CN104487601B - The high-tensile steel of excellent in low temperature toughness and manufacture method thereof - Google Patents

The high-tensile steel of excellent in low temperature toughness and manufacture method thereof Download PDF

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CN104487601B
CN104487601B CN201380037119.XA CN201380037119A CN104487601B CN 104487601 B CN104487601 B CN 104487601B CN 201380037119 A CN201380037119 A CN 201380037119A CN 104487601 B CN104487601 B CN 104487601B
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ferrite
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CN104487601A (en
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尾上爱
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Kobe Steel Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals

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  • 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

The present invention provides a kind of high-tensile steel, it consists of the chemical composition meeting regulation, the CEQ (quality %) specified by following (1) formula is more than 0.345 and less than 0.428, and the σ specified by following (2) formula is more than 2080, and the microscopic structure of t/4 (t: thickness of slab) position is the line and staff control of ferrite and pearlite, the average equivalent circular diameter of described ferrite crystal grain is below 7.0 μm, thus can realize high intensity and low-temperature flexibility is the most excellent.CEQ=[C]+[Mn]/6+ ([Cr]+[Mo]+[V])/5+ ([Cu]+[Ni])/15... (1)；σ=2.90 × { 602781.57 (1154 × CEQ 3.25)2}1/2/0.963+400×[Ni]...(2)。

Description

The high-tensile steel of excellent in low temperature toughness and manufacture method thereof
Technical field
The present invention relates to high-tensile steel and the manufacture method thereof of excellent in low temperature toughness.Particularly relate to for improving in exposure The purposes used in the environment of being exposed to low temperature, this high tension steel that such as pressure vessel, boats and ships, marine structure etc. are suitable for The technology of the low-temperature flexibility of plate.
Background technology
Build the steel plate (high-tensile steel) that pressure vessel, boats and ships and marine structure etc. are used, both required high-strength Degree, requires that again the toughness (low-temperature flexibility) under low temperature and weldability are the most excellent.The most in recent years, go out from a security point Send out, it is desirable to the more high tenacity under extremely low temperature.
In order to make the toughness of steel plate improve, the method doing one's utmost to control the addition of alloying element is advisable, but so, by force Degree guarantee become difficulty.Otherwise, if add alloying element in order to ensure intensity, then toughness reduces on the contrary.So, intensity with Toughness is contrary characteristic, makes both characteristics exist side by side extremely difficult.
As for making one of effective way that strength and toughness both characteristics of steel plate improve, can enumerate containing conduct The method of the Ni of alloying element.The most a large amount of steel plates proposing to contain Ni, but practical situation such as 3.5%Ni steel, 9%Ni As steel is representative, if containing Ni the most in a large number, then can not play this effect to greatest extent.In contrast, about containing 1 ～the steel plate of a small amount of Ni of about 2%, such as being proposed by patent documentation 1, the most still can not meet low even if meeting high intensity Toughness under Wen, it is difficult to simultaneously meet intensity and low-temperature flexibility.
Prior art literature
Patent documentation
Patent documentation 1: No. 3741078 publications of Japanese Patent No.
Summary of the invention
Invent problem to be solved
The present invention completes in view of such situation, its object is to, it is provided that though a kind of Ni content 2.0% with Under, the high-tensile steel that still high intensity and low-temperature flexibility are also excellent, and useful for manufacturing such high-tensile steel Method.
For solving the means of problem
The high-tensile steel of the present invention that can reach above-mentioned purpose is characterised by, contains C:0.03～0.09% respectively (represent " quality % ", relate to below chemical composition all with), Si:0.05～0.35%, Mn:0.9～1.6%, P:0.01% with Under (without 0%), below S:0.01% (without 0%), Al:0.01～0.06%, Ni:0.2～2.0%, Nb:0.007～ 0.017%, Ti:0.007～0.017%, Ca:0.0005～0.003% and N:0.0025～0.0050%, surplus is by ferrum and not Evitable impurity constitute, following (1) formula the CEQ (quality %) specified is more than 0.345 and less than 0.428, and by under The σ that (2) formula of stating specifies is more than 2080, and the microscopic structure of t/4 (t: thickness of slab) position is the mixing of ferrite and pearlite Tissue, the average equivalent circular diameter of described ferrite crystal grain is below 7.0 μm.Further, described what is called " average equivalent circular diameter ", It it is the meansigma methods of the diameter (equivalent circle diameter) of the bowlder that ferrite crystal grain is converted into same homalographic.
