A kind of technique improving rare earth high-strength steel impact flexibilityTechnical field
The present invention relates to heat treatment cut deal technical fields, more particularly, to a kind of raising rare earth high-strength steel impact flexibilityTechnique.
Background technique
High-tensile structural steel is widely used in coal mine machinery, engineering machinery, such as hydraulic support, portal crane, plate fortuneDefeated vehicle etc. is required to have high-intensitive and preferable low-temperature impact toughness.Therefore, many scientific research personnel are dedicated to improving in recent yearsThe obdurability of high-strength steel improves its impact flexibility on the basis of guaranteeing high-intensitive to obtain comprehensive mechanical performance more carefullyHigh strength steel plate.Current most of iron and steel enterprises use out-line quenching+high tempering hardening and tempering process, are air-cooled to room after temperingTemperature.
Characteristic resources of the rare earth element as Baotou region are also obviously improved effect to steel impact flexibility, withSteel industry went the promotion of production capacity and transition and upgrade in recent years, played rare earth resources advantage, the market position for improving rare earth steel mustSo become important topic, current research is limited to illustrate the independent role that RE Modified is mingled with or emphasizes rare earth element more.
Summary of the invention
The present invention is directed to the influence in the presence of rare earth to low-alloy high-strength steel heterogeneous microstructure, and research obtains cerium CeThe form and purification crystal boundary that field trash can be improved, improve the intensity of crystal boundary, reduce what crackle was extended by the perforation of defectMay, to improve impact flexibility, austenite grain boundary can also be refined so as to improve impact flexibility, while adding cerium Ce energyEnough making the ductile-brittle transition temperature of steel reduces by 10 DEG C or so.
In order to solve the above technical problems, the present invention adopts the following technical scheme:
It is a kind of improve rare earth high-strength steel impact flexibility technique, include the following steps: KR desulphurization and slag skimming → converter smelting →LF refining → RH refining and rare earth treatment → continuous casting → heating → rolling → acceleration cooling → heat treatment；
Wherein:
KR desulfurization and converter smelting include: molten steel sulfur content S≤0.010% after molten iron pretreatment, temperature >=1280 DEG C.IronWater takes off slag completely before entering converter, and converter terminal controls C-T and coordinates tapping, and P≤0.010%, S≤0.015%, tap time 4-7min, tapping 1/5 when be added；Ferro-aluminum is added to carry out deoxidation to molten steel, the alloy in addition to Al is added by normal requirement, tapping 2/5Amount adds alloy, and suitable modification agent and lime is added in view terminal oxygen content in tapping process；
External refining includes: that the refining of LF furnace uses Oxides Metallurgy Technology to carry out slag making and deoxidation operation to molten steel, quicklyWhite slag is made, and guarantees white slag time 15min or more, stablizes basicity of slag；Alloy is wanted with adding to target as far as possible before LF refining is outboundRange is sought, guarantees that S content is lower than 0.003%, B-Fe=0.018-0.020 is added after feeding silk Argon 5min；
RH refining and rare earth treatment include: RH not adjusting component as far as possible, and all the components adjustment will be completed in LF, at RH vacuumRare earth alloy is added for 15-17 minutes in reason in feed bin, and rare earth alloy additional amount is 35kg/ furnace, and RH depth vacuum is followed after rare earth is addedThe ring time guarantees 15min or more, and the argon gas soft blow time guarantees 10min or more.
Continuous casting includes: to strengthen to guarantee airtightness and middle packet liquid level coverture thickness between big packet-middle packet-crystallizer, is strengthenedMiddle packet argon gas purging, avoids air-breathing in continuous casting process, and whole process increases the control of N amount within 5ppm；1520 DEG C of liquidus curve, middle packet overheatDegree controls 23-33 DEG C, and plate slab production pulling rate executes stable state casting in pulling speed of continuous casting use, and production thickness of strand 250mm connectsCasting is whole to carry out protective casting；
Heating includes: 1220-1260 DEG C of heating temperature, and slab center portion temperature of coming out of the stove is greater than 1180 DEG C, it is ensured that soaking zone is protectedTemperature >=40 minutes, guarantees that steel billet is grilled thoroughly, uniformly；
Rolling mill practice includes: two stages controlled rolling, and a stage start rolling temperature is greater than 1100 DEG C, reduction ratio 60%~70%；Two860~900 DEG C of stage start rolling temperature, >=12%, last three passage adds up reduction ratio and is not less than >=40% reduction ratio per pass；Roll rear water cooling: 650~750 DEG C of final cooling temperature, stacking slow cooling；
Heat treatment process includes: for quenching+tempering, and hardening heat is 910 ± 10 DEG C, and time inside furnace is according to t=1.4min× thickness+soaking time calculates, and thickness unit is mm, is air-cooled to room temperature after quenching；600-640 DEG C of tempering temperature, time inside furnaceIt is calculated according to t=2.6min × thickness+soaking time, sprays surface of steel plate using high pressure water after tempering, steel billet temperature is down to 300DEG C or less come out of the stove；Thickness unit is mm.
