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《Materials Science & Technology》2013,29(2):135-140
AbstractContinuous and discontinuous cooling tests were performed using a quench deformation dilatometer to develop a comprehensive understanding of the structural and kinetic aspects of the bainite transformation in low carbon TRIP (transformation induced plasticity) steels as a function of thermomechanical processing and composition. Deformation in the unrecrystallised austenite region refined the ferrite grain size and increased the ferrite and bainite transformation temperatures for cooling rates from 10 to 90 K s-1. The influence of niobium on the transformation kinetics was also investigated. Niobium increases the ferrite start transformation temperature, refines the ferrite microstructure, and stimulates the formation of acicular ferrite. The effect of the bainite isothermal transformation temperature on the final microstructure of steels with and without a small addition of niobium was studied. Niobium promotes the formation of stable retained austenite, which influences the mechanical properties of TRIP steels. The optimum mechanical properties were obtained after isothermal holding at 400°C in the niobium steel containing the maximum volume fraction of retained austenite with acicular ferrite as the predominant second phase. 相似文献
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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. 相似文献
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Zhengyou TANG Hua DING Linxiu DU Long LI 《材料科学技术学报》2007,23(6):790-794
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. 相似文献
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采用分离式Hopkinson压杆对热冲压淬火-配分(HS-Q&P)钢在0~12000 s^(-1)应变速率范围内进行动态压缩实验,利用SEM,EBSD,XRD等分析表征手段探究动态压缩过程中试样的变形行为。结果表明:实验钢在不同速率下的变形行为基本相似且分为3个阶段,在平台处应力有小幅度增加,增幅更多体现在应变上。在压缩过程中出现的绝热升温会带来软化效应。残余奥氏体的存在会提高实验钢的强度和塑性变形能力。钢中残余奥氏体发生相变诱导塑性(transformation induced plasticity,TRIP)效应减少的体积分数与马氏体增加的体积分数基本一致,证明TRIP效应为钢中主要的强化机制。同时,通过SEM可观测到残余奥氏体发生TRIP效应转变成细小针状马氏体,随着应变速率增加,晶格畸变越来越严重,EBSD图像中可以观测到部分形变孪晶,在不同应变速率下,〈001〉取向的晶粒都会更容易产生形变孪晶。 相似文献
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Zhuang LI Di WU 《材料科学技术学报》2006,22(6):763-768
Influence of hot deformation and subsequent austempering on the mechanical properties of hot rolled multiphase steel was investigated. Thermo-mechanical control processing (TMCP) was conducted by using a laboratory hot rolling mill, where three different kinds of finishing rolling reduction, and austemperings with various isothermal holding duration were applied. The results have shown that a multiphase microstructure consisting of polygonal ferrite, granular bainite and larger amount of stabilized retained austenite can be obtained by controlled rolling processes. Mechanical properties increase with increasing the amount of deformation because of the stabilization of retained austenite. Ultimate tensile strength (σb), total elongation (σ) and the product of ultimate tensile strength and total elongation (σb-σ) reach the maximum values (791 MPa, 36% and 28476 MPa%, respectively) at optimal processes. 相似文献
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Xu Cheng Roumen Petrov Lie Zhao Michael Janssen 《Engineering Fracture Mechanics》2008,75(3-4):739-749
Load-controlled fatigue tests are conducted for four positive R values on a low-alloy TRIP steel for two different heat treatments: an optimal treatment leading to a multiphase microstructure containing retained austenite, ferrite, bainite and martensite, and a non-optimal treatment leading to a ferritic–martensitic dual-phase microstructure. A significantly increased resistance to fatigue crack growth is found for the optimal case with respect to the non-optimal case. The amount of crack closure is found to be larger in case of the non-optimally treated (ferritic–martensitic) steel. Close to the crack tip, an increased hardness suggests martensite formation. An EBSD technique is used to quantify the volume of retained austenite ahead of the crack tip, within the plastic zone. It is found that martensite formation only occurs within the monotonic plastic zone during fatigue. By evaluation of the retained austenite fraction during straining in static tensile tests, the plastic strain levels within the plastic zone are assessed. Additionally, the effect of martensite formation on fracture toughness is estimated. 相似文献
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Effect of microstructure on transformation-induced plasticity of silicon-containing low-alloy steel 总被引:3,自引:0,他引:3
Fe-0.6C-1.5Si-0.8Mn steel was studied to determine the effect of the microstructure on transformation-induced plasticity (TRIP) of silicon-containing low-alloy steel. A remarkable increase in elongation through TRIP can develop in the steel subjected to the following heat treatments: (1) austemper combined with subcritical annealing (SA Aus-T): subcritical annealing at 993K followed by austempering at 673K and then light tempering (after austenitization at 1173K); (2) austemper coupled with interrupted quenching (IQ Aus-T): interrupted quenching at 533K followed by austempering at 673K and light tempering (after austenitization at 1173K).
