CN104487601A - High-tensile-strength steel plate with excellent low -temperature toughness and manufacturing process therefor - Google Patents
High-tensile-strength steel plate with excellent low -temperature toughness and manufacturing process therefor Download PDFInfo
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- 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
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- 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
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- 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
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- 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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- 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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Abstract
A high-tensile-strength steel plate having both high strength and excellent low-temperature toughness is provided. This steel plate satisfies a prescribed chemical composition, and has a CEQ value (mass%) of 0.345 to 0.428 as defined by formula (1) and a sigma value of 2080 or more as defined by formula (2). Further, the microstructure of the steel plate at a position of t/4 (wherein t is plate thickness) is a ferrite/pearlite mixed structure wherein the mean equivalent-circle diameter of the ferrite grains is controlled to 7.0 [mu]m or less. CEQ = [C]+[Mn]/6+([Cr]+[Mo]+[V])/5+([Cu]+[Ni])/15 (1) sigma= 2.90*{602781.57-(1154*CEQ-3.25)2}1/2/0.963+400* [Ni] (2).
Description
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 the purposes used under the environment being exposed to low temperature, such as pressurized vessel, boats and ships, marine structure etc. the technology of the low-temperature flexibility of this high-tensile steel that is suitable for.
Background technology
Build the steel plate (high-tensile steel) that pressurized vessel, boats and ships and marine structure etc. use, both required high strength, require again the toughness under low temperature (low-temperature flexibility) and weldability also excellent.Particularly in recent years, from the view point of security, require the more high tenacity under the low temperature of pole.
In order to make the toughness of steel plate improve, the method for addition doing one's utmost to control alloying element is advisable, but so, and the guaranteeing of intensity becomes difficulty.Otherwise if add alloying element in order to ensure intensity, then toughness reduces on the contrary.So, strength and toughness is contrary characteristic, these two kinds of characteristics is existed side by side extremely difficult.
As one of effective way for making these two kinds of characteristics of the strength and toughness of steel plate improve, can enumerate containing the method as the Ni of alloying element.Also a large amount of proposition contains the steel plate of Ni up to now, but practical situation are representated by 3.5%Ni steel, 9%Ni steel, if not in a large number containing Ni, then can not play this effect to greatest extent.In contrast, about containing about 1 ~ 2% the steel plate of a small amount of Ni, such as proposed by patent documentation 1, even if but meet high strength also still can not meet low temperature under toughness, be difficult to meet intensity and low-temperature flexibility simultaneously.
Prior art document
Patent documentation
Patent documentation 1: Japanese Patent No. 3741078 publication
Summary of the invention
Invent problem to be solved
The present invention completes in view of such situation, its object is to, even if provide a kind of Ni content below 2.0%, and still high strength and the also excellent high-tensile steel of low-temperature flexibility, and for the manufacture of the useful method of such high-tensile steel.
For solving the means of problem
The feature can reaching the high-tensile steel of the present invention of above-mentioned purpose is, (" quality % " is represented respectively containing C:0.03 ~ 0.09%, relate to below chemical composition all with), Si:0.05 ~ 0.35%, Mn:0.9 ~ 1.6%, below P:0.01% (not containing 0%), below S:0.01% (not containing 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 iron and inevitable impurity, 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 microstructure of t/4 (t: thickness of slab) position is the mixed structure of ferrite and pearlite, the average equivalent circular diameter of described ferrite crystal grain is less than 7.0 μm.Further, described what is called " average equivalent circular diameter " is the mean value of the diameter (equivalent circle diameter) of bowlder ferrite crystal grain being 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] represent the content (quality %) of C, Mn, Cr, Mo, V, Cu and Ni respectively.
In above-mentioned (1) formula, except the basal component (C, Mn, Ni) of steel plate of the present invention, also element (Cr, Mo, V, Cu etc.) contained as required can also be comprised, time not containing these elements, delete this project to calculate the value of CEQ, during containing these elements, calculate the value of CEQ according to above-mentioned (1) formula.
In high-tensile steel of the present invention, as required, above also effective containing belonging to any one in following (a) ~ (c) further, according to contained composition, the characteristic of high-tensile steel improves.