CEQ=[C]+[Mn]/6+ ([Cr]+[Mo]+[V])/5+ ([Cu]+[Ni])/15 ... (1)
σ=2.90 × { 602781.57-(1154 × CEQ-3.25)2}1/2/0.963+400×[Ni] …(2)
Wherein, [C], [Mn], [Cr], [Mo], [V], [Cu] and [Ni] represents containing of C, Mn, Cr, Mo, V, Cu and Ni respectively Amount (quality %).
In above-mentioned (1) formula, in addition to the basis (C, Mn, Ni) of steel plate of the present invention, it is also possible to also comprise according to need Want contained element (Cr, Mo, V, Cu etc.), during without these elements, delete this project to calculate the value of CEQ, containing these During element, calculate the value of CEQ according to above-mentioned (1) formula.
In the high-tensile steel of the present invention, as required, belong in following (a)～(c) any one is contained further More than kind also effectively, according to contained composition, the characteristic of high-tensile steel is improved.
(a) below B:0.002% (without 0%)
(b) below Cu:0.35% (without 0%)
C () (does not contains selected from below Cr:0.3% (without 0%), below Mo:0.2% (without 0%) and below V:0.06% 0%) more than one in the group constituted
When manufacturing the high-tensile steel of the present invention, for having the steel plate of above-mentioned such chemical composition composition, at t/4 When (t: thickness of slab) position is the temperature field of 950～875 DEG C, making reduction ratio is more than 30%, is 820 in t/4 (t: thickness of slab) position Below DEG C and Ar3During more than transformation temperature temperature field, making reduction ratio is more than 30% to depress, in t/4 (t: thickness of slab) position It is set to when the temperature field less than 875 DEG C and higher than 820 DEG C and two-phase temperature field not depress, after pressure, makes average cooling rate It is less than 2.0 DEG C/sec to cool down, the line and staff control making microscopic structure be ferrite and pearlite.
Invention effect
According to the present invention, in the composition system that Ni content is less than 2.0%, can play Ni's to greatest extent by becoming The chemical composition composition of additive effect, and sets suitable pressure condition, it is possible to realize the micro-of ferrite crystal grain in steel plate Refinement, it is possible to realize high intensity and the high-tensile steel of low-temperature flexibility also excellence.Such high-tensile steel, as building pressure The steel plate that container, boats and ships and marine structure etc. are used is exceedingly useful.
Accompanying drawing explanation
Fig. 1 is the plot representing CEQ value with the relation of tensile strength TS.
Fig. 2 is the plot representing σ value with the relation of fracture transition temperature vTrs.
Detailed description of the invention
If add alloying element in order to ensure the intensity of high-tensile steel, then toughness reduces.This is because alloying element Interpolation make under low temperature ductile fracture difficulty.On the contrary, the ductile fracture under the interpolation of Ni makes low temperature is susceptible to.
Under such situation, the present inventor in order to realize the high-tensile steel of high intensity and excellent in low temperature toughness and from Various angles are studied.If it is it was found that make promotion ductile fracture that reduction alloying element brings and the rush that Ni brings Enter the effect quantitatively of ductile fracture, and in the way of meeting the relation of above-mentioned (1) formula and (2) formula, control chemical composition composition, High intensity then can be made to exist side by side with low-temperature flexibility, thus complete the present invention.
The fact deriving above-mentioned (2) formula is as follows.In order to improve steel plate toughness at low temperatures, need to suppress brittle fracture, Particularly cleavage fracture.Therefore the mechanism of cleavage fracture it is conceived to.First in the ferrite crystal grain of a part, produce plasticity become Shape, the dislocation of ferrite intracrystalline moves.The dislocation of movement stops because of crystal boundary, gathers.If at this moment crystal boundary exists representated by cementite The second phase, then the accumulation of dislocation causes stress is concentrated and is caused the second phase cracking, microcosmic be full of cracks occurs.The microcosmic be full of cracks occurred It is in progress between adjacent ferrite crystal grain, makes cleavage fracture occur.
The be full of cracks being known to occur is propagated to adjacent ferrite crystal grain, for making the stress required for cleavage fracture generation (cleavage fracture stress) σ0[such as, " the grinding of Micromechanics about the fracture toughness of mild steel can be calculated by following (3) formula Study carefully " Tian Chuanzhe issues page 17 (Nagoya University Ph.D. Dissertation) also in May, 1994].This stress σ0The biggest, cleavage fracture More being difficult to occur, toughness is more improved.
