Characteristics of Susceptible Microstructure for Hydrogen-Induced Cracking in the Coarse-Grained Heat-Affected Zone of
- PDF / 4,677,060 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 27 Downloads / 150 Views
NTRODUCTION
HYDROGEN-INDUCED cracking (HIC) is one of the most damaging welding failures within the weld metal or coarse-grained heat-affected zone (CGHAZ) of steel. Since this cracking is normally generated after welding at low temperatures below 473 K and can occur after incubating for several hours or days, it is often called ‘‘cold cracking’’ or ‘‘delayed cracking’’.[1] Although the mechanism for HIC during welding is still not clearly understood, it is generally accepted that there are three necessary factors: (1) hydrogen, (2) susceptible microstructure, and (3) tensile residual stresses.[1–11] In various industry fields, efforts are made to prevent HIC in welding by controlling the aforementioned factors.[1] The amount of diffusible hydrogen can be
YONGJOON KANG and SANGWOO SONG are with the Joining Technology Department, Korea Institute of Materials Science, Changwon 51508, Korea. Contact e-mail: [email protected] MINJEONG KIM and NAMKYU KIM are with the Joining Technology Department, Korea Institute of Materials Science and also with the Department of Materials Science and Engineering, Pusan National University, Busan 46241, Korea. GIDONG KIM is with the Joining Technology Department, Korea Institute of Materials Science and also with the Department of Nuclear Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Korea. Manuscript submitted November 12, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
reduced by the selection of low-hydrogen welding processes (such as gas tungsten rather than shielded metal arc processes) and consumables (such as low-hydrogen rather than cellulosic electrodes). In addition, appropriate preheating and post-weld heat treatments can help the hydrogen diffuse out of the weldment. In addition to removing the diffusible hydrogen, preheating is effective in avoiding the formation of susceptible microstructure as it reduces the cooling rate of the weldment after welding. Likewise, post-weld heat treatments can relieve the residual stresses in the weldment. However, the risk of HIC still remains, in particular when welding thick, high-strength steel plates. Furthermore, the above-mentioned remedies cannot be employed for some applications due to the reduction in high productivity and cost-effectiveness. For example, shielded metal arc welding process with cellulosic electrodes is commonly employed in the construction of oil and gas pipelines.[6,12] Many researchers[5,13–15] have used empirical observations to recommend welding criteria, such as diffusible hydrogen and hardness, to reduce the probability of HIC. The maximum hardness, which is correlated with the microstructure, is the most widely-used criterion; it is recommended to be limited to 350 Hv to avoid HIC.[5,16] This hardness criterion seems reasonable considering that martensite is susceptible to HIC and its hardness is higher than that of other microstructures. However, Kurji et al.[5] have observed that weldments with maximum hardness below 350 Hv can be highly susceptibility to HIC. This has r
Data Loading...
