Study on Slurry Paste Boronizing of 410 Martensitic Stainless Steel Using Taguchi Based Desirability Analysis (TDA)

Introduction

Boronizing is a thermo-chemical process of diffusing the boron atoms into a metal or an alloy to obtain the desired degree of surface hardness, corrosion and wear resistance. The boriding of steels often produce a single phase (Fe₂B) or a double phase boride layer (Fe₂B + FeB) and many methods are available to form hard boride layer on the ferrous alloys. The boronized metal parts are extremely wear resistant when compared to the parts subjected to hardening, carburizing, nitriding or nitrocarburizing. Further the process is highly resistant to galling and thermal spalling.

The martensitic stainless steel is generally used in applications involving corrosion and wear resistance like gas turbine blades, bushings, valves and mine ladder rungs. The mechanical properties of martensitic stainless steel were observed to degrade in the temperature range of 400°C to 580°C. The process of boronizing could improve the surface properties of grade 410 martensitic stainless steel. The thickness of the boride layer was observed to depend on the process duration and temperature. Further a parabolic relation was observed between the boronizing time and boride layer thickness (Tabur et al., 2009; Uslu et al., 2007). Electrolytic boronizing could improve the surface hardness of titanium by forming a layer of titanium boride (Huang et al., 2013). The formation of a mono-phase Fe₂B layer on boronized AISI 4140 Steel was observed to improve the wear rate and the coefficient of friction (Joshi and Hosmani, 2014). The tribological properties of pure copper bearings as well as boronized Fe-based SAE 1020 and TS-DDK 40 journal bearings were improved by boronizing at 950^oC (Unlu and Atik, 2010; Unlu and Atik, 2010). The indentation property of the cobalt boride layer formed on the surface of ASTM F-75 alloy were observed to be much dependent on the exposure time in powder-pack boriding process (Campos et al., 2013). The hardness of boride layer formed in nickel 201 alloy was found to be ten times greater than that observed in the parent material (Gunes and Kayali, 2014). The dual phase boride layer was observed to possess better tribological properties that the single phase boride layer (Cimenoglu et al., 2014). The ductile iron as well as the difficult to machine material like Incoloy 825 could be boronized and the formation of boride layer was found to be influenced by the boronizing temperature and process duration (Aytekin and Akcin, 2013; Kayali and Yalcin, 2011). The plasma paste boronizing and plasma-electrolysis boronizing were observed as the process variants, which could improve the rate of boron diffusion into the surface compared to the traditional boronizing process. Further a gradual transition in hardness was observed while moving from the surface towards the core (Gunes et al., 2011; Béjar and Henríquez, 2009). It was observed from the existing literature, that the boride layer thickness, surface hardness and wear resistance depends on the process parameters in slurry paste boronizing (SPB) like the paste thickness, process duration and temperature (Aytekin and Akcin, 2013; Kayali and Yalcin, 2011; Gunes et al., 2011; Béjar and Henríquez, 2009; Gunes and Kayali, 2014; Cimenoglu et al., 2014; Unlu and Atik, 2010).