Have improvement HAZ-soften repellence hot-rolled high-strength steel band andThe method producing described steelThe present invention relates to have the HAZ-of improvement soften repellence hot-rolled high-strength steel band andThe method producing described steel.
Traditionally, manufactured the steel with high-yield strength by austenitizing and quenching, but logicalCross this technology, it may not be possible to realize surface quality and the impact flexibility such as optimized.Preparation expenseThe highest.
EP1375694 describes to be produced by hot rolling has good processing characteristics and welding performanceHigh intensity, the method for high-ductility steel.But, the inventors discovered that these steel are prone to HAZ-and soften.Heat affected area (HAZ) is for being changed its microscopic structure and character by welding or hot intensive cutting operationThe region of base material.Encirclement is result in from welding process and the heat cooled down again subsequentlyChange in the region of this weld seam.The heat affected area forming the weld seam in this steel neighbouring is that welding is lostOne of most common region of effect.Modern thermo-mechanical rolling (TMCP) steel, lean due to themChemical composition, and low carbon content especially, it is therefore desirable to the welding parameter carefully controlled is to realizeSufficient intensity in weld seam HAZ.For conventional mild steel and some TMCP pipe line steel, such asX70 and X80, HAZ soften often owing to the high heat that in HAZ, heat dissipates slowly inputsThe result of welding sequence.For the TMCP steel of higher level, such as X100, due to substrate goldThe microscopic structure that the ultra fine grain size belonged to and its bainite and martensite are dominated, HAZ softens canEven occur under medium welding heat inputs.Hardness and the reduction of intensity in HAZ areThe weak spot of welded pipeline configuration.Therefore, according to base material and the character of welding condition,The degree limiting this softening generation is important.Leading by most research is softened about HAZTerritory is high-strength medium plate, such as pipe applications, and closer to the phase for automobile applicationAHSS。
WO2007/129676 relates to the hot pressing steel part manufactured by high-carbon cold-rolled steel sheet material, this steelSheet material by austenitizing, hot pressing to produce steel part and to be quenched realizing the minimum of 1.8GPa and drawStretch intensity.Treat the ferrite that cold rolling hot-rolled steel contains at least 50%.
EP2028284 discloses seamless steel pipe and EP1662014 discloses low-carbon hot-rolling steel board,It batches between 450～650 DEG C and is heated again to the most rapidly between 550～750 DEG CTo realize three-phase ferrite, bainite and island martensite soma.
It is an object of the invention to realize high-strength hot-rolled steel band, it is more high-strength than now availableDegree hot-rolled steel band is less prone to HAZ-and softens.
At first aspect, by have the HAZ of improvement soften repellence hot-rolled high-strength micro-The steel band of alloying has reached this purpose, its thickness having between 2～16mm, has bagContaining the microscopic structure of martensite, tempered martensite and/or bainite, and wherein this steel with weight %Meter contains:
● 0.07～the C of 0.30%；
● 0.8～the Mn of 2.0%；
● 0.01～the Al of 0.08%sol；
● 0.2～the Cr of 1.5%；
● 0.1～the Mo of 0.7%；
● the B of 0.0005～0.005；
● 0.01～the Nb of 0.07%；
● the Si of most 0.5%；
● the P of most 0.03%；
● the S of most 0.015%；
● the Ti of most 0.05%；
● the V of most 0.1%；
● the Cu of most 0.2%；
● the Ni of most 0.2%；
● the N of most 0.008%；
● the calcium interpolation controlled for sulphide shape of the most most 0.015%；
● being in other elements of the amount of impurity level, surplus is ferrum；
The yield strength of this steel band is at least 960MPa.
All of composition % is all given with weight %, unless otherwise specified.
Thinking of the present invention based on the fact that, by the combination of chemical element of the amount described in selecting,And particularly niobium and the existence of molybdenum, good hardening can be kept.Due to low manganese and carbon content,During casting process, structure of steel is not critical for the segregation of manganese and carbon.This rigidity is verified in bandThe local relief of the coiling temperature in material is not critical, and which promotes steel and produces, and to its machineryThe uniformity of character has advantageous effect, this flatness and residual stress to final products againThere is active influence.This steel sheets height is suitable for welding and cut, and it has simultaneouslyGood fatigue strength, not by described Effects of Heat Treatment.And, this steel sheets has excellenceBending property, good impact flexibility and tempering time to soften good repellence.Subsequently,Precipitation element in the cooling period obtainable solution for separating out of HAZ after being weldedExistence ensure that HAZ soften repellence be obviously improved.
