CN105229190A - The High Strength Steel of excellent in fatigue characteristics and manufacture method thereof - Google Patents

The High Strength Steel of excellent in fatigue characteristics and manufacture method thereof Download PDF

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Publication number
CN105229190A
CN105229190A CN201480026771.6A CN201480026771A CN105229190A CN 105229190 A CN105229190 A CN 105229190A CN 201480026771 A CN201480026771 A CN 201480026771A CN 105229190 A CN105229190 A CN 105229190A
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steel
cooling
high strength
fatigue
strength steel
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CN105229190B (en
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中岛孝一
长谷和邦
远藤茂
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JFE Steel Corp
JFE Engineering Corp
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NKK Corp
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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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

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  • Metallurgy (AREA)
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  • Physics & Mathematics (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

The present invention relates to the Plate Steel of more than thickness of slab 30mm, and High Strength Steel and the manufacture method thereof of excellent in fatigue characteristics are provided.A kind of High Strength Steel of excellent in fatigue characteristics, become to be grouped in mass % containing C:0.10 ~ 0.20%, below Si:0.50%, Mn:1.0 ~ 2.0%, below P:0.030%, S:0.0005 ~ 0.0040%, Sol.Al:0.002 ~ 0.07%, Ca:0.0005 ~ 0.0050%, rest part is made up of Fe and inevitable impurity, and metal structure is the ferrite of principal phase and the bainite of the 2nd phase and pseudopearlite.

Description

The High Strength Steel of excellent in fatigue characteristics and manufacture method thereof
Technical field
The present invention relates to the Plate Steel of thickness of slab 30mm ~ 50mm, relate to be suitable for boats and ships, marine structure, bridge, buildings, tank etc. be strongly required the welded structure of safety of structure, the High Strength Steel of the resistivity excellence of fatigue cracking generation and fatigue cracking development and manufacture method thereof.
Background technology
The steel used in the works such as boats and ships, marine structure, bridge, tank, except the mechanical properties such as intensity, toughness, welding property excellent, for the repetition load in working at ordinary times, caused by wind, earthquake etc. repeat vibrations, the safety of structure of works must be had.
For repetition load, repeat vibrations, require excellent in fatigue characteristics.Especially, in order to peventing member ruptures so final destruction, think the emergence and development of the fatigue cracking effectively suppressing steel to have.
When common welded structure, soldered edge easily becomes stress concentration portion, and the stretching unrelieved stress caused by welding also plays a role, and therefore mostly becomes the generation source of fatigue cracking.Prevent strategy as it, knownly carry out, without welding rod welding (weldingwithoutweldingrod), or passing through shot peening and importing compressive residual stress to soldered edge.
But welded structure has a large amount of soldered edge, in addition, on cost, also burden is large.Therefore, these methods are not suitable for implementing with technical scale, and the raising that the fatigue characteristic of used steel self are passed through in the raising of the resistent fatigue characteristic of welded structure mostly realizes.
Non-patent literature 1 discusses and repeatedly carries out laboratory scale special thermal treatment with the steel limiting composition and the propagation of fatigue crack behavior of the 2 kinds of steel manufactured.In the literature, investigate in detail and describe following item: to making hard phase (Vickers' hardness: 565, point rate of phase: 36.4%, the mean sizes of phase: 149 μm) in soft phase (Vickers' hardness: steel A dispersed 148) and with hard phase (Vickers' hardness: 546, point rate of phase: 39.2%) by soft phase (Vickers' hardness: the propagation of fatigue crack 149) surrounding the steel B of mesh-shape is studied, its result, the propagation of fatigue crack speed of steel B significantly reduces.
Describe a kind of steel plate with fatigue cracking development inhibition in patent documentation 1, it is characterized in that, the matrix of hard portion forms metal structure with the soft part being scattered in this matrix, and the difference of hardness of this 2 part counts more than 150 with Vickers' hardness.
A kind of Plate Steel of fatigue strength excellence is described in patent documentation 2, it is characterized in that, metal structure is by the organizational composition comprising ferrite and hard second phase, and the Line Integral rate of above-mentioned hard second phase in the section structure parallel with surface of steel plate be 20 ~ 80%, Vickers' hardness is 250 ~ 800, average equivalent circular diameter is 10 ~ 200 μm, and the largest interval between hard second phase is less than 500 μm.
