CN101314831A - Steel plate with excellent weariness fissure advance inhibition character and brittle break inhibition character - Google Patents
Steel plate with excellent weariness fissure advance inhibition character and brittle break inhibition character Download PDFInfo
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- CN101314831A CN101314831A CNA2008100040732A CN200810004073A CN101314831A CN 101314831 A CN101314831 A CN 101314831A CN A2008100040732 A CNA2008100040732 A CN A2008100040732A CN 200810004073 A CN200810004073 A CN 200810004073A CN 101314831 A CN101314831 A CN 101314831A
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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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
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
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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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- 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
Abstract
The steel plate in the invention contains C and other chemical components, the excess id iron and unavoidable impurity; the steel plate is composed by ferrito martensite as main part; in the position of t/4 depth (t: plate thickness), the equivalent diameter (high-angle boundary) of the average circle of the area surrounded by high-angle boundary over 15 degrees is less than 15 microns; and the average rate of the azimuth difference of the adjacent crystal grain being 55 to 60 degrees is more than 0.30; in the position of t/2 depth, the high-angle boundary is less than 20 micros. Because of such composition, the fatigue cracking development restrain and brittle failure restrain are excellent.
Description
Technical field
The present invention relates to steel plate, particularly relate to the advance rate that suppresses be full of cracks, thereby guarantee good fatigue lifetime, and suppress the also excellent steel plate of characteristic of the generation of brittle rupture mainly as the structural wood use of boats and ships and bridge.
Background technology
In with the various structured materials headed by shipbuilding and the bridge field, because the situation of stress application is many repeatedly, therefore in order to ensure the security of structured material, in the steel that use as former material, fatigue characteristic are well very important in design.
The fatigue process of steel is thought and is divided into generation and in case such 2 processes of progress of the be full of cracks that takes place in the be full of cracks of stress concentration portion substantially.And, in common mechanical component, macroscopic be full of cracks be considered to use boundary, how not consider for the progress of be full of cracks in the design.Yet, in welded structure, even fatigue cracking takes place also can not cause immediately destroying, if can the delayed crazing advance rate, then can prolong and reach the destructive life-span, can find be full of cracks, need not replace in early days and also can continue to use by making regular check on etc.
, in welded structure, exist in a large number as the weld toe and the defective part of stress concentration portion, what prevent fatigue cracking fully is impossible practical problems, and very wise move also must not calculate in such design on economy.Promptly, for the fatigue lifetime that makes welded structure good, significantly prolong the be full of cracks progress life-span from the state that existed of be full of cracks, more more effective than the generation that prevents to chap itself, for this reason, postpone as far as possible the advance rate of be full of cracks of steel such be designed to important item.
Technology as the characteristic (hereinafter referred to as " fatigue cracking progression inhibiting characteristic ") of improving the speed that suppresses the fatigue cracking progress, up to now also propose to have various, for example open in the 2000-17379 communique the spy, proposition has a kind of steel plate of fatigue cracking progression inhibiting excellent, wherein, when steel normal to a surface method is decided to be ND, (100) of α iron mask have the orientation parallel with ND (100) //crystal grain of ND}, with (111) mask of α iron have the orientation parallel with ND (111) //boundary of the intergranule of ND}, extremely I haven't seen you for ages for the progress direction of edge be full of cracks more than 30 μ m crosscuts, 1 place, and being parallel to the mensuration face of surface of steel plate, the ratio of the α of steel plate inside (111) face strength ratio and α (100) face strength ratio is 1.25～2.0.
Property such as fatigue is high more as paying close attention to more then for fatigue characteristic at the heavily stressed steel plate that uses down, but, because aforementioned techniques is based on ferrite (for example more than the 70 area %), so particularly there is the problem that can not be suitable in the intensity level about only can corresponding 390～490MPa in the part that fatigue cracking becomes problem.
In addition in aforementioned techniques, demonstration be for crystallization control orientation like that as described above, and force the worker at the cryogenic temperature zone or the α temperature field that make ferrite separate out γ-α two phase regions more than the 70 area %.With respect to such ferritic structure, in the tissue (being referred to as " single bainite structure ") based on bainite, known itself and austenite have certain position relation and generate, by the method same with aforementioned techniques, and can not the crystallization control orientation.
