CN104032237A - Composite microalloyed high-strength steel forging with tensile strength of 700MPa and production method thereof - Google Patents
Composite microalloyed high-strength steel forging with tensile strength of 700MPa and production method thereof Download PDFInfo
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Abstract
A composite microalloyed high-strength steel forging with 700 MPa-level tensile strength and a production method thereof. The invention relates to a low-welding crack sensitivity high-strength steel forging with 700 MPa-level tensile strength and a production method thereof. The forging piece comprises the following chemical components in percentage by weight: c: 0.07-0.12%; mn: 1.2-1.8%; si: 0.2-0.4%; s is less than or equal to 0.006 percent; p is less than or equal to 0.015 percent; ni: 1.3-1.8%; cr: 0.15 to 0.3 percent; mo: 0.2-0.4%; nb: 0.02-0.1%; v is less than or equal to 0.1 percent; ti: less than or equal to 0.02 percent; cu is less than or equal to 0.25 percent; b: less than or equal to 0.001 percent, and the balance of Fe and inevitable impurities; at the same time PcmLess than or equal to 0.26 percent. The thickness of the forged piece in the invention can reach 200mm, and the mechanical property meets the following requirements: the yield strength is more than or equal to 560MPa, the tensile strength is more than or equal to 700MPa, the elongation is more than or equal to 17 percent, and KV is2(-40℃)≥80J。
Description
Technical field
The invention belongs to high-strength low-alloy steel production field, be specifically related to a kind of tensile strength 700MPa level low-welding crack-sensitive high-strength steel forging and production method thereof.
Background technology
Along with China's metallurgical industry and " transmitting electricity from west to east " and " developing rapidly of the Important Project such as West-east Gas; hardening high-strength steel and forging are widely applied in the construction with steel penstock, Hydropower Unit volute, natural gas storage tank and metallurgical suite of equipment gas storage spherical tank in generating with its good over-all properties; demand increases year by year, also day by day urgent to the application requiring of more high-strength hardened and tempered steel and supporting forging thereof.
Chinese Patent Application No.: 200910063768.2 disclose " a kind of low welding crack sensitivity steel with tensile strength at 700 MPa level and production method thereof ", adopt following chemical composition (wt%): C:0.08～0.12%, Mn:1.2～2.0%, Si:0.15～0.4%, S≤0.006%, P≤0.015%, Ni:0.25～0.55%, Mo:0.15～0.28%, V:0.02～0.1% and Cu:0.18～0.3%, Cr:0.15～0.3%, Ti:0.008～0.02%, two or more in B:0.0007～0.0027%, all the other are Fe and inevitable impurity.But this patent is to be 60mm by the steel plate maximum ga(u)ge that traditional Clean Steel technique is rolled, modified treatment production goes out; The steel tensile strength R that adopts this patent to produce
m>=690MPa ,-20 DEG C of KV
2>=47J.
Chinese Patent Application No.: 20131053273.5 disclose " a kind of thin strap continuous casting 700MPa level high-strength air corrosion-resistant steel manufacture method ", it comprises the steps: 1) smelting molten steel chemical component weight per-cent is C:0.03-0.1%, Si≤0.4%, Mn:0.75-2.0%, P:0.07-0.22%, S≤0.01%, N≤0.012%, Cu:0.25-0.8%, Cr:0.3-0.8%, Ni:0.12-0.4%, in addition, also comprise microalloy element Nb, V, Ti, in Mo at least one, Nb:0.01-0.1%, V:0.01-0.1%, Ti:0.01-0.1%, Mo:0.1-0.5%, all the other are Fe and inevitable impurity, 2) thin strap continuous casting, direct pouring goes out the Cast Strip that thickness is 1-5mm, 3) Cast Strip is cooling, and rate of cooling is greater than 20 DEG C/s, 4) the online hot rolling in Cast Strip, hot-rolled temperature 1050-1250 DEG C, draft is 20-50%, deformation rate > 20s
-1, the online recrystallize of austenite occurs after hot rolling, and hot-rolled strip thickness is 0.5-3.0mm, 5) cooling, batch rate of cooling 10-80 DEG C/s, coiling temperature 520-670 DEG C.The steel band microstructure obtaining is mainly made up of the bainite being evenly distributed and acicular ferrite.
