reason or requiring a quench rate sufficiently rapid to retain the copper in solid solution. Preferably the precipitation hardening temperature range is between about 1000 and 1200F (538 and 649C).
Wh~n producing low alloy steel plate in the as hot rolled condition in accordance with the controlled hot rolling process of the present invention a yield strength of at least ao ksi at room temperature iB obtained without the necessity for precipitation hardening or other streng~lening step as is presently required for ASTM A710 Grade A Class 1 alloy steel~. This provides reduction in processing costs, and improved surface since less scale is produced. Better flatness is also obtained, particularly in wide, relatively thin plate within the range of 3/15 to 3/8 thickness. At the same time good toughness in both the longitudinal and trans-verse directions is achieved.
Re~erring to Figs. 1 and 2 of the drawing, t0nsileand toughness properties are plotted for steels which have been subjected to the controlled hot rolling process of the present invention and precipitation hardenedO It is evident from Fig. 1 that a steel oE the invention 7~3~
1 exhibits substantially higher tensile and yield strengths than A5TM A710 Grade A and a steel otherwise within the ranges of the present steel except for omission of molyb-denum. Similarly, Fig. 2 discloses a ductile-to-brittl~
transition ~emperature for the steel og the invention substantially superior to that of ASTM A710 Grade A and comparable to that of the steel otherwise within the ranges of the present invention except for omission of molybdenum.
After preliminary laboratory tests, which are not reported herein, a series of production trials was con-ducted. As summarized in Table I, Heat A was prepared with all essential elements within the preferred ranges of the steel of the invention. Slabs from this heat were hot rolled to plate o varying thicknesses using both conventional hot rolling and the controlled hot rollincJ
process of the present invention~ The slab reheating temperature or hot rolling was within the range of 2250~
to 2350F (1232 to 1288~C). Controlled rolling in these trials involved 65~ to 70~ reduction in thickness at temperatures between 1500 and 1700F. Hot roll finish temperatures were between about 1450 and 1500F.
Conventional hot rolling involved only small reductions below 1700F and finish temperatures at about 1600F.
Samples of all thicknesses were further subjected to precipitation hardening after hot rolling at a temperature o 1100F (593C) for a period of one hour, followed by air cooling.
As shown in Table I, in the as-rolled condition, samples which were subjected to the controlled hot rolling process of the invention showed a slight superiority in yield and tensile strength over samples subjected to conventional hot rolling. Of greater si~nificance was the dramatic superiority in -toughness in the as-rolled condltion exhibited by all sample~
~ 36~
1 subjected to the controlled hot rolling process of the invention.
The precipitation hardened samples exhibited a signi-ficant increasé in yield and tensile strength as compared to the same samples in the as-rolled condition, and samples subjected to the controlled hot rolling process of the invention were sligthly superior in yield strength as compared to precipitation hardened samples subjected to conventional hot rolling. Again the toughness of samples in the precipitation hardened condition subjected to controlled hot rolling showed a marked superiority over samples which were subjected to conventional hot rolling prior to precipitation hardening.
For purpose 5 of direct comparison, 9 amples of Heat A
were subjected to the same tests as Heat B of ASTM A710 Grade A steel, analyzing, in weight percent, 0.035%
carbon, 0.44% manganese, 0.010% phosphorus, O.Ol5~
sulfur, 0.28% silicon, 0.68~ chromium, 0.89~ nickel, 0.21~ molybdenum, 1.16~ copper, 0,044% aluminum, 0.~45%
columbium, and balance essentially iron. Samples of both heats were hot rolled in accordance with the controlled rolling process of the present invention to plates of 1/2 inch (12.~ mm) thickness, and a sample of each steel was al50 subjected to precipitation hardening at llOO~F
~593C) for one hour. In other respects preparation was the same as reported above.
The comparative transverse tensile properties and longitudinal and transverse toughness values are set forth in Table II. It is apparent that the yield strength of Heat A in the as-control rolled condition was substantially equivalent to that of Heat B in the pre-cipitaton hardened condition. In the precipitation hardened condition the yield strength of Heat A was substantially higher than ~hat of Heat B. The toughness of the steel of the invention in the longitudinal ~2~3~
1 direction was substantially higher in the as-control rolled condition than that of Heat B in the precipitation hardened condition.
Additional heats of steels in accordance with the invention were prepared, and the composi~ions thereof are set forth in Table III.