Can be such as the shape accurately defined by laser by the steel thermal cutting according to the present invention.?Observe in cut article, achieve notable smooth cutting surfaces.On the other hand,Find that the strength difference between base material and the soft zone produced in the cutting process of technology (shouldRegion is located close to hardening zone) it is little or non-existent, this is also due to after this thermal cuttingCooling period the most obtainable for separate out solution in separate out element existence.ThisJointly fatigue strength had favorable influence a bit.Additionally, relatively low carbon content reduces firmlyChange the peak hardness in district so that no matter at the processing of article or this cutting table in actual useIn the face of brittle insensitive with cracking.
In terms of controlling intensity, carbon is important element, but needs to be not limited to a certain degreeTo provide the well balanced of toughness, welding performance and processability.This C content is remained phaseTo between low 0.07～0.30%, to realize good toughness, (all of composition % is all with weight %Represent).Being combined with low temperature coiling temperature, this microscopic structure will be containing martensite and/or bainite.Definite amount depends strongly on composition, cooldown rate on the run-out table and coiling temperature.?Under relatively low C content, this Ms temperature is by a relatively high, and therefore, martensite will be to a certain degreeUpper self tempering.According to requirement of strength, it was found that suitably carbon window.For having at least 960MPaThe steel of yield strength, preferably carbon content is at least 0.07 and/or most 0.13%.For toolHaving the steel of the yield strength of at least 1100MPa, carbon content is preferably at least 0.13 and/or at most0.18%, and for having the steel of the yield strength of at least 1300MPa, carbon content is preferably at least0.19%, between more preferably at least 0.23 and/or most 0.30%.
Suitably greatest carbon content is 0.27%, or even 0.25%.
As manganese, chromium, molybdenum and the element of boron, it is provided that promote bainite and/or the formation of martensiteHardenability.This Fe content is limited to 0.8～2.0%.When manganese exceedes this upper limit, segregationRisk becomes obvious, and this can deleteriously affect the uniformity of microscopic structure.Water less than 0.8%At ordinary times, the effect to hardenability is insufficient.The most minimum manganese level is 1.1%.
Add boron to promote hardenability.The formation avoiding boron nitride is important, because it willMake boron invalid for the raising of hardenability.According to the titanium in the compositions of the present invention act as protectProtect boron, because Ti forms titanium nitride, and be therefore formed without BN.The amount of the boron of alloyingIt is at least 0.0005%B (i.e. 5ppm), but less than 0.005%B (i.e. 50ppm) to reduce crystal grainSize and raising hardenability.If adding titanium to be generally at least as alloy element, the amount of titanium0.01%Ti, but less than 0.05%, to combine nitrogen N and to prevent the generation of boron nitride BN.Within the scope of the invention alternative for using aluminum to combine nitrogen, and thus protects boron.At TiNThe formation of granule is considered need not the situation of (such as because of they effects to Charpy toughness)Under, can be preferably to select by the boron that aluminum protection is free.
During hot rolling, niobium analyzes in the middle part of austenite, from there through the recrystallization of austeniteRetardation the crystal grain refinement of the final microscopic structure changed is had contribution.Additionally, protect on the turnStay the niobium in solution, particularly under cooldown rate faster, reduction transition temperature is had and haveThe effect of power, therefore it is also advantageous for hardenability.(＜ at a low coiling temperature500 DEG C), it is contemplated that niobium is little by the contribution of precipitation strength, because this temperature is for thin NbCPrecipitation the lowest.Suitably Nb content is at least 0.02%, preferably at least 0.025%.
