CN105154761A - Steel with excellent anti-ductile crack generation characteristics in weld heat-affected zone and base material and manufacturing method therefor - Google Patents

Steel with excellent anti-ductile crack generation characteristics in weld heat-affected zone and base material and manufacturing method therefor Download PDF

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Publication number
CN105154761A
CN105154761A CN201510543254.2A CN201510543254A CN105154761A CN 105154761 A CN105154761 A CN 105154761A CN 201510543254 A CN201510543254 A CN 201510543254A CN 105154761 A CN105154761 A CN 105154761A
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steel
ductile fracture
affected zone
hard phase
resistance
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贞末照辉
伊木聪
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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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • 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
    • 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
    • C21D2211/008—Martensite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

A steel material has a composition of C: 0.02 to 0.2%, Si: 0.01 to 0.5%, Mn: 0.5 to 2.5%, P: 0.05% or lower, S: 0.05% or lower, Al: 0.1% or lower, and N: 0.01% or lower and, as required, one or two or more elements selected from Cu: 0.01 to 2%, Ni: 0.01 to 5%, Cr: 0.01 to 3%, Mo: 0.01 to 2%, Nb: 0.1% or lower, V: 0.1% or lower, Ti: 0.1% or lower, B: 0.01% or lower, Ca: 0.01% or lower, and REM: 0.1% or lower in terms of % by mass, and the balance Fe with inevitable impurities, in which the microstructure at the 1/4 position of the plate thickness contains ferrite and a hard phase, the area fraction of the hard phase is 50 to 90%, and the average aspect ratio of the ferrite is 1.5 or more.

Description

The steel that the occurrence features of resistance to ductile fracture in welding heat affected zone and mother metal portion is excellent and manufacture method thereof
The application is international filing date is on December 25th, 2009, application number be 200980152648.8, denomination of invention is the divisional application of the application of " steel that the occurrence features of resistance to ductile fracture in welding heat affected zone and mother metal portion is excellent and manufacture method thereof ".
Technical field
The present invention relates to applicable steel and the manufacture method thereof being used in the welded structures (weldedstructure) such as pipeline (pipeline), bridge, buildings (architecturalstructure) of claimed structure security, especially relate to the excellent steel of the occurrence features of resistance to ductile fracture (resistanceofductilecrackinitiation) in welding heat affected zone (weldedheataffectedzone) and mother metal portion and manufacture method thereof.Specifically, ductility/fragility section transition temperature (ductile-brittlefracturetransitiontemperature) vTrs of the intensity that excellent with the occurrence features of resistance to ductile fracture in welding heat affected zone and mother metal portion and tensile strength TS is more than 490MPa, Charpy impact test (Charpyimpacttest) (with JISZ2242 be defined as benchmark) is that the structural steel with high tenacity of less than 0 DEG C is for object.
Background technology
There will be a known the welded structures such as pipeline, bridge, buildings when being exposed under the large outer load (externalload) of earthquake etc., concentrate position (stressconcentrationzone) that ductile fracture (ductilecrack) occurs in toe of weld portion (weldtoe) equal stress, the ductile fracture occurred becomes trigger point (trigger), thus produces brittle rupture (brittlefracture) and cause the breakage (break) of works, the situation of destruction (fracture).
In order to avoid breakage, the destruction of this kind of welded structure, the situation forming the occurrence features of resistance to ductile fracture of the steel of described welded structure excellent is very important.
The excellent high tensile steel of a kind of occurrence features of resistance to ductile fracture is recorded in patent documentation 1, it is characterized in that, the ferrite percentage rate (ferriteareafraction) of the microtexture (microstructure) in steel surface portion is 10 ~ 40%, the percentage of bainite (bainite) is more than 50%, and median size (averagegrainsize) is less than 5 μm.
A kind of braking characteristic (arrestrability) and the excellent steel plate of the destruction characteristic of resistance to ductile fracture (resistanceofductilefracture) is recorded in patent documentation 2, it is the steel plate that microtexture is made up of ferritic structure, pearlitic structure (pearlitestructure) and bainite structure in fact, when being divided into the central part these three layers in two surface elements of steel plate and thickness of slab direction, there is specific microtexture respectively.
When two surface elements of steel plate are each more than 5% of thickness of slab, by there is the ferritic structure of more than 50% and the layer that the bainite percentage of this part is less than 5 ~ 25% is formed, this ferritic structure has the ferrite grain that the suitable particle diameter of circle is less than 7 μm, aspect ratio (aspectratio) is 2 ~ 4, when the central part in the thickness of slab direction of steel plate is more than 50% of thickness of slab, by having, the suitable median size of circle is 4 ~ 10 μm, aspect ratio is the ferrite grain of less than 2 and the layer that the bainite percentage of this part is less than 10% is formed.
