TPWJ, 2013, #5, 14-20 pages
INFLUENCE OF DIFFUSIBLE HYDROGEN ON DELAYED CRACKING RESISTANCE OF HIGH-CARBON STEEL WELDED JOINTS
Journal The Paton Welding Journal
Publisher International Association «Welding»
ISSN 0957-798X (print)
Issue № 5, 2013 (May)
E.O. Paton Electric Welding Institute, NASU, Kiev, Ukraine
Influence of diffusible hydrogen in deposited metal on the change of resistance to and nature of delayed fracture of HAZ metal in welded joints of high-strength wheel steel of grade 2 with 0.58 wt.% C was studied. «Pencil» method was used to determine diffusible hydrogen content in the deposited metal in CO2 welding by PP-AN180MN flux-cored wire, the amount of which can vary in the range from 0.3 up to 2.2 cm3
/100 g. At testing by the implant method the influence of diffusible hydrogen on the change of critical stress values at delayed fracture of wheel steel joints was evaluated. Scanning electron microscopy methods were used to study the influence of diffusible hydrogen on the nature of HAZ metal fracture; characteristic fracture zones and structural component parameters were determined. It is established that at diffusible hydrogen content in the deposited metal on the level of 0.3 cmσ0.23σ0.2/100 g delayed fracture resistance of the joints is the highest, and depending on structural condition of metal of HAZ overheated zone critical fracture stresses are equal to (0.35-0.45)σ0.2. Fracture occurs predominantly in the brittle mode along the boundaries and through the grain body, fraction of tough structural component is not more than 20 %. At increase of diffusible hydrogen content HAZ metal becomes brittle and delayed fracture resistance decreases. The most abrupt drop of critical stress characteristics to 0.1σ0.2 value is characteristic for the metal of HAZ with martensite-bainite structure, which has 70 % of martensite. 13 Ref., 2 Tables, 6 Figures.
Keywords: arc welding, diffusible hydrogen, wheel steel, delayed fracture, HAZ, structure
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