稀土元素对Si—Mn—V钢淬火,回火过程中组织结构转变的影响

采用透射电镜,X射线,膨胀仪等方法,对含稀土和不含稀土的4种低、中碳Si—Mn-V钢(20SiMn2V;20SiMn2VRE;40SiMn2V和40SiMn_2VRE)进行了淬火、回火过程中组织结构转变的对比试验,结果表明:稀土元素可以细化低、中碳钢的奥氏体晶粒度;降低M_s点;细化马氏体板条束和板条晶尺寸;并增加中碳钢马氏体中位错亚结构的相对比例。而对低、中碳钢淬火回火组织中残余奥氏体的体积和热稳定性影响甚微。稀土元素明显地抑制了低碳马氏体在低温回火过程中的分解,阻碍板条晶内片状渗碳体的析出,并推迟其长大球化过程。稀土元素也明显地抑制了中碳马氏体中高温回火过程中粒状渗碳体的析出和球化过程。     

Microstructure evolution of an ultra-high strength metal alloy with tempering temperature

Optical microscopy (OM) and transmission electron microscopy (TEM) were used to investigate the effect of tempering temperature on the experimental extra-high carbon steels.It is found that tempering reaction can reduce austenite content and influence the stability of the austenite.As-normalized microstructure is a mixture of twinned martensite and retained austenite.Tempered at 250 ℃ for 2 h,lath martensite can occasionally be found nearby the diffusionally decomposed austenite arca.It also is found that tempering at 650 ℃ for 2 h,nanoparticles of carbides precipitate in the martensite and decomposed austenite.     

热处理对国外P92钢显微组织及晶粒度的影响

对国外P92钢进行不同温度(1040、1060、1080 ℃)淬火和1060 ℃淬火+不同温度(740、760、780 ℃)、不同时间(1、3、5、7 h)的回火热处理,研究热处理参数对其显微组织、晶粒度及硬度的影响。结果表明,经淬火后P92钢组织为板条状马氏体+残留奥氏体,随淬火温度的升高,马氏体组织板条逐渐变粗大,平均晶粒度由9级增大至7级。P92钢经1060 ℃淬火后,随着回火温度的升高和回火时间的延长,P92钢硬度逐渐降低,回火马氏体板条逐渐合并并向回火索氏体过渡,且回火过程中碳化物在晶界和晶内析出并不断长大。     

Effect of silicon on the spheroidization of cementite in hypereutectoid high carbon chromium bearing steels

The effect of silicon on the spheroidization of cementite in hypereutectoid high carbon chromium bearing steels has been investigated on the basis of microstructural analysis and thermodynamic calculations. The results showed that an increase of silicon content in high carbon chromium bearing steels retards the spheoridization of cementite. The thermodynamic calculations revealed that the shrinkage of the austenite phase field in bearing steels with increasing silicon content gave rise to an increase of volume fraction of cementite at an annealing temperature, possibly resulting in incomplete spheroidization. Furthermore, due to the low solubility of silicon in cementite, an increase of silicon content can raise the activity or chemical potential of carbon atoms in austenite at the austenite/cementite interfaces. Consequently, the difference in chemical potential of carbon atoms at the interfaces would be reduced with increasing silicon content, causing a decrease of the driving force for their diffusion from cementite to austenite.     

层片型双相组织的形成过程

本文用金相显微镜、透射电镜和扫描电镜观察了09SiCrMnMoRE钢经1100℃预淬及各种亚温温度不同保温时间淬火后所得双相组织的形貌,探讨了层片型双相组织的形成机理.观察表明,在亚温加热中,奥氏体优先在晶界及板条群界形核,也在板条界经碳化物析出与溶解而后形核.奥氏体与铁素体间存在K-S关系.奥氏体呈片状沿马氏作板条界及群界定向生长有利于减小界面能及应变能.其结果导致淬火后得到层片型双相组织.     

马氏体温变形超细化过共析钢

利用Gleeble 1500热模拟试验机进行单轴热压缩实验, 研究了含Al和不含Al两种过共析钢马氏体温变形和等温回火过程中的组织超细球化演变及超细球化组织的力学性能. 结果表明: 与马氏体等温回火相比, 马氏体温变形加快马氏体的分解动力学, 在较短的时间 内即获得超细化 (α+θ)复相组织. 温变形过程中的组织超细化演变主要经历渗碳体粒子的析出与粗化及铁素体基体的动态回复和动态再结晶; 而在等温回火过程中, 铁素体主要发生静态回复和晶粒长大, 并没有再结晶现象发生. 合金元素Al的加入在等温回火和温变形过程中均抑制马氏体的分解, 阻碍渗碳体粒子的粗化和铁素体晶粒的长大, 导致复相组织的细化. 同时, Al的加入使马氏体温变形和等温回火后所得超细化 (α+θ) 复相组织在不降低总延伸率的前提下, 强度得以明显提高.     