At present both at home and abroad with regard to high-strength weather resisting steel and manufacture method application thereof several similar above-mentioned patents, the wherein weather resisting steel of 700MPa intensity rank, mostly adopt Nb, V, Ti, Mo combined microalloying technology, improve the comprehensive mechanical property of weather resisting steel by refined crystalline strengthening and precipitation strength.The low-carbon low-alloy steel product strength that utilizes above-mentioned this method for continuous casting sheet band to produce is higher, but main problem to be the unit elongation of product not high and low-temperature flexibility is poor.Because common thin band continuous casting technique hot rolling draft is no more than 50%, by the poor effect of deformation refine austenite crystal grain, thereby the plasticity of such steel and low-temperature flexibility poor.
Summary of the invention
One of object of the present invention is to provide a kind of tensile strength 700MPa level low-welding crack-sensitive high-strength steel forging, this forging not only has the outstanding mechanical property such as high strength, high tenacity, high weldability and good plasticity, and this forging maximum ga(u)ge of still meeting the requirement of low-welding crack-sensitive reaches the 700MPa level low alloy steel forgings of 200mm.
For achieving the above object, in weight percentage, forging is made up of following chemical composition: C:0.07～0.12%; Mn:1.2～1.8%; Si:0.2～0.4%; S≤0.006%; P≤0.015%; Ni:1.3～1.8%; Cr:0.15～0.3%; Mo:0.2～0.4%; Nb:0.02～0.1%; V≤0.1%; Ti :≤0.02%; Cu≤0.25%; B :≤0.001%, all the other are Fe and inevitable impurity; The welding crack sensibility indices P of forging simultaneously
cm≤ 0.26%.
As preferred version of the present invention, the chemical component weight per-cent of forging is C:0.089%, Mn:1.335%, Si:0.25%, S:0.0038%, P:0.007%, Ni:1.31%, Cr:0.18%, Mo:0.2%, Nb:0.028%, V:0.0035%, Ti:0.013%, Cu:0.026%, B:0.0009%, and all the other are Fe and inevitable impurity.
As preferred version of the present invention, the chemical component weight per-cent of forging is C:0.11%, Mn:1.32%, Si:0.316%, S:0.0037%, P:0.006%, Ni:1.33%, Cr:0.28%, Mo:0.28%, Nb:0.031%, V:0.034%, Ti:0.016%, Cu:0.023%, B:0.0009%, and all the other are Fe and inevitable impurity.
As preferred version of the present invention, the chemical component weight per-cent of forging is C:0.086%, Mn:1.31%, Si:0.31%, S:0.0042%, P:0.007%, Ni:1.44%, Cr:0.15%, Mo:0.28%, Nb:0.035%, V:0.038%, Ti:0.011%, Cu:0.024%, B:0.0008%, and all the other are Fe and inevitable impurity.
As preferred version of the present invention, the chemical component weight per-cent of forging is C:0.08%, Mn:1.299%, Si:0.30%, S:0.0039%, P:0.007%, Ni:1.655%, Cr:0.285%, Mo:0.25%, Nb:0.036%, V:0.01%, Ti:0.012%, Cu:0.023%, B:0.0008%, and all the other are Fe and inevitable impurity.
Two of object of the present invention is to provide the production method of above-mentioned tensile strength 700MPa level low-welding crack-sensitive high-strength steel forging, comprises that desulfurizing iron is skimmed, converter smelting, the refining of LF stove, RH vacuum-treat, slab casting, heating of plate blank, rolling, cooling and tempering process;
In slab casting cycle, set Heating temperature: 1200～1230 DEG C, time inside furnace: 220～400 minutes, to ensure the abundant austenitizing of slab;
In the operation of rolling, adopt the controlled rolling of two stages, the finish rolling I stage carries out in austenite perfect recrystallization humidity province, and 980 DEG C≤finishing temperature≤1100 DEG C, intermediate blank is treated temperature; The finish rolling II stage carries out in non-recrystallization zone, start rolling temperature≤900 DEG C, and finishing temperature is 840 ± 10 DEG C, non-recrystallization zone cumulative deformation >=60%;
After slab controlled rolling, enter laminar cooling system, rate of cooling is 20～40 DEG C/s, and final cooling temperature is at 450～500 DEG C;
Slab after rolling adopts quenching-and-tempering process, and quenching temperature is 910～930 DEG C, and soaking time is thickness of slab × 1.5 minute; Tempering temperature is 630～670 DEG C, soaking time: thickness of slab × 2.5～thickness of slab × 3 minute; Described thickness of slab unit is mm.
