低合金強靭鋼の熔接の研究(第1報)

Abstract

In the study of oxy-acetylene gas cutting of low alloy high strength steel, the relation between crack sensitivity of heat affected zone and following subjects are researched applying bending tests.Gas cutting speedPre-heating temperaturePost-heating temperatureHardness of mother steelCondition of cutting surfaceComposition of steeletc.Experiments are made in this study, in order to know the metallergical nature of heat affected zone and its effect for weldability of mother steel. Following results are shown by these experiments.1. Increase of bending angle in bending test and decrease of maximum hardness at heat affected zone show that 100°C pre-heating gives remarkable effect to improve the crack sensitivity of steel.2. 200°C or over 400°C post-heating gives effect for the decreasing of crack sensitivity value, through 100°C pre-heating gives better effect.300°C post-heating which belongs to the range of temper brittleness should be avoidable.3. Less cutting speed gives better bending effect generally.4. Less hardness by high tempering temperature gives better bending effect to mother steel, just same as the effect of post-heating temperature. 300°C tempering gives less bending effect.5. Removing of cutting carf makes bending effect a little better, despite removing of heat affected zone gives remarkable effect.6. Value of bending test of rolled steel is far higher than cast steel.7. X-ray spectrochemical analysis and michro-structure proof the increase of Ni, Cu, Mo content and the decrease of C, Cr, Mn content on the gas cutting surface.8. It is suposed that the cementite zone and the high carboned zone inside made by carbon defusion out of mother steel.9. It became clear that the application of suitable gas cutting is quite effective for the welding edge of low alloy high strength steel.