Keiji Koterazawa

Relation between sensitization and stress corrosion cracking in prior cold-worked SUS 304 steel.

The effect of sensitization on stress corrosion cracking (SCC) of prior cold-worked SUS 304 steel was investigated in boiling 35% MgCl2 solution, and the results were compared with the behavior of intergranular corrosion obtained by Strauss test.The mechanical properties of cold-worked specimens were affected markedly by annealing temperature as compared with annealing time. The cold-worked specimen showed the maximum mechanical strength by annealing at 637K, above which the strength gradually decreased with increasing annealing temperature. The region of sensitization in T-T-S curves shifted to the lower temperature side with increasing prestrain. The susceptibility to intergranular corrosion became maximum at 20% prestrain, but it decreased at 40% prestrain. The susceptibility to SCC of the prestrained specimens increased with increasing annealing temperature and time, and this tendency was consistent with that in the above-mentioned mechanical strength. The susceptibility to intergranular cracking in boiling 35% MgCl2 solution decreased for the specimens treated in the region of sensitization, and this result was not consistent with that of intergranular corrosion behavior in Strauss test solution.

Effects of cold work on Hydrogen induced cracking and hydrogen embrittlement of iron single crystal.

The effects of cold work on Hydrogen induced cracking (HIC) and hydrogen embrittlement (HE) of iron single crystal were studied by cathodic charging tests with or without loading. The hydrogen induced cracks were produced at six kinds of {110} planes in the annealed specimen, while those cracks were produced at both primary and secondary slip planes in the prestrained one.When the stress more than the threshold one was applied, many hydrogen induced cracks were produced at the (110) plane, which was nearly perpendicular to the loading axis, in both the annealed and prestrained specimens. These hydrogen induced cracks connected each other with dimple or quasi-cleavage cracks, and then the specimen finally fractured due to hydrogen embrittlement.

Mechanical Properties of Rapidly Stretched Copper and Copper Alloy

This investigation has been conducted to make clear the effect of strain rate on the internal structure and the mechanical properties of rapidly stretched copper and copper alloy.Tough pitch copper, 7/3 brass and free cutting brass specimens have been used in this study.The main results obtained are as follows;(1) The strain rate sensitivity of mechanical properties is recognized in annealed and prestretched specimens of tough pitch copper, 7/3 brass and free cutting brass. Their yield strength, tensile strength and elongation increase with increment in their strain rate.(2) It is proved that the work of hardening has been more effectively made in the rapidly stretched tough pitch copper than in the statically stretched material.(3) Concerning 7/3 brass and free cutting brass, there is little difference in the effective work of hardening it between the case in the rapidly stretched specimen and that in the statically stretched one.

Fatigue Strength of Rapidly Stretched Stainless Steel

This investigation has been conducted to make clear the effect of strain rate at pre-stretching on the fatigue strength. The 18%Cr-8%Ni stainless steel has been used for specimens in this study.The specimens pre-stretched 30% rapidly have presented high fatigue limit than the specimens pre-stretched 30% statically.It is recognized that this fact is due to higher amount of promoting martensite transformation in the case by rapid pre-stretching than in the case by static pre-stretching.

Mechanical Properties of Rapidly Stretched Aluminium and Aluminium-Magnesium Alloy

This investigation has been conducted to make clear the effect of strain rate on the internal structure and the mechanical properties of rapidly stretched aluminium and aluminium-magnesium alloy. Pure aluminium (99.99% Al) and aluminium-magnesium alloy (4.65% Mg) specimens have been used in this study. The main results obtained are as follows;(1) The yield strength and the tensile strength of pure aluminium in rapid tensile testing are larger than that in static tensile testing. The strain rate gives a remarkable effect on the resistance in deformation of pure aluminium.(2) The yield strength of aluminium-magnesium alloy in rapid tensile testing is larger than that in static tensile testing, but the tensile strength in rapid tensile testing is smaller than in static tensile testing.(3) The yield strength, the tensile strength and the hardness of rapidly pre-stretched pure aluminium are larger than those of statically pre-stretched sort. It is recognized that this fact is mainly due more to the promoted recovery by static pre-stretching at room temperature than to rapid one.(4) An interesting observation worth mentioning in the static tensile testing of the aluminiummagnesium alloy is that after a certain strain is reached the load starts to oscillate, but in the rapid tensile testing, it is not recognized.(5) The yield strength of rapidly pre-stretched aluminium-magnesium alloy is smaller than that of statically pre-stretched sort, and the tensile strength of the rapidly pre-stretched is almost the same as that statically pre-stretched.