In this case, V has the effect similar but the strongest with Nb.But, NbThe main cause of the interpolation with V is to improve HAZ-to soften repellence.In the relevant portion of HAZ,Thermal cycle makes the temperature having reached to allow the precipitation strength by Nb and V, therefore result in hardThe increase of degree, this is due to the precipitation of the element being maintained in solution by low coiling temperature.It is believed that main contribution is produced by Nb and V carbide, nitride or carbonitride.?In lower degree, it is believed that the MoC precipitate with similar effect can be formed.If it does, closeSuitable minimum V content is 0.04%.
Steel according to the present invention is aluminium deoxidation or aluminum-silicon killed steel, so that oxygen content is down to minima,Not react between carbon and oxygen during solidifying.The aluminum to steel is added at production periodAmount therefore include needing for those of deoxidation.The amount kept in the final product is (also referred to asSolvable aluminum (Alsol)) it is 0.01～0.08%Al.In the context of the present invention, aluminum contentMean solvable aluminum.
Except aluminum, silicon also functions as deoxidizer in the steel of the present invention.It starts from the most at least 0.10%SiAnd at most 0.50%Si also functions as solution strengthening thing, this On Impact Toughness and processing characteristics have and haveThe effect of benefit.Higher than 0.5%, silicon deleteriously affects the surface quality extremely unacceptable degree of steel,And along with the silicone content increased, become more difficult by the removal of the hot rolling iron scale of pickling.
The phosphorus P being included as impurity should be most 0.03%, and sulfur S should be even lower,And most 0.015% should be defined as, it means that limit these content to realize good impactToughness and bending property.As necessary, by using the band containing Ca-Si or Ca-Fe (Ni)Core welding wire processes this melt can improve further performance.During Calcium treatment, owing to surface is openedPower effect, aluminium oxide and silicon oxide field trash be converted into melted spherical form calcium-aluminate andSilicate.Staying the calcium-aluminate field trash in molten steel inhibits MnS to send out during the solidification of steelThe formation of stricture of vagina (stringer).The composition of precipitation of Sulfide inclusion and mould during steel solidificationThis change in terms of formula is referred to as oxide morphology or sulphide shape controls.Which results in castingMake period less spray nozzle clogging, preferable mechanical performance, because the long MnS hairline stretched fillsWhen crackle produces point.The general quantity of calcium in the steel that sulphide shape controls be 0.0015～The Ca of 0.015%.Suitably maximum is the Ca of 0.005%.
Chromium should be 0.2～1.5%.Molybdenum should preferably last 0.1%Mo～0.7%Mo.Add twoPlant element to improve hardening and tempering repellence.This makes the precipitation under higher coiling temperature becomeFor may, can use it for reducing and even preventing the softening of steel, and be used for alleviating due toThe intensity fluctuation that the cooling period of coiled material causes owing to local temperature difference is different.The most minimum molybdenum containsAmount is 0.15%.
In view of the cosmetic issue relevant to copper, preferably avoid and be frequently used for this intensity levelElement in steel such as copper and mickel alloying.Because often copper is combined nickel carries out alloying to subtractThe adverse effect of light copper, so this is also needs.Therefore preferably nickel and/or copper is with most impurityLevel exists or is more preferably completely absent.
The microscopic structure of the steel according to the present invention is characterized as being mainly by showing that tempered martensite formsMicro-assembly robot, it is characterised in that the little carbide in Widmannstatten structure and/or bainite.It is desirable thatThis microscopic structure does not contains ferrite and pearlite composition, because these will deleteriously affect to be achievedIntensity level.It practice, the ferrite that there are some small pieces may is that inevitably, butThis amount can be less than the level significantly affecting intensity level.Should will be formed under high transition temperatureAbove-described harmful and the most unwanted ferrite composition and shape under low transition temperatureThe ferritic portion of the bainite become or ferrite side plate or acicular ferrite understand separately.The former composition is unwanted, and the latter is not.
