Metadynamic Recrystallization of the As-cast 42CrMo Steel after Normalizing and Tempering during Hot Compression

The existing researches of hot ring rolling process are mainly based on forged billet. Compared with the existing process, the new ring casting-rolling compound forming process has significant advantages in saving materials and energy, reducing emission and reducing the production cost. The microstructure evolution of the casting materials during hot deformation is the basis of the research of the new process. However, the researches on the casting materials are rare. The metadynamic recrystallization of the as-cast 42CrMo steel after normalizing and tempering during the hot compression is investigated. The tests are performed on the Gleeble-1500 thermal-mechanical simulator. The influence rule of the deformation parameters on the metadynamic recrystallization is obtained by analyzing the experimental data. The kinetic model of the rnetadynamic recrystallization is deduced. The analysis results show that the metadynamic recrystallization fraction increases with the increase of the deformation temperature and the strain rate. The metallographic experiments are used to investigate the influence rule of the deformation parameters on the grain size of the metadynamic recrystallization. The experimental results show that the grain of the metadynamic recrystallization could be refined with the increase of the strain rate and the decrease of the deformation temperature during hot compression. The occurrence of the metadynamic recrystallization during the hot deformation is more difficult in as-cast 42CrMo steel than in forged 42CrMo steel. The research can provide the foundation for the further research of the hot deformation behaviors of the as-cast structure and theoretical support for the new ring casting-rolling compound process.

Study on Contact Fatigue Life and Failure Mechanism of Subquenched 42CrMo Steel

The effect of undissolved ferrite amount in subcritically quenched 42CrMo steel on contact fatigue properties and failure mechanism were studied. The amount of undissolved ferrite in the steel were 0%,3%,10%,15% and 20% in volume fraction, respectively. The experimental results show that the existence of undissolved ferrite can increase the contact fatigue life The contact fatigue life can be prolonged with increasing the amounts of undissolved ferrite The grain size can be fined by using subcritical quenching process and the area of phase boundaries can also be greatly increased. The stress relaxation and grain refinement due to occurring of plastic deformation are main reasons for improving the fatigue life. The existence of undissolved ferrite can increase the crack initiation period. Under the experiment conditions, when the amount of undissolved ferrite is 10%, the longest contact fatigue life can be the obtained.

Vacuum brazing of TiAl to 42CrMo steel with Ag-Cu-Ti filler metal

Vacuum brazing of TiAl to 42CrMo steel was carried out at 8601000℃ for 5min using Ag-33Cu- 4.5Ti （mass fraction, %） filler metal. Formation phases and microstructures of the joints were investigated by SEM and EPMA. The strength of the joints were evaluated by means of tensile tests. The results show that five interfacial formation phases occur in the brazing seam: AlCuTi and AlCu2Ti compounds, Ag solid solution, Ag-Cu eutectic phase and the reaction layer of TiC adjacent to the steel. The tensile strength of the brazed joints changes with the chang of brazing temperature. When the brazing temperature is 900℃, the tensile strength of the joint is 347MPa. TiAl turbine and 42CrMo steel shaft was brazed and the strength of TiAl/42CrMo turbine rotor was evaluated by means of tensile test, when the tensile load reached 100kN the joint of the rotor kept well.

基于应力三轴度的铸态42CrMo钢高温拉伸断裂行为分析

利用Gleeble-3500型热模拟试验机对不同缺口半径(0.5,1.0,2.0,4.0 mm)的铸态42CrMo钢缺口试样进行不同温度(1223,1273,1373 K)下的热拉伸试验,基于应力三轴度分析了其高温拉伸断裂行为。结果表明:较高拉伸温度下缺口试样的流变应力较小;随着缺口半径减小,缺口试样流变应力和峰值应力增加,断裂应变减小;当缺口半径为0.5,1.0 mm时,应力三轴度最大值向最小横截面圆心转移;当缺口半径为2.0,4.0 mm时,拉伸过程中最小横截面圆心处的应力三轴度始终最大;随着缺口半径增加,应力三轴度减小;温度由1223 K升至1373 K,试样断口组织平均晶粒尺寸增大;缺口半径由0.5 mm增加至4.0 mm,平均晶粒尺寸增大,微空洞且尺寸及面积分数增加。

