快速加热后冷轧低碳钢的时效特性
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摘要
利用DIL805A/D热膨胀仪和内耗分析法研究了两种不同时效特性的冷轧低碳钢板在快速加热热处理后的时效差异。首先,通过两种材料奥氏体相变点Ac_1与Ar_1的测定、热处理过程中微观组织的变化、碳化物的溶解与析出差异分析发现,在快速加热过程中,两种试样的相变点均大幅提高到960℃以上,以渗碳体为主的碳化物均发生显著回溶,但在冷却过程中,初始组织为大颗粒渗碳体的2号试样,回溶的渗碳体再次析出,而初始组织为游离状渗碳体的1号试样,则无渗碳体的再次析出。其次,通过对热处理后试样不同时间段的内耗分析发现,在刚完成热处理后,1号试样的Snoke峰远高于2号试样,但2周后前者的内耗峰值显著下降,而后者的内耗峰较为稳定,这说明1号试样的固溶碳由于加热时碳化物回溶、冷却时却无法析出而大幅增加,并在随后的自然时效过程中由于过饱和固溶碳显著析出,导致强烈的时效现象,相反的,2号试样由于在冷却过程中碳化物可以再次析出,因此,时效稳定。
The aging difference of two cold rolled low carbon steel plates with different aging characteristics after rapid heating was studied by using DIL805 A/D thermal expansion instrument and internal consumption analysis method.The results show that both specimens' austenite transformation temperature Ac_1 is greatly promoted up to 960 ℃ and the cementite is re-dissolved obviously during the heating process by means of the measurement of austenite transformation temperature Ac_1 and Ar_1,analysis of microstructure and carbide precipitation and dissolution.However,during the cooling process in the No.2 specimen with large granular carbides in the initial microstructure,the dissolved carbides precipitate again; in the No.1 specimen containing free carbides,there is no carbides re-precipitated.Through the internal friction analysis for different phrase,it is discovered that the Snoke peak of sample No.1 is higher than that of sample No.2 after heating treatment and appears a sharp decline two weeks late,at the same time,Snoke peak of sample No.2 keeps stable,which indicates that solid solution carbon atom in the sample No.1 increases significantly because free cementite is dissolved but fails to precipitate during the heat treatment,and on the other hand,supersaturaed solid solution carbon begins to precipitate strongly,therefor,the aging is notable.On the contrary,the aging of sample No.2 seems stable because its cementite precipitates again during the cooling process.
The aging difference of two cold rolled low carbon steel plates with different aging characteristics after rapid heating was studied by using DIL805 A/D thermal expansion instrument and internal consumption analysis method.The results show that both specimens' austenite transformation temperature Ac_1 is greatly promoted up to 960 ℃ and the cementite is re-dissolved obviously during the heating process by means of the measurement of austenite transformation temperature Ac_1 and Ar_1,analysis of microstructure and carbide precipitation and dissolution.However,during the cooling process in the No.2 specimen with large granular carbides in the initial microstructure,the dissolved carbides precipitate again; in the No.1 specimen containing free carbides,there is no carbides re-precipitated.Through the internal friction analysis for different phrase,it is discovered that the Snoke peak of sample No.1 is higher than that of sample No.2 after heating treatment and appears a sharp decline two weeks late,at the same time,Snoke peak of sample No.2 keeps stable,which indicates that solid solution carbon atom in the sample No.1 increases significantly because free cementite is dissolved but fails to precipitate during the heat treatment,and on the other hand,supersaturaed solid solution carbon begins to precipitate strongly,therefor,the aging is notable.On the contrary,the aging of sample No.2 seems stable because its cementite precipitates again during the cooling process.
引文
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[2]Hamid Azizi-alizamini,Matthas Militzer,Warreen Poole.Austenite formation in plain low-carbon steels[J].Metallurgical and Materials Transactions A,2011,42(6):1544-1557.
[3]胡德林.金属学与热处理[M].西安:西北工业大学出版社,2007:220.
[4]Lesch C,Alvarez P,Bleck W,et al.Rapid transformation annealing:a novel method for grain refinement of cold-rolled low-carbon steels[J].Metallurgical and Materials Transactions A,2007,38(9):1882-1890.
[5]余斌,李晓源,时捷,等.等温球化退火对某高碳钢中碳化物的影响[J].金属热处理,2016,41(1):91-93.Yu Bin,Li Xiaoyuan,Shi Jie,et al.Effect of isothermal spheroidizing annealing on carbide in high carbon steel[J].Heat Treatment of Metals,2016,41(1):91-93.
[6]邝春福,张深根,李俊,等.快速热处理对低碳钢烘烤硬化性能的影响[J].材料热处理学报,2014,28(4):262-268.Kuang Chunfu,Zhang Shengen,Li Jun,et al.Effect of rapid heat treatment on bake hardening behavior of a low carbon steel[J].Chinese Jourrnal of Material Research,2014,28(4):262-268.
[7]Momeni A,Dehghani K,Abbasi S,et al.Bake hardening of a low carbon steel for automotive applications[J].Metalurgija Journal of Metallurgy,2007,13(2):131-138.
[8]许云波,侯晓英,王业勤,等.快速加热连续退火对超高强TRIP钢显微组织与力学性能的影响[J].金属学报,2012,48(2):176-182.Xu Yunbo,Hou Xiaoying,Wang Yeqin,et al.Effects of rapid heating continuous annealing on microstructure and mechanical properties of ultrahigh-strength trip-aided steel[J].Acta Metallurgica Sinica,2012,48(2):176-182.
[9]沈中城,张进峰,严勇健,等.精密扭摆内耗仪的研究进展及其钢中固溶碳测定[J].上海交通大学学报,2010,44(5):683-686.Shen Zhongcheng,Zhang Jinfeng,Yan Yongjian,et al.Review of precision torsion pendulum mechanical spectrometer and measurement of solution carbon in steel[J].Journal of Shanghai Jiaotong University,2010,44(5):683-686.