Effects of Ti/N Ratio on Coarse-Grain Heat-Affected Zone Microstructure Evolution and Low-Temperature Impact Toughness of High Heat Input Welding Steel

Abstract

Coarse-grain heat-affected zone (CGHAZ) properties of steel deteriorate when it is welded using high heat input, which always restricts the promotion and use of high heat input welding steel. TiN particles significantly inhibit the growth of austenite and improve the microstructure and properties of high heat input welding steel. Effects of different Ti/N ratios on the CGHAZ microstructure and properties of high heat input welding steel were studied using welding thermal simulations and in situ observations. Results showed that a higher Ti/N ratio led to the abnormal growth of austenite grains and promoted the nucleation and growth of lath ferrite, which made the microstructure of the CGHAZ heterogeneous. In contrast, austenite grains were more uniform at a lower Ti/N ratio. Thus, the microstructure was refined, the brittle structure was reduced, and the properties of the CGHAZ were improved. In addition, when Ti/N = 5.85, the impact absorption energy of the CGHAZ obviously fluctuated. However, when Ti/N = 2.82, the impact absorption energy of the CGHAZ was higher and more stable. These results provided a new idea for the development of high heat input welding steel based on TiN theory.

Effect of Ca Addition on Inclusions of Welding Heat-Affected Zone in Pressure Vessel Steels

“…Low-heat-input welding is not sufficient for the production of pressure vessel steels because of its slow speed [5,6]. However, during high-wire-energy welding of pressure vessel steels, in the coarse-grained zone of the welding HAZ, the solid base metal usually has obvious microstructure coarsening and performance deterioration due to the influence of welding thermal cycling [7]. In order to solve the problem of decreasing strength and toughness of pressure vessel steel in high-heat-input welding production, many scholars around the world have carried out research on this problem, mainly focusing on the use of microalloying elements in 2 of 14 oxide inclusions and refining the austenite grain size to obtain good toughness of the IAF microstructure as the main way to improve the toughness of the welding HAZ [8][9][10].…”