(C/d)σ0 2+τe2{1+4/π(C/d)1/2×(τi/τe)}2
=4E γf/{(1-v2)d} …(3)
Wherein, it is expressed as follows respectively, the minor axis of the C: the second phase, d: ferritic particle diameter, σ0: cleavage fracture stress, τ e: have Effect shear stress, the frictional force of τ i: dislocation, E: Young's modulus, γf: surface energy, v: Poisson's ratio.
In above-mentioned (3) formula, Section 1 [(C/d) σ0 2], it is straight about the crystal grain in the tissue be given as initial condition The item of the size ratio of the minor axis of footpath and carbide, Section 2 [τ e2{1+4/π(C/d)1/2×(τi/τe)}2], it is about accumulating in The item of the dislocation of crystal boundary.Additionally the right [4E γf/{(1-v2) d}], it is about the formula as Florence Griffith (Griffith) The item of the unstable propagation conditions of the be full of cracks known.
In this Young's modulus E, surface can γfIt is constant with Poisson's ratio v.Due to τ i, " τ e, so being expressed as τ i/ τ e=0. Additionally effectively shear stress τ e can be showed by yield stress τ,(yield stress).
If according to above result, above-mentioned (3) formula can be rewritten as following (4) formula so.Additionally Young's modulus E= 206000 (MPa), surface can γf=14 (Jm-2), and Poisson's ratio v=0.3.
σ0=(d/C)1/2×(4Eγf/{π(1-v2)d}-τ2)1/2…(4)
Wherein, τ: yield stress
Based on above-mentioned (4) formula, the present inventor studies the parameter type of domination low-temperature flexibility the most further.Its result is sentenced Bright, when using fixing manufacturing condition, obtained tissue, the most ferritic particle diameter, the minor axis of the second phase can be considered as greatly Fix on body, by the value (value of σ) of described (2) formula of the CEQ (carbon equivalent) specified by described (1) formula and Ni content defined If more than 2080, then it is able to ensure that good low-temperature flexibility.
The value (σ value) of the σ represented by above-mentioned (2) formula is the value determined by the content of each element.By specifying the value of this σ, The chemical composition composition that can simultaneously meet intensity and low-temperature flexibility can be made to make clear.Specifically, if the value of σ is less than 2080, Then the balance of Ni and the addition element beyond it is deteriorated, it is impossible to play the effect of Ni to greatest extent, though the high intensity of meeting, Low-temperature flexibility also deteriorates.The value of σ is preferably more than 2150, and more preferably more than 2200.It addition, the preferred upper limit of the value of σ is Less than 2600.
But, even if the value of σ meets more than 2080, if value (quality %) ratio 0.345 of the CEQ of described (1) formula defined Little, then intensity improves the content deficiency of element, and intensity will also decrease.Even if additionally the value of σ is more than 2080, Ni content is less than When 0.2%, the additive effect of Ni is not enough, still cannot ensure the good low-temperature flexibility of steel plate.And, if the content of Ni is superfluous, Then the balance of the effect that intensity and toughness are brought is broken by Ni, the suppression of the ductile fracture under ascending effect surpasses low temperature in intensity Effect, low-temperature flexibility deteriorates.Thus, Ni content needs with 2.0% as the upper limit.Further, the preferred lower limit of Ni content is 0.5% Above (more preferably more than 0.7%), the preferred upper limit is less than 1.8% (more preferably less than 1.5%).
The opposing party and, if the value (quality %) of the CEQ specified by described (1) formula is bigger than 0.428, then strength and toughness is flat Weighing apparatus is broken, and low-temperature flexibility will reduce.Therefore, in order to ensure necessary toughness, the value (quality %) of CEQ is less than 0.428.Also Having, the preferred lower limit of the value (CEQ value) of CEQ is more than 0.350 (more preferably more than 0.355), and the preferred upper limit is 0.425 Below (more preferably less than 0.420).
In the present invention, it is intended that the line and staff control that the microscopic structure of t/4 position is ferrite and pearlite, add up to 100 area %.But, the present invention is not being resulted in the range of impact as the effect of purpose, however not excluded that have ferrite group Knit with pearlitic structrure beyond other tissue (such as bainite, martensite) pettiness amount be mixed into.According to circumstances, can allow Containing of other tissue ends in 10 area about %.It addition, it is the most special with the blending ratio of pearlite about ferrite Limit, for ferrite 70～90 area %: pearlite 10～30 area about %.
