超级贝氏体组织中残余奥氏体的TRIP效应研究

针对超级贝氏体组织中残余奥氏体的应力诱发相变及对钢的力学性能影响,设计试验钢60Mn2SiCr,经900 ℃完全奥氏体化保温30 min,在260 ℃盐浴炉中等温处理12 h后,将试样在疲劳试验机上进行加载试验;利用扫描电镜(Scanning electron microscope, SEM)、透射电镜(Transmission electron microscope, TEM)、X射线衍射仪(X-ray diffracmeter, XRD)和拉伸试验机等仪器设备对加载前后的样品,分别进行显微组织形貌观察和相组成的定性定量检测分析以及力学性能测试;结果显示,等温处理后样品的显微组织为超级贝氏体(贝氏体铁素体BF+残余奥氏体AR),残余奥氏体体积分数为9.4%,其含碳量为1.296%;经加载后试样显微组织中残余奥氏体体积分数下降至6.1%,含碳量达1.439%;钢的强塑积提高近20%。这说明等温处理获得超级贝氏体组织的钢,经施加载荷给予应力作用,显微组织中残余奥氏体发生转变,即超级贝氏体组织中的残余奥氏体能够通过相变诱发塑性(Transformation induced plasticity, TRIP)效应的产生,提高钢的力学性能。     

奥氏体化时间对I&Q&P工艺处理低碳硅锰钢组织和拉伸性能的影响

在不同奥氏体化时间下对低碳硅锰钢进行IQP处理,研究了奥氏体化时间对试验钢组织与拉伸性能的影响。结果表明:短时间奥氏体化不能完全消除之前锰元素在双相区的配分结果;奥氏体化时间达到300s后,试验钢的室温组织为板条状马氏体和残余奥氏体;随奥氏体化时间延长,试验钢的抗拉强度先升高后降低,最高可达1 267 MPa,但试验钢的伸长率则不断降低;刚完成完全奥氏体化时,晶粒尺寸较小,且碳、锰的聚集程度最佳,此时残余奥氏体的含量最高,形变过程中TRIP效应明显,使得伸长率的降低得以补偿;奥氏体化时间为300s时,试验钢的强塑积最高,可达30 345 MPa·%。     

800MPa级冷轧相变诱发塑性钢的组织与性能

采用全自动热模拟试验机测定了新开发的800 MPa级相变诱发塑性钢的CCT曲线,据此制定了12种工艺对试验钢进行退火处理;通过拉伸试验测定了经不同工艺退火处理试验钢的力学性能,确定出了最优热处理工艺;对经最优工艺退火处理钢的显微组织和残余奥氏体的稳定性进行了研究。结果表明:各种工艺处理钢均获得了800 MPa以上的抗拉强度,获得最佳综合力学性能(强塑积最大)的热处理工艺为830℃退火120 s后,先以20℃.s-1的速率缓冷至700℃,再以40℃.s-1的速率冷至400℃,并在400℃等温处理400 s,最后以20℃.s-1的速率冷至室温;经最优工艺退火处理后钢的显微组织为50%铁素体+38%贝氏体+12%残余奥氏体,残余奥氏体主要分布在铁素体晶界处,或铁素体与贝氏体的晶界处,还有小部分存在于大的铁素体晶粒内;在拉伸过程中试验钢中残余奥氏体的相变大部分发生变形量为10%~20%阶段。     

基于流变学理论的TRIP600钢本构模型研究

相变诱发塑性(Transformation induced plasticity,TRIP)钢在成形过程中容易发生开裂,主要是由于发生残余奥氏体向马氏体的转变,导致外力与变形不协调。其力学行为不仅有传统的弹性变形和塑性变形,还表现出与时间相关的黏性性质,因此在对其进行本构建模时有必要考虑时间因素对变形行为的影响作用。利用流变模型既可以通过不同构件的组合准确、合理地描述TRIP钢的软、硬相性质,还可以通过各个构件弹性、塑形及黏性系数的变化与组合描述TRIP钢在变形过程中残余奥氏体向马氏体转变的行为特性,即TRIP效应。本文基于流变学理论,对TRIP600的流变学本构模型进行研究和探讨,并最终建立TRIP600分别在蠕变和松弛试验条件下统一的本构方程。     