(a) below B:0.002% (not containing 0%)
(b) below Cu:0.35% (not containing 0%)
(c) be selected from the group that below Cr:0.3% (not containing 0%), below Mo:0.2% (not containing 0%) and below V:0.06% (not containing 0%) form more than one
When manufacturing high-tensile steel of the present invention, for the steel plate with above-mentioned such chemical composition composition, when t/4 (t: thickness of slab) position is the temperature field of 950 ~ 875 DEG C, make draft be more than 30%, be less than 820 DEG C and Ar in t/4 (t: thickness of slab) position
3during more than transformation temperature temperature field, draft is made to be more than 30% to depress, be lower than 875 DEG C in t/4 (t: thickness of slab) position and do not depress higher than when the temperature field of 820 DEG C and two-phase temperature field, make average cooling rate be less than 2.0 DEG C/sec after pressure to cool, make microstructure be the mixed structure of ferrite and pearlite.
Invention effect
According to the present invention, be in the composition system of less than 2.0% at Ni content, by becoming the chemical composition composition that can play the additive effect of Ni to greatest extent, and set suitable pressure condition, the miniaturization of the ferrite crystal grain in steel plate can be realized, can high strength be realized and the also excellent high-tensile steel of low-temperature flexibility.Such high-tensile steel, the steel plate used as construction pressurized vessel, boats and ships and marine structure etc. is exceedingly useful.
Accompanying drawing explanation
Fig. 1 is the graph of the relation representing CEQ value and tensile strength TS.
Fig. 2 is the graph of the relation representing σ value and fracture transition temperature vTrs.
Embodiment
If add alloying element in order to ensure the intensity of high-tensile steel, then toughness reduces.This is because the interpolation of alloying element makes the ductile fracture difficulty under low temperature.On the contrary, the interpolation of Ni makes the ductile fracture under low temperature easily occur.
Under such situation, the present inventor is in order to realize high strength and the high-tensile steel of excellent in low temperature toughness and studying from various angle.It found that, if the effect quantitatively of the promotion ductile fracture that the promotion ductile fracture making reduction alloying element bring and Ni bring, and control chemical composition composition in the mode of the relation meeting above-mentioned (1) formula and (2) formula, high strength and low-temperature flexibility then can be made to exist side by side, 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 rupture, particularly cleavage fracture.Therefore the mechanism of cleavage fracture is conceived to.First in the ferrite crystal grain of a part, viscous deformation is produced, the dislocation moving of ferrite intracrystalline.The dislocation of movement stops, gathers because of crystal boundary.If at this moment crystal boundary exists the second-phase representated by cementite, then the stress concentration caused that gathers of dislocation causes second-phase to ftracture, and microcosmic be full of cracks occurs.The microcosmic be full of cracks occurred is in progress between adjacent ferrite crystal grain, and cleavage fracture is occurred.
The be full of cracks of known generation is propagated to adjacent ferrite crystal grain, stress (cleavage fracture stress) σ occurred for making cleavage fracture
0can be calculated [such as, " research about the micromechanics of the fracture toughness property of soft steel " Tian Chuanzhe also issues the 17th page (Nagoya University Ph.D. Dissertation) in May, 1994] by following (3) formula.This stress σ
0larger, cleavage fracture is more difficult to occur, and toughness more improves.
(C/d)σ
0 2+τe
2{1+4/π(C/d)
1/2×(τi/τe)}
2
＝4Eγ
f/{(1-v
2)d} …(3)
Wherein, be expressed as follows respectively, C: the minor axis of second-phase, d: ferritic particle diameter, σ
0: cleavage fracture stress, τ e: effectively shear-stress, τ i: the frictional force of dislocation, E: Young's modulus, γ
f: surface energy, v: Poisson's ratio.
In above-mentioned (3) formula, Section 1 [(C/d) σ
0 2], be the item of the size ratio of the minor axis about the crystal grain diameter in the tissue provided as starting condition and carbide, Section 2 [τ e
2{ 1+4/ π (C/d)
1/2× (τ i/ τ e) }
2], be the item about the dislocation accumulating in crystal boundary.The right [4E γ in addition
f/ { (1-v
2) d}], be the item of the unstable propagation conditions about the known be full of cracks of the formula as Florence Griffith (Griffith).