In order to ensure the good low-temperature flexibility of steel plate, (it is expressed as " ferrum using the line and staff control as ferrite Yu pearlite Ferritic-pearlite ") microscopic structure in ferrite crystal grain (not including the ferrite crystal grain in pearlite) average equivalent circle Mode below a diameter of 7.0 μm is controlled also being important important document.By making the average equivalent circular diameter of ferrite crystal grain It it is below 7.0 μm, it can be ensured that the good low-temperature flexibility (fracture transition temperature vTrs is less than-80 DEG C) of high-tensile steel. The preferred upper limit of this ferrite particle diameter is below 6.7 μm (below more preferably 6.5 μm).Additionally ferrite particle diameter is preferred Lower limit is more than 0.5 μm (more than more preferably 1.0 μm).
In the high-tensile steel of the present invention, in order to meet the basic characteristic as this steel plate, it is also desirable to suitably adjust Composition (C, Si, Mn, P, S, Al, Nb, Ti, Ca and N) beyond above-mentioned Ni, it is as follows that its scope limits reason.
(C:0.03～0.09%)
C is important element in the intensity guarantee steel plate.In order to play such effect, need to make C contain 0.03% Above.But, if the content surplus of C, toughness reduces, and therefore making the upper limit is 0.09%.Further, C content be preferably 0.05% with On, less than 0.08%.
(Si:0.05～0.35%)
Si works as deoxidizer when steel-smelting, plays the effect making the intensity of steel increase.In order to play so Effect, need to make Si contain more than 0.05%.But, if the content of Si is superfluous, then toughness reduces, and therefore the upper limit is 0.35%.Further, Si content is preferably more than 0.07% (more preferably more than 0.1%) and less than 0.30%.
(Mn:0.9～1.6%)
Mn is useful as the intensity rising element of steel plate.In order to effectively play such effect, need to make Mn contain Have more than 0.9%.It is preferably more than 1.1%.But, if the content of Mn is superfluous, then toughness deteriorates on the contrary, therefore suppresses Less than 1.6%.It is preferably less than 1.5%.
(below P:0.01% (without 0%))
P is the element making toughness deteriorate, it is therefore desirable to do one's utmost to reduce.Need suppression in the present invention below 0.01%.
(below S:0.01% (without 0%))
S is the element making toughness deteriorate.It is thus desirable to do one's utmost to reduce, suppress in the present invention below 0.01%.
(Al:0.01～0.06%)
Al is the element worked as deoxidizer.In order to play such effect, Al content is more than 0.01%.But Being that if Al content is superfluous, then the cleanliness of steel plate is hindered, therefore making its upper limit is 0.06%.Further, Al content is preferably More than 0.02%, less than 0.05%.
(Nb:0.007～0.017%)
Nb is to have the element of the micronized effect of ferrite crystal grain by the recrystallization inhibition of austenite grain.For The such effect of performance, needs to make Nb contain more than 0.007%.But, if the content of Nb is superfluous, then toughness reduces, therefore Making its upper limit is 0.017%.Further, the preferred lower limit of Nb content is more than 0.010%, the preferred upper limit be 0.015% with Under.
(Ti:0.007～0.017%)
Ti is strong nitride forming element, just brings the micro-of the crystal grain that the fine precipitation from TiN brings under trace into play Thinning effect.In order to effectively play such effect, need to make Ti contain more than 0.007%.It is preferably more than 0.01%.But It is, if superfluously containing Ti, causing the reduction of toughness on the contrary, it is therefore desirable to below 0.017%, preferably less than 0.015%.
(Ca:0.0005～0.003%)
Ca be the control by field trash and for improving the effective element of toughness of steel plate.In order to play such effect Really, need to make Ca contain more than 0.0005%.But, if superfluously containing Ca, then toughness reduces, it is therefore desirable to 0.003% Below.Further, the preferred lower limit of Ca content is more than 0.001%, and the preferred upper limit is less than 0.002%.
(N:0.0025～0.0050%)
N is to form TiN by appropriate containing with Ti, is the effective element of toughness for improving steel plate.In order to effectively Ground plays such effect, needs to make N contain more than 0.0025%.But, if N content surplus, solid solution N increases, makes steel plate Toughness reduces, it is therefore desirable to making its upper limit is 0.0050%.Further, the preferred lower limit of N content is more than 0.003%, preferably The upper limit be less than 0.0045%.