Open in the 2004-27355 communique the spy, a kind of steel of fatigue cracking progress excellent are proposed, wherein, in bainite structure or martensitic stucture, maximum tension stress under compression is ± 0.012, toggle speed 0.5Hz, when being applied to the cumulative decrescence repeated load 15 times of wave number 12 of maximum strain, the stress σ during 1 time maximum strain
1Stress σ during with 15 times maximum strain
15Ratio σ
1/ σ
15Shown softening repeatedly parameter is more than 0.65, below 0.95.And, in this technology, though be by with the similar composition of Primary Steel system in by general method for making manufacturing, just can become the steel plate of fatigue cracking progression inhibiting excellent, but, may not be clear and definite with the difference of general material, only by the aforementioned so softening parameter of regulation, the characteristic of talkative hope has not just obtained performance.In addition, also exist fracture transition temperature vTrs to surpass 0 ℃ embodiment, the possibility that can not fully satisfy as the characteristic of works is arranged.
On the other hand, in order to ensure security as works, and the hope be full of cracks generation that inhibition causes because of brittle rupture in steel [below, be called " brittle rupture rejection characteristic " or CTOD (Crack-Tip Opening Displacement) characteristic].If this is because brittlement crevasse crack takes place, then structure spy autoclasia.When above-mentioned such fatigue cracking takes place, at low temperature region, even this be full of cracks (fatigue cracking) can be inhibited, still brittle rupture can take place.Therefore on the safety of works, also need fully to suppress the generation of brittle rupture.But the related technology of steel that the both sides of fatigue cracking progression inhibiting characteristic and brittle rupture rejection characteristic are all excellent does not propose up to now as yet.
Summary of the invention
The present invention is conceived to above-mentioned such situation and does, its purpose is, provide a kind of fatigue cracking progression inhibiting characteristic and brittle rupture rejection characteristic all excellent steel plate, it is by in the steel plate based on bainite, and each the crystal orientation relation on the prescribed position of thickness of slab direction is suitably stipulated.
By reaching the steel plate so-called of the present invention of above-mentioned purpose, in quality % contain C:0.06～0.12%, below the Si:0.5%, Mn:1.4～2%, Al:0.01～0.06%, below the P:0.025%, below the S:0.01%, Nb:0.005～0.025%, Ti:0.005～0.03%, N:0.002～0.009% and B:0.0005～0.003%, surplus is iron and unavoidable impurities
And this steel plate is by based on bainite organizational composition mutually,
When thickness of slab is decided to be t, at the distance case depth is the position of t/4, to be that big angle crystal boundary area surrounded more than 15 ° is during as crystal grain by 2 crystalline azimuth differencees, the leveled circular equivalent diameter of this crystal grain is below the 15 μ m, and the azimuth difference of the intergranule of adjacency is that 55～60 ° average ratio is more than 0.30
At the distance case depth is the position of t/2, will be big angle crystal boundary area surrounded more than 15 ° during as crystal grain by 2 crystalline azimuth differencees, and the leveled circular equivalent diameter of this crystal grain is below the 20 μ m.Also have, in the present invention, so-called " based on bainite ", the meaning is that bainite accounts for the state more than the 90 area % in tissue.In addition, will be the leveled circular equivalent diameter of big angle crystal boundary area surrounded more than 15 ° this crystal grain during as crystal grain by 2 crystalline azimuth differencees, be designated hereinafter simply as " big angle crystal boundary footpath ".
Steel plate of the present invention also can contain more than a kind of selection in (1) Cu:0.05～0.5%, Cr:0.05～0.4%, Ni:0.05～1%, Mo:0.03～0.3% and V:0.005～0.1% as required in quality %. (2) Ca:0.0001～0.005% and rare earth element: at least a in 0.0005～0.003%.In addition, steel plate of the present invention, also preferred thickness of slab is 40～100mm, tensile strength is more than the 570MPa.
In steel plate of the present invention, in the steel plate that has based on the tissue of bainite, by each crystal orientation relation of the prescribed position of thickness of slab direction is suitably stipulated, can realize the steel plate that fatigue cracking progression inhibiting characteristic and brittle rupture rejection characteristic are all excellent, such steel plate can be used as the former material with the various structured materials headed by shipbuilding and the bridge field.
Description of drawings
Fig. 1 is that the degree of depth of expression among the embodiment is that the crystal orientation difference of t/4 position is the graphic representation of the relation of 55～60 ° average ratio and fatigue cracking advance rate.
Fig. 2 is that the degree of depth among the expression embodiment is the crystal boundary footpath, big angle and δ c of t/2 position
-10 ℃The graphic representation of relation.