Can the hot-rolled steel band being directly hot-rolled down to the present invention of 2mm～16mm thickness be prepared as resistance toGrind and there is different SMYSs.Only by within the scope of the invention change analyze and/Or the rear rolling cooldown rate of band and/or the temperature before batching, the most general threshold valueIt is 960,1100 and 1300MPa.Also this kind of high yield stress steel can be used in target, at thisThe performance that in target, organization need structural steel is generally required, the best processing characteristics, weldingPerformance and impact flexibility, it means that according to the hot-rolled steel band of the present invention as welding knotStructure steel also can shape.During the steel that will be explained in the following description is analyzed, all ofContent % is weight %, and the surplus of steel is ferrum Fe and inevitable impurity, unless otherwise limitFixed.One-tenth-value thickness 1/10 even for the tropocal wood of at most 16mm, it is possible to reach the value of 960MPa.For the value of at most 12mm, can reach the value of 1100 and 1300MPa.Higher thickness is at certainResult in relatively low cooldown rate in kind of degree, and therefore result in before phase in version lessThe austenite of enrichment.This causes the intensity level that some is relatively low, it is meant that use these lean compositions,S1100 or S1300 level can not be obtained for the thickness tropocal wood more than 12mm.Preferably,Minimum thickness is 3mm and/or maximum gauge is 10mm.It should be noted that as defined in the present inventionIntensity level be measure in a longitudinal direction (i.e. tensile sample is on the longitudinal direction of this band(by the direction of motion of milling train) obtains).(i.e. tensile sample exists value in a lateral directionOn the width of this band obtain) with in a longitudinal direction value possibility different, and generally thanThese on longitudinal direction are high and low on elongation percentage in intensity.
In one embodiment, the carbon content of steel is 0.07～0.13%, and yield strength isAt least 960MPa.
In one embodiment, the carbon content of steel is 0.13～0.18%, and yield strength isAt least 1100MPa.
In one embodiment, wherein carbon content is at least 0.19%, preferably 0.23～0.30%Between, and yield strength is at least 1300MPa.
The suitable ultimate tensile strength of the hot-rolled steel according to the present invention is 1700MPa.
According to second aspect, the present invention is embodied in for preparing hot-rolled high-strength microalloyingThe method of steel band, this steel band has the thickness between 2～16mm, has the HAZ-of improvementSoften the yield strength of repellence and at least 960MPa, have and comprise martensite, tempered martensiteAnd/or the microscopic structure of bainite, and wherein this steel contains in terms of weight %:
● 0.07～the C of 0.30%；
● 0.8～the Mn of 2.0%；
● 0.01～the Al of 0.08%sol；
● 0.2～the Cr of 1.5%；
● 0.1～the Mo of 0.7%；
● the B of 0.0005～0.005；
● 0.01～the Nb of 0.07%；
● the Si of most 0.5%；
● the P of most 0.03%；
● the S of most 0.015%；
● the Ti of most 0.05%；
● the V of most 0.1%；
● the Cu of most 0.2%；
● the Ni of most 0.2%；
● the N of most 0.008%；
● the calcium interpolation controlled for sulphide shape of the most most 0.015%；
● with other elements of the amount of impurity level, surplus is ferrum.
This band is higher than Ar3At a temperature of carry out hot finishing, wherein the method includes below at leastStep:
● finish rolling to 2～the final thickness of 16mm
● in most 10 seconds of last hot rolling pass, be enough to the microscopic structure through rollingIt is changed into the cooldown rate of the microscopic structure comprising martensite and/or bainite, cools down this hot-rolled stripThe coiling temperature of material to 20～500 DEG C.
This hot rolling technology is conventional hot rolling technology, whether from the thickness with 150～350mmSlab (i.e. conventional continuous casting steel billet), or or (i.e. sheet blank continuous casting or very less than 150To Strip casting) start.Preferably when steel is still for austenite, finish rolling has compact grained to provideSteel, and good impact flexibility is thus provided.Preferably coiling temperature is low needing with realizationEngineering properties.Preferably coiling temperature is less than 400 DEG C.By rapid cooling after hot rolling or directly quenchFire, the steel of preparation the type, it is thus achieved that excellent impact flexibility because occur from compact grained,Processed austenite is to martensite and/or the phase transformation of bainite.It also improves surface quality,Because removing initial iron scale before rolling in descaling mill.Also, it is not necessary to it is the most highThe additional annealing of expensive length processes to dissolve all of precipitate.In tropocal wood rolling line,The warm rangeability of this slab to be rolled to 1100～1250 DEG C is reheated in reheating furnace, andKeep several hours.In this case, the dissolving of particular carbon compound such as Cr and Mo carbide,And the homogenization of tissue is the most thoroughly.On the other hand, under high heating-up temperatureThe growth of austenite crystal does not make final products more crisp, because first passing through in the operation of rollingThe recrystallization during high temperature rolling in starting stage and the heat in the final stage of course of hot rollingTurning of the deformed austenite crystal grain that the sluggishness that austenite during mechanical press changes causes and formedAttenuate and changed austenite crystal.Cooling period on the run-out table, the austenite of gross distortionCrystal grain is changed into the thinnest transmutation product.It is high that this causes being combined with excellent impact flexibilityYield stress.If using sheet blank continuous casting and Direct Rolling facility (wherein in rolling beginningFront element does not the most separate out as Cr and Mo carbide), then preparation cost and the production timeAlso can reduce further.
