Cracking Parameter of High Strength Steels related to heat affected zone cracking

Abstract

Weld cracking susceptibility, or simply, weldability, is a most significant problem in utilizing high strength steels.
A new formula, based on the result of restraint weld cracking test, is herein proposed for the calculation of the cracking parameter Pc:
Pc=C, %+Si, %/30+Mn, %/20+Cu, %/20+Ni, %/60+Cr, %/20+Mo, %/15+V, %/10+5B, %+t, mm/600+H, cc/100g/60
(t: plate thickness, H: diffusible hydrogen in weld metal)
Cracking parameters calculated from this formula have a good correlatioh with the test data obtained from the y-groove restraint carcking tests using 200 types of high strength steel.
The carbon equivalents adopted in JIS and the result of weld carcking tests correspondingly indicate that the steel with higher carbon equivalent is more susceptible to weld cracking. However, data are scattered so widely that the carbon equivalents cannot be applied for estimating weld cracking susceptibilities of high strength steels.
Since the carbon equivalent specified in JIS does not include the terms of diffusible hydrogen and plate thickness, even the steels with the same carbon equivalents reveal a higher cracking susceptibility when their diffusible hydrogen content or plate thickness value increases.
Comparing with some typical carbon equivalents, which have been suggested so far, Pc's present the best agreement in predicting the weld cracking susceptibilities.
Although there is a weak trend that the higher the maximum hardness in HAZ, the higher the weld carcking susceptibility is, the maximum hardness does not represent strictly the weld cracking susceptibility.
The relationship is investigated between cracking parameters, Pc's, and the preheating temperature to prevent weld cracking and the following equation is obtained.
T(°C)=1440 Pc-392