At this Young's modulus E, surface energy γ
fconstant with Poisson's ratio v.Due to τ i, " τ e, so be expressed as τ i/ τ e=0.Effectively shear-stress τ e can be showed by yielding stress τ in addition,
(yielding stress).
If according to above result, above-mentioned (3) formula can be rewritten as following (4) formula like this.Young's modulus E=206000 (MPa), surface energy γ in addition
f=14 (Jm
-2), and Poisson's ratio v=0.3.
σ
0＝(d/C)
1/2×(4Eγ
f/{π(1-v
2)d}-τ
2)
1/2…(4)
Wherein, τ: yielding stress
Based on above-mentioned (4) formula, the present inventor's experimentally studies the parameter type of domination low-temperature flexibility further.Its result is distinguished, when adopting fixing manufacturing condition, the tissue obtained, namely the minor axis of ferritic particle diameter, second-phase can be considered as fixing substantially, by the value (value of σ) of described (2) formula of the CEQ (carbon equivalent) that specified by described (1) formula and Ni content defined if be more than 2080, then can guarantee 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 simultaneously can 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 ofelements beyond it is deteriorated, and can not play the effect of Ni to greatest extent, even if meet high strength, low-temperature flexibility is also deteriorated.The value of σ is preferably more than 2150, is more preferably more than 2200.In addition, the preferred upper limit of the value of σ is less than 2600.
But, even if the value of σ meet more than 2080, if the value (quality %) of the CEQ of described (1) formula defined is little than 0.345, then intensity improve element contain quantity not sufficient, intensity also will reduce.Even if the value of σ is more than 2080 in addition, Ni content lower than 0.2% time, the additive effect of Ni is not enough, still can not guarantee the good low-temperature flexibility of steel plate.And if the content of Ni is superfluous, then the balance of Ni to the effect that intensity and toughness are brought is broken, in intensity, ascending effect surpasses the inhibition of the ductile fracture under low temperature, low-temperature flexibility deterioration.Thus, Ni content needs with 2.0% for the upper limit.Further, the preferred lower limit of Ni content is more than 0.5% (being more preferably more than 0.7%), and the preferred upper limit is less than 1.8% (being more preferably less than 1.5%).
The opposing party and, if the value (quality %) of the CEQ specified by described (1) formula is larger than 0.428, then the balance of strength and toughness is broken, and low-temperature flexibility will reduce.Therefore, in order to ensure the toughness of necessity, the value (quality %) of CEQ is less than 0.428.Further, the preferred lower limit of the value (CEQ value) of CEQ is more than 0.350 (being more preferably more than 0.355), and the preferred upper limit is less than 0.425 (being more preferably less than 0.420).
In the present invention, have a mind to make the microstructure of t/4 position be ferrite and pearlitic mixed structure, add up to 100 area %.But, in the scope that can not impact as the effect of object the present invention, do not get rid of and have other the tissue beyond ferritic structure and pearlitic structure (such as bainite, martensite) pettiness amount to be mixed into.According to circumstances, can allow other tissue containing ending in 10 area about %.In addition, being not particularly limited about ferrite and pearlitic mixture ratio, is ferrite 70 ~ 90 area %: perlite 10 ~ 30 area about %.
In order to ensure the good low-temperature flexibility of steel plate, carry out controlling also being important important document in the mode that the average equivalent circular diameter of the ferrite crystal grain (not comprising the ferrite crystal grain in perlite) in the microstructure as ferrite and pearlitic mixed structure (being expressed as " ferrite-pearlite ") is less than 7.0 μm.By making the average equivalent circular diameter of ferrite crystal grain be less than 7.0 μm, the good low-temperature flexibility (fracture transition temperature vTrs is less than-80 DEG C) of high-tensile steel can be guaranteed.The preferred upper limit of this ferrite particle diameter is less than 6.7 μm (being more preferably less than 6.5 μm).The preferred lower limit of ferrite particle diameter is more than 0.5 μm (being more preferably more than 1.0 μm) in addition.
In high-tensile steel of the present invention, in order to satisfied as the basic characteristic of this steel plate, also need the composition (C, Si, Mn, P, S, Al, Nb, Ti, Ca and N) suitably adjusted 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 guaranteeing steel plate.In order to play such effect, need to make C contain more than 0.03%.But if the content surplus of C, toughness reduces, and therefore makes the upper limit be 0.09%.Further, C content is preferably more than 0.05%, and less than 0.08%.
