临界热处理对低合金TRIP钢组织与力学性能的影响

研究了临界热处理工艺对基于奥氏体逆相变原理设计的Fe-0.1C-2.5Mn-0.6Ni低合金TRIP钢组织与力学性能的影响。结果表明:试验钢经两相区临界退火仅能获得少量的残留奥氏体,且残留奥氏体含量随着退火温度的升高呈现先增加后降低的趋势,740℃退火后钢中的残留奥氏体含量最高。试验钢临界退火后在高温回火处理过程中马氏体会通过逆相变转变成奥氏体,使得钢中的残留奥氏体含量大幅提高。680℃回火后,试验钢中的残留奥氏体含量达到最大值10.4%,钢的塑性和韧性由于相变诱发塑性(TRIP)效应而显著提高。与传统TRIP钢相比,本文研究的TRIP钢更适合于厚板材、厚壁管材的生产制造。     

变形速度对TRIP钢冲压成形性的影响

在TRIP钢相变动力学模型的基础上,推导了残余奥氏体体积比变化速率与变形速度的关系,详细分析了变形模式和变形速度对残余奥氏体转变的影响规律,讨论了相变诱发塑性效应对TRIP钢冲压成形性的作用机理,并通过圆筒件拉深成形试验,验证了不同变形速度下TRIP钢的成形性。结果表明,残余奥氏体体积比变化速率随变形速度的增加而增加;变形速度和变形模式对相变诱发塑性效应的发挥影响较大,变形过快导致后续变形所需塑性补充不足;TRIP钢良好塑性得以发挥,必须具有合适的变形条件。     

热处理工艺对低碳硅锰TRIP钢力学性能的影响

低碳硅锰钢经临界区等温淬火，残留有大量的奥氏体。该钢在Ma～Md温度之间形变，因钢中大量稳定的残余奥氏体的应变诱导马氏体相变和相变诱发塑性(TRIP)，可获得高的强度、塑性以及良好的强度与塑性的配合。通过对其力学性能测试与显微组织分析，对低碳硅锰钢热处理工艺及钢中残余奥氏体的相变诱发塑性行为进行了探讨。结果表明：钢在400℃等温淬火的热处理工艺，所获得的力学性能最佳。     

TRIP钢热变形等温淬火

通过实验室热轧机采用3种不同的终轧变形量进行热轧试验,对TRIP钢热变形等温淬火进行了研究.结果表明,热轧后能够获得多边形铁素体、粒状贝氏体和大量稳定的残留奥氏体组织.残留奥氏体的稳定性随终轧变形量的增加而增加,残留奥氏体越稳定,其相变诱发塑性效果越好.由于大压下量终轧,在变形过程中应变诱导铁素体相变造成铁素体晶粒细化,有助于热轧TRIP钢获得较好的力学性能.热轧TRIP钢在终轧变形量为50%时,抗拉强度、屈服强度和总伸长率分别达到776 MPa、528 MPa和32%.     

超高强度低合金TRIP钢的氢脆

研究了三种不同基体组织的超高强度低合金相变诱发塑性（TRTP）钢中充入的氢量及其对韧性的影响。这些TRIP钢．特别是具有贝氏体铁素体基体组织的TPIP钢，充入的氢量比常规回火马氏体钢要多。这主要与残余奥氏体吸收多量氢溶质有关。TRIP钢、特别是退火马氏体基体组织TRIP钢的氢脆被大大地抑制。可以认为，导致钢中氢脆性低的原因是大量的氢进入了残余奥氏体，均匀细小的组织，残余奥氏体的TRIP效应和出现准韧窝断口。     

超高强度低合金TRIP钢的氢脆

研究了三种不同基体组织的超高强度低合金相变诱发塑性(TRIP)钢中充入的氢量及其对韧性的影响。这些TRIP钢,特别是具有贝氏体铁素体基体组织的TPIP钢,充入的氢量比常规回火马氏体钢要多。这主要与残余奥氏体吸收多量氢溶质有关。TRIP钢、特别是退火马氏体基体组织TRIP钢的氢脆被大大地抑制。可以认为,导致钢中氢脆性低的原因是大量的氢进入了残余奥氏体,均匀细小的组织,残余奥氏体的TRIP效应和出现准韧窝断口。     

预应变对TRIP钢力学性能及硬化行为的影响

为了研究TRIP钢不同变形量后的使用性能,对TRIP690冷轧镀锌板进行了分别为5%、10%、15%、20%的预应变准静态拉伸,研究不同预应变对TRIP钢的力学性能及加工硬化行为的影响,并通过XRD技术测量残留奥氏体的变化规律。结果表明:预应变对TRIP钢的屈服强度、屈强比、平均加工硬化值影响显著,其中屈服强度和屈强比均随预应变量增大而显著增大,抗拉强度和强塑积均小幅增大;同时由于随拉伸预应变量增大,残留奥氏体持续地向马氏体发生渐进式转变,残留奥氏体含量降低,且剩余的残留奥氏体较为稳定难以诱发相变,使得材料的加工硬化能力明显减弱。     

