Effect of oxygen on hydrogen cracking in high-strength weld metal
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I.
INTRODUCTION
HY- 100/HY- 180
series steels combine excellent fracture toughness properties with high strength. However, when welded, the joints are highly susceptible to hydrogen-induced cracking, t~'21 High-strength low-alloy (HSLA) steels are being developed which provide an excellent combination of strength, fracture toughness, and resistance to hydrogen-induced cracking, t3'4] However, both heat-affected zone and weld metal cracking can occur when welding high-strength steels, and limited research has been carried out evaluating the detailed effects of weld metal composition on hydrogen-induced cracking in high-strength steel weld metal. Pressouyre and Bernstein, tS,6j in their trap theory of hydrogen embrittlement, modeled hydrogen interaction with traps such as TiC particles in the Fe-Ti-C system. Based on the assumption of some critical hydrogen level being exceeded in order to cause embrittlement, traps were classified as beneficial or detrimental depending on their ability to increase the time required to reach this critical hydrogen concentration or to disperse hydrogen in such a way that the critical local hydrogen concentration was not attained. A number of irreversible hydrogen trapping sites have been confirmed, viz., grain boundary regions ~71 and MnS/lattice, t81 A1203/lattice, t9,1~ and SiO2/ lattice interfaces, tH~ Pressouyre and Zmudminski tgl observed crack nucleation at A1203 particles when hydrogen was cathodically charged into 10-mm x 10-mm 3.5 pet Ni steel blanks and showed that the embrittlement
K. SHINOZAKI, formerly Visiting Research Scientist, Department of Metallurgy and Materials Science, University of Toronto, is Research Instructor, Department of Welding Engineering, Osaka University, Osaka, Japan. X. WANG, formerly Visiting Scientist, Department of Metallurgy and Materials Science, University of Toronto, is Research Scientist, Beijing Institute of Control Engineering, Beijing, People's Republic of China. T.H. NORTH, WIC/NSERC Professor, is with the Department of Metallurgy and Materials Science, University of Toronto, ON M5S 1A4, Canada. Manuscript submitted March 29, 1989. METALLURGICAL TRANSACTIONS A
index* is increased as the oxygen content in the steel *The embrittlement index, F = 100 (pct RA,c - pct RAc)/(pct RA,c), where RAc is the reduction in area in tensile specimens taken from samples cathodically charged with hydrogen, and RA,c is the reduction in area in test specimens from uncharged samples. Higher F values mean greater susceptibility to hydrogen embrittlement.
increased from 15 to 200 ppm. Shielded metal arc (SMA), submerged arc (SAW), and flux cored arc (FCAW) welding processes produce welds containing oxygen contents as high as 850 ppm, and since oxygen is almost completely insoluble at room temperature, steel weld metals contain (MnO)(SiO2) and/or (MnO)(SiO2)(A1203) inclusions having diameters ranging from less than 0.1 /zm to as high as 3/.I,m. [13'141 Since weld metals contain such high oxide inclusion concentrations, their influence on microstructure an
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