引張強度50kgf/mm^2級高張力鋼溶接熱影響部の限界CTODに及ぼす局所脆化域の影響

概要

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An investigation was made to clarify the influence of Local Brittle Zone (LBZ) on critical CTOD (δc) of multi-pass weld Heat-Affected Zone (HAZ) and metallurgical factors controlling the toughness of the LBZ by using four HT50 structural steels of various chemical compositions. The multi-pass welded joint exhibited low δc in case the fatigue-crack front of a COD specimen reached LBZ. The LBZ was identified to be a grain-coarsened zone reheated between Ac_1 and Ac_3 by the subsequent welding pass. Simulated HAZ with double thermal cycle reproduced the main microstructure of the LBZ. In the simulated HAZ COD test, cleavage fracture was initiated from a high carbon-martensite-island formed by the reheat-thermal cycle. By temper-thermal cycle due to further welding pass, the martensite-islands were decomposed into cementite-ferrite aggregates to various degree, depending on the chemical compositions of the steels. The higher degree of the decomposition resulted in the greater increase in δc- Close correlation was found between the minimum value of the measured δc in the welded joints and δc of the simulated HAZ with triple thermal cycle.
社団法人日本鉄鋼協会の論文
1988-06-01