Further, the high-strength steel includes following chemical component: C=0.08-0.15%, Si=by mass percentage0.3-0.5%, Mn=1.5-1.8%, P≤0.015%, S≤0.015%, Als=0.015-0.03%, Cr=0.2-0.3%, V=0.4-0.8%, Ti=0.01-0.02%, Nb=0.03-0.06%, Mo=0.2-0.3%, Ce >=0.0003ppm, remaining is Fe and inevitable impurity.
Further, the high-strength steel includes following chemical component: C=0.14%, Si=by mass percentage0.32%, Mn=1.5%, P=0.013%, S=0.002%, Als=0.023%, V=0.43%, Ti=0.014, Cr=0.25%, Nb=0.044%, Mo=0.244, Ce=0.0005ppm, remaining is Fe and inevitable impurity.
Further, glowing furnace holding temperature is 910 DEG C or so in heat treatment process, and soaking time is greater than 20 minutes.
Further, tempering furnace holding temperature is 400 DEG C or more in heat treatment process, and soaking time is greater than 10 minutes.
Further, heat treatment process light plate temperature be down to 300 DEG C or less come out of the stove after it is air-cooled.
Compared with prior art, advantageous effects of the invention:
The present invention passes through addition rare earth element first, improves crystal boundary, strengthens the austenite grain boundary of temper embrittlement state, preventsWhat impact generated under low-temperature condition prolongs intercrystalline cracking, effectively improves the impact flexibility of steel；Meanwhile high pressure water jets are used after temperingSurface of steel plate is spilt, steel billet temperature is quickly reduced, due to having refined austenite grain and crystal boundary is made to be serrated, increases crystal boundary faceProduct, when tempering, alleviate pollution of the magazines such as carbon and nitrogen, phosphorus to crystal boundary, so as to mitigate temper brittleness.
This method improves the low-temperature impact toughness of steel plate by adding rare earth element, secondly by after tempering that steel plate is fastQuickly cooling but, by rare earth element is solidificated in boundary surfaces, can not only effectively reduce the ductile-brittle transition temperature of steel plate, and effectivelyInhibition temper brittleness, while improving the low-temperature impact toughness of steel plate, the performance for increasing high-strength steel steel plate is steadyIt is qualitative, substantially improving performance qualification rate.
Detailed description of the invention
Fig. 1 is high-strength steel impact fracture schematic diagram in embodiment 1；
Fig. 2 is metallographic structure schematic diagram at high-strength steel center in embodiment 1；
Fig. 3 is metallographic structure schematic diagram at high-strength steel center in embodiment 2.
Specific embodiment
Embodiment 1
Produce 690MPa grades of high strength steel plate production technologies, the composition quality percentage composition of steel are as follows: C=0.14%, Si=0.32%, Mn=1.5%, P=0.013%, S=0.002%, Als=0.023%, Nb=0.044%, V=0.043%, Ti=0.014%, Cr=0.41%, Mo=0.244%, Ce=0.0005ppm；
Main technological steps and parameter are as follows:
Molten iron pretreatment must first be carried out by entering furnace molten iron, molten steel sulfur content s≤0.010% after processing, temperature >=1250 DEG C,Molten iron must take off slag completely before entering converter, and molten iron and steel scrap is added in converter steelmaking process, and molten iron and steel scrap proportion are molten iron85% or so, steel scrap 15% or so.Converter terminal controls C-T and coordinates tapping, P≤0.012%, S≤0.015%, stringent pushing off the slagTapping, tap time 4-7min, and when tapping 1/5 is added alloy, and 2/5 amount of tapping adds alloy, contains in tapping process depending on terminal oxygenSuitable modification agent and lime is added in amount, and oxygen is no less than 250m, and is fitted depending on the variation of charge weight, terminal C, molten steel oxidationWork as adjustment, molten steel is then transported to LF refining furnace and carries out refining operation.