预应变对TRIP钢力学性能及硬化行为的影响北大核心CSCD

为了研究TRIP钢不同变形量后的使用性能,对TRIP690冷轧镀锌板进行了分别为5%、10%、15%、20%的预应变准静态拉伸,研究不同预应变对TRIP钢的力学性能及加工硬化行为的影响,并通过XRD技术测量残留奥氏体的变化规律。结果表明:预应变对TRIP钢的屈服强度、屈强比、平均加工硬化值影响显著,其中屈服强度和屈强比均随预应变量增大而显著增大,抗拉强度和强塑积均小幅增大;同时由于随拉伸预应变量增大,残留奥氏体持续地向马氏体发生渐进式转变,残留奥氏体含量降低,且剩余的残留奥氏体较为稳定难以诱发相变,使得材料的加工硬化能力明显减弱。     

纳米贝氏体钢残奥细化及其力学性能调控研究进展

纳米贝氏体钢作为新型超高强度钢,因其具备良好的强塑性能匹配,吸引着广大专家学者研究其力学性能调控机制.本文介绍了纳米贝氏体钢中残留奥氏体的形态及其TRIP效应,概述了加速贝氏体转变的多种调控手段,如合金元素、等温贝氏体转变温度、奥氏体化温度以及预马氏体相变等,及其对残留奥氏体的尺寸、形状和体积分数的影响;同时对多步转变和其他一些细化残留奥氏体尺寸的方法做了介绍,力争为高强度纳米贝氏体钢的研发提供理论支持.     

镍含量对2200 MPa级超高强度钢力学性能的影响

通过比较含Ni量(质量分数)分别为1.92%和4.92%的中碳Cr-Ni-Mo系超高强度钢不同回火温度下的力学性能,得到了残留奥氏体分解及其对试验钢力学性能影响的规律.结果表明,200 ℃回火后两种试验钢的强度、伸长率和-40 ℃冲击吸收功分别＞2200 MPa、＞10%和＞10J.4.92%Ni钢的屈服强度低,在拉伸过程中残留奥氏体应变诱导马氏体相变和相变诱发塑性(TRIP),伸长率有明显提高.随着回火温度的升高,残留奥氏体分解,4.92%Ni钢的屈强比升高,应变硬化指数和伸长率均下降.     

EFFECTS OF CARBON CONTENT AND ROLLING PROCESSING ON RETAINED AUSTENITE FOR HOT-ROLLED TRIP STEELS

The effects of finishing rolling temperature and coiling temperature on retained austenite were studied for hot-rolled transformation induced plasticity (TRIP) steels with different carbon content. The experimental results showed that an appropriate volume fraction of retained austenite from 6% to 11% could be obtained according to the different carbon content less than 0.20% by controlled finishing rolling and coiling for the hot-rolled TRIP steels. It can be concluded that carbon content has a significant effect on the fraction of retained austenite and coiling processing plays stronger role on retaining austenite than fishing rolling processing.     

冷轧双相钢中残余奥氏体稳定性的研究

研究了不同退火温度和变形条件对DP780钢残余奥氏体含量、尺寸、稳定性的影响。结果表明,通过优化连续退火工艺参数,可以获得5%～7%稳定的残余奥氏体。随着变形量的增加,90%的残余奥氏体发生了TRIP效应,不仅提高了DP780钢的强塑性,也改善了其成形性能。     

低碳-硅-锰系TRIP钢的组织演变规律研究

采用彩色金相、SEM、TEM和X射线衍射技术研究了低碳-硅-锰TRJP钢在单向拉伸状态下的组织演变规律.结果表明,TRIP钢变形前的组织为F、B和残余奥氏体,经拉伸变形后部分残余奥氏体在应变作用下转变为孪晶结构的马氏体,提高了钢的强度;TRIP钢的断裂为韧性断裂,位于F晶界处的残余奥氏体发生相变从而松弛了应力,延缓了断裂的产生,使TRIP钢板获得高塑性.     

REVIEW AND PROSPECT OF HIGH STRENGTH LOW ALLOY TRIP STEEL

Research status of high strength low alloy TRIP (transformation induced plasticity) steels for automobile structural parts is briefly described. Composition and microstruc-ture factors especially the morphology, size and volume fraction of retained austenite, which largely influence the strength and ductility of the steel, are reviewed and discussed one after another. Modelling of the inter-critical annealing and martempering processes as well as the designing of the TRIP steel aided by commercial software are introduced. Some special aspects of the dynamic mechanical properties of TRIP steel are firstly reported.     