Samples of steels from Heats C and D in Table III
and of Heat A were subjected to both conventional and controlled hot rolling, austenitizing, quenching and precipitation hardeningO Plates of varying thickness were produced for testing. The austenitizing was effected by reheating to a temperature of about 1650F
(gO0C~, holding for about 30 to 75 minutes and qu~nching - in water. Precipitation hardening was effected either at 1200F or 1100F for 30 minutes, followed by air cool.ing.
Tensile and toughness properties of these speci.mens are set forth in Tab].e IV, rom which it will be noted that a yield strength in excess of 90 ksi was obtained at least for plate thicknesses up to and including one inchO For the thicker plates wherein the yield strength ranged between 86.4 and 88.3 ksi, sornewhat hiyher yi.eld strengths could undoubtedly be obtained by precip~t.ation hardening at 1000F (538C).
It will be evident that outstanding toughness was achieved in the longitudinal direction for all specimens regardless of whether the hot rolling w~s conventional or conducted in accordanc~ with the controlled hot rolling process of the present invention. Transverse toug~ness ~alues were also generally e~cellent and well above the aim of 35 ft-lbs at -80F.
Referring next to Figs~ 3 and 4, microstructures are shown of specimens taken from the steel of Heat A at the mid thickness of 3/4 inch ~19 mm) thick plates~ Fig. 3 illustrates the recrystallized grain structure obtained in the as~rolled condition when subjected to conventional 63~
1 hot rolling. Fig. 4 shows the deformed grain structure obtained by the controlled hot rolling process of the present invention, which is predominantly fine grained and acicular ferrite.
Fig. 5 illustrates the grain structure of an ~STM
A710 Grade A steel (Heat B3 after hot rolling in accord ance with the controlled hot rolling process of the present invention, with the specimen being taken at the mid thickness position of 1/2 inch plate. The micro-structure comprises polygonal ferrite, pearlite and bainite which resulted from recrystalliYed austenite before transformation.
Fig. 6 illustrates the microstructure of the steel of the invention (Heat No. A), taken at the mid thickness position of 1/2 inch plate when subjected to the con~
trolled hot rolling process of the present invention.
The microstructure is a very fine acicular errite with some lower-bainite obtained by transformation from an austenite phase which had not completely recrystallized.
In Figs. 3 and 4 the same ~teel was subjected to different hot rolling conditions, and the marked dif-ference in microstructures shows the criticality of the controlled hot rolling process of the invention when practiced on a steel of the specified composition in the a8-rolled condition. In Figs~ 5 and 6, different steels were subjected to the identical controlled hot rolling process of the invention, and the steel of the present invention transformed to a very fine acicular ferrite microstructure, whereas the conventional prior art steel transformed to a poly~onal ferrite, pearlite and bainite microstructure, thus il~ustrating the critieality of the composition of the present steel.
It is thus evident that the present invention in-volves criticality with respect to composition regardless of the condition of the final product. It is further 3~
1~
1 evident that the controlled hot rolling process of the invention is critical for production of as-rolled and as rolled and precipitation hardened plates having the desired combination of properties. For the production of austenitized, quenched and precipitation hardened shapes, ~he hot rolling process is not critical.
, .
TA B L E
TT,~ A~D~u~
~h c~l C~r~itisn, wt.~
Hea~ C Mn P S Si_ Cr Ni Mo Cu Al Cb A 0.04 1.45 Q.014 0.007 0.30 0.06 0.96 0.20 1.14 Q.036 0.041 As-Rolled As-Rolled ~ 1100F P~.
~long. ~ ElongO
~hi~kn~ in in inc~ R~l 1 i n~ ksiU3'S ~ ksi 8 " ~ , ksi UIY;, ksi 2 " % RA
3/8Conventional 87.6 103.0 18 53 ND* 117.8 33 57 3/8Fresent In~ention B6.2 106.0 14 49 104.9 114.8 29 46 1/2 " " 81.9 105.4 13.5 55 107.5 116.2 ~1 57 3/4Conv~n~i~n~l 82.1 102.9 18 54 103c7 117.8 42 52 3/4Present Invention 83.5 104.4 18 51 99.9 107.9 46 58 3~4ConvPn~i~n~l 83.3 104.6 18 60 97.9 113.4 40 55 ~ ~-3j4Present In~ention 84.2 105.3 18 50 98.1 110.4 39 51 * ~D = nct detPrmin~
~B
Charpy V-~ctch Impact Energy at -5QF
Thickness Energy, f~-Ib - As rolled* Energy, t-lb - As-Rollad ~ llOO~F PH*
inch ~lling SperimPn Lcngitud~nal ~1~ ~vtlse Sp~im~n Lcngi~ud~nal ~1~ ~vt~se 3/8 Conv~tjnn~ 3/4-size 31 19 3~4-size 26 19 3/8 Present Inve~tion " 65 38 " 55 3~
1/2 " " Full-size 78 46 Full-siz2 45 23 3~4 C~nt i~ 6 10 ' 14 iO
3/4 Pres~nt Invention " 37 43 " 67 32 ~f4 C~l1V~ L I f~ial 18 ~5 26 75 3/4 Present Invention " 69 50 " 76 31 -- * Average of three rqrli~te tes~s TA B LE I I
v~se Tensile Prc~ties - 12.5 ~n Pla~es Rolled Acc~rdirlg to Pre~ent Invention Heat Test Co~ditic:YnYS, ksi UIS, ksi % Eiong. in 8" ~ Elong. in 2"
A As-RDlled 81.9 105.4 13.5 ND
As--Rolle~ ~ 1100F E~ 1~7.5 116.2 ~D 41 B As-R~lled + 1100F ~ 83.3 98.8 ND 31 MD = Not De~in~
Langitudin~l and 'r~dl~v~,s~ Cha~ ~7~1O~h I~pact Energ~ at -50F
Fnergys ft-lb*
He~,t Test CarlditionSp~i~PnL~ngitudinal Transve~se N ~
A As-Rolled Full-size 78 46 C--`
" As-Rolle~ + 1100F PH " " 45 23 B As-R~lled + 1100F P~ " " 56 ~D
*2~verage o three replicate ,,~ ng for E~ea~ A and cw~ fi~ Heat !3 lot Det~rm;ned ~ A B I. 1~ I 3[ I
Heat C Mn P S Si ~ ~ FD Cu Al Cb C O.C6 1.4(~ 0.01~) O.(~t)4 0.24 0.0~3 0.85 0.18 1.1~ 0.050 0.1~44 D 0.05 1.42 0.010 0.005 0.30 0.23 0.87 0.17 1.13 0.033 0.()5t) TA B LE I V
% Elong.
Plate in He2t Thi l~kni~sF~ h Rl~l l i n~~L~ ~i_uL esy~ urs, ksi 2 " %RA
A 3/8 C~nvPnti~ l 1200F ~D 46.0 44 58 3/8 Present Inventi~ " 98.3 104.7 31 65 " 1/~ " " " 98.3 1040~ 36 63 3/4 Corn~.-n~ n~l ~t 88.1 98.6 48 65 3/4 Present Irlventian " S4.7 101.8 38 47 C 1 ConvPnti~n~l 1100F 95.9 101.4 24 69 A 1 1/4 " 1200F 88.3 96.7 55 63 D 1--1/4 " 1100F 87.0 98.0 25 67 " 2 " " 86~4 98.9 25 72 ~D = Not De~rmi nf~
Charpy V ~ . I~ct Ener~y at -80F G
Pltat~3 Ener~, ft-lb* r Heat ~ h Rt ll;n~ T~tl.~es Sp~;~nLc)ngitudir~
A 3/8 Conv~n~ l 1200F 3/4-size 42 35 3/8 P~eserlt Invention " " " 97 58 1/2 " " " Full-size 129 62 3/4 Co~Iv~n~ t- 1.07 81 3/4 Present I~lventitn " " " 90 61 C 1 Co~v~ n~l llOOF 1- ~, 119 98 A 1-1/4 ll 1200F '~ c~ 112 79 3 1-1/4 " 1100F " " 106 68 " 2 " " '~ " 42 60 ~e of t~ree rep~ieate ~est~ 3~ ot Detf~TinG~1
Claims (14)
1. A process for producing a low alloy steel shape of at least 4.8 mm thickness exhibiting a yield strength of at least 56 kg/mm2 at room temperature and a Charpy V-notch impact strength (longitudinal) of at least 27 Joules at -46°C in the hot reduced condition together with excellent weldability including retained toughness in the heat affected zone of a weldment, characterized by the steps of providing a steel starting material consisting essentially of, in weight percent, from about 0.02% to 0.07% carbon, 1.2% to 2.0% manganese, 0.020 maximum sulfur, up to 0.5% silicon, 0.1% to 0.4%
molybdenum, 0.01% to 0.1% columbium, about 0.01% to 0.10%
acid soluble aluminum, about 0.8% to 2.0% copper, about 0.4% to 2.0% nickel, residual chromium, and balance iron except for incidental impurities, hot reducing said starting material to a desired final thickness with a total reduction in thickness of at least 30% while within the temperature range of about 760° to 927°C whereby to avoid substantial recrystallization of austenite and to obtain a predominant heavily deformed austenite phase;
and cooling at a rate which transforms said austenite phase to a predominantly fine acicular ferrite and lower-bainite phase.
molybdenum, 0.01% to 0.1% columbium, about 0.01% to 0.10%
acid soluble aluminum, about 0.8% to 2.0% copper, about 0.4% to 2.0% nickel, residual chromium, and balance iron except for incidental impurities, hot reducing said starting material to a desired final thickness with a total reduction in thickness of at least 30% while within the temperature range of about 760° to 927°C whereby to avoid substantial recrystallization of austenite and to obtain a predominant heavily deformed austenite phase;
and cooling at a rate which transforms said austenite phase to a predominantly fine acicular ferrite and lower-bainite phase.
2. The process claimed in claim 1, characterized in that said total reduction in thickness is at least 50%
while within the temperature range of 760° to 871°C.
while within the temperature range of 760° to 871°C.
3. The process claimed in claim 1, characterized by the further step of precipitation hardening by heating within the range between about 482°C and the AC1 point, whereby to obtain a shape having a yield strength of at least 60 kg/mm2 at room temperature and a Charpy V-Notch impact strength (longitudinal) of at least 27 Joules at -46°C.
4. The process claimed in claim 3, characterized in that said precipitation hardening comprises heating within the range between about 538° and 649°C.
5. The process claimed in claim 1, characterized in that said steel starting material consists essentially of from about 0.03% to 0.05% carbon, about 1.3% to 1.65%
manganese, about 0.01% maximum sulfur, about 0.15% to 0040% silicon, about 0.15% to 0.30% molybdenum, about 0.02% to 0.05% columbium, about 0.02% to 0.06% acid soluble aluminum, about 1.0% to 1.3% copper, about 0.7 to 1.0% nickel, less than-0.25% chromium, and balance iron except for incidental impurities.
manganese, about 0.01% maximum sulfur, about 0.15% to 0040% silicon, about 0.15% to 0.30% molybdenum, about 0.02% to 0.05% columbium, about 0.02% to 0.06% acid soluble aluminum, about 1.0% to 1.3% copper, about 0.7 to 1.0% nickel, less than-0.25% chromium, and balance iron except for incidental impurities.
6. A process for producing a low alloy steel shape of at least 4.8 mm thickness exhibiting a yield strength of at least 56 kg/mm2 at room temperature and a Charpy V-Notch impact strength (longitudinal) of at least 68 Joules at -62°C in the austenitized, quenched, and precipitation hardened condition together with excellent weldability including retained toughness in the heat affected zone of a weldment, characterized by the steps of providing a steel starting material consisting essentially of, in weight percent, from about 0.02% to 0.07% carbon, 1.2% to 2.0% manganese, 0.020% maximum sulfur, up to 0.5% silicon, 0.1% to 0.4% molybdenum, 0.01% to 0.1% columbium, about 0.01% to 0.10% acid soluble aluminum, about 0.8% to 2.0% copper, about 0.4%
to 2.0% nickel, residual chromium, and balance iron except for incidental impurities; hot reducing said starting material to a desired final thickness; cooling to a temperature at which the steel transforms to fer-rite, reheating the hot reduced shape to a temperature of about 871° to 982°C and within the austenization range whereby to transform said ferrite to austenite, quenching at a rate which transforms substantially all said austenite to predominantly fine acicular ferrite and lower-bainite and which avoids substantial precipitation of copper-rich particles; and precipitation hardening by heating within the range between about 482°C and the AC
point.
to 2.0% nickel, residual chromium, and balance iron except for incidental impurities; hot reducing said starting material to a desired final thickness; cooling to a temperature at which the steel transforms to fer-rite, reheating the hot reduced shape to a temperature of about 871° to 982°C and within the austenization range whereby to transform said ferrite to austenite, quenching at a rate which transforms substantially all said austenite to predominantly fine acicular ferrite and lower-bainite and which avoids substantial precipitation of copper-rich particles; and precipitation hardening by heating within the range between about 482°C and the AC
point.
7. The process claimed in claim 6, characterized in that said hot reduced shape is reheated to a temperature of about 899° to 927°C and that said precipitation hardening comprises heating within the range between about 538° and 649°C.
8. The process claimed in claim 6, characterized in that said steel consists essentially of from about 0.03%
to 0.05% carbon, about 1.3% to 1.65% manganese, about 0.01% maximum sulfur, about 0.15% to 0.40% silicon, about 0.15% to 0.30% molybdenum, about 0.02% to 0.05%
columbium, about 0.02% to 0.06% acid soluble aluminum, about 1.0% to 1.3% copper, about 0.7% to 1.0% nickel, less than 0.25% chromium, and balance iron except for incidental impurities.
to 0.05% carbon, about 1.3% to 1.65% manganese, about 0.01% maximum sulfur, about 0.15% to 0.40% silicon, about 0.15% to 0.30% molybdenum, about 0.02% to 0.05%
columbium, about 0.02% to 0.06% acid soluble aluminum, about 1.0% to 1.3% copper, about 0.7% to 1.0% nickel, less than 0.25% chromium, and balance iron except for incidental impurities.
9. The process claimed in claim 6, characterized in that said hot reducing step comprises a reduction in thickness of at least 30% while within the temperature range of about 760° to 927°C whereby to avoid substantial recrystallization of austentite and to obtain a predominant heavily deformed austenite phase.
10. Low alloy steel shape of at least 4.8 mm thick-ness exhibiting a yield strength of at least 56 kg/mm2 at room temperature and a Charpy V-notch impact strength (longitudinal) of at least 27 Joules at -46°C in the hot reduced condition, together with excellent weldability including retained toughness in the heat affected zone of a weldment, characterized by a predominantly acicular ferrite and lower bainite microstructure, said steel consisting essentially of, in weight percent, from about 0.02% to 0.07% carbon, from 1.2% to 2.0% manganese, 0.020% maximum sulfur, up to 0.5% silicon, 0.1% to 0.4%
molybdenum, 0.01% to 0.1% columbium, about 0.01% to 0.10%
acid soluble aluminum, about 0.8% to 2.0% copper, about 0.4% to 2.0% nickel, residual chromium and balance iron except for incidental impurities.
molybdenum, 0.01% to 0.1% columbium, about 0.01% to 0.10%
acid soluble aluminum, about 0.8% to 2.0% copper, about 0.4% to 2.0% nickel, residual chromium and balance iron except for incidental impurities.
11. Low alloy steel shape as claimed in claim 10, characterized in that said steel consists essentially of from about 0.03% to 0.05% carbon, about 1.3% to 1.65%
manganese, about 0.01% maximum sulfur, about 0.15% to 0.40% silicon, about 0.15% to 0.30% molybdenum, about 0.02% to 0.05% columbium, about 0.02% to 0.06% acid soluble aluminum, about 1.0% to 1.3% copper, about 0.7%
to 1.0% nickel, less than 0.25% chromium, and balance essentially iron.
manganese, about 0.01% maximum sulfur, about 0.15% to 0.40% silicon, about 0.15% to 0.30% molybdenum, about 0.02% to 0.05% columbium, about 0.02% to 0.06% acid soluble aluminum, about 1.0% to 1.3% copper, about 0.7%
to 1.0% nickel, less than 0.25% chromium, and balance essentially iron.
12. Low alloy steel shape as claimed in claim 10, characterized by a yield strength of at least 60 kg/mm2 at room temperature in the precipitation hardened condition.
13. Low alloy steel shape as claimed in claim 10, characterized by a Charpy V-notch impact strength (longi-tudinal) of at least 68 Joules at -62°C after austenization, quenching and precipitation hardening.
14. Low alloy steel shape as claimed in claim 10, in the form of hot rolled plate having a thickness up to at least about 50 mm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US47635383A | 1983-03-17 | 1983-03-17 | |
| US476,353 | 1990-02-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1207639A true CA1207639A (en) | 1986-07-15 |
Family
ID=23891504
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000449354A Expired CA1207639A (en) | 1983-03-17 | 1984-03-12 | Low alloy steel plate and process for production therefor |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0123406A3 (en) |
| JP (1) | JPS605822A (en) |
| KR (1) | KR840007899A (en) |
| BR (1) | BR8401222A (en) |
| CA (1) | CA1207639A (en) |
| ES (1) | ES530726A0 (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3883051T2 (en) * | 1987-04-24 | 1993-12-02 | Nippon Steel Corp | Process for the production of steel sheets with good toughness at low temperatures. |
| DE4033700C1 (en) * | 1990-10-19 | 1992-02-06 | Stahlwerke Peine-Salzgitter Ag, 3150 Peine, De | |
| JP2634961B2 (en) * | 1991-03-06 | 1997-07-30 | 新日本製鐵株式会社 | Manufacturing method of 80kgf / mm2 class high strength steel with excellent weldability |
| CH687879A5 (en) * | 1993-12-01 | 1997-03-14 | Met Cnam Paris Max Willy Tisch | Reinforcement, machine, apparatus and Metallbaustaehle in fines Dumaguete with stable anticorrosive coating. |
| CA2206349A1 (en) * | 1994-11-28 | 1996-06-06 | Max-Willy Tischhauser | Process for producing high quality, fine-grained structural steel with a stable anticorrosive layer for concrete-reinforcing mechanical apparatus and metal constructions engineering |
| US5810951A (en) * | 1995-06-07 | 1998-09-22 | Ipsco Enterprises Inc. | Steckel mill/on-line accelerated cooling combination |
| US6264767B1 (en) | 1995-06-07 | 2001-07-24 | Ipsco Enterprises Inc. | Method of producing martensite-or bainite-rich steel using steckel mill and controlled cooling |
| US6309482B1 (en) | 1996-01-31 | 2001-10-30 | Jonathan Dorricott | Steckel mill/on-line controlled cooling combination |
| CN100335670C (en) | 2002-02-07 | 2007-09-05 | 杰富意钢铁株式会社 | High strength steel plate and method for production thereof |
| JP5385899B2 (en) * | 2007-05-06 | 2014-01-08 | ニューコア・コーポレーション | Thin cast strip with added microalloy and method for producing the same |
| CN115838904A (en) * | 2022-12-20 | 2023-03-24 | 衡阳华菱钢管有限公司 | Method for manufacturing 850 MPa-grade high-strength high-toughness seamless steel pipe |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3539404A (en) * | 1967-05-15 | 1970-11-10 | Youngstown Sheet And Tube Co | Method of making a low alloy steel |
| US3726723A (en) * | 1970-05-11 | 1973-04-10 | American Metal Climax Inc | Hot-rolled low alloy steels |
| CA952415A (en) * | 1970-05-20 | 1974-08-06 | Eiji Miyoshi | Process and apparatus for manufacture of strong tough steel plates |
| JPS5215523B1 (en) * | 1970-11-18 | 1977-04-30 | ||
| GB1436846A (en) * | 1973-03-16 | 1976-05-26 | Int Nickel Ltd | Steels |
| CA988751A (en) * | 1974-07-22 | 1976-05-11 | Madhavarao Krishnadev | Extra low-carbon copper-manganese - columbium high strength steel |
| US3955971A (en) * | 1974-12-11 | 1976-05-11 | United States Steel Corporation | Alloy steel for arctic service |
| JPS6017806B2 (en) * | 1977-06-10 | 1985-05-07 | 新日本製鐵株式会社 | Manufacturing method for specially shaped steel pipes with excellent toughness |
| JPS5933168B2 (en) * | 1977-06-10 | 1984-08-14 | 新日本製鐵株式会社 | Manufacturing method for high-strength, high-toughness special-shaped steel pipes |
| JPS5421917A (en) * | 1977-07-20 | 1979-02-19 | Nippon Kokan Kk <Nkk> | Method of manufacturing non-quenched high-tensile steel having high toughness |
-
1984
- 1984-03-12 CA CA000449354A patent/CA1207639A/en not_active Expired
- 1984-03-15 EP EP84301762A patent/EP0123406A3/en not_active Withdrawn
- 1984-03-16 ES ES530726A patent/ES530726A0/en active Granted
- 1984-03-16 BR BR8401222A patent/BR8401222A/en unknown
- 1984-03-16 JP JP59050822A patent/JPS605822A/en active Pending
- 1984-03-16 KR KR1019840001338A patent/KR840007899A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| ES8503725A1 (en) | 1985-03-01 |
| EP0123406A3 (en) | 1987-10-07 |
| ES530726A0 (en) | 1985-03-01 |
| JPS605822A (en) | 1985-01-12 |
| EP0123406A2 (en) | 1984-10-31 |
| BR8401222A (en) | 1984-10-23 |
| KR840007899A (en) | 1984-12-11 |
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| MKEX | Expiry |