CN101514428A - Steels with excellent toughness for welding heat affected section and method of producing the same - Google Patents

Steels with excellent toughness for welding heat affected section and method of producing the same Download PDF

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Publication number
CN101514428A
CN101514428A CNA200910009654XA CN200910009654A CN101514428A CN 101514428 A CN101514428 A CN 101514428A CN A200910009654X A CNA200910009654X A CN A200910009654XA CN 200910009654 A CN200910009654 A CN 200910009654A CN 101514428 A CN101514428 A CN 101514428A
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oxide compound
contain
steel
following
rem
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出浦哲史
杉村朋子
冈崎喜臣
名古秀德
太田裕己
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Kobe Steel Ltd
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Kobe Steel Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C2202/00—Physical properties

Abstract

Provided steels with excellent HAZ toughness even at high-heat input welding and method of producing the same. As the composition of steels, especially containing Zr, REM and/or Ca and conforming to conditions as follow, (a) the steels are oxidate containing Zr, REM and/or Ca, (b) when measuring the composition of the whole oxidate contained in the steels scaling as alone oxidate conforming to ZrO2:5-50%, the REM oxidate: 10-50% and/or CaO:5-50%, and (C) is contained in the whole oxidate of the steels, number of oxidate with 0.1-2.0[mu]m equivalent circular diameter is more than 120 per square millimeter, number of oxidate with exceed 5.0 [mu]m equivalent circular diameter is less than 5 per square millimeter.

Description

The steel of the tenacity excellent of welding heat affected zone and manufacture method thereof
Technical field
The present invention relates to be used in the steel of bridge and high-rise, boats and ships etc., the steel and the manufacture method thereof of the tenacity excellent of the welding heat affected zone of particularly high heat energy input welding (below, abbreviate " HAZ " as).
Background technology
In recent years, along with the maximization of above-mentioned various welded structures, become inevitable as the welding of the Plate Steel more than the thickness of slab 50mm.For this reason, in all areas, be purpose all to improve welding procedure efficient and to reduce construction cost, be the situation of pointing to high heat energy input welding.But, when carrying out high heat energy input welding, HAZ is heated to slow cooling behind the pyritous austenite region, and the austenite grain is grown up when therefore having heating, the HAZ that the grain boundary ferrite that generates from austenite grain boundary during slow cooling causes organizes thickization, the problem of the easy deterioration of toughness of this part.Thus, even wish to establish a kind of high heat energy input welding of implementing, also can guarantee the technology of the toughness (hereinafter referred to as " HAZ toughness ") among the HAZ high-levelly.
As being applicable to that improving the HAZ flexible represents technology, can exemplify by promote inclusion with oxide compound and nitride etc. be cause the intracrystalline ferrite transformation organize the miniaturization technology.This technology by being present in the described inclusion of intracrystalline, makes fine ferrite transformation tissue growth for when postcooling is finished in welding, suppresses thick ferritic generation, guarantees HAZ toughness thus.Therefore in described inclusion,, carry out high heat energy input or superelevation heat energy input welding also can be guaranteed excellent HAZ flexible advantage even have particularly because oxide compound is heat-staple.
As the technology of utilizing oxide compound, in patent documentation 1, propose by control O concentration and Ca concentration, disperse imperceptibly to make MnS compound separate out contain the Ti oxide compound, promote with it be the technology of the intracrystalline ferrite transformation (that is the thick grain boundary ferrite generation of inhibition) of nuclear.In patent documentation 2, disclose and relate to compound interpolation Ti and Mn system, and by generating the complex body that contains Ti oxide compound and MnS as the intracrystalline ferrite core, and obtain the technology of the welding of HAZ tenacity excellent with high tension steel.In patent documentation 3, disclose oxide compound and/or CaO and ZrO by the REM that generates specified amount 2, obtain the technology of the steel of HAZ tenacity excellent.
[patent documentation 1] spy opens flat 6-200319 communique
[patent documentation 2] spy opens flat 9-157787 communique
[patent documentation 3] spy opens the 2007-100213 communique
Summary of the invention
In view of above-mentioned condition, the objective of the invention is to, even a kind of steel and manufacture method thereof of HAZ tenacity excellent when carrying out high heat energy input welding is provided.
The steel of tenacity excellent that can solve the welding heat affected zone of the present invention of above-mentioned problem contain: the C:0.02～0.12% (meaning of quality %, down together), Si:0.50% following (containing 0%), Mn:1～2.0%, Ti:0.005～0.10%, P:0.030% following (containing 0%), S:0.020% following (containing 0%), Al:0.05% following (containing 0%), N:0.0040～0.030%, 0:0.0005～0.010%, and contain: Zr:0.0002～0.050% and REM:0.0002～0.050% and/or Ca:0.0005～0.010%, surplus is made of iron and unavoidable impurities, and have following purport: (a) described steel comprise the oxide compound that contains Zr and REM and/or Ca, when (b) composition of the whole oxide compounds that comprise in the described steel of mensuration converts as oxide alone, satisfy ZrO 2: 5～50%, the oxide compound of REM (is M when representing REM with the mark of M 2O 3): 10～50% and/or CaO:5～50%, and (c) among the whole oxide compounds that in described steel, comprise, diameter of equivalent circle is every square millimeter more than 120 at the oxide compound of 0.1～2.0 μ m, and the oxide compound that diameter of equivalent circle surpasses 5.0 μ m is every square millimeter below 5.
Described steel also can contain the element with inferior other,
(1) Ni:1.5% following (not containing 0%) and/or Cu:1.5% following (not containing 0%);
(2) Cr:1.5% following (not containing 0%) and/or Mo:1.5% following (not containing 0%);
(3) Nb:0.1% following (not containing 0%) and/or V:0.1% following (not containing 0%);
(4) B:0.0050% following (not containing 0%).
