A low transformation temperature (LTT) welding consumable has been developed to prevent cold cracking in high strength steel welded joints without preheating. In the LTT welded joint, the residual tensile stress is reduced by martensitic expansion of weld metal formed by the LTT consumable. In the weld cracking tests, cold cracking in the LTT weld metal is successfully prevented under high restraint conditions, but cold cracking occurs at very low joint restraint strength in case the weld metal is fully martensitic. Chemical compositions of the consumable are designed to retain austenite in martensite in the newly developed weld metal to absorb the diffusible hydrogen into the austenite to prevent cold cracking. In the newly developed LTT weld metal, cold cracking is almost fully suppressed without preheating under every joint restraint condition.

A newly developed low transformation temperature welding wire, of which the transformation start temperature is lower than that of conventional welding wires, was applied to fabrication of fillet welded T joints. The welding angular distortion and the temperature profile of the weld metal were continuously measured during the welding process. The angular distortion of the fabricated T joint was reduced when the weld metal reached the martensitic transformation start temperature. The residual angular distortion was less with the low transformation temperature welding wire than that with the conventional welding wires. The welding distortion of T joints was calculated by a numerical simulation with consideration of the effect of phase transformation under weld thermal cycles. The welding distortion was reproduced with high accuracy in the numerical simulation. Results of the numerical simulation also determined that there was a direct correspondence between the transformation expansion of the weld metal and the angular distortion.

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