On the Weldability of High Tensile Steels by Rapid Dilatation Test

Abstract

The authors measured the transformation temperatures of some high tensile structral steels under the thermal cycle similar to that of the H.A.Z. of welded plate, using a high sensitive rapid-action dilatometer and tried to find out the correlations among the hardenabilities obtained from I.LW. maximum hardness test and Jominy test and the crack sensitivity obtained from C.T.S. test. The results are as follows :
1. Hydrogen considerably drops the end of transformation temperature down below that of virgin steel, and the increasing of the content decreases the end of transformation temperature.
2. The end of transformation temperature decrease with the increase of Dearden and O'Neill's Ceq., and the smaller the cooling rate, the larger the rate of the decrase of the end of transformation temperature. Adopting the critical temperature of under bead crack determined by cottrell, we can obtain the critical Ceq. for under bead crack which may become the smaller with increasing hydrogen content.
3. Hardness is not increased so much by adding hydrogen.
4. Jominy's hardnesses show higher values then thase of the dilatometric specimens, under the same cooling rates with Jominy test.
5. The crack sensitivity of H.A.Z. increases with The increase of the diffusible hydrogen of electrode and Ceq. of materials. This is to be construed as the decreasing of the end of transformation temperature with the increasing of hydrogen content and Ceq.. The increase of Ceq. drops the critical cooling rate for under bead crack, and the Si-Mn type steels seems to be inferior to vanity type steels.