低硅含铝TRIP钢残余奥氏体变形过程中稳定性研究EI北大核心CSCD

采用预拉伸实验对低硅含铝TRIP钢变形过程中残余奥氏体的演变规律进行研究,建立残余奥氏体变形过程中稳定性与加工硬化指数n之间的对应关系,在此基础上通过设计不同热处理工艺,获得具有不同初始残余奥氏体特性的TRIP钢以及具有不同组织构成的TRIP钢,并分析了TRIP钢的残余奥氏体稳定性。结果表明:TRIP钢中的残余奥氏体随着变形的深入,稳定性逐渐增加;残余奥氏体越稳定,TRIP钢的瞬时加工硬化值越稳定(n值越稳定);随着初始碳含量的增加,残余奥氏体在变形过程中的稳定性也随之提高。在变形过程中,残余奥氏体的稳定性受残余奥氏体碳含量,分布以及周围相等因素的共同影响。     

中锰Q&P钢残余奥氏体的稳定性及其TRIP效应

通过单向拉伸及平面应变实验研究了Mn含量为7%的中锰淬火-配分(QP)钢残余奥氏体的机械稳定性,利用X射线衍射仪(XRD)测定试验钢残余奥氏体的含量,通过观察试验钢的拉伸曲线及扫描电镜(SEM)、透射电镜(TEM)照片,分析变形前后的微观组织,研究中锰QP钢的变形机制。结果表明:应力状态对残余奥氏体稳定性有较大的影响,平面应变更有利于相变诱导塑性(TRIP)效应的发挥;中锰QP钢的拉伸变形特征是由超细晶硬化机制和TRIP效应相互作用产生的,通过微观组织观察发现中锰QP钢的塑性变形主要是残余奥氏体的TRIP效应,其中薄膜状的残余奥氏体的稳定性最高。     

配分工艺对低碳Q&P钢中残余奥氏体的影响

为提高钢的塑性,在马氏体钢基础上通过Q&P工艺得到一定量的残余奥氏体,达到高强度与高塑性的良好结合.利用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)和拉伸实验等方法研究了低碳Q&P钢微观组织,在此基础上讨论了配分工艺对残余奥氏体的影响以及残余奥氏体对Q&P钢延伸率的影响.研究结果表明:Q&P钢室温组织主...     

TRIP钢板在单向拉伸变形下的相变行为研究

TRIP钢的塑性取决于残余奥氏体的含量及其相变速度.研究TRIP钢中残余奥氏体在单向拉伸变形下的相变行为,首先回顾了TRIP钢板的研究进展,然后对一种低碳硅锰系TRIP700钢板在单向拉伸变形下的力学性能和相变性能进行了试验研究,并用扫描电镜方法分析了该TRIP钢在变形过程中微观组织的变化.结果表明,该低碳硅锰系TRIP钢板兼有高强度和高韧性的特点,在单向拉伸变形中残余奥氏体的含量与等效应变的关系可用来logfγ0-logγ=kε.表示.     

贝氏体区等温时间对TRIP钢残奥及力学性能影响

为研究贝氏体区等温时间对热轧TRIP钢残余奥氏体和力学性能的影响,采用金相显微镜、X射线衍射、拉伸实验等方法对3种不同贝氏体区等温时间下制备的热轧TRIP钢进行分析.结果表明:随着贝氏体等温时间的延长,残余奥氏体量减少而残余奥氏体碳含量增加,残余奥氏体晶粒尺寸及残余奥氏体形貌变化不大;热轧TRIP钢的力学性能随着贝氏体...     

热轧TRIP钢残余奥氏体及其稳定性研究

采用X射线衍射(XRD)、透射电镜(TEM)和拉伸实验等方法,研究三种工艺制备的热轧TRIP钢残余奥氏体及其碳含量和稳定性.结果显示:贝氏体区停留时间对残余奥氏体量影响较大,当在贝氏体区模拟卷取时,残余奥氏体量最多;适当的增加弛豫时间,会增加最终组织中残余奥氏体的碳含量;残奥碳含量,还有残余奥氏体的形状和晶粒大小及周围...     