Namely, the technology of patent documentation 2 relates to a kind of steel plate, its surface of plate from steel plate has three layers towards thickness of slab direction, this layer has the ferrite/pearlitic structure be made up of the ferrite grain that aspect ratio is different, and then in this ferrite/pearlitic structure that the bainite structure as hard phase is suitably distributed to as soft phase.Wherein, the large processing ferrite grain of aspect ratio is formed energetically respectively at two surface elements of steel plate, and suitably disperse by making bainite structure and improve braking characteristic, on the other hand, axle ferrite grain tissue is waited uniformly by being controlled to by the central part of steel plate, and suppress bainite structure, and improve stretch characteristics important ductile failure during normal temperature, by two surface elements of this steel plate and central part are controlled to above-mentioned three-decker, and meet the contrary characteristic of " braking characteristic " and " ductile failure characteristic " these two.
In addition, the technology of patent documentation 3, also in the same manner as the technology of patent documentation 2, is form processing ferrite grain in the steel plate skin section of ferrite pearlific steel, and the microtexture of steel plate inside is formed as the technology waiting axle ferrite grain uniformly.
That is, in patent documentation 3, record strictly controlled rolling condition and steel plate skin section be formed as the manufacture method of the braking characteristic of specific microtexture and the Plate Steel of ductile failure characteristic good.
Specifically, when the thickness of rolling midway is t, be more than 0.05t and the surface region of below 0.15t (surfacelayerzone), at Ar relative to distance two surface in thickness of slab direction 3more than transformation temperature and in the non-recrystallization temperature field (nonrecrystallizationtemperaturezone) of less than 900 DEG C, apply suitable viscous deformation (equivalentplasticstrain) ε becoming ε>=0.5.
Then, suitable amount of plastic deformation (residualandcumulativeequivalentplasticstrain) the ε r of the residual accumulation in described surface region meets in the time of ε r>=0.5, is more maintained in Ar by the temperature of the interior region of core side by than the position being thickness of slab t/4 apart from two surfaces 3more than transformation temperature, and utilize the speed of cooling of 2 ~ 15 DEG C/s that described surface region is cooled to the temperature range of 450 ~ 650 DEG C, then again start rolling.
In the rolling again started, described interior region is applied to the residual accumulation suitable viscous deformation ε r of 0.35≤ε r<0.55, at Ar 3more than transformation temperature terminate rolling, and make described surface region backheat (recuperate) to Ar by processing heating (processingheat) and inner sensible heat (internalsensibleheat) 3below transformation temperature, then cool in the mode making average cooling rate become 1 ~ 10 DEG C/s.
In addition, the technology of patent documentation 1 ~ 3 is all to be rolled or at finishing temperature Ar at austenitic non-recrystallization territory (grain refined temperature field) 3more than be rolled, thus in austenite, form fine subgrain, the tissue after phase transformation is carried out to the technology of miniaturization.
Patent documentation 1: Japanese Unexamined Patent Publication 2008-202119 publication
Patent documentation 2: Japanese Unexamined Patent Publication 2000-328177 publication
Patent documentation 3: Japanese Unexamined Patent Publication 2003-221619 publication
Summary of the invention
But the technology of patent documentation 1 ~ 3 is when making skin section tissue change to welding heat affected zone by welding etc., and worry can lose the effect that resistance to ductile fracture occurs.
In addition; the scale breaker (scalebreaker) used the process of the steel slab surface from process furnace extraction described in the embodiment of patent documentation 1; or this two stage rolling of rolling process under the temperature field of rolling process under grain refined temperature field described in the embodiment of patent documentation 2 and setting, and then many-sided rolling of the tissue for the tissue and steel plate inside that are divided into top layer as described in Patent Document 3 or temperature controlled manufacturing process all miscellaneous.
Therefore, the present invention makes in view of the problem of above-mentioned prior art, the steel that its object is to provide the occurrence features of resistance to ductile fracture in a kind of welding heat affected zone and mother metal portion excellent by easy method and manufacture method thereof.
The present inventors to achieve these goals, the mother metal tissue that the occurrence features of resistance to ductile fracture of welding heat affected zone is excellent has been carried out studying with keen determination, find to present on 1/4 position of the thickness of slab of average tissue in the thickness of slab direction of steel plate, when by mother metal organization formation being ferrite and hard phase that the area percentage of ferritic average aspect ratio and hard phase (hardphase) is specified, the occurrence features of resistance to ductile fracture of welding heat affected zone is excellent, and, the occurrence features of resistance to ductile fracture in the mother metal portion of this kind of steel is also excellent, and then found the manufacturing condition of the steel plate possessing this microtexture.
The present invention is based on above-mentioned opinion, completing through further studying, that is,
(1) steel that the occurrence features of resistance to ductile fracture in a kind of welding heat affected zone and mother metal portion is excellent, it is characterized in that, there is following composition, namely in mass %, contain: C:0.02 ~ 0.2%, Si:0.01 ~ 0.5%, Mn:0.5 ~ 2.5%, below P:0.05%, below S:0.05%, below Al:0.1%, below N:0.01%, remainder is made up of Fe and inevitable impurity, the microtexture of 1/4 position of thickness of slab is made up of ferrite and hard phase, the area percentage of described hard phase is 50 ~ 90%, and described ferritic average aspect ratio is more than 1.5.
