60Si2CrVAT钢短时淬火后亚稳奥氏体等温转变动力学
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摘要
用热膨胀法和X射线衍射法研究了60Si2Cr VAT弹簧钢在Q-I-Q-T(Quenching-Isothermal-Quenching-Tempering)新工艺的Q-I阶段,即材料奥氏体化后短时淬火再等温这一过程中的亚稳态残留奥氏体的等温转变动力学。实验表明:随等温温度的升高,残留奥氏体含量先升后降。不同温度短时淬火等温冷却后均得到马氏体、贝氏体和残留奥氏体的复相组织。随等温温度的升高,发生完全转变的时间明显缩短,转变量明显减少,转变孕育期也从280℃的54 s减少到500℃的0.96 s。实验获得的亚稳奥氏体等温阶段的TTT曲线呈近C型特征。从亚稳奥氏体的转变量与等温时间的关系曲线可知曲线分为2个阶段,其中第Ⅰ阶段亚稳奥氏体的转变速率明显大于第Ⅱ阶段的转变速率,其等温转变动力学可以用对数曲线进行描述。
The isothermal transformation kinetics of metastable austenite in the novel Q-I-Q-T( Quenching-Isothermal-QuenchingTempering) process were studied by means of dilatometric technique and XRD( X-ray diffraction). Results show that the volume fraction of residual austenite increases at first and then decreases with the isothermal temperature increasing. After short-time quenching and isothermal treatment at different temperatures,all the samples have complex microstructure containing martensite,bainite and austenite.The TTT curve has near-C characteristic,in which the transition time is short and the transformation amount reduces significantly with the isothermal temperature increasing and the start time of the transition decreases from 54 s at 280 ℃ to 0. 96 s at 500 ℃. According to the curve of transformation amount of metastable austenite versus isothermal time,two stages can be clearly watched where the transformation speed of metastable austenite in the first stage is distinctly greater than that in the second stage. The law curve of isothermal transformation kinetics can be given accord with logistic curve.
The isothermal transformation kinetics of metastable austenite in the novel Q-I-Q-T( Quenching-Isothermal-QuenchingTempering) process were studied by means of dilatometric technique and XRD( X-ray diffraction). Results show that the volume fraction of residual austenite increases at first and then decreases with the isothermal temperature increasing. After short-time quenching and isothermal treatment at different temperatures,all the samples have complex microstructure containing martensite,bainite and austenite.The TTT curve has near-C characteristic,in which the transition time is short and the transformation amount reduces significantly with the isothermal temperature increasing and the start time of the transition decreases from 54 s at 280 ℃ to 0. 96 s at 500 ℃. According to the curve of transformation amount of metastable austenite versus isothermal time,two stages can be clearly watched where the transformation speed of metastable austenite in the first stage is distinctly greater than that in the second stage. The law curve of isothermal transformation kinetics can be given accord with logistic curve.
引文
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[2]梁益龙,谭起兵.稀土对Mn-RE系贝氏体钢CCT曲线及组织的影响[J].金属热处理,2009,34(8):48-51.LIANG Yi-long,TAN Qi-bing.Effect of rare earth on CCT curves and m icrostructure of Mn-RE bainite steel[J].Heat Treatment of Metals,2009,34(8):48-51.
[3]高卫星,梁益龙.Q-I-Q-T热处理新工艺下两种奥氏体化温度对60Si2Cr VAT弹簧钢疲劳强度的影响[J].材料导报,2013,27(4):81-84.GAO Wei-xing,LIANG Yi-long.Effect of austenitizing temperature on a spring steel 60Si2Cr VAT fatigue strength with the Q-I-Q-T new heat treatment[J].Materials Review,2013,27(4):81-84.
[4]Speer J G,Matlock D K,De Cooman B C,et al.Carbon partitioning into austenite after martensite transformation[J].Acta Mater,2003,51:2611-2622.
[5]Speer John G,Fernado C Rizzo Assuncao.The“quenching and partitioning”process:background and recent progress[J].Material Research,2005,8(4):417-423.
[6]徐祖耀.淬火-碳分配-回火(Q-P-T)工艺浅介[J].金属热处理,2009,34(6):1-7.Hsu T Y.A brief introduction to quenching-partitioning-tempering(Q-P-T)process[J].Heat Treatment of Metals,2009,34(6):1-7.
[7]Meyer M De,Mahieu J,Cooman B C De.Empirical micro structure prediction method for combined intercritical annealing and bainitic transformation of TRIP Steel[J].Material Science and Technology,2002,18(10):1121.-1132.
[8]Chiang J,Boyd J D,Pilkey A K.Effect of microstructure on retained austenite stability and tensile behaviour in an aluminum-alloyed TRIP steel[J].Materials Science&Engineering A,2015,638:132-142.
[9]王立军,余伟,武会宾,等.Si对超高强钢残留奥氏体回火稳定性与力学性能的影响[J].材料热处理学报,2010,31(10):30-36.WANG Li-jun,YU Wei,WU Hui-bin,et al.Effects of Si on tempering stability of retained austenite and mechanical properties of ultra-high strength steels[J].Transactions of Materials and Heat Treatment,2010,31(10):30-36.
[10]Hyun Jo Jun,S H Park,S D Choi,et al.Decomposition of retained austenite during coiling process of hot rolled TRIP-aided steels[J].Materials Science and Engineering A,2004(379):204-209.
[11]徐祖耀.钢热处理的新工艺[J].热处理,2007,22(1):1-10.Hsu T Y.New processes for steel heat treatment[J].Heat Treatment,2007,22(1):1-10.
[12]文翠娥,孙培祯,谢长生,等.硅对6Cr NIMnsi Mo V钢TTT图的影响[J].金属热处理学报,1992,13(3):22-27.WEN Cui-e,SUN Pei-zhen,XIE Chang-sheng,et al.Effect of silicon on TTT curve of 6Cr NIMnsi Mo V steel[J].Journal of Metal Heat Treatment,1992,13(3):22-27.