高張力鋼熔接部의 低溫균열 感受性에 關한 硏究 = A Study on Cold Cracking Susceptibility of HT-80 Steel Weld Metal

다국어 초록 (Multilingual Abstract)

Recently, increasing of strength of weld metal there is every indication that the cracking occurs within the weld metal of the welded joint.
In this research, effect of preheating and diffusible hydrogen on the crack susceptibility of HT-80 steel weld metal was conducted by LB-TRC test(modified the original TRC test) and crack phenomena from restraint stress and hydrogen effect were also conducted by fractographic investigation.
The main conclusions are summarized as follows :
1) Lower critical stress curve obtained from LB-TRC was very similar to the original TRC test results and influences of root gap were not observed.
2) Lower critical stress was increased with increasing preheating temperature but decreased when diffusible hydrogen increased.
Fracture time was prolonged by increasing preheating temperature.
3) Lower critical stress for two pass welding was lower than one pass welding.
4) For the low stress fracture mode, crack was initiated at the root zone of the weld metal, and then grew in dendrite and finally fractured at the upper zone of the weld metal in shear lip pattern. But in the case of high stress, Shear lip pattern was observed inner zone of the weld metal.
5) Fractographical results show different fracture mode for individual stress applied on the weld metal. Fracture mode observed was intergranular crack and quasi cleavage crack including river pattern which is typical delayed cracking due to hydrogen influence.