(2) excellent according to the occurrence features of resistance to ductile fracture in welding heat affected zone described in (1) and mother metal portion steel, in becoming to be grouped into also containing be selected from Cu:0.01 ~ 2%, Ni:0.01 ~ 5%, Cr:0.01 ~ 3%, Mo:0.01 ~ 2%, below Nb:0.1%, below V:0.1%, below Ti:0.1%, below B:0.01%, below Ca:0.01%, below REM:0.1% in mass % one or more.
(3) steel that the occurrence features of resistance to ductile fracture in basis (1) or the welding heat affected zone described in (2) and mother metal portion is excellent, it is characterized in that, the tissue of surface of steel plate is made up of ferrite and hard phase, ferritic area occupation ratio is more than 40%, and the average aspect ratio of ferrite particle diameter is more than 2.
(4) manufacture method of the steel that the occurrence features of resistance to ductile fracture in a kind of welding heat affected zone and mother metal portion is excellent, it is characterized in that, reheat the steel of the composition had described in (1) or (2) to more than 1000 DEG C, the rolling rate implementing the temperature field more than 900 DEG C is more than 50% and finishing temperature is Ar 3point ~ Ar 3after the rolling of-50 DEG C, at Ar 3-10 DEG C ~ Ar 3start water-cooled at-70 DEG C, below 500 DEG C, terminate water-cooled.
(5) according to the manufacture method of the excellent steel of the occurrence features of resistance to ductile fracture in welding heat affected zone described in (4) and mother metal portion, it is characterized in that, after having carried out water-cooled, and then at maximum heating temperature lower than Ac 1temper is carried out under the condition of point.
[invention effect]
According to the present invention, can easily and stable and produce following steel in a large number, even if described steel are such as produce the gross distortion that earthquake etc. causes on steel structure, also can suppress the steel concentrating the generation of the ductile fracture in portion can suppressing can prevent the welding heat affected zone of collapsing of steel structure or breakage and the ductile fracture in mother metal portion to occur from toe of weld portion equal stress, thus industrially play special effect.
Accompanying drawing explanation
Fig. 1 is the figure of the ductile fracture generation test method representing welding heat affected zone.
Fig. 2 is the figure representing the impact that the area percentage of hard phase and the ductile fracture of ferritic Mean aspect comparison 1400 DEG C of simulated thermal cycles materials occur.
Fig. 3 is the figure of the ductile fracture generation test method representing mother metal portion.
Fig. 4 is the figure representing the impact that the area percentage of hard phase and the ductile fracture in ferritic Mean aspect comparison mother metal portion occur.
Embodiment
In the present invention, one-tenth to be grouped into and microtexture specifies.In the explanation becoming to be grouped into, as long as be not specifically noted, quality % is only represented by %.
[one-tenth is grouped into]
C:0.02～0.2％
C is the element with the effect making the intensity of steel increase, and contributes to the generation of hard phase in the present invention especially.Need containing more than 0.02% to obtain this kind of effect.On the other hand, containing during more than 0.2%, ductility (ductility), bendability (bendingworkability) can be reduced, and reduce weldability (weldability).Therefore, C is limited in the scope of 0.02 ~ 0.2%.Be more preferably 0.02 ~ 0.18%.
Si:0.01～0.5％
Si works as reductor, and has solid solution and improve the effect of the intensity of steel.Need containing more than 0.01% to obtain this kind of effect.On the other hand, containing reducing toughness more than 0.5% and reducing weldability.Therefore, Si is limited in the scope of 0.01 ~ 0.5%.More preferably 0.01 ~ 0.4%.
Mn:0.1～2.5％
Mn has the intensity the effect improving toughness that increase steel by improving hardenability.In order to obtain this kind of effect, and need containing more than 0.1%.On the other hand, containing weldability can be made to decline more than 2.5%.Therefore, Mn is limited in the scope of 0.1 ~ 2.5%.Be more preferably 0.5 ~ 2.0%.
Below P:0.05%
Because P can cause the deterioration of toughness, therefore preferably reduced as far as possible, but can be allowed to 0.05%.Therefore, P is defined as less than 0.05%.Be more preferably less than 0.04%.
Below S:0.05%
S exists as inclusion in steel, can make the deterioration of ductility, toughness, therefore preferably be reduced as far as possible, but can allow to 0.05%.Therefore, S is defined as less than 0.05%.Be more preferably less than 0.04%.
Below Al:0.1%
Al works as reductor and contributes to the element of the miniaturization of crystal grain, but more than 0.1% excessively containing the decline that can cause toughness.Therefore, Al is defined as less than 0.1%.Be more preferably less than 0.05%.