Above-mentioned steel can be by following operation manufacturing, and these process sequences comprise: (1) adjusts the operation that dissolved oxygen content is 0.0010～0.0060% molten steel; (2) stirring described molten steel makes the oxide compound come-up separation in the molten steel thus whole oxygen amounts are adjusted into 0.0010～0.0070% operation; (3) add the operation of adding Zr, REM and/or Ca again behind the Ti.After described operation (3), can also comprise that (4) stir the operation of molten steel in the scope that is no more than 40 minutes.
According to the present invention, generate the oxide compound (ZrO of specified amount as the nuclear of intracrystalline ferrite transformation 2, the oxide compound of REM and/or the oxide compound of CaO, also preferably contain Ti 2O 3Oxide compound), and also suitably control the size and the number (size-grade distribution) of the oxide compound that exists in the steel, particularly have a mind to control the generation of the thick oxide compound that causes the reduction of HAZ toughness, can improve HAZ toughness even therefore under high heat energy initial conditions, weld also.
Embodiment
The present invention has changed disclosed intracrystalline ferrite transformation technology in the patent documentation 3, even relate to the technology that also can obtain the steel of HAZ tenacity excellent under higher heat energy initial conditions when welding.
As mentioned above, in patent documentation 3, disclose and utilized ZrO 2, the oxide compound of REM and/or CaO oxide compound as the steel of the nuclear (starting point) of intracrystalline ferrite transformation.Consider that described oxide compound is heat-staple, even for example owing to be exposed to for a long time under 1400 ℃ the high temperature, solid solution does not disappear yet, even therefore carry out high heat energy input welding or superelevation heat energy input welding, its performance is not lost yet.
And, discussion result according to present inventors, find that the whole oxide compounds in these steel (are not limited to become the above-mentioned oxide compound of the nuclear of intracrystalline ferrite transformation, with whole oxide compounds is object) size and number and the HAZ flexible improve have very dark related, if particularly will suppress in the thick oxide compound that diameter of equivalent circle surpasses 5.0 μ m is below 5, be roughly high heat energy input welding about 50kJ/mm even import heat, also can obtain the steel of HAZ tenacity excellent.The present invention finishes according to above-mentioned discovery.
In this manual in order to distinguish the oxide compound of the nuclear that becomes the intracrystalline ferrite transformation, that is, and " ZrO 2, REM oxide compound (be M when representing REM with M 2O 3) and/or CaO " oxide compound and steel in whole oxide compounds of comprising, for convenience of description, the former is called especially " ZrREM/Ca is an oxide compound ", the latter is called especially " all oxide compounds ".In addition, the essential composition (Zr, REM and/or Ca) that will constitute above-mentioned " ZrREM/Ca is an oxide compound " is called intracrystalline ferrite transformation karyogenesis element especially.In addition, in this manual, among the whole oxide compounds that in steel, contain, will be called " small oxide compound " at the oxide compound of 0.1～2.0 μ m in diameter of equivalent circle, on the other hand, will be called " thick oxide compound " in the oxide compound that diameter of equivalent circle surpasses 5.0 μ m.
According to the present invention, owing to significantly suppressed the number of thick oxide compound, (give after keeping for 5 seconds under 1400 ℃ the Heating temperature than disclosed HAZ toughness evaluation method in the patent documentation 3 even therefore carry out, by giving with 300 seconds from 800 ℃ of thermal cyclings that are cooled to 500 ℃, be determined at endergonic method in-40 ℃) big heat energy input welding, also can improve HAZ toughness (with reference to following embodiment).
[being oxide compound (a)] about ZrREM/Ca
At first, be that oxide compound describes to ZrREM/Ca as the starting point of intracrystalline ferrite transformation.Described ZrREM/Ca be the meaning of oxide compound for must contain the oxide compound of Zr, and contain any one of oxide compound of the oxide compound of REM or Ca, or contain the oxide compound of REM and the oxide compound of Ca simultaneously.The element (intracrystalline ferrite transformation karyogenesis element) that constitutes ZrREM/Ca and be oxide compound is Zr, REM and/or Ca, also can contain composition in the oxide compound forming element of Ti, Mn, Si, Al etc. and other the steel except that described.
Described ZrREM/Ca is the not restriction especially of existing way of oxide compound, can be used as the oxide alone that contains intracrystalline ferrite transformation karyogenesis element separately and exist, also can be used as the composite oxides that contain two or more intracrystalline ferrite transformation karyogenesis elements and exist.As the example of oxide alone, the oxide compound ZrO of Zr is for example arranged 2The oxide compound CaO of Ca; The oxide compound of REM is to be M when representing REM with the mark of M 2O 3, M 3O 5, MO 2Deng.In addition, these oxide compounds are aggegation and existing mutually also, and other compounds of sulfide and nitride etc. also can exist in the compound mode of separating out in the described oxide compound.
Described ZrREM/Ca is the oxide compound that oxide compound also preferably contains Ti.When having the oxide compound of Ti to exist, can promote the intracrystalline ferrite transformation, HAZ toughness further improves.The oxide compound of Ti can be used as oxide alone (Ti for example 2O 3, Ti 3O 5, TiO 2) exist, can be oxide compound with described ZrREM/Ca also exists in the mode of composite oxides.
The average composition of oxide compound [(b) about]
The composition of whole oxide compounds that steel of the present invention comprise in measuring steel satisfies ZrO during with mass conversion as oxide alone 2: 5～50%, the oxide compound of REM (is M when representing REM with the mark of M 2O 3): 10～50% and/or CaO:5～50%, thus as the nuclear of intracrystalline ferrite transformation and play a role effectively.If be lower than the lower value of each oxide compound, as the quantity not sufficient of the oxide compound of the ferritic product nucleus of intracrystalline, can not bring into play and improve the effect of HAZ flexible when then welding.On the other hand, as surpassing the higher limit of each oxide compound, thickization of oxide compound then, the number of the small oxide compound that effectively plays a role as the ferritic product nucleus of intracrystalline tails off, and can not effectively bring into play and improve the effect of HAZ flexible.
