Effect of Heat Input on Microstructure and Impact Toughness of Coarse‐Grained Heat‐Affected Zone in Al–Ca and Ti–Ca Killed Steels

Abstract

The microstructural evolution and toughness properties of simulated coarse‐grained heat‐affected zone (CGHAZ) in Ti–Ca killed steel with different heat input are studied and compared with Al–Ca killed steel. It is found that the impact toughness of CGHAZ in Ti–Ca killed steel with heat inputs of 50, 100, and 200 kJ cm−1 is ≈129, ≈105, and ≈44 J, respectively. However, the toughness of Al–Ca killed steel decreases from ≈28 to ≈23 J and then to ≈18 J. In Ti–Ca killed steel, Ti–Ca–Al–Mn–S oxides with appropriate size of ≈0.3–2 μm effectively promote the nucleation of acicular ferrite (AF). In addition, the high‐density number of ≈1329 inclusions mm−2 is one of the most important reasons for the formation of AF. However, dominant Al–Ca–Mn–S oxides in Al–Ca killed steel cannot effectively promote the nucleation of AF and mainly act as a potential propagation site of impact crack. In Ti–Ca killed steel, predominantly interlocked AF with high‐angle grain boundaries and high‐density of dislocations remarkably improves the toughness of CGHAZ.

Effect of Zr addition on toughness in the simulated heat-affected zone of high-titanium low-alloy steels

“…In Figure 12(b,d), the volume fraction of AFs was increased to 61.2% in the T1 steel and 73.5% in the Z1 steel after the thermal simulation welding with a heat of 300 kJ cm −1 . AFs played an essential role in changing crack propagation direction [32,33]. FSPs and PFs were the primary nucleated ferrite on the grain boundary of the austenite, which was not a desirable microstructure to enhance the toughness of steel [34][35][36].…”