<strong>Cr-Mo</strong>微合金冷镦钢的显微组织、力学性能及强化机制

doi:10.11900/0412.1961.2021.00084

金属学报

2022, Vol. 58

Issue (9): 1189-1198 DOI: 10.11900/0412.1961.2021.00084

研究论文

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Cr-Mo微合金冷镦钢的显微组织、力学性能及强化机制

陈继林¹^,²^,³(

), 冯光宏¹, 马洪磊², 杨栋², 刘维²

^1.钢铁研究总院冶金工艺研究所北京 100081
^2.邢台钢铁有限责任公司邢台 054027
^3.河北省线材工程技术研究中心邢台 054027

Microstructure, Mechanical Properties, and Strengthening Mechanism of Cr-Mo Microalloy Cold Heading Steel

CHEN Jilin¹^,²^,³(

), FENG Guanghong¹, MA Honglei², YANG Dong², LIU Wei²

^1.Metallurgical Technology Institute, Central Iron and Steel Research Institute, Beijing 100081, China
^2.Xingtai Iron and Steel Co., Ltd., Xingtai 054027, China
^3.Hebei Engineering Research Center for Wire Rod, Xingtai 054027, China

引用本文:

陈继林, 冯光宏, 马洪磊, 杨栋, 刘维. Cr-Mo微合金冷镦钢的显微组织、力学性能及强化机制[J]. 金属学报, 2022, 58(9): 1189-1198.
Jilin CHEN, Guanghong FENG, Honglei MA, Dong YANG, Wei LIU. Microstructure, Mechanical Properties, and Strengthening Mechanism of Cr-Mo Microalloy Cold Heading Steel[J]. Acta Metall Sin, 2022, 58(9): 1189-1198.

全文: PDF(3959 KB) HTML

摘要:

采用OM、SEM、TEM、拉伸实验和硬度测试等方法,对Cr-Mo微合金化冷镦钢在不同控轧控冷(TMCP)工艺下的组织与力学性能进行了表征和测试,并分析了强化机制。结果表明,TMCP工艺参数对Cr-Mo微合金化冷镦钢的组织与力学性能有显著影响,随着终轧温度的升高及冷速的增加,钢中铁素体及珠光体的复相组织逐渐向贝氏体铁素体转变,位错密度逐渐增加,抗拉强度呈现单调上升的规律,而延伸率呈起伏趋势。在终轧温度为935℃时,显微组织主要为均匀分布的短棒状和粒状贝氏体相,其间存在位错缠结,该工艺下具有最佳的强韧性匹配,其抗拉强度和延伸率分别达到了925 MPa和20%,距淬火端部7 mm (J7)处的硬度为53.1 HRC。终轧温度为900℃时,细晶强化是最主要的强化机制,占总强度的31%~36%；终轧温度在935℃以上时,位错强化为主要强化机制,占总强度的35%~38%。淬透性结果表明,Cr-Mo微合金化冷镦钢的淬透性不受显微组织及力学性能的影响,保持着良好的淬火性能,同时建立了Cr-Mo微合金钢的端淬曲线的模型,实现了淬透性的预测。

关键词 ： Cr-Mo微合金化, 冷镦钢, 终轧温度, 强化机制

Abstract：

Lightweight and safety of automobiles is the development trend of high-strength automobile fasteners, which is conducive to saving resources and protecting the environment. High-strength fasteners connect parts of engine, and their strength affects the overall life of the engine, thereby affecting the safety performance of the vehicle. Presently, high-strength fastener steels for cars are mainly 35CrMo, and the fastener strength reaches 10.9/12.9 level, which must fulfill sufficient delayed fracture and fatigue properties. Therefore, it is important to develop cold heading steel with high fatigue and strong plasticity matching. In this study, the microstructure, mechanical properties, and strengthening mechanism of Cr-Mo microalloyed cold heading steel, under different thermomechanical control processes (TMCPs), were investigated using OM, SEM, and TEM. The results show that the TMCP parameters affect the structure and mechanical properties of the experimental steel. With an increase in the finish rolling temperature and acceleration of the cooling rate, the ferrite-pearlite composite structure in the steel gradually changes to bainitic, dislocation density gradually increases, tensile strength monotonously increases, and elongation fluctuates. When the finish rolling temperature is 935^oC, the microstructure is mainly uniformly distributed bainite phase, which is in the form of short rod and granular, and there is dislocation entanglement. The experimental results show that this process has the best strength and toughness matching. Its tensile strength and elongation reach 925 MPa and 20%, respectively, and the hardness at 7 mm from the quenched end (J7) is 53.1 HRC. When the finish rolling temperature is 900^oC, grain refinement strengthening is the main strengthening mechanism, accounting for 31%-36% of the yield strength; when the finish rolling temperature is more than 935^oC, dislocation strengthening is the main strengthening mechanism, accounting for the total strength of 35%-38%. The hardenability results show that the hardenability of the experimental steel is unaffected by the microstructure and mechanical properties, and it maintains high-quality hardenability. In addition, a model of the end quenching curve of the Cr-Mo microalloyed steel is established to predict hardenability.

Key words： Cr-Mo microalloying cold heading steel finish rolling temperature strengthening mechanism

收稿日期: 2021-02-26

ZTFLH:

TG142.1

作者简介: 陈继林,男,1986年生,高级工程师,博士

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https://www.ams.org.cn/CN/10.11900/0412.1961.2021.00084 或 https://www.ams.org.cn/CN/Y2022/V58/I9/1189

表1 Cr-Mo微合金钢的轧制工艺

图1 Cr-Mo微合金钢在不同工艺下显微组织的OM像和SEM像

图2 Cr-Mo微合金钢在不同工艺下显微组织的TEM像

图3 Cr-Mo微合金钢中的位错及孪晶

图4 Cr-Mo微合金钢室温拉伸应力-应变曲线

表2 Cr-Mo微合金钢室温拉伸力学性能

图5 Cr-Mo微合金钢在工艺2下室温拉伸断口形貌的SEM像

图6 Cr-Mo微合金钢的末端淬透性曲线

图7 Cr-Mo微合金钢距离淬火端7 mm处显微组织的OM像

表3 Cr-Mo微合金钢的屈服强度(σy)及其分量的计算值 (MPa)

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