Described ZrO 2Be preferably more than 10%, more preferably more than 13%, more preferably more than 15%.On the other hand, the upper limit is preferably 45%, and more preferably 40%.
The oxide compound of described REM is preferably more than 15%, more preferably more than 20%, more preferably more than 30%.On the other hand, the upper limit is preferably 45%, and more preferably 40%.Also have, the meaning of the oxide compound of REM is when representing REM with M, in steel with M 2O 3, M 3O 5, MO 2Deng mode exist, be that the oxide compound with REM all is scaled M 2O 3The time amount.
Described CaO is preferably more than 10%, more preferably more than 15%, more preferably more than 18%.On the other hand, the upper limit is preferably 45%, and more preferably 40%.More preferably 30%.
Also have, the residual component that above-mentioned oxide compound is formed has no particular limits, and can enumerate the oxide compound (SiO for example of the oxide compound forming element that contains in the steel of the present invention 2And Al 2O 3, MnO etc.).The resultant of these oxide compounds is preferably and roughly is lower than 5%.
The mensuration of the composition of the whole oxide compounds that comprise in the steel is as described below, with EPMA (ElectronProb X-ray Micro Analyzer; Electron beam microprobe x-ray analysis meter) observes, the oxide compound of generally acknowledging in the viewing area is carried out quantitative analysis.Detailed condition determination describes in following embodiment hurdle.
The size-grade distribution of whole oxide compounds [(c) about]
Then, number and the size to whole oxide compounds of giving feature of the present invention (being not limited to described ZrREM/Ca is oxide compound, but the whole oxide compounds that exist in the steel) is illustrated.
The whole oxide compounds that contain in the steel of the present invention satisfy following relation: in the small oxide compound of diameter of equivalent circle 0.1～2.0 μ m is every square millimeter more than 120, and is every square millimeter below 5 in the thick oxide compound that diameter of equivalent circle surpasses 5.0 μ m.
Present inventors investigate in minute detail the size-grade distribution and the HAZ flexible relation of whole oxide compounds, particularly clear and definite following practical work: it is very dark related that diameter of equivalent circle is that small oxide compound and the HAZ toughness that thick oxide compound that surpasses 5.0 μ m and the input of high heat energy are welded of 0.1～2.0 μ m has, it is the number of small oxide compound that HAZ toughness is improved what very big contribution was arranged, the starting point that thick oxide compound becomes brittle rupture can cause the HAZ flexible to reduce, in addition, the small oxide compound that is lower than 0.1 μ m in diameter of equivalent circle is helpless to the raising HAZ flexible effect that the dispersion of oxide compound produces on substantially.Therefore, in order to improve HAZ toughness, the number of small oxide compound is preferably many as far as possible, because the number that becomes the thick oxide compound of heterogeneous pass with small oxide compound also has the tendency that becomes many, so need suitably control the number of small oxide compound and thick oxide compound.
The number of small oxide compound is preferably every square millimeter more than 200, and preferred number is every square millimeter more than 500, and further preferred number is every square millimeter more than 1000.
Thick oxide compound is few more good more, and preferred number is every square millimeter below 3, and preferred number is below 1, is preferably 0.For the number of the oxide compound beyond the above-mentioned size, the present invention does not do any restriction, and the oxide compound of controlling above-mentioned size can obtain desirable HAZ toughness to obtain affirmation by experiment.
So-called above-mentioned " diameter of equivalent circle " is the circular diameter that equates with area oxide compound that estimate, is to obtain confirming on the sightingpiston of infiltration type electron microscope (TEM).
Then, the one-tenth in the steel of the present invention (mother metal) is grouped into describes.Steel of the present invention, contain as basal component: C:0.02～0.12%, Si:0.50% following (containing 0%), Mn:1～2.0%, Ti:0.005～0.10%, P:0.030% following (containing 0%), S:0.020% following (containing 0%), Al:0.05% following (containing 0%), N:0.0040～0.030% and O (oxygen): 0.0005～0.010%, and contain: Zr:0.0002～0.050% and REM:0.0002～0.050% and/or Ca:0.0005～0.010%.It is described to be defined in the reasons are as follows of scope like this.
C is the element that can not be short of of guaranteeing steel (mother metal) intensity.In order to bring into play such effect, need contain more than 0.02%.Preferably contain more than the C:0.04%, more preferably more than 0.05%.Yet, surpass 0.12% when welding in HAZ the toughness deterioration of island martensite body (MA) a large amount of generations not only causing HAZ, also bring detrimentally affect to weldability.Therefore C is below 0.12%, is preferably below 0.1%, more preferably below 0.08%.
Si is the element that helps to guarantee steel strength by solution strengthening.Yet Si surpasses 0.50%, when welding in HAZ the toughness deterioration of island martensite body (MA) a large amount of generations not only causing HAZ, also bring detrimentally affect to weldability.Therefore Si is decided to be below 0.50%, is preferably below 0.3%, more preferably below 0.2%, more preferably below 0.18%.Also have, in order to ensure the intensity of steel, the Si of interpolation preferably contains more than 0.02%, more preferably more than 0.05%, can further preferably contain more than 0.1%.
Mn is the element that helps to improve steel (mother metal) intensity.In order to bring into play such effect effectively, need contain more than 1%.Mn is preferably more than 1.0%, more preferably more than 1.2%, can further preferably contain more than 1.4%.But, surpass 2.0%, then the weldability deterioration of steel (mother metal).Therefore Mn need be suppressed at below 2.0%.Be preferably below 1.8%, more preferably below 1.6%.
