Optimization of cryogenic treatment to maximize the wear resistance of 18% Cr martensitic stainless steel by Taguchi method

Deep cryogenic treatment (DCT) is a one time permanent process, carried out on steel components in such a way that the material is slowly cooled down to the cryogenic temperature, after which it is held at that temperature for a specified period of time and is heated back to room temperature at a slow rate followed by low temperature tempering. The main advantage of DCT is to enhance the wear resistance. The various levels of DCT process parameters have their own influence upon the wear resistance of the material. In this study, the Taguchi method has been used to optimize the process parameters of DCT for a commercial piston ring, made up of 18% Cr martensitic stainless steel (SR34) to obtain maximum wear resistance. The DCT parameters considered for optimization are: the cooling rate, the soaking temperature, the soaking time, the tempering temperature and the tempering time. in this regard, two iterations of Taguchi design have been used to arrive at the optimum DCT parameters. During the first iteration, L(16)2(15) orthogonal array (OA) was used to conduct the Taguchi experiment so as to study the significance of these factors and the effect of their possible two-factor interactions. in the second iteration, L(9)3(4) OA was used to conduct the Taguchi experiment to arrive at the optimal levels. Wear test was conducted on a reciprocatory friction and wear monitor (RFWM) by weight loss method, as per ASTM standards G-181 and G-133. The relative importance of the controlling parameters of DCT and their interactions for enhancing the wear resistance was evaluated in terms of their percentage contributions using analysis of variance (ANOVA). The optimum levels of the significant DCT parameters for SR34 steel ring were arrived based on the maximum S/N ratio. A confirmation test was conducted subsequently, and the results were found to be within the confidence interval. (c) 2007 Elsevier B.V. All rights reserved.