中碳Cr-Mn-Si低合金钢的过冷奥氏体连续冷却转变曲线

doi:10.13251/j.issn.0254-6051.2024.12.024

摘要/Abstract

摘要： 利用Formast-FⅡ型膨胀仪测定了中碳Cr-Mn-Si低合金钢在不同冷却速度下的热膨胀曲线,结合显微组织观察绘制出试验钢的过冷奥氏体连续冷却转变曲线(CCT曲线)。研究了冷却速度对中碳Cr-Mn-Si低合金钢的显微硬度及过冷奥氏体相变开始温度的影响,并分析了中碳Cr-Mn-Si低合金钢大型锻件热处理后不同位置的组织性能。结果表明,中碳Cr-Mn-Si低合金钢的Ac₃=855 ℃、Ac₁=770 ℃、Ms=375 ℃、Mf=200 ℃。当冷速≤0.28 ℃/s时,高温区主要发生铁素体和珠光体转变,中温区发生贝氏体转变;当冷速为0.28~0.83 ℃/s时,中温区发生贝氏体转变,低温区发生马氏体转变;当冷速≥1.66 ℃/s时只发生马氏体转变。随着冷却速度的增大,试验钢的显微硬度先直线上升后缓慢升高,相转变开始温度先大幅下降之后基本保持稳定。热处理后的中碳Cr-Mb-Si低合金钢大型锻件边部为马氏体和贝氏体的复相组织,R/2和心部为贝氏体组织,试件边部的抗拉强度(1467.0 MPa)、硬度(475 HV5)值最高,表明适量的马氏体在保持贝氏体组织良好塑性的同时显著提升材料的强度。

关键词: 中碳Cr-Mn-Si低合金钢, CCT曲线, 冷却速度, 显微硬度, 相变温度

Abstract: Thermal expansion curves of a medium carbon Cr-Mn-Si low alloy steel under different cooling rates were determined by using Formast-FⅡ dilatometer, and the continuous cooling transformation (CCT) curve of the undercooled austenite of the tested steel was plotted in combination with the observation of the metallographic microstructure. The effect of cooling rate on the microhardness and the onset temperature of the undercooled austenite phase transformation of the tested steel was investigated, and the microstructure and properties of the medium carbon Cr-Mn-Si low alloy steel large forgings at different positions after heat treatment were analyzed. The results show that Ac₃=855 ℃, Ac₁=770 ℃, Ms=375 ℃ and Mf=200 ℃ for the medium carbon Cr-Mn-Si low alloy steel. When the cooling rate is less than or equal to 0.28 ℃/s, the ferrite and pearlite transformation mainly occurs in the high temperature zone, and the bainite transformation occurs in the middle temperature zone. When the cooling rate is 0.28-0.83 ℃/s, the bainite transformation mainly occurs in the middle temperature zone, and the martensite transformation occurs in the low temperature zone. When the cooling rate is greater than or equal to 1.66 ℃/s, only the martensite transformation occurs. With the increase of cooling rate, the microhardness of the tested steel firstly rises linearly and then increases slowly, and the phase transformation start temperature firstly decreases sharply and then basically remains stable. The edge of heat-treated medium carbon Cr-Mb-Si low alloy steel large forgings microstracture is martensite and bainite complex, the positions at R/2 and the core microstracture are bainite, the tensile strength (1467.0 MPa) and hardness (475 HV5) values at the edge position are the highest, indicating that appropriate amount of martensite can significantly improve the strength of bainite structure while maintaining good plasticity.

Key words: medium carbon Cr-Mn-Si low alloy steel, CCT curve, cooling rate, microhardness, phase transition temperature

中图分类号:

TG161

高鑫, 宁静, 苏杰, 高齐, 姜庆伟. 中碳Cr-Mn-Si低合金钢的过冷奥氏体连续冷却转变曲线[J]. 金属热处理, 2024, 49(12): 142-147.

Gao Xin, Ning Jing, Su Jie, Gao Qi, Jiang Qingwei. Continuous cooling transformation curves of undercooled austenite of medium carbon Cr-Mn-Si low alloy steel[J]. Heat Treatment of Metals, 2024, 49(12): 142-147.

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