Below N:0.01%
N is the element of the intensity being increased steel in the same manner as C by solution strengthening, but the excessive decline containing toughness can be caused, therefore N is defined as less than 0.01%.Be more preferably less than 0.005%.
Above-mentioned composition is basal component, but in the present invention, can also be one kind or two or more containing what be selected from Cu:0.01 ~ 2%, Ni:0.01 ~ 5%, Cr:0.01 ~ 3%, Mo:0.01 ~ 2%, below Nb:0.1%, below V:0.1%, below Ti:0.1%, below B:0.01%, below Ca:0.01%, below REM:0.1% according to desired characteristic.
Cu:0.01～2％
Cu has the element being increased the effect of the intensity of steel by increase hardenability or solid solution.Need in order to ensure this kind of effect containing more than 0.01%.On the other hand, containing more than 2% can make weldability decline, and easily produces flaw when steel manufacture.Therefore, add time be 0.01 ~ 2% scope.Be more preferably 0.01 ~ 1%.
Ni:0.01～5％
Ni contribute to the raising of low-temperature flexibility, hardenability increase, containing the red brittleness contributing to preventing Cu during Cu, therefore add as required.Interpolation by more than 0.01% and this kind of effect can be confirmed, but the interpolation of more than 5% can cause the decline of steel product cost and reduce weldability.Therefore, add time be 0.01 ~ 5% scope.Be more preferably 0.01 ~ 4.5%.
Cr:0.01～3％
Cr increases the intensity of steel by improving hardenability or increase temper softening resistance, therefore add as required.By this kind of effect can be confirmed containing more than 0.01%.On the other hand, the interpolation more than 3% can make weldability and toughness decline.Therefore, add time be 0.01 ~ 3% scope.Be more preferably the scope of 0.01 ~ 2.5%.
Mo:0.01～2％
Mo increases the intensity of steel by improving hardenability or increase temper softening resistance, therefore add as required.By this kind of effect can be confirmed containing more than 0.01%.On the other hand, the interpolation more than 2% can make weldability or toughness decline.Therefore, add time be 0.01 ~ 2% scope.Be more preferably the scope of 0.01 ~ 1%.
Below Nb:0.1%
Nb separates out as carbide (carbide) or carbonitride (carbonitride) when tempering, and increases the element of the intensity of steel by precipitation strength (precipitationstrengthening).And Nb also has makes the miniaturization of austenite grain when rolling and the effect improving toughness.In order to obtain this effect, be preferably more than 0.001%.But containing more than 0.1% can make toughness decline.Therefore, be less than 0.1% when adding.Be more preferably less than 0.05%.
Below V:0.1%
V is when tempering as carbide or Carbonitride Precipitation, and passes through precipitation strength and increase the element of the intensity of steel.And, also have and make the miniaturization of austenite grain when rolling and the effect improving toughness.In order to obtain this effect, be preferably more than 0.001%.But containing more than 0.1% can make toughness decline.Therefore, be less than 0.1% when adding.Be more preferably less than 0.05%.
Below Ti:0.1%
Ti has makes austenite miniaturization and the effect improving toughness in welding heat affected zone, therefore adds as required.More than 0.001% is preferably in order to obtain this effect.But the interpolation more than 0.1% can make toughness decline, and causes the surging of steel product cost.Therefore, be less than 0.1% when adding.Be more preferably less than 0.05%.
Below B:0.01%
B has in a small amount of effect increasing the intensity of steel containing sometimes improving hardenability, therefore adds as required.More than 0.0001% is preferably in order to obtain this effect.But the interpolation of less than 0.01% can make weldability decline.Therefore, be less than 0.01% when adding.Be more preferably less than 0.005%.
Below Ca:0.01%
Ca improves base metal tenacity by the morphology Control of CaS inclusion, and then improves the toughness of welding heat affected zone, therefore adds as required.More than 0.0001% is preferably in order to obtain this effect.But the interpolation more than 0.01% can reduce toughness due to the increase of CaS inclusion.Therefore, be less than 0.01% when adding.Be more preferably less than 0.009%.
Below REM:0.1%
REM is the element of the toughness improving welding heat affected zone, adds as required.More than 0.0001% is preferably in order to obtain this effect.But the interpolation more than 0.1% can cause the decline of toughness.Therefore, be less than 0.1% when adding.Be more preferably less than 0.05%.
It should be noted that, REM is the general name of rare earth element and Y, Ce etc., refers to the total amount of these rare earth elements at this said addition.
[microtexture]
The tissue that steel of the present invention possess 1/4 position of thickness of slab is made up of ferrite and hard phase, and the area percentage of hard phase is 50 ~ 90%, and the average aspect ratio of ferrite particle diameter is the microtexture of more than 1.5.The area percentage of hard phase be less than 50% more than 90% or the average aspect ratio of ferrite particle diameter be less than in the scope of 1.5, likely can produce ductile fracture.
