A Review on Inclusion-Assisted Microstructure Control in C-Mn and Low-Alloy Steel Welds

Abstract

Inclusion-assisted microstructure control has been a key technology to improve the toughness of C-Mn and low-alloy steel welds over the last two to three decades. Microstructure of weld metals and heat-affected zone (HAZ) is refined by different inclusions, some of which work as a nucleation site of acicular ferrite or intragranular ferrite and some of which as pinning particles against the grain growth of austenite. In the present paper, mechanisms proposed for intragranular ferrite formation in weld metals and HAZ are reviewed and the feasibility of each mechanism is examined. Factors affecting the intragranular ferrite formation in weld metals and HAZ are compared to find consistent explanation applicable to the both. As the result, by considering the difference of microstructural characteristics between weld metals and HAZ, rational, self-consistent explanations are given to why lattice matching is preferred when acicular ferrite is formed on inclusions in weld metals and why manganese depletion works only in HAZ for the formation of polygonal intragranular ferrite.