Metallurgical features of steel plates with ultra fine grains in surface layers and their formation mechanism

Abstract

Steel plates with heavy gauge, which are mainly applied to large steel structures, are consequently subject to improved low-temperature toughness as well as weldability by the application of general TMCPs. The advanced TMCP has been developed so as to industrially manufacture SUF (Surface layers with Ultra Fine grains) steel plates with high crack arrestability in avoiding unexpected catastrophic damage of large steel structures. The advanced TMCP is characterized by the accelerated cooling in the midst of rolling followed by controlled rolling in the reheating process, while the general TMCPs are described by the controlled rolling in air cooling followed by various types of accelerated cooling after the rolling. Mechanical properties governed by metallurgical features of surface layers are extremely improved by the adoption of SUF steel plates. In addition, the formation mechanism of ultra fine grains in the surface layers of SUF steel plates are discussed from metallographic viewpoints.