Use of suliphiding by electroerosion alloying method for scuff resistance increase of steel and cast iron parts friction surfaces

Abstract

There is known a sulphiding method that prevents seizing, and provides creating a film of sulfides on a part surface. The sulfides increase the surface activity of metals and alloys, as well as the process of wetting the surfaces with active agents, and they also increase seizing resistance. An iron sulfide (FeS) film increases wearing resistance of friction surfaces and improves running-in adility thereof. A ferro - sulfide coating has relatively high porosity and it absorbs a large amount of grease providing the material with the self-lubricating property. Traditionally, a sulphiding method is a process of saturating a metal surface layer (of steel, cast iron, titanium alloys, etc.) with sulfur in appropriate salt baths. A depth of a sulphided layer is up to 50 microns. Besides increasing a surface roughness and dimensions of a part being processed, the disadyantages of the conventional sulphiding method includes the neces sity to heat the entire part, and accordingly, the structural changes of metal, distortions and warpage, large processing time, high consumption of electricity, negative impact on the environment, and others. A new method for sulphiding steel and cast iron part surfaces by electroerosion alloying (EEA) with the use of a special electrode is proposed, which method is characterized in that while manufacturing the electrode, on its surface, in any known manner (punching, threading, pulling, etc.), there is formed at least a recess to be filled with sulfur as a consistent material, and then there is produced EEA by the obtained electrode without waiting for the consistent material to become dried. In the course of the sulfur saturation (sulphiding) process of the surfaces of steel 20 and ductile cast iron by EEA method with the use of a special electrodetool made of stainless steel 12X18H10T (12H18N10T) at the device of "Elitron - 22A" model, with increasing discharge energy from 0.02 to 0.55 J, the sulphided layer depth increases from 10 to 75 microns, and the surface roughness Ra increases from 0.7-0.8 to 6.2-6.7 microns. With deepening, the sulfur concentration is gradually reduced from 0.60-0.85 and 0.50-0.85 % on the surface, respectively, for steel 20 and ductile cast iron, and also respectively, from about 0.05-0.06 and 0.04-0.05 % at the depth of 75 microns. An amount of alloying elements of the electrode-tool made of steel 12X18H10T (12X18H10T), i.e. chromium, nickel and titanium, gradually decreases with deepening the coating for steel 20, respectively, from 16, 9, 9, and 0.9% on the surface to 1.2 and 0.2 % at the depth of 60 microns.