The SA Aus-T treatment produced the triple structures of carbide-free upper bainite, retained austenite (γR), and free ferrite. As a result of the IQ Aus-T treatment, the triple structures of carbide-free upper bainite, γR, and tempered martensite appeared. The results are described and microstructural factors in TRIP are discussed. 相似文献
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Optimization of high strength and high formability of multiphase cold rolled sheet TRIP-aided steels is based on the composition and the austempering conditions. The effect of intercritical annealing temperature on the volume fraction and carbon concentration of the retained austenite was investigated in two different TRIP-aided steels. Experimental results show that the optimum annealing temperatures are 860 °C for Al-containing and 810 °C for Si-containing TRIP steels. It was demonstrated that the measurement of retained austenite can be successfully performed for textured TRIP steels by XRD. 相似文献
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《Computational Materials Science》2011,50(2):720-730
In this paper, the microstructure-based finite element modeling method is used as a virtual design tool in investigating the respective influence of various material design parameters on the deformation behaviors of transformation-induced plasticity (TRIP) steels. For this purpose, the separate effects of several different material design parameters, such as the volume fraction and stability of austenite phase and the strengths of the constituent phases, on the ultimate tensile strength (UTS) and ductility/formability of TRIP steels are quantitatively examined using different representative volume elements (RVEs) representing different TRIP steels. The computational results suggest that higher austenite stability is helpful in enhancing the ductility and formability of TRIP steels by delaying the martensitic transformation to a later stage, whereas increase of austenite volume fraction and/or ferrite strength alone is not beneficial to improve the performance of TRIP steels. The results also indicate that various material design parameters must be adjusted concurrently to develop high-performance TRIP steels. The information based on investigations in this paper can help guide the development of high-performance TRIP steels by providing the microstructure level deformation mechanisms. 相似文献
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Armindo Werlang Filho Bruno Vaz de Souza 《Materials and Manufacturing Processes》2016,31(14):1836-1843
Austempering conditions such as temperature and time and their influence on austempered ductile iron machinability were analyzed. Austenitization at 910°C for 90 min and austempering into molten salt bath at 300°C, 360°C, and 420°C for 30, 60, and 90 min each were performed. Microstructures were analyzed by optical microscopy and hardness measurements. Samples were further machined in a lathe for machinability tests. The lathe was instrumented considering power and cutting time and machinability evaluation performed referring to cutting force and material removal. Microstructures at 300°C for 30 min showed ausferrite with retained austenite and martensite. Retained austenite decreased and acicular ferrite sheaves appeared at 60-min austempering time. Mixed bainite was also present at 90-min austempering. Ausferrite and retained austenite were observed in all austempering periods at 360°C, whereas at 420°C only bainite and fine pearlite were present. Hardness increased with increasing temperature at 30-min austempering and decreased with increasing time. However, an exception was observed at 420°C. The highest machinability performance was achieved at 360°C at 60-min austempering, and the lowest performance at 420°C at 90-min austempering. 相似文献
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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。 相似文献
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以节约化、经济化、轻量化为立足点,利用“TRIP效应”解决强塑性同步提高的矛盾,制备出一种1 GPa级TRIP型BF钢,研究了不同组织调控的微观形貌和强塑性机制。结果表明,合理的成分设计和将热轧初始组织调控为(20~30)%铁素体和(70~80)%针状贝氏体,有利于将最终成品的显微组织调控为(75~85)% BF和≥15%的第二相残γ组织,使1 GPa级TRIP型BF钢具有优良的综合性能。两相组织的合理配比及其形貌特征,对TRIP型BF钢的强塑性有显著的影响。在82%的BF组织基体中均匀分布着片层宽度为80~130 nm的第二相残γ组织,在两相协调变形机制作用下可达到优良的强塑性匹配:延伸率20.3%,强塑积达到22.0 GPa·%;当BF组织板条的宽度为0.15~0.45 μm且薄膜状残γ组织的宽度为50~90 nm时,强度达到1099 MPa,发生碰撞时剩余的残γ组织(约6%)发挥“TRIP效应”从而提高防撞件的吸能和安全性。 相似文献
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Min Cheol Jo Selim Kim Dong Woo Suh Hong Kyu Kim Yong Jin Kim Seok Su Sohn Sunghak Lee 《材料科学技术学报》2021,84(25):219-229
High-strength bainitic steels have created a lot of interest in recent times because of their excellent com-bination of strength,ductility,toughness,and high ballistic mass efficiency.Bainitic steels have great potential in the fabrication of steel armor plates.Although various approaches and methods have been conducted to utilize the retained austenite(RA)in the bainitic matrix to control mechanical properties,very few attempts have been conducted to improve ballistic performance utilizing transformation-induced plasticity(TRIP)mechanism.In this study,high-strength bainitic steels were designed by controlling the time of austempering process to have various volume fractions and stability of RA while maintaining high hardness.The dynamic compressive and ballistic impact tests were conducted,and the relation between the effects of TRIP on ballistic performance and the adiabatic shear band(ASB)for-mation was analyzed.Our results show for the first time that an active TRIP mechanism achieved from a large quantity of metastable RA can significantly enhance the ballistic performance of high-strength bainitic steels because of the improved resistance to ASB formation.Thus,the ballistic performance can be effectively improved by a very short austempering time,which suggests that the utilization of active TRIP behavior via tuning RA acts as a primary mechanism for significantly enhancing the ballistic performance of high-strength bainitic steels. 相似文献