回火温度对Nb-Ti微合金化Mn系低碳贝氏体钢屈强比的影响
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摘要
测试了Nb-Ti微合金化Mn系低碳贝氏体钢经不同温度回火后的拉伸性能,研究了回火温度对实验钢屈强比(Yield ratio)的影响,通过引入Swift公式分析了实验钢经不同温度回火后的应变硬化指数n和材料常数b的变化规律,建立了显微组织与屈强比之间的关系模型。结果表明:实验钢在280～600℃温度范围内回火2 h后,随着回火温度的升高,屈强比和材料常数b逐渐增加,应变硬化指数n呈现下降趋势,同时屈强比和ln(b/n~2)呈线性递增关系。显微分析表明,回火后屈强比的变化主要是由于回火过程中贝氏体板条的粗化造成的;同时结合透射电镜(TEM)观察讨论了回火过程中微合金化元素Nb, Ti的碳氮化物析出对贝氏体钢屈强比的影响。
In order to reduce the cost of alloying elements, Nb-Ti micro-alloyed Mn series low carbon bainitic steels were developed. The effect of tempering temperatures on tensile properties and yield ratio of Mn-series low carbon steel was investigated in the present study. The as-rolled steel plate samples with 30 mm thickness were tempered for 2 h within the temperature ranging from 280 to 600 ℃. With the increase of tempering temperature from 280 to 600 ℃, the tensile strength decreased from 871 to 765 MPa, and the yield ratio increased from 0.81 to 0.95. The strain-hardening exponent n and material constant b were determined through swift equation. The results showed that n decreased and b increased with the tempering temperature increasing. Besides, the yield ratio had a linear relationship with ln(b/n~2). Microstructure observation showed that the microstructure of the as-rolled steel was mostly bainite laths. The bainitic laths coarsened during tempering and the width of bainitic laths increased with the increase of tempering temperature. Based on mathematic fitting, the empirical model for the relationship between yield ratio and bainite lath width was established and the mechanism on the change of yield ratio after tempering was discussed. Transmission electron microscope(TEM) observation revealed that fine carbonitride precipitates with size of less than 50 nm dispersed on bainite reduced the yield ratio. Therefore, the yield ratio of Mn series low carbon bainitic steels culd be adjusted through the formation of these ultra-fine precipitates during tempering process in future.
In order to reduce the cost of alloying elements, Nb-Ti micro-alloyed Mn series low carbon bainitic steels were developed. The effect of tempering temperatures on tensile properties and yield ratio of Mn-series low carbon steel was investigated in the present study. The as-rolled steel plate samples with 30 mm thickness were tempered for 2 h within the temperature ranging from 280 to 600 ℃. With the increase of tempering temperature from 280 to 600 ℃, the tensile strength decreased from 871 to 765 MPa, and the yield ratio increased from 0.81 to 0.95. The strain-hardening exponent n and material constant b were determined through swift equation. The results showed that n decreased and b increased with the tempering temperature increasing. Besides, the yield ratio had a linear relationship with ln(b/n~2). Microstructure observation showed that the microstructure of the as-rolled steel was mostly bainite laths. The bainitic laths coarsened during tempering and the width of bainitic laths increased with the increase of tempering temperature. Based on mathematic fitting, the empirical model for the relationship between yield ratio and bainite lath width was established and the mechanism on the change of yield ratio after tempering was discussed. Transmission electron microscope(TEM) observation revealed that fine carbonitride precipitates with size of less than 50 nm dispersed on bainite reduced the yield ratio. Therefore, the yield ratio of Mn series low carbon bainitic steels culd be adjusted through the formation of these ultra-fine precipitates during tempering process in future.
引文
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[8] Gao G H, Zhang H, Bai B Z. Effect of tempering temperature on low temperature impact toughness of A low carbon Mn-series bainitic steel [J]. Acta Metallurgica Sinican, 2011, 47(5): 513.(高古辉, 张寒, 白秉哲. 回火温度对Mn系低碳贝氏体钢的低温韧性的影响 [J]. 金属学报, 2011, 47(5): 513.)
[9] Kim S K, Kim Y M, Lim Y J, Kim N J. Relationship between yield ratio and the material constants of the swift equation [J]. Metals and Materials International, 2006, 12(2): 131.
[10] Kim Y M, Kim S K, Kim N J. Correlation of yield ratio with materials constants of constitutive equation [J]. Materials Science Forum, 2005, 475: 289.
[11] Gutierrez I, Altuna M A. Work-hardening of ferrite and microstructure-based modelling of its mechanical behaviour under tension [J]. Acta Materialia, 2008, 56(17): 4682.
[12] Ramazani A. Quantification of the effect of transformation-induced geometrically necessary dislocations on the flow-curve modelling of dual-phase steels [J]. International Journal of Plasticity, 2013, 43(9): 128.
[13] Ashby M F. Work hardening of dispersion-hardened crystals [J]. Philosophical Magazine, 1966, 14(132): 1157.
[14] Ashby M F. The deformation of plastically non-homogeneous materials[J]. Philosophical Magazine, 1970, 21(170): 399.
[15] He S H, He B B, Zhu K Y, Huang M X. On the correlation among dislocation density, lath thickness and yield stress of bainite [J]. Acta Materialia, 2017, 135: 382.
[16] Ohmori A, Torizuka S, Nagai K. Strain-hardening due to dispersed cementite for low carbon ultrafine-grained steels [J]. ISIJ International, 2004, 44(6): 1063.
[17] Song R, Ponge D, Raabe D. Improvement of the work hardening rate of ultrafine grained steels through second phase particles [J]. Scripta Materialia, 2005, 52(11): 1075.
[2] Antoine P, Vandeputte S, Vogt J B. Empirical model predicting the value of the strain-hardening exponent of a Ti-IF steel grade [J]. Materials Science and Engineering: A, 2006, 433: 55.
[3] Jiao D T, Cai Q W, Wu H B. Effects of cooling process after rolling on microstructure and yield ratio of high-strain pipeline steel X80 [J]. Acta Metallurgica Sinica, 2009, 45(9): 1111.(焦多田, 蔡庆伍, 武会宾. 轧后冷却制度对X80级抗大变形管线钢组织和屈强比的影响 [J]. 金属学报, 2009, 45(9): 1111.)
[4] Huang L Q, Wang Y F, Di G B, Yang Y D, Han C L. Influence of tempering temperature on microstructure and mechanical properties of F/B structural steel [J]. Iron and Steel, 2017, 52(9): 79.(黄乐庆, 王彦锋, 狄国标, 杨永达, 韩承良. 回火温度对F/B结构钢组织及性能的影响 [J]. 钢铁, 2017, 52(9): 79.)
[5] Wang F. Study on controlled rolling and cooling process and performance of aseismatic steel plate for building [J]. Hot Working Technology, 2018, 47(11): 124 .(王锋. 建筑用抗震钢板的控轧控冷工艺与性能研究 [J]. 热加工工艺, 2018, 47(11): 124.)
[6] Yan W, Zhu L, Sha W D, Shan Y Y, Yang K. Change of tensile behavior of a high-strength low-alloy steel with tempering temperature [J]. Materials Science and Engineering: A, 2009, 517(1-2): 369.
[7] Tong M W, Venkatsurya P K C, Zhou W H, Misra R D K, Guo B, Zhang K G, Fan W. Structure-mechanical property relationship in a high strength microalloyed steel with low yield ratio: the effect of tempering temperature [J]. Materials Science and Engineering: A, 2014, 609: 209.
[8] Gao G H, Zhang H, Bai B Z. Effect of tempering temperature on low temperature impact toughness of A low carbon Mn-series bainitic steel [J]. Acta Metallurgica Sinican, 2011, 47(5): 513.(高古辉, 张寒, 白秉哲. 回火温度对Mn系低碳贝氏体钢的低温韧性的影响 [J]. 金属学报, 2011, 47(5): 513.)
[9] Kim S K, Kim Y M, Lim Y J, Kim N J. Relationship between yield ratio and the material constants of the swift equation [J]. Metals and Materials International, 2006, 12(2): 131.
[10] Kim Y M, Kim S K, Kim N J. Correlation of yield ratio with materials constants of constitutive equation [J]. Materials Science Forum, 2005, 475: 289.
[11] Gutierrez I, Altuna M A. Work-hardening of ferrite and microstructure-based modelling of its mechanical behaviour under tension [J]. Acta Materialia, 2008, 56(17): 4682.
[12] Ramazani A. Quantification of the effect of transformation-induced geometrically necessary dislocations on the flow-curve modelling of dual-phase steels [J]. International Journal of Plasticity, 2013, 43(9): 128.
[13] Ashby M F. Work hardening of dispersion-hardened crystals [J]. Philosophical Magazine, 1966, 14(132): 1157.
[14] Ashby M F. The deformation of plastically non-homogeneous materials[J]. Philosophical Magazine, 1970, 21(170): 399.
[15] He S H, He B B, Zhu K Y, Huang M X. On the correlation among dislocation density, lath thickness and yield stress of bainite [J]. Acta Materialia, 2017, 135: 382.
[16] Ohmori A, Torizuka S, Nagai K. Strain-hardening due to dispersed cementite for low carbon ultrafine-grained steels [J]. ISIJ International, 2004, 44(6): 1063.
[17] Song R, Ponge D, Raabe D. Improvement of the work hardening rate of ultrafine grained steels through second phase particles [J]. Scripta Materialia, 2005, 52(11): 1075.