Cold Cracking Susceptibility of Steel Welds and the Development of a Preheat-free 980MPa Grade Welding Wire

摘要

The methods to predict critical preheat temperature such as AWS D1.1 have used carbon equivalent and diffusible hydrogen as factors of cold cracking susceptibility, but there still exist some differences among them. In this paper, these factors have been considered from a viewpoint of the reduction of preheat temperature for high strength steels. The good relation between carbon equivalent and ideal critical diameter implies the tendency that the high strength steels need high preheat temperatures. The effect of hydrogen is proved to be logarithmic and because of this effect the preheat-free welding of 780MPa grade steels is considered possible with the sufficiently low hydrogen content like 0.5ml/100g. The retained austenite traps hydrogen and is expected to reduce actual hydrogen content that causes cold cracking occurrence. By utilizing the retained austenite a prototype wire shown in this paper can be applied to the welding of 980MPa grade steels without preheating in the case of 1.5ml/100g hydrogen content, which is more practical hydrogen level than 0.5ml/100g.