The Kolsterising improves the wear resistance of stainless steel surface, without degrading their corrosion resistance. There are no additions of chemical elements to the steel during the process.
It is claimed that austenitic stainless steel which contain molybdenum, such as 1.4401 (316) can also have enhanced corrosion resistance after Kolsterising.The Kolsterising process does not apply a coating on the surface but is a low temperature surface carbon diffusion treatment. Although large quantities of carbon are diffused into the surface visiblechromium carbides are not formed.
The resulting surface treated layers can have hardnesses in the range of 1000 to 1200 VPN (approx 72 HRC). The thickness of the hardened layer is dependent on the process conditions used, but includes 22 or 33 micron effective case depths. Complex shapes can be effectively hardened by this process.Surface property enhancements and benefits associated with Kolsterising. The main properties enhancements from the Kolsterising process, claimed by the developers of the process includeImprovement of wear and galling resistance.
Improvement of cavitation erosion resistance
Increased fatigue strength
Good dimensional stability. There should be no degradation of corrosion resistance and the magnetic properties of austenitic stainless steel (low magnetic permeability) are not affected by the process. The pitting and crevice corrosion resistance of molybdenum containing grades like 1.4404 (316) in chloride environments is claimed to be improved by the process.
The surface hardened layer also has good toughness properties and there is no risk of delamination or peeling of the surface hardened layer.
The improvement in fatigue resistanceis due to the formation of compressive stresses in the treated surface layer, which also helps enhance the Stress Corrosion Cracking SCC resistance of Kolsterised parts.
There is little or no change in dimensions or shape when stainless steel are Kolsterised and no change in steel colour (appearance). The process can be applied to finished parts with a high standard of dimensional accuracy. These high levels of dimensional accuracy also mean that seals may not be needed, enhancing the operational temperature ranges of components with possible reductions in maintenance costs.Range of stainless steel that can be Kolsterised. A wide range of austenitic and duplex stainless steel can be treated. These include
Nickel based alloys including Hastelloy C22 and C276 and Inconel 625 and 718 can also be Kolsterised.Applications for Kolsterising The fields of application for Kolsterized surfaces includes automotive, valve manufacturing, marine, oil and gas,fastener, food/beverage, pharmaceutical and medical industries.Specifically, valve parts (balls, needles, seats and housings) in petrochemical industries, parts for NACE MR 0175 sulphide stress corrosion cracking sour gas applications and beverage filling machine pistons and seals.
Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)