Transformation potential predictions for the stress-induced austenite to martensite transformation in steel

The stress-induced transformation behavior of retained austenite is considered in this work. With the development of transformation-induced plasticity (TRIP) steels this deformation mode is of growing importance. Twinned martensite structures were calculated using the crystallographic theory of martensite. An available work criterion was used to predict the transformation potentials for 16 different in-plane stress states for sheet sample geometry. By rotating the twinned martensite structures over all crystallographic orientations using Euler angles, the magnitude of the transformation potential was plotted as an orientation distribution plot for comparison with typical texture components. From these data, the Brass and Copper orientation components that are typical in retained austenite such as in TRIP steels were found to have low transformation potential values. Grains aligned with these orientations would require higher stresses to transform than other orientations, and may therefore never transform. This correlates to experimental observations that heavily deformed TRIP steel contains residual retained austenite.     

Dependency of Deformation Behavior of Retained Austenite in TRIP Steels on Microstructural and Chemical Homogeneity

The room-temperature stability of the retained austenite against strain-induced martensitic transformation, its deformation behavior, the response to the bainitic isothermal treatment, the appearance of yield point elongation and other peculiarities of plastic flow, and the mechanical properties of transformation-induced plasticity(TRIP) steel were tailored based on the chemical homogeneity and the relative distribution of the retained austenite, bainite, and ferrite in the microstructure. The presence of ferritic-pearlitic banded structure in the initial microstructure resulted in an inhomogeneous TRIP microstructure, in which the retained austenite and bainite were confined to some bands and it was found to be responsible for the resultant inferior mechanical properties. The appearance of discontinuous yielding for the chemically inhomogeneous material was related to the martensitic transformation of unstable retained austenite at the initial stage of tensile deformation. These results are essential for better understanding of the behavior of advanced high-strength steels and their applications.     

离子研磨对TRIP780钢中残留奥氏体含量和稳定性的影响

研究了经离子研磨对TRIP780钢中残留奥氏体含量与稳定性的影响。首先利用电解抛光技术对TRIP780钢进行样品制备以去除样品表面的应力层,然后利用离子研磨仪对所得样品进行离子研磨,再借助场发射扫描电镜对TRIP780钢中的残留奥氏体进行形貌观察与分析,利用电子背散射衍射技术(EBSD)对离子研磨前后的TRIP钢中残留奥氏体含量进行定性和定量分析。结果表明,与电解抛光相比,离子研磨技术同样可以很好的去除样品表面应力层,但是对于TRIP780钢,经过离子研磨后样品中残留奥氏体的含量大幅度减少,从原来的10.1%骤降至0.02%。从残留奥氏体的菊池花样可以看出,经离子研磨后的残留奥氏体菊池花样明显变差,甚至模糊不清。经离子研磨后的TRIP780钢中残留奥氏体含量明显下降,同时其相结构确实发生了转变,由原来的面心立方结构转变为体心立方结构(即fcc→bcc),由此表明残留奥氏体在受到离子轰击后极其不稳定,易发生相变,这一点在残留奥氏体的准原位试验中得到了进一步的验证。同时离子研磨诱发了晶格的畸变,导致菊池花样清晰度明显下降,花样分辨率降低。     

EFFECTS OF TEST TEMPERATURE AND STRAIN RATE ON THE MECHANICAL PROPERTIES IN AN INTERCRITICALLY HEAT-TREATED BAINITE-TRANSFORMED STEEL

1.IntroductionThe demand for high strength steels with excellent ductility has increased in the automotive indus-try in order to improve manufacturing and safety and to reduce weight. High strength transforma-tion-induced plasticity (TRIP) steel sheets have received increased attention, as they have both high strength and ductility due to the martensitic transformation of retained austenite during plastic defor-mation.Transformation-induced plasticity was the phenomenon first found in steel …     

EFFECT OF AUSTEMPERING ON TRANSFORMATION INDUCED PLASTICITY OF HOT ROLLED MULTIPHASE STEELS

Effect of austempering on the transformation induced plasticity (TRIP) of hot rolled multiphase steel was investigated. Polygonal ferrite, granular bainite, and a large amount of stabilized retained austenite could be obtained in the hot rolled multiphase steel. Strain induced martensite transformation (SIMT) of retained austenite and TRIP effectively occur under straining owing to austempering after hot rolling, and mechanical properties of the present steel remain at a relatively high constant value for austempering at 400℃. The mechanical properties of the steel exhibited a good combination of tensile strength (791MPa) and total elongation (36%) because the stability of retained austenite is optimal when the steel is held for 20min.