It should be noted that, the higher limit of the average aspect ratio of ferrite particle diameter does not need to be particularly limited to, but from the ability etc. of roller mill, is less than 5.And the area percentage of hard phase is more preferably 52 ~ 90%, the average aspect ratio of ferrite particle diameter is more preferably more than 1.6.Further preferably more than 1.7.
In the mixed structure of the two-phase be made up of ferrite and hard phase, the yield ratio of mother metal declines, even if under for the state of mother metal or after the simulated thermal cycles (simulatedheatcycle) simulating welding heat affected zone, (strainconcentration) is concentrated in the distortion that also can relax stress concentration portion.This kind of effect cannot obtain when single-phase ferrite or single-phase hard phase.
In addition, the tissue of the surface of steel plate (surperficial apart from plate is 1mm) of steel of the present invention is made up of ferrite and hard phase, and ferritic area occupation ratio, more than 40%, is more preferably more than 50%.And the average aspect ratio of ferrite particle diameter is more than 2.Ferritic area occupation ratio is less than 40% or the average aspect ratio of ferrite particle diameter when being less than 2, and the occurrence features of resistance to ductile fracture of welding heat affected zone is poor.
In the present invention, hard phase is bainite, martensite or bainite/martensite mixed structure, comprises the island-like martensite (islandmartensite, M-Aconstituent:M-A constituent element) (MA) that area percentage is less than 5%.
Fig. 2 represents the simulated thermal cycles test film (simulatedheatcyclespecimen) (maximum heating temperature 1400 DEG C) using weld part, investigate the result of the occurrence features of resistance to ductile fracture, as shown in Figure 2, when the area percentage of the hard phase of mother metal is 50 ~ 90% and ferritic average aspect ratio is more than 1.5, even if the generation of ductile fracture also cannot be confirmed after simulated thermal cycles.
Result shown in Fig. 2 is, from 1/4 center of the thickness of slab of the steel and the steel that make microtexture change that make the composition in the scope of the invention with various manufacture method (when thickness of slab is below 25mm, 1/2 center of thickness of slab) choose the test film of 12mm thickness (=thickness of slab direction) × 12mm width × 200 length, the simulated thermal cycles (time arriving maximum heating temperature is 6s, speed of cooling from maximum heating temperature to room temperature be 40 DEG C/s) being applied to weld part by hot modeling test machine (Gleebletester) is obtained as sample.
Fig. 1 represents test film shape and test conditions.Utilize clamp (clamp) 5 to import the parts after one-sided through breach (singlethrough-thicknessedgenotch) to the thickness of slab direction of mediad length 3mm in simulated thermal cycles portion 2 at the sample (test film 1) being applied with simulated thermal cycles to limit, undertaken by the displacement of the clip tens(i)ometer (clipgage) 3 between the knife-edge support (knife-edge) 4 of screw threads for fastening after the tension load (tensileload) (arrow 6) of 0.6mm, removing load, cut the presence or absence occurred of breaking evaluating notch tip into/mirror ultrafinish to test film width midway portion.The situation from the ductile fracture at the bottom of breach being more than 50 μm is defined as and breaks.
By mother metal being formed as the complex tissue of ferrite and hard phase, in tissue after simulated thermal cycles, to decline by making yield ratio (0.2% endurance/tensile strength) and the degree concentrated of the distortion in notch tip portion reduces and produces the result shown in Fig. 2.
In addition, this kind of excellent characteristic also can commonly confirm in the mother metal portion not applying simulated thermal cycles.
Namely, Fig. 4 represents that the microtexture having investigated mother metal portion is on the result of the impact of the occurrence features of resistance to ductile fracture, as shown in Figure 4, when the area percentage of the hard phase of mother metal is 50 ~ 90% and ferritic average aspect ratio is more than 1.5, the generation of ductile fracture cannot be confirmed.
The result in the mother metal portion shown in Fig. 4 is from making the steel of the composition in the scope of the invention with various manufacture method and the test film that 12mm thickness (=thickness of slab direction) × 12mm width × 200 length is chosen at 1/4 center (when thickness of slab is below 25mm, being 1/2 center of thickness of slab) changing the thickness of slab of the steel of microtexture carries out (Fig. 3).
Fig. 3 represents test film shape and test conditions.Clamp 5 is utilized to limit the parts after the one-sided through breach of thickness of slab direction importing of the mediad length 3mm at sample (test film 1), undertaken by the displacement of the clip tens(i)ometer 3 between the knife-edge support 4 of screw threads for fastening after the tension load (arrow 6) of 0.8mm, removing load, cuts the presence or absence occurred of breaking evaluating notch tip into/mirror ultrafinish to test film width midway portion.The situation from the ductile fracture at the bottom of breach being more than 50 μm is defined as and breaks.
Result shown in Fig. 4 is thought because by mother metal being formed as the complex tissue of ferrite and hard phase, and yield ratio (0.2% endurance/tensile strength) is declined, the degree that the distortion reducing notch tip portion is concentrated.
