Martynenko V. Regulation of properties of a welded joint by means of a complex shielding medium

Dissertation is devoted to creating a technology of surface stability of low-carbonated and low- alloy steels( on St.3 и 09Г2) by arc with nonconsumable electrode (arc with carbon and volfram electrodes), studying the influence of main parameters of surface hardening on the structure and mechanical properties of a stable layer. During the first experiments it was figured out that for the surface hardening an arc with a неплавким electrode can be used. It allows to conduct the local heating at a high speed of cooling. It is stated that the high hardness of surface layer of low-carbon steels with ferrite-pearlite structure can be achieved by additional heating without fusing of the surface. One heating of the steel surface results in hardening at the depth of 0,2 mm is from 270 HV. At the second heating the hardess of the surface layer at the depth of 0,2 mm makes up to 380 HV. The third heating provides the creating of mostly martensite structure in a surface layer and results in the increase of temperature at a depth of 03 mm up to 400 HV, and at a depth of 0,6 mm - up to 360 HV. When processing the surface by magnet scanning of carbon arc a model with width of instability zone of 2 mm and minimum hardness of 44 HV was received. Distance between the maximums of hardness is about 2,5 mm. A piece with hardness less than 450 HV is less than 1 mm. Application of magnet scanning of the arc helps increase the hardness in a zone of over connection of stable rows and diminish the number of passing. The main principles of surface hardening of low-carbonate and low-alloy, and constructing steels, as well as the calculating algorithm for thermical cycles and fields of maximum temperatures offered in the dissertation are used to renovate the crane wheels on Damen Shipyards "Okean".