After slab rolls, being organized as granular bainite is acicular ferrite and super-refinement ferrite bainite.
After slab tempering, be organized as evenly tiny tempered sorbite, on lath-shaped ferrite matrix, be distributed with and separate out carbonitride.
The beneficial effect of technical scheme of the present invention is as follows:
It is the core technology means of the present invention in production high-performance welding high-strength steel that microalloying combines with controlled rolling and controlled cooling.Adopt cooling controlling and rolling controlling process, can in the situation that the very low and alloying element content of carbon content is lower, effectively improve the obdurability of steel and improve weldability and the various processing characteristics of steel, combine with the microalloy element such as Nb, V, Ti, effect is better.The essence of controlled rolling is to obtain tiny austenite crystal, to obtain tiny ferrite crystal grain and tiny other phase-change product (nodular troostite or tiny bainite etc.) after γ-α phase transformation, effectively improves the obdurability of steel.Control cold essence and be and prevent after controlled rolling tiny austenite crystal and ferrite crystal grain recrystallize or grow up again, to obtain small grains and respective organization after phase transformation.Containing in the steel of microalloy element, controlled rolling and controlled cooling also helps and obtains microalloy carbonitride tiny and that be evenly distributed, improves dislocation desity, thereby improves strengthening effect.
The main line of combined microalloying Steel Alloy design is that the strong carbonitride forming element Nb that adds appropriate proportioning in low alloy steel, V, Ti, Mo etc. carry out microalloying, and combines with Controlled Rolling And Controlled Cooling means and produce tensile strength 700MPa high-performance welding high-strength steel forging.The principle that this technology utilizes deformation and phase transformation to combine, thermal distortion thinning microstructure is remained to subsequently in cooling phase-change process, for phase transformation thinning microstructure creates conditions, finally obtain the micro-alloyed steel crystal grain of refinement, thereby meet high strength, high tenacity and the low-welding crack-sensitive requirement of steel.
Forged steel tool of the present invention has the following advantages:
1), adopt composite micro-alloying low-carbon bainitic steel Composition Design
The present invention follows low-carbon (LC), low P on Composition Design
cmthe Mn-Ni-Mo-V of value is low-carbon bainite composition of steel, meets weldability requirement.Require the not pre-thermo-welding of high strength forgings, do not produce welding cold cracking.Reduce carbon content, can obtain good welding property; Control carbon content 0.07～0.12%, add the elements such as Cr, Mn, Mo to reduce bainite formation temperature; Add Ni element to improve steel low-temperature flexibility and improve center performance; Adopt Nb, V, Ti microalloying to carry out complex intensifying, making to reduce carbon content becomes possibility, utilizes the composite precipitation of the microalloy elements such as Nb, V, Ti to separate out to ensure forged steel to obtain enough intensity simultaneously and improves the low-temperature impact toughness of forged steel; Without B or micro-B design, avoid forming in steel large size BN complex inclusion.The composition of low S, P, has ensured the pure of steel, thereby has guaranteed that invention steel has good comprehensive mechanical property.
2), adopt two stage controlled rolling and controlled cooling rolling technologys
The present invention adopts the technique of two the stage controlled rolling and controlled coolings in austenite perfect recrystallization district+austenite non-recrystallization district to obtain tensile strength 700MPa high-performance welding high-strength steel forging.Two stage controlled rolling process production efficiencys are high, workable.At austenite perfect recrystallization district+austenite non-recrystallization, district is rolled respectively, by the control to finishing temperature, the microalloy elements such as most Nb, V, Ti can keep admittedly melting state, until when ferrite transformation, in the middle of ferrite, separate out, play precipitation strength effect; By the control to non-recrystallization district total deformation, Nb, V, the Ti of part separate out at austenite region strain inducing, play the effect of crystal grain thinning.Finally making forged steel obtain tiny ferrite bainite through the cooling controlling and rolling controlling process measure of two stages is main tissue, after tempering, obtain follow homogeneous microstructure, the crystal grain of Carbonitride Precipitation of microalloy element tiny, toughness is high and tempered sorbite or the tempering bainite tissue of moderate strength, thereby ensure that forged steel has good comprehensive mechanical property.