The steel plate of the expansionary excellence of a kind of fatigue cracking is described in patent documentation 3, it is characterized in that, metal structure is counted the bainite structure of 60 ~ 85% with area occupation ratio, is added up to martensitic stucture and the pearlitic structure of 0 ~ 5%, and rest part is ferritic structure.
Prior art document
Patent documentation
Patent documentation 1: Japanese Patent No. 2962134 publication
Patent documentation 2: Japanese Patent No. 3860763 publication
Patent documentation 3: Japanese Patent No. 4466196 publication
Non-patent literature
Non-patent literature 1:H.SUZUKIANDA.J.MCEVILY:MetallurgicalTransactionsA, Volume10A, P475 ~ 481,1979
Summary of the invention
But the steel recorded in non-patent literature 1 needs the thermal treatment in 5 stages, is unpractical in order to carry out engineering production with Industrial products scale from the viewpoint of cost, productivity.In addition, with propagation of fatigue crack characteristic mutually on the contrary ductility decline, this steel cannot be applied to works.
About patent documentation 1,2, also use heat process before and after hot rolling, not preferred in the efficiency therefore on engineering is produced.Such as, in patent documentation 2, in order to improve the characteristic of thick-wall materials, implement the thermal treatment of diffusion heat treatments-hot rolling-2 phase region.
In patent documentation 3, with the smaller 15mm thickness of slab material of thickness of slab for object, do not correspond to the thick-wall materials of more than thickness of slab 30mm.In order to ensure the intensity of thick-wall materials, need the alloying element adding C etc.But C amount is 0.1% to the maximum, the likely undercapacity when wall thickening in patent documentation 3.
In addition, above-mentioned arbitrary invention all seek to improve fatigue cracking generation and fatigue cracking developing any one, do not carry out the research of the steel plate having two kinds of characteristics concurrently.The suppression that fatigue cracking produces, by increasing fatigue strength, namely increases the yielding stress of female steel plate and improves.But high-strength steel, more becomes large at the stress concentration of fatigue cracking tip and encourages fatigue cracking development.
Therefore, the present invention relates to the Plate Steel of thickness of slab 30mm ~ 50mm, object is steel and the manufacture method thereof of the resistivity excellence providing fatigue cracking generation and fatigue cracking development.
The present inventor etc. conduct in-depth research repeatedly in order to reach above-mentioned problem, even also have the high-strength steel plate of excellent fatigue characteristic for the Plate Steel of thickness of slab 30mm ~ 50mm, obtain following opinion.
1. thickness of slab is greater than to the Plate Steel of 30mm, produces and fatigue cracking these two kinds of characteristics expansionary to improve fatigue cracking simultaneously, importantly make the mixed structure be made up of the bainite of the ferrite of principal phase and the 2nd phase and pseudopearlite.This tissue can realize by carrying out manufacturing at suitable condition and range.In the present invention, measured by the C containing more than 0.10%, stably can reach the high strength caused by the Line Integral rate of the 2nd phase increases.
2. and then, for high-strength thick wall material, in order to ensure fatigue characteristic, the sulfide utilizing Ca to add to carry out controls effectively to play a role.Ca fixes S by forming CaS, generates the complex inclusion with MnS.During MnS Individual existence, be stretched when rolling, become the starting point of destruction.But by CaS being made the complex inclusion with MnS, thus be scattered in imperceptibly in parent phase, the resistivity of fatigue cracking generation and fatigue cracking development improves.
The present invention is studied further above-mentioned opinion and is made, and its purport is as follows.
[1] a kind of High Strength Steel of excellent in fatigue characteristics, become to be grouped in mass % containing C:0.10 ~ 0.20%, below Si:0.50%, Mn:1.0 ~ 2.0%, below P:0.030%, S:0.0005 ~ 0.0040%, Sol.Al:0.002 ~ 0.07%, Ca:0.0005 ~ 0.0050%, rest part is made up of Fe and inevitable impurity, and metal structure is the ferrite of principal phase and the bainite of the 2nd phase and pseudopearlite.
The High Strength Steel of the excellent in fatigue characteristics [2] as described in [1], is characterized in that, becomes to be grouped in mass % further containing the one be selected from Ti:0.003 ~ 0.03%, Nb:0.005 ~ 0.05% or two kinds.