Embodiment
Present inventors are conceived to the steel plate as bainite structure especially in order to solve described problem, and the method that just is used for suppressing the fatigue cracking advance rate of this steel plate from all angles is studied.Its result obtains as drawing a conclusion.Promptly, in above-mentioned such bainite structure, it is with respect to austenite, having several position relations generates, but will form according to the chemical ingredients of steel plate, there is relationship change in the orientation of each lattice of selections such as the generation temperature of tissue, other conditions, at crystal grain boundary, can distinguish that especially the fatigue cracking progress is inhibited with certain crystal orientation difference.And, distribute if suitably stipulate crystal orientation, then discovery can realize the steel plate that the inhibition of fatigue cracking progress is well realized.Below, the longitude and latitude along the present invention is done describes for action effect of the present invention.
Be in the such single phase structure of main body mutually with bainite, thinking that crystal boundary becomes the impedance of be full of cracks progress, when the be full of cracks progress,, thinking that then the progress of be full of cracks can be suppressed if improve crystal boundary and the frequency that be full of cracks conflicts.That is, the conclusion that obtains is that by the refinement crystal boundary, raising gets final product with the frequency of collisions of be full of cracks.But at the azimuth difference at the two ends that form crystal boundary little (for example being lower than 15 °) low angle boundary (small inclination boundary), because the crystal boundary energy is little, its effect is little, so need be that big angle crystal boundary (high spud angle boundary) more than 15 ° is an object with above-mentioned azimuth difference.In addition, even among the crystal boundary of big angle, the azimuth difference of the intergranule of adjacency is that 55～60 ° ratio is high more, then distinguishes the inhibition also effective more (with reference to aftermentioned Fig. 1) to the be full of cracks progress.
In other words, at the distance case depth is the position of t/4, as being the crystal grain that the big angle crystal boundary more than 15 ° is surrounded by described azimuth difference, the mean value that is converted into the diameter (equivalent circle diameter) of the bowlder of same area is the following crystal grain of 15 μ m, in the distribution of the azimuth difference of the crystal grain of adjacency, azimuth difference is that 55～60 ° average ratio is (more than 30%) more than 0.30, can realize the steel plate of fatigue cracking progression inhibiting excellence thus.In steel plate of the present invention, when improving the fatigue cracking progression inhibiting, why the position relation of crystal grain is that the position of t/4 is estimated at the distance case depth, is that the fatigue cracking progression inhibiting need be inhibited in integral thickness because this is the representative position of thickness of slab integral body.
Also have, described " azimuth difference " is also referred to as " deviation angle " or " inclination angle ", hereinafter referred to as " crystal orientation is poor ".In addition, poor in order to measure such crystal orientation, shown in the embodiment, adopt EBSP method (Electron Backscattering Pattern method) to get final product as described later.
In addition, also find,, can suppress brittle rupture by being that the position of t/2 makes big angle crystal boundary footpath miniaturization (being to make it below 20 μ m specifically) at the distance case depth according to the research that present inventors carry out.Because brittle rupture is position (the being the thickness of slab central part) generation of t/2 at the distance case depth generally, so by making the miniaturization of organizing of this position, think and can suppress brittle rupture.Also have, " is the crystal grain of the position of t/2 apart from case depth " of the present invention, with the distance case depth be t/4 the position the same, be meant " is big angle crystal boundary institute area surrounded more than 15 ° by 2 crystalline azimuth differencees ".
Steel plate of the present invention, it also is one of feature that the chemical ingredients composition is suitably adjusted.Below, illustrate that the scope of chemical ingredients limits reason.
(C：0.06～0.12％)
C is the needed element of intensity that is used to guarantee steel plate.In order to obtain high strength, promptly approximately about 570MPa the wall thickness of the steel plate of use (depend on) need make it to contain more than 0.06%.But, surpass 0.12% if make it to contain superfluously, weldability deterioration then, and, thickization of piece size, the ratio of low angle boundary increases, and demonstrates the tendency that the ratio of the big angle crystal boundary of the crystal orientation difference with 55～60 ° reduces.Thus, C content is 0.06～0.12%.Also have, the preferred lower limit of C content is 0.07%, and preferred upper limit is 0.11%.
(Si:0.5% is following)
Si is used for deoxidation and guarantees the needed element of intensity, recommends more preferably to contain with the amount more than 0.05% preferably with more than 0.01%.But, surpass 0.5% if contain superfluously, then the weldability deterioration.Also have, Si content more preferably on be limited to 0.4%.