动态残余奥氏体测量装置研究

介绍一种将应力，应变与饱和磁性法相结合对高强度，超高强度等钢，能在试样拉伸过程中快速，连续地测量拉伸变形量和残余奥氏体的相对变化量，该装置为研究钢中残余奥氏体的机构稳定性，提供了一种新的测试手段，也为指导热处理工艺以及零部件的全使用可靠性提供了实验数据。     

纳米贝氏体/马氏体钢的热稳定性

将低温贝氏体相变前淬火得到由马氏体、贝氏体铁素体和残余奥氏体组成的纳米贝氏体钢,使用扫描电镜(SEM)、X射线衍射(XRD)和透射电镜(TEM)等手段观察在不同温度回火的纳米贝氏体钢的显微组织和硬度变化,研究了预相变马氏体对纳米贝氏体钢热稳定性的影响。结果表明:含有马氏体的纳米贝氏体钢在中低温(473~773 K)回火后其硬度比回火前的高,回火温度高于823 K其硬度迅速下降到266.2HV(923 K)。预形成的马氏体在473~573 K回火后向附近的残余奥氏体排碳,后者的碳含量提高到峰值1.52%,提高了残余奥氏体的热稳定性,延迟后者在高温时的分解,从而提高了纳米贝氏体钢的高温热稳定性;回火温度高于723 K则残余奥氏体分解成碳化物,贝氏体铁素体粗化、回复形成新的铁素体晶粒。     

高强贝氏体基体钒微合金化TRIP钢的性能

对一种钒微合金化TRIP钢进行冷轧连续退火,研究了钢的组织特征和力学性能。结果表明,贝氏体基TRIP钢的组织由贝氏体/马氏体和少量的残余奥氏体组成。随着贝氏体区等温时间的延长,钢的抗拉强度下降,屈服强度和延伸率提高。残余奥氏体由块状向薄膜状转变,体积分数增加,薄膜状残余奥氏体主要分布在贝氏体板条间,厚度为50-90 nm。在400℃等温180 s连续退火钢板呈现出相对低抗拉强度(960 MPa)、高屈服强度(765 MPa)和高延伸率(22.0%)的特性,而且加工硬化指数(0.20)、各向异性指数(0.94)和强塑积(21120 MPa.%)也较为优良。     

动态碳配分对先进高强钢组织与力学性能的影响

目的 为了使钢表现出更好的吸能特性,以具有较高的强度以及较好的塑性。方法 提出了一种新型一步法成形碳配分一体化工艺,即热冲压-动态碳配分(HS-DP)工艺。所提出的HS-DP工艺采用盐浴热处理的方式进行物理模拟。采用扫描电子显微镜(SEM)、X射线衍射(XRD)和拉伸试验等方法,研究了新工艺中的冷却速率对低碳先进高强钢的微观组织和力学性能的影响。针对冷却速率对残余奥氏体含量的影响进行了分析,重点研究了残留奥氏体的体积分数和碳含量对钢伸长率的影响。结果 经过HS-DP工艺处理的钢显微组织主要由初始淬火态马氏体相、最终淬火态马氏体相和残余奥氏体相共存组成。结论 实验钢表现出优异性能,说明了热冲压动态碳配分工艺前景广阔。     

Intercritical annealing pre-treatment used in a hot-dip galvanised TRIP steel

An intercritical annealing pre-treatment was added before the conventional two-step heat treatment process, and the effect of the isothermal bainitic transformation (IBT) time on the steel's microstructure and mechanical properties were investigated. The microstructure was investigated using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, while the mechanical properties were evaluated using tensile testing. The microstructure of the three-step hot-dip galvanised transformation induced plasticity (TRIP) steel consists of ferrite, bainite, retained austenite, and martensite. The mechanical properties of the steel after the three-step heat treatment process are excellent, with a tensile strength above 770?MPa and elongation above 29%. The effect of IBT time on the mechanical properties was insignificant because the intercritical annealing pre-treatment increases the bainitic transformation rate.     