(Si：0.05～0.35％)
Si works as reductor when steel-smelting, plays the effect making the intensity of steel increase.In order to play such 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% (being 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 more than 0.9%.Be preferably more than 1.1%.But if the content of Mn is superfluous, then toughness is deteriorated on the contrary, therefore suppresses below 1.6%.Be preferably less than 1.5%.
(below P:0.01% (not containing 0%))
P is the element making toughness deterioration, therefore needs to do one's utmost to reduce.Need in the present invention to suppress below 0.01%.
(below S:0.01% (not containing 0%))
S is the element making toughness deterioration.Therefore need 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 reductor.In order to play such effect, Al content is more than 0.01%.But if Al content is superfluous, then the cleanliness of steel plate is hindered, its upper limit is therefore made to be 0.06%.Further, Al content is preferably more than 0.02%, and less than 0.05%.
(Nb：0.007～0.017％)
Nb is the element by the recrystallize inhibition of austenite grain with the micronized effect of ferrite crystal grain.In order to play such effect, need to make Nb contain more than 0.007%.But if the content of Nb is superfluous, then toughness reduces, and therefore makes its upper limit be 0.017%.Further, the preferred lower limit of Nb content is more than 0.010%, and the preferred upper limit is less than 0.015%.
(Ti：0.007～0.017％)
Ti is strong nitride forming element, just brings the micronized effect of the crystal grain brought from the fine precipitation of TiN under trace into play.In order to effectively play such effect, need to make Ti contain more than 0.007%.Be preferably more than 0.01%.But, if superfluously containing Ti, cause the reduction of toughness on the contrary, therefore need below 0.017%, be preferably less than 0.015%.
(Ca：0.0005～0.003％)
Ca is for the effective element of toughness improving steel plate by the control of inclusion.In order to play such effect, need to make Ca contain more than 0.0005%.But if superfluously containing Ca, then toughness reduces, and therefore needs below 0.003%.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 forms TiN by containing in right amount with Ti, is the effective element of toughness for improving steel plate.In order to effectively play such effect, need to make N contain more than 0.0025%.But if N content surplus, solid solution N increases, the toughness of steel plate is reduced, therefore need to make its upper limit be 0.0050%.Further, the preferred lower limit of N content is more than 0.003%, and the preferred upper limit is less than 0.0045%.
What specify in the present invention contains element as above-mentioned, and surplus is iron and inevitable impurity.As this inevitable impurity, being mixed into of the element introduced because of the situation of raw material, material, producing apparatus etc. can be allowed.In addition as required, above also effective containing belonging to any one in following (a) ~ (c), the composition contained by correspondence, the characteristic of high-tensile steel improves.As described below containing preferable range setting reason during these elements.
(a) below B:0.002% (not containing 0%)
(b) below Cu:0.35% (not containing 0%)
(c) be selected from the group that below Cr:0.3% (not containing 0%), below Mo:0.2% (not containing 0%) and below V:0.06% (not containing 0%) form more than one
(below B:0.002% (not containing 0%))
B has by generating BN the effect making to cause dysgenic solid solution N to reduce to toughness.But if B content is too much, then make the precipitate of B increase, toughness is deteriorated on the contrary, therefore preferably suppress below 0.002%.Further, the preferred lower limit of B content is more than 0.0001%, lower than 0.0001% time, solid solution N reducing effect is insufficient.The preferred upper limit is less than 0.001%.
(below Cu:0.35% (not containing 0%))
Cu improves effective element for intensity.If the content of Cu is too much, then easily there is crackle during hot-work, therefore preferably make its upper limit be less than 0.35%.Further, the preferred lower limit of Cu content is more than 0.001%, lower than 0.001% time this effect insufficient.The preferred upper limit is less than 0.30%.
(be selected from the group that below Cr:0.3% (not containing 0%), below Mo:0.2% (not containing 0%) and below V:0.06% (not containing 0%) form more than one)
Cr, Mo and V all make Carbonitride Precipitation, are the elements contributing to intensity rising.But contain if make it, then make toughness reduce, therefore preferably Cr suppresses below 0.3%, and Mo suppresses below 0.2%, and V suppresses below 0.06% superfluously.Further, in order to effectively play their effect, preferred Cr contains more than 0.01%, Mo and contains more than 0.01%, V and contain more than 0.001%.