(Mn：1.4～2％)
Mn is intensity and the toughness effective elements that is used to guarantee steel plate, in order to bring into play such effect, need make it to contain more than 1.4%.Yet if contain superfluously, weldability, crack sensitivity deterioration therefore need be for below 2%.Also have, the preferred lower limit of Mn content is 1.5%, and preferred upper limit is 1.8%.
(Al：0.01～0.06％)
Al is the useful element that is used for deoxidation, does not have deoxidation effect if be lower than 0.01%.Yet, if make it to contain superfluously, make the toughness deterioration of weld part, therefore need be for below 0.06%.
(P:0.025% is following)
P is in the crystal grain segregation, is the impurity that ductility and toughness is played deleterious effect, and the degree of the purity of practical steel still, is considered in therefore preferred the least possible aspect, can be suppressed at below 0.025%.Also have, P is an inevitable involved impurity in the steel, and making its amount is 0% to be difficult on industrial production.
(S:0.01% is following)
Alloying element chemical combination in S and the steel plate and form various inclusiones is the impurity that ductility and toughness to steel plate play deleterious effect, and the degree of the purity of practical steel still, is considered in therefore preferred the least possible aspect, can be suppressed at below 0.01%.Also have, S is an inevitable involved impurity in the steel, and it is 0% very difficult on industrial production making its amount.
(Nb：0.005～0.025％)
Nb reduces the full starting temperature of transformation Bs of Bei Shi, and is bringing into play the effect of thinning microstructure unit by suppressing phase transformation.In addition, though bainite is held K-S relation (relation of Kurdjiumov-Sachs) and phase transformation in phase transformation, phase transformation at low temperatures can make the fine piece that is made of single mutation (variant) (so-called twin) generate.In order to bring into play such effect, need contain Nb with the amount that (is preferably more than 0.012%) more than 0.005%.Yet,, damage weldability, so Nb content is (to be preferably below 0.020%) below 0.025% if contain superfluously.
(Ti：0.005～0.03％)
Ti is the same with Nb, and suppress phase transformation and Bs is reduced, be effective elements forming on the fine piece.Yet superfluous if Ti content becomes, weldability is impaired.Ti content is (to be preferably more than 0.007%) more than 0.005% thus, (is preferably below 0.025%) below 0.03%.
(N：0.002～0.009％)
Elements such as N and Ti and Al form nitride, are the elements that HAZ toughness is improved.In order to bring into play such effect, need N to contain more than 0.002% and (be preferably more than 0.003%).Also have, solid solution N becomes the reason of the toughness deterioration that makes HAZ.Because the increase of total nitrogen, aforesaid nitride increases, and solid solution N amount is also superfluous, therefore in the present invention it is suppressed at below 0.009%.
(B：0.0005～0.003％)
B is the same with Nb, suppresses phase transformation and Bs is reduced, thereby fine piece is formed effectively.In order to bring into play such effect, need make it to contain more than 0.0005%.Yet superfluous if B content becomes, weldability is impaired, is below 0.003% therefore.
The basal component of steel plate of the present invention as described above, surplus is made of iron and unavoidable impurities (for example O etc.).In addition in steel plate of the present invention, make that to contain following compositions as required among the described composition also effective.
(more than a kind of selection from the group that Cu:0.05～0.5%, Cr:0.05～0.4%, Ni:0.05～1%, Mo:0.03～0.3% and V:0.005～0.1% are constituted)
These elements are the same with Nb, suppress phase transformation and Bs is reduced, thereby fine piece is formed effectively.Therefore these elements are contained sometimes, preferably containing Cu, Cr and Ni is more than 0.05%, and Mo is more than 0.03%, and V is more than 0.005%.But superfluous if its quantitative change gets, then weldability is impaired.Therefore make these elements contain sometimes the upper limit, as described above regulation like this.Also have,, also can sneak into, therefore contained sometimes, be considered as unavoidable impurities with the amount of lacking than above-mentioned lower limit because of raw material etc. causes inevitably trace even these elements do not make it to contain energetically.
(Ca:0.0001～0.005% and rare earth element: 0.0005～0.003% at least a)
Ca and REM be by the fixing of S on flexible improves effective elements, in order to bring into play this effect, preferably make it all to contain more than 0.0005%.Yet, also be saturated even contain its effect superfluously, therefore preferred Ca is below 0.005%, REM is below 0.003%.Make Ca contain sometimes more preferably be limited to 0.001% down.