Mechanical and Transformation Behaviors of a C-Mn-Si-Al-Cr TRIP Steel under Stress

Transformation induced plasticity （TRIP） steels combine high strength and excellent ductility, making them suited for application in crash-relevant parts in the automotive industry. However, the high Si contents in the conventional TRIP steel will generate surface defects on the hot rolled strip, which is difficult to process in continuous galvanizing lines. In order to solve the above problem the TRIP steel with the addition of Al replacing majority of Si was designed. In the present paper, the volume fraction of various phases in a C-Mn-Si-Al-Cr TRIP steel was determined by metallographic examination and X-ray diffraction analysis, and the multi-phase microstructures were characterized using an atomic force microscope based on their height difference. Tensile tests were performed at different temperatures ranging from -40℃ to 90℃. The results show that transition temperature Ms^σ in the present TRIP steel cannot be determined due to its lower volume fraction of retained austenite, different from the conventional TRIP steel. While the yield stress and tensile strength at different temperatures are higher than those of the conventional TRIP steel, which is attributed to the addition of Cr. In order to evaluate the effect of martensitic transformation on the total elongation, the sample without retained austenite obtained by quenching in liquid nitrogen was carried out under tensile test. The results indicate that the elongation of the original sample containing 9% retained austenite is about 20% higher than that of the sample quenched in liquid nitrogen, which demonstrates that the retained austenite plays an important role in improving the elongation of the TRIP steel.     

预奥氏体化对中Mn TRIP钢组织及力学性能的影响

为了提高钢的综合力学性能,用盐浴法对中Mn TRIP钢进行了热处理.采用SEM、TEM、XRD和拉伸测试研究了预奥氏体化处理对中Mn TRIP钢显微组织及力学性能的影响.实验结果表明:全马氏体冷轧态组织经两相区退火处理后,会析出大量渗碳体颗粒,随着退火时间延长,渗碳体颗粒逐渐溶解,马氏体组织逐渐转变为奥氏体和铁素体双相片层状组织;而在两相区退火处理前添加两相区预奥氏体化处理后,渗碳体析出被有效抑制,双相片层组织迅速形成;相比于常规两相区退火处理,预奥氏体化处理能够提高组织中残余奥氏体体积分数和综合力学性能.     

Microstructures and Mechanical Properties of Si-AI-Mn TRIP Steel with Niobium

Microstructure consisting of ferrite, bainite and retained austenite can be obtained through intercritical annealing and isothermal treatment in bainite transformation region for low silicon TRIP （transformation induced plasticity） steel containing niobium. Effects of strain rate, Nb content and soaking temperature in bainite region on microstructure and mechanical properties of test steels were investigated. It is shown that as strain rate ranges from 10^-2 to 10^-4 s^-1, the volume fraction of transformed martensite from retained austenite, as well as tensile strength, elongation rate and strength-ductility product, increases. When Nb is added, the volume fraction of retained austenite decreases, but tensile strength and yield strength increase. While Nb content reaches 0.014%, the steel exhibits high elongation and combination of strength and ductility. Higher retained austenite volume fraction and good mechanical properties are obtained in the test steels when the soaking temperature in bainite region is 400℃. The maximum values of tensile strength, total elongation rate and strength-ductility product can reach 739 MPa, 38% and 28082 MPa%, respectively.     

Microstructures and Mechanical Properties of Si-Al-Mn TRIP Steel with Niobium

Microstructure consisting of ferrite, bainite and retained austenite can be obtained through intercritical annealing and isothermal treatment in bainite transformation region for low silicon TRIP (transformation induced plasticity) steel containing niobium. Effects of strain rate, Nb content and soaking temperature in bainite region on microstructure and mechanical properties of test steels were investigated. It is shown that as strain rate ranges from 10-2 to 10-4 s-1, the volume fraction of transformed martensite from retained austenite,as well as tensile strength, elongation rate and strength-ductility product, increases. When Nb is added, the volume fraction of retained austenite decreases, but tensile strength and yield strength increase. While Nb content reaches 0.014%, the steel exhibits high elongation and combination of strength and ductility. Higher retained austenite volume fraction and good mechanical properties are obtained in the test steels when the soaking temperature in bainite region is 400℃. The maximum values of tensile strength, total elongation rate and strength-ductility product can reach 739 MPa, 38% and 28082 MPa%, respectively.