Effect of Heat Treatment on Structure and Properties of Martensite Stainless Steel for Ice-Class Ships Obtained by Direct Laser Deposition Method

Abstract

At present, to increase competitiveness of shipyards for manufacturing of shipbuilding parts new high technologies are used. Additive production methods, including direct laser deposition (DLD) technology, which meets all the requirements of competitiveness, are increasingly being applied. Heavy-duty large-size parts such as propellers, blades, hubs and other critical parts used in shipbuilding have become possible to produce with DLD. In the process of DLD it is possible to produce parts, including shipbuilding steels used in the Arctic conditions, with the required mechanical characteristics not inferior to similar brands of materials obtained by casting or plastic deformation methods. The work is devoted to research of thermal process influence on structure and mechanical properties formation of deposited samples from steel powder 06Cr15Ni4CuMo. Features of formation of microstructure components by means of optical microscopy, X-ray structure analysis (XRD) are investigated, and also CCT diagram is constructed. Tensile and impact toughness tests have been conducted. As a result, it was found that the material obtained by the DLD method in its initial state significantly exceeds the strength characteristics of heat-treated castings of similar chemical composition, but is inferior to it in terms of plasticity and viscosity. The increase of viscosity and plasticity up to the level of cast material in the grown samples is achieved during the subsequent heat treatment, which leads to the formation of the structure of tempered martensite and reduction of its content in the two-stage tempering in the metal structure. The strength of the material is also reduced to cast metal after heat treatment.