Ti generates the nitride of TiN etc. and the oxide compound of Ti in steel, be to help to improve HAZ flexible element.In order to bring into play such effect, Ti need contain more than 0.005%, is preferably more than 0.007%, more preferably more than 0.010%.But owing to can make the toughness deterioration of steel (former material) during excessive interpolation Ti, so Ti should be suppressed at below 0.10%.Ti is preferably below 0.07%, more preferably below 0.06%.
P is the element of easy segregation, and particularly segregation destroys crystal boundary in the crystal grain boundary in steel, makes HAZ toughness deterioration.Therefore P need be suppressed at below 0.030%.P is preferably below 0.02%, more preferably below 0.01%.In addition, P can contain about 0.001% usually inevitably.
S also is that segregation makes the toughness deterioration in the element of easy segregation, the particularly crystal grain boundary in steel equally with P.In addition, S combines with Mn and generates sulfide (MnS), is the deleterious element that makes the ductility deterioration of the toughness of mother metal and thickness of slab direction.Therefore S need be suppressed at below 0.020%.S is preferably below 0.015%, more preferably below 0.010%.In addition, S can contain about 0.0005% usually inevitably.
Al is the element that works as reductor.But excessive interpolation is reduced oxide and form thick Al oxide compound, HAZ toughness deterioration then.Therefore, Al need be suppressed at below 0.05%.Al is preferably below 0.040%, more preferably below 0.035%.In addition, Al can contain about 0.0005% usually inevitably.
N separates out the element that contains the Ti nitride, this nitride, and by the pinning effect, the thickization promotion ferrite transformation of the austenite grain that generates in HAZ when preventing to weld helps the HAZ flexible to improve.In order to bring into play such effect, need contain more than 0.0040%, N is preferably more than 0.005%, more preferably more than 0.006%.Because the many more miniaturizations that promote to form the austenite grain that contains the Ti nitride more of N, therefore the toughness raising to HAZ effectively plays a role.But N surpasses 0.030%, and then solid solution N amount increases, the toughness deterioration of mother metal self, and HAZ toughness also reduces.Therefore N need be suppressed at below 0.030%.Be preferably below 0.025%, more preferably below 0.02%, more preferably below 0.015%.
O (oxygen) is in order to make the element of necessity that the small oxide compound as intracrystalline ferrite product nucleus that helps HAZ toughness to improve generates.But O is lower than at 0.0005% o'clock, and described small oxide amount deficiency can not improve HAZ toughness.Therefore O need contain more than 0.0005%.O is preferably more than 0.0010%, more preferably more than 0.0015%.But excessive interpolation then makes thickization of oxide compound, makes HAZ toughness deterioration on the contrary.Therefore O should be suppressed at below 0.010%.O is preferably below 0.008%, more preferably below 0.005%.
Zr generates ZrO 2The element of necessity.Owing to contain ZrO 2, the small dispersion of oxide compound becomes easily, and this small dispersive oxide compound is owing to as the ferritic product nucleus of intracrystalline, help the HAZ flexible to improve.But Zr is lower than at 0.0002% o'clock, owing to described small oxide amount as the ferritic product nucleus of intracrystalline tails off, can not improve HAZ toughness.Therefore Zr need contain more than 0.0002%.Zr is preferably more than 0.0005%, more preferably more than 0.0010%.But excessive interpolation Zr, then thick oxide compound generates in a large number, HAZ toughness deterioration.In addition, form the small Zr carbide that causes precipitation strength, cause mother metal self toughness to reduce.Therefore Zr is suppressed at below 0.050%.Zr is preferably below 0.04%, more preferably below 0.01%, more preferably below 0.008%.
REM (rare earth element) and Ca are the elements that generates necessity of each autoxidisable substance.Because contain their oxide compound, the small dispersion of oxide compound becomes easily, this small dispersive oxide compound is owing to as the ferritic product nucleus of intracrystalline, help the HAZ flexible to improve.In steel of the present invention, REM and Ca can separately or merge use respectively.
REM separately or with Ca and time spent, should contain more than 0.0002%, be preferably more than 0.0005%, more preferably more than 0.0010%, more preferably more than 0.0015%.But excessive interpolation REM then forms thick oxide compound, and HAZ toughness is deterioration on the contrary.Therefore REM should be suppressed at below 0.050%.REM is preferably below 0.04%, more preferably below 0.01%.
In addition, in the present invention, the so-called REM meaning is to contain lanthanon (15 kinds of elements from La to Ln) and Sc (scandium) and Y (yttrium).In these elements, preferably contain at least a element of from La, Ce and Y, selecting, can more preferably contain La and/or Ce.
Ca separately or with the situation of REM and usefulness in, should contain more than 0.0005%, be preferably more than 0.001%, more preferably more than 0.0015%.But excessive interpolation Ca then forms thick oxide compound, and HAZ toughness is deterioration on the contrary.Therefore Ca is suppressed at below 0.010%.Ca is preferably below 0.008%, more preferably below 0.005%.
Steel of the present invention contain the above-mentioned element as necessary composition, and surplus can be iron and unavoidable impurities (for example Mg and As, Se etc.).
Steel of the present invention also contain with other inferior effective element.
(1) Ni:1.5% following (not containing 0%) and/or Cu:1.5% following (not containing 0%);
(2) Cr:1.5% following (not containing 0%) and/or Mo:1.5% following (not containing 0%);
(3) Nb:0.1% following (not containing 0%) and/or V:0.1% following (not containing 0%);
(4) B:0.0050% following (not containing 0%).
It is described that these elements are defined in the reasons are as follows of scope like this.
