Improving materials and welding technology for dissimilar welded joints in austenitic and pearlitic steels

Abstract

The first layer of the deposit on the edges of low-alloy steels in producing welded joints with 08Cr18Ni10Ti steel is made using materials based on 02Cr24Ni13 composition (TsL-25L electrodes, welding wire SV-02Cr24Ni13) producing the deposited metal with a reduced carbon content and the required content of the ferritic phase (2 -5%). Welding with these materials results in the required parameters of technological properties in welding and efficiency of the austenitic -ferritic deposited metal:. resistance to solidification cracking; . preventing the formation of a structure containing very hard brittle compounds;. preventing the formation of the sigma phase and, correspondingly, embrittlement in tempering;. the mechanical properties and fatigue strength satisfy the requirements of PNAE G-7-002-86.Welded joints in pipelines made of dissimilar steels are produced by a technology consisting of preliminary deposition of the edges of components made of a pearlitic steel followed by filling the welding gap with the material similar to that of the welded austenitic steel. In assembling the pipelines of energy power units, the first layer of the preliminary deposit in dissimilar joints is produced using materials of the type 11Kh15N15T6AG2 (electrodes EA-395/9), producing a single-phase austenitic structure [1]. These materials prevent the formation of the martensitic component in the structure of the first layer in all hardfacing methods (Figure 1).At the same time, it is always important to remember the potential susceptibility of the single-phase austenitic structure to the formation of cracks -tears [2]. These defects have been detected many times in the metal of welded joints in standard pipelines. According to the experimental results, these defects were identified as liquation (weld zone) cracks, formed in the inter-pass zones heated to temperatures in the vicinity of the solidus temperature when producing multipass welded joints or deposits. It is quite difficult to prevent the formation of these defects because the cracks (tears) are situated below the layer of the deposited metal ( Figure 2). The special features of the distribution of the defects complicate detection of these defects in primary inspection. Subsequent technological operations, including preparation of the surface for non-destructive inspection, result in the opening and displacement of the surface in the form of indications.No universal practical solutions are available for preventing the cracking susceptibility of the stable austenitic compositions at the present time. Only certain specific compositions have the required level of hot cracking resistance. The negative effect of the combination of individual phases, taking part in the formation of low-melting intergranular film interlayers (or leading to the effect of adsorption decrease of strength at the intergranular boundaries) is well known. The presence of uncontrolled impurities in the steel for welding wires and the uncontrolled raw materials base for electrode coatings, etc. are very im...