3), adopt rational quenching-and-tempering process
Forged steel of the present invention makes to occur a kind of granular structure in its metallographic structure through cooling controlling and rolling controlling process measure, is the ground M/A phase structure that distributes block on α-Fe matrix, is referred to as granular bainite.Because this ferrite adds bainite structure toughness deficiency, need to carry out tempering, bainite is decomposed, improve toughness.Tempering essence is by poor toughness and the high martensite of intensity or bainite decompose, obtaining homogeneous microstructure, crystal grain is tiny, toughness is high and tempered sorbite or the tempering bainite of moderate strength.Tempered sorbite adds than the ferrite of normalizing state that pearlitic structure is even, crystal grain is tiny, and the tiny and reason such as be evenly distributed of the carbide particle of separating out, so have the obdurability higher than normalized steel.Tempering main purpose is to eliminate the structural stress of steel, makes to organize more even, and performance is more stable, makes the carbonitride of microalloy element further separate out simultaneously, to increase precipitation strength effect, thereby improves the obdurability of steel.
The present invention adopt novel chemical composition design and the two stage controlled rolling and controlled coolings that match and reasonably Quenching plus tempering process be to ensure that forging has the prerequisite that rational microtexture and every mechanical property meet the demands.Reasonably thermal treatment process can ensure that forged steel has uniform microtexture, thereby ensures that forging has the good index such as normal tensile property, low-temperature flexibility.Forged steel of the present invention has determined that through serial quenching-and-tempering process performance test its best quenching-and-tempering process is as follows:
Optimal quenching temperature is 910～930 DEG C, soaking time: (thickness of slab × 1.5) minute; Optimum tempering temperature is 630～670 DEG C, soaking time: (thickness of slab × 2.5～3) minute.
Forged steel of the present invention, after two stage controlled rolling and controlled coolings and rational modified thermal treatment, has extremely excellent comprehensive mechanical property, cold and hot working performance and welding property.Steel of the present invention can adopt the method welding such as covered arc welding, union-melt weld, shielded welding, tig welding, can be used for manufacturing 10000m
3the members such as above large natural gas spherical gasholder and pressure steel pipe of hydropower station, Hydropower Unit volute, particularly:
(1), this forging possesses low-welding crack-sensitive, welding property excellence, can simplify weldprocedure, reduces costs, and adapts to large production requirement.
(2), this forging yield strength>=560MPa, tensile strength>=700MPa, unit elongation>=17%, KV
2(40 DEG C)>=80J, intensity is greater than the steel grade in existing low temperature bearing device low alloy steel forging NB/T47009-2010.
(3), forging production technique is controlled, production cost is low, can high efficiency production.
Brief description of the drawings
Fig. 1 is example 3 metallographic microstructure photos of the present invention.
Fig. 2 is example 6 metallographic microstructure photos of the present invention.
Fig. 3 a and Fig. 3 b are pattern, size and distribution photo and the energy spectrogram of observing Second Phase Precipitation thing on example 3 transmission electron microscopes of the present invention.
Fig. 4 a and Fig. 4 b are pattern, size and distribution photo and the energy spectrogram of observing Second Phase Precipitation thing on example 6 transmission electron microscopes of the present invention.
Fig. 3 a, 3b and Fig. 4 a, 4b all show that the microstructure of steel of the present invention meets expection, are tempered sorbite (on acicular ferrite matrix, be distributed with and separate out carbonitride).Ferrite grain size is on average about 8.75 μ m (corresponding grain size number is 10.5 grades), is uniform-distribution with spherical [Nb, Ti] (C, N) precipitated phase particle of 6～25nm on ferrite matrix.
Embodiment
The present invention in order to achieve the above object, has designed a kind of brand-new tensile strength 700MPa level vanadium niobium titanium-combined microalloying high-strength steel forging, and forging is made up of following chemical composition: C:0.07～0.12%; Mn:1.2～1.8%; Si:0.2～0.4%; S≤0.006%; P≤0.015%; Ni:1.3～1.8%; Cr:0.15～0.3%; Mo:0.2～0.4%; Nb:0.02～0.1%; V≤0.1%; Ti :≤0.02%; Cu≤0.25%; B :≤0.001%, all the other are Fe and inevitable impurity; The welding crack sensibility indices P of forging simultaneously
cm≤ 0.26%.
Welding crack sensibility indices P
cmdetermine according to the following formula:
P
cm＝C+Si/30+Ni/60+(Mn+Cr+Cu)/20+Mo/15+V/10+5B(％)。
The alloying element that the present invention adds is based on following principle:
C：0.07～0.12％。C improves the most effective element of steel strength, and along with the increase of carbon content, in steel, Fe3C amount increases, and the tensile strength of steel and yield strength improve.But, carbon content increases, plasticity index unit elongation and the impact toughness decreased of steel, particularly low-temperature flexibility significantly declines, ductile-brittle transition temperature significantly improves, when welding, heat affected zone can produce the phenomenon of hardening, and welding cold crack sensitivity increases, and can not meet the service requirements of Natural Gas Spherical, pressure steel pipe of hydropower station and Hydropower Unit volute.In addition C still affects the principal element of Pcm, control Pcm Zhi≤0.26% of steel, makes it have low welding crack sensibility, and in steel, C content is controlled at 0.07～0.12%.
Si：0.2～0.4％。Si enters ferrite and plays solution strengthening effect, reduce yield tensile ratio, but Si can improve the ductile-brittle transition temperature of steel significantly, also can worsen plasticity and welding property simultaneously, and therefore, the content of Si is controlled at 0.2～0.4% and is advisable.
Mn：1.20～1.80％。Mn is mainly the hardening capacity that improves steel, ensures that slab has enough through hardening abilities.Meanwhile, Mn has significant solution strengthening effect, can refine austenite crystal grain in soft steel, thus refinement ferrite.When Mn content is less than 2%, do not reduce the toughness of steel.Mn deferrable F-B phase transformation, reduces Bs point, promotes to form compact grained ferrite.
Ni：1.30～1.80％。Improve the toughness of steel.Ni expands austenitic area element, can reduce A1 and A3 point, suppresses thick proeutectoid ferrite, significantly improves the toughness of steel, particularly low-temperature flexibility, reduces the ductile-brittle transition temperature of steel;
Mo：0.2～0.4％。Mo can postpone pearlitic transformation effectively, does not affect bainitic transformation, promotes to form bainite.Mn, Mo, B combine use, are more conducive to obtain acicular ferrite, instead of polygonal ferrite.But add Mo also can improve the hardenability of steel, thereby improve steel welding cold crack sensitivity, so the content of controlling Mo is 0.2～0.4%.
Nb：0.02～0.1％。Superheated susceptivity and the temper brittleness of Nb energy crystal grain thinning and reduction steel, improve intensity, but plasticity and toughness decline to some extent.When add niobium in ordinary low-alloy steel, can improve anti-hydrogen under weather-resistant and high temperature, nitrogen, ammonia corrosion ability.Niobium can improve welding property.In austenitic stainless steel, add niobium, can prevent intergranular corrosion phenomenon.The most outstanding effect of Nb is the recrystallize suppressing in high temperature deformation process, forge or rolling in after every a time, the carbonitride of V, Nb, Ti is separated out because of strain inducing, Nb, Ti, the V carbonitride of separating out are deposited in crystal boundary and dislocation, pinning austenite grain boundary effectively, can recrystallize and the motion of dislocation thereby stop, suppress the carrying out of Austenite Recrystallization Process, wherein Nb, Ti are stoping the effect of austenite recrystallization more remarkable.In high temperature austenite district, Nb is taking the effect of dragging of admittedly molten atom as main; In the austenitic area of lesser temps, taking strain inducing separate out and not molten Nb (CN) particle to the pinning effect of crystal boundary as main.When the Nb separating out (CN) size of particles, to be greater than 200O nm inoperative to austenite recrystallization, therefore, in the time that the addition of Nb exceedes 0.05%, is no longer subject to C content influence, and strengthening effect is reached capacity and do not have adjection.Therefore the content 0.03～0.05% of controlling interpolation Nb just can play crystal grain thinning and precipitation strength effect, is the most cost-effective means.
