Hydrogen-Induced Cold Cracking in High-Frequency Induction Welded Steel Tubes
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INTRODUCTION
HYDROGEN-INDUCED cold cracking is one of the main concerns in the weld heat-affected zone of carbon-manganese and high-strength low-alloy steels. The cracking is also termed as hydrogen-induced cracking (HIC), delayed cracking, or underbead cracking.[1] They are caused by hydrogen present in the weld material or in the HAZ, susceptible microstructure, and thermal or residual stresses.[2] The susceptibility of the tubular steels in service to HIC depends upon metallurgical as well as environmental factors.[3] The hydrogen atoms diffuse through the wall of the tubes and are trapped at the heterogeneous sites in the steel. Eventually, when the critical hydrogen concentration depending upon the composition and microstructure of steel is attained at the sites, blistering and/or cracks due to hydrogen take place.[4,5] The cracking occurs at temperatures below 423 K (150 C) and starts after several minutes to several days. Basically cold cracking is considered to be a typical heat-affected zone (HAZ) defect in the joints of conventional structural steels. However, with the introduction of new higher strength thermo-mechanically treated and quenched and tempered steels (with reduced carbon equivalent), cold cracking was also found to be confined to the weld metal, comparable strength of which could be attained by higher level of alloying.[6,7] The yield strength of 680-800 MPa was reported as typical for weld metal hydrogen-induced cold cracking in multi pass welds.[8,9] Both welding process and welding consumables have significant effect on the hydrogen-induced cold cracking of the above steels. It was reported[10,11] that while welding armor grade Q&T steel, that closely conformed KUMKUM BANERJEE, formerly with the Research and Development Department, Tata Steel Limited, Jamshedpur, Jharkhand 831007, India, is now Associate Professor with the Department of Metallurgical & Materials Engineering, National Institute of Technology Karnataka, Surathkal, Mangalore 575025, India. Contact e-mail: [email protected] Manuscript Submitted July 18, 2015. Article published online February 2, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
to AISI 4340 specification, the welds with austenitic stainless steel consumables offered a greater resistance to HIC than their respective welds with low-hydrogen ferritic (LHF) steel consumables. The welds made by flux-cored arc welding (FCAW) process exhibited greater resistance to HIC than their respective shielded metal arc welding (SMAW) welds. The effect of welding method in controlling the weldment microstructure was demonstrated by Magudeeswaran et al.[11] The HAZ in the SMAW specimens was reported to be predominantly bainitic, while it was martensitic in the case of GMAW. The weldment microstructure, in turn, dictated the cold crack initiation and propagation—the cracks initiated in the fusion line, propagated through the weld metal in the SMAW specimen, while the propagation was through the HAZ and weld metal in the GMAW specimen. Further, the role of microstructure in contro
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