日本金属学会誌

J. Japan Inst. Metals, Vol. 59, No. 8 (1995),
pp. 821-826

Relationship between Exposed Area and Dissolution Depth of α Martensiteof Type 304 Stainless Steel in H2SO4-NaCl Solution

Hidehiko Kamide and Kenji Fujitsuka

Department of Mechanical Systems Engineering, Muroran Institute of Technology, Muroran

Abstract:

The relationship between the exposed area and the dissolution depth of α martensite of type 304 stainless steel was studied to clarify the dependence of stress corrosion cracking susceptibility of 304 stainless steel on the NaCl concentration of 2.5 kmol/m3 H2SO4 solutions.
The time to failure of 20% prestrained specimen showed the highest SCC susceptibility at the NaCl concentration of 0.4 kmol/m3. The number of cracks and the crack depth decreased with increasing NaCl concentration.

The dissolution tests of α martensite induced by sub-zero treatment in liquid nitrogen were conducted in 2.5 kmol/m3 H2SO4-(0.4{~}2.0) kmol/m3 NaCl solution at Ecorr+50 mV (vs SCE). The exposed area of α martensite was measured by an image analysis computer and its dissolution depth was measured by using the focus of an optical microscope. The dissolution depth increased linearly with the logarithm of the exposed area at each NaCl concentration. The critical exposed area for corrosion initiation was estimated from this linearity by extrapolating to the dissolution depth of zero. This area decreased with decreasing NaCl concentration and at the concentration of 0.4 kmol/m3 after 14.4 ks was smaller than the exposed area of strain induced α martensite. This behaviour was dependent upon corrosion resistance of the steel in each solution.

The results show that SCC crack in this system initiates when the critical exposed area of α martensite which depends upon the chemical composition of both the steel and the solution is smaller than the exposed area of strain induced α martensite.


(Received December 13, 1994)

Keywords:

stress corrosion cracking, 304 stainless steel, H2SO4-NaCl solution, α martensite, dissolution depth, critical exposed area


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