Steel plate of the present invention though be to be the organizational composition of main body by bainite, cool off under austenitic state, thereby becomes supercooled state, also can become bainite structure.Such bainite structure keeps the position relation of certain certain direction and phase transformation with austenite, and still, if make it phase transformation at low temperatures especially, then the parameter that can select is limited, and causes certain crystal orientation difference to have big peak value.In order to reduce transformation temperature, effective means is the interpolation of alloying element and the increase of speed of cooling etc.
As concrete creating conditions, be that the steel billet that will satisfy the important document of described chemical ingredients composition is heated to 1000～1200 ℃ temperature range and carries out hot rolling.In order to make phase-change organization's miniaturization, effectively rolling austenite structure and make it recrystallize.And about austenitic recrystallization temperature (minimum temperature that recrystallize begins) is made up of chemical composition of steel, but, then be generally about 850～900 ℃ if chemical ingredients of the present invention is formed.In order to be rolled (promptly in order to carry out hot rolling) in this temperature range (more than the recrystallization temperature), can make Heating temperature is more than 1000 ℃.But if Heating temperature is too high, then therefore initial stage austenite structure thickization too can not make phase-change organization's miniaturization fully.Therefore Heating temperature is below 1200 ℃.
Secondly, at the distance case depth is that the position of t/2 is in 850～900 ℃ temperature range rolling, the accumulation draft that is calculated by following formula (1) is more than 15%, and can will be that the 2mm and the degree of depth are that the temperature head of the position of t/2 is adjusted in 45 ℃ apart from case depth.
Accumulation draft=(t
0-t
1)/t
0* 100 ... (1)
(in the formula (1), t
0The thickness of the steel disc the when temperature of the position of the t/2 of expression steel disc is 900 ℃, t
1The thickness of the steel disc the when temperature of the position of the t/2 of expression steel plate is 850 ℃.)
By control like this, can reduce equably apart from case depth is the crystal grain and the big angle crystal boundary footpath of the position of t/2.In detail, by being that the position of t/2 is that 850～900 ℃ temperature range (directly over the recrystallization temperature) is implemented rolling fully at the distance case depth, at the distance case depth is the position of t/2, can form fine austenite structure, consequently can form fine phase-change organization.With respect to this, if insufficient at this temperature range draft, then thick austenite might form.In addition when this temperature range rolling, if be 2mm and be that the temperature head of the position of t/2 becomes excessive apart from case depth apart from case depth, then as the phase-change organization that obtains, deviation might take place in thick and fine mixing mutually in the inhibition of brittle rupture.Also have, as adopt with above-mentioned be the benchmark of temperature head of the position of t/2 apart from case depth, why being the position of " is 2mm apart from case depth ", is because skin section directly is subjected to from externalities such as water, so will select to stablize the position of estimating as skin section.
Apart from case depth is the temperature of the position of t/2, can be tried to achieve by the method shown in the following embodiment.Be that the 2mm and the degree of depth are the temperature head of the position of t/2 apart from case depth in addition, can control by adjusting thermoregulator thickness of slab, water-cooled time and air cooling time.
Also have, rolling by implementing at austenite non-recrystallization temperature field, import strain to austenite crystal, also can make the phase-change organization's miniaturization that generates thereafter, but its effect is not too big.Therefore the rolling micronized effect at the non-recrystallization temperature field is unworthy expectation, can be at (Ar
3Transformation temperature+10 ℃) above temperature finishes rolling.In view of the above, by the high strength of bringing into play the acceleration cooling (for example water-cooled) after rolling fully and the effect of organizing miniaturization.
About the cooling after rolling, preferably quicken cooling with the speed of cooling more than 5 ℃/second.Stopping temperature about quickening refrigerative in addition, need be cooled to the temperature that tissue becomes the bainite main body, is below 450 ℃ therefore.By so quickening cooling, can make phase-change organization's phase-change organization of the position of t/4 (particularly) fully, can realize the high strength of steel plate and fatigue cracking progression inhibiting fully.
Except above-mentioned manufacturing process, also can carry out temper as required 500～700 ℃ temperature range.
According to described such manufacture method, can produce the important document that satisfies chemical ingredients composition of the present invention and organize important document, and tensile strength is the above steel plate of 570MPa.The thickness of slab of steel plate of the present invention is preferably 40～100mm.
Below, enumerate embodiment and be described more specifically the present invention, but the present invention is not subjected to the restriction of following embodiment certainly, on can meeting, can certainly suitably change enforcement in the scope of following aim, these all are included in the technical scope of the present invention.
