Effect of precipitate–precipitate interaction on residual stress in welded structure Hamida Fekirini a , Boualem Serier a , Farida Bouafia a,b,⇑ , Bel Abbes Bachir Bouiadjra a , Sardar Sikandar Hayat c , Sid Ahmed Bouafia b a LMPM, Mechanical Engineering Department, University of Sidi Bel Abbes, Sidi Bel Abbes 22000, Algeria b Institute of Science and Technology, University of Ain Temouchent, BP 284 RP, Ain Temouchent, 46000, Algeria c Department of Physics, Hazara University, Mansehra 21300, Pakistan article info Article history: Received 21 March 2012 Received in revised form 21 May 2012 Accepted 5 June 2012 Keywords: Weld Finite element method Precipitate Residual stress abstract The process of assembly by welding led to the creation of micro-structural heterogeneities zones. Gener- ally these zones can be discontinuities macroscopic geometrical (macro-geometry of the weld nugget) or/and geometrical or metallurgical defects. At the origins of stress concentration, these regions are favor- able sites where fatigue cracks can initiate and propagate. Our work concerns the role of the existence of the precipitate during the process of welding on the level of the microscopic internal stress thermal ori- gin. The distribution of this stress in the steel matrix around these defects was the subject of a numerical analysis by the finite element method. The originality of this study lies in the angle of attack in the vol- ume fraction of the precipitate and the effect of precipitate–precipitate interaction on the distribution and the level of this stress. The precipitate in the steel matrix resulting from a process of welding gener- ates thermal stress whose level reaches its maximum value with the interface matrix–precipitate. Far from this interface the matrix is completely released of this stress. This stress can constitute a risk of damage to the welding joint. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Carbon is one of the most important alloying elements in iron and steel, which is a solid solution in austenite and ferrite or forms carbide with other elements. The types and quantities of carbide have a decisive effect on mechanical properties, deformation behavior and many other properties of steel. The carbides in Fe–C system include the well-known h-Fe 3 C (cementite), and other metastable iron carbide phases such as Fe 5 C 2 (Hagg carbide) and Fe 2 C(e and g). The Fe 2 C carbide, which is identified as epsilon (e)-carbide by Jack [1] with a hexagonal crystal structure, precipi- tates in tempered steels. It has also been shown afterwards that the Fe 2 C forming in tempered martensite has an orthorhombic struc- ture isomorphous with the transition metal carbides of the M 2 C type [2], which is designated as eta (g)-carbide. Although the cold deformation becomes one of the study focuses on high carbon steels, the investigation of the properties of metastable carbide Fe 2 C is far from sufficient. Cementite dissolution due to pearlite cold deformation occurs [3–5] as well as metastable carbide Fe 2 C is observed during the dissolution of the pearlite [6]. Faraoun et al. [7] calculated the electronic and magnetic properties of g-Fe 2 C, but the properties of e-Fe 2 C and the relative stability of g-Fe 2 C and e-Fe 2 C have not been concerned. In certain steel welded parts, the solid-state austenite–martens- ite transformation during cooling has a significant influence on the residual stresses and distortion [8]. The martensitic transformation is a diffusionless solid-state shear deformation [9]. In steels, the martensite is formed from austenite containing carbon atoms and, in view of the diffusion less nature of its formation; it ideally inherits the carbon atoms of the parent austenite. The carbon atoms are trapped in octahedral interstitial sites between iron atoms, producing a body centered tetragonal (bct) structure, and are in super-saturation relative to the body centered cubic (bcc) ferrite [10]. Many researchers have studied the solid-state phase transformation of the welded structures [11–12]. Therefore, in the welding process, it is important to study the distribution and the level of residual stress induced in a matrix by the phenomena of precipitation Fe 2 C compounds resulting from the process of welding. The precipitate characteristics influence welds metal microstructure development, especially the formation of high toughness acicular ferrite phase. The important inclusion charac- teristics are as follows; size distribution, number density, volume fraction, and composition. In order to clarify the effect of phase transformation on welding residual, one kind of steel, namely medium carbon steel (S45C), is selected in this study. Our work concerns the role of the existence of the precipitate during the process of welding on the level of the 0927-0256/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.commatsci.2012.06.005 ⇑ Corresponding author at: LMPM, Mechanical Engineering Department, Univer sity of Sidi Bel Abbes, Sidi Bel Abbes 22000, Algeria. Tel.: +213 7 75 81 39 55; fax: +213 4 85 44 100. E-mail address: fbouafia2011@yahoo.fr (F. Bouafia). Computational Materials Science 65 (2012) 207–215 Contents lists available at SciVerse ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci