Influence of gas shielding conditions upon the thermal processes in weld joints when welding with a consumable elecrode

Abstract

Abstract. The author has studied the dependence of changes in heat distribution in steel 30HGSA weld joints upon the gas shielding conditions. It has been established that under the double-jet gas shielding the rate of temperature saturation in the welded plates is a little higher and temperatures of weld metal and the heat-affected area equalize by 1…1.4 seconds earlier than it happens under the traditional single-jet shielding. The developed redetermined formula for calculation heat distribution in the process of automatic single-pass welding of plates under the double-jet gas shield conditions allows to estimate the thermal cycle of a point with an error of less than 10%.Key words: welding with a consumable electrode, heat distribution, gas shield, welding thermal cycle.The majority of welding processes suppose heating the component parts by various heat sources. In fusion welding the weld joint quality is determined by the heating and cooling conditions. The history of a thermal process determines the melting productivity of the basic and adding material, the direction and completeness of the metallurgical processes in the weld pool, conditions of the joint and the heat-affected area metal formation, as well as the running ability of the weld joints [1].Control of the thermal cycle in the joint material is one of the main tasks of modern welding production. Theoretical and experimental study of heat and mass transfer phenomena have large practical value as well as the study of complex physical-chemical processes and structural-phase transformations which take place in the process of welding while heating and cooling the workpieces. The theory of welding processes in our country (Russia) and abroad pays much attention to the problem of estimation of thermal fields and cooling rates which are important for the hardened steels welding.Modern theories and works [1-4] considering welding thermal processes and formulating basic laws and notions of thermal field distribution do not take a number of significant factors into consideration, i.e. heat exchange with the environment, welding method and other. The calculations often contain composite functions. It increases the calculation time, involving complicated mathematical apparatus and computing machinery. Besides, the calculated data often differ from the practical results.The most accurate and adequate description of the thermal processes can be made by the results of experimental study of the thermal fields distribution. The experimental picture of the thermal field distribution can be received by thermocouple or by thermal imaging equipment.Formation of structure and phase state of metal depends on its chemical composition and heating conditions [1][2][3][4][5][6][7][8][9][10][11][12]. The welding thermal cycle and the cooling rate determine the structural-phase state of the heat-affected area of hardened steels [2, 5-7, 13 and other].In order to study the dependence of changes in thermal cycle and cooling rate of steel 30HGSA weld joints upon the gas shieldin...