LF refining carries out molten steel to make white slag and deoxidation operation, it is ensured that the content of the elements such as oxygen, sulphur is controlled lower in steelLevel, quickly make white slag, and guarantee white slag time 15min or more, stablize basicity of slag；Alloy is matched as far as possible before LF refining is outboundTarget call range is added to, OT≤20ppm, N≤40ppm guarantee that S content is lower than 0.003%.
Rare earth alloy is added after 4 minutes in RH application of vacuum in feed bin, and 10% cerium-iron alloy, additional amount 31.5 is addedKilogram/furnace, the RH depth vacuum cycle time guarantees 15min or more after rare earth is added, and the argon gas soft blow time guarantees 10min or more.
1520 DEG C of the steel grade liquidus curve, the middle packet degree of superheat control 23-33 DEG C, and plate slab produces pulling rate in pulling speed of continuous casting useStable state casting is executed, thickness of strand 250mm is produced, continuous casting whole process carries out protective casting；Strengthen big packet-middle packet-crystallizer itBetween guarantee airtightness and middle packet liquid level coverture thickness, packet argon gas purging, prevents molten steel secondary oxidation and nitrogen pick-up in reinforcing.It is offlineSlab progress 24 hours or more heaps are cold.
Heating cycle: bringing-up section temperature is not higher than 1260 DEG C, 1220 DEG C~1260 DEG C of soaking temperature, it is ensured that soaking zone heat preservation>=40 minutes, guarantee that steel billet is grilled thoroughly, uniformly.Rolling mill practice: two stages controlled rolling, a stage start rolling temperature are greater than 1100 DEG C, pressureRate 60%~70%；860~900 DEG C of two-stage rolling temperature, >=12%, last three passage is accumulative to be depressed reduction ratio per passRate is not less than >=40%；Roll rear water cooling, 650~750 DEG C of final cooling temperature, stacking slow cooling.To reduce steel internal defect defect, fitWhen increasing roughing single pass rolling reduction, after rolling in the case where guaranteeing template, raising cooling rate is controlled by accelerating cooling as far as possiblePhase-change organization refines crystal grain, carries out tissue preparation for subsequent modifier treatment.
Heat treatment: output finished product walks heat treatment process after precisely cutting.Steel plate is through shot-blasting machine to eliminate surface of steel plateIron scale；Through roller hearth type non-oxidation glowing furnace, glowing furnace holding temperature is 910 DEG C or so, and soaking time is greater than 20 minutes, is protectedIt is accurate to demonstrate,prove temperature control, homogeneous heating, steel plate non-oxidation；Through roller-bottom type tempering furnace, tempering furnace holding temperature is 400 DEG C or more,Soaking time is greater than 10 minutes, should ensure that temperature control is accurate in heat treatment process, homogeneous heating.High pressure water jets are used after temperingSpill surface of steel plate, steel billet temperature be down to 300 DEG C or less come out of the stove after it is air-cooled.
The plate property produced according to the above technical scheme such as table 1:
1 mechanical property representative value of table
- 40 DEG C of Charpy-type tests are done by the high-strength steel steel plate that the technical program produces, low-temperature impact fracture is disconnected for toughnessMouthful, as shown in Figure 1.Metallographic microstructure is as shown in Fig. 2, can be seen that tissue from metallographic microstructure is tempered sorbite groupIt knits, even tissue, is typical quenching+tempering tissue.It can also be seen that the steel plate complete through hardening.
Embodiment 2
Produce 690MPa grades of high strength steel plate production technologies, the composition quality percentage composition of steel are as follows: C=0.13, Si=0.31,Mn=1.51, P=0.013, S=0.002, Al=0.023, Nb=0.042, V=0.044, Ti=0.013, Cr=0.41, Mo=0.247, Ce=0.0003ppm.
