Effects of inclusion size and acicular ferrite on cold cracking for high-strength steel welds of YS 600 MPa grade

Abstract

The influences of microstructure and inclusion on cold cracking were studied in high-strength steel welds of YS 600 MPa grade using the Y-groove test. The weld microstructure showed a mixture of acicular ferrite, bainite and predominantly martensite. Cold crack fractography identified intergranular fracture (IF) and quasi-cleavage fracture (QCF). Bainite and martensite predominated on the surface and subsurface of IF while the QCF showed inclusions that nucleated acicular ferrite. The influence of inclusions on cold cracking can be described as follows: (i) the inclusions acted as nucleation sites of QCF, (ii) the inclusions contributed to the nucleation and growth of micro-cracks and (iii) new cracks were produced from inclusions when a crack impinged on the inclusions. Inclusions smaller than 2 μm increased the cold crack resistance by contributing to the nucleation of acicular ferrite. Inclusions larger than 2 μm increased the cold crack susceptibility by inducing crack nucleation in welds.

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

“…The interlocked AF laths or plates have a chaotic orientation, which can result in retardation for crack propagation in steel . The crack tip deformation made the crack follow a tortuosity path and increased the length of propagation, thereby absorbing more energy . It can be confirmed that the obtained interlocking AF was the main reason for maintaining high toughness of Ti–Ca deoxidized steel.…”

“…It may be noted that the crack propagation path was deflected when it passed through the interlocked AF, as shown in the upper part of Figure f. The obtained zigzag crack path can improve the low‐temperature toughness …”

The Microstructure and Property of the Heat Affected zone in C-Mn Steel Treated by Rare Earth

“…In general Al deoxidization has a great influence on the size of inclusions in RE treated steel. The size of effective inclusion which can induce the nucleation of AF are mainly 1~4 μm, which has been widely recognized [17]. From Figure 6 it can be easily found that the number percent of inclusion size of 1~4 μm in steel No.3 is less than that in steel No.2, which is adverted to the formation of AF.…”

Effect of Martensite–Austenite Constituent on Low-Temperature Toughness in YS 500 MPa Grade Steel Welds

“…The M-A constituent content was low for the CGHAZ, resulting in the large CVN value. The FGHAZ had a decreased fraction of brittle BF and increased fraction of ferrite (quasi-ferrite and AF) with excellent impact toughness [31,32]. Therefore, its CVN energy increased dramatically and Vickers hardness decreased by more than 20 Hv with an increasing ferrite fraction despite the FGHAZ having a large fraction of massive M-A.…”