Subzero-加工せる18-8系不銹鋼について（第2報）耐酸性

抄録

Corrosion tests were carried out on statically compressed stainless steel containing 2.00% Mn, 10.26% Ni, 18.11% Cr and 1.52% Mo. The working was done at 20° and −183°. Since the Md point of steel lies below 20° the influence of the working and that of martensite formed by subzero-working on the corrosion resistivity of such steel could be discussed separately. The corrosives used were aqueous solutions of 62.7% HNO₃, 5% H₂SO₄, 20% H₂SO₄ and 2.4% HCl in boiling conditions. Main results obtained are as follows: (1) In the solutions of 62.7% HNO₃ and 5% H₂SO₄, all specimens, except one tempered at 600° which showed low resistivity, became passive, and the resistivity was found to be almost independent of the working and the amount of martensite. (2) In the solution of 20% H₂SO₄, a specimens strongly attacked and the more the degree of working and the amount of martensite, the more strongly. The resistivity was improved by tempering up to 400°, but was markedly reduced by tempering at 600°. (3) In the solution of 2.4% HCl, little influence of working and much influence of martensite amount was found. The specimens having martensite showed lower resistivity than those free from martensite, and by tempering they behaved as in the case of 20% H₂SO₄. On the other hand, martensite-free specimens, even in a severely worked state, became more stable against HCl solution by tempering up to 600°. (4) Neither working nor strain-induced martensite affects the tendency to become passive. Hence the resistivity of the steel against concentrated nitric acid and dilute sulphuric acid is scarecely influenced by working, but under non-passive state as in the case of the corrosion in hydrochloric acid, it is reduced by working, especially by the formation of martensite caused by the working.