雾化射流对42CrMo钢车削断屑性能影响的实验研究

金属加工过程中,切屑周期性断裂有利于切削过程的稳定进行,实现高质高效加工。雾化射流是一种重要的冷却方式,把压缩空气与切削液混合并断续喷射形成雾状。与切削液溢流冷却相比,雾化射流射出的小液滴渗透性更好,冷却介质能更准确地施加到刀具前刀面和切屑内表面位置。为了探究雾化射流对42CrMo钢车削断屑性能的影响,采用三种冷却方式(干切削、切削液溢流及雾化射流)和两种进给量(0.15mm/r, 0.18mm/r)进行车削实验,对切屑的宏观长度、卷曲半径、切削力和刀—屑接触长度进行观测。在相同的进给量下,采用雾化射流冷却方式可以获得更短的切屑宏观长度、更小的切屑卷曲半径、更小的切削力、更短的刀—屑接触长度以及更小的切屑内表面粗糙度。

超声喷丸工艺参数对42CrMo钢表面质量的影响

通过单因素试验法研究了超声喷丸工艺对42CrMo超高强度钢表面质量的影响,对42CrMo钢超声喷丸处理前后的表面粗糙度、表面硬度、截面显微硬度和微观组织进行了表征分析。结果表明,随着喷丸时间的延长,表面粗糙度和表面硬度逐渐增大直至稳定,稳定值分别为1.08μm和433.60 HV;超声振幅、弹丸直径的增加和喷丸距离的减小可以有效地提升试样的超声喷丸强度,在试样表面产生更加剧烈的塑性变形,虽然提高了表面粗糙度,但是获得了深度更大的硬化层和梯度结构晶粒细化层,分别为2.8 mm和40μm。

Heat Treatment Properties of 42CrMo Steel for Bearing Ring of Varisized Shield Tunneling Machine

The heat treatment properties of 42CrMo steel for bearing ring of varisized shield tunneling machine were investigated by optical microscope （OM）, scanning electron microscope （SEM）, transmission electron microscope （TEM）, and impact tests. The addition of 0.03 wt% C into 42CrMo steel can increase the hardness. But it reduces the impact energy by 46 J because of the appearance of coarser carbides in the matrix and the carbides along the austenite grain boundary. The addition of 0.40 wt% Mn into 42CrMo steel can improve hardenability. However, the toughness of steel is also reduced by 26 J mainly because of the coarsening of carbides and the strengthening of matrix. Both hardenability and toughness of 42CrMo steel can be improved by adding 1.49 wt% Ni and reducing 0.32 wt% Cr. The depth of hardening layer can be raised to 45 mm, and the impact energy at -20 ℃ is 120 J. Thus, it is concluded that a good combination of hardness, hardenability, and toughness of 42CrMo steel can be achieved by alloying with adding some content of C and Ni. Detailed content of C and Ni should be on the requirements of heat treatment properties of steel for bearing ring of varisized shield tunneling machine.

曲轴用42CrMo钢激光重熔数值模拟与试验验证

为探究曲轴用42CrMo钢在激光重熔处理过程中熔池流动和形貌演变规律,建立高度拟合原始形貌的二维仿真模型,利用有限元法对不同激光功率下试样表面进行仿真分析,并结合试验对比分析表面粗糙度和显微硬度变化规律。结果表明,利用熔池流动模型可良好预测42CrMo钢表面熔池流动和表面微起伏变化;熔池内部流速呈现先增大后减小趋势,通过调控激光功率可在实现表面重熔的同时提升试样表面质量;经激光重熔处理后42CrMo钢表面硬度显著提升,达到曲轴工况需求;仿真模型对表面粗糙度和熔池深度预测结果与试验结果基本吻合。

Analysis of Valence Electron Structure in Compound Layer of Steel 42CrMo Plasma Nitrided with Rare Earth Addition

The valence electron structure (VES) in compound layer of steel plasma-nitrided at 560°C with rare earth (RE) addition was calculated based on the empirical electron theory (EET) of solids and molecules and BLD method. The results show that the presence of RE atoms diffused into surface layer leads to an increase of phase structure factor, which explains the catalyzing and micro-alloying effects of RE.

