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PhD dissertation-Xin Yue.pdf (28.92 MB)

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Evaluation of Heat-affected Zone Hydrogen-induced Cracking in High-strength Steels

Yue, Xin
http://rave.ohiolink.edu/etdc/view?acc_num=osu1374109768

Abstract Details

2013, Doctor of Philosophy, Ohio State University, Welding Engineering.
Shipbuilding is heavily reliant on welding as a primary fabrication technique. Any high performance naval steel must also possess good weldability. It is therefore of great practical importance to conduct weldability testing of naval steels. Among various weldability issues of high-strength steels, hydrogen-induced cracking (HIC) in the heat-affected zone (HAZ) following welding is one of the biggest concerns. As a result, in the present work, research was conducted to study the HAZ HIC susceptibility of several naval steels. Since the coarse-grained heat-affected zone (CGHAZ) is generally known to be the most susceptible to HIC in the HAZ region, the continuous cooling transformation (CCT) behavior of the CGHAZ of naval steels HSLA-65, HSLA-100, and HY-100 was investigated. The CGHAZ microstructure over a range of cooling rates was characterized, and corresponding CCT diagrams were constructed. It was found that depending on the cooling rate, martensite, bainite, ferrite and pearlite can form in the CGHAZ of HSLA-65. For HSLA-100 and HY-100, only martensite and bainite formed over the range of cooling rates that were simulated. The constructed CCT diagrams can be used as a reference to select welding parameters to avoid the formation of high-hardness martensite in the CGHAZ, in order to ensure resistance to hydrogen-induced cracking. Implant testing was conducted on the naval steels to evaluate their susceptibility to HAZ HIC. Stress vs. time to failure curves were plotted, and the lower critical stress (LCS), normalized critical stress ratio (NCSR) and embrittlement index (EI) for each steel were determined, which were used to quantitatively compare HIC susceptibility. The CGHAZ microstructure of the naval steels was characterized, and the HIC fracture behavior was studied. Intergranular (IG), quasi-cleavage (QC) and microvoid coalescence (MVC) fracture modes were found to occur in sequence during the crack initiation and propagation process. This was rationalized using Beachem's model. Based on the implant test results, it can be concluded that with respect to HAZ HIC susceptibility, the four steels from the most susceptible to the least, are HY-100, BA-160, HSLA-100 and HSLA-65. Increasing diffusible hydrogen content showed that HSLA-100 has better tolerance to the increase in hydrogen levels than BA-160 and HY-100, with HY-100 exhibiting the least tolerance to hydrogen increase in weld joint. For the BA-160 steel, the effect of welding parameters on HAZ HIC susceptibility was investigated. It was shown that both increasing heat input and using preheat can improve the HAZ HIC resistance of BA-160. It was also found that using a PWHT at 650°C for 1 hour to reduce HIC susceptibility of BA-160 steel is also beneficial for the strength recovery in the softened as-welded CGHAZ. This is attributed to the re-precipitation of strengthening phases during the PWHT process that are dissolved in the CGHAZ during heating to the high temperature and do not re-precipitate completely during cooling.
John Lippold (Advisor)
Sudarsanam Babu (Committee Member)
Glenn Daehn (Committee Member)
Yogeshwar Sahai (Other)
248 p.
Engineering; Materials Science
High-strength steels; Heat-affected zone; Hydrogen-induced cracking; The implant test; Continuