Materials Sciences and Applications, 2013, 4, 656-662 http://dx.doi.org/10.4236/msa.2013.410081 Published Online October 2013 (http://www.scirp.org/journal/msa) Cracking Phenomenon in Spot Welded Joints of Austenitic Stainless Steel Ahmed M. Al-Mukhtar 1,2 , Qasim M. Doos 3 1 Faculty of Geosciences and Geoengineering, Technische Universität Bergakademie Freiberg, Freiberg, Germany; 2 Al-Khawirizmie College of Engineering, Baghdad University, Baghdad, Iraq; 3 Mechanical Engineering Department, College of Engineering, Baghdad University, Baghdad, Iraq. Email: almukhtar@uni.de Received August 5 th , 2013; revised September 21 st , 2013; accepted October 9 th , 2013 Copyright © 2013 Ahmed M. Al-Mukhtar, Qasim M. Doos. 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 spot welds nugget cracking of austenitic stainless steel at temperatures between 700˚C - 1010˚C was investigated. Traditionally, the cracks have been observed around the spot nugget in welded temperature. Actually, these cracks are developed due to incomplete melting and inappropriate electrode pressure, which causes an expulsion of molten metal. These cracks start to grow and cause either the interface or plug fracture according to the loading type. In this work, the micro-cracks in the weld nugget were indicated for this type of steel at elevated temperature. Cracks appear in a certain range of temperature; about 700˚C - 750˚C. The cracks like defect and cavitations were presented. According to the fracture mechanics point of view, these cracks reduce the mechanical strength. Therefore, these cracks have to be taken into account with a certain precaution. Moreover, considering the working temperature and reducing the element may develop ferrite particles. Keywords: Austenitic Stainless Steel; Cracking; Ferrite Contents; Fatigue Cracks; Spot Welded Joints; Weld Nugget; Weld Notches 1. Introduction Welding cracks of the welded joints are considered as a serious defect. They start to grow from a certain defect until final failure. The failure tends to occur due to the crack orientation around the heat affected zone (HAZ) [1-3]. A typical through-thickness stress distribution and the fatigue critical location have been studied also at the edge of a spot weld nugget. Traditionally, the maximum stress occurs also at the interface between the two sheets [4]. Only a few studies deal with the cracking of the nug- get area, and the ferrite contents of the austenitic stain- less steel. In contrast, most studies deal with the alumi- num welding, hot cracking, the welding process type, and the alloy compositions that determine the cracking sus- ceptibility. Most literature showed that the cracks are initiated from the HAZ in aluminum alloy, i.e. from the periphery of spot weld nugget. The cracks were formed at elevated temperatures in the presence of liquid metal due to the metallurgical factors [5]. In addition, Lippold et al. [6] observed the crack ini- tiation and propagation in the weld fusion zone and the HAZ of 5083-aluminium alloy. It was found that the cracking susceptibility depended on the Magnesium con- tents. Therefore, Toyota reported the solidification fail- ure in the nugget or liquation cracking in the HAZ for one of the 5000 series of aluminum alloys containing above 5% weight of Mg [5]. The preheating will de- crease the thermal stresses and the temperature gradient. Hence, the cracking ability will be decreased. Mirsalehi et al. [7] proposed a crack propagation-based fatigue life approach for resistance spot welds. Moreover, the effect of welding residual stresses was taken into ac- count. The effects of spot weld diameter as well as the location of crack initiation have been predicted. Lin et al. [8] examined the fatigue crack paths near the spot welds in the square-cup, lap-shear and coach-peel specimens. The stress intensity factor (SIF) solutions have been used to predict the fatigue lives. SIF and fatigue lives for welding joint can be calculated using Fracture Analysis Code-2 dimension (Franc2D) for different types of mate- rials, cracks and weld geometries [9,10]. However, there is an increasing use of stainless steel Copyright © 2013 SciRes. MSA