[embodiment]
With the steel converter melting that the chemical ingredients shown in the following table 1 is formed, under various coolings, rolling condition, make steel plate.Creating conditions at this moment is presented in the following table 2.Also have, in following table 2, " AcC " meaning is " quickening cooling (utilizing the cooling of water) ", and " AC " meaning is " air cooling ", and " QT " meaning is " Q-tempering ".Also have, the temperature of the t/2 portion of steel disc is calculated by the process control computer that has adopted method of finite difference, and the temperature head of dark 2mm and t/2 portion is carried out the thickness of slab, cooling time, air cooling time etc. of temperature adjustment and adjusted by control.The step of concrete temperature treatment is as follows.
(temperature-measuring method in rolling)
1. use control computer based on the atmosphere temperature and the time inside furnace that finish to heating from the heating beginning, is calculated the Heating temperature of the position (is the position of t/2 apart from case depth) of the bad regulation of steel.
2. adopt the Heating temperature that calculates, data based on the method for cooling (water-cooled or air cooling) between pass sequence in rolling (pass schedule) and mill train, adopt the rolling temperature of the position arbitrarily of suitable Calculation Method calculating thickness of slab directions such as method of finite difference, and implement rolling.
3. the surface temperature of steel plate adopts the radial pattern thermometer on the rolling line to survey.But, also can be with process control computer elder generation theory of computation value.
4. when roughing being begun, when roughing finishes, the surface temperature of the steel plate of surveying respectively when finish to gauge begins, contrast with the accounting temperature of calculating by process control computer.
5. the difference of accounting temperature and observed temperature is more than ± 30 ℃ the time, so that the gauging surface temperature mode consistent with observed temperature calculated again and as the accounting temperature on the process control computer, when be lower than ± 30 ℃ the time, directly adopt the accounting temperature that calculates by process control computer.
6. adopt the accounting temperature of aforementioned calculation, management is as the rolling temperature in the zone of controlled member.
For each steel plate that obtains, measure bainite branch rate, be that the crystal boundary footpath, big angle and the crystal orientation difference of the position of t/4 is 55～60 ° ratio, is crystal boundary footpath, big angle, tensile strength TS, fatigue cracking advance rate and brittlement crevasse crack rejection characteristic (the δ c of the position of t/2 apart from case depth apart from case depth according to following method
-10 ℃).Its result is in table 3 kind of expression.
(bainite divides rate)
From the degree of depth of steel plate is the position of t/4, to be parallel to the rolling direction of steel plate, and make with respect to the mode of showing out of the Surface Vertical of steel plate and cut down sample, it is ground, adopt the diamond lap slurry to carry out mirror finish as abrasive thereafter with the sand paper of the wet type of #150～#1000.With this mirror ultrafinish sheet with 2% nitric acid-ethanolic soln (nital) etch after, observe the visual field of 150 μ m * 200 μ m with 400 observation multiplying power, measure bainite by image analysis and divide rate.Also have, the tissue of the lath-shaped beyond the ferrite all is considered as bainite, adds up to the bainite branch rate of trying to achieve 5 visuals field, adopts its mean value.
(degree of depth is the crystal boundary footpath, big angle of the position of t/4 and t/2)
At the distance case depth is in the cross section of the rolling direction that is parallel to steel plate of position of t/4 and t/2, measures crystal boundary footpath, big angle by FE-SEM-EBSP (using the Electron Back-Scattered Diffraction image method of evaporation of electron type scanning electron microscope).Specifically, adopt the EBSP device (trade(brand)name: " OIM ") of Tex SEM Laboratries society combined with EF-SEM, with inclination angle (crystal orientation is poor) be boundary more than 15 ° as crystal grain boundary, measure crystal boundary footpath, big angle.At this moment condition determination is to measure the zone: 200 μ m, measure pitch: 0.5 μ m shows that confidence index (confidence index) measuring point littler than 0.1 of the reliability that fixes the position got rid of at interval from analytic target.Calculate the mean value in the crystal boundary footpath, big angle of so trying to achieve, as " the big angle crystal boundary footpath (leveled circular equivalent diameter) " among the present invention.Also having, directly is below the 2.0 μ m for the big angle crystal boundary, is judged as to measure to disturb, and gets rid of from the object of mean value calculation.