Correlations of Ni Contents,Formation of Reversed Austenite and Toughness for Ni-Containing Cryogenic Steels

It has been widely demonstrated that addition of Ni in low-carbon steels can effectively improve the cryogenic toughness,but the mechanism behind it has yet to be clarified.In the present work,the evolutions of microstructure and mechanical properties after quenching and tempering for Ni-containing cryogenic steels with different Ni contents(3.5-9 wt%) were investigated.The results showed that after quenching and tempering,the Ni-containing cryogenic steels were composed of tempered martensite and reversed austenite.The volume fraction of reversed austenite has increased from 0 up to 6.3%when the Ni content increases from 3.5%to 9%.The Charpy impact tests indicated that the lowtemperature toughness was markedly improved with the increase in Ni content,which can be correlated with the increase in reversed austenite amount.The main contribution of reversed austenite to the toughness lies in:(1) the elimination of cementite precipitates improved the plastic deformation capacity of matrix,and(2) the crack propagation is hindered through plastic deformation.     

回火温度对大尺寸锻态35CrMo钢微观组织和力学性能的影响

研究了回火温度对大尺寸锻态35CrMo钢调质处理后组织特性及力学性能的影响,特别针对回火过程中渗碳体的析出动力学及大尺寸试块的组织性能不均匀性展开了分析。结果表明,锻坯热处理前的铁素体、珠光体带状组织经调质处理后完全消除,最终组织为含有大量渗碳体析出的回火马氏体,同时试块心部包含少量分布于原奥氏体晶界的回火贝氏体。回火过程中渗碳体的析出分为C扩散控制的快速长大阶段和Cr扩散控制的尺寸稳定阶段。锻态35CrMo钢经调质处理后仍存在力学性能各向异性,随着回火温度的升高,试验钢横、纵向强度下降,塑性和韧性同步提升。经综合考虑,当回火温度为570 ℃时,其强度、塑性和韧性具有最优匹配。     

55SiCr弹簧钢中的残留奥氏体与碳化物

通过扫描电镜(SEM)、电子背散射衍射(EBSD)、透射电镜(TEM)、X射线衍射仪(XRD)、热膨胀仪、洛氏硬度计等手段研究了弹簧钢55SiCr的组织和相变点以及残留奥氏体和碳化物在热处理过程中的组织演变。结果表明:55SiCr弹簧钢淬火后残留奥氏体以块状分布在基体上;随回火温度的升高,残留奥氏体减少并呈粒状和薄膜状分布;C在残留奥氏体中富集,使其稳定性增强;Si抑制了碳化物的析出,提高了残留奥氏体的稳定性。低温回火时,Si延缓了渗碳体析出;高温回火时,C原子扩散速率提高,促进渗碳体析出,引起体积的收缩。慢速加热回火时,C有足够的时间扩散,从而促进渗碳体的形成,使渗碳体的形成温度提前;快速加热回火时,C来不及扩散,抑制了渗碳体的析出。回火加热速率一样时,试验钢的硬度随回火温度的提高而下降。当回火温度为400 ℃时,硬度值最大为51 HRC;当回火温度为650 ℃时,硬度值最小为37 HRC。当加热速率为0.1 ℃/s时,硬度值最小为33 HRC;当加热速率为200 ℃/s时,硬度值最大为40 HRC。     

临界淬火工艺处理高强结构钢Q690GJ的韧化机理

研究了QT(淬火+回火)和QLT(淬火+临界淬火+回火)热处理对高强结构钢Q690GJ微观组织及低温韧性的影响。通过金相、扫描电镜等方法,对低温冲击试样、无塑性转变试样进行了微观分析。结果表明:QLT工艺处理的Q690GJ钢低温韧性明显优于QT工艺。微观组织分析表明:QLT工艺处理试验钢组织为板条马氏体+残留奥氏体,临界淬火工艺形成了更多数量的、且较为稳定的残留奥氏体软相,提高了起裂前的塑性变形能力;同时形成更多取向混乱的马氏体板条束,有效阻碍了裂纹的扩展,从而提高低温韧性、降低无塑性转变温度。     