In the present invention, regulation is the most above-mentioned containing element, and surplus is ferrum and inevitable impurity.Inevitable as this Impurity, it is possible to allow being mixed into of element introduced because of the situation of raw material, material, manufacture equipment etc..According further to needs, contain Having any one that belong in following (a)～(c) above the most effective, the composition contained by correspondence, the characteristic of high-tensile steel obtains To improving.As described below containing preferred range set reason during these elements.
(a) below B:0.002% (without 0%)
(b) below Cu:0.35% (without 0%)
C () (does not contains selected from below Cr:0.3% (without 0%), below Mo:0.2% (without 0%) and below V:0.06% 0%) more than one in the group constituted
(below B:0.002% (without 0%))
B has the effect making the solid solution N having undesirable effect toughness reduce by generating BN.But, if B content mistake Many, then make the precipitate of B increase, toughness deteriorates on the contrary, the most preferably suppresses below 0.002%.Further, B content is preferred Lower limit be more than 0.0001%, during less than 0.0001%, solid solution N reduction effect is insufficient.The preferred upper limit is 0.001% Below.
(below Cu:0.35% (without 0%))
Cu is to improve effective element for intensity.If the content of Cu is too much, then it is susceptible to crackle during hot-working, therefore Preferably making its upper limit is less than 0.35%.Further, the preferred lower limit of Cu content is more than 0.001%, during less than 0.001% this One effect is insufficient.The preferred upper limit is less than 0.30%.
((do not contain selected from below Cr:0.3% (without 0%), below Mo:0.2% (without 0%) and below V:0.06% 0%) more than one in the group constituted)
Cr, Mo and V all make Carbonitride Precipitation, contribute to the element that intensity rises.But, if be allowed to contain superfluously Having, then make toughness reduce, therefore preferably Cr suppresses below 0.3%, and Mo suppresses below 0.2%, V suppression 0.06% with Under.Further, containing more than 0.01% to effectively play their effect, preferably Cr, Mo contains more than 0.01%, and V contains More than 0.001%.
Make above-mentioned such tissue to manufacture the steel plate of the present invention, need to specify its manufacturing condition closely. That is, when manufacturing the high-tensile steel of the present invention, t/4 (t: thickness of slab) position makes the reduction ratio be when the temperature field of 950～875 DEG C More than 30%, t/4 (t: thickness of slab) position is below 820 DEG C and Ar3Make during more than transformation temperature temperature field reduction ratio be 30% with On, the steel plate so formed for having above-mentioned such chemical composition carries out depressing (substantially controlled rolling), and t/4 Do not depress when (t: thickness of slab) position is at the temperature field less than 875 DEG C and higher than 820 DEG C with at two-phase temperature field, make after pressure Average cooling rate is less than 2.0 DEG C/sec and cools down, and needs to make microscopic structure become Ferrite-Perlite structure.The party The range set reason of each condition of method is as follows.
The temperature of t/4 (t: thickness of slab) position, can carry out Difference Calculation by unsteady flo w once passes heat transfer equation And try to achieve, in addition to the slab thickness before and after board briquette, room temperature, water temperature, rolling, if understanding slab, roll and air Pyroconductivity, then also be able to calculate [such as, (a) " wicket is single, ' and about hot rolling material variations in temperature anticipation calculate The basic research of method ', plasticity and processing, 1970, volume 11, No. 118, p.816-824 ", (b) " family gram, ridge, in one Youth, rattan Tian Wenfu, god's tail width, ' the roughing model formation of hot strip mill ', and ferrum and steel, 1977, volume 63, A29-A32 ", C () " western ridge is clean, ' the high-accuracy high-efficiency rate rolling technique of the paired cross rolling mill of slab ', sending out of rolling technique rolling therory Exhibition and the trend faced the future, joint research meeting rolling therory portion of Tie Gang association of Japan can compile, 1994, p.69-78 " etc.].