[(1) Ni and/or Cu]
Ni and Cu all are the elements that help to improve the intensity of steel.Ni and Cu can distinguish independent or compound interpolation.But because Ni above 1.5%, then significantly improves the intensity of mother metal and makes the toughness deterioration, HAZ toughness also reduces.Therefore Ni is preferably below 1.5%.Ni is more preferably below 1.2%, more preferably below 1%.In addition, when playing a role effectively, preferably contain more than 0.05% by interpolation Ni.Ni is more preferably more than 0.1%, more preferably more than 0.2%.
Cu is also same with Ni, and as surpassing 1.5%, then owing to the intensity that significantly improves mother metal makes the toughness deterioration, HAZ toughness also reduces.Therefore Cu is preferably below 1.5%.Cu is more preferably below 1.2%, more preferably below 1%.In addition, when playing a role effectively, preferably contain more than 0.05% by interpolation Cu.Cu is more preferably more than 0.1%, more preferably more than 0.2%.
[(2) Cr and/or Mo]
Cr and Mo all are the elements that help to improve the intensity of steel.Cr and Mo can distinguish independent or compound interpolation.If but Cr surpasses 1.5%, then owing to the intensity that significantly excessively improves mother metal makes the toughness deterioration, HAZ toughness also reduces.Therefore Cr is preferably below 1.5%.Cr is more preferably below 1.2%, more preferably below 1%.In addition, when playing a role effectively, preferably contain more than 0.1% by interpolation Cr.Cr is more preferably more than 0.2%, more preferably more than 0.5%.
Mo is also same with Cr, and as surpassing 1.5%, then owing to the intensity that significantly excessively improves mother metal makes the toughness deterioration, HAZ toughness reduces.Therefore Mo is preferably below 1.5%.Mo is more preferably below 1.2%, more preferably below 1%.In addition, when playing a role effectively, preferably contain more than 0.1% by interpolation Mo.Mo is more preferably more than 0.2%, more preferably more than 0.3%.
[(3) Nb and/or V]
Nb and V all separate out as nitride, this nitride, and by the pinning effect, thickization of austenite grain when preventing to weld is the element with the effect that makes the raising of HAZ toughness.Nb and V can distinguish independent or compound interpolation.If but Nb surpasses 0.1%, thickization of then separating out of nitride makes HAZ toughness deterioration on the contrary.Therefore Nb is preferably below 0.1%.Nb is more preferably below 0.08%, more preferably below 0.05%.In addition, when playing a role effectively, preferably contain more than 0.002% by interpolation Nb.Nb is more preferably more than 0.005%, more preferably more than 0.008%.
V is also same with Nb, if surpass 0.1%, thickization of then separating out of nitride makes HAZ toughness deterioration on the contrary.Therefore V is preferably below 0.1%.V is more preferably below 0.08%, more preferably below 0.05%.In addition, when playing a role effectively, preferably contain more than 0.002% by interpolation V.V is more preferably more than 0.005%, more preferably more than 0.01%.
[(4) B boron]
B is the element that toughness is improved by the generation that suppresses grain boundary ferrite.But B ultrasonic crosses 0.0050%, then separates out as BN on austenite grain boundary, causes toughness to reduce.Therefore B is preferably below 0.0050%.B is more preferably below 0.0040%.In addition, when playing a role effectively, preferably contain more than 0.0010% by interpolation B.B is more preferably more than 0.0015%.
Then, when making steel of the present invention, the method for making that can suitably adopt is illustrated.Manufacture method of the present invention comprises in proper order: (1) is adjusted into the dissolved oxygen content of molten steel the operation of 0.0010～0.0060% scope; (2) make the oxide compound come-up separation in the molten steel that whole oxygen amounts are adjusted into 0.0010～0.0070% operation by stirring described molten steel, in addition also comprise the operation of adding Zr, REM and/or Ca again behind (3) interpolation Ti.
In the molten steel of so adjusting dissolved oxygen content and whole oxygen amounts,, can generate desirable oxide compound as the ferritic product nucleus of intracrystalline by adding the alloying element of regulation with the order of regulation.Especially in the present invention, do not generate thick oxide compound, thus, after operation (1) was adjusted dissolved oxygen content as described, it was very important adjusting described whole oxygen amounts as above-mentioned operation (2).So-called dissolved oxygen content, the meaning is not form oxide compound, the oxygen of the free state that in molten steel, exists, whole oxygen that so-called all oxygen amounts, the meaning are in the molten steel to be comprised, that is, and free oxygen and form the summation of the oxygen of oxide compound.Below, each operation is described.
[about operation (1)]
At first, the dissolved oxygen content with molten steel is adjusted into 0.0010～0.0060% scope.The dissolved oxygen content of molten steel is lower than at 0.0010% o'clock, because the dissolved oxygen content deficiency in the molten steel just can not guarantee that the ZrREM/Ca as the nuclear of intracrystalline ferrite transformation is that oxide compound reaches specified amount, can not get the HAZ toughness of excellence.In addition, owing to the dissolved oxygen content deficiency, then fail to form the Zr formation nitride of oxide compound, REM and Ca form sulfide, therefore become the reason that makes mother metal self toughness deterioration.Therefore above-mentioned dissolved oxygen content is more than 0.0010%.Described dissolved oxygen is preferably more than 0.0015%, more preferably more than 0.0020%.
On the other hand, if described dissolved oxygen content surpasses 0.0060%,, in founding operation,, and generate thick oxide compound and make HAZ toughness deterioration on the contrary for preferably then because the oxygen amount in the molten steel is too much, and the oxygen in the molten steel and described element reaction are violent.Therefore described dissolved oxygen content should be suppressed at below 0.0060%.Described dissolved oxygen content is preferably below 0.0050%, more preferably below 0.0045%.
In any case, the dissolved oxygen content that carried out in converter and electric furnace in the molten steel of initial refining all surpasses 0.0100% usually.Wherein in method for making of the present invention, need the dissolved oxygen content in the molten steel be adjusted in the above-mentioned scope by the whole bag of tricks.