MECHANISM OF TEMPER MARTENSITE EMBRITTLEMENT

计算了残余奥氏体分解和马氏体分解的相变总驱动力,渗碳体自马氏体析出和自奥氏体析出的形核驱动力、长大速率和孕育期。计算结果揭示:尽管奥氏体分解的驱动力大于马氏体分解约一个数量级,但渗碳体自马氏体析出的形核驱动力远大于自奥氏体的析出,长大速率约大两个数量级,孕育期比奥氏体析出的约小一个数量级。可见在低温短时回火时,渗碳体先从马氏体内析出;当回火时间较长时,由于奥氏体分解的相变总驱动力较大,以及由于马氏体条内析出渗碳体引起的收缩,促使条间残余奥氏体的分解,形成回火马氏体脆性。因此当不计及杂质(及渗碳体)在原始奥氏体晶界的偏聚对,回火马氏体脆性的机制应为这两个分解先后互相关联的过程。     

稳恒磁场对马氏体转变的影响

利用自制的磁场热处理设备对中、高碳钢进行了施加磁场与不施加磁场的淬火处理,研究了奥氏体在NaCl溶液中冷却时的组织转变,观察了相变后的组织变化.结果表明,在中、高碳钢发生奥氏体向马氏体转变时,稳恒磁场可使马氏体的形核率增加,提高马氏体的转变开始温度,使相变在更宽的温度区间进行,促进了奥氏体向板条马氏体的转变.     

热处理对超超临界材料KT5331AS0组织和性能的影响

研究了热处理工艺对超超临界材料KT5331AS0(10Cr11Co3W3NiMoVNbNB)的组织和性能的影响.结果表明:KT5331AS0钢在1050～1150℃加热淬火、660～720℃回火,其组织都是回火板条马氏体;随淬火加热温度的升高,板条马氏体逐渐长大,但长大趋势不明显;随回火温度的升高,南于碳化物的析出,产生沉淀强化,使其具有较高的持久强度.KT5331AS0钢在1080～1100℃加热淬火、680～700℃回火后具有较好的综合力学性能.     

淬火方式对Ti微合金化中碳钢组织和性能的影响

设计了一种Ti微合金化中碳钢,在控制轧制后采用在线直接淬火+低温回火(DQ+LT)和离线再加热淬火+低温回火(RQ+LT)两种热处理工艺。通过力学性能检测和微观组织观察,研究了不同淬火方式(DQ和RQ)对Ti微合金化中碳钢微观组织和析出相的影响。结果表明:淬火方式对试验钢的微观组织特征和力学性能产生了显著影响。DQ和RQ淬火方式获得的晶粒形态分别呈现扁平化和等轴化,扁平化马氏体板条较细长,方向性明显,基体位错密度高,而等轴晶粒的有效晶粒尺寸更细,晶粒内马氏体板条均匀、无方向性,基体上有大量细小的碳化物和(Ti, Mo)C析出相。组织上的差异使得DQ工艺试验钢存在横、纵向性能不均匀、低温冲击性能较差等不足,而RQ工艺试验钢的横、纵向性能均匀、强韧性匹配良好。     

Factors that determine the level of the yield strength and the return of the yield-point elongation in low-alloy ferrite-martensite steels

The results of laboratory investigations of dual-phase steels with different contents of carbon and alloying elements after the controlled cooling from the two-phase field and the final low-temperature tempering are presented. It is shown that the ratio of the yield strength to the tensile strength of dual-phase steels, just as the return of the yield-point elongation, depends on the volume fraction of martensite, temperature of the martensite transformation of the austenite component, quenching stresses, concentration of carbon in ferrite, and the temperature of the final tempering.     

回火温度对新一代传动齿轮钢C61组织及性能的影响

采用扫描电镜、透射电镜、X射线衍射仪、显微硬度计、拉伸试验机和冲击试验机等分析手段对C61齿轮钢试样经1000 ℃淬火+回火处理后组织和碳化物的析出行为及力学性能进行了研究。结果表明,试验钢在淬火和深冷状态下,一次碳化物基本溶解,基体为板条马氏体组织,此时固溶强化作用提供了较好的强韧化基础。当回火温度为420 ℃时,析出的M₃C渗碳体为其提供了较高的强度,但这种析出相的存在对冲击性能具有较大的损伤;M₃C渗碳体会在482 ℃回火时溶解,10~20 nm尺寸的棒状M₂C碳化物在板条马氏体内的弥散析出,提供了较高强度的同时改善了冲击性能。随着回火温度的继续升高,大量逆转变奥氏体生成,不仅有效提高冲击性能,同时强度下降也更为明显;且M₂C碳化物粗化长大,第二相的强化作用降低。综合得出,试验钢在482 ℃的回火条件下能达到较好的强韧化匹配,抗拉强度和屈服强度分别为1781 MPa和1546 MPa,冲击吸收能量为97 J,硬度峰值为52 HRC。     