The High Strength Steel of the excellent in fatigue characteristics [3] as described in [1] or [2], it is characterized in that, become to be grouped in mass % further containing be selected from Cr:0.1 ~ 0.5%, Mo:0.02 ~ 0.3%, V:0.01 ~ 0.08%, Cu:0.1 ~ 0.6%, Ni:0.1 ~ 0.5% more than one.
The High Strength Steel of the excellent in fatigue characteristics [4] according to any one of [1] ~ [4], is characterized in that, becomes to be grouped into further containing below O:0.0040%, and meets following formula (1).
0＜(Ca-(0.18+130×Ca)×O)/1.25/S≤0.8···(1)
Wherein, Ca, O, S in formula (1) represent the content (quality %) of each composition.
[5] manufacture method for the High Strength Steel of excellent in fatigue characteristics, is characterized in that, after the steel raw material that the one-tenth had according to any one of [1] ~ [4] is grouped into is heated to 950 ~ 1250 DEG C, at Ar 3the above rolling carrying out accumulation draft more than 50% of point, with the speed of cooling of more than 5 DEG C/sec from Ar 3the temperature province of the temperature province accelerating cooling to 350 of point more than-60 DEG C DEG C ~ 600 DEG C.
The manufacture method of the High Strength Steel of the excellent in fatigue characteristics [6] as described in [5], it is characterized in that, above-mentioned speed of cooling is below the speed of cooling of the cooling curve had in the CCT figure of the steel raw material that the one-tenth according to any one of above-mentioned [1] ~ [3] is grouped into when being in ferrite transformation protuberance.
The manufacture method of the High Strength Steel of the excellent in fatigue characteristics [7] as described in [5] or [6], is characterized in that, after above-mentioned accelerating cooling, further with Ac 1the following temperature of point carries out temper.
According to the present invention, steel and the manufacture method thereof of fatigue cracking generation and the expansionary excellence of fatigue cracking can be obtained.Such as, even if produce fatigue cracking year in year out from stress concentration portion, weld part etc., also can delay propagation thereafter and improve the security of steel structure, industrially exceedingly useful.
Accompanying drawing explanation
Fig. 1 is the schematic diagram of CCT figure (continuous cooling transformation diagram) representing steel raw material.
Embodiment
One-tenth of the present invention is grouped into, the regulation of manufacturing condition and metal structure is described in detail.
1. be grouped into about one-tenth
Below, one-tenth of the present invention is grouped into is described.In addition, the % in becoming to be grouped into all is set to quality %.
C：0.10～0.20％
For C, in order to obtain as the intensity needed for structural steel, need the content of more than 0.10%.But if amount is greater than 0.20%, then can damage weldability, therefore C amount is set to the scope of 0.10 ~ 0.20%.Be preferably the scope of 0.10 ~ 0.18%.Be more preferably the scope of 0.11 ~ 0.17%.
Below Si:0.50%
Si is as the useful element of deoxidant element, by playing its effect containing more than 0.01%.But if amount is greater than 0.50%, then the toughness of mother metal and welding heat affected zone significantly declines, and weldability significantly declines.Therefore, Si amount is set to less than 0.50%.Be preferably the scope of 0.05 ~ 0.40%.
Mn：1.0～2.0％
Mn is from guaranteeing that the viewpoint of strength of parent is added.But its effect is insufficient when amount is less than 1.0%.In addition, if amount is greater than 2.0%, then excessively improve hardening capacity, the toughness of heat affected zone is significantly declined.Therefore, Mn amount is set to the scope of 1.0 ~ 2.0%.Be preferably the scope of 1.0 ~ 1.8%.Be more preferably the scope of 1.0 ~ 1.6%.
Below P:0.030%
If P amount is greater than 0.030%, then the toughness of mother metal and heat affected zone is made significantly to decline.Therefore, P amount is set to less than 0.030%.Be preferably less than 0.02%.
S：0.0005～0.0040％
For S, in order to generate required CaS or MnS, needing more than 0.0005%, if amount is greater than 0.0040%, then making the degraded toughness of mother metal.Therefore, S amount is set to the scope of 0.0005 ~ 0.0040%.Be preferably the scope of 0.001 ~ 0.0035%.Be more preferably the scope of 0.001 ~ 0.0030%.
Sol.Al：0.002～0.07％
Sol.Al needs more than 0.002% in the deoxidation of steel, preferably containing more than 0.01%.But, if amount is greater than 0.07%, then make the toughness of mother metal decline.Therefore, Sol.Al amount is set to the scope of 0.002 ~ 0.07%.Be preferably the scope of 0.005 ~ 0.07%.Be more preferably the scope of 0.01 ~ 0.06%.