(the crystal orientation difference that apart from case depth is the position of t/4 is 55～60 ° a ratio)
Utilize the automatic analysis software of OIM, by measuring the azimuth difference of each crystal boundary, trying to achieve (calculating) is that the crystal orientation difference of the position of t/4 is 55～60 ° a ratio apart from case depth.When measuring this ratio, for example be that big angle crystal boundary institute area surrounded more than 15 ° is as crystal grain (big angle crystal grain) with 2 crystalline azimuth differencees, if with the crystal grain of this big angle crystal grain adjacency be 6, and wherein have only 1 to satisfy azimuth difference: in the time of 55～60 °, then " ratio " is 1/6.Such calculating is implemented and equalization for whole big angles crystal grain, and the azimuth difference of trying to achieve the intergranule of adjacency is 55～60 ° a average ratio.That is, among the crystal grain of big angle, even the crystal orientation difference is 55～60 ° a ratio to be comprised and is lower than 0.30, if but during equalization (in average ratio) be more than 0.30, then still satisfy important document of the present invention.
(tensile strength)
Extract NK U14A test film from the position of the dark t/4 of each steel plate, follow JIS Z2241 and carry out tension test, measure tensile strength TS thus.The benchmark of tensile strength is more than the 570MPa.
(fatigue cracking advance rate)
According to ASTM E647, adopt the small-scale test sheet, implement the test of fatigue cracking progress, try to achieve the fatigue cracking advance rate thus.At this moment, the value at stabilized growth zone Δ K=20 (MPa √ m) that the PARIS rule of following formula (2) defined is set up is estimated as typical value.Also have, about the metewand of fatigue cracking advance rate, because common steel are 4～6 * 10
-5Advance rate about mm/ circulation (during Δ K=20) is therefore to be lower than 3.0 * 10
-5The mm/ circulation is benchmark.
da/dn＝C(ΔK)
m…(2)
(in the formula (2), a: expression be full of cracks length, n: expression multiplicity, C, m: expression is by the constant of the conditional decision of material, load etc.)
(evaluation of brittlement crevasse crack rejection characteristic)
The brittlement crevasse crack rejection characteristic, " front opening racking test (CTOD test) chaps " based on WES1108 (formulations on the February 1 nineteen ninety-five) defined of Corporation Japan welding association (WES) distribution, the front opening racking test chaps, measure the unstable aperture displacement (δ c) that destroys when beginning, estimate according to this result.Also have, when chapping the front opening racking test, also consider " about the guide of welding heat affected zone CTOD test method " of WES1109 (formulation on April 1 nineteen ninety-five) defined in light of actual conditions.
Test film adopts P.6 " the standard three point bending test sheet " shown in Figure 6 of WES1108 (formulation on February 1 nineteen ninety-five).Test temperature is-10 ℃, measures δ c
-10 ℃(mm).In the present invention, δ c
-10 ℃For being qualified more than the 0.20mm.
[table 3]
(-) be undetermined owing to hang down TS
Result by table 3 can carry out following investigation.At first, test No.3,7,8,11,13,16,18,21 and 23 satisfies the important document of organizing of the present invention, and fatigue cracking progress and brittle rupture are suppressed fully.With respect to this, be short of any one of important document of organizing of the present invention, at be full of cracks advance rate or δ c
-10 ℃On can not draw satisfied result.
Result based on table 3, crystal orientation difference in dark t/4 position is that 55～60 ° the ratio and the relation of fatigue cracking advance rate are presented among Fig. 1, but remove (the test No.15,19,26) of big angle, dark t/4 position thickization of crystal boundary, by making described ratio is more than 0.30, and the progress of fatigue cracking is suppressed (be full of cracks advance rate＜3.0 * 10 as can be known
-5The mm/ circulation).Crystal boundary footpath, dark in addition big angle, t/2 position and δ c
-10 ℃Relation be presented among Fig. 2, directly be below the 20 μ m by the big angle crystal boundary that makes this position, brittle rupture (the δ c that is inhibited as can be known
-10 ℃〉=0.20mm).
Claims (4)
1. steel plate, it is characterized in that, in quality % contain C:0.06～0.12%, below the Si:0.5%, Mn:1.4～2%, Al:0.01～0.06%, below the P:0.025%, below the S:0.01%, Nb:0.005～0.025%, Ti:0.005～0.03%, N:0.002～0.009% and B:0.0005～0.003%, surplus is iron and unavoidable impurities
And this steel plate is by based on bainite organizational composition mutually,
When thickness of slab is decided to be t, at the distance case depth is the position of t/4, to be that big angle crystal boundary area surrounded more than 15 ° is during as crystal grain by 2 crystalline azimuth differencees, the leveled circular equivalent diameter of this crystal grain is below the 15 μ m, and the azimuth difference of the intergranule of adjacency is that the average ratio of 55～60 ° crystal grain is more than 0.30
At the distance case depth is the position of t/2, will be big angle crystal boundary area surrounded more than 15 ° during as crystal grain by 2 crystalline azimuth differencees, and the leveled circular equivalent diameter of this crystal grain is below the 20 μ m.