In addition, think that another major cause is by increasing ferritic average aspect ratio, that is, by making specifically to gather tissue growth, and under the state of mother metal and after simulated thermal cycles, make slipping plane (slipplane) relative to breaking and direction also larger inclination occurs.Aspect ratio refers to the ferrite particle diameter of ferrite particle diameter (major diameter)/thickness of slab direction (minor axis) of the rolling direction in the cross section parallel with rolling direction.
It should be noted that, when the maximum heating temperature of simulated thermal cycles is 760 DEG C, 900 DEG C, 1200 DEG C, also can obtain the result same with Fig. 2.
Steel of the present invention obtain by implementing hot-rolled process, water-cooled operation or further tempering process successively to the steel of mentioned component.
Hot rolling reheats more than 1000 DEG C, and the rolling rate implementing the temperature field more than 900 DEG C is more than 50% and finishing temperature becomes Ar 3point ~ Ar 3the rolling of-50 DEG C.Preferred finishing temperature is for being less than Ar 3point ~ Ar 3-40 DEG C.By being formed as this finishing temperature scope, machining deformation can being applied to the ferrite generated in rolling, ferritic aspect ratio can be improved.When reheating temperature lower than 1000 DEG C, hot rolling steel being applied to the accumulation rolling rate of wishing cannot be implemented.
In addition, the accumulation rolling rate of more than 900 DEG C lower than 50% time, intensity, the toughness of wishing cannot be guaranteed.When finishing temperature is more than Ar 3during point, ferritic aspect ratio is not more than 1.5.When finishing temperature is lower than Ar 3when-50 DEG C, the percentage of the hard phase obtained by water-cooled is not afterwards more than 50%.
Water-cooled operation after hot rolling, immediately at Ar 3-10 DEG C ~ Ar 3start water-cooled at-70 DEG C, below 500 DEG C, terminate water-cooled.Temperature is started higher than Ar in water-cooled 3when-10 DEG C, become area percentage lower than 10% ferrite (hard phase of area percentage more than 90%).And water-cooled starts temperature lower than Ar 3when-70 DEG C or when (within 300 seconds) start water-cooled after hot rolling not immediately, become area percentage higher than 50% ferrite (hard phase that area percentage is less than 50%) or do not wish in the present invention separate out perlite separate out, desired characteristic cannot be met.
After implementing above-mentioned cooling, Ac can also be less than 1temper is implemented under point.Toughness, ductility can be improved by implementing temper, desired intensity or toughness can be adjusted to.Tempering temperature is more than Ac 1during point, generate island-like martensite in large quantities, and toughness declines.
It should be noted that, Ar 3point, Ac 1point, based on the amount (quality %) of each composition, can utilize following formula to calculate.
Ar 3(℃)＝910-310C-80Mn-20Cu-15Cr-55Ni-80Mo
Ac 1(℃)＝723-14Mn+22Si-14.4Ni+23.3Cr
Below, based on embodiment, the present invention is described in detail.
[embodiment]
Implement hot rolling with the steel of the composition shown in the condition his-and-hers watches 1 shown in table 2, form the steel plate of thickness of slab 12 ~ 100mm.
For the steel plate obtained, the ductile fracture implemented after structure observation, tension test, toughness test, simulated thermal cycles is tested, the ductile fracture of mother metal is tested.Test method is as shown in (1) below ~ (5).
(1) structure observation
The cross section parallel with rolling direction, choose test film from the steel plate obtained, after mirror ultrafinish, nital etching, carry out 1/4 position of thickness of slab and the structure observation of the lower 1mm in surface.Observe respectively at field of view number: carry out under 20 visual fields.Area percentage is by carrying out 2 values to ferrite and hard phase and obtain with multiplying power × 200.Obtain the length of each the ferritic rolling direction existed in this visual field and the length in thickness of slab direction in multiplying power × 400 time, obtain the length in the length/thickness of slab direction of rolling direction, obtain their mean value as ferritic average aspect ratio.
(2) tension test
Be defined as benchmark with JISZ2201 (1998), to make draw direction be the mode with the rolling direction of steel plate direction at a right angle, have chosen the JIS5 test film of whole thickness from the steel plate obtained.Tension test is carried out for benchmark with JISZ2241 (1998), obtains 0.2% endurance (σ 0.2), tensile strength (TS), have rated static tensile properties.
(3) toughness test
Be defined as benchmark with JISZ2242 (2005), in the mode making length direction become the direction parallel with rolling direction, have chosen V notched specimen from the steel plate obtained, obtain ductility/fragility section transition temperature, evaluate toughness.Test film is chosen centered by 1/4 position of thickness of slab when thickness of slab is more than 20mm, chooses centered by 1/2 position of thickness of slab when thickness of slab is less than 20mm.