Ca：0.0005～0.0050％
By forming CaS, chemistry fixes S to Ca, generates the complex inclusion with MnS.During MnS Individual existence, be stretched when rolling, become the starting point of destruction.But by making the complex inclusion with MnS, thus be scattered in imperceptibly in parent phase, the resistivity of fatigue cracking generation and fatigue cracking development improves.In order to play this effect, need at least containing more than 0.0005%.But even if amount is greater than 0.0050%, effect also can be saturated.Therefore, Ca amount is set to the scope of 0.0005 ~ 0.0050%.Be preferably the scope of 0.001 ~ 0.0040%.Be more preferably the scope of 0.001 ~ 0.0030%.
Be more than basic chemical composition of the present invention, rest part is made up of Fe and inevitable impurity.And then, to improve for the purpose of intensity, toughness, also can containing be selected from Ti, Nb more than one as selection element.
Ti：0.003～0.03％
In order to improve toughness further, Ti can be contained.Generate TiN during Ti heating before the rolling, make the miniaturization of austenite particle diameter, toughness is improved.When its content is less than 0.003%, its effect is insufficient, even if amount is greater than 0.03%, effect also can be saturated.Therefore, during containing Ti, Ti amount is preferably set to the scope of 0.003 ~ 0.03%.
Nb：0.005～0.05％
In order to improve intensity, Nb can be contained.When its content is less than 0.005%, its effect is insufficient, if be greater than 0.05%, then toughness can be made to decline.Therefore, during containing Nb, its amount is preferably set to the scope of 0.005 ~ 0.05%.Be more preferably the scope of 0.003 ~ 0.030%.
And then, to improve for the purpose of intensity, High Strength Steel of the present invention except above-mentioned composition, also can containing be selected from Cr, Mo, V, Cu, Ni more than one as selection element.
Cr：0.1～0.5％
When Cr is less than 0.1%, its effect is insufficient, if amount is greater than 0.5%, then weldability declines.Therefore, during containing Cr, Cr amount is preferably set to the scope of 0.1 ~ 0.5%.Be more preferably the scope of 0.1 ~ 0.4%.
Mo：0.02～0.3％
When Mo is less than 0.02%, its effect is insufficient, if amount is greater than 0.3%, then weldability significantly declines.Therefore, during containing Mo, Mo amount is preferably set to the scope of 0.02 ~ 0.3%.Be more preferably the scope of 0.02 ~ 0.20%.
V：0.01～0.08％
When V is less than 0.01%, its effect is insufficient, if amount is greater than 0.08%, then toughness significantly declines.Therefore, during containing V, V amount is preferably set to the scope of 0.01 ~ 0.08%.Be more preferably the scope of 0.01 ~ 0.07%.
Cu：0.1～0.6％
When Cu is less than 0.1%, its effect is insufficient, if amount is greater than 0.6%, then the possibility of Cu cracking improves.Therefore, during containing Cu, Cu amount is preferably set to the scope of 0.1 ~ 0.6%.Be more preferably the scope of 0.1 ~ 0.3%.
Ni：0.1～0.5％
When the content of Ni is less than 0.1%, its effect is insufficient, if amount is greater than 0.5%, then the rising of steel product cost is remarkable.Therefore, during containing Ni, Ni amount is preferably set to the scope of 0.1 ~ 0.5%.Be more preferably the scope of 0.1 ~ 0.4%.
O, except mentioned component composition, is preferably set to less than 0.0040% by High Strength Steel of the present invention.
Below O:0.0040%
If O amount is greater than 0.0040%, then degraded toughness, be therefore set to less than 0.0040%.
High Strength Steel of the present invention preferably meets following formula (1) further.
0＜(Ca-(0.18+130×Ca)×O)/1.25/S≤0.8···(1)
Wherein, Ca, O, S in formula represent the content (quality %) of each composition.
