Features of quality indicators of metal of boiler tubes rolled from continuously cast billets produced by Dniprostal metallurgical works LLC

Abstract

Purpose. Study of patterns of formation of structure and properties as well as the surface quality of boiler tubes in the process of tube rolling at TPA 30-102 tube rolling unit from non-worked continuously cast billets (CCB) of steel 20 produced by Dniprostal Metallurgical Works LLC. Methodology. Metallographic examination (macrostructure, microstructure, contamination by non-metallic inclusions); tensile and impact bend tests at room and elevated temperatures, determination of susceptibility to mechanical aging, long-term strength tests, visual inspection of the billet and the tube surface. Findings. Quality indicators of metal of the CCB produced by Dniprostal Metallurgical Works LLC and hot-rolled tubes produced at TPA 30-102 tube rolling unit from the CCB including service properties were investigated. Regularities of influence of quality of the initial CCB metal, technology of tube processing (hot rolling and heat treatment) on the formation of structure and properties as well as on the state of the boiler tube surface were established. Draft Technical Specifications were developed for the CCB produced by Dniprostal Metallurgical Works LLC intended for production of boiler tubes. Originality. For the first time, based on the revealed regularities of influence of the initial CCB on the formation of quality indicators of tube metal, Technical Specifications for high-duty continuously cast billets produced by Dniprostal Metallurgical Works LLC have been developed which make it possible to produce boiler tubes of high service reliability. Practical value. The research results will allow enterprises of Interpipe Ukraine JSC to produce boiler tubes of high service reliability from continuously cast billets produced by Dniprostal Metallurgical Works LLC. The use of billets of home production will reduce the cost of boiler tubes and eliminate the shortage of boiler tube billets in Ukraine. Keywords: continuously cast billet, hot rolling, elongation ratios, boiler tubes, heat treatment, macrostructure and microstructure, cast structure residues, mechanical properties, heat resistance, defects.