TPWJ, 2014, #2, 2-11 pages
RESISTANCE TO COLD CRACK FORMATION OF HAZ METAL OF WELDED JOINT ON HIGH-STRENGTH CARBON STEELS
Journal The Paton Welding Journal
Publisher International Association «Welding»
ISSN 0957-798X (print)
Issue № 2, 2014 (February)
E.O. Paton Electric Welding Institute, NASU. 11 Bozhenko Str., 03680, Kiev, Ukraine. E-mail: email@example.com
Influence of preheating temperature and heat input during surfacing on change of delayed fracture resistance of HAZ metal on high-strength steel at variation of carbon content in it from 0.55 to 0.75 % was investigated. Effect of carbon content in steel on indices of critical stresses at HAZ metal delayed fracture was evaluated by Implant tests. Influence of a cooling rate on nature of metal fracture and typical rupture zone and parameters of structural constituents were studied and determined using the methods of scanning electron microscopy. It is determined that HAZ metal is predisposed to the delayed fracture in electric arc surfacing due to formation of quenched structures with high dislocation density and internal stresses in area of overheating. Increase of cooling rate and carbon content in steel promotes rise of fracture susceptibility and decrease level of critical stresses to 0.07s0.2. Formation of more plastic structures at reduction of the cooling rate in 600-500 °C temperature interval promotes increase of the delayed fracture resistance of HAZ metal on high-strength carbon steels to scr У 0.45s0.2 level. A diagram of effect of carbon content in steel on HAZ metal resistance to the delayed fracture was plotted in form of w6/5 = f(C). It is determined that the process of delayed fracture in HAZ metal on steel with carbon content not more than 0.60 % can be prevented at cooling rate w6/5 not more than 16 °C/s, w6/5 Г 8 °C/s with 0.60-0.65 % C and w6/5Г 5°C/s with 0.65-0.75 % C. Under such conditions, the structures, having sufficiently high capability to microplastic strain without microcrack generation, are formed in the metal of HAZ overheating area. 18 Ref., 2 Tables, 11 Figures.
electric arc surfacing, high-strength carbon steel, HAZ, preheating, heat input, delayed fracture, structure, rupture
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