INVESTIGATION OF THE CORROSION RESISTANCE OF STEEL SS330 (СТ3 in Russ.) IN THE FREE AND ANNEALED STATES

Abstract

For the manufacture of field pipelines, low-carbon of steel SS330 is often used. It is well welded, almost does not harden and therefore is very convenient for operation in structural elements. Studies of samples made of steel grade SS330 were carried out for the initial and heat-treated states by the following methods: 1) investigation of mechanical properties: - tensile test; - hardness test; 2) microstructural analysis. At the beginning of the research, annealing was performed to obtain an equilibrium structure. According to the results of the experiment, it was noted that after annealing, the structure of SS330 steel acquired low strength and hardness with high plasticity. After annealing, tensile tests of the steel samples of SS330 steel were carried out. Tensile tests make it possible to determine the strength and ductility characteristics of metals under static uniaxial loading. Tensile tests of metal were carried out to determine the main indicators of mechanical properties and to compare these properties in the initial and heat-treated states. Hardness measurements were performed using the Rockwell method. Microanalysis is an indispensable tool for assessing structural changes in the size, shape and orientation of grains, individual structural and phase components. The microstructure of samples of steel SS330 was studied using an optical microscope «Metam RV-21-1Ц», with which it is possible to study the microstructure at a magnification of 200 times. It is shown that the structure of steel is ferrite-perlite. In the initial state, there is a small scribbling and a liquation band. This section has a large chemical heterogeneity, is contaminated with impurities (oxides, nitrides, sulfides, silicides), differs in the values of the characteristics of mechanical properties from the base metal of the pipe. The structure of SS330 steel in its initial state is fine-grained. After annealing, it becomes more uniform, the deformation texture disappears.