サブ・ゼロ溶接法について(第1報)

Abstract

It is well known that in the case of welding high strength steel rapid cooling causes embrittlement and cold cracking in HAZ, on the other hand slow cooling causes softening in it. And the hgher the strength of steel, the more difficult it is to get enough notch toughness of weld metal as that of base metal. The purpose of this study is to weld high strength steel by austenitic steel electrode wire in order to get high weld-ing speed. And proof stress of austenitic weld metal is to be increased by refrigeration (sub-zero treatment) and aging after welding. As a rseult of the preliminary experiment by cast specimens, it was found theat the cast steel of composition of 17.5% chromium equivalent and 9% nickel equivalent will be increased in its strength and hardness by refrigeration and aging. And welded steel plate could locally be refrigerated by methylalcohol and dry ice mixture or by liquid nitrodgen.As results of sub-zero welding of HT-80 high strength steel, the following mechanical properties of weld metal were obtained after refrigration at -50°C;0.2% proof stress, 68kg/mm2tensile strength, 113kg/mm2elongation, 12%Charpy impact value, 2.8kg:-m/cm2 (at 0°C and -80°C)And the mechanical properties of weld metal refrigerated at -72°C and aged at 450°C for one hour were as follows;0.2% prooof stress, 100kg/mm2tensile strength, 126kg/mm2elongation, 15%Charpy impact value, 2.4kg-m/cm2 (at -80°C)