Hui-Jun Yi*, Yong-Jun Lee, Jong-Yun Kim and Sung-Su Kang
The Journal of Mechanical Science and Technology, vol. 25, no. 9, pp.2185-2193, 2011

Abstract : The effects of the microstructural constituents, chemical composition, and retained austenite on high-strength weld metal were studied using preheat-free steels and GMAW solid wires with a low hydrogen content. The cold cracking susceptibility of these GMAW wires was evaluated using the y-groove Tekken test. The results showed that acicular ferrite produced the greatest resistance to cold cracking and that the microstructure of the deposit was more important than the hardness and diffusible hydrogen content in low-hydrogen weld metal. Crack blunting and branching occurred when a crack propagated through fine acicular ferrite because of the fine interlocking nature of the microstructure. Alloying elements for nucleating acicular ferrite, such as Ti, Al, and V, are required for proper austenite grain size, and sequence of inclusion formation was identified in the present paper. Furthermore, the retained austenite was not found to play the role of a hydrogen trapping site and so had no effect on the cold cracking susceptibility at a low preheating temperature (≤100℃) and low heat input (≤1.5 KJ/mm) to the weld metal.

Keyword : Weld metal; Cold crack; Acicular ferrite; Grain size; Retained austenite