(4) ductile fracture after simulated thermal cycles is tested
The test film of 12mm thickness (=thickness of slab direction=t) × 12mm width, total length 200mm is have chosen from 1/4 center (when thickness of slab is below 25mm, being 1/2 center of thickness of slab) of the thickness of slab of the steel plate obtained.Use hot modeling test machine, the simulated thermal cycles (arriving the time of maximum heating temperature: 6s, the speed of cooling from maximum heating temperature to room temperature: 40 DEG C/s) that maximum heating temperature is the welding heat affected zone of 760 DEG C, 900 DEG C, 1200 DEG C, 1400 DEG C is applied with to this test film.
Then, as shown in Figure 1, one-sided through breach is imported in the thickness of slab direction of simulated thermal cycles portion mediad length 3mm.Breach is processed by electrodischarge machining(E.D.M.) and implements, and notch tip radius is 0.1mm.
For test, the both ends, left and right clamping test film with limited length 50mm, are applied with tension load.In test, utilize clip tens(i)ometer to measure the displacement between the knife-edge support that to be arranged on by screw threads for fastening near breach, carrying out because of the displacement of clip tens(i)ometer, after the tension load of 0.6mm, removing load.Then, in test, cut and carry out mirror ultrafinish into width midway, the situation occurred that breaks at the bottom of breach with the microscopic study of multiplying power × 50.Ductile fracture occurs to be defined as ductile fracture opens up more than 50 μm situation from breach end stretch.
(5) ductile fracture of mother metal is tested
From the steel plate obtained, at 1/4 center (when thickness of slab is below 25mm, 1/2 center for thickness of slab) of thickness of slab, have chosen the test film of 12mm thickness (=thickness of slab direction=t) × 12mm width, total length 200mm.
As shown in Figure 3, one-sided through breach has been imported to the thickness of slab direction of the test film mediad length 3mm of the test film obtained.Breach is processed by electrodischarge machining(E.D.M.) and implements, and notch tip radius is 0.1mm.
For test, the both ends, left and right clamping test film with limited length 50mm, are applied with tension load.In test, utilize clip tens(i)ometer to measure the displacement between the knife-edge support that to be arranged on by screw threads for fastening near breach, carrying out because of the displacement of clip tens(i)ometer, after the tension load of 0.8mm, removing load.Then, in test, cut and carry out mirror ultrafinish into width midway, the situation occurred that breaks at the bottom of breach with the microscopic study of multiplying power × 50.Ductile fracture occurs to be defined as ductile fracture opens up more than 50 μm situation from breach end stretch.
About the test film being applied with simulated thermal cycles, the experimental result obtained is as shown in table 3.Utilize specify in the present invention composition, No.1 ~ No.10 made by manufacture method steel plate all become the tissue of regulation of the present invention.And known, there is excellent intensity and toughness and the occurrence features of resistance to ductile fracture of welding heat affected zone is excellent.
On the other hand, C does not meet the steel plate (steel grade K*) of the No.11 of the lower limit of scope of the present invention is low tensile strength.And the toughness that C, P, S exceed the steel plate (steel grade L*) of the No.12 of the upper limit of scope of the present invention is low, and the ductile fracture occurrence features of welding heat affected zone is poor.
The toughness that temperature and the accumulation rolling rate of more than 900 DEG C lower than the present invention that reheat of slab departs from the steel plate of the No.13 of scope of the present invention is low.Finishing temperature and water-cooled start temperature and do not generate ferrite higher than the steel plate of the No.14 of scope of the present invention and do not become the tissue that the present invention specifies, the occurrence features of resistance to ductile fracture of welding heat affected zone is poor.
Water-cooled starts temperature and stops temperature not becoming value given to this invention higher than the hard phase percentage of the steel plate of the No.16 of scope of the present invention, ferritic average aspect ratio lower than the steel plate of the No.15 of scope of the present invention and water-cooled, be all low tensile strength, and the occurrence features of resistance to ductile fracture of welding heat affected zone is poor.The steel plate that tempering temperature exceedes the No.17 of scope of the present invention is low toughness owing to generating island-like martensite in a large number, and the occurrence features of resistance to ductile fracture of welding heat affected zone is poor.
About mother metal portion, the experimental result obtained is as shown in table 4.The tissue of regulation of the present invention is all become with the steel plate of the No.18 ~ No.27 made by the composition specified in the present invention, manufacture method.And can confirm, there is excellent intensity and toughness, and the occurrence features of resistance to ductile fracture be excellent.
On the other hand, C does not meet the steel plate (steel grade W*) of the No.28 of the lower limit of scope of the present invention is low tensile strength.And the toughness that C, P, S exceed the steel plate (steel grade X*) of the No.29 of the upper limit of scope of the present invention is low.Slab reheat temperature lower than scope of the present invention and the accumulation rolling rate of more than the 900 DEG C toughness that do not meet the steel plate of the No.30 of scope of the present invention is low.
Finishing temperature and water-cooled start temperature and do not generate ferrite higher than the steel plate of the No.31 of scope of the present invention and do not become tissue given to this invention, and the occurrence features of resistance to ductile fracture is poor.
