CN104364405B - Welding super high tensile steel plate - Google Patents

Welding super high tensile steel plate Download PDF

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CN104364405B
CN104364405B CN201380028579.6A CN201380028579A CN104364405B CN 104364405 B CN104364405 B CN 104364405B CN 201380028579 A CN201380028579 A CN 201380028579A CN 104364405 B CN104364405 B CN 104364405B
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formula
steel plate
steel
less
toughness
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CN104364405A (en
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渡部义之
原卓也
藤冈政昭
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Nippon Steel Corp
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Nippon Steel Corp
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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Abstract

The chemical composition of this steel plate is: in terms of quality %, C:0.015%～0.045%, Mn:1.80%～2.20%, Cu:0.40%～0.70%, Ni:0.80%～1.80%, Nb:0.005%～0.015%, Mo:0.05%～0.25%, Ti:0.005%～0.015%, B:0.0004%～0.0020%, N:0.0020%～0.0060%, O:0.0015%～0.0035%, at the thickness of slab central part in cross section, thickness of slab direction, diameter of equivalent circle be the oxide particle of more than 2 μm be 20/mm2Hereinafter, and Ti oxide that diameter of equivalent circle is 0.05～0.5 μm is 1.0 × 103～1.0 × 105Individual/mm2。

Description

Welding super high tensile steel plate
Technical field
The present invention relates to require the weldability of large welded structures thing purposes of high security, weldering as marine structure etc. Connect the super high tensile steel plate of the tenacity excellent of heat affected zone.
Background technology
In recent years, the energy demand vigorous with the whole world is echoed mutually, and the exploitation of the marine resources such as oil and natural gas enlivens. Meanwhile, due to the efficient activity excavating, producing and harshization etc. of development environment, point to the maximization of marine structure, right Steel require thicknessization, high intensity.And, the marine structure that ocean is arranged also requires the high security for destroying, right The weldability of excellence, the toughness of welding heat affected zone is required in steel plate.
It is said that in general, there is steel plate thickness, high intensity, the most unfavorable in the toughness of the weldability of steel plate, welding heat affected zone Tendency.This is because in terms of guaranteeing intensity, it is necessary to the alloying element of a large amount of toughness adding infringement welding heat affected zone.Institute The weldability of meaning has wide in range implication, represents hardening and the welding cold crack sensitivity of welding heat affected zone in the narrow sense, many P is formed by various carbon equivalents Ceq and welding crack sensibilityCMRepresent Deng composition parameter.High alloy composition, these indexs are more Height, hardening and the welding cold crack sensitivity of welding heat affected zone are the highest, it is considered that weldability is poor.Welding heat affected zone Toughness may not be completely the same with the size of the index of these weldabilities, but it is known for there is high dependency.
As it has been described above, generally, the thicknessization of steel plate and/or high intensityization and raising weldability, the toughness of welding heat affected zone Directivity contrary, make composition design that these contrary steel plate characteristics take into account, manufacturing technology become problem.
As not damaging weldability, need not with Shangdi, chemical composition raising is realized steel plate to necessary amount in other words Thicknessization and/or the means of high intensity, have processing and heat treatment, i.e. TMCP (Thermo-Mechanical Control Process, thermomechanical controls technique) and the quenching and tempering (quenching-temper) of interpolation B (boron), this is for this area It is known for technical staff, even if it is open the most not carry out technology.But, even if the most insufficient by these means, This is also the fact that.
TMCP is the technique being controlled the steel manufacturing process entirety reaching heating-rolling-cooling, at thick material In the case of, after rolling, the water-cooling process also referred to as accelerating cooling or control cooling is effective for high intensity. But, cool down the physical phenomenon owing to being heat transfer, even if the thickness of slab central part of thick material also cannot be obtained sufficiently by water-cooled Rate of cooling, it is difficult to guarantee thickness and high intensity with low composition.
On the other hand, the B (boron) used in high-strength hardened and tempered steel is by inclined with solid solution condition at original austenite crystal prevention Analysis, even the denier of ppm grade, also can significantly improve the hardenability of steel, and this is known, is effective for high intensity 's.But, this significantly improves the hardening of welding heat affected zone the most simultaneously.Requiring that extra high safety is (welding heat affected The high destruction toughness in portion) marine structure in the case of, weld heat input during construction is limited lower, its hardening Improve further.The hardening of welding heat affected zone is as mentioned above and welding cold crack sensitivity and the toughness of welding heat affected zone Also there is high dependency, use the aspect of B (boron) to have problems unconditionally.Additionally, in the high hardenability using B (boron) In the case of, its effect is just to play after B (boron) exists with solid solution condition, therefore, controls the composition of precipitation of boron compound, work Skill control be integral, with the combination of TMCP in the case of, there is the knowledge in modifier treatment cannot be direct applied Situation.Thus, carried out by modifier treatment, i.e. quenching-temper the technique that manufactures heat treatment duration with become we Face, is disadvantageous compared with TMCP.And then, in recent years, from the viewpoint of carrying capacity of environment, energy are saved, Micro Alloying i.e. TMCP Changing and constantly becoming social requirement is truth.
Wherein, as having the thickness of slab equal with the main target of the present application described later, welding of yield strength connects The marine structure steel of the crack tip opening displacement CTOD excellent of head, such as, Patent Document 1 discloses and relate to And the Cu containing the more Cu of more than 0.8% separates out the invention of shaped steel.But, when Cu adds the most in a large number, heating time or Produce Cu crackle during hot rolling, there is the problem becoming to be difficult to manufacture.
