Abstract
HY-80 and HY-100 steels, widely used in constructing large ocean vessels and submarine hulls, contain mixed microstructures of tempered bainite and martensite and provide high tensile strength and toughness. Weld integrity in HY steels has been studied to verify and optimize welding conditions. In this study, the T-joint weld coupons, HY80 and HY100, were fabricated from HY-80 and HY-100 steel plates with a thickness of 30 mm as base metals by submerged-arc welding. Flux-cored arc welding was performed on an additional welding coupon consisting of HY-100 to evaluate the effect of repair welds (HY100RP). Microstructures in the heat-affected zones (HAZ) were thoroughly analyzed by optical observation. Instrumented indentation testing, taking advantage of local characterization, was applied to assess the yield strength and the residual stress of the HAZ and base regions. The maximum hardness over 400 HV was found in the HAZ due to the high volume fraction of untempered martensite microstructure. The yield strength of the weld coupons was evaluated by indentation testing, and the results showed good agreement with the uniaxial tensile test (within 10% range). The three coupons showed similar indentation residual stress profiles on the top and bottom surfaces. The stress distribution of the HY100 coupon was comparable to the results from X-ray diffraction. HY100RP demonstrated increased tensile residual stress compared to the as-welded coupon due to the effect of the repair weld (323 and 103 MPa on the top and bottom surfaces). This study verifies the wide applicability of indentation testing in evaluating yield strength and residual stress.
Highlights
HY-80 and HY-100 steels are quenched and tempered low-alloy steels that were developed for the construction of large ocean vessels and submarine hulls [1]
Many studies have shown the effect of repair welding on residual stress distribution in different materials [16,17,18,19]
This paper investigated the mechanical properties and residual stress in a T-joint weld fabricated from HY-80 and HY-100 and a T-joint weld of HY-100 repaired with flux-cored arc welding
Summary
HY-80 and HY-100 steels are quenched and tempered low-alloy steels that were developed for the construction of large ocean vessels and submarine hulls [1]. As a result of quench hardening followed by tempering, HY series steels show mixed microstructures of tempered bainite and martensite [2,3]. These steels are designed to provide better tensile strength and toughness with high ductility compared to conventional carbon steels with lower weight, and they offer better structural performance. Many studies have shown the effect of repair welding on residual stress distribution in different materials [16,17,18,19]. The effects of the stress and welding on the J-R curve and crack propagation have been investigated [20,21,22,23,24]
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