Ca, O and S need to meet with above-mentioned formula (Ca-(0.18+130 × Ca) × O)/1.25/S to be greater than 0 and to be that the mode of the relation of less than 0.8 contains.In this case, the form separated out on CaS and have the complex sulfide of MnS is become.During MnS Individual existence, be stretched when rolling, become the starting point of destruction.But by CaS being made the complex inclusion with MnS, thus fine dispersion is in parent phase, suppress the generation of fatigue cracking.If the value of (Ca-(0.18+130 × Ca) × O)/1.25/S is greater than 0.8, then MnS does not generate, O and S is with the whole crystallization of form of Ca system oxysulfide.Therefore, its size becomes thick, and the stress concentration at parent phase/inclusion interface becomes large and is difficult to guarantee fatigue strength.When (Ca-(0.18+130 × Ca) × O)/1.25/S is less than 0, CaS is non-crystallizable, and therefore S separates out with the form that MnS is independent, and this MnS is stretched because of rolling when steel plate manufactures, and does not maintain fine dispersion.Therefore, (Ca-(0.18+130 × Ca) × O)/1.25/S be set to be greater than 0 and be less than 0.8 scope.
2. about metal structure
In order to realize the high strength of more than tensile strength 510MPa, metal structure is set in fact the mixed structure of ferrite and bainite and pseudopearlite.The mixed structure of ferrite and bainite and pseudopearlite is as undertissue in fact: the Line Integral rate of their total is more than 95%, as rest part, in one kind or two or more containing in the martensite, island-like martensite, retained austenite etc. of less than 5% of Line Integral rate.
In addition, principal phase be greater than in Line Integral rate 50% tissue, the preferred ferritic Line Integral rate of ferrite of principal phase is more than 55%.In addition, the 2nd is the tissue that Line Integral rate is less than 50% mutually.
For the thick-wall materials of thickness of slab 30mm ~ 50mm, in order to realize the raising of high strength and fatigue characteristic, preferably add up to as the bainite of the 2nd phase and pseudopearlite with Line Integral rate score loose more than 15%.By making in Line Integral rate more than 15%, the intensity of mother metal, the raising of fatigue strength can be expected.In addition, pseudopearlite is the perlite (lamelliform perlite) being dispersed into stratiform relative to carbide and ferritic phase, thin layer shape is disintegrated and carbide bends, or be dispersed into the block tissue using massive carbide as main body, sometimes also comprise a part of lamelliform carbide (counting less than 40% with Line Integral rate relative to carbide total amount).Think that the form of carbide is for time block, relative to filmated situation, decline at the stress concentration of parent phase/the 2nd phase interface, fatigue cracking produces suppressed, and fatigue strength improves.
3. about manufacture method
Preferably the steel with above-mentioned composition is carried out melting with the melting such as converter, electric furnace mechanism by well-established law, make the steel raw materials such as steel billet with Continuous casting process or ingot casting ~ cogging method etc. by well-established law.In addition, for melting method, casting, aforesaid method is not limited to.In addition, from the view point of economy, preferably carry out the casting of the steel disc utilizing the steel making technology of converter process and utilize continuous casting process.Thereafter, the shape needed for performance is rolled into.Manufacturing condition of the present invention is below shown.
The temperature condition of the steel specified in the present invention refers to the medial temperature in steel disc or steel plate thickness of slab direction.The medial temperature in thickness of slab direction is obtained by analog calculation etc. by thickness of slab, surface temperature and cooling conditions etc.Such as, by the temperature distribution using method of finite difference to calculate thickness of slab direction, the medial temperature in thickness of slab direction can be obtained.
(1) Heating temperature: 950 ~ 1250 DEG C
When carrying out hot rolling, need to make steel disc fully austenitizing, therefore Heating temperature is set to more than 950 DEG C.On the other hand, be greater than the temperature of 1250 DEG C if be heated to by steel disc, then austenite grain starts coarsening, causes detrimentally affect to toughness, and therefore Heating temperature is set to the scope of 950 ~ 1250 DEG C.From the view point of toughness, the scope of preferred Heating temperature is 1000 DEG C ~ 1100 DEG C.
(2) at Ar 3the accumulation draft that point is above: more than 50%
In rolling, toughness is improved, at Ar in order to crystal grain is maintained fine 3the temperature province importing processing deformation that point is above.For accumulation draft, by being set to more than 50%, the abundant miniaturization of the ferrite crystal grain after phase transformation and realize toughness improve.Therefore, by the accumulation draft in rolling at Ar 3point is above is set to more than 50%.Should illustrate, Ar 3point is obtained by following formula (2).
Ar 3＝910-310[％C]-80[％Mn]-20[％Cu]-55[％Ni]-15[％Cr]-80[％Mo](2)
Here, each symbol of element refers to the content (quality %) of each element, and situation about not containing is set to 0.
