Thermodynamic calculation of retained austenite content in Q&P steel

doi:10.13251/j.issn.0254-6051.2022.01.005

Abstract

Abstract: Based on CALPHAD method, the diffusion model of Q&P steel during partitioning process was established, and a set of task flow for calculating the microstructure transformation of specific components under specific Q&P process was established. By calculating the martensite/retained austenite content in the primary quenching process of Q&P steel and the carbon enrichment of retained austenite in the partitioning process, combined with the built-in constitutive model of martensite transformation based on Gibbs free energy in Thermo-Calc software, the retained austenite content at room temperature was predicted. The model was used to calculate the retained austenite content at room temperature of steel grades (Fe-0.2C-1.28Mn-0.37Si-0.0018B, wt%) in the literature. The results show that the calculated martensite transformation temperature is 60 ℃ higher than the experimental data, and the calculated retained austenite content at room temperature is 4.41%, which is basically consistent with the experimental data, thus verifying the semi-quantitative nature of the calculation model. This model is used to further calculate and analyze the influence of carbon and manganese content and heat treatment system on the primary retained austenite content of AQT980 and AQT1180 steels. The calculation results show that the increase of carbon and manganese content can reduce the temperature of phase transformation points (A₃, Ms, Mf) in steel. At a fixed quenching temperature, the increase of carbon content and manganese content in the steel can significantly increase the primary retained austenite content. When the contents of carbon and manganese are constant, the increase of primary quenching temperature will significantly increase the primary residual content.

Key words: Q&P steel, thermodynamic analysis, retained austenite, CALPHAD method

CLC Number:

TG161

Hou Yaqing, Zhang Yu, Yu Mingguang, Wang Jingjing, Yang Li, Su Hang. Thermodynamic calculation of retained austenite content in Q&P steel[J]. Heat Treatment of Metals, 2022, 47(1): 25-31.

References

[1]景财年. 相变诱发塑性钢的组织性能[M]. 北京: 冶金工业出版社, 2012.
[2]Gerdemann F L H, Speer J G, Matlock D K. Microstructure and hardness of steel grade 9260 heat-treated by the quenching and partitioning (Q&P) process[J]. Materials Science and Technology, 2004, 1: 439-449.
[3]涂英明, 景财年. 高强度淬火-配分钢的研究现状及发展方向[J]. 金属热处理, 2017, 42(9): 132-137.
Tu Yingming, Jing Cainian. Research status and development trend of high strength quenching and partitioning steel[J]. Heat Treatment of Metals, 2017, 42(9): 132-137.
[4]Fischer F D, Reisner G, Werner E, et al. A new view on transformation induced plasticity (TRIP)[J]. International Journal of Plasticity, 2000, 16(7): 723-748.
[5]Cherkaoui M, Berveiller M, Lemoine X. Couplings between plasticity and martensitic phase transformation: overall behavior of polycrystalline TRIP steels[J]. International Journal of Plasticity, 2000, 16(10): 1215-1241.
[6]王亚婷, 万德成, 冯树明, 等. 淬火温度对中锰QP钢组织和性能的影响[J]. 金属热处理, 2020, 45(5): 172-176.
Wang Yating, Wan Dengcheng, Feng Shuming, et al. Effect of quenching temperature on microstructure and mechanical properties of medium manganese QP steel[J]. Heat Treatment of Metals, 2020, 45(5): 172-176.
[7]万德成, 杨晓彩, 王芳, 等. 一步配分处理中碳低合金DQP钢的组织演变[J]. 金属热处理, 2018, 43(12): 42-46.
Wan Decheng, Yang Xiaocai, Wang Fang, et al. Microstructure evolution of medium carbon low alloy DQP steel after direct quenching and isothermal partitioning[J]. Heat Treatment of Metals, 2018, 43(12): 42-46.
[8]苏航. 热力学、动力学计算技术在钢铁材料研究中的应用[M]. 北京: 科学出版社, 2012.
[9]Fei Huyan, Hedström Peter, Höglund Lars, et al. Athermodynamic-based model to predict the fraction of martensite in steels[J]. Metallurgical and Materials Transactions A, 2016, 47(9): 4404-4410.
[10]Edmonds D, He K, Rizzo F, et al. Quenching and partitioning martensite-A novel steel heat treatment[J]. Materials Science and Engineering A, 2006, 438: 25-34.
[11]Speer J G, Matlock D K, De Cooman B C, et al. Comments on “On the definitions of paraequilibrium and orthoequilibrium”[J]. Scripta Materialia, 2005, 52(1): 83-85.
[12]谢振家. 高性能低合金钢中残留奥氏体调控机理及性能研究[D]. 北京: 北京科技大学, 2016.
[13]付波. 高强韧多相钢工艺, 组织, 性能及相互关系的物理模拟[D]. 北京: 北京科技大学, 2015.
[14]Jiang H T, Tang D, Mi Z L, et al. Effect of partitioning parameters on the retained austenite in low-carbon Q&P steel[J]. Materials Science and Technology, 2011, 19(1): 99-103.
[15]Clarke A J, Speer J G, Matlock D K, et al. Influence of carbon partitioning kinetics on final austenite during quenching and partitioning[J]. Scripta Materialia, 2009, 61(2): 149-152.
[16]周媛, 李麟, 史文, 等. Si-Mn系TRIP钢两相区等温处理的组织转变模拟[J]. 材料热处理学报, 2002, 23(1): 15-18.
Zhou Yuan, Li Lin, Shi Wen, et al. Computer simulations of transformations during intercritical annealing in silicon-manganese TRIP steel[J]. Transactions of Materials and Heat Treatment, 2002, 23(1): 15-18.
[17]王晓东. TRIP钢微结构-性能的表征与设计[D]. 上海: 上海交通大学, 2006.
[18]田亚强, 张宏军, 陈连生, 等. 低碳高强钢合金元素配分行为对残留奥氏体和力学性能的影响[J]. 金属学报, 2014, 50(5): 531-539.
Tian Yaqiang, Zhang Hongjun, Chen Liansheng, et al. Effect of alloy elements partitioning behavior on retained austenite and mechanical property in low carbon high strength steel[J]. Acta Metallurgica Sinica, 2014, 50(5): 531-539.
[19]Van Bohemen S M C, Sietsma J. Effect of composition on kinetics of athermal martensite formation in plain carbon steels[J]. Materials Science and Technology, 2009, 25(8): 1009-1012.
[20]Magee C L. The nucleation ofmartensite[J]. Phase transformations ASM International, 1970, 115: 115-156.
[21]Lee S J, Tyne C. A kinetics model for martensite transformation in plain carbon and low-alloyed steels[J]. Metallurgical and Materials Transactions A, 2012, 43(2): 422-427.
[22]Skrotzki B. The course of the volume fraction of martensite vs temperature function M_x(T)[J]. Le Journal de Physique IV, 1991, 1(C4): 367-372.
[23]杨栋. 低碳高强Q&P钢元素配分行为研究[D]. 唐山: 河北联合大学, 2014.