Study on microstructure evolution and austenitizing process of 1800 MPa grade ultra-high strength hot stamping steels
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摘要: 对不同奥氏体化温度及保温时间条件下的1800 MPa级超高强热成形钢组织性能演变进行了试验研究，确定了最佳的热成形奥氏体化工艺制度。结果表明，当奥氏体化温度及保温时间分别达到840 ℃、3 min时，1800 MPa级超高强热成形钢淬火后的组织均为马氏体，且马氏体组织随着奥氏体化温度的升高及保温时间的增加逐渐粗大，抗拉强度逐渐下降。当奥氏体化温度为840 ℃时，抗拉强度、伸长率及强塑积分别可以达到1861.3 MPa、6.88%、12.81 GPa·%；当保温时间为3 min时，抗拉强度、伸长率及强塑积分别可以达到1851.28 MPa、6.84%、12.66 GPa·%。最佳奥氏体化工艺制度为：奥氏体化温度840 ℃，保温时间3 min。Abstract: The evolution of microstructures and properties of 1800 MPa ultra-high strength hot stamping steels under different austenitizing temperatures and holding times were experimentally studied in this paper, and the optimum hot stamping austenitizing process was established. The results show that when the austenitizing temperature and holding time reach 840 ℃ and 3 min, respectively, the quenched microstructures of the hot stamping steel is consisted of martensite, and the martensite becomes coarser with the increase in temperature and holding time. The tensile strength decreases gradually with the increase of the austenitizing temperature and holding time. When the austenitizing temperature is 840 ℃, the tensile strength, elongation and strength-ductility product can reach 1861.3 MPa, 6.88% and 12.81 GPa·%, respectively. When the holding time is 3 min, the tensile strength, elongation and strength-ductility product can reach 1851.28 MPa, 6.84% and 12.66 GPa·%, respectively. The austenitizing temperature of 840 ℃ and holding time of 3 min are selected as the optimum austenitizing parameters.
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图 1 不同奥氏体化温度下热成形钢的淬火组织
Figure 1. Quenching microstructures under different austenitizing temperatures
（a）810 ℃；（b）840 ℃；（c）870 ℃；（d）900 ℃；（e）930 ℃；（f）960 ℃；（g）990 ℃
图 2 不同奥氏体化温度下热成形钢的淬火组织（SEM）
Figure 2. Quenching microstructures under different austenitizing temperatures
（a）840 ℃；（b）870 ℃；（c）900 ℃；（d）930 ℃； （e）960 ℃；（f）990 ℃
图 3 不同奥氏体化温度下热成形钢的力学性能变化
Figure 3. Changes of mechanical properties at different austenitizing temperatures
图 4 不同保温时间下热成形钢的淬火组织
Figure 4. Quenching microstructures at different holding times
（a）1 min；（b）3 min；（c）5 min；（d）7 min；（e）9 min
图 5 不同保温时间下热成形钢的淬火组织（SEM）
Figure 5. Quenching microstructures at different holding times
（a）3 min；（b）5 min；（c）7 min；（d）9 min
图 6 不同保温时间下热成形钢的力学性能变化
Figure 6. Changes of mechanical properties at different holding times
图 7 最佳工艺制度下超高强钢组织及EBSD表征
(a)SEM 表征；(b)EBSD表征；(c)相邻晶粒取向差分布
Figure 7. Microstructure and EBSD analysis of the ultra-high strength steel with the optimum austenitizing process
图 8 淬火后试样CSL晶界特征及占比
(a)晶界分布；(b)重位点阵占比
Figure 8. Characteristics and proportion of the CSL grain boundary of the steel
表 1 1800 MPa级热成形钢主要化学成分
Table 1. Main composition of 1800 MPa hot stamping steel
% C Mn Si Al B Cr Ti Nb 0.29 1.40 0.26 0.04 0.003 0.25 0.027 0.051 
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