Application of Macro-Instrumented Indentation Test for Superficial Residual Stress and Mechanical Properties Measurement for HY Steel Welded T-Joints

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.

Material Properties of HY 80 Steel after 55 Years of Operation for FEM Applications

“…The chemical composition of the breakthrough structure and the material model proposal was also considered in the paper [ 2 ]. However, in CAE programs, functions are used to describe the plastic characteristic depending on the strain rate and temperature .…”

“…Steels of increased strength have been used to construct the hulls of submarines, the structure of which is exposed to high loads caused by water pressure when submerged, impacts when lying on the bottom, and the effects of explosions of underwater mines and depth bombs. Commonly used by the United States for shipbuilding in the post-war years were HY 80, HY 100, HY 130, and HY 200 [ 1 , 2 ]. In 1960, HY 80 steel was used to make the hull of the first nuclear-powered submarine USS Thresher (SSN-593), which unfortunately ended its service tragically in April 1963.…”

“…Owing to these additives, they are characterised by increased strength, good plasticity, impact strength, and corrosion resistance. Moreover, steels of this type show good weldability, making it possible to build ships in sections and then join them [ 2 ].…”

Non-destructive testing of physical and mechanical properties of local zones in welded joints

“…Currently, the instrumented indentation method has bloomed with an outburst of new techniques and devices for recording and processing indentation diagrams [1][2][3][4]. However, as follows from the existing standards (ISO 14577, GOST R 56232), only hardness and Young's modulus can be determined from these diagrams.…”

Structure, defect substructure and fracture surface of low-carbon alloy steel welds

“…High rates of development of the territories in the Far North accentuated the problem of quality of welding of metal constructions being in service at low temperatures. A fundamental task is to produce welded joint with high operating characteristics providing the increase in reliability of work of fabricated metal products under the extreme conditions [1][2][3][4][5].…”