Metallurgical and Materials Engineering

... o C - 60 0 C. At higher temperatures, the plating bath became harsh and deposition of zinc was observed to come in spots and also not uniform as compared to low temperatures. This was as a result of too rapid movement of zinc ions. ... [13] N. Kanani, Electroplating: Basic ...

ABSTRACT The conditions influencing the phenomenon of heat affected zone (HAZ) cracking during tungsten inert gas (TIG) welding of a gamma-prime (γ’) precipitation strengthened nickel-base superalloy, IN 738, is discussed here. The discussion is reinforced with the dependence of the cracking on particle size variation of the γ’ precipitates and base alloy hardness. Microstructural analysis of the magnitude of HAZ cracking in the alloy indicates that while resistance to cracking susceptibility is poor in the standard heat treatment (SHT) condition, the modified heat treated (MHT) alloy exhibits significantly improved resistance to HAZ cracking. The improvement in resistance to HAZ cracking in the MHT alloy is attributed to the lower hardness of the alloy which permits stress relaxation in the base alloy compared to the SHT alloy. In contrast to what is expected based on the recommended manufacturer SHT procedure, preweld microstructural modification presents a viable way of limiting cracking susceptibility in TIG welded IN 738 superalloy. Keywords: joining, superalloy, HAZ cracking.

Ferritic stainless steel is a flexible grade of the stainless steel family with properties closely matching those of the more popular and expensive austenitic grade. Yet, it is grossly underspecified for application because it is erroneously considered inferior to the austenitic. The recent volatility in the cost of nickel, a major constituent of the austenitics which has pushed up the cost and destabilizes the austenitic stainless steel market has now shifted attention to the ferritic though with caution due to the lack of sufficient technical information on the suitability or otherwise of the grade for the specified service. Interestingly, incidences of successful application of the grade in the recent past are now documented in the literature owing to decades of intensive research and development in improving the grades that are currently available. This article therefore, discusses the metallurgy of ferritic stainless steel in terms of the crystal structure, the alloying composition and the microstructure which control the properties and the application window. The existing practices for improving the weldability of the grade are briefly reviewed. A summary of application area for representative grades is equally presented.