Evolution of Microstructure in Welding Heat-Affected Zone of G115 Steel with the Different Content of Boron

Zhongyi Chen; Dongxu Kou; Zhengzong Chen; Fan Yang; Yonglin Ma; Yiming Li

doi:10.3390/ma15062053

Evolution of Microstructure in Welding Heat-Affected Zone of G115 Steel with the Different Content of Boron

Materials (Basel). 2022 Mar 10;15(6):2053. doi: 10.3390/ma15062053.

Authors

Zhongyi Chen¹, Dongxu Kou¹, Zhengzong Chen², Fan Yang³, Yonglin Ma¹, Yiming Li⁴

Affiliations

¹ School of Material and Metallurgy, Inner Mongolia University of Science and Technology, Baotou 014010, China.
² Institute for Special Steels, China Iron and Steel Research Institute, Haidian, Beijing 100081, China.
³ Inner Mongolia Shangdu Power Company, Xilin Gol League, Xilinhot 027200, China.
⁴ Key Laboratory of Advanced Metals and Materials, School of Materials and Metallurgy, Inner Mongolia University of Science and Technology, Baotou 014010, China.

Abstract

Welding thermal simulation was performed to investigate the effects of boron content (0, 60, and 130 ppm), welding peak temperature (T_p), and cooling time from 800 to 500 °C (t_8/5) on the microstructure, carbide, subgrain, and microhardness of heat-affected zone (HAZ) in G115 steel. According to the experimental results, the microstructure of coarse-grained HAZ (CGHAZ), fine-grained HAZ (FGHAZ), inter-critical HAZ (ICHAZ), and sub-critically HAZ (SCHAZ) was martensite, martensite containing a small amount of undissolved carbide, martensite, and over-tempered martensite, tempered martensite, respectively. The presence of B element improved the thermal stability of M₂₃C₆ carbide, thereby resulting in a greater amount of undissolved carbides with a larger diameter in the materials with higher B content under the same T_p. Element B is effective in improving A_c1 and A_c3 for the material. Besides, compared with the material without and containing 60 ppm B, the A_c1 and A_c3 of the material containing 130 ppm B increased by 95 and 108 °C, 69 and 77 °C, respectively. Meanwhile, the FGHAZ area of the material containing 130 ppm B was significantly lower than the material without or containing 60 ppm B, indicating that element B can significantly reduce the formation range of FGHAZ. The alloy content in austenite of ICHAZ of materials without or containing 60 ppm B increased, compared with CGHAZ, its M_s and M_f declined by 50 and 7 °C, 46 and 7 °C, respectively. In contrast, the alloy content in austenite of the material with 130 ppm B content decreases, its M_s and M_f was 37 °C and 32 °C higher than CGHAZ, respectively. The microhardness of HAZ was ranked in descending order as CGHAZ, FGHAZ, ICHAZ, and SCHAZ. Differently, the microhardness of CGHAZ and FGHAZ showed an increasing trend with the rise of B content but exhibited a decreasing trend with the rise of t_8/5.

Keywords: G115 steel; M23C6 carbide; boron; heat-affected zone; phase transformation.