Making it to become above-mentioned tissue like this to manufacture steel plate of the present invention, needing to specify its manufacturing condition closely.That is, when manufacturing high-tensile steel of the present invention, t/4 (t: thickness of slab) position makes draft be that more than 30%, t/4 (t: thickness of slab) position is below 820 DEG C and Ar when the temperature field of 950 ~ 875 DEG C
3draft is made to be more than 30% during more than transformation temperature temperature field, so the steel plate with above-mentioned such chemical composition composition is carried out depressing (being essentially controlled rolling), and t/4 (t: thickness of slab) position lower than 875 DEG C and higher than 820 DEG C temperature field and at two-phase temperature field time do not depress, make average cooling rate be less than 2.0 DEG C/sec after pressure to cool, need to make microstructure become Ferrite-Perlite structure.The range set reason of each condition of the method is as follows.
The temperature of t/4 (t: thickness of slab) position, can Difference Calculation be carried out by once passing heat transfer equation to unsteady flo w and try to achieve, except board briquette, room temperature, water temperature, beyond slab thickness before and after rolling, if known slab, the thermal conductivity of roll and air, then also can calculate [such as, a () " wicket is single, ' basic research about the anticipation computing method of the temperature variation of the material of hot rolling ', plasticity and processing, 1970, 11st volume, No. 118, p.816-824 ", (b) " family gram, ridge, in in a youth, rattan Tian Wenfu, god's tail is wide, ' the roughing model formation of hot strip mill ', iron and steel, 1977, 63rd volume, A29-A32 ", c () " western ridge is clean, ' the high-accuracy high-efficiency rate rolling technique of the paired cross rolling mill of slab ', development and the trend faced the future of rolling technique rolling therory, the joint research of Tie Gang association of Japan can be compiled in rolling therory portion, 1994, p.69-78 " etc.].
In order to manufacture high-tensile steel of the present invention by above-mentioned such manufacturing condition, use the steel plate with above-mentioned such chemical composition composition as blank steel plate, this blank steel plate uses based on ferritic structure the steel plate of (such as, ferritic phase is 50 more than area %) substantially.In order to make the ferrite crystal grain miniaturization of such blank steel plate, the draft at regulation recrystallization temperature, non-recrystallization temperature.Further, following shown temperature manages using the temperature of the t/4 of the position as the average behaviour playing steel plate (t: thickness of slab) position.
First, in order to make austenite crystal miniaturization, need to depress fully (pressure after heating) in recrystallization temperature territory.Under recrystallization temperature territory, apply the pressure of draft more than 30%, accumulation dislocation in austenite crystal can be made thus, with this dislocation for motivating force can generate new crystal grain.In the steel plate with above-mentioned such chemical composition composition, there is recrystallize basically by the high-temperature-range (recrystallization temperature territory) more than 875 DEG C applies pressure.But if the temperature applying pressure is too high, then the recrystallize produced also easily grows, the austenite crystal coarsening before under meeting specific pressure.Therefore, as effectively depressing temperature field (recrystallize significant temp territory) to the miniaturization of austenite crystal, 950 ~ 875 DEG C are set as.For the pressure in this temperature field, in order to effectively play above-mentioned effect, needing to make draft be more than 30% (being preferably more than 35%), but being generally less than 60%.
Secondly, in order to increase the deformation bands of the product nucleus that can become ferrite crystal grain, also depress fully at non-recrystallization temperature field.If apply pressure with the temperature lower than recrystallization temperature territory, then austenite crystal can not generate new crystal grain, and becomes flat tissue, and deformation bands is imported into intracrystalline.But, easily produce duplex grain structure in the pressure of the high temperature side of non-recrystallization temperature field, easily generate thick ferrite crystal grain.Therefore, the temperature field applying pressure is less than 820 DEG C and Ar
3low temperature side (low temperature side of non-recrystallization temperature field) more than transformation temperature, is not depressing lower than 875 DEG C and higher than the temperature field (high temperature side of non-recrystallization temperature field) of 820 DEG C.For the pressure of the low temperature side at non-recrystallization temperature field, in order to effectively play above-mentioned effect, needing to make draft be more than 30% (being preferably more than 35%), but being generally less than 80%.In addition in the pressure of the low temperature side of non-recrystallization temperature field, and do not mean that the gamut spreading all over this temperature field is depressed, if the draft of more than 30% can be guaranteed, then also can stop pressure under the temperature (" rolling end temp " such as, shown in embodiment) in this temperature field.