As the method for adjusting the dissolved oxygen content in the molten steel, for example can enumerate the method and interpolation Si and the Mn that use RH formula degassing a refining unit to carry out the vacuum C deoxidation, the methods of the deoxidation element of Ti, Al etc. etc. also can these methods of appropriate combination be adjusted dissolved oxygen content.In addition, also can use ladle heating-type a refining unit and simple type molten steel treatment facility etc. to replace RH formula degassing a refining unit to adjust dissolved oxygen content.At this moment, owing to can not adjust dissolved oxygen content, therefore, in the adjustment of dissolved oxygen content, adopt the method for the deoxidation element that adds Si etc. to get final product by the vacuum C deoxidation.When adopt adding the method for deoxidation element of Si etc., when tapping, adds ladle the deoxidation element for well from converter.
[about operation (2)]
Be connected on described operation (1) afterwards, stir molten steel, the come-up of the oxide compound in the molten steel is separated thus whole oxygen amounts are adjusted into 0.0010～0.0070%.Thus in the present invention, the molten steel that stirring and dissolving oxygen amount is suitably controlled is removed unwanted oxide compound, adds the intracrystalline ferrite transformation karyogenesis element of Zr etc., thereby can prevent the generation of thick oxide compound.In described patent documentation 3, owing to do not carry out this operation (2), generate thick oxide compound, and can not guarantee good HAZ toughness (with reference to following embodiment).
Therefore above-mentioned whole oxygen amount is lower than at 0.0010% o'clock, and the quantity not sufficient of desirable oxide compound can not guarantee to help that HAZ toughness improves as the amount of the oxide compound of intracrystalline ferrite product nucleus.Therefore described whole oxygen amounts are more than 0.0010%.Described whole oxygen amount is preferably more than 0.0015%, more preferably more than 0.0020%.
On the other hand, if described whole oxygen amount surpasses 0.0070%, then whole oxide amounts become superfluous in the molten steel, and thick oxide compound generates, HAZ toughness deterioration.Therefore described whole oxygen amounts should be suppressed at below 0.0070%.Described whole oxygen amount is preferably below 0.0060%, more preferably below 0.0050%.
Whole oxygen amounts in the molten steel, roughly relevant and change with churning time, can control by adjusting churning time etc. thus.Specifically be to stir molten steel, remove the oxide compound of come-up after, on one side suitably measure whole oxygen amounts in the molten steel, suitable whole oxygen amounts in the control molten steel on one side.
[about operation (3)]
After adjusting to the whole oxygen amounts in the molten steel in the described scope, added Ti after, add Zr, REM and/or Ca and cast.By add above-mentioned element in the molten steel of adjusting whole oxygen amounts, the ZrREM/Ca that obtains desirable nuclear as the intracrystalline ferrite transformation is an oxide compound.Because the Ti oxide compound is that oxide compound is compared with ZrREM/Ca, and is little with the interfacial energy of molten steel, if add alloying element in proper order, because therefore Ti oxide compound microminiaturization consequently can make to help the small oxide compound of HAZ flexible to generate with this.
There is no particular limitation for the form of REM that adds in the subtend molten steel and Ca, Zr, Ti, for example, as REM, add pure La and pure Ce, pure Y etc., or pure Ca, pure Zr, pure Ti, also can add Fe-Si-La alloy, Fe-Si-Ce alloy, Ti-Si-Ca alloy, Fe-Si-La-Ce alloy, Fe-Ca alloy, Ni-Ca alloy etc. in addition.In addition, also can in molten steel, add mishmetal.So-called mishmetal is the mixture of cerium family rare earth element, specifically, contains: about Ce:40～50%, about La:20～40%.But, in mishmetal, contain as the Ca of impurity manyly, so the situation that mishmetal contains Ca need satisfy the scope of stipulating among the present invention.
[about operation (4)]
In the present invention, to promote that removing thick oxide compound is purpose, after above-mentioned operation (3), preferably stirs molten steel in the scope that is no more than 40 minutes.If churning time surpasses 40 minutes, the aggegation in molten steel of then small oxide compound, thickization of bonded oxide compound, HAZ toughness deterioration.Therefore churning time was preferably in 40 minutes.In the churning time more preferably 35 minutes, more preferably in 30 minutes.There is no particular limitation for the lower value of the churning time of molten steel, and it is uneven that the too short concentration of then adding element of churning time becomes, and can not obtain as the whole desirable effect of steel.Therefore need desirable churning time corresponding to container dimensional.
Be adjusted into the molten steel that composition like this obtains, after slab is made in continuous casting according to rule, carry out hot rolling according to rule and get final product.
Steel of the present invention, can use as the material of the works of for example bridge and high-rise, boats and ships etc., still not little～middle heat energy input welding, even also can prevent the toughness deterioration of welding heat affected zone in the high heat energy input welding of input heat energy more than 50KJ/mm.
Steel of the present invention are object with the steel of Plate Steel more than the about 3mm of thickness of slab etc.By the present invention, thickness of slab is more than the 50mm, and particularly the above Plate Steel of 80mm is carrying out can bringing into play the effect of raising HAZ flexible effectively when the high heat energy input of heat energy input more than 50kJ/mm welded.
Below, illustrating in greater detail the present invention by embodiment, the unqualified character of the present invention of following embodiment also can be implemented suitable change in the scope that is fit to upper and lower described purport, and these all are included in the technical scope of the present invention.
[embodiment]
Use vacuum dissolving stove (capacity 150kg), under following table 1, the described condition of table 2, refining contain the chemical ingredients shown in following table 3, the table 4 (quality %) surplus be iron and unavoidable impurities for the examination steel, the ingot bar of casting cooling 150kg.Subsequently, heat, rolling, make Plate Steel.
