The effect of nitrogen additions upon the pitting resistance of 18 pct Cr, 18 pct Mn Stainless Steel |
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Authors: | A G Hartline |
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Affiliation: | (1) Bar Products Division, Allegheny Ludlum Steel Corporation, 12189 Watervliet, N. Y. |
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Abstract: | The effect of nitrogen additions upon the pitting resistance of 18 pct Cr, 18 pct Mn stainless steel has been investigated
by potentiokinetic techniques in a 1000 ppm NaCl solution. Nitrogen additions increased the pitting resistance of the steel
irrespective of structure, however, the ferritic steel was less pit resistant than the (duplex) steels containing both austenite
and ferrite which, in turn, were less pit resistant than the totally austenitic steels. For steels having a duplex structure,
the effect of nitrogen on the pitting resistance was observed to follow a linear function of the relative amount of austenite
in these steels due to the area effects of the austenite and ferrite which are galvanically coupled in these steels. The addition
of nitrogen was found to increase the amount of austenite at a rate of approximately 200 times the percent nitrogen addition
from 36 pct austenite for the 0.02 pct N steel to 100 pct for the 0.40 pct nitrogen steel. The addition of nitrogen to the
totally austenitic steels increased the pitting resistance at the rate of approximately 0.31 volts per pct nitrogen added,
but no mechanism was found for the increased resistance.
This paper is based on a presentation made at a symposium on “New Developments in Ferritic and Duplex Stainless Steels,” held
at the Fall Meeting in Cleveland, Ohio, on October 19, 1972, under the sponsorship of the Corrosion Resistant Metals Committee
of TMS-IMD and the Corrosion and Oxidation Activity of the ASM. |
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