Surface Hardening of Stainless Steels by Kolsterising

In many applications stainless steels need a hard and wear resistant surface. The common used austenitic stainless steels have excellent corrosion properties but very poor tribological characteristics. Depending on the demand of a high corrosion resistance there are only a few technologies to meet the necessary standard. A very successful process is the diffusion of carbon into the surface by the Kolsterising process which is done at very low temperatures so that no chromium carbides are precipitated. A high carbon content, dissolved in the lattice improves surface hardness and wear resistance by maintaining corrosion resistance. A surface hardness of over 1000 HV, a considerable improvement of wear resistance, an elimination of fretting (cold welding) and corrosion resistance in many hazardous environments are the results when Kolsterising is applied on austenitic stainless steels. Results of the influence of this hardening process on different properties of austenitic and duplex stainless steels are presented. Some examples for very successful applications of this surface treatment in different fields like automotive industry, medical industry, food processing and consumer industry are shown

New Lean Alloy Alternatives for 300 Series Stainless Steels – a Corrosion Perspective

Rising Prices of nickel and molybdenum in the past few years have led to unprecedented interest in substitution of leaner-content alloys for standard 300-series austenitic stainless steels in a lot of applications. Due to the high prices of different alloying elements and to periodic large fluctuations that cause similar large fluctuations in the costs of using 300-series stainless steels; a lot of new materials entered the markets in Europe and also in the rest of the world. A big disadvantage consists in the fact that there are a lot of corrosion results, however, a direct comparison of the corrosion resistance of these new materials does not exist up to now or only incompletely. In this project comparative investigations were carried out and always one or several representatives of a material group were incorporated. These material groups are: Lean Duplex Stainless Steels, Manganese Alloyed Austenitic and Duplex Stainless Steels and Ferritic Stainless Steels. These materials were investigated in a lot of different test procedures and in different conditions focused on the application in civil engineering and common use. Beside the electrochemical investigations all materials were exposed in different surface states in the atmosphere, once in coastal nearness and once in a city centre area. Other exposition tests with material coupons where done in the atmosphere of indoor swimming pools and at the case of food processing machines were corrosion processes are caused by the cleaning procedure. First results are reporte