回火温度对含钒42CrMo钢-40℃冲击韧性的影响

对含钒42CrMo钢进行了870℃油淬和540~650℃回火,采用扫描电子显微镜、电子背散射衍射和透射电子显微镜检测了钢的-40℃冲击韧性、显微组织、应力、位错密度和晶粒取向差。结果显示:随着回火温度的升高,钢的-40℃冲击吸收能量从26 J提高到了118 J,回火索氏体中的碳化物从条状转变为球状;较高温度回火的钢比较低温度回火的钢具有更多的大角度晶界、较小的应力和较低的位错密度;回火索氏体中的条状、针状碳化物主要为Fe__(3)C,球状碳化物主要为M__(7)C__(3)和VC,弥散分布的球状碳化物有利于改善钢的低温冲击韧性。

Combined Cellular Automaton Model for Dynamic Recrystallization Evolution of 42CrMo Cast Steel

The dynamic recrystallization(DRX) simulation performance largely depends on simulated grain topological struc?tures. However, currently solutions used di erent models for describing two?dimensional(2 D) and three?dimensional(3 D) grain size distributions. Therefore, it is necessary to develop a more universal simulation technique. A cellular automaton(CA) model combined with an optimized topology deformation technology is proposed to simulate the microstructural evolution of 42 CrMo cast steel during DRX. In order to obtain values of material constants adopted in the CA model, hot deformation characteristics of 42 CrMo cast steel are investigated by hot compression metal?lographic testing. The proposed CA model deviates in two important aspects from the regular CA model. First, an optimized grain topology deformation technology is utilized for studying the hot compression e ect on the topology of grain deformation. Second, the overlapping grain topological structures are optimized by using an independent component analysis method, and the influence of various thermomechanical parameters on the nucleation process, grain growth kinetics, and mean grain sizes observed during DRX are explored. Experimental study shows that the average relative root mean square error(RRMSE) of the mean grain diameter obtained by the regular CA model is equal to 0.173, while the magnitude calculated using the proposed optimized CA model is only 0.11. This paper pro?poses a novel combined CA model for simulating the microstructural evolution of 42 CrMo cast steel, which notably uses a ICA?based grain topology deformation method to optimize the overlapping grain topological structures in simulation.

42CrMo钢超声滚压残余应力及等效塑性应变研究

基于接触力学模型,建立了超声滚压加工残余应力分布的理论模型,模拟了不同静压力、进给速度和振幅下的超声滚压加工过程,分析了超声滚压加工后残余应力和等效塑性应变的分布情况。结果表明,试样表面会发生不同程度的塑性变形并产生残余压应力。随着深度的增加,残余压应力逐渐增大,在深度为0.4 mm处达到最大值,之后逐渐转为残余拉应力,最后残余拉应力和残余压应力趋于平衡。随着深度的增加,等效塑性应变先增大后逐渐减小,最后在深度约1 mm处达到0。加工参数中静压力对残余应力和等效塑性应变的影响最为显著,最大残余压应力和等效塑性应变随着静压力的增大而增大,最大残余压应力和最大等效塑性应变分别为-910.07 MPa和0.46。对比残余应力实验和仿真结果,发现二者残余应力随加工参数的变化规律一致,并且误差范围基本保持在10%以内,验证了有限元模型的准确性和有效性。

42CrMo传动轴花键轴套断裂失效分析

通过光学显微镜、扫描电镜、显微硬度计等方法对传动花键轴套断裂失效的原因进行分析。结果表明,花键轴套的化学成分及硬度均符合要求。花键轴套长期在残留腐蚀介质和应力的作用下发生应力腐蚀开裂及扩展。由于叠加焊接应力和套装应力的耦合作用,形成穿透性裂纹,导致花键轴套承受载荷水平降低,最终在扭矩的作用下在穿透性应力腐蚀裂纹尖端发生扭转断裂。

中碳合金钢42CrMo的ECAP工艺参数模拟及试验研究

高端滚动轴承在服役过程中存在的尺寸稳定性差和滚动疲劳寿命低等问题,严重制约着我国高端装备制造业的发展水平。因此,急需开发具有高强韧性、耐磨、耐疲劳特性的轴承钢。中碳轴承钢作为超高速高精密滚动轴承极具潜力的轴承钢材料,对不同工艺条件下的中碳合金钢ECAP(equal channel angular pressing)工艺参数开展研究,分析了ECAP过程对42CrMo钢的挤压载荷、等效应变、等效应力及温度场数值变化和分布规律。研究结果表明,适当提高挤压初始温度和挤压速度,均可以有效降低挤压载荷和等效应力;加大挤压速度可以明显提升试件挤出温度,但不利于试件ECAP过程形变的均匀性;减小摩擦系数可以显著降低挤压载荷,有助于提高晶粒细化的均匀程度。综合考虑,选定挤压温度950℃,挤压速度10 mm/s、摩擦系数0.03条件下设计试验,可以有效提高ECAP细化晶粒的能力,同时为试件进行下一步热处理提供良好初始条件。以上试验研究是对中碳钢细晶强化的全新探索,可以为其他性能相近的金属材料开展ECAP研究提供技术参考。

