Method of treating ferrous surfaces subjected to high friction strains

Method of increasing the wear resistance and the corrosion resistance of opposed bearing surfaces of parts subjected to severe reciprocal friction, when the product of the pressure distributed over the bearing surfaces by the relative speed of the latter exceeds 0.4 MPa.m/s, said method being suitable for ferrous metal parts made of iron, additional metallic elements and carbon, with a minimum concentration by weight of 2.5% of additional metal elements or 0.45% by weight of carbon, said method comprising:

• effecting thermochemical diffusion of nitrogen to harden the bearing surfaces by nitriding or nitrocarburizing in a molten salt bath at a temperature of 570.degree. C..+-.15.degree. C. followed by performing a reaction providing resistance to wet corrosion, and wherein:
• (i) said nitriding or nitrocarburizing molten salt bath is made up of alkaline carbonates and cyanates and further contains sulfur-containing substances in the following percentages by weight:
• 30%<CNO<45%
• 15%<CO.sub.3.sup.2- <25%
• 15%<›NA.sup.+ ! Na.sup.+ <25%
• 20%<K.sup.+ <30%
• 1%<Li.sup.+ <6%
• 1 ppm<S.sup.2- <100 ppm
• (ii) the time for which said parts are immersed in said nitriding or nitrocarburizing molten salt bath is between 15 minutes and 45 minutes, to thereby obtain a nitride surface layer of the parts ranging between 10 and 20 .mu.m, and an equivalent hardened depth, measured from a hardened steel surface under said nitride surface layer, ranging between 20 and 120 .mu.m;
• and
• (iii) said reaction providing resistance to wet corrosion is a chemical surface reaction selected from the group comprising oxidizing reactions and phosphating reactions.