The critical influence of La content on the microstructure-toughness relationship in the simulated coarse-grained heat-affected zone of high-strength low-alloy steels

Abstract

The present study was envisaged to investigate the role of La content on the particle, microstructure and toughness in the simulated coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steels. Three steels with La content of 0.016 wt.%, 0.046 wt.% and 0.093 wt.% were prepared and simulated in a 100 kJ/cm heat input welding thermal cycle. Subsequently, the particle and microstructure of selected specimens were characterized and the impact absorb energy was measured at −20 °C. The results indicated that the La2O2S inclusions in 0.016 wt.%-La steel were gradually modified to LaS-LaP in 0.046 wt.%-La steel and to LaP in 0.093 wt.%-La steel. A higher fraction of acicular ferrite was obtained in the simulated CGHAZ of 0.016 wt.%-La steel, since the inclusion of La2O2S was more powerful to induce the formation of acicular ferrite. Furthermore, the fraction of M-A constituents in the simulated CGHAZ increased with increasing La content. The impact toughness in the simulated CGHAZ of 0.016 wt.%-La steel was the highest, owing to the high fraction of the fine-grained acicular ferrite and low fraction of M-A constituent.

Evolution of inclusions in novel cryogenic high-Mn austenitic steel weld metal with cerium addition

“… where ΔG 0 is the standard Gibbs free energy, R is the molar gas constant, T is the thermodynamic temperature and a i is the activity value. The relationship between activity and concentration can be expressed by Equation (7) [29]: where the activity coefficient f i was calculated from weld metal composition with interaction coefficients as shown in Equation (8) [30]: …”

“…where G 0 is the standard Gibbs free energy, R is the molar gas constant, T is the thermodynamic temperature and a i is the activity value. The relationship between activity and concentration can be expressed by Equation ( 7) [29]:…”