Effect of immersion in corrosion medium on mechanical properties and sulfide corrosion susceptibility of 80kg/mm2 class high strength steels
1968 Volume 37 Issue 8 Pages 810-816
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1968 Volume 37 Issue 8 Pages 810-816
We discussed the embrittlement of 80 kgl/mm2 class high strength steels which occured when they were immersed in a 0.5% acetic acid solution saturated with H2S at the temperature of 35°C, and about the effect of immersion in this solution on the time to failure of sulfide corrosion cracking.
When test pieces were immersed in the solution, the elongation and reduction-of-area diminished with immersion time, but the yield stress and tensile strength did not practically change.
The test pieces which had become brittle by sufficient immersion in the solution recovered their ductility by ageing at 50°C. As this phenomenon occurs by discharging of absorbed hydrogen during the ageing, it is confirmed that the embrittlement occurring in the solution is due to the diffusible hydrogen absorbed in steel.
The volume of hydrogen absorbed in steel increased with immersion time in the first stage of immersion, but after very long immersion it decreased with immersion time because of the lowering of corrosion rate due to the disturbance by the accumulated corrosion products on the surface of test piece.
Time to failure, grew shorter by the immersion of test piece in the above solution before sulfide corrosion cracking test. The differences in time to failure between as-received pieces and immersed pieces became larger with a decrease of applied stresses, though the periods of immersion were the same (48 hours). When the applied stress was 20kg/mm2, the difference increased up to the value of 12300 minutes.
In the region of applied stress below the value of 45kg/mm2, the time-to-failure of test pieces which were aged at 50°C after the immersion coincided nearly with that of the as-received test pieces. But in the region of applied stress above the value of 45kg/mm2, they did not coincide with each other.
Judging from the above fact, it was estimated that the shortening of the time-to-failure of immersed test piece in the region of applied stress below the value of 45kg/mm2 was mainly due to the diffusible hydrogen absorbed in steel during the immersion.
