| Abstract |
| During fabrication and operation of the industrial steel structures, many defects and/or cracking occurred mainly in the weldments. Various causes can exist but the initiation and propagation of HAC(Hydrogen Assisted Cracking) in the weld HAZ(Heat Affected Zone) must be prevented because of its characteristics of catastrophic failure. This study described an investigation of a possible mechanism of HAC in the conventional structural steel weld HAZ. Proposed mechanism was based on simulation of PMHAZ(Partially Melted HAZ), cracking test of HAZ, diffusible hydrogen content. thermal history of welding, preheat treatment and the extensive microstructural and fractographic examinations. The fracture surface had mixture of intergranular and/or quasi-cleavage and/or microvoid coalescence morphologies which are typical in the hydrogen related fracture surface. The fracture mode was related to the stress intensity and hydrogen content at crack tip. HAC occured by microscopic plasticity. HAC initiated in the PMHAZ of martensite/bainite structures with concentrated hydrogen content along the melted and resolidified grain boundary, and propagated along the fusion line adjacent to the PMHAZ. |
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| Key Words |
| HAC, PMHAZ, Microscopic plasticity, Stress intensity factor, Weld thermal cycle. Fracture morphology, Gleeble simulation, Diffusible hydrogen concent, Implant cracking test |
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