Further, comparing two-phase temperature field that non-recrystallization temperature field is low temperature or than lower temperature field, namely lower than Ar
3if depress in the temperature field of transformation temperature, although then the intensity of steel plate improves, the stress concentration with work strengthening becomes remarkable, and the toughness deterioration of steel plate, does not therefore depress.
After having carried out above-mentioned pressure (being controlled rolling substantially) like this, need to make rolling end temp to the average cooling rate of room temperature to be less than 2.0 DEG C/sec and cool, make microstructure become Ferrite-Perlite structure.If average cooling rate is at this moment faster than 2.0 DEG C/sec, then generates the generally low bainite structure of toughness, microstructure can not be made to become " Ferrite-Perlite structure ".Average cooling rate is preferably less than 1.0 DEG C/sec, is more preferably less than 0.5 DEG C/sec.
High-tensile steel of the present invention can advantageously be suitable for as so-called Plate Steel.Thickness of slab is now about more than 7mm, and the upper limit is not particularly limited, but is generally the degree of below 40mm.
Below, enumerate embodiment and further illustrate the present invention, but the present invention does not limit by following embodiment certainly, in the scope that can meet the forward and backward purport stated, also suitably can be changed enforcement, these are all included in technical scope of the present invention.
The application is based on the interests of the Japan patent application 2012-199798 CLAIM OF PRIORITY applied on September 11st, 2012.The full content of the specification sheets of No. 2012-199798th, Japan's patent application of application on September 11st, 2012 is quoted in order to reference in this application.
[embodiment]
For the steel ingot of the various chemical composition compositions shown in following table 1, implement controlled rolling with the manufacturing condition shown in following table 2, manufacture TMCP (thermo-mechanical controlprocess) steel plate of thickness of slab 40mm.Further, the Ar of each steel ingot is also shown in table 1
3transformation temperature, this value is tried to achieve according to following (5) formula.
Ar
3transformation 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] represent the content (quality %) of C, Si, Mn, Ni, Cu, Cr and Mo respectively.
[table 1]
[table 2]
For each steel plate obtained as described so, respectively by following main points, implement the evaluation of microstructure (ferrite particle diameter, ferrite+perlite point rate and bainite divide rate), steel plate characteristic (tensile strength TS and low-temperature flexibility (fracture transition temperature vTrs)).
(ferrite particle diameter, ferrite+perlite point rate and bainite divide the mensuration of rate)
The mensuration of ferrite+perlite point rate and bainite point rate is, use opticmicroscope for t/4 (t: the thickness of slab) position of each steel plate, 1 visual field is observed: the region of 600 μm × 800 μm, measures by image analysis software, tries to achieve the mean value in 5 visuals field with multiplying power 100 times.In addition, ferrite particle diameter is t/4 (t: the thickness of slab) position at each steel plate, observe 5 visuals field with 100 times, the diameter size of ferrite crystal grain being assumed to bowlder is tried to achieve as diameter of equivalent circle and makes it equalization (average equivalent circular diameter).
(tension test)
From the total thickness of each steel plate, along the direction vertical relative to rolling direction, extract the 1B test film of JISZ2201, carry out tension test by the main points of JISZ 2241, measure tensile strength TS.And tensile strength is qualified at more than 485MPa.
(evaluation of low-temperature flexibility)
In t/4 (t: the thickness of slab) position of each steel plate, ASTMA370-05 (0.500-in.Round Specimen) test film is extracted along the direction vertical with rolling direction, according to ASTM A 370-05, carry out Charpy impact test, measure fracture transition temperature vTrs.And fracture transition temperature vTrs is evaluated as excellent in low temperature toughness below-80 DEG C.
These results are shown in following table 3 together with σ value with CEQ value.
[table 3]
Can be analyzed as follows (also have, following No. represents the test No. in table) by these results.The known excellent in low temperature toughness meeting the steel plate of No.1 ~ 10 of important document given to this invention, and guarantee high-tensile TS.
In contrast, the steel plate of No.11 ~ 21 is short of a certain important document specified in the present invention, certain deterioration in characteristics.First, No.11,16, because Ni content is fewer than scope given to this invention, can not meet good toughness.In addition, CEQ value is also little, can not guarantee the intensity specified.
Although No.12 Ni content is in the scope that the present invention specifies, CEQ value diminishes, even if therefore meet low-temperature flexibility, can not guarantee the intensity specified.No.13 is because Ni content compares the scope surplus that the present invention specifies, CEQ value also becomes greatly in addition, even if so meet intensity, can not meet low-temperature flexibility.
Although No.14,15 chemical compositions compositions are in scope given to this invention, CEQ value and σ value at least any one does not meet prescribed value, even if therefore meet intensity, can not low-temperature flexibility be met.
No.17,18 is due to the temperature field (recrystallization temperature territory) of 950 ~ 875 DEG C given to this invention and less than 820 DEG C and Ar
3at least any one deficiency of the draft of temperature field (low temperature side of non-recrystallization temperature field) more than transformation temperature, so ferrite particle diameter becomes large, can not meet low-temperature flexibility.Although No.19 CEQ value is not enough, by applying the pressure of two-phase temperature field, intensity can be met by work strengthening.But the stress concentration come with work strengthening becomes remarkable, can not meet low-temperature flexibility.
No.20, because the average cooling rate after rolling is high, so generate the generally low bainite structure of toughness, can not meet low-temperature flexibility.Although No.21 Ni content is in scope given to this invention, but applying pressure lower than 875 DEG C and higher than the temperature field (high temperature side of non-recrystallization temperature field) of 820 DEG C, thick duplex grain structure produces, and therefore can not guarantee good low-temperature flexibility.In addition, ferrite particle diameter becomes large, and CEQ value is also little, therefore can not meet intensity.
Based on these data, the relation of CEQ value and tensile strength TS is shown in Figure 1.The relation of σ value and fracture transition temperature vTrs is shown in Figure 2 in addition.In Fig. 1,2, the diamond indicia " ◆ " of all filling represents example, and warning triangle " △ " represents comparative example.Result is known thus, controls in suitable scope by CEQ value, σ value, in the intensity improving high-tensile steel and low-temperature flexibility effectively.
Utilizability in industry
The present invention meets the chemical composition composition of 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 microstructure of t/4 (t: thickness of slab) position is ferrite and pearlitic mixed structure, the average equivalent circular diameter of described ferrite crystal grain is less than 7.0 μm, can realize high strength thus and the also excellent high-tensile steel of low-temperature flexibility.
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] represent the content (quality %) of C, Mn, Cr, Mo, V, Cu and Ni respectively.
Claims (3)
1. a high-tensile steel for excellent in low temperature toughness, is characterized in that, contains in mass % respectively
C：0.03～0.09％、
Si：0.05～0.35％、
Mn：0.9～1.6％、
Below P:0.01% and containing 0%,
Below S:0.01% and containing 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 iron and inevitable impurity, the CEQ in mass % 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 microstructure of t/4 position is the mixed structure of ferrite and pearlite, the average equivalent circular diameter of described ferrite crystal grain is less than 7.0 μm, and wherein t is thickness of slab
CEQ＝[C]+[Mn]/6+([Cr]+[Mo]+[V])/5+([Cu]+[Ni])/15...(1)
σ=2.90 × { 602781.57 1 (1154 × CEQ 1)
2}
1/2/ 0.963+400 × [Ni] ... (2)
Wherein, [C], [Mn], [Cr], [Mo], [V], [Cu] and [Ni] represent the mass percentage content of C, Mn, Cr, Mo, V, Cu and Ni respectively.
2. high-tensile steel according to claim 1, wherein, in mass % containing belonging in following (a) ~ (c) more than any one,
(a) below B:0.002% and not containing 0%;
(b) below Cu:0.35% and not containing 0%;
(c) be selected from below Cr:0.3% and containing 0%, below Mo:0.2% and containing 0% and below V:0.06% and containing more than one in 0% group formed.
