Effect of intercritical annealing holding time on microstructure and properties of medium manganese steel in I&Q&P process
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摘要: 利用SEM、XRD、拉伸试验机、Thermo-Calc软件与DICTRA模块模拟计算临界退火过程中元素的变化与Mn元素扩散情况，采用临界退火-淬火-配分（I&Q&P）工艺，研究热轧态6Mn中锰钢在10，30，60 min不同临界退火时间下的组织及其力学性能影响机制。结果表明：随退火时间延长，显微组织由初始的块状铁素体与马氏体逐渐转变为板条马氏体基体上弥散分布的残余奥氏体的微观结构。残余奥氏体体积分数从10 min退火时的17.6%增至60 min时的21.1%，碳含量从0.78%提升至1.31%。DICTRA模拟结果显示随退火时间的增加，γ与α之间两相界面不断扩大，Mn元素在奥氏体内形成梯度分布，显著提高了奥氏体的稳定性。经60 min退火后试样综合力学性能最优，其中抗拉强度
1121 MPa，断后伸长率29.1%，强塑积达32.6 GPa·%。-
关键词:
- 临界退火-淬火-配分 /
- 中锰钢 /
- 力学性能 /
- Thermo-Calc 软件、DICTRA动力学 /
- Mn配分
Abstract: The microstructural evolution and mechanical properties of hot-rolled 6Mn medium manganese steel subjected to a critical intercritical annealing–quenching–partitioning (I&Q&P) process were investigated using SEM, XRD, tensile testing, and Thermo-Calc software with the DICTRA module. Annealing durations of 10, 30, and 60 minutes were employed to elucidate the effect of annealing time on phase transformation behavior and mechanical performance of the studied steel. The results show that as annealing time prolongs, the microstructure gradually transforms from initial blocky ferrite and martensite to lath martensite with finely dispersed retained austenite. The volume fraction of retained austenite increases from 17.6% with 10-minutes holding time to 21.1% with 60 minutes holding time, while its carbon content rises from 0.78% to 1.31%. DICTRA simulations reveal that as the annealing time extends, the γ/α phase interface broadens continuously, and Mn partitioning into austenite forms a concentration gradient, significantly enhancing austenite stability. After annealing for 60 minutes, the specimen exhibits optimal mechanical properties, with an ultimate tensile strength of 1121 MPa, total elongation of 29.1%, and a product of strength and elongation (PSE) of 32.6 GPa·%. -
图 2 试验钢的相变点数据
(a) GLeeble-3500试验机实测CCT曲线; （b）JmatPro7软件模拟CCT曲线
Figure 2. Phase transformation characteristics of the experimental steel
图 3 不同退火温度下力学性能
Figure 3. Mechanical properties of the experimental steel annealed at different temperatures
图 4 不同退火条件下的XRD图谱
Figure 4. XRD patterns of the experimental steel obtained under different annealing conditions
(a)10 min; (b)30 min; (c)60 min
图 5 计算预测数据与实测数据对比
Figure 5. Comparison between calculated predictions and experimental data
图 6 SEM表征不同退火时间试验钢的形貌
Figure 6. SEM micrographs of the experimental steel annealed for different durations
(a) 10 min; (b) 30 min; (c) 60 min
图 7 DICTRA模拟临界退火过程结果
(a) Mn元素在奥氏体内分布情况(左侧为γ相，右侧为α相)；(b)退火过程中γ/α两相界面移动情况
Figure 7. DICTRA simulation results of the critical annealing process
图 8 625 ℃时不同退火时间下试验钢的拉伸曲线
Figure 8. Tensile curves of the tested steel annealed for different time at 625 ℃
图 9 试验钢加工硬化曲线
Figure 9. Work hardening curves of the experimental steel annealed at 625 °C for different time
表 1 试验钢设计成分
Table 1. Chemical composition of experimental steel
% C Mn Si Cr S P Fe 0.3 6.0 1.2 0.5 0.007 0.007 Bal. 
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表 2 不同退火温度条件下试验钢力学性能（保温60 min）
Table 2. Mechanical properties of the experimental steel annealed at different temperature (Soaking time: 60 min)
Annealing
temperature/℃YS/MPa UTS/MPa TE/% PSE/（GPa·%） 600 933±3.5 961±7.9 32±4.2 30.8 625 852±4.4 1121 ±6.529±2.3 32.5 650 548±2.6 1281 ±8.316±3.3 20.5
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表 3 RA 含量的计算及实测结果
Table 3. Calculated and measured RA fraction
Annealing
temperature/℃RA calculated by
Thermo-Calc/%RA calculated
by Equ.(3)/%RA
measured/%600 19.8 15.3 19.3 625 32.1 27.5 22.1 650 51.5 27.9 21.2
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表 4 625 ℃时不同退火时间对RA和C含量的影响
Table 4. Effect of annealing times on RA fraction and carbon content at 625 ℃
Annealing time/min RA fraction/% Carbon content in RA/% 10 17.3 0.78 30 19.1 0.79 60 21.1 1.31
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表 5 625 ℃时不同退火时间下的力学性能
Table 5. Mechanical properties of steel annealed at 625 ℃ for different times
Annealing time/min YS/MPa UTS/MPa TE/% PSE/（GPa·%） 10 960±3.5 979±4.9 13±3.2 12.7 30 1063 ±6.71109 ±7.421±2.5 23.3 60 852±5.4 1121 ±6.529±1.3 32.5
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