Prior art literature
Patent documentation
Patent documentation 1: Japanese Laid-Open 2011-1625 publication
Summary of the invention
The problem solved is wanted in invention
The present invention is in view of above-mentioned truth, it is therefore intended that provide the large-scale welding requiring high security as marine structure etc. The weldability of works purposes, the super high tensile steel plate of tenacity excellent of welding heat affected zone.
Main target be have thickness of slab be 50～100mm, tensile strength be 600～700MPa, yield strength be 500～ 690MPa, the minimum CTOD value of crack tip opening displacement of welding heat affected zone are the characteristic of more than 0.25mm, purposes requirement The ocean knot of crack tip opening displacement CTOD (the Crack-Tip Opening Displacement) characteristic of welded-joint Structure thing steel plate.It addition, in order to ensure the sufficient safety for destroying, minimum CTOD value is high.Purposes is the most especially Limit, as the toughness evaluation of welding heat affected zone, compared with Xia Shi impact characteristics, it is believed that CTOD characteristic is tightened up evaluation Method, using marine structure steel plate as main target.Therefore, the present invention obviously can be widely as boats and ships, steelframe, bridge The welded structure steel plate such as beam, various tanks is applied.
For solving the means of problem
In order to solve the various problem points of indication, problem in background technology, to effectively using B (boron) under TMCP premise Method carried out further investigation, research, it was found that do not damage weldability, the optimal hands making the toughness of welding heat affected zone improve Section.Main point is: (a) make in order to ensure solid solution B (boron) B-N-Ti measure balance suitably change, (b) in order to relax by (Gu Molten) B cause the indurative extremely low Cization of welding heat affected zone, (c) in order to ensure intensity and weldability, welding heat affected zone The P of toughnessCMSuitableization, (d) in order to ensure the Ti deoxygenated without Al of the toughness of welding heat affected zone, (e) in order to suppress Thick oxide without low O (oxygen) change etc. in the case of Al.These points are not independent phenomenon, but have mutually close pass System, is therefore not easy to realize simultaneously, and the present inventor is realized first by system and careful experiment, and completes the present invention.
Idea of the invention is as described below.
(1) chemical composition of the steel plate of the 1st aspect of the present invention is: in terms of quality %, C:0.015%～0.045%, Mn:1.80%～2.20%, Cu:0.40%～0.70%, Ni:0.80%～1.80%, Nb:0.005%～0.015%, Mo: 0.05%～0.25%, Ti:0.005%～0.015%, B:0.0004%～0.0020%, N:0.0020%～0.0060%, O:0.0015%～0.0035%, Si:0%～0.40%, below P:0.008%, below S:0.005%, Al:0%～ 0.004%, Cr:0%～0.30%, V:0%～0.06%, Mg:0%～0.0050%, remainder: ferrum and impurity, following Value represented by formula 1 is more than 2.0, and the value represented by following formula 2 is more than 0%, the FB represented by following formula 3 be 0.0003% with On, the welding crack sensibility index i.e. P represented by following formula 4CMValue is more than 0.18% and less than 0.23%, in thickness of slab direction The thickness of slab central part in cross section, diameter of equivalent circle be the oxide particle of more than 2 μm be 20/mm2Hereinafter, and diameter of equivalent circle is The Ti oxide of 0.05～0.5 μm is 1.0 × 103～1.0 × 105Individual/mm2。
[Ni]/[Cu] formula 1
[N]-[Ti]/3.4 formula 2
FB=[B]-0.77 × ([N]-0.29 × ([Ti]-2 × ([O]-0.89 × [Al]))) formula 3
PCM=[C]+[Si]/30+ [Mn]/20+ [Cu]/20+ [Ni]/60+ [Cr]/20+ [Mo]/15+ [V]/10+5 [B] Formula 4
Here, [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V], [Ti], [B], [N], [O], [Al] are respectively Refer to the content represented with quality % of C, Si, Mn, Cu, Ni, Cr, Mo, V, Ti, B, N, O, Al.
Wherein, in above-mentioned formula 3, when the item of ([O]-0.89 × [Al]) is less than 0, by ([O]-0.89 in above-mentioned formula 3 × [Al]) item be set to 0 to calculate above-mentioned FB, additionally, in above-mentioned formula 3, the item of ([Ti]-2 × ([O]-0.89 × [Al])) When being less than 0, it is set to the item of ([Ti]-2 × ([O]-0.89 × [Al])) in above-mentioned formula 30 to calculate above-mentioned FB, enter And, in above-mentioned formula 3, when the item of ([N]-0.29 × ([Ti]-2 × ([O]-0.89 × [Al]))) is less than 0, by above-mentioned formula 3 In the item of ([N]-0.29 × ([Ti]-2 × ([O]-0.89 × [Al]))) be set to 0 to calculate above-mentioned FB, and then, work as FB When≤0, if FB=0.
(2) in the steel plate described in above-mentioned (1), and then, the Bp represented by following formula 5 can be more than 0.09% and Less than 0.30%.
Bp=(884 × [C] × (1-0.3 × [C]2)+294) × FB formula 5
(3) above-mentioned (1) or (2) described in steel plate in, and then, in above-mentioned chemical composition, in terms of quality %, can be by Si It is limited in less than 0.15%.
(4) above-mentioned (1)～(3) in the steel plate described in any one in, and then, in above-mentioned chemical composition, in terms of quality %, Mg can be limited in less than 0.0003%.
(5) above-mentioned (1)～(4) according to any one of steel plate in, thickness of slab can be more than 50mm and below 100mm, anti- Tensile strength can be more than 600MPa and below 700MPa, yield strength can be more than 500MPa and below 690MPa.
Invention effect
According to the present invention, the extra-high tension steel of the tenacity excellent of weldability, welding heat affected zone can be provided at a low price, in sea While the maximization of the welded structures such as ocean works, safety can be improved further.
