Study On Surface Precipitation Hardening Stainless Steel

Stainless steel is a generic term for a family of corrosion resistant alloy steels containing 10. 5% or more chromium. In addition to chromium, nickel, molybdenum, titanium, niobium and other elements may also be added to stainless steels in varying quantities to produce a range of stainless steel grades. In comparison with other four kinds of stainless steels (austenitic, ferritic, duplex and martensitic), the precipitation hardening stainless steel (PHSS) combines highest strength and hardness with good corrosion resistance, and is suitable for easy fabrication, but the use of PHSS is limited because of its more expensive cost.A kind of new surface precipitation hardening stainless steel (SPHSS) , which has a similar property with PHSS is developed on the surface of iron or plain steel by use of Double Glow Surface Technology. The SPHSS is composed of base materials (iron or plain steel) and the surface alloyed layer based on them, containing the alloy elements of Cr, Mo, Ni and Co. The process of SPHSS, consisted of double glow plasma surface alloying (Xu-Tec Process), solution treatment, cold treatment and aging, is introduced in this paper.Experimental results show that: (1) using power metallurgy alloy Co55Cr25Ni5Mol5 as source material, the composition of the top alloyedlayer on the surface of iron is about Co24Crl3Ni4Mo4, similar with the composition of Martensitic PHSS; (2) supplied in a solution treated condition, the structure of alloyed layer is composed of plate martensitic with hardness of 230-300HV (in which it is machinable) and can be hardened in a single low temperature ageing process (450-600HV) ; (3) SPHSS is moderated to better wear resistance and excellent corrosion resistance in 5%HCL solution than pure iron and OCrl8Ni9, and its corrosion resistance in 5%NaCl solution is comparable to grade of OCrl8Ni9 and pure iron.The extraordinary and unique properties of SPHSS, especially its lower price, will make these exceptional alloy materials of construction in many industries in the future.