Tadashi Kasuya

Cold Cracking Susceptibility Of Austenitic And Martensitic Weld Metals

Cold cracking susceptibility of the weld metal made with a 16 %Cr-7 %Ni wire was investigated using the y groove weld cracking test. This wire was made on an experimental basis to be applied to 980 MPa grade steel without preheating. The welding was conducted at the condition of 260 A-26 V-23 cm/min with no preheating. The test results show that no cracking was observed when the diffusible hydrogen was 1.5 ml/100 g, while some cracks were found when the diffusible hydrogen was 4 ml/100 g. And the acoustic emission monitoring showed that the cracks occurred in the weld metal after the temperature decreased below 100 °C. Since the strength of the weld metal made with this prototype wire is over 980 MPa, this wire can be a candidate for the application of 980 MPa grade steel without preheating.

Development of Welding Materials for High Heat Input Welding Compatible with Thick Steel Plates of 460 MPa Yield Point Class for Very Large Container Ships

Electrogas arc welding with high efficiency (Two-electrode Vibratory Electrogas Arc Welding, 2E-VEGA® process) and flux-cored wires for the 2E-VEGA process have been developed. They can be applied to YP460 MPa class extremely thick steel plates for very large container ships. The travel speed of the developed 2E-VEGA process is about twice as high as that of the ordinary 1E-VEGA process. Weld metal obtained with the present process and the present wires satisfied the target requirements of YP (yield point or proof stress) ≥ 460 MPa, TS (tensile strength) ≥ 570 MPa, vE−20 (−20 °C Charpy absorbed energy) ≥ 53 J and Hv (hardness number) ≤ 210 Hv in Vickers scale, even when 30 kJ/mm arc energy welding for 51 mm-thick plates was conducted. Using the present process and the present wires, sufficient fracture toughness of joints welded with high arc energy can be obtained.

Hydrogen Evolution Measurements for a Martensitic-Austenitic Weld Metal

Hydrogen evolutions for martensitic-austenitic weld metals were measured at 45 °C. The specimen without the austenite released hydrogen in about two days, and this result agrees with the 72 h holding time required by JIS Z3118. In the case of the specimens that contain the retained austenite, hydrogen release continued for about 100 days or more. We derived the analytic solution of the McNabb & Foster diffusion equation by regarding the austenitic microstructures as trapping sites to compare the experimental and calculation results, and showed that both of them are in good agreement. We also showed that the initial ratio of free and trapped hydrogen atoms is not necessarily equal to the thermal equilibrium condition at the measurement temperature, which can be analysed using the present solution.