Detailed description of the invention
The present invention is described in detail below.
The present invention using provide as marine structure etc. require high security large welded structures thing purposes weldability, For the purpose of the extra-high tension steel of the tenacity excellent of welding heat affected zone, to have thickness of slab be 50～100mm, tensile strength is for 600 ～700MPa, yield strength be 500～690MPa, the minimum CTOD value of the crack tip opening displacement of welding heat affected zone be The steel plate of the characteristic of more than 0.25mm is main target.
First, restriction scope and reason to the composition of steel of the extra-high tension steel of the present invention illustrate.Here record % refer to quality %.
C:0.015%～0.045%
In using the present invention of high hardenability of B, in order to suppress the superfluous hardening of welding heat affected zone, C needs Suppress relatively low.But, when C amount is too low, for compensation intensity (tensile strength), it is necessary to increase alloying element amount, infringement economy Property.In order to suppress cost of alloy and to stably obtain in the thick material as the target of the present invention as yield strength be 500 ～the intensity of 560MPa level steel (for the strength grade of steel grade, be not the scope of actual yield strength), the present invention is limited to More than 0.015%.From the viewpoint of economy, its lower limit can be set to 0.018%, 0.020%, 0.023% or 0.025%.It addition, when more than 0.045%, work mutually with B effect, the hardening of welding heat affected zone becomes superfluous, The toughness making welding heat affected zone deteriorates, therefore, using 0.045% as the upper limit.In order to make the hardening of welding heat affected zone drop Low, its upper limit can be set to 0.042%, 0.040%, 0.037% or 0.035%.
Si:0%～less than 0.40%
Si inevitably contains in steel, particularly encourages hard and crisp MA in welding heat affected zone The generation of (Martensite-Austenite, martensite-austenite) composition (hereinafter referred to as MA), makes welding heat affected zone Toughness deterioration.Therefore, Si is the lowest more preferred.C amount is being limited in the present invention of relatively low scope, if containing 0.40% being Only, then MA growing amount is few, can allow from the viewpoint of the toughness of welding heat affected zone.But, it is contemplated that as welding knot During various welding condition of structure thing steel, it is clear that the most less, its upper limit can be set to 0.30%, 0.25%, 0.20%, 0.15% or less than 0.10%.Need not the lower limit of regulation Si, its lower limit is 0%.In order to improve the base metal tenacity of steel plate or enter Row deoxidation, can contain Si, as required, its lower limit can be set to 0.01%, 0.02% or 0.03%.
Mn:1.80%～2.20%
Mn is less expensive element, but, strength-enhancing effect is big, to the toughness of mother metal and welding heat affected zone not Good impact is the least.It is being set to without in the present invention of the Ti deoxidation of Al, in order to make the toughness of welding heat affected zone improve, in welding In heat affected zone, the generation of Intragranular Acicular Ferrite with Ti oxide etc. as core becomes important, but, now, Mn also plays important Effect.It separates out MnS to Ti oxide, forms the thinning area of Mn in its vicinity, and phase transition temperature increases compared with matrix, helps Grow and promote ferrite transformation.Consider the intensity of mother metal, toughness, the toughness of welding heat affected zone and then cost of alloy etc., In the present invention, Mn is limited to more than 1.80%.For this lower limit, do not have on metallurgy, technical critical meaning, can embody The present invention as the excellent specific property of purpose in the range of, limit for the feature of clear and definite composition.In order to improve characteristic, can be by Its lower limit is set to 1.85% or 1.90%.Mn is also cheap element, it is desirable to do one's utmost to use Mn.But, when Mn amount is too much, encourage The center segregation of continuous casting plate blank and microscopic segregation, form the embrittlement region of local thus damage mother metal or welding heat affected The probability of the toughness in portion increases, and therefore, is limited in less than 2.20%.In order to improve the toughness of mother metal or welding heat affected zone, Its upper limit can be set to 2.15% or 2.10%.
Below P:0.008%, below S:0.005%
P, S contain as inevitable impurity, and from base metal tenacity, HAZ toughness, a small amount of situation of both of which is relatively Good, but, there is also the restriction in commercial production, respectively using 0.008%, 0.005% as the upper limit.In order to obtain preferably HAZ toughness, can be set to 0.006%, 0.005% or 0.004% by the upper limit of P respectively, the upper limit of S is set to 0.004%, 0.003% or 0.002%.P, S are inevitable impurity, it is not necessary to the lower limit of regulation P, S.If necessary, it is also possible to will The lower limit of P, S is set to 0%.
Cu:0.40%～0.70%
Cu makes the intensity of mother metal improve, and on the other hand, the degradation of the toughness of mother metal and welding heat affected zone is less, because of This is useful element.In the present invention as in the extra-high tension steel of target, preferably add more than 0.40%.In order to improve mother metal Intensity, its lower limit can be set to 0.45%, 0.50% or 0.55%.When Cu is more than 0.70%, demonstrate that precipitation-hardening is existing As, the material of steel, particularly intensity the most significantly change.Therefore, in the present invention, as Strength Changes the most continuously The scope controlled, is limited to less than 0.70%.By Cu amount is limited to less than 0.7%, mutually work with Ni described later amount, The effect that the danger that Cu crackle when having hot rolling occurs almost disappears.As required, its upper limit can be set to 0.65%, 0.60% or 0.55%.
