Improvement Of The Treatment Technique Of Electrochemically Induced Surface Annealing

Electrochemically induced surface annealing (EISA) is a new phase transformation behavior discovered recently in metastable austenite stainless steels. The deformation induced martensite in metastable austenite stainless steels effect their physical and chemical properties. The martensite can be removed by electrochemical treatment, and the hardness of cold-worked stainless steel can be maintained. Methods such as XRD, hardness analysis are employed in this thesis. The results verify that saturated solution of Na₂CO₃ and K₂CrO₄ are good medium for EISA treatment, and the pitting resistance of stainless steel treated in the solutions of Na₂CO₃ and K₂CrO₄ increases a bit, and the effect of factors such as time, temperature, concentration of medium and the widthes of positive and negative impulse on the no-immersion EISA of stainless steel are also studied. The results show that the martensite content decreases with the increase of the no-immersion EISA time and almost keeps constant after 8 hours. When the temperature raises, the change trend of content of martensite after the no-immersion EISA is like parabola. When the concentration of NaNO₂ is less 6M, there is litter effect on the content of martensite; when the concentration of NaNO₂ is 6-9M, the content of martensite will decrease by the no-immersion EISA. In the positive 60-280s and negative 30-280s, the surface content of martensite will decrease treated 8 hours by EISA. The results of impulse width show that hardness of samples treated with the no-immersion EISA do not change with the content of martensite and pitting resistance is improved.