Evaluation of fracture strength and material degradation for weldment of high temperature service steel using advanced small punch test

This paper presents an effective and reliable evaluation method for fracture strength and material degradation of the micro-structure of high temperature service steel weldment using advanced small punch (ASP) test developed from conventional small punch (CSP) test. For the purpose of the ASP test, a lower die with a minimized Φ1.5 mm diameter loading ball and an optimized deformation guide hole of Φ3 mm diameter were designed. The behaviors of fracture energy (E_sp), ductile-brittle transition temperature (DBTT) and material degradation from the ASP test showed a definite dependency on the micro-structure of weldment. Results obtained from ASP test were compared and reviewed with results from CSP test, Charpy impact test, and hardness test. The utility and reliability of the proposed ASP test were verified by investigating fracture strength, behavior of DBTT, and fracture location of each micro-structure of steel weldment for test specimen in ASP test. It was observed that the fracture toughness in the micro-structure of FL + CGHAZ and ICHAZ decreased remarkably with increasing aging time. From studies of all micro-structures, it was observed that FGH AZ microstructure has the most excellent fracture toughness, and it showed absence of material degradation.     

Environmental strength evaluation of welded steel joint in seawater

A study on corrosion fatigue was experimentally conducted for the as-welded and PWHT specimens of the steels, HT80 and SM53B in 3.5% NaCl solution. Submerged arc welding was done. PWHT was carried out at comparatively high temperature of 650° C. Besides, in order to simulate the residual stress in weld HAZ, the stress of 98MPa was applied during PWHT. Corrosion fatigue crack growth was dependent upon the materials and PWHT conditions. In the case of HT80, crack growth in corrosion environment was faster than that in air. However, the crack growth of the main crack for SM53B in 3.5% NaCl solution was decreased in comparison with that in air, unlike HT80. The sensitivity to corrosion environment was reduced due to PWHT. The applied stress in HAZ during PWHT acted to enhance the crack growth compared with that of the PWHT specimen without stress.     

Environmental strength evaluation of welded steel joint in sea water

Corrosion fatigue crack growth behaviours were experimentally evaluated for the parent metal, as-welded and PWHT specimens of SM53B steel. Multi-pass welding was done by a submerged arc welder. Metallographic observations along the weld fusion boundary were made to investigate the variation of microstructures through the thickness direction. PWHT was carried out at 650°C with holding time of 1/4hr and 40hr. The corrosion fatigue test was conducted in 3.5% NaCl solution with the frequency of 3Hz. In all cases, crack growth in corrosive environment was faster than that of in air. Besides, at the low †K region, crack growth was greatly influenced by corrosive environment and the heat treatment condition.