V：0.01～0.1％。V is strong carbonitride forming element.Because the carbonitride solubleness of V is larger, V, Ti easily form nano level M (CN) type carbonitride, in the time of hot rolling, V (CN) separates out at austenite grain boundary strain inducing, stop Austenite Grain Growth, tissue after refinement phase transformation, and the V separating out on austenite grain boundary (CN) particle also can be for ferrite provides the more nucleation site of horn of plenty, obtains more tiny ferrite crystal grain during to ferritic transformation at austenite; V (CN) separates out in austenite inside, can induce two kinds of ferritic forming cores of intracrystalline, wait axle ferrite and acicular ferrite, thereby these refinement ferrites can significantly improve normal temperature and the hot strength of steel.But when V and Cr, Mo exist simultaneously, can in drawing process, form complicated carbonitride and reduce plasticity and the toughness of welding joint.The welding joint of the ben Cr of being, Mo, V steel thick-walled vessel is higher to the susceptibility of crackle in the time that postwelding eliminates stress thermal treatment (SR processing), therefore no matter be to ensure to crack in plasticity and toughness or the process of avoiding eliminating stress, all must strictly control the content (being limited in 0.01～0.1%) of V.
Cu：0.10～0.25％。Cu mainly plays precipitation strength effect in steel, is conducive in addition obtain good low-temperature flexibility, improves the antifatigue extended capability of steel.But in the time of Cu too high levels, when Steel Rolling, very easily produce check crack.Therefore Cu content is controlled at 0.10～0.25%.
Cr：0.15～0.30％。Cr dwindles austenite γ phase block elements, forms γ and encloses mutually, in steel, infinitely dissolves each other in α iron.Increase the hardening capacity of steel and have secondary hardening effect, improving carbon steel wear resistance.Under its content, be limited to 0.15%.The in the situation that of the compound interpolation of Cr-Cu-Ni, add Cr can improve steel welding cold crack sensitivity.The content of Cr is controlled at 0.15～0.30% in the present invention.
Ti:0.01～0.02%, Ti is a kind of strong carbide and nitride forming element, it can improve room temperature strength and the hot strength of steel significantly, because Ti can play crystal grain thinning, therefore also can improve the toughness of steel.The effect of Ti is the N dissolving in fixing steel, otherwise N will be combined with B and be caused B inefficacy.Research shows, wants to be completely fixed N, and the concentration of Ti should be approximately 3.4 times of N concentration.But excessive Ti can cause toughness to decline.Another effect of Ti is to oxide morphology control action kou.Because Ti and S have stronger avidity, increase containing Ti amount and can form (MnTi) S or the Ti4C2S2 that are difficult for viscous deformation, can improve performance ununiformity, improve impelling strength.In addition, appropriate Ti can improve the toughness of weld metal, but excessive Ti can in steel, form be again mingled with make it reduce.In low-alloy high-strength steel, consider from the toughness that improves weld metal, add that to be no more than 0.02% Ti comparatively suitable, utilize Second Phase Particles TiN, the Ti (CN) etc. of Ti formation to stop the grain growth of coarse grain zone, welded heat affecting zone, ensure that welding joint has good low-temperature flexibility.
B：0.0005～0.001％。B is the element that strongly improves hardening capacity, B adds, can effectively suppress forming core and the generation of proeutectoid ferrite, due to the dgnamic segregation of B on austenite grain boundary, strongly inhibited γ-α phase transformation, impels austenite in the time quenching, to form the martensite of tiny low-carbon (LC), thereby improve yield strength and the tensile strength of steel, in addition, the interaction of B and N, can obviously improve the low-temperature flexibility of testing steel.Because Ti has been completely fixed the N in steel, therefore, all B that add adding before rolling, hankers having obtained dissolving.Along with the increase of B content, intensity is improved, and bainite mark in result tissue increases, and tensile strength index in the time that B content exceedes 0.002% tends towards stability.But while exceeding 0.001% along with B content, low-temperature flexibility sharply worsens.It is owing to having caused that along with the increase of B content the B segregation in γ grain boundary and γ crystal grain causes that the reason that produces this result is pushed off.In addition, in steel B too high levels can make to eliminate stress after processing (SR processing) " B phase " be netted and separate out, produce SR crackle.B easily forms carbide and nitride, and is easily collected at original austenite crystal prevention, impels dislocation desity in the neighbourhood to increase, and can be used as the trap of hydrogen in partial area, thereby impels grain boundary separation occurs herein.So B content is chosen in 0.0005～0.001%.
Research shows, while adding B separately, conventionally understands austenite grain boundary Precipitation Fe after rolling
23(CB)
6thereby, significantly reduce the strengthening effect of B, cause the transformation of γ → α not to be effectively suppressed, therefore in steel, add Nb to stop Fe
23(CB)
6formation because Nb is more easily combined with C, along with the increase of the Nb content dissolving, the tendency that forms bainite has also increased greatly.The appropriate dissolving of Nb can stable austenite and is shown with B compound interpolation and promote the effect of bainite transformation.
The combined action mechanism of Nb and B can be described like this: first, Nb can hinder the recrystallize of distortion γ effectively, so make γ crystal boundary stable by stoping because recrystallize forms new crystal boundary, this just makes B have time enough to be diffused near γ crystal boundary, thereby has increased the hardening capacity of γ.Secondly, Nb can reduce C diffusivity and activity in γ, and therefore, the Nb dissolving in γ can protect B, and is unlikely to form the C compound of B, as Fe
23(CB)
6.The 3rd is in γ, to dissolve Nb itself to have considerable influence for suppressing γ → α transformation.Obviously also need more research to illustrate its accurate mechanism, because the solubility limit of Nb in γ is 0.03%, therefore in typical low-carbon bainite steel Nb content conventionally not higher than 0.04%.
P
cm≤ 0.26%, P
sR< 0%; Wherein, P
sRfor reheat cracking susceptibility index, P
sR=Cr+Cu+2Mo+10V+7Nb+5Ti-2 (%).Control the total body burden of alloying element, to ensure that steel plate has good welding property and eliminates reheat cracking susceptibility.
P≤0.015％，S≤0.006％。The impurity elements such as P, S, As, Sb, Sn are the toughness that affects steel, the particularly major cause of low-temperature flexibility and weldability.Not only strictly control P, S content, also reduce as much as possible the impurity elements such as As, Sb, Sn.
The production method of described tensile strength 700MPa level low-welding crack-sensitive low alloy steel forging, adopts that desulfurizing iron is skimmed, converter smelting, the refining of LF stove, RH vacuum-treat, slab casting, heating of plate blank, rolling, cooling and tempering process; Wherein:
In slab casting cycle, set Heating temperature: 1200～1230 DEG C, time inside furnace: 220～400 minutes, to ensure the abundant austenitizing of slab;
In the operation of rolling, adopt the controlled rolling of two stages, the finish rolling I stage carries out in austenite perfect recrystallization humidity province, finishing temperature >=920 DEG C, intermediate blank is treated temperature, object is by the recrystallization zone abundant refine austenite tissue of recrystallize repeatedly.The finish rolling II stage carries out in non-recrystallization zone, start rolling temperature≤900 DEG C, 840 ± 10 DEG C of finishing temperatures, non-recrystallization zone cumulative deformation >=60%; Object is by the distortion in non-recrystallization zone, and the number of nuclei while making phase transformation increases, the brilliant rate of refinement;
After slab controlled rolling, enter laminar cooling system, rate of cooling is 20～40 DEG C/s, and final cooling temperature is at 450～500 DEG C;
Slab after rolling adopts quenching-and-tempering process, and optimal quenching temperature is 910～930 DEG C, soaking time: (thickness of slab × 1.5) minute; Optimum tempering temperature is 630～670 DEG C, soaking time: (thickness of slab × 2.5～3) minute, the unit of described thickness of slab is millimeter.
For clearly demonstrating the technical characterstic of this programme, carry out 9 embodiments by steel chemical composition of the present invention and manufacturing technique requirent, and by reference to the accompanying drawings, the technical scheme in the present invention has been set forth.
The chemical composition of 9 embodiment steel is in table 1, and rolling and thermal treatment process are in table 2, and mechanical property is in table 3 and table 4.
The chemical composition of table 1 embodiment steel
Rolling and the quenching-and-tempering process of table 2 embodiment steel
The mechanical property of table 3 embodiment steel
The low temperature impact properties of table 4 embodiment steel
Can be learnt by above-described embodiment: the present invention by rationally controlling carbon content on Composition Design, adopt Nb, V, Ti etc. to carry out combined microalloying processing, and improve the purity of forged steel, adopt two stage controlled rolling and controlled coolings and the rational quenching-and-tempering process of coupling, thereby guarantee that forging of the present invention has high strength, high tenacity and low-welding crack-sensitive, also ensured that forging of the present invention has good over-all properties.