硅-锰系TRIP钢热处理工艺的研究

硅-锰系TRIP钢仅含碳、硅、锰等合金元素，采用亚温等温淬火及完全淬火加亚温等温淬火热处理，获得铁素体、贝氏体和残余奥氏体三相组织，残余奥氏体分别呈块状和针状。该钢在Ms～Md温度之间拉伸试验表明其力学性能提高显著。完全淬火加亚温等温淬火试样在50℃拉伸时，伸长率最高值达41．5％。     

冷轧TRIP钢中残余奥氏体的热稳定性

为了研究冷轧TRIP钢中残余奥氏体的热稳定性,利用差示扫描量热法(Differential scanning calorimetry,DSC)分析0.25C-1.78Mn-1.23A1-0.54Cu-0.33Ni冷轧相变诱导塑性(Transformation induced plasticity,TRIP)钢中残余奥氏...     

相变诱发塑性钢板的时效回弹行为

在对冷轧相变诱发塑性钢TRIP780和烘烤硬化钢BH180两种钢板基本力学性能分析的基础上,通过U形件冲压成形试验分析这两种钢板的回弹对压边力和模具圆角半径变化的敏感性。对U形件冲压成形卸载后1 min至零件放置12周期间的回弹进行监测,重点对随时间变化的回弹即时效回弹进行详细的分析和讨论。采用X射线衍射对TRIP780钢中奥氏体体积分数随时效时间的变化趋势进行研究。结果表明,TRIP780钢不仅具有高强度、良好塑性和回弹大的特点,而且有显著的时效回弹,BH180基本没有时效回弹。TRIP780钢U形件卸载后1天内时效回弹最大,然后趋于稳定,卸载12周后时效回弹相对初始回弹的最大比例达到20%。X射线衍射结果表明时效回弹与相变诱发塑性效应有内在联系。TRIP780钢对压边力的变化更为敏感,可利用这个规律进行回弹控制。     

弛豫-析出-控制相变工艺生产热轧TRIP钢的显微组织与力学性能

采用扫描电镜、X射线衍射仪、透射电镜和拉伸试验机等,研究了通过弛豫-析出-控制相变工艺制备的热轧TRIP钢显微组织与力学性能。结果表明:通过对轧后TRIP钢在弛豫阶段保温时间的控制可准确得到设定比例的铁素体;在铁素体量较多,贝氏体量较少的情况下,较强的TRIP效应使得试验钢的抗拉强度并没有下降;较多的残余奥氏体和较高的残余奥氏体力学稳定性,使得热轧TRIP钢的强度和塑性得到良好匹配。     

应变速率对高碳硅锰TRIP钢力学性能的影响

研究了0.63C 1.75Si 1.68Mn高碳硅锰TRIP钢室温低应变速率下的拉伸性能。应变速率由4.6×10-3s-1降至4.6×10-6s-1时,高碳硅锰TRIP钢伸长率由14%～15%提高到22%左右;屈服强度由1015MPa提高到1198MPa;抗拉强度由1448MPa提高到1546MPa;拉伸试样中残留奥氏体量减少,这表明在低应变速率下应变诱导相变、相变诱发塑性能充分进行。因此,该钢种特别适合于用做岩石蠕变条件下工作的煤巷超高强度锚杆材料。     

控冷工艺对热轧TRIP钢组织和性能的影响

采用光学显微镜、X射线衍射仪和拉伸试验机等研究了轧后冷却工艺对热轧TRIP钢组织和性能的影响。结果表明：弛豫时间对热轧TRIP钢组织影响较大,随弛豫时间增加,带状组织等级越来越高,铁素体组织也略显粗大;模拟卷取制备的热轧TRIP钢组织中残余奥氏体含量和残余奥氏体中碳含量均较高;贝氏体区停留时间延长,则屈服强度和伸长率增...     

Geometric accuracy of incremental sheet forming for TRIP590

TRIP steels have both high strength and good ductility, and they are typically used in automotive industry for the purpose of safety and energy saving. Deforming TRIP steel by ISF is practically valuable, but the application is significantly restricted by its geometric accuracy. At present, there is not enough research on geometric accuracy for TRIP steels. In this study, we explored the geometric accuracy of ISF for TRIP590 by referring to 1060Al steel and 08F steel. We found that the accuracy of TRIP590 steel was the lowest, which was because of the phase transformation of the material which occurred during deformation. To verify this, X-ray diffraction was employed to figure out the volume fraction of retained austenite. The results have shown that there is always TRIP effect during ISF process, and the relationship between natural logarithm of austenite volume fraction and the equivalent strain is negative linear. Lastly, it is proved that multiple reverse compensations could improve the geometric accuracy for TRIP steels.     