淬火- 非等温碳分配下淬火温度对显微组织的影响

以低碳Si- Mn钢为研究对象,在MMS- 300热力模拟实验机上,分析了在DQ&P（Direct quenching & Partitioning）工艺的非等温碳分配条件下,淬火温度对试样显微组织、残余奥氏体含量和残余奥氏体中碳含量的影响。结果表明：试样的显微组织由板条状马氏体、残余奥氏体及少量铁素体组成;在320 ℃较高的淬火温度条件下,马氏体板条边界变得不明锐且弯曲,同时,碳化物沉淀含量增加;残余奥氏体含量随淬火温度的升高先增加后减少,在240 ℃时达到最大值;残余奥氏体中碳含量随淬火温度先减少后增加。     

临界区回火温度对Fe-4Mn-1.2Cr-0.3Cu-0.6Ni中锰钢微观组织和力学性能的影响

研究了临界区回火温度对Fe-4Mn-1.2Cr-0.3Cu-0.6Ni中锰钢组织与力学性能的影响。通过热轧后直接淬火+临界区回火的工艺制备试验钢。采用光学显微镜(OM)、电子探针显微分析仪(EPMA)的扫描功能、透射电镜(TEM)、拉伸试验及冲击试验等对轧后淬火态和回火态试验钢的显微组织及力学性能进行了表征。结果表明,试验钢热轧后淬火可获得较高位错密度的板条马氏体,经过临界区回火后获得在回火马氏体基体上分布残留奥氏体的复合组织。随着临界区回火温度的升高,试验钢的抗拉强度呈升高趋势,而屈服强度先下降后增加,伸长率的变化趋势与试验钢中的残留奥氏体含量相关,冲击性能随临界区回火温度的升高呈先升高后降低的趋势。630 ℃回火后试验钢的拉伸性能最佳,650 ℃回火后试验钢的冲击性能最佳,确定最佳临界区回火温度区间为630~650 ℃。     

Recrystallization and the possibility of the realization of the α-γ diffusionless transformation during the ultrarapid laser heating of steels

Analysis is given of phase and structural transformations occurring upon ultrarapid laser heating in steels with different initial structures, namely, after annealing, after preliminary quenching, quenching and tempering, and after quenching with subsequent deformation and tempering. It is shown that a significant suppression of diffusion processes occurs during laser heating; this circumstance substantially affects the nature of the phase and structural transformations proceeding during laser processing. Special attention is given to studying the process of recrystallization and to the phenomenon of structural heredity during laser heating. The process of recrystallization during laser heating is considered as consisting of two stages, namely, an ordered lattice rearrangement (α-γ transformation) and the recrystallization of austenite that suffered phase-transformation-induced hardening (“phase naklep”). The effect of tempering and plastic deformation on the recrystallization of a preliminarily quenched steel consists in the intensification of the second stage, i.e., of the recrystallization of the transformation-hardened austenite. It is shown that the α-γ transformation during the laser heating of steels with the initial structure of lath martensite occurs by the “mechanism of recovery,” i.e., via the formation and growth of austenite nuclei. In steels with the initial structure of pearlite, the nucleation of austenite during laser heating can occur by a shear martensite-like diffusionless mechanism with the observance of characteristic orientation relationships between the initial ferrite and the newly formed austenite.     

淬火温度对中合金马氏体耐磨铸钢组织和性能的影响

对自行设计的矿山球磨机衬板用中合金马氏体耐磨铸钢在900、950、1000、1050、1100 ℃淬火后回火,研究了淬火温度对试验钢组织和性能的影响。试验结果表明,经过淬火、回火处理后的试验钢显微组织由板条马氏体和残留奥氏体组成。当保持回火温度250 ℃不变,随着淬火温度的升高,马氏体组织先变细密后又变粗大,抗拉强度、冲击性能及残留奥氏体含量均呈现先增大后减小的趋势,在1050 ℃淬火取得最优综合力学性能:抗拉强度1623 MPa,冲击性能14.4 J,此时试验钢的强化机理为孪晶马氏体和高密度位错缠结。通过冲击磨损试验解释了试验钢在该工艺下的磨损行为与磨损机理。