According to the present invention, remain as austenite at steel, i.e. higher than Ar3Finishing temperature under shouldFinal hot rolled thickness made by steel.Band be cooled in last hot rolling pass after be not later than 10Second starts, and the most quickly cools down it to allow austenite to be changed into bainite and/or martensiteMicroscopic structure, cooldown rate is preferably at least 30 DEG C/s, be reduced to 20～500 DEG C batch temperatureDegree, is preferably decreased to the coiling temperature of 20～450 DEG C.The nearlyest shellfish completely of the result obtainedFamily name's body and/or martensitic microstructure so that bainite and/or martensite content are preferably at least90 volume %, preferably at least 95 volume %.This microscopic structure is not it is also preferred that contain and at high temperature formedFerrite and without pearlite composition, therefore make microscopic structure substantially completely for bainite/genevaBody, the most for this purpose, ferrite side plate or acicular ferrite are considered as bainiteTissue.In the coiling temperature scope less than 100 DEG C, not by martenaging martempering, although at thisUnder a little low temperature, for low-carbon (LC) grade, may occur in which some self temperings, and when coiling temperature is at leastWhen 100 DEG C, martensite is tempered.At a temperature of higher than 200 DEG C, martensite is tempered and this carbonIt is precipitated.
In preferred embodiments, for containing most 0.12% the steel of carbon content, batchTemperature is most 450 DEG C, more preferably 425 DEG C, the steel of the carbon content for containing at least 0.13%,For most 275 DEG C, more preferably 250 or 225 DEG C.
In one embodiment, the acceleration cooling period after hot rolling and before batching, coldBut speed is 5～100 DEG C/s.
In one embodiment, final rolling temperature is higher than Ar3And also below 920 DEG C, and preferablyAlso below 900 DEG C.
According to the 3rd aspect, automobile, truck, shipbuilding will be used for according to the steel of the present invention, executeWork engineering, heave-load device, earth-moving equipment or the production of derrick car parts.
Following non-limiting example is utilized to further illustrate the present invention.Table 1 shows kindThe steel composition of each of S700, S960, S1100 and S1300.
In addition to the composition (except B and N(ppm) of table 1. steel, all in terms of weight % × 1000.All of steelAll through Ca process, imp=impurity level)
It is main by tempered martensite group that SEM microscopic structure shows that all of hot-rolled steel sample is respectively provided withThe microscopic structure become, the little carbide being characterised by Widmannstatten structure.Owing to these are relatively lowThe high M of C steelsTemperature, and also due to be used for simulating the Slow cooling batching cooling, therefore willCause the tempering of martensite.Show several variants of orientation relationship between carbide and matrixThe pattern of carbide, be characterised by tempered martensite.Austenite grain boundary before is also visible, and show that some along rolling direction extends, as used optics metallographic observation to arrive.By forceDegree level depends strongly on coiling temperature and (sees Fig. 1 and S1300 material of S1100 materialFig. 2), its microscopic structure referred to required for being mainly made up of tempered martensite understands.
Fig. 3 shows that the steel (a, c) according to the present invention and comparative steel (b, d) are in Y-axisOn HAZ emollescence.Clearly visible, for the softening of the reduction of HAZ, the present invention'sSteel has exceeded comparative steel.Steel b and d respectively S960-Nb and S960+Cr-Nb(seesTable 1), and a and c be respectively S960 base and S960+V.