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<p>The microstructural heterogeneity in thick-Sect.&#xa0;15CrNi3MoV steel forgings caused by cooling rate gradients during quenching critically impacts their mechanical reliability. Combining finite element simulation and multi-scale physical simulations, the microstructure evolution was decoded, and an optimised heat treatment process was designed for a 10-t large-tube forging. Key findings reveal that the cooling rate dictates phase transformation: the surface forms martensite, while the centre develops martensite and granular bainite with metastable martensite-austenite (M-A) constituents. During tempering, prolonged holding at 650&#xa0;°C drives the decomposition of M-A constituents into fine carbides, with 12-h tempering achieving optimal strength–toughness balance. Crucially, carbide uniformity eliminates property gradients across 140&#xa0;mm in thickness, suppressing embrittlement risks. Moreover, in the 180-mm-thick plate, the large-sized M-A constituents formed due to incomplete quenching, resulting in the carbide aggregations after tempering, which deteriorates the impact toughness. By integrating numerical simulation with validations from laboratory-scale and pilot-scale physical simulations, the relationship between microstructure and properties can be precisely predicted. Implementing the optimised process (890&#xa0;°C/8&#xa0;h water quenching + 650&#xa0;°C/12&#xa0;h tempering) on the 10-t large-tube forging demonstrates homogeneous properties. Thus, a generic methodology was provided for tailoring heat treatment protocols in ultra-thick alloy steel components.</p>

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Regulation of microstructure and mechanical properties of 15CrNi3MoV steel large-tube forging

  • 期刊论文

  • 发表日期：

    2025年6月21日

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  • Bing Wang,
  • Hong-lin Zhang,
  • Ru-zong Zhai,
  • Bin Xu,
  • Ming-yue Sun,
  • Dian-zhong Li

摘要

The microstructural heterogeneity in thick-Sect. 15CrNi3MoV steel forgings caused by cooling rate gradients during quenching critically impacts their mechanical reliability. Combining finite element simulation and multi-scale physical simulations, the microstructure evolution was decoded, and an optimised heat treatment process was designed for a 10-t large-tube forging. Key findings reveal that the cooling rate dictates phase transformation: the surface forms martensite, while the centre develops martensite and granular bainite with metastable martensite-austenite (M-A) constituents. During tempering, prolonged holding at 650 °C drives the decomposition of M-A constituents into fine carbides, with 12-h tempering achieving optimal strength–toughness balance. Crucially, carbide uniformity eliminates property gradients across 140 mm in thickness, suppressing embrittlement risks. Moreover, in the 180-mm-thick plate, the large-sized M-A constituents formed due to incomplete quenching, resulting in the carbide aggregations after tempering, which deteriorates the impact toughness. By integrating numerical simulation with validations from laboratory-scale and pilot-scale physical simulations, the relationship between microstructure and properties can be precisely predicted. Implementing the optimised process (890 °C/8 h water quenching + 650 °C/12 h tempering) on the 10-t large-tube forging demonstrates homogeneous properties. Thus, a generic methodology was provided for tailoring heat treatment protocols in ultra-thick alloy steel components.