热处理工艺对高性能桥梁耐候钢组织及力学性能的影响

Effect of heat treatment process on microstructure and mechanical properties of high-performance bridge weathering steel

关键词:  桥梁耐候钢  回火温度  调质处理  组织  力学性能

Key words:  bridge weathering steel  tempering temperature  quenching and tempering treatment  microstructure  mechanical properties 〖FQ(+30mm。23,ZX-WZ〗收稿日期: 20240527. 网络出版日期: 20241228. 基金项目: 河南省博士后科研启动项目(HN2021107)  安徽省高等学校科学研究项目(2023AH051090). 作者简介: 李立志(2000—),男,硕士研究生. 通信作者: 张可,E-mail: [e-mail]. 期刊网址: http://hit.alljournals.cn/mst_cn/ch/index.aspx 随着交通运输行的提升。调质态实验钢的屈服强度总体在750 MPa

摘要:

近年来,桥梁耐候钢不断朝着高强度、高韧性、低屈强比、耐腐蚀和易焊接的方向发展,然而,桥梁耐候钢的屈服强度越高,其实现低屈强比和高韧性的难度就越大。为了考察不同热处理工艺对桥梁耐候钢的屈服强度、屈强比和低温韧性的影响,开发出综合力学性能优异的高性能桥梁耐候钢,本文采用OM、SEM等手段,并结合拉伸、低温冲击等实验,对比研究了TMCP、回火及调质工艺对桥梁耐候钢的微观组织、力学性能和屈强比的影响。研究表明:实验钢的轧态组由多边形铁素体和少量粒状贝氏体组成,屈服强度为515 MPa,抗拉强度为734 MPa,-40 ℃冲击功为46 J。经450~550 ℃回火后的组织相较于轧态组织更细小,粒状贝氏体中的M/A岛经回火后逐渐分解,使实验钢的韧性大幅提高,冲击功均高于210 J,但强度变化不明显；M/A岛分解后形成的大量渗碳体是实验钢屈强比没有显著提高的主要原因。此外,实验钢经920 ℃淬火和500~600 ℃回火后,回火索氏体的板条特征逐渐减少直至消失,渗碳体由带状转变为粒状且呈弥散分布,可获得750 MPa以上的屈服强度,且40 ℃冲击功大于275 J,但屈强比较高在0.96以上。实验钢经500 ℃回火1 h时,可获得屈服强度高于500 MPa、屈强比低于0.80、-40 ℃冲击功大于240 J的高性能桥梁耐候钢。

Abstract:

In recent years, bridge weathering steel has been continuously developed towards higher strength, improved toughness, lower yield ratio, enhanced corrosion resistance, and better weldability. However, the higher the yield strength of bridge weathering steel, the greater the difficulty in achieving low yield ratio and high toughness. In order to investigate and compare the effects of different heat treatment processes on the yield strength, yield ratio, and low-temperature toughness of bridge weathering steels, this study employs OM, SEM, and other analytical techniques, alongside tensile and low-temperature impact testing, to systematically compare the effects of thermomechanical controlled processing (TMCP), tempering, and quenching and tempering on the microstructure, mechanical properties, and yield ratio of the bridge weathering steels. The findings indicate that the rolled structure of the experimental steel comprises polygonal ferrite and a minor amount of granular bainite, with a yield strength of 515 MPa, tensile strength of 734 MPa, and impact energy of 46 J at 40 ℃. After tempering at 450550 ℃, the microstructure becomes finer compared to the as-rolled state, and the M/A islands within the granular bainite progressively decompose, significantly enhancing the toughness of the experimental steel, with impact energy exceeding 210 J; however, there is no notable change in strength. The extensive formation of cementite following the decomposition of M/A islands is the primary factor preventing a substantial increase in the yield-to-tensile strength ratio of the experimental steel. Additionally, after quenching at 920 ℃ and tempering at 500600 ℃, the lath characteristics of tempered sorbite gradually diminish and vanish, while cementite transforms from lamellar to granular and disperses. This process results in a yield strength exceeding 750 MPa and an impact energy greater than 275 J at 40 ℃, although the yield ratio exceeds 0.96. Tempering at 500 ℃ for one hour produces high-performance bridge weathering steel with a yield strength over 500 MPa, a yield ratio below 0.80, and an impact energy surpassing 240 J at 40 ℃. Keywords: bridge weathering steel；tempering temperature；quenching and tempering treatment；microstructure；mechanical properties 〖FQ(+30mm。23,ZX-WZ〗收稿日期: 20240527. 网络出版日期: 20241228. 基金项目: 河南省博士后科研启动项目(HN2021107)；安徽省高等学校科学研究项目(2023AH051090). 作者简介: 李立志(2000—),男,硕士研究生. 通信作者: 张可,E-mail: [e-mail]. 期刊网址: http://hit.alljournals.cn/mst_cn/ch/index.aspx 随着交通运输行的提升。调质态实验钢的屈服强度总体在750 MPa