Main technological steps and parameter are as follows:
Molten iron pretreatment must first be carried out by entering furnace molten iron, molten steel sulfur content s≤0.010% after processing, temperature >=1250 DEG C,Molten iron must take off slag completely before entering converter, and molten iron and steel scrap is added in converter steelmaking process, and molten iron and steel scrap proportion are molten iron85% or so, steel scrap 15% or so.Converter terminal controls C-T and coordinates tapping, P≤0.012%, S≤0.015%, stringent pushing off the slagTapping, tap time 4-7min, and when tapping 1/5 is added alloy, and 2/5 amount of tapping adds alloy, contains in tapping process depending on terminal oxygenSuitable modification agent and lime is added in amount, and oxygen is no less than 250m, and is fitted depending on the variation of charge weight, terminal C, molten steel oxidationWork as adjustment, molten steel is then transported to LF refining furnace and carries out refining operation.
LF refining carries out molten steel to make white slag and deoxidation operation, it is ensured that the content of the elements such as oxygen, sulphur is controlled lower in steelLevel, quickly make white slag, and guarantee white slag time 15min or more, stablize basicity of slag；Alloy is matched as far as possible before LF refining is outboundTarget call range is added to, OT≤20ppm, N≤40ppm guarantee that S content is lower than 0.003%.
Rare earth alloy is added after 4 minutes in RH application of vacuum in feed bin, and 10% cerium-iron alloy, additional amount 31.5 is addedKilogram/furnace, the RH depth vacuum cycle time guarantees 15min or more after rare earth is added, and the argon gas soft blow time guarantees 10min or more.
1520 DEG C of the steel grade liquidus curve, the middle packet degree of superheat control 23-33 DEG C, and plate slab produces pulling rate in pulling speed of continuous casting useStable state casting is executed, thickness of strand 250mm is produced, continuous casting whole process carries out protective casting；Strengthen big packet-middle packet-crystallizer itBetween guarantee airtightness and middle packet liquid level coverture thickness, packet argon gas purging, prevents molten steel secondary oxidation and nitrogen pick-up in reinforcing.It is offlineSlab progress 24 hours or more heaps are cold.
Heating cycle: bringing-up section temperature is not higher than 1260 DEG C, 1220 DEG C~1260 DEG C of soaking temperature, it is ensured that soaking zone heat preservation>=40 minutes, guarantee that steel billet is grilled thoroughly, uniformly.
Rolling mill practice: two stages controlled rolling, a stage start rolling temperature are greater than 1100 DEG C, reduction ratio 60%~70%；Two-stage860~900 DEG C of start rolling temperature, >=12%, last three passage adds up reduction ratio and is not less than >=40% reduction ratio per pass；After rollingWater cooling, 650~750 DEG C of final cooling temperature, stacking slow cooling.It is appropriate to increase roughing single pass pressure to reduce steel internal defect defectLower amount, after rolling in the case where guaranteeing template, raising cooling rate controls phase-change organization by acceleration cooling as far as possible, refines crystal grain,Tissue is carried out for subsequent modifier treatment to prepare.
Heat treatment: output finished product walks heat treatment process through precisely cutting.Steel plate is through DISA shot-blasting machine to eliminate surface of steel plateIron scale；Through LOI roller hearth type non-oxidation glowing furnace, glowing furnace holding temperature is 910 DEG C or so, and soaking time is greater than 20 pointsClock guarantees that temperature control is accurate, homogeneous heating, steel plate non-oxidation；Through LOI roller-bottom type tempering furnace, tempering furnace holding temperature is 400DEG C or more, soaking time is greater than 10 minutes, should ensure that temperature control is accurate in heat treatment process, homogeneous heating.It is used after temperingHigh pressure water spray surface of steel plate, steel billet temperature be down to 300 DEG C or less come out of the stove after it is air-cooled.
The plate property produced according to the above technical scheme such as table 2:
2 mechanical property representative value of table
By the high-strength steel steel plate that the technical program produces, metallographic microstructure is as shown in figure 3, can be with from metallographic microstructureFind out, organizes as tempered sorbite tissue, even tissue, for typical quenching+tempering tissue.
Above example can be seen that the high strength steel plate mechanical property produced using above-mentioned ingredient and technique much higher than countryStandard, meeting requirement embodiment described above of the relevant industries to high-strength steel sheet low-temperature impact toughness is only to of the inventionPreferred embodiment is described, and is not intended to limit the scope of the present invention, without departing from the spirit of the design of the present invention, thisThe various changes and improvements that field those of ordinary skill makes technical solution of the present invention should all fall into the claims in the present inventionIn the protection scope that book determines.