Ni:0.80%～1.80%
[Ni]/[Cu] ＞ 2.0 formula 1
Ni is known as high toughening element, and the deterioration of the toughness of welding heat affected zone is few, have make mother metal intensity, The effect that toughness improves.Therefore, Ni is exceedingly useful element in the present invention such extra-high tension steel.Particularly at this In the chemical composition of bright such extremely low carbon, need to utilize alloying element compensation intensity, at least need containing more than 0.80% Ni.In order to improve the toughness of welding heat affected zone, its lower limit can be set to 0.90%, 1.00%, 1.05% or 1.10%.Separately On the one hand, Ni is also the alloy of high price, and content is preferably limited to the irreducible minimum of necessary characteristic such as available intensity, toughness etc..Examine Considering in the case of the intensity and maximum thickness of slab (100mm) of the target as the present invention, maximum demand is 1.80%, it is set to The upper limit, it is clear that be not the upper limit in terms of characteristic or metallurgy.As required, can by its ceiling restriction 1.75%, 1.70%, 1.65%, 1.60%, 1.55% or 1.50%.It addition, as it has been described above, in the steel of the present invention containing slightly many Cu, In order to suppress the Cu crackle of strand, Ni containing have more than Cu amount 2.0 times be effective, in claim 1, be defined to [Ni]/ [Cu] ＞ 2.0.
Nb:0.005%～0.015%
Nb be the austenite non-recrystallization temperature province in rolling process is expanded to high-temperature area, enjoy to tissue The element that miniaturization effective controlled rolling effect aspect is useful.The miniaturization of tissue is make that intensity, toughness all improves effective Means.Reliably enjoy the aspect of this effect, need at least to contain 0.005%.As required, its lower limit can be set to 0.006%, 0.007% or 0.008%.Manifest the Nb of such effect exceedingly useful to mother metal in welding heat affected zone also Make hardening increase, encourage MA generation etc., its toughness is harmful to.Therefore, it is necessary to the upper limit is suppressed 0.015%.In order to improve The toughness of welding heat affected zone, it is also possible to its upper limit is set to 0.013%, 0.011% or 0.010%.
Mo:0.05%～0.25%
Mo is extremely effective from the viewpoint of the intensity improving mother metal, at the high-strength steel sheet of the such thickness of the present invention In be indispensable element.Particularly in the present invention using B, by containing both simultaneously, show further Hardenability improves effect.In order to enjoy the excellent effect of such Mo, at least need containing 0.05%.In order to reliably play This hardenability improves effect, and its lower limit can be set to 0.07%, 0.09%, 0.11% or 0.13%.But, due to effect Greatly, thus too much interpolation makes hardening significantly improve, and significantly encourages MA and generates, accordingly, it would be desirable to be limited in less than 0.25%. In order to suppress MA to generate, it is also possible to its upper limit is set to 0.23%, 0.21%, 0.19% or 0.17%.
Ti:0.005%～0.015%
[N]-[Ti]/3.4 >=0% formula 2
The present invention is the Ti dexidized steel without Al.For the necessity in the deoxidation of steel, and in order to make Ti oxide generate, Make Intragranular Acicular Ferrite generate with it for core in welding heat affected zone, make microscopic structure miniaturization, at least need containing Ti: 0.005%.In order to improve the toughness of welding heat affected zone, it is also possible to its lower limit is set to 0.006% or 0.007%.But, contain Amount increases, and when becoming surplus relative to N in stoichiometry, the superfluous Ti after nitride is formed generates TiC, makes sweating heat shadow The probability of the toughness deterioration in sound portion increases, therefore using 0.015% as the upper limit.Additionally, meanwhile, prevent TiC from doing one's utmost From the viewpoint of generation, in claim 1, as the stoichiometric relation with N, it is defined as representing N superfluous (Ti is not enough) [N]-[Ti]/3.4 >=0%.It addition, for Zhun Que, it should also consider the consumption of the Ti that deoxidation causes, but, it is to avoid numerous Miscellaneous, experimentally confirm essentially without big impact simultaneously.In order to formula 2 is set to more than 0%, it is also possible to the upper limit of Ti is set It is 0.013%, 0.012%, 0.011% or 0.010%.
B:0.0004%～0.0020%
FB=[B]-0.77 × ([N]-0.29 × ([Ti]-2 × ([O]-0.89 × [Al]))) >=0.0003% Formula 3
B is one of important element in the present invention.It is very big that the hardenability of B improves effect, by using B, can significantly press down Alloyage element.Content for this B at least needs 0.0004%.As required, it is also possible to its lower limit is set to 0.0005%, 0.0006% or 0.0007%.But, it is only insufficient by regulation B content.This is because for the hardenability using B, Need to make it exist with solid solution condition.B easily forms nitride, also becomes important with the stoichiometric balance of N.But, by Higher than B in the nitride Forming ability of Ti, therefore also allow for this point, in claim 1, be defined as FB=[B]- 0.77 × ([N]-0.29 × ([Ti]-2 × ([O]-0.89 × [Al]))) >=0.0003%.About the upper limit, even if containing needing More than measuring, effect is the most saturated, therefore, inventor as the characteristic of steel is not produced dysgenic scope through experimental In the scope that ground confirms, it is set to 0.0020%, but, may not have critical meaning.As required, it is also possible to its upper limit is set to 0.0018%, 0.0016%, 0.0015% or 0.0014%.
In order to ensure the B (effective B) existed with solid solution condition in steel, find to need the expression defined in above-mentioned formula 3 The most above-mentioned FB of parameter of effectively B amount is limited in more than 0.0003%.In order to more effectively use B, it is also possible to above-mentioned FB is set to More than 0.0004% or 0.0005%.
The upper limit of FB=[B]-0.77 × ([N]-0.29 × ([Ti]-2 × ([O]-0.89 × [Al]))) does not has spy Do not limit, but, limited scope by each element and naturally limited.
Wherein, in above-mentioned formula 3, when the item of ([O]-0.89 × [Al]) is less than 0, by ([O]-0.89 in above-mentioned formula 3 × [Al]) item be set to 0 to calculate above-mentioned FB.