The effects of retained austenite on dry sliding wear behavior of carburized steels

Ring-on-square tests on two kinds of low-alloy carburized steel which were AISI 8620 and 4140 were carried out to study the dry sliding wear behavior. The influence of different retained austenite level of 6% to 40% was evaluated while trying to eliminate other factors. Test results show that the effects of grain size and carburized steel species are negligible in dry sliding wear behavior. While the influence of retained austenite is negligible at 20 kg load condition, wear resistance is decreased at 40 kg load condition as the retained austenite level is increased from 6% to 30%. However, wear resistance is again increased above about 30% of retained austenite level at 40 kg load condition.     

淬火分配工艺对60Si2Mn弹簧钢显微组织和力学性能的影响

对60Si2Mn弹簧钢进行了不同淬火温度(140,160,180℃)的淬火分配(Q&P)处理,研究Q&P处理后该钢的显微组织和力学性能,并与传统淬火+回火(Q&T)工艺处理后的进行对比.结果表明:经Q&P处理后,60Si2Mn弹簧钢的显微组织均为残余奥氏体和马氏体,残余奥氏体的体积分数均大于12％,而经Q&T处理后的显...     

新型空冷贝氏体钢性能及组织的研究

本文对一种新型空冷贝氏体钢的力学性能和显微组织进行了研究。力学试验结果表明,试验钢的抗拉强度σb为1339MPa,塑性指标δ5为18.2％,ψk为59.3％,冲击韧度为120J·cm-2,弯曲疲劳极限达到700MPa。透射电镜分析表明,该新型贝氏体钢的显微组织主要为束状贝氏体铁素体+少量残余奥氏体,残余奥氏体膜对贝氏体铁素体束进行了分割和包围,这种组织使试验钢具有优良的性能指标。     

Q&P钢的显微组织及力学性能

采用盐浴炉对硅-锰系Q&P(quenching and partitioning)钢进行了Q&P工艺处理,研究了分配时间对热处理后试验钢显微组织、力学性能、残余奥氏体含量及残余奥氏体中碳含量的影响。结果表明:试验钢的显微组织为板条马氏体和残余奥氏体,残余奥氏体以两种形态分布在不同位置,一种是以薄膜状分布在马氏体板条间,另一种是以块状分布在原奥氏体晶界处;在300℃的分配温度下进行较长时间保温能取得较好的强塑积,随着分配时间的延长,试验Q&P钢的残余奥氏体含量及残余奥氏体中的碳含量均不断增加,分配时间为1 200 s时所得试验钢的强塑积最高,可达37 300 MPa.%以上。     

The magnetic properties of grade BHC-2УШ maraging steel subjected to plastic deformation

The results of the measurements of the magnetic properties of plastically tensile-deformed samples of grade 08X15H5д2T maraging steel are represented. Preliminary the samples were subjected to annealing, quenching, and ageing with a variation in temperature and holding time for obtaining of the various initial contents of retained austenite. It was found that the testing of the content of retained austenite in the deformed state is possible by saturation induction B _s . The use of the structural-sensitive parameter N′ (an analogue of the internal demagnetization factors) allows one to determine the content of retained austenite in the undeformed state and in the prerupture state and the qualitative separation of plastically deformed and undeformed products of grade BHC-2УШ steel.     

Study on relative wear resistance and wear stability of high-speed steel with high vanadium content

In this work, a new concept of wear stability was put forward by authors, and it was quantitatively expressed by factor of wear stability. Different hardness, impact toughness and retained austenite content high-speed steel with high vanadium content samples were obtained by varying heat treatment conditions. The effects of hardness, impact toughness and retained austenite content on relatively wear resistance and wear stability were studied under abrasive wear condition. Results show that relative wear resistance increases with increasing hardness or decreasing impact toughness, whereas the wear stability rises with the increasing of hardness or impact toughness. The analyzing results reveal that mechanical behaviors are only apparent factors to influence wear behaviors. Relative wear resistance substantially depends on retained austenite content (Ar). At retained austenite content of about 30 vol.%, the relative wear resistance is optimal. However, wear stability is scarcely influenced by retained austenite content, which depends on the maximum changing amount of retained austenite under certain condition (ΔAr) in essence. With increasing ΔAr, wear stability linearly decreases.