When founding for the examination steel, carry out the composition adjustment, and use at least a element deoxidation of from C, Si and Mn, selecting and adjust the dissolved oxygen content of molten steel for the element beyond Ti, Zr, Al, REM and the Ca with vacuum dissolving stove.Adjusted dissolved oxygen content is as described in following table 1, the table 2.
The molten steel of adjusting dissolved oxygen content was stirred about 1～10 minute, separate the whole oxygen amount of adjusting molten steel by making the oxide compound come-up in the molten steel.Adjusted whole oxygen amount is shown in following table 1, table 2.
In the molten steel of adjusting whole oxygen amounts, added Ti after, add Zr and REM and/or Ca.In addition, Ti is that mode, Zr with the Fe-Ti alloy are that mode, REM with the Fe-Zr alloy is to contain La: about 25% and Ce: the mode of about 50% mishmetal, Ca add respectively in the mode of Ni-Ca alloy or Ca-Se alloy or Fe-Ca pressed compact.But the No.35 of table 4 does not stir the molten steel of adjusting dissolved oxygen content, and has directly added Ti.
After adding above-mentioned element, casting cooling ingot bar.The time of stirring molten steel is shown in following table 1, table 2.
The ingot bar that hot rolling obtains, the Plate Steel of manufacturing 50～80mm.Sample is downcut in transverse section from D/4 (wherein, D is the thickness of the steel plate) position of the Plate Steel that obtains, measures the composition of the whole oxide compounds that contain in this sample, calculates as the average composition of oxide alone with the oxide compound of mass conversion.
Observing the surface of the sample that downcuts with Shimadzu Seisakusho Ltd.'s system " EPMA-8705 (device name) " with 600 multiplying power, is that the one-tenth of the particle more than the 0.2 μ m is grouped into and carries out quantitative analysis to maximum diameter.By the beam split of characteristic X-ray wavelength dispersion the one-tenth of particle central part is grouped under following observation condition and carries out quantitative analysis, observation condition is acceleration voltage 20kV, test portion electric current 0.01 μ A, and viewing area area 1～5cm2 analyzes 100 of numbers.To be Mn, Ti, Zr, La, Ce, Ca, Si, Al and O (oxygen) obtain the relation of the electron beam intensity of each element and concentration of element as the premeasuring line with known substance to the analytic target element, then, carry out quantitatively according to the electron beam intensity that obtains from above-mentioned particle and described measuring line in advance concentration of element this particle.
In the quantitative result that obtains be with oxygen level particle more than 5% as oxide compound, average with mass conversion as oxide alone, as the average composition of oxide compound.Average composed as follows the stating shown in table 5, the table 6 of whole oxide compounds.In addition, the oxide compound of REM when representing metallic element with M, in steel with M 2O 3And M 3O 5, MO 2Mode exist, whole oxide compounds are scaled M 2O 3, measure and form.In addition, when a kind of inclusion is observed multiple element, be converted into the composition that oxide alone is calculated oxide compound from the ratio of representing the X line strength that these elements exist.
The result who observes above-mentioned sample surfaces with EPMA is that observed oxide compound is the composite oxides that contain Ti and Zr and REM and/or Ca mostly, also generates the Ti as oxide alone 2O 3, ZrO 2, the oxide compound of REM, CaO.
In addition, measure that oxygen level is the diameter of equivalent circle of the oxide compound 5% or more in the quantitative result obtain, calculate diameter of equivalent circle (particle diameter) and be the number of oxide compound of 0.1～2.0 μ m and diameter of equivalent circle (particle diameter) number above the oxide compound of 5.0 μ m.The individual number conversion table of oxide compound in following table 5, the table 6 is shown every 1m 2Viewing area in number.
Then, in order to estimate the toughness that welding the time is subjected to the HAZ of heat affecting, simulate high heat energy input welding and carry out reproducing test as the welding shown in following.It is that the sample that will downcut from Plate Steel is heated to 1400 ℃ that test is reproduced in welding, in this temperature maintenance after 30 seconds, gives refrigerative heat cycle.Speed of cooling adjust to from 800 ℃ to 500 ℃ cooling time be 300 seconds.
The impact characteristics of cooled sample is the absorption energy (vE that carries out in the V charpy impact test evaluation of measuring-40 ℃ -40).VE -40Qualified more than 100J (HAZ toughness is good).Measurement result is shown in table 5, table 6.
Can do following investigation from following table 1～table 6.The example of the prerequisite of regulation is in the present invention satisfied in No.1～31st, and the composition of measuring whole oxide compounds during with mass conversion, contains specified amount ZrO as oxide alone 2, REM oxide compound and/or CaO, after so adjusting, owing to do not generate the like this thick oxide compound that particle diameter surpasses 5.0 μ m, particle diameter is that the small oxide compound of 0.1～2.0 μ m generates in a large number, thereby obtains the good steel of HAZ toughness.
On the other hand, No.32～54th exceeds the example outside arbitrary prerequisite of stipulating among the present invention.No.32 is the insufficient example of the dissolved oxygen content of molten steel, can not guarantee to help the oxide amount as intracrystalline ferrite product nucleus of HAZ toughness raising, can not improve HAZ toughness.No.33 is the example of the dissolved oxygen content surplus of molten steel, makes HAZ toughness deterioration on the contrary because thick oxide compound generates.No.34 is the insufficient example of the dissolved oxygen content of molten steel, can not guarantee to help the oxide amount as intracrystalline ferrite product nucleus of HAZ toughness raising, can not improve HAZ toughness.
No.35 is and present inventors' example that disclosed similar steel are formed in patent documentation 3.After adjusting the dissolved oxygen content of molten steel,, add the scope that the preceding whole oxygen amounts of Ti have exceeded the defined of stipulating among the present invention owing to do not stir the whole oxygen amounts of molten steel adjustment.Therefore thick oxide compound becomes many, HAZ toughness deterioration.
