Journal of Minerals and Materials Characterization and Engineering, 2013, 1, 222-230 http://dx.doi.org/10.4236/jmmce.2013.15035 Published Online September 2013 (http://www.scirp.org/journal/jmmce) Effects of Gas Metal Arc Welding Techniques on the Mechanical Properties of Duplex Stainless Steel Tanimu Ibrahim 1 , Danjuma S. Yawas 2 , Shekarau Y. Aku 2 1 Plant and Equipment Department, Salini Nigeria Limited, Abuja, Nigeria 2 Mechanical Engineering Department, Ahmadu Bello University, Zaria, Nigeria Email: terrytanimu@yahoo.com Received July 5, 2013; revised August 9, 2013; accepted August 22, 2013 Copyright © 2013 Tanimu Ibrahim et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT The study has compared the effect of gas metal arc welding techniques on some mechanical properties of duplex stainless steel. The samples after welded were given post weld heat treatment (quenching in engine and neem oil). After the analyses, it was established that duplex stainless steel can be weld successfully using gas metal arc welding process (GMAW). Both Lubricating oil and neem oil can serve as quenching medium for post welding heat treatment of duplex stainless steel. The results of the studies also show that welding and heat treatment really affect the mechanical proper- ties of the alloy; the control strength was 811.47 MN/m 2 while that of the welded samples ranged from 177.07 to 257.32 MN/m 2 . The control impact energy was 162.70 J, while that of the welded samples ranged from 38.64 J to 56.20 J. The research also shows that the stress relief heat treatment gives better strength (A 3 = 331 MN/m 2 ) compared to those that were quenched in lubricating oil (A 2 = 329 MN/m 2 ) and neem oil (A 1 = 222 MN/m 2 ), but the reverse is the case in terms of toughness. Keywords: Duplex Stainless Steel; Welding Techniques; Tensile Strength; Hardness Number; Impact Energy; Heat Treatment 1. Introduction A large number of failures in industries are either directly or indirectly attributed to welds because of the inhomo- geneity within the weldment, stress concentration, resid- ual stress, inclusion of impurities etc. which invariably make it the weakest region [1]. However a vast majority of repairs of failed components in industries are carried out using one of the welding processes and the success depends on many factors such as weldability of the mate- rial, type of damage, availability of suitable welding te- chnique, possibility of carrying out pre-heating or post weld heat treatment, post repair inspection by non-des- tructive testing (NDT) techniques [1]. Duplex stainless steels are two phase alloys based on the iron-chromium-nickel system. These alloys usually comprise of equal proportions of the body centered cubic (BCC) ferrite and face centered cubic (FCC) austenite phase in their microstructure and generally have low car- bon content as well as additions of molybdenum, nitro- gen, tungsten, and copper. Typical chromium contents range from 20% to 30% by weight, nickel ranges from 5% to 10% by weight [2]. Duplex stainless steels solidify as 100% ferrite, but about half of the ferrite transforms to austenite during cooling through temperatures above 1040˚C. This beha- vior is accomplished by increasing Cr and decreasing Ni content as compared to the austenitic grades [2]. Duplex stainless steels are ferromagnetic, a property that can easily differentiate them from common austeni- tic grades of stainless steels. Generally the ratio of ferrite to austenite in duplex stainless steels depends mainly on the chemical composition. The presence of ferrite with austenite provides better intergranular corrosion (IGC) resistance, other advantages offered by these alloys over convection 300 series stainless steels are strength, chlo- ride stress-corrosion cracking resistance, and pitting cor- rosion resistance [2]. Duplex stainless steels are increasingly used as struc- tural materials in building and architecture because of their exceptional mechanical properties. Their room tem- perature yield strength in the solution annealed condition is more than twice that of standard austenitic stainless steels not alloyed with nitrogen. Over the last few years, they have started playing an increasingly important role in the construction of bridges, wherever specific envi- Copyright © 2013 SciRes. JMMCE