42CrMo钢的等通道转角挤压成型工艺

为解决传统等径角挤压(equal channel angular pressing,ECAP)模具在挤压过程中可能存在的飞边和装拆困难等问题,采用ECAP工艺,以42CrMo钢为挤压材料,通过总结分析ECAP试验过程中模具脱模困难的原因,提出一种对称分模模具及配套模架的设计方案。该方案通过设计模架并优化模具配合间隙,避免挤压试件飞边的产生,只需操纵压机将凸模抬起即可快速脱模。在Deform软件中建立不同模具间隙下42CrMo钢ECAP的有限元模型,研究了模具间隙对42CrMo试件ECAP成形的影响规律。在此基础上,进行了ECAP试验,观察挤压后试件表面质量,通过试验结果与数值模拟结果一致性对比,验证了数值模拟结果的可靠性与准确性。研究结果表明,模具设计方案有效防止飞边产生,试验效果较好。金相显微组织观察表明,挤压后的42CrMo钢晶粒细化效果显著。

方形光斑多点激光冲击强化42CrMo钢表面残余应力和变形的数值模拟研究

通过改进的数值模拟方法研究方形光斑多点激光冲击对42CrMo钢表面残余应力和变形的影响。结果表明,随着冲击波峰值压力的增加,表面残余应力和表面变形都有所增大。同时,针对采煤机截齿表面进行激光冲击强化数值模拟,证明其表面可形成残余应力。

42CrMo钢热变形行为及热加工图研究

使用Gleeble-3800热模拟机对42CrMo钢在变形温度为1123~1223 K,变形速率为0.1~10 s^(-1)下进行热压缩实验,研究了其热变形行为,构建了42CrMo钢的本构方程;通过对材料常数(α,n,Q和ln A)的分析,得到了流动应力的预测模型;绘制了42CrMo钢的热加工图,得到最优热加工工艺区间。结果表明:材料对温度、应变速率敏感,其流变应力随着变形温度增加和应变速率降低而减小。流动应力预测模型预测精度为0.987,42CrMo钢最优工艺范围为:变形温度1140~1223 K,应变速率0.1~1.5 s^(-1)。本研究可对42CrMo钢热变形加工工艺制定提供指导。

大规格42CrMoS钢棒的横向冲击韧性及其主要影响因素

在直径为380 mm的锻态42CrMoS钢棒的不同部位处取样,进行850℃水冷淬火或风冷淬火以及相同工艺高温回火处理,研究了热处理后的显微组织、硫化物夹杂形貌和数量及其对横向冲击韧性的影响。结果表明:钢棒未出现严重的元素偏析;在水冷淬火和风冷淬火条件下不同部位的横向冲击吸收功分别在21.6~35.6 J和12.7~17.7 J;钢棒中硫化物的形貌比其数量对横向冲击韧性的影响更显著,细小、均匀分布的点状硫化物对横向冲击韧性的不利影响相对较小;在风冷淬火和高温回火试样中显微组织中每增加10%面积分数的贝氏体,其横向冲击功下降6%左右,回火索氏体组织对横向冲击韧性影响程度的权重大约是贝氏体组织的2.5倍。

K418/42CrMo异种金属连续驱动摩擦焊次生摩擦面研究

采用连续驱动摩擦焊进行K418高温合金/42CrMo异种金属的焊接,对焊接接头金相组织、元素含量等进行了分析。结果表明:焊缝处K418侧各主要元素向42CrMo侧发生扩散,42CrMo侧碳元素向K418侧发生扩散,K418侧近焊缝区形成了次生摩擦面,焊接完毕后析出带状碳化物,带状碳化物与焊缝之间的K418发生再结晶。

转炉流程生产42CrMo圆钢实践

介绍了开发生产42CrMo圆钢的生产实践。通过优化成分设计,严格控制冶炼、轧制各工序参数,生产的42CrMo合金结构圆钢化学成分偏差小、纯净度高,w(P)≤0.016%,w(S)≤0.010%。氧质量分数不超过2.0×10^(-5),氮质量分数不超过5.0×10^(-5)。低倍组织检验全部合格,金相组织为P+F+B,组织晶粒细小均匀,晶粒度稳定在8级。圆钢夹杂物含量较少,球状氧化物类夹杂物0.5级。各项力学性能指标均满足GB/T 3077—2015的相关规定。