Claims (8)
1. a tensile strength 700MPa level combined microalloying high-strength steel forging, is characterized in that in weight percentage, and forging is made up of following chemical composition: C:0.07～0.12%; Mn:1.2～1.8%; Si:0.2～0.4%; S≤0.006%; P≤0.015%; Ni:1.3～1.8%; Cr:0.15～0.3%; Mo:0.2～0.4%; Nb:0.02～0.1%; V≤0.1%; Ti :≤0.02%; Cu≤0.25%; B :≤0.001%, all the other are Fe and inevitable impurity; The welding crack sensibility indices P of forging simultaneously
cm≤ 0.26%.
2. tensile strength 700MPa level vanadium niobium titanium-combined microalloying high-strength steel forging according to claim 1, the chemical component weight per-cent that it is characterized in that forging is C:0.089%, Mn:1.335%, Si:0.25%, S:0.0038%, P:0.007%, Ni:1.31%, Cr:0.18%, Mo:0.2%, Nb:0.028%, V:0.0035%, Ti:0.013%, Cu:0.026%, B:0.0009%, and all the other are Fe and inevitable impurity.
3. tensile strength 700MPa level vanadium niobium titanium-combined microalloying high-strength steel forging according to claim 1, the chemical component weight per-cent that it is characterized in that forging is C:0.11%, Mn:1.32%, Si:0.316%, S:0.0037%, P:0.006%, Ni:1.33%, Cr:0.28%, Mo:0.28%, Nb:0.031%, V:0.034%, Ti:0.016%, Cu:0.023%, B:0.0009%, and all the other are Fe and inevitable impurity.
4. tensile strength 700MPa level vanadium niobium titanium-combined microalloying high-strength steel forging according to claim 1, the chemical component weight per-cent that it is characterized in that forging is C:0.086%, Mn:1.31%, Si:0.31%, S:0.0042%, P:0.007%, Ni:1.44%, Cr:0.15%, Mo:0.28%, Nb:0.035%, V:0.038%, Ti:0.011%, Cu:0.024%, B:0.0008%, and all the other are Fe and inevitable impurity.
5. tensile strength 700MPa level vanadium niobium titanium-combined microalloying high-strength steel forging according to claim 1, the chemical component weight per-cent that it is characterized in that forging is C:0.08%, Mn:1.299%, Si:0.30%, S:0.0039%, P:0.007%, Ni:1.655%, Cr:0.285%, Mo:0.25%, Nb:0.036%, V:0.01%, Ti:0.012%, Cu:0.023%, B:0.0008%, and all the other are Fe and inevitable impurity.
6. according to the production method of the tensile strength 700MPa level vanadium niobium titanium-combined microalloying high-strength steel forging described in claim 1～5 any one, it is characterized in that: comprise that desulfurizing iron is skimmed, converter smelting, the refining of LF stove, RH vacuum-treat, slab casting, heating of plate blank, rolling, cooling and tempering process;
In slab casting cycle, set Heating temperature: 1200～1230 DEG C, time inside furnace: 220～400 minutes, to ensure the abundant austenitizing of slab;
In the operation of rolling, adopt the controlled rolling of two stages, the finish rolling I stage carries out in austenite perfect recrystallization humidity province, and 980 DEG C≤finishing temperature≤1100 DEG C, intermediate blank is treated temperature; The finish rolling II stage carries out in non-recrystallization zone, start rolling temperature≤900 DEG C, and finishing temperature is 840 ± 10 DEG C, non-recrystallization zone cumulative deformation >=60%;
After slab controlled rolling, enter laminar cooling system, rate of cooling is 20～40 DEG C/s, and final cooling temperature is at 450～500 DEG C;
Slab after rolling adopts quenching-and-tempering process, and quenching temperature is 910～930 DEG C, and soaking time is thickness of slab × 1.5 minute; Tempering temperature is 630～670 DEG C, soaking time: thickness of slab × 2.5～thickness of slab × 3 minute; Described thickness of slab unit is mm.
7. the production method of tensile strength 700MPa level vanadium niobium titanium-combined microalloying high-strength steel forging according to claim 6, is characterized in that: after slab rolls, being organized as granular bainite is acicular ferrite and super-refinement ferrite bainite.
8. the production method of tensile strength 700MPa level vanadium niobium titanium-combined microalloying high-strength steel forging according to claim 6, it is characterized in that: after slab tempering, be organized as evenly tiny tempered sorbite, on lath-shaped ferrite matrix, be distributed with and separate out carbonitride.
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