• Journal of Welding and Joining
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• v.3 no.1
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• pp.22-31
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• 1985

Hot straining embrittlement is one of the most important factors which cause the brittle fracture initiation even in the service temperature in the case of mild steel and high tensile steel. Therefore it is necessary to analyze thoroughly the hot straining embrittlement occurred in weld HAZ of the structural steels. The behaviors of plastic deformation and fracture toughness at the notch tip of the hot strained weld HAZ in structural steels (SB 41 KS, SA 588-Grade A ASTM) have been studied by the recrystallization technique and crack opening displacement (COD) test method. The obtained results are summarized as follows; 1. The plastic zone is formed at the notch tip of weld HAZ owing to nomotonic and cyclic hot stran, and the maximum plastic strain increases with the accumulated hot straining amounts. 2. The distribution of the effective strain at the plastic deformed zone in HAZ can be determined as follows; (.epsilon. over bar $_{p}$ )$_{\chi}$=.epsilon. over bar $_{cr}$ ( $R_{/chi}$/.chi.)$^{m}$ where, .epsilon. over bar $_{cr}$ : (SB 41; .epsilon. over bar $_{cr}$ = 0.2, SA 588; .epsilon. over bar $_{cr}$ = 0.1) 3. The embrittlement of weld HAZ in SB 41 and SA 588 is influenced by hot strain, and the degree of embrittlement becomes deeper with hot straining amounts. 4. The embrittlement of weld HAZ of SB 41 is not influenced by the hot straining amounts until .epsilon. over bar $_{max}$ = 0.36, $R_{\chi}$ = 0.065mm, however the embrittlement of structure in SA 588 is considerably influenced even by a small quantity of the hot straining amounts.s.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.314-321
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• 1987

Post weld heat treatment (PWHT) of weldment of the low alloy Cr-Mo steel, in general, is carried out not only to remove residual stress and hydrogen existing in weldment but to improve fracture toughness of weld heat affected zone (HAZ). There occur some problems such as toughness decrement and stress relief cracking (SRC) in the coarse grained region of weld HAZ when PWHT is practiced. Especially, embrittlement of structure directly relates to the mode of fracture and is appeared as the difference of fracture surface such as grain boundary failure. Therefore, in this paper, the effect of heating rate on PWHT embrittlement under the various kinds of stresses simulated residual stress in weld HAZ was evaluated by COD fracture toughness test and observation of fracture surface. Fracture toughness of weld HAZ decreased with increment of heating rate under no stress, but it was improved to increment of heating rate under the stress. Grain boundary failure didn't almost appear at the heating rate of 600.deg.C/hr but it appeared from being the applied stress of 294 MPa at 220.deg.C/hr and 196 MPa at 60.deg.C/hr.