2. steel plate according to claim 1 is characterized in that, also contains more than a kind of selection from Cu:0.05～0.5%, Cr:0.05～0.4%, Ni:0.05～1%, Mo:0.03～0.3% and V:0.005～0.1% in quality %.
3. steel plate according to claim 1 is characterized in that, also contains Ca:0.0001～0.005% and rare earth element in quality %: at least a in 0.0005～0.003%.
4. according to each described steel plate in the claim 1～3, it is characterized in that thickness of slab is 40～100mm, tensile strength is more than the 570MPa.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2007-142486 | 2007-05-29 | ||
| JP2007142486 | 2007-05-29 | ||
| JP2007142486A JP4934505B2 (en) | 2007-05-29 | 2007-05-29 | Steel sheet with excellent fatigue crack growth suppression characteristics and brittle fracture suppression characteristics |
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| CN101314831B CN101314831B (en) | 2010-12-01 |
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| CN2008100040732A Expired - Fee Related CN101314831B (en) | 2007-05-29 | 2008-01-18 | Steel plate with excellent weariness fissure advance inhibition character and brittle break inhibition character |
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| JP (1) | JP4934505B2 (en) |
| KR (1) | KR20080104940A (en) |
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| CN105452511A (en) * | 2013-09-20 | 2016-03-30 | 株式会社神户制钢所 | Thin steel plate having excellent fatigue properties and production method therefor |
| CN106460114A (en) * | 2014-05-22 | 2017-02-22 | 株式会社神户制钢所 | Thick steel plate |
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| JP5759109B2 (en) * | 2010-03-09 | 2015-08-05 | 株式会社神戸製鋼所 | Steel material excellent in brittle crack propagation stop property and method for producing the same |
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| JP4220871B2 (en) * | 2003-03-19 | 2009-02-04 | 株式会社神戸製鋼所 | High-tensile steel plate and manufacturing method thereof |
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| JP4317499B2 (en) * | 2003-10-03 | 2009-08-19 | 新日本製鐵株式会社 | High tensile strength steel sheet having a low acoustic anisotropy and excellent weldability and having a tensile strength of 570 MPa or higher, and a method for producing the same |
| JP4676871B2 (en) * | 2005-12-19 | 2011-04-27 | 株式会社神戸製鋼所 | Steel sheet with excellent fatigue crack growth control |
| JP4058097B2 (en) * | 2006-04-13 | 2008-03-05 | 新日本製鐵株式会社 | High strength steel plate with excellent arrestability |
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2007
- 2007-05-29 JP JP2007142486A patent/JP4934505B2/en not_active Expired - Fee Related
- 2007-12-27 KR KR1020070139020A patent/KR20080104940A/en not_active Application Discontinuation
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN102753719A (en) * | 2009-12-28 | 2012-10-24 | Posco公司 | High strength steel sheet having excellent brittle crack resistance and method for manufacturing same |
| CN102753719B (en) * | 2009-12-28 | 2015-08-19 | Posco公司 | There is high tensile steel plate and the manufacture method thereof of excellent resistance to brittle fracture |
| CN102011068A (en) * | 2010-12-13 | 2011-04-13 | 首钢总公司 | 800 MPa-grade low-yield-ratio structural steel plate and production method thereof |
| CN103160738A (en) * | 2011-12-14 | 2013-06-19 | 鞍钢股份有限公司 | Low-cost boron-containing steel and manufacturing method thereof |
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| CN105452511A (en) * | 2013-09-20 | 2016-03-30 | 株式会社神户制钢所 | Thin steel plate having excellent fatigue properties and production method therefor |
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| CN115279933A (en) * | 2020-06-30 | 2022-11-01 | 株式会社神户制钢所 | Thick steel plate and method for producing same |
| CN115279933B (en) * | 2020-06-30 | 2023-08-22 | 株式会社神户制钢所 | Thick steel plate and method for manufacturing same |
Also Published As
| Publication number | Publication date |
|---|---|
| KR20080104940A (en) | 2008-12-03 |
| CN101314831B (en) | 2010-12-01 |
| JP2008297575A (en) | 2008-12-11 |
| JP4934505B2 (en) | 2012-05-16 |
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