Effects of temperature on tensile and impact behavior of dissimilar welds of rotor steels Ming-Liang Zhu, Fu-Zhen Xuan * Key Laboratory of Safety Science of Pressurized System, MOE, School of Mechanical Engineering, East China University of Science and Technology, 130, Meilong Street, PO Box 402, Shanghai 200237, PR China article info Article history: Received 5 November 2009 Accepted 31 January 2010 Available online 8 February 2010 Keywords: Dissimilar welding Tensile Temperature Rotor steels abstract Tensile and impact behavior of dissimilar weld joints of newly developed rotor steels 23CrMoNiWV88 and 26NiCrMoV145 were conducted at various temperatures below 350 °C. Inhomogeneous microstruc- tures and asymmetrical micro-hardness along the dissimilar welding joint were observed. With the increase of temperature, strength decreased which was associated with the increased plasticity, and frac- ture location changed from weld metal (WM) to intermediate pressure (IP) base metal (BM) at around 300 °C. Compared to the homogeneous impact specimen with two fracture zones at fracture surface, a combined quasi-cleavage and ductile fracture mode with three zones is observed at the fracture surface of the dissimilar weld joint when the testing temperature is in the range of 0–40 °C. The occurrence of separated zones are mainly ascribed to the multi-layer welding process and thus improved the impact toughness of the welding joint. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction To meet various property requirements in an integrated struc- ture, dissimilar welds are widely used in engineering to join differ- ent metals together. In the past several decades, a mass of studies have been carried out on the manufacture of traditional fusion welding [1–5], advanced friction stir welding [6–8] and the proper- ties of dissimilar weld joints, e.g., fatigue [9], creep [10], fracture [11], limit load [12], structure integrity assessment [13], residual stress [14] and so on. However, the performance of welded joints is affected not only by material properties of base metal (BM), weld metal (WM) and heat affected zone (HAZ), but also by the geome- try of the weldment constituents and the location of preexisting defects. The strength design and reliability assessment of dissimi- lar weld joints is still a complex issue in practice. In addition, temperature changes during service will affect the performance of dissimilar weld joints and this has not been adequately dis- cussed in the existing researches. Recently, in view of increasing capacity while reducing delivery time, welding methods have been widely used in power industry field to manufacture large components such as the welded turbine rotors [15]. In addition, multilayer or multipass technique is often utilized in welding thick plates [16–18] due to its advantage of normalizing prelayer (prepass) microstructures to increase ductil- ity and improve quality [19,20]. In fact, the welded components such as welded rotor of nuclear power plants often works at mod- erate temperatures. Therefore, it is quite significant to investigate effects of temperature on performance of dissimilar welds used in nuclear power plants. In this work, tensile and impact behavior of the dissimilar weld- ing joint of two nuclear rotor steels, i.e., 23CrMoNiWV88 for inter- mediate pressure (IP) part and 26NiCrMoV145 for low pressure (LP) part, were investigated at various temperatures. Effects of temperature on strength, fracture location and fracture surface are highlighted in this report. 2. Experiments The chemical compositions of the dissimilar welding BM are shown in Table 1. From Table 1 it can been seen that IP BM has a large content of Cr while LP BM exhibits a larger content of Ni. Be- fore welding, IP steel was quenched at 920 °C for 36.5 h with water spraying and tempered at 645 °C for 30 h while LP steel was quenched at 840 °C for 55 h with water immersion and tempered at 585 °C for 60 h. Mechanical properties of IP and LP are listed in Table 2. As shown in Fig. 1, the IP and LP steels were butt-welded by tungsten inert gas (TIG) welding at the bottom and submerged arc welding (SAW) at the top in the radial direction. Post weld heat treatment (PWHT) was performed at 620 °C for 10 h. In this re- search, specimens for tensile and impact tests were cut off only from the SAW welding part, as depicted in Fig. 1. Surfaces of specimens for optical microscope observations were mechanically polished and then chemically etched in a solution of 0261-3069/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2010.01.055 * Corresponding author. Tel.: +86 21 64252819; fax: +86 21 64253425. E-mail address: fzxuan@ecust.edu.cn (F.-Z. Xuan). Materials and Design 31 (2010) 3346–3352 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes