CN118064796A - Ultra-high strength steel with excellent welding performance and manufacturing method thereof - Google Patents
Ultra-high strength steel with excellent welding performance and manufacturing method thereof Download PDFInfo
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- CN118064796A CN118064796A CN202211476327.7A CN202211476327A CN118064796A CN 118064796 A CN118064796 A CN 118064796A CN 202211476327 A CN202211476327 A CN 202211476327A CN 118064796 A CN118064796 A CN 118064796A
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- 238000003466 welding Methods 0.000 title claims abstract description 40
- 229910000797 Ultra-high-strength steel Inorganic materials 0.000 title claims abstract description 31
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 14
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 76
- 239000010959 steel Substances 0.000 claims abstract description 76
- 238000005496 tempering Methods 0.000 claims abstract description 20
- 229910000734 martensite Inorganic materials 0.000 claims abstract description 12
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 12
- 238000005452 bending Methods 0.000 claims abstract description 7
- 238000010791 quenching Methods 0.000 claims abstract description 7
- 230000000171 quenching effect Effects 0.000 claims abstract description 7
- 239000012535 impurity Substances 0.000 claims abstract description 6
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 6
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 6
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 5
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 4
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 3
- 238000010438 heat treatment Methods 0.000 claims description 19
- 238000001816 cooling Methods 0.000 claims description 16
- 238000005266 casting Methods 0.000 claims description 10
- 238000005096 rolling process Methods 0.000 claims description 8
- 229910052804 chromium Inorganic materials 0.000 claims description 7
- 238000004321 preservation Methods 0.000 claims description 6
- 238000003723 Smelting Methods 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 3
- 239000002244 precipitate Substances 0.000 claims description 3
- 230000009467 reduction Effects 0.000 claims description 3
- 239000000758 substrate Substances 0.000 claims description 3
- 229910052742 iron Inorganic materials 0.000 claims description 2
- 239000000126 substance Substances 0.000 claims description 2
- 239000002105 nanoparticle Substances 0.000 claims 1
- 238000000034 method Methods 0.000 abstract description 13
- 230000008569 process Effects 0.000 abstract description 12
- 230000035945 sensitivity Effects 0.000 abstract description 2
- 238000001556 precipitation Methods 0.000 description 21
- 230000000694 effects Effects 0.000 description 14
- 238000005728 strengthening Methods 0.000 description 14
- 229910001566 austenite Inorganic materials 0.000 description 9
- 229910000859 α-Fe Inorganic materials 0.000 description 8
- 230000002542 deteriorative effect Effects 0.000 description 6
- 229910000510 noble metal Inorganic materials 0.000 description 6
- 229910045601 alloy Inorganic materials 0.000 description 5
- 239000000956 alloy Substances 0.000 description 5
- 238000005098 hot rolling Methods 0.000 description 5
- 230000009466 transformation Effects 0.000 description 5
- 229910052799 carbon Inorganic materials 0.000 description 3
- 229910052750 molybdenum Inorganic materials 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 238000001878 scanning electron micrograph Methods 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000009863 impact test Methods 0.000 description 2
- 230000006698 induction Effects 0.000 description 2
- 230000005012 migration Effects 0.000 description 2
- 238000013508 migration Methods 0.000 description 2
- 239000010955 niobium Substances 0.000 description 2
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 2
- 229910001562 pearlite Inorganic materials 0.000 description 2
- 229910052761 rare earth metal Inorganic materials 0.000 description 2
- 238000007670 refining Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 241000219307 Atriplex rosea Species 0.000 description 1
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- 229910000746 Structural steel Inorganic materials 0.000 description 1
- PPWPWBNSKBDSPK-UHFFFAOYSA-N [B].[C] Chemical compound [B].[C] PPWPWBNSKBDSPK-UHFFFAOYSA-N 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 125000004432 carbon atom Chemical group C* 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000016507 interphase Effects 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 239000012629 purifying agent Substances 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
Classifications
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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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- 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
- C21D1/18—Hardening; Quenching with or without subsequent tempering
-
- 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
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
-
- 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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
-
- 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
- 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
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
-
- 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
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
-
- 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
- C21D2211/004—Dispersions; Precipitations
-
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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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
An ultra-high strength steel with excellent welding performance and a manufacturing method thereof, wherein the ultra-high strength steel comprises the components with the mass percentage of ：C 0.15～0.20％,Si 0.31～0.50％,Al 0.020～0.20％,Mn 0.8～1.6％,Cr0.20～1.0％,Ti 0.05～0.15％,V 0.020～0.080％,N≤0.005％,P≤0.020％,S≤0.0050％,O≤0.0040％,Ti+V≥0.09％, and the balance of Fe and other unavoidable impurities. The invention adopts a quenching and tempering process to produce, and the steel plate structure is carbide of high-temperature tempered martensite and nano TiC precipitated phase + V, cr. According to the invention, on the premise that the yield strength is more than or equal to 960MPa, the tensile strength is more than or equal to 980MPa, the elongation is more than or equal to 18%, the crack sensitivity coefficient P cm is 0.20-0.25%, the tensile strength of a welded joint is more than or equal to 980MPa after the steel plate is subjected to gas shielded butt welding, the bending center diameter d=4a of a transverse sample is qualified after 180 DEG bending, and the impact energy of a heat affected zone at minus 40 ℃ is more than or equal to 60J, so that the steel plate is the ultra-high strength steel with excellent welding performance.
Description
Technical Field
The invention relates to the technical field of high-strength steel, in particular to ultra-high-strength steel with excellent welding performance and a manufacturing method thereof.
Background
Engineering machinery is an important component of the equipment industry. With the development of large-scale, high-end and light-weight engineering machinery industry, the strength level of steel is continuously improved, and the strength level is generally increased from 500-600 MPa to 800MPa, 900MPa and even 1000MPa. Because the service environment of the high-strength steel for engineering machinery is harsh, the high-strength steel has strict requirements on the elongation, bending performance, toughness and welding performance of the steel plate.
Quenched and tempered high-strength steel with the current yield strength of 960MPa has been widely applied in the engineering machinery industry. In order to ensure higher toughness, the tempering temperature is often higher, and the ultra-high strength with yield larger than 960MPa is maintained at the higher tempering temperature, a large amount of noble metal elements such as Cr, mo, V and the like which resist tempering softening are required to be added. For example, chinese patent No. CN103014538B discloses a high-strength steel plate with 960 MPa-grade yield strength and a manufacturing method thereof, wherein the ultrahigh-strength structural steel with 960 MPa-grade yield, 18% elongation A50 and 50J impact at minus 60 ℃ is obtained by adding less than or equal to 0.70% Cr, less than or equal to 0.30% Ni and less than or equal to 0.30% Mo. Chinese patent CN113430458a discloses a super high strength steel plate with yield strength higher than 1040MPa and its manufacturing method, in which Cr is added into the steel: 0.20 to 0.60 percent, mo:0.20 to 0.80 percent, V:0.02 to 0.12 percent of element.
Besides the mechanical properties of the steel, the engineering machinery industry also requires that the steel have good mechanical properties after welding, such as strong matching of the welding joint (i.e. the strength of the welding joint is not lower than that of the base metal), good bending properties of the welding joint, high toughness of a welding heat affected zone, and the like. In order to improve the strength of the welded joint, more Cr, V and Mo elements resistant to high-temperature softening are needed to be added, so that the alloy cost of the steel grade is greatly improved. At present, related patents on ultra-high strength steel for engineering machinery of the strength level hardly mention the requirement of ensuring such high welding performance. Therefore, there is a need to develop a high-strength steel having a relatively low cost while having both high strength and excellent welding performance.
Disclosure of Invention
The invention aims to provide ultra-high strength steel with excellent welding performance and a manufacturing method thereof, and by adding a proper amount of low-cost Ti, si and Al elements and a small amount of noble metal elements such as Cr, V and the like and combining the control of hot rolling coiling temperature, nano TiC precipitated phases are formed in a structure, so that the strength of the steel is improved. Meanwhile, the high-temperature stability of TiC precipitated phase is utilized, so that the TiC precipitated phase is difficult to dissolve or coarsen in the welding process, and the strength of the welded joint is improved.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
The ultra-high strength steel with excellent welding performance has the chemical components of ：C：0.15～0.20％,Si：0.31～0.50％,Al：0.020～0.20％,Mn：0.8～1.6％,Cr：0.20～1.0％,Ti：0.05～0.15％,V：0.020～0.080％,N≤0.005％,P≤0.020％,S≤0.0050％,O≤0.0040％,Ti+V≥0.09％, wt% and Fe and other inevitable impurities.
Further, the balance being Fe and other unavoidable impurities.
Still further, it satisfies: si+Al is more than or equal to 0.3 and less than or equal to 0.7; can ensure that a dispersed nano TiC precipitated phase is formed in the tissue before heat treatment, thereby better realizing the invention effect.
And one or more of Mo less than or equal to 0.20%, cu less than or equal to 0.40%, nb less than or equal to 0.030%, ni less than or equal to 0.50%, B less than or equal to 0.0020%, RE less than or equal to 0.0020% and Ca less than or equal to 0.005%.
The microstructure of the ultra-high strength steel is carbide of high-temperature tempered martensite and nano TiC precipitated phase + V, cr.
The yield strength of the ultra-high strength steel is more than or equal to 960MPa, the tensile strength is more than or equal to 980MPa, the elongation is more than or equal to 18%, and the crack sensitivity coefficient P cm is 0.2-0.25%, wherein P cm = C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B.
After the ultra-high-strength steel is subjected to gas shielded butt welding, the tensile strength of a welding joint is more than or equal to 980MPa, the bending center diameter d=4a of a transverse sample is 180 DEG, the bending is qualified, and the impact energy of a heat affected zone at minus 40 ℃ is more than or equal to 60J.
In the composition design of the ultra-high strength steel with excellent welding performance, the invention comprises the following steps:
C: c is a basic element in steel and is also an important element for strengthening martensitic steel. C of more than 0.15% can ensure the strength of the quenched steel plate; however, a higher C content results in an increase in the overall C equivalent, and cracking is likely to occur during welding. Therefore, the C content of the present invention is in the range of 0.15 to 0.2%.
Si and Al: si and Al are essential elements in steel and are also important elements in the present invention. Si improves the solid solution strengthening effect, and Al element can play a better role in deoxidization. In addition, si and Al elements can inhibit precipitation of carbide during tempering and improve toughness of steel. In the invention, si and Al have more important functions of remarkably promoting the transformation from austenite to ferrite when the content of the Si and the Al is more than or equal to 0.3, improving the migration rate of the austenite to ferrite transformation interface during coiling, and matching the diffusion rate of the Ti with the diffusion rate of the TiC during the precipitation of the TiC, thereby improving the phase-to-phase output of the TiC during the ferrite transformation process, refining the size of TiC precipitation phases and improving the precipitation strengthening effect of the TiC. When the content of Si+Al is more than or equal to 0.7, the phase change and interface migration rate is too fast, tiC is not precipitated and the strengthening effect is lost. In addition, excessively high Si tends to cause red scales on the surface of the steel, and at the same time, excessive oxide inclusion defects are formed, deteriorating the toughness of the steel. Therefore, the present invention requires 0.3.ltoreq.Si+Al.ltoreq.0.7.
Mn: mn element is more than 0.8%, so that the hardenability of the steel can be improved; however, when the Mn content exceeds 1.6%, inclusions such as segregation and MnS are liable to occur, and the toughness of the martensitic high-strength steel is deteriorated. Therefore, the Mn content of the present invention ranges from 0.80 to 1.60%.
Cr: cr element is more than 0.2%, so that the hardenability of the steel can be improved, a full martensitic structure is formed during quenching, cr forms Cr carbide during tempering, and the tempering softening resistance is realized; however, cr content exceeding 1.0% causes a large spark during welding, which affects the welding quality. Therefore, the Cr content of the present invention is in the range of 0.20 to 1.0%.
Mo: the Mo element can improve the hardenability of the steel, and is beneficial to forming a full martensitic structure during quenching; mo reacts with C to form carbide particles during high-temperature tempering, and has the functions of resisting high-temperature tempering softening and softening a welded joint; however, too high a Mo content results in an increase in carbon equivalent, deteriorating welding performance, while Mo is a noble metal, and increases costs. Therefore, the Mo content range of the present invention is 0.2% or less.
Ni: the Ni element has the functions of refining martensite structure and improving the toughness of steel; the Ni element may also improve the toughness of the weld heat affected zone. Too high a Ni content results in an increase in carbon equivalent, deteriorating welding performance, while Ni is a noble metal, and increases costs. The Ni content range of the invention is less than or equal to 0.50 percent.
Cu: the Cu element can produce certain precipitation strengthening effect during tempering, and in addition, the corrosion resistance of the ultra-high strength steel for engineering machinery can be improved by adding certain Cu element. The Cu content range of the invention is less than or equal to 0.40 percent.
Nb: nb is a microalloy element, forms nano-scale precipitates with C, N and other elements, and inhibits the growth of austenite grains when heating; nb can raise the non-recrystallization critical temperature Tnr and expand the production window, and the content of niobium is less than or equal to 0.030 percent.
Ti: the Ti element is one of the most important elements of the present invention. Ti has strong binding force with C atoms in steel to form carbide. The component design thought of the invention mainly aims to lead the steel to form tiny dispersed Ti nano carbide in the process of converting austenite into ferrite, thereby greatly playing the precipitation strengthening effect of the carbide and ensuring the strength of the steel. Meanwhile, the Ti carbide is stable and still can not be obviously dissolved at a higher temperature, so that the Ti carbide can still remain in a tissue after welding, and the strength of a welded joint is improved. When the Ti content is 0.05% or more, the remarkable precipitation strengthening effect is exhibited, but when the Ti content is more than 0.15%, ti is difficult to be completely dissolved and deactivated when the slab is heated, and too much Ti causes coarsening of TiN inclusion, deteriorating toughness of steel. Therefore, the Ti content of the present invention is in the range of 0.05 to 0.15%.
V: the V element can refine grains and improve the toughness of the steel. And V reacts with C in the tempering process to form carbide, so that the precipitation strengthening effect is further achieved. V belongs to noble metal, and too much V can raise the cost. Therefore, V of the present invention is in the range of 0.020 to 0.080%.
B: the trace B can improve the hardenability of the steel and improve the strength of the steel; however, B exceeding 0.0020% tends to segregate, form a carbon-boron compound, seriously deteriorating toughness and weldability of the steel. Therefore, the boron content range of the present invention is 0.0020% or less.
RE: the rare earth elements can improve the morphology of inclusions in steel, so that the inclusions are more finely dispersed, and especially for the high Ti component steel grade, the size morphology of TiN inclusions can be obviously improved, and the toughness and fatigue performance of the steel are improved. Too much rare earth element leads to an increase in cost. The RE range of the invention is less than or equal to 0.0020 percent.
Ca: the Ca element can play a role of a purifying agent in the steel smelting process, so that the toughness of the steel is improved; however, ca content exceeding 0.005% tends to form a compound of Ca having a large size, which in turn deteriorates toughness. Therefore, the Ca content of the present invention is in the range of 0.005% or less.
N: the present invention requires strict control of the range of N element, and an N content exceeding 0.005% tends to cause formation of coarse precipitate particles, deteriorating toughness. Therefore, the N content of the invention is less than or equal to 0.005 percent.
P, S and O: p, S and O are used as impurity elements to influence the plasticity and toughness of steel, and the control range of the invention is less than or equal to 0.020 percent of P, less than or equal to 0.0050 percent of S and less than or equal to 0.0040 percent of O respectively.
In addition, the invention also requires that: ti+V is more than or equal to 0.09%, which is to fully play the precipitation strengthening effect of TiC and VC in the heat treatment process. When Ti+V is more than or equal to 0.09%, the micro-nano precipitation of TiC and VC can generate 120-200MPa precipitation strengthening effect.
The invention relates to a production method of ultra-high strength steel with excellent welding performance, which comprises the following steps:
1) Smelting and casting;
Smelting and casting into blanks according to the components;
2) Heating a casting blank;
3) Rolling; the finishing temperature is more than or equal to 880 ℃;
4) Cooling and coiling
Cooling the rolled steel plate to 550-700 ℃ at a cooling rate of more than or equal to 60 ℃/s, coiling, and then air-cooling to room temperature; obtaining a hot rolled substrate with microstructure of ferrite, nano TiC precipitated phase and pearlite;
5) Quenching heat treatment
Heating the hot rolled substrate to Ac 3 < + > (30-80) > DEG C, preserving the temperature of the core of the steel plate for 5-40 min after reaching the temperature, and rapidly cooling to room temperature at a cooling speed of more than or equal to 100 ℃/s;
6) Tempering heat treatment
The tempering temperature is 500-650 ℃, the temperature of the steel plate core is kept at the furnace temperature for more than or equal to 5min, and the steel plate core is air-cooled to room temperature, so that the carbide structure of high-temperature tempered martensite+nano TiC precipitated phase + V, cr is obtained.
Preferably, in the step 2), the heating temperature of the casting blank is more than or equal to 1230 ℃, and the heat preservation is started after the core of the casting blank reaches the furnace temperature, and the heat preservation time is more than 1.5h.
Preferably, in the step 3), the reduction rate of the last pass of rolling is less than or equal to 25%.
In the method for manufacturing the ultra-high strength steel with excellent welding performance, which is disclosed by the invention, the following steps are adopted:
In the step 2) of casting blank heating, the heating temperature is controlled to be more than or equal to 1230 ℃, and the heat preservation time of the casting blank core part is controlled to be more than 1.5 hours, so that the full solid solution of Ti and other alloy elements can be ensured, and the precipitation strengthening effect can be better exerted.
In the rolling process of the step 3), the reduction rate of the last pass of rolling is not more than 25%, and the final rolling temperature is not less than 880 ℃, so as to reduce deformation induction precipitation of TiC in the hot rolling process. The last pass has overlarge pressing rate, high deformation energy stored in austenite, low solid solubility of Ti at the overlarge final rolling temperature, and both promote deformation induction precipitation of TiC in the austenite, so that the precipitation amount of TiC in the coiling process is reduced. The TiC particles which are induced to be precipitated have larger size, hardly contribute to the strength and simultaneously impair the toughness of the steel grade.
In the cooling process of the step 4), after hot rolling, cooling to 550-700 ℃ at a cooling speed of more than or equal to 60 ℃ per second is carried out, so that ferrite phase transformation occurs during coiling of the steel, tiC is dispersed and precipitated on a ferrite/austenite interface, namely interphase precipitation occurs, so that dispersed nano-scale TiC precipitated phases are obtained, the precipitation strengthening effect is greatly exerted, and meanwhile, the strength of the steel plate and the joint strength of the steel plate after welding are improved.
In the step 5), the quenching temperature is Ac 3 + (30-80) DEG C, wherein Ac 3 is the austenite transformation ending temperature, and according to an empirical formula, ac 3 =955-350C-25Mn+51Si+106Nb+100Ti+68Al-11 Cr-33Ni-16Cu+67Mo; the quenching temperature is higher than Ac 3 plus 30 ℃ to ensure that the steel plate can be completely austenitized; the temperature is lower than Ac 3 plus 80 ℃ to prevent coarsening of austenite grains and deteriorate the toughness of the steel; cooling to room temperature at 100 deg.c/s or higher to obtain fully martensitic structure.
In the tempering heat treatment process, as the tempering temperature of the steel of the component system exceeds 500 ℃ and the core of the steel plate is kept for more than 5 minutes after reaching the furnace temperature, the internal stress of the steel plate can be effectively removed, meanwhile, the dislocation in martensite is recovered to improve the plasticity of the steel, and alloys Mo, cr and V can react with C to form tiny alloy carbide at the temperature, so that the yield strength of the steel is improved; tempering temperatures exceeding 650 ℃ coarsen alloy carbides, which can deteriorate the toughness and reduce the strength of the steel; the optimal matching of the strength and the plasticity can be realized by adjusting the tempering temperature and the tempering time.
The invention has the beneficial effects that:
1. According to the invention, a higher Ti element is added, the strength of steel grade and the strength of a welded joint are improved through nano TiC precipitated phase, and the addition of noble metal elements Cr, mo and V is reduced;
2. The invention reasonably controls the content of Si and Al elements and the coiling temperature, promotes the alternate precipitation of TiC in the coiling process, ensures that the TiC precipitation is full and tiny and dispersed, and improves the precipitation strengthening effect.
Drawings
FIG. 1 is a photograph of a scanning electron micrograph of a steel sheet after hot rolling and coiling according to example 4 of the present invention;
FIG. 2 is a photograph of a scanning electron micrograph of a steel sheet after heat treatment according to example 4 of the present invention.
Detailed Description
The invention is further described below with reference to examples and figures.
The components of the steel of the embodiment of the invention are shown in table 1, and table 2 shows the manufacturing process parameters of the steel of the embodiment of the invention; the performance parameters of the inventive example steels are shown in table 3.
Fig. 1 and 2 show scanning electron micrograph images after coiling and after heat treatment, respectively, of example 4 of the present invention.
As can be seen from the photograph, the hot rolled base plate consists of ferrite and pearlite, and nano precipitated phases are dispersed in the base body (fig. 1); the heat treated structure is tempered martensite structure, and the structure can also see a dispersed nano-scale carbide precipitated phase (figure 2), which is the embodiment of the nano-scale precipitation strengthening effect realized by adding high Ti component, adding Si and Al and combining the hot rolling process.
Mechanical properties of the examples were tested according to national standard GB/T228.1-2010 "tensile test Standard for Metal materials", and the quenched and tempered steel sheets of each example and comparative example were subjected to longitudinal tensile and longitudinal impact tests, and the properties of the templates of each example are shown in Table 3.
Standard welding processes are used: two steel plates are butt welded by forming a groove of 30 degrees on one side; adopting a 90 Kg-grade welding wire and 10KJ/cm welding heat input; and adopting gas shielded welding, wherein the shielding gas is 80% Ar+20% CO 2, and the gas flow is 20L/Min. After welding, the steel plate was subjected to tensile, bending and impact tests, and various mechanical property indexes were obtained, as shown in table 3.
From the mechanical property, the steel has ultrahigh strength, the yield is more than or equal to 960MPa, and the elongation is more than 18%. The strength of the welded joint can meet the requirement of equal strength matching, namely the joint strength is more than or equal to 980MPa. The welded joint has good cold bending performance, is qualified under the conditions of d=4a and 90 degrees, has higher toughness in a welding heat affected zone, and has impact energy of more than 60J at minus 40 ℃. The strength grade of the common ultra-high strength steel welded joint is difficult to achieve, and the impact of the welded joint at minus 40 ℃ is generally below 40J.