Additionally, in above-mentioned formula 3, when the item of ([Ti]-2 × ([O]-0.89 × [Al])) is less than 0, by above-mentioned formula 3 The item of ([Ti]-2 × ([O]-0.89 × [Al])) be set to 0 to calculate above-mentioned FB.
And then, in above-mentioned formula 3, the item of ([N]-0.29 × ([Ti]-2 × ([O]-0.89 × [Al]))) is less than 0 Time, the item of ([N]-0.29 × ([Ti]-2 × ([O]-0.89 × [Al]))) in above-mentioned formula 3 is set to 0 above-mentioned to calculate FB。
And then, when FB≤0, if FB=0.
It addition, above-mentioned formula 3 is to pass through stoichiometric proportion on the basis of the intensity of the adhesion considered between each element (effective B measures to ask the solid solution B in the steel obtained to measure；FB) formula.Although need not specify especially the upper limit of above-mentioned FB, but It is to be set to 0.0010%.
Finding after research further, the parameter risen as the HAZ hardness avoiding being caused by B, preferably by defined in formula 5 B parameter Bp is set to 0.09%～0.30%.
Bp=(884 × [C] × (1-0.3 × [C]2)+294) × FB formula 5
It addition, Bp is the empirical formula resolving derivation in being tested by the molten steel in substantial amounts of laboratory, by (being measured by C The maximum hardness of anticipation) × (contribution of FB) carried out parametrization.FB is the most, and HAZ hardness the most easily increases, particularly to this CTOD characteristic have big impact.When Bp is more than 0.30%, significant hardness is sometimes occurred to rise in welding penetration line (FL) portion, Find desired value i.e. more than the 0.25mm in order to meet CTOD characteristic, be preferably limited to less than 0.30%.As required, it is also possible to The upper limit of Bp is set to 0.27% or 0.25%.In the welding steel that embodiment relates to, when FB is more than 0.0003%, Bp must Being so more than 0.09%, therefore, Bp is to obtain the target as welding steel of the present embodiment less than 0.09% The region of effect of solid solution B, thus, it is also possible to Bp is set to more than 0.09%.As required, it is also possible to the lower limit of Bp is set It is 0.12% or 0.15%.
N:0.0020%～0.0060%
N is the element inevitably contained in steel-making, and when being reduced to more than necessary amount, steel-making load is high, in industry In production the most preferred.N forms nitride by adding Ti, and this nitride is at high temperature stable, therefore has at steel During heating before the hot rolling of material or thick from the growth of the austenite crystal of welding molten thread welding heat affected zone slightly away The effect of bigization pinning, thus, it is preferable to containing more than 0.0020%.But, time too much, as it has been described above, be combined formation nitridation with B The probability of thing increases, and the hardenability that can weaken B improves effect.Go out from absolute magnitude and the stoichiometric relation of above-mentioned B, Ti Sending out, the upper limit is restricted naturally, but, in addition, in the case of more than 0.0060%, produce when steel billet manufactures Surface blemish, therefore, is set to 0.0060% by the upper limit.It is preferably less than 0.0055%, more preferably less than 0.005%.
O:0.0015%～0.0035%
From the generative nature of the Ti oxide generating core as Intragranular Acicular Ferrite in welding heat affected zone, O is necessary It is more than 0.0015%.But, when O is too much, the site of oxide and number become excessive, as the generation starting point of brittle break The probability worked improves, and as result, makes toughness deteriorate, accordingly, it would be desirable to by ceiling restriction 0.0035%.In order to better Obtain well the toughness of stable welding heat affected zone, be preferably set to less than 0.0030%, be more preferably set to less than 0.0028% Or less than 0.0025%.
Al:0%～0.004%
In the present invention without the Ti deoxidation of Al, Al is one of inevitable impurity.In claim 1, still limit Although determining the upper limit is due to inevitable, but content more than 0.004% time, the composition change of oxide, it is impossible to as intracrystalline ferrum The probability that the core of ferritic works improves, and therefore, is limited to less than 0.004%.As required, it is also possible to its upper limit is set to 0.003% or 0.002%.Need not the lower limit of special provision Al amount, its lower limit is 0%.But, in the refining process of steel, Sometimes Al it is mixed into, it is also possible to its lower limit is set to 0.0001% or 0.0003%.
In steel of the present embodiment, in addition to mentioned component, remainder comprises ferrum (Fe) and impurity.This In, impurity refers to, when industrially manufacturing steel, because of the raw material of Ore or waste material etc. or the various factors of manufacturing process not The composition that can be mixed into avoiding, is not producing the composition allowed in the range of harmful effect to the present invention.
In steel plate of the present embodiment, in addition to mentioned component, it is also possible to contain further Cr, V, Ca, Mg and One kind or two or more in REM.The lower limit of these compositions need not specify especially, and its lower limit is 0%.Even if additionally, these Alloying element adds wittingly, or being mixed into the form of impurity, as long as its content is within the scope of the claims, and these steel Just it is construed in scope of the presently claimed invention.
Cr:0%～0.30%
Cr, in order to reduce the CTOD characteristic of welding heat affected zone, is set to less than 0.30%.In order to improve this CTOD characteristic, also Its upper limit can be set to 0.20%, 0.15%, 0.10% or 0.05%.Need not the lower limit of regulation Cr amount especially, under it It is limited to 0%.But, also have situation about being mixed into as impurity, it is also possible to its lower limit is set to 0.001%.
V:0%～0.06%
V is the effective element of the raising for strength of parent.But, during more than 0.06%, infringement CTOD characteristic, therefore, As will not significantly damage the scope of CTOD characteristic, the upper limit is set to less than 0.06%.In order to ensure more excellent CTOD characteristic, Its upper limit can also be set to 0.04%, 0.02% or 0.01%.Need not the lower limit of the content of regulation V, its lower limit is 0%. Also there is situation about being mixed into as impurity, it is also possible to its lower limit is set to 0.001%.
