Abstract ▼ AI-Helper

When doing high heat input welding of TMCP steel, we can expect softening zone is made and hardness of weldment is decreased. In this paper, accelerated cooling effect of TMCP steel is compared with SM50YB steel. The properities of weldment which has softening zone are investigated with newly develo...

When doing high heat input welding of TMCP steel, we can expect softening zone is made and hardness of weldment is decreased. In this paper, accelerated cooling effect of TMCP steel is compared with SM50YB steel. The properities of weldment which has softening zone are investigated with newly developed SP test and examine the possibility of recovering for softening zone by Post Wled Heat Treatment. The result of this study can be summarized as follows: 1. As a result of studing an object of the orientation dependence behavior between the base metal microstructure of TMCP steel and SM50YB steel, we know that the orientation dependence behavior of the fracture toughness value for the each orientation of TMCP steel is smaller than SM50YB steel 2. From the result of the hardness distribution and SP displacement distribution under room temperature for weldment of TMCP steel, we identify that softening zone of HAZ microstructure by weld heat cycle. We can expect that the toughness is decreased. 3. The result of (DBIT)sp move for the high temperature than base metal with the turn of HAZ, fusion line, weld metal. And the uppershelf energy in SP energy dependence curve of HAZ microstructure is lower than base metal, therfore, we identify that the lower hardness by softening in HAZ microstructure. 4. In doing the PWHT about the weldment of TMCP steel, hardness of softening zone with the several condition (600℃ water cooling after 15 min. (holding time), 720℃ air cooling after 15 min., 850℃ air cooling after 15 min., 850℃ 1 sec water cooling after 15 min.) is recovered up to base metal and SP test shows that the toughness is also recovered. 5. SP Ductile-Brittle Transition Temperature(DB1T_sp) of the HAZ microstructure in weldment under the condition of 850℃ water cooling after 1 sec, is similar to the base metal. By PWHT which is suitable for welding condition, then we know that recovering a softening zone is possible.

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