3. the manufacture method of the high-tensile steel of an excellent in low temperature toughness, it is characterized in that, for the steel plate of the chemical composition composition had described in claim 1 or 2, make when t/4 position is the temperature field of 950 ~ 875 DEG C draft be more than 30% to depress, be less than 820 DEG C and Ar in t/4 position
3draft is made to be more than 30% to depress during more than transformation temperature temperature field, and be lower than 875 DEG C in t/4 position and do not depress higher than when the temperature field of 820 DEG C and two-phase temperature field, make average cooling rate be less than 2.0 DEG C/sec after depression to cool, make microstructure become ferrite and pearlitic mixed structure, wherein t is thickness of slab.
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| JP2012199798A JP5981813B2 (en) | 2012-09-11 | 2012-09-11 | High strength steel sheet with excellent low temperature toughness and method for producing the same |
| JP2012-199798 | 2012-09-11 | ||
| PCT/JP2013/072679 WO2014041996A1 (en) | 2012-09-11 | 2013-08-26 | High-tensile-strength steel plate with excellent low -temperature toughness and manufacturing process therefor |
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| CN105624553A (en) * | 2015-12-31 | 2016-06-01 | 江西理工大学 | High-strength steel plate with improved low-temperature impact toughness and manufacturing method thereof |
| CN112779463A (en) * | 2019-11-01 | 2021-05-11 | 株式会社神户制钢所 | High-tension steel plate with excellent low-temperature toughness of base metal and joint and manufacturing method thereof |
| CN114269709A (en) * | 2020-07-14 | 2022-04-01 | 杰富意化学株式会社 | MnCoZn-based ferrite |
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| JP6771429B2 (en) * | 2016-08-29 | 2020-10-21 | 株式会社神戸製鋼所 | Thick steel plate and its manufacturing method |
| WO2018043067A1 (en) * | 2016-08-29 | 2018-03-08 | 株式会社神戸製鋼所 | Thick steel sheet and production method therefor |
| JP6866791B2 (en) * | 2016-12-20 | 2021-04-28 | 日本製鉄株式会社 | Toughness predictor, toughness prediction method, and program |
| KR102255822B1 (en) * | 2019-12-06 | 2021-05-25 | 주식회사 포스코 | Normalling heat treatable steel sheet having godd low impact toughness and method for the same |
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| JP2004002934A (en) * | 2002-05-31 | 2004-01-08 | Kobe Steel Ltd | Thick steel plate with excellent toughness at low temperature, and its manufacturing method |
| CN102119236A (en) * | 2009-10-28 | 2011-07-06 | 新日本制铁株式会社 | Steel plate for line pipes with excellent strength and ductility and process for production of same |
| JP2011208222A (en) * | 2010-03-30 | 2011-10-20 | Sumitomo Metal Ind Ltd | Method for manufacturing steel material for mixed loading of lpg and ammonium |
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| JP2004002934A (en) * | 2002-05-31 | 2004-01-08 | Kobe Steel Ltd | Thick steel plate with excellent toughness at low temperature, and its manufacturing method |
| CN102119236A (en) * | 2009-10-28 | 2011-07-06 | 新日本制铁株式会社 | Steel plate for line pipes with excellent strength and ductility and process for production of same |
| JP2011208222A (en) * | 2010-03-30 | 2011-10-20 | Sumitomo Metal Ind Ltd | Method for manufacturing steel material for mixed loading of lpg and ammonium |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105624553A (en) * | 2015-12-31 | 2016-06-01 | 江西理工大学 | High-strength steel plate with improved low-temperature impact toughness and manufacturing method thereof |
| CN105624553B (en) * | 2015-12-31 | 2017-05-03 | 江西理工大学 | High-strength steel plate with improved low-temperature impact toughness and manufacturing method thereof |
| CN112779463A (en) * | 2019-11-01 | 2021-05-11 | 株式会社神户制钢所 | High-tension steel plate with excellent low-temperature toughness of base metal and joint and manufacturing method thereof |
| CN114269709A (en) * | 2020-07-14 | 2022-04-01 | 杰富意化学株式会社 | MnCoZn-based ferrite |
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| KR20150038631A (en) | 2015-04-08 |
| KR101695113B1 (en) | 2017-01-11 |
| JP2014055317A (en) | 2014-03-27 |
| WO2014041996A1 (en) | 2014-03-20 |
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