No.36 and No.37 are after adding Zr and Al and REM and/or Ca, because the long-time molten steel that stirs, the thick oxide compound of the mutual aggegation of the oxide compound in the molten steel generates in a large number.So HAZ toughness deterioration.
No.38 is the too much example of Si, and island martensite body (MA) is a large amount of among the HAZ during welding generates HAZ toughness deterioration.No.39 is the too much example of Mn, because the intensity of mother metal significantly improves, mother metal self toughness reduces, and HAZ toughness also reduces.No.40 is the too much example of P, and P is in crystal grain boundary generation segregation HAZ toughness deterioration.No.41 is the too much example of S, and S is in crystal grain boundary generation segregation HAZ toughness deterioration.No.42 is the too much example of Al, generates thick oxide compound, HAZ toughness deterioration.
No.43 is the very few example of Ti, owing to help the small nitride as intracrystalline ferrite product nucleus of HAZ toughness raising to tail off, and can not improve HAZ toughness.No.44 is the too much example of Ti, thickization of oxide compound HAZ toughness deterioration.No.45 is the too much example of REM, the oxide compound of excessive generation REM, and form thick oxide compound, HAZ toughness is deterioration on the contrary.
No.46 is the very few example of Zr, owing to help the small oxide compound as intracrystalline ferrite product nucleus of HAZ toughness raising to tail off, and can not improve HAZ toughness.No.47 is the too much example of Zr, and thick oxide compound generates HAZ toughness deterioration.No.48 is the too much example of Ca, the excessive generation of CaO, and form thick oxide compound, HAZ toughness is deterioration on the contrary.
No.49 is the too much example of N, and solid solution N amount increases the toughness deterioration of mother metal self, and HAZ toughness also reduces.No.50 is the very few example of N, owing to suppressed to contain the generation of Ti nitride, can not prevent thickization of austenite grain, HAZ toughness deterioration by the pinning effect.
No.51 is the very few example of O, and the small oxide amount deficiency as intracrystalline ferrite product nucleus can not improve HAZ toughness.No.52 is the too much example of O, thickization of oxide compound HAZ toughness deterioration.
No.53 is the too much example of N, significantly improves because the intensity of mother metal becomes, and base metal tenacity deterioration, HAZ toughness also just reduce.No.54 is the too much example of Cu, significantly improves because the intensity of mother metal becomes, and base metal tenacity deterioration, HAZ toughness also just reduce.
Table 1
Figure A20091000965400191
Figure A20091000965400201
Table 2
No. Dissolved oxygen content (ppm) Have or not come-up to separate Whole oxygen amounts (ppm) The strong mixing time after the interpolation (minute)
32 5 Have 12 8
33 65 Have 69 8
34 5 Have 7 8
35 55 No 73 8
36 25 Have 32 50
37 32 Have 38 44
38 25 Have 29 8
39 25 Have 31 8
40 23 Have 30 8
41 30 Have 37 8
42 22 Have 34 8
43 26 Have 28 8
44 29 Have 39 8
45 15 Have 17 8
46 53 Have 59 8
47 18 Have 21 8
48 12 Have 13 8
49 24 Have 31 8
50 26 Have 34 8
51 12 Have 13 8
52 58 Have 64 8
53 30 Have 40 8
54 29 Have 35 8
Figure A20091000965400211
Figure A20091000965400221
Figure A20091000965400231
Figure A20091000965400251
Figure A20091000965400261

Claims (4)

1, a kind of steel of tenacity excellent of welding heat affected zone, it is characterized in that, contain C:0.02～0.12% in quality %, Si:0.50% is following and contain 0%, Mn:1～2.0%, Ti:0.005～0.10%, P:0.030% is following and contain 0%, S:0.020% is following and contain 0%, Al:0.05% is following and contain 0%, N:0.0040～0.030%, 0:0.0005～0.010%, and contain Zr:0.0002～0.050% and REM:0.0002～0.050% and/or Ca:0.0005～0.010%, surplus is made of iron and unavoidable impurities, and
(a) described steel comprise the oxide compound that contains Zr and REM and/or Ca,
(b) measure the composition of the whole oxide compounds that comprise in the described steel and when being converted into oxide alone, satisfy ZrO 2: 5～50% and the oxide M of the REM during with M symbolic representation REM 2O 3: 10～50% and/or CaO:5～50%, and,
(c) among the whole oxide compounds that comprise in described steel, be every square millimeter more than 120 in the oxide compound of diameter of equivalent circle 0.1～2.0 μ m, the oxide compound that surpasses 5.0 μ m in diameter of equivalent circle is every square millimeter below 5.
2, steel according to claim 1 is characterized in that, also contain select at least a as other elements in quality % from following (A)～(D) in the described steel,
(A) Ni:1.5% following but do not contain 0% and/or Cu:1.5% following but do not contain 0%;
(B) Cr:1.5% following but do not contain 0% and/or Mo:1.5% following but do not contain 0%;
(C) Nb:0.1% following but do not contain 0% and/or V:0.1% following but do not contain 0%;
(D) B:0.0050% is following but do not contain 0%.
3, a kind of manufacture method of steel of tenacity excellent of welding heat affected zone is a method of making claim 1 or 2 described steel, it is characterized in that, comprises following operation in regular turn: (1) adjusts the operation that dissolved oxygen content is 0.0010～0.0060% molten steel; (2) by stirring described molten steel the oxide compound come-up in the molten steel is separated, thereby whole oxygen amounts are adjusted into 0.0010～0.0070% operation; (3) behind the interpolation Ti, the operation of adding Zr and REM and/or Ca.
4, manufacture method according to claim 3 is characterized in that, after described operation (3), comprises that also (4) stir the operation of molten steel in the scope that is no more than 40 minutes.
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