In order to be manufactured the high-tensile steel of the present invention by above-mentioned such manufacturing condition, use and there is above-mentioned suchization Studying the steel plate being grouped into as blank steel plate, based on ferritic structure (such as, this blank steel plate substantially uses Ferritic phase is 50 more than area %) steel plate.In order to make the ferrite crystal grain miniaturization of such blank steel plate, it is stipulated that tie again Reduction ratio at a temperature of brilliant temperature, non-recrystallization.Further, temperature shown in following is using as the average behavior playing steel plate The temperature of t/4 (t: the thickness of slab) position of position is managed.
First, in order to make austenite crystal miniaturization, need sufficiently to depress (after heating in recrystallization temperature territory Pressure).Under recrystallization temperature territory, apply the pressure of reduction ratio more than 30%, thus enable that accumulation dislocation in austenite crystal, New crystal grain can be generated for driving force with this dislocation.In the steel plate with above-mentioned such chemical composition composition, substantially Apply pressure by the high-temperature-range (recrystallization temperature territory) more than 875 DEG C and recrystallization occurs.But, if applying the temperature of pressure Spend height, then the recrystallization produced the most easily grows, can be than the austenite crystal coarsening before pressure.Accordingly, as to Ovshinsky Temperature field (recrystallization effective temperature territory) is effectively depressed in the miniaturization of body crystal grain, is set as 950～875 DEG C.For in this temperature For pressure in degree territory, in order to effectively play above-mentioned effect, need to make reduction ratio be more than 30% (preferably 35% with On), but usually less than 60%.
Secondly, in order to increase the Zona transformans generating core that can become ferrite crystal grain, also enter at non-recrystallization temperature field Row sufficiently pressure.If applying pressure with the temperature lower than recrystallization temperature territory, then austenite crystal can not generate new crystal grain, And becoming flat tissue, Zona transformans is imported into intracrystalline.But, the pressure at the high temperature side of non-recrystallization temperature field easily produces Duplex grain structure, easily generates thick ferrite crystal grain.Therefore, the temperature field applying pressure is less than 820 DEG C and Ar3Phase Low temperature side (low temperature side of non-recrystallization temperature field) more than height, at the temperature field less than 875 DEG C and higher than 820 DEG C (the most again The high temperature side in crystallization temperature territory) do not depress.For the pressure at the low temperature side of non-recrystallization temperature field, in order to effectively Ground plays above-mentioned effect, and needing to make reduction ratio is more than 30% (preferably more than 35%), but usually less than 80%.Additionally In the pressure of the low temperature side of non-recrystallization temperature field, it is not meant to that the gamut spreading all over this temperature field is depressed, if Can ensure that the reduction ratio of more than 30%, then can also in this temperature field temperature (such as, shown in embodiment " rolling terminates Temperature ") under stop pressure.
Further, two-phase temperature field that non-recrystallization temperature field is low temperature is being compared or than lower temperature territory, i.e. low In Ar3If depressing in the temperature field of transformation temperature, although then the intensity of steel plate improves, but concentrate with the stress of work strengthening Become notable, the toughness deterioration of steel plate, do not depress.
After having carried out above-mentioned such pressure (substantially controlled rolling), need to make rolling end temp to room temperature Average cooling rate is less than 2.0 DEG C/sec and cools down, and makes microscopic structure become Ferrite-Perlite structure.If at this moment Average cooling rate is faster than 2.0 DEG C/sec, then generate the bainite structure that toughness is the lowest, it is impossible to make microscopic structure become " ferrum element Body-pearlitic structrure ".Average cooling rate is preferably less than 1.0 DEG C/sec, more preferably less than 0.5 DEG C/sec.
The high-tensile steel of the present invention can advantageously be suitable for as so-called steel plate.Thickness of slab now is about more than 7mm, The upper limit is not particularly limited, but the degree of usually below 40mm.
Hereinafter, enumerate embodiment and further illustrate the present invention, but the present invention is not limited by following embodiment, certainly at energy Enough meeting and can also suitably be changed enforcement in the range of the forward and backward purport stated, these are all contained in the technology model of the present invention In enclosing.
The application is based on Japan's patent application 2012-199798 CLAIM OF PRIORITY filed in JIUYUE in 2012 11 days Interests.Filed in JIUYUE in 2012 11 days, the full content of the description of Japan's patent application the 2012-199798th is at this Application is quoted for reference.
[embodiment]
The steel ingot formed for the various chemical compositions shown in table 1 below, implements control with the manufacturing condition shown in table 2 below System rolling, manufactures TMCP (the thermo-mechanical control process) steel plate of thickness of slab 40mm.Further, in table 1 also Show the Ar of each steel ingot3Transformation temperature, this value is tried to achieve according to following (5) formula.