Water-cooled starts temperature and stops temperature all not becoming value given to this invention higher than the hard phase percentage of the steel plate of the No.33 of scope of the present invention, ferritic average aspect ratio lower than the steel plate of the No.32 of scope of the present invention and water-cooled, and be all low tensile strength, and the occurrence features of resistance to ductile fracture is poor.Tempering temperature exceedes the steel plate of the No.34 of value of the present invention owing to generating island-like martensite in a large number, and be therefore low toughness, the occurrence features of resistance to ductile fracture is poor.
Label declaration:
1: test film
2: simulated thermal cycles portion
3: clip tens(i)ometer
4: knife-edge support
5: clamp
6: tension load
Table 1
Note: * mark represents outside the scope of the invention, steel grade K, L, W, X are comparative steel
Wherein, each alloying element amount is amount (%) to note (1): Ar3 (DEG C)=910-310C-80Mn-20Cu-15Cr-55Ni-80Mo
Wherein, each alloying element amount is amount (%) to note (2): Ar1 (DEG C)=723-14Mn+22Si-14.4Ni+23.3Cr
Table 2
Note: * mark represents outside the scope of the invention.
Table 3
Note: * mark represents outside the scope of the invention.
Note (1): B: bainite, M: martensite, P: perlite, TB: tempering bainite, TM: tempered martensite, MA: island-like martensite
Note (2): zero: ductile fracture does not occur, ×: ductile fracture occurs
Table 4
Note: * mark represents outside the scope of the invention.
Note (1): B: bainite, M: martensite, P: perlite, TB: tempering bainite, TM: tempered martensite, MA: island-like martensite
Note (2): zero: ductile fracture does not occur, ×: ductile fracture occurs.

Claims (5)

1. the steel that the occurrence features of resistance to ductile fracture in a welding heat affected zone and mother metal portion is excellent, its tensile strength TS is the intensity of more than 490MPa and the ductility of Charpy impact test/fragility section transition temperature vTrs is less than 0 DEG C, it is characterized in that, there is following composition, namely in mass %, contain: C:0.02 ~ 0.18%, Si:0.01 ~ 0.4%, Mn:0.1 ~ 2.0%, below P:0.04%, below S:0.04%, below Al:0.05%, below N:0.005%, remainder is made up of Fe and inevitable impurity, the microtexture of 1/4 position of thickness of slab is made up of ferrite and hard phase, this hard phase is bainite, martensite or bainite/martensite mixed structure, comprise the island-like martensite that area percentage is less than 5%, the area percentage of described hard phase is 50 ~ 90%, and described ferritic average aspect ratio is more than 1.6.
2. the steel that the occurrence features of resistance to ductile fracture in welding heat affected zone according to claim 1 and mother metal portion is excellent, is characterized in that,
In becoming to be grouped into also containing be selected from Cu:0.01 ~ 1%, Ni:0.01 ~ 4.5%, Cr:0.01 ~ 2.5%, Mo:0.01 ~ 1%, below Nb:0.05%, below V:0.05%, below Ti:0.05%, below B:0.005%, below Ca:0.009%, below REM:0.1% in mass % one or more.
3. the steel that the occurrence features of resistance to ductile fracture in welding heat affected zone according to claim 1 and 2 and mother metal portion is excellent, is characterized in that,
Tissue apart from plate surface 1mm is made up of ferrite and hard phase, this hard phase is bainite, martensite or bainite/martensite mixed structure, comprise the island-like martensite that area percentage is less than 5%, ferritic area occupation ratio is more than 40%, and the average aspect ratio of ferrite particle diameter is more than 2.
4. the manufacture method of the steel that the occurrence features of resistance to ductile fracture in a welding heat affected zone and mother metal portion is excellent, the tensile strength TS of these steel is the intensity of more than 490MPa and the ductility of Charpy impact test/fragility section transition temperature vTrs is less than 0 DEG C, it is characterized in that, reheat the steel of the composition had described in claim 1 or 2 to more than 1000 DEG C, the rolling rate implementing the temperature field more than 900 DEG C is more than 50% and finishing temperature is Ar 3point ~ Ar 3after the rolling of-50 DEG C, at Ar 3-10 DEG C ~ Ar 3start water-cooled at-70 DEG C, below 500 DEG C, terminate water-cooled, at this, Ar 3put the amount (quality %) based on each composition and utilize following formula and calculate,
Ar 3(℃)＝910-310C-80Mn-20Cu-15Cr-55Ni-80Mo。
5. the manufacture method of the steel that the occurrence features of resistance to ductile fracture in welding heat affected zone according to claim 4 and mother metal portion is excellent, is characterized in that,
After having carried out water-cooled, and then at maximum heating temperature lower than Ac 1temper is carried out under the condition of point, at this, Ac 1put the amount (quality %) based on each composition and utilize following formula and calculate,
Ac 1(℃)＝723-14Mn+22Si-14.4Ni+23.3Cr。
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Application publication date: 20151216