Mg:0%～0.0050%
Mg can contain as required.During containing Mg, generate the fine oxide containing Mg, therefore, for γ particle diameter Miniaturization is effective.But, when the content of Mg is more than 0.0050%, oxide becomes too much, occasionally results in ductility reduction, because of This, be set to 0.0050% by its upper limit.Can also by its ceiling restriction be 0.0030%, 0.0020%, 0.0010% or 0.0003%.Need not the lower limit of the content of regulation Mg, its lower limit is 0%.
In welding steel of the present embodiment, in addition to mentioned component, in order to improve steel self further Intensity, toughness etc., or as the impurity from auxiliary materials such as waste materials, can be containing following alloying element.
Ca is mixed into as impurity sometimes, therefore, it can be set to its upper limit 0.0010%, 0.0005% or 0.0003%.
REM (Rare Earth Metal) is mixed into as impurity, sometimes accordingly it is also possible to its upper limit be set to 0.0010%, 0.0005% or 0.0003%.Here, REM be 15 kinds of elements of lanthanide series plus Y and Sc obtain 17 kinds The general name of element.
The toughness of Sb infringement HAZ, accordingly it is also possible to be set to 0.03% by the upper limit of the content of Sb.In order to make HAZ toughness carry High, it is also possible to the upper limit of the content of Sb is set to 0.01%, 0.005%, 0.003% or 0.001%.
Due to the toughness of As and Sn infringement HAZ, accordingly it is also possible to the upper limit of the content of As and Sn is set to 0.02%.Root According to needs, it is also possible to the upper limit of the content of As and Sn is set to 0.005%, 0.003% or 0.001%.In addition, it is not necessary that especially The lower limit of ground regulation Ca, REM, Sb, As, Sn, its lower limit is 0%.
Additionally, in order to improve intensity and toughness, it is also possible to Pb, Zr, Zn and W are set to less than 0.1%, 0.01% or Less than 0.005%.Need not determine especially their lower limit, be 0%.
Co contains as impurity sometimes in Ni.Co damages HAZ toughness, accordingly it is also possible to the upper limit of the content of Co set It is 0.05% or 0.002%.Need not determine its lower limit especially, its lower limit is 0%.
On the basis of various elements as defined above, need further exist for the following formula of alternatively referred to as overall control The P of 4CMIt is limited in suitable scope.It addition, following formula 4 is as welding crack sensibility index (PCMFormula known to). Even if this is because each element all restrictions scope, in the case of all lower limits or the upper limit, hardenability becomes not enough Or superfluous, in the former case, high intensity, in the latter case, sweating heat cannot be realized in the case of steel plate Affect the hardening in portion, MA generates and becomes superfluous, it is impossible to guarantee toughness.In order under the present invention thickness of slab as target stably Guarantee intensity and stably guarantee the toughness of welding heat affected zone, needing PCMIt is set to 0.18～0.23%.
PCM=[C]+[Si]/30+ [Mn]/20+ [Cu]/20+ [Ni]/60+ [Cr]/20+ [Mo]/15+ [V]/10+5 [B] Formula 4
Here, quality % contained during each element is steel.
And then, it is known that in order to meet CTOD characteristic, make to be calculated as the number of oxide of more than 2 μm for 20 with diameter of equivalent circle Individual/mm2The Ti oxide being calculated as 0.05～0.5 μm with diameter of equivalent circle in steel below and as phase change core has 1.0 × 103 ～1.0 × 105Individual/mm2It is important.Diameter of equivalent circle is that the oxide number of more than 2 μm is more than 20/mm2Time, this oxidation Thing becomes the starting point destroying generation, CTOD deterioration in characteristics.Additionally, the Ti oxide that diameter of equivalent circle is 0.05～0.5 μm is less than 1.0×103Individual/mm2Time, the Ti oxide number as intracrystalline phase transformation ferritic generation core becomes insufficient, more than 1.0 × 105Individual/mm2Time, Ti oxide becomes the starting point destroying generation, and in the case of any one, CTOD characteristic all deteriorates.
On the basis of the composition of steel as defined above, for the high-strength steel sheet that stably commercial production is thick, also need Manufacture method to be limited.
Then, for the welding manufacture method of extra-high tension steel, an example is described.
Steel of the present invention is the most preferably manufactured by continuous casting process.Its reason is, the solidification cooling of molten steel is fast, Fine Ti oxide and Ti nitride can be generated in a large number in slab.Manufacturer at welding steel of the present embodiment In method, preferably the average cooling rate of central part to the strand of 800 DEG C near freezing point is set to more than 5 DEG C/min.Its Reason is, obtains 20/mm in steel2The number of the following oxide being calculated as more than 2 μm with diameter of equivalent circle and obtaining 1.0×103～1.0 × 105Individual/mm2The Ti oxide being calculated as 0.05～0.5 μm with diameter of equivalent circle.The rate of cooling of strand In the case of 5 DEG C/min, it is difficult to obtain fine oxide, thick oxide increases.On the other hand, averagely cool down Speed is even more than 50 DEG C/min, and the quantity of fine Ti oxide also will not be significantly increased, and even makes manufacturing cost increase, Accordingly it is also possible to average cooling rate to be set to less than 50 DEG C/min.
It addition, the average cooling rate of the central part of strand can be by measuring the rate of cooling of casting billet surface, by passing Heat calculates and obtains.Additionally, average cooling rate can be asked by Calculation of Heat Transfer by measuring casting temperature or cooling water inflow etc. Go out.
When the rolling of slab, it reheats temperature and is preferably set to 1000～1100 DEG C.Surpass this is because reheat temperature When crossing 1100 DEG C, Ti nitride coarsening, the toughness deterioration of mother metal maybe cannot expect that HAZ toughness improves effect.Additionally, be less than In the case of the reheating temperature of 1000 DEG C, rolling counteracting force increases, and rolling load improves, and hinders productivity ratio.
After reheating, need to be manufactured by TMCP.First, accumulation drafts is carried out at a temperature of more than 950 DEG C It it is the rolling of more than 30%.Rolling in high-temperature area is in order to by the thick austenite entirety particulate of heated state Changing, accumulation drafts is the highest more preferred, but, restricted by slab thickness and subsequent rolling condition.The rolling of the condition of high temperature Tissue actually cannot be held, but, confirming in the factory and laboratory experiment of the present inventor, accumulation drafts is 30% Time above, as long as rolling-cooling condition hereafter is in suitable scope, then stability of characteristics.
Then, at a temperature of 720～950 DEG C, accumulation drafts is more than 40%, and accumulation overall reduction is more than 60%, Rolling is terminated at a temperature of 700～750 DEG C.These temperature provinces are about the non-recrystallization temperature province of austenite.But, In the case of thick material, having Temperature Distribution in thickness of slab direction, the temperature near thickness of slab central part is high, therefore, the most again The rolling of crystallization temperature region is insufficient.Therefore, present invention limiting temperature in two stages, accumulation drafts.720～950 At a temperature of DEG C accumulation drafts be the rolling of more than 40% be to need from table back surface layer minimum to substantially thickness of slab 1/4 The austenite non-recrystallization amount of rolling wanted.And then, accumulation overall reduction is set to more than 60%, at a temperature of 700～750 DEG C Terminate rolling be in order to also can carry out at thickness of slab central part tissue miniaturization degree imparting austenite non-recrystallization region in Pressure.Although thickness of slab central part relatively for drafts in austenite non-recrystallization region less, but, with the present invention Suitable pressure under the relatively low heating-up temperature of middle restriction, high-temperature area is worked mutually, it is possible to good strong can ensure that Degree, the degree of tough sexual balance will organize miniaturization.Under departing from these rolling conditions limiting scope, the most true Accept the degraded toughness of thickness of slab central part.
And then, the cooling after rolling needs to start within 80 seconds after the end of rolling water-cooled, and is cooled to less than 280 DEG C. Preferably start water-cooled rapidly after rolling, but, in large-scale actual production equipment, from milling train end to cooling device, need one The time of delivery determining degree is inevitable.In this case, to rolling after cooling let cool period ferrite Separating out, this is undesirable in intensity, and, due to the precipitation in letting cool, the probability height that this ferrite is thick, this is tough Also it is undesirable in property.Accordingly, it would be desirable to start water-cooled after the end of rolling within 80 seconds.Within being preferably 60 seconds.Water-cooled needs Even if being cooled to till the thickness of slab central part becoming heat transfer speed limit is also fully completed phase transformation, accordingly, it would be desirable to be cooled to 280 DEG C Below.Even if it addition, in order to also enjoy acceleration cooling effect, preferably in the present invention as the thickness of slab central part of the thick material of target With substantially 1.2m3/m2/ point more than water yield density cool down.
After cooling, it is necessary to be tempered within the temperature range of 400～550 DEG C further.By carrying out temper, no It is only capable of improving the intensity of mother metal, tough sexual balance, moreover it is possible to the most stably control.And then, also can relax inequality during cooling One property, the elimination for the residual stress in steel is the most effective, they the change of shape during cut-out caused also is pressed down System.In the case of less than the tempering at 400 DEG C, these effects are little, and in the case of the tempering more than 550 DEG C, intensity reduces Greatly, it is difficult to guarantee the present invention high intensity as target.
It addition, above-mentioned temperature is all steel surface temperature.
As it has been described above, welding manufacturer's rule of extra-high tension steel of the tenacity excellent of weldability, welding heat affected zone After the steel billet of the composition of steel having described in above-mentioned (1) or strand are heated to the temperature of 1000～1100 DEG C, will be at 950 DEG C Accumulation drafts at a temperature of above is set to more than 30%, is set to by the accumulation drafts at a temperature of 720～950 DEG C More than 40%, accumulation overall reduction is set to more than 60%, at a temperature of 700～750 DEG C, terminates rolling, after the end of rolling Start water-cooled within 80 seconds, be cooled to less than 280 DEG C, then, be tempered under the temperature range of 400～550 DEG C further.
Embodiment
Hereinafter, based on example and comparative example, the present invention will be described.
Manufactured the steel plate of various composition of steel by converter, continuously casting, slab operation, have rated mother metal characteristic and weldering Connect the toughness of heat affected zone.
Welding is set to: by usually used as test welding use submerged arc welding (submerged arc welding) method, The vertical multilamellar that mode weld heat input at " レ " type groove is 4.5kJ/mm welding is become according to welding penetration line (FL). About the toughness evaluation of welding heat affected zone, carry out according to API (American Petroleum Institute) standard RP The CTOD test of 2Z and BS (British Standards) standard 7448.Gap position is being referred to as CGHAZ (Coarse Grain HAZ) welding molten thread at, at test temperature-10 DEG C, implement 6 tests respectively.