Ar3Transformation temperature=868-369 × [C]+24.6 × [Si]-68.1 × [Mn]-36.1 × [Ni]-20.7 × [Cu]- 24.8×[Cr]+29.6×[Mo] …(5)
Wherein, [C], [Si], [Mn], [Ni], [Cu], [Cr] and [Mo] represents C, Si, Mn, Ni, Cu, Cr and Mo respectively Content (quality %).
[table 1]
[table 2]
For each steel plate obtained as described so, respectively by following main points, enforcement microscopic structure (ferrite particle diameter, Ferrite+pearlite point rate and bainite divide rate), steel plate characteristic (tensile strength TS and low-temperature flexibility (fracture transition temperature VTrs) evaluation).
The mensuration of rate (ferrite particle diameter, ferrite+pearlite point rate and the bainite divide)
The mensuration of ferrite+pearlite point rate and bainite point rate is, uses optical microscope for the t/4 of each steel plate (t: thickness of slab) position, with 1 visual field of multiplying power 100 times observation: the region of 600 μ m 800 μm, surveys by image analysis software Fixed, try to achieve the meansigma methods in 5 visuals field.It addition, ferrite particle diameter is t/4 (t: the thickness of slab) position at each steel plate, with 100 times of observations 5 visuals field, are assumed to the size of ferrite crystal grain the diameter of bowlder and try to achieve and be allowed to equalization as diameter of equivalent circle (averagely Diameter of equivalent circle).
(tension test)
From the total thickness of each steel plate, along the direction vertical relative to rolling direction, extract No. 1B test of JISZ2201 Sheet, carries out tension test by the main points of JISZ 2241, measures tensile strength TS.And tensile strength at more than 485MPa is Qualified.
(evaluation of low-temperature flexibility)
In t/4 (t: the thickness of slab) position of each steel plate, extract ASTMA370-05 along the direction vertical with rolling direction (0.500-in.Round Specimen) test film, according to ASTM A 370-05, carries out Charpy-type test, measures fracture and turns Temperature vTrs.And fracture transition temperature vTrs is evaluated as excellent in low temperature toughness below-80 DEG C.
These results are shown in Table 3 below together with CEQ value and σ value.
[table 3]
(the test No. that also, following No. represents in table) can be analyzed as follows by these results.Understand and meet this The No.1 of the important document of invention defined～the excellent in low temperature toughness of the steel plate of 10, and guarantee high-tensile TS.
In contrast, a certain important document specified in the steel plate shortcoming present invention of No.11～21, certain deterioration in characteristics.First, No.11,16 because Ni content fewer than scope given to this invention, it is impossible to meet good toughness.It addition, CEQ value is the least, no Can ensure that the intensity of regulation.
Although No.12 Ni content is in the range of present invention provide that, but CEQ value diminishes, even if therefore meeting low-temperature flexibility, The intensity of regulation can not be guaranteed.No.13 is because Ni content compares the scope surplus that present invention provide that, additionally CEQ value also becomes greatly, Even if so meeting intensity, low-temperature flexibility can not be met.
Although No.14,15 chemical compositions form in scope given to this invention, but CEQ value and σ value is the most any One is unsatisfactory for setting, even if therefore meeting intensity, can not meet low-temperature flexibility.
No.17,18 due to the temperature field (recrystallization temperature territory) of 950～875 DEG C given to this invention and less than 820 DEG C And Ar3At least any one deficiency, the institute of the reduction ratio of temperature field (low temperature side of non-recrystallization temperature field) more than transformation temperature Become big with ferrite particle diameter, it is impossible to meet low-temperature flexibility.Although No.19 CEQ value is not enough, but by applying two-phase temperature field Pressure, disclosure satisfy that intensity by work strengthening.But, the stress come with work strengthening is concentrated and is become notable, it is impossible to Meet low-temperature flexibility.
No.20 is because the average cooling rate after rolling is high, so generating the bainite structure that toughness is the lowest, it is impossible to full Foot low-temperature flexibility.Although No.21 Ni content is in scope given to this invention, but in the temperature less than 875 DEG C and higher than 820 DEG C Degree territory (high temperature side of non-recrystallization temperature field) applies pressure, and thick duplex grain structure produces, and therefore cannot ensure good Low-temperature flexibility.It addition, ferrite particle diameter becomes big, CEQ value is the least, therefore can not meet intensity.