The above results show that the examples of the present invention have a specific elemental composition, particularly a specific higher Ti content and a combination of Si and Al elements, and are subjected to specific coiling and heat treatment, whereby the steel sheet obtained attains a weld joint strength with equal strength matching and excellent weld heat affected zone toughness while securing high strength and high toughness.
The ultra-high strength steel with excellent welding performance can be used in various fields requiring high strength steel, in particular to the application of the steel plate for engineering machinery requiring high strength, high welding strength and toughness of a heat affected zone.
Claims (10)
1. The ultra-high strength steel with excellent welding performance has the chemical components of ：C：0.15～0.20％,Si：0.31～0.50％,Al：0.020～0.20％,Mn：0.8～1.6％,Cr：0.20～1.0％,Ti：0.05～0.15％,V：0.020～0.080％,N≤0.005％,P≤0.020％,S≤0.0050％,O≤0.0040％,Ti+V≥0.09％, wt% and Fe and other inevitable impurities.
2. The ultra-high strength steel excellent in weldability according to claim 1, wherein the balance is Fe and other unavoidable impurities.
3. Ultra-high strength steel excellent in weldability according to claim 1 or 2, characterized by further satisfying: si+Al is more than or equal to 0.3 and less than or equal to 0.7.
4. The ultra-high strength steel excellent in weldability according to claim 1,2 or 3, further comprising one or more of 0.20% or less of Mo, 0.40% or less of Cu, 0.030% or less of Nb, 0.50% or less of Ni, 0.0020% or less of B, 0.0020% or less of RE, and 0.005% or less of Ca.
5. The ultra-high strength steel excellent in weldability according to any one of claims 1 to 4, wherein the microstructure of the ultra-high strength steel is high temperature tempered martensite+nano-sized TiC precipitate phase+ V, cr carbide.
6. The ultra-high strength steel excellent in weldability according to any one of claims 1 to 5, wherein the ultra-high strength steel has a yield strength of 960MPa or more, a tensile strength of 980MPa or more, an elongation of 18% or more, and a crack susceptibility P cm of 0.2 to 0.25%,
Pcm＝C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B。
7. The ultra-high strength steel with excellent welding performance according to any one of claims 1 to 6, wherein after the ultra-high strength steel is subjected to gas shielded butt welding, the tensile strength of a welded joint is equal to or more than 980MPa, the transverse specimen bending center diameter d=4a, 180-degree bending pass is achieved, and the impact energy of a heat affected zone at-40 ℃ is equal to or more than 60J.
8. The method for producing an ultra-high strength steel excellent in weldability according to any one of claims 1 to 7, comprising the steps of:
1) Smelting and casting;
smelting and casting into billets from the composition according to any one of claims 1 to 4;
2) Heating a casting blank;
3) Rolling; the finishing temperature is more than or equal to 880 ℃;
4) Cooling and coiling
Cooling the rolled steel plate to 550-700 ℃ at a cooling rate of more than or equal to 60 ℃/s, coiling, and then air-cooling to room temperature;
5) Quenching heat treatment
Heating the hot rolled substrate to Ac 3 < + > (30-80) > DEG C, preserving the temperature of the core of the steel plate for 5-40 min after reaching the temperature, and rapidly cooling to room temperature at a cooling speed of more than or equal to 100 ℃/s;
6) Tempering heat treatment
The tempering temperature is 500-650 ℃, the heat preservation is carried out for more than or equal to 5 minutes after the steel plate core reaches the furnace temperature, and the steel plate core is air cooled to room temperature.
9. The method for producing ultra-high strength steel excellent in weldability, according to claim 8, wherein in step 2), the heating temperature of the cast slab is not less than 1230 ℃, and the heat preservation is started after the core of the cast slab reaches the furnace temperature, and the heat preservation time is >1.5 hours.
10. The method for producing ultra-high strength steel excellent in weldability according to claim 8, wherein in the step 3), the rolling reduction of the last pass is 25% or less.
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