Evaluation of the effectiveness of the use of rotary friction welding in the production of joints from steel grade 20Cr13

Abstract

Shell and tube heat exchangers, widely used in industry, often operate at elevated temperatures and pressures, as well as corrosive environments. The material versions of devices operating in such conditions provide for the use of corrosion- and heat-resistant steels, in particular, 20Cr13. This steel has limited weldability, therefore, in the manufacture of tube bundles of heat exchangers from it, operations of pre-heating and concurrent heating, as well as heat treatment, are used in the welding process. One of the potential solutions to eliminate these operations is the use of friction welding instead of arc welding methods. The aim of the study is to evaluate the effectiveness of the use of rotary friction welding in the production of joints from steel grade 20Cr13. To do this, samples were made with a welded joint and from the base metal, and then microstructure studies and tensile tests were carried out. The study of the microstructure was carried out according to GOST R 57180-2016 “Welded joints. Methods for determining mechanical properties, macrostructure and microstructure.” Tensile tests were carried out at room temperature in accordance with GOST 1497-84 “Metals. Tensile test methods” (type II samples) and GOST 6996-66 “Welded joints. Methods for Determining Mechanical Properties” (type IV samples). The study of the microstructure showed that the metal of the welded joint has a two-phase pearlite-ferrite structure, which is characteristic of unannealed metal, and the base metal is granular perlite, which is characteristic of annealed metal in the delivered condition. Tensile tests have shown that the average value of the tensile strength of samples with a welded joint is 3.8% higher than the analogous value of samples from the base metal, however, the relative elongation after rupture is almost 2 times lower than the analogous value of samples from the base metal. Based on the results of the research, it was concluded that friction welding makes it possible to obtain high-quality joints from steel 20Cr13 without the use of pre-heating and concurrent heating, since there are no flaws, inclusions, cracks and other defects on the obtained samples. The weld metal has a two-phase pearlite-ferrite structure, which is characteristic of unannealed metal, which explains its low ductility relative to the base metal. In this case, the strength of samples with a welded joint turned out to be somewhat higher than the strength of samples from the base metal.