When hot-rolled temperature starts temperature lower than ferrite transformation, generate ferrite in pressure process and strength degradation, therefore hot rolling end temp is at least set to Ar 3more than point.
(3) cooling starts temperature: Ar 3point more than-60 DEG C
If it is too low that cooling starts temperature, then uprise at the last stage ferrite growing amount of accelerating cooling, strength degradation.Therefore, from Ar 3the temperature of more than-60 DEG C begins to cool down.
(4) speed of cooling: more than 5 DEG C/sec
Continue after hot rolling to implement accelerating cooling.By speed of cooling is set to more than 5 DEG C/sec, tissue does not have coarsening, can obtain fine grained structure, can obtain the intensity of the excellence as target, toughness and fatigue characteristic.When speed of cooling is less than 5 DEG C/sec, organize coarsening, and ferrite divides rate to become large, cannot obtain as the strength of parent of target, fatigue strength, fatigue cracking expansionary.In addition, as the upper limit of speed of cooling, below the speed of cooling when cooling curve preferably had in the CCT figure of the steel raw material of mentioned component composition is in ferrite transformation protuberance.When speed of cooling is greater than the speed of cooling being in ferrite transformation protuberance, a bainite point rate uprises, and cannot obtain ductility and the toughness of, mother metal expansionary as the fatigue cracking of target.In order to obtain required tissue, within the scope of this speed of cooling, thickness of slab is preferably 30mm ~ 50mm.
In addition, CCT figure (continuous cooling transformation diagram) is made by following usual method: the cylindrical sample gathering multiple φ 8 × 12mm from the steel with mentioned component composition, processing and heat treatment is carried out with the cooling mode under the processing corresponding with rolling and various speed of cooling, the expansion of Simultaneously test test film and investigate transformation temperature in hot-work reproduction test device.Obtain the speed of cooling of the curve (CCT figure is logarithm due to transverse axis (time), therefore becomes curve) of the constant speed of cooling of the ferrite transformation protuberance (side that in the region of ferrite transformation, speed of cooling is the fastest occurs) of the CCT figure by gained as shown in Figure 1.In the present invention, cool with more than 5 DEG C/sec and for the speed of cooling below the speed of cooling when cooling curve in CCT figure is in ferrite transformation protuberance, thus generate pseudopearlite, fatigue strength improves.
(5) cooling stops temperature: 600 ~ 350 DEG C
By stopping temperature being set to 350 DEG C ~ 600 DEG C cooling, the tissue needed for being obtained by hot rolling and cooling subsequently can be formed.If cooling stops temperature higher than 600 DEG C, then the dispersion amount of bainite, pseudopearlite becomes insufficient, if lower than 350 DEG C, is then difficult to guarantee ductility toughness.Temperature is stopped, more preferably 400 DEG C ~ 550 DEG C as cooling.
(6) tempering temperature: Ac 1below point
Need to carry out the shape corrections of steel or ductility, toughness raising time, can be less than Ac after accelerating cooling 1point carries out tempering.If tempering temperature is greater than Ac 1point, then generate island-like martensite, degraded toughness.In addition, Ac 1point is obtained by following formula (3).
Ac 1＝723-11[％Mn]+29[％Si]-17[％Ni]+17[％Cr](3)
Here, each symbol of element refers to the content (quality %) of each element, and situation about not containing is set to 0.
Embodiment 1
For the steel disc that the one-tenth shown in table 1 is grouped into, make under the manufacturing condition shown in table 2 thickness of slab 30 ~ 50mm for examination steel, the metal structure of the steel plate that inquiry agency obtains is observed, mechanical properties and fatigue strength, fatigue cracking developing characteristics.In addition, speed of cooling when cooling curve in CCT figure (continuous cooling transformation diagram) is in ferrite transformation protuberance is made by following usual method and obtains: from the cylindrical sample having steel that the one-tenth shown in table 1 is grouped into and gather multiple φ 10 × 12mm, processing and heat treatment is carried out with the cooling mode under the processing corresponding with rolling and various speed of cooling, the expansion of Simultaneously test test film and investigate transformation temperature in hot-work reproduction test device.
[table 1]
[table 2]
Structure observation uses grinding from the sample of the sample of arbitrary station acquisition, implements in thickness of slab 1/4 position in the rolling direction cross section utilizing 3% nital etched (L cross section).In addition, the area occupation ratio of ferrite, bainite, pseudopearlite is measured by observation by light microscope.These values implement with 5 visuals field 1 sample, obtains with the form of the mean value at their total visual field.
Tensile properties is the test film (NKV1 test film) being used in total thickness × punctuate spacing 200mm that rolling direction and right angle orientation (C direction) gather, and implements tension test, obtain tensile properties according to the regulation of a NK ship's classification K section.
Toughness is gathered abreast from thickness of slab 1/4 position and rolling direction by 2mmV v notch v Charpy impact test sheet (NKV4 test film), implement Charpy impact test according to the regulation of a NK ship's classification K section, the mean value (vE-40 (J)) being used in 3 at test temperature-40 DEG C is evaluated.
Fatigue strength is the pole tension test sheet using φ 12mm × punctuate spacing 24mm, evaluates with value during 1,000,000 secondary stress load repeatedly.For test film, according to JISZ2273, thickness of slab 50mm material is from thickness of slab 1/4 station acquisition, and thickness of slab 30mm material is from thickness of slab 1/2 station acquisition.
Fatigue cracking developing characteristics is according to ASTME647, uses the CT test film of thickness of slab 25mm to investigate to fatigue cracking development test during C future development be full of cracks.For test film, thickness of slab 50mm material is from thickness of slab 1/4 station acquisition, and thickness of slab 30mm material is from thickness of slab 1/2 station acquisition.Test conditions carries out in stress ratio 0.1, atmosphere at room temperature, evaluates 25MPam in stress amplification coefficient scope (Δ K) 1/2time fatigue cracking tempo.
Test-results is shown in table 3.
[table 3]
Test-results is with yielding stress YS:390N/mm 2above, tensile strength TS:510N/mm 2above, elongation: more than 19%, more than vE-40:100J, fatigue strength: more than 340Mpa, fatigue cracking tempo: 1.0 × 10 -7(m/ circulation) is below as whether qualified determinating reference.
Confirmed by table 3, the No.1-1 ~ 8-1 as example of the present invention is all yielding stress YS is 390N/mm 2above, tensile strength TS is 510N/mm 2above, there is excellent mother metal characteristic.In addition, the fatigue strength of steel of the present invention is more than 340MPa, and fatigue cracking tempo is 1.0 × 10 -7(m/ circulation) below, fatigue characteristic are also excellent.On the other hand, depart from the No.9-1 ~ 12-1 of the comparative example of scope of the present invention as chemical composition, manufacturing condition, any one the above characteristic in above-mentioned is poor.
Embodiment 2
For the steel disc that the one-tenth shown in table 4 is grouped into, make under the manufacturing condition shown in table 5 thickness of slab 30 ~ 50mm for examination steel, the metal structure of the steel plate that inquiry agency obtains is observed, mechanical properties and fatigue strength, fatigue cracking developing characteristics.In addition, speed of cooling when cooling curve in CCT figure (continuous cooling transformation diagram) is in ferrite transformation protuberance is made by following usual method and obtains: from the cylindrical sample having steel that the one-tenth shown in table 4 is grouped into and gather multiple φ 10 × 12mm, processing and heat treatment is carried out with the cooling mode under the processing corresponding with rolling and various speed of cooling, the expansion of Simultaneously test test film and investigate transformation temperature in hot-work reproduction test device.
[table 4]
[table 5]
Structure observation uses grinding from the sample of the sample of arbitrary station acquisition, implements in thickness of slab 1/4 position in the rolling direction cross section utilizing 3% nital etched (L cross section).In addition, the area occupation ratio of ferrite, bainite, pseudopearlite is measured by observation by light microscope.These values implement with 5 visuals field 1 sample, obtains with the form of the mean value at their total visual field.
Tensile properties is the test film (NKV1 test film) being used in total thickness × punctuate spacing 200mm that rolling direction and right angle orientation (C direction) gather, and implements tension test, obtain tensile properties according to the regulation of a NK ship's classification K section.
Toughness is gathered abreast from thickness of slab 1/4 position and rolling direction by 2mmV v notch v Charpy impact test sheet (NKV4 test film), implement Charpy impact test according to the regulation of a NK ship's classification K section, the mean value (vE-40 (J)) being used in 3 at test temperature-40 DEG C is evaluated.
Fatigue strength is the pole tension test sheet using φ 12mm × punctuate spacing 24mm, evaluates with value during 1,000,000 secondary stress load repeatedly.For test film, according to JISZ2273, thickness of slab 50mm material is from thickness of slab 1/4 station acquisition, and thickness of slab 30mm material is from thickness of slab 1/2 station acquisition.
Fatigue cracking developing characteristics is according to ASTME647, uses the CT test film of thickness of slab 25mm to investigate to fatigue cracking development test during C future development be full of cracks.For test film, thickness of slab 50mm material is from thickness of slab 1/4 station acquisition, and thickness of slab 30mm material is from thickness of slab 1/2 station acquisition.Test conditions carries out in stress ratio 0.1, atmosphere at room temperature, evaluates 25MPam in stress amplification coefficient scope (Δ K) 1/2time fatigue cracking tempo.
Test-results is shown in table 6.
[table 6]
Test-results is with yielding stress YS:390N/mm 2above, tensile strength TS:510N/mm 2above, elongation: more than 19%, more than vE-40:100J, fatigue strength: more than 340Mpa, fatigue cracking tempo: 8.5 × 10 -8(m/cycle) below as whether qualified determinating reference.
Confirmed by table 6, the No.1-2 ~ 8-2 as example of the present invention is all yielding stress YS is 390N/mm 2above, tensile strength TS is 510N/mm 2above, there is excellent mother metal characteristic.In addition, the fatigue strength of steel of the present invention is more than 340MPa, and fatigue cracking tempo is 8.5 × 10 -8(m/ circulation) below, fatigue characteristic are also excellent.Can say that through type (1) is greater than 0 and is less than 0.8, can obtain the expansionary more excellent High Strength Steel of fatigue cracking.On the other hand, depart from the No.9-2 ~ 16-2 of the comparative example of the scope of the invention as chemical composition, manufacturing condition, any one the above characteristic in above-mentioned is poor.

Claims (7)

1. the High Strength Steel of an excellent in fatigue characteristics, in mass %, become to be grouped into containing C:0.10 ~ 0.20%, below Si:0.50%, Mn:1.0 ~ 2.0%, below P:0.030%, S:0.0005 ~ 0.0040%, Sol.Al:0.002 ~ 0.07%, Ca:0.0005 ~ 0.0050%, rest part is made up of Fe and inevitable impurity, and metal structure is the ferrite of principal phase and the bainite of the 2nd phase and pseudopearlite.
2. the High Strength Steel of excellent in fatigue characteristics as claimed in claim 1, is characterized in that, in mass %, becomes to be grouped into further containing the one be selected from Ti:0.003 ~ 0.03%, Nb:0.005 ~ 0.05% or two kinds.
3. the High Strength Steel of excellent in fatigue characteristics as claimed in claim 1 or 2, it is characterized in that, in mass %, become to be grouped into further containing be selected from Cr:0.1 ~ 0.5%, Mo:0.02 ~ 0.3%, V:0.01 ~ 0.08%, Cu:0.1 ~ 0.6%, Ni:0.1 ~ 0.5% more than one.
4. the High Strength Steel of the excellent in fatigue characteristics according to any one of claims 1 to 3, is characterized in that, becomes to be grouped into further containing below O:0.0040%, and meets following formula (1),
0＜(Ca-(0.18+130×Ca)×O)/1.25/S≤0.8···(1)，
Wherein, Ca, O, S in formula (1) represent the content of each composition, and wherein, the content of each composition in mass %.
5. a manufacture method for the High Strength Steel of excellent in fatigue characteristics, is characterized in that, after the steel raw material that the one-tenth had according to any one of Claims 1 to 4 is grouped into is heated to 950 ~ 1250 DEG C, at Ar 3point is above carries out the rolling that accumulation draft is more than 50%, with the speed of cooling of more than 5 DEG C/sec from Ar 3the temperature province of the temperature province accelerating cooling to 350 of point more than-60 DEG C DEG C ~ 600 DEG C.
6. the manufacture method of the High Strength Steel of excellent in fatigue characteristics as claimed in claim 5, it is characterized in that, described speed of cooling is below the speed of cooling of the cooling curve had in the CCT figure of the steel raw material that the one-tenth according to any one of described Claims 1 to 4 is grouped into when being in ferrite transformation protuberance.
7. the manufacture method of the High Strength Steel of the excellent in fatigue characteristics as described in claim 5 or 6, is characterized in that, after described accelerating cooling, further with Ac 1the following temperature of point carries out temper.
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