Based on these data, the relation of CEQ value and tensile strength TS is shown in Figure 1.Additionally σ value and fracture transition temperature The relation of vTrs is shown in Figure 2.At Fig. 1, in 2, the diamond indicia " ◆ " being stuffed entirely with represents example, warning triangle " △ " table Show comparative example.Thus result understands, and controls in suitable scope by CEQ value, σ value, improve the intensity of high-tensile steel with In low-temperature flexibility effectively.
Industrial applicability
The present invention meets the chemical composition composition of regulation, following (1) formula the CEQ (quality %) specified is more than 0.345 And less than 0.428, and the σ specified by following (2) formula is more than 2080, and the microscopic structure of t/4 (t: thickness of slab) position is ferrum Ferritic and the line and staff control of pearlite, the average equivalent circular diameter of described ferrite crystal grain is below 7.0 μm, it is possible to realize The high-tensile steel that high intensity and low-temperature flexibility are also excellent.
CEQ=[C]+[Mn]/6+ ([Cr]+[Mo]+[V])/5+ ([Cu]+[Ni])/15 ... (1)
σ=2.90 × { 602781.57-(1154 × CEQ-3.25)2}1/2/0.963+400×[Ni] …(2)
Wherein, [C], [Mn], [Cr], [Mo], [V], [Cu] and [Ni] represents containing of C, Mn, Cr, Mo, V, Cu and Ni respectively Amount (quality %).

Claims (3)

1. the high-tensile steel of an excellent in low temperature toughness, it is characterised in that contain in terms of quality % respectively
C:0.03～0.09%,
Si:0.05～0.35%,
Mn:0.9～1.6%,
Below P:0.01% and without 0%,
Below S:0.01% and without 0%,
Al:0.01～0.06%,
Ni:0.2～2.0%,
Nb:0.007～0.017%,
Ti:0.007～0.017%,
Ca:0.0005～0.003% and
N:0.0025～0.0050%, surplus is made up of ferrum and inevitable impurity, by following (1) formula regulation with quality % The CEQ of meter is more than 0.345 and less than 0.428, and σ specify by following (2) formula is more than 2080, and the showing of t/4 position Micro-assembly robot is the line and staff control of ferrite and pearlite, and the average equivalent circular diameter of described ferrite crystal grain is below 7.0 μm, its Middle t is thickness of slab,
CEQ=[C]+[Mn]/6+ ([Cr]+[Mo]+[V])/5+ ([Cu]+[Ni])/15 ... (1)
σ=2.90 × { 602781.57-(1154 × CEQ-3.25)2}1/2/0.963+400×[Ni]…(2)
Wherein, [C], [Mn], [Cr], [Mo], [V], [Cu] and [Ni] represents the quality hundred of C, Mn, Cr, Mo, V, Cu and Ni respectively Proportion by subtraction content.
High-tensile steel the most according to claim 1, wherein, containing belonging to appointing in following (a)～(c) in terms of quality % Anticipate more than one,
(a) below B:0.002% and without 0%；
(b) below Cu:0.35% and without 0%；
(c) selected from below Cr:0.3% and without 0%, below Mo:0.2% and without 0% and below V:0.06% and without 0% More than one in the group constituted.
3. the manufacture method of the high-tensile steel of an excellent in low temperature toughness, it is characterised in that for having claim 1 or 2 Chemical composition composition steel plate, making reduction ratio when the temperature field that t/4 position is 950～875 DEG C is 30% pressure carried out above Under, in t/4 position it is less than 820 DEG C and Ar3Making reduction ratio during more than transformation temperature temperature field is more than 30% to depress, And it is not depress, after depression when the temperature field less than 875 DEG C and higher than 820 DEG C and two-phase temperature field in t/4 position Make average cooling rate be less than 2.0 DEG C/sec to cool down, make microscopic structure become the mixing group of ferrite and pearlite Knitting, wherein t is thickness of slab,
Wherein, Ar3Transformation temperature=868-369 × [C]+24.6 × [Si]-68.1 × [Mn]-36.1 × [Ni]-20.7 × [Cu]-24.8 × [Cr]+29.6 × [Mo]
In formula, [C], [Si], [Mn], [Ni], [Cu], [Cr] and [Mo] represents the quality of C, Si, Mn, Ni, Cu, Cr and Mo respectively Degree.
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