Shown in table 1-1～table 1-4 shown in the chemical composition of steel, table 2-1～table 2-4 in manufacturing condition, steel Oxide number and mother metal characteristic, the toughness (CTOD characteristic) of welding heat affected zone.Steel plate (the present invention manufactured in the present invention Steel: composition of steel No.1～15,29～51 and example No.A1 of the present invention～L2) in, yield strength (YS) is in the position of steel plate 1/4 thickness The place of putting is shown as 526～611Mpa, is shown as 516～594Mpa in the position of steel plate 1/2 thickness, and tensile strength (TS) is at steel The position of plate 1/4 thickness is shown as 616～680Mpa, is shown as 604～656Mpa in the position of steel plate 1/2 thickness, closes Fracture transition (vTrs) result of the test in base metal tenacity is shown as-48～-81 DEG C in the position of steel plate 1/4 thickness, The position of steel plate 1/2 thickness is shown as-40～-68 DEG C, and the minimum CTOD value of-10 DEG C is shown as 0.29～0.94mm Good destruction toughness.Additionally, from the P of steel of the present inventionCMValue, CTOD value show good weldability.
In contrast, depart from the present invention restriction scope comparative example steel plate (compare steel: composition of steel No.16～28,52 ～62 and comparative example No.a～strength of parent x) low, or base metal tenacity is poor, or the poor toughness of welding heat affected zone.
That is, comparative example a～c, comparative example e～o, comparative example q～v composition of steel outside the scope of the invention, be not meet on State the steel of engineering properties.The comparative example f of particularly composition of steel No.21 is unsatisfactory for Ni/Cu ＞ 2.0, therefore, produces when hot rolling and splits Stricture of vagina, manufactures and becomes difficulty.And then, composition of steel within the scope of the present invention, FB or PCMValue comparative example d outside the scope of the invention, W, x are unsatisfactory for FB >=0.0003% or PCMValue is more than 0.18% and less than 0.23%, and therefore, strength of parent is low or high, Or base metal tenacity is poor, or the poor toughness of welding heat affected zone.
Table 1-2
Table 1-4
Table 2-1
Table 2-2
Table 2-3
Table 2-4
Industrial applicability
According to the present invention, the extra-high tension steel of the tenacity excellent of weldability, welding heat affected zone can be provided at a low price, in sea While the maximization of the welded structures such as ocean works, safety can be improved further.

Claims (7)

1. a steel plate, it is characterised in that its chemical composition is: in terms of quality %,
C:0.015%～0.045%,
Mn:1.80%～2.20%,
Cu:0.40%～0.70%,
Ni:0.80%～1.80%,
Nb:0.005%～0.013%,
Mo:0.06%～0.25%,
Ti:0.005%～0.015%,
B:0.0004%～0.0020%,
N:0.0020%～0.0060%,
O:0.0015%～0.0035%,
Si:0%～0.40%,
Below P:0.008%,
Below S:0.005%,
Al:0%～0.004%,
Cr:0%～0.30%,
V:0%～0.06%,
Mg:0%～0.0050%,
Remainder: ferrum and impurity,
Value represented by following formula 1 more than 2.0,
Value represented by following formula 2 is more than 0%,
FB represented by following formula 3 is more than 0.0003%,
Welding crack sensibility index i.e. P represented by following formula 4CMValue is more than 0.18% and less than 0.23%,
At the thickness of slab central part in cross section, thickness of slab direction, diameter of equivalent circle be the oxide particle of more than 2 μm be 20/mm2Hereinafter, And the Ti oxide that diameter of equivalent circle is 0.05～0.5 μm is 1.0 × 103～1.0 × 105Individual/mm2,
[Ni]/[Cu] formula 1
[N]-[Ti]/3.4 formula 2
FB=[B]-0.77 × ([N]-0.29 × ([Ti]-2 × ([O]-0.89 × [Al]))) formula 3
PCM=[C]+[Si]/30+ [Mn]/20+ [Cu]/20+ [Ni]/60+ [Cr]/20+ [Mo]/15+ [V]/10+5 [B] formula 4
Here, [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V], [Ti], [B], [N], [O], [Al] refer respectively to The content represented with quality % of C, Si, Mn, Cu, Ni, Cr, Mo, V, Ti, B, N, O, Al,
Wherein, in described formula 3, when the item of ([O]-0.89 × [Al]) is less than 0, by described formula 3 ([O]-0.89 × [Al]) item be set to 0 to calculate described FB,
Additionally, in described formula 3, when the item of ([Ti]-2 × ([O]-0.89 × [Al])) is less than 0, by described formula 3 The item of ([Ti]-2 × ([O]-0.89 × [Al])) is set to 0 to calculate described FB,
And then, in described formula 3, when the item of ([N]-0.29 × ([Ti]-2 × ([O]-0.89 × [Al]))) is less than 0, will The item of ([N]-0.29 × ([Ti]-2 × ([O]-0.89 × [Al]))) in described formula 3 is set to 0 to calculate described FB,
And then, when FB≤0, if FB=0.
Steel plate the most according to claim 1, it is characterised in that and then, the Bp represented by following formula 5 be more than 0.09% and Less than 0.30%,
Bp=(884 × [C] × (1-0.3 × [C]2)+294) × FB formula 5.
Steel plate the most according to claim 1 and 2, it is characterised in that and then, in described chemical composition, in terms of quality %, Si It is limited in less than 0.15%.
Steel plate the most according to claim 1 and 2, it is characterised in that and then, in described chemical composition, in terms of quality %, Mg It is limited in less than 0.0003%.
Steel plate the most according to claim 1 and 2, it is characterised in that thickness of slab is more than 50mm and below 100mm, and tension is strong Degree is more than 600MPa and below 700MPa, and yield strength is more than 500MPa and below 690MPa.
Steel plate the most according to claim 1 and 2, it is characterised in that and then, in described chemical composition, bag in terms of quality % Containing Ni:1.05%～1.80%.
Steel plate the most according to claim 1 and 2, it is characterised in that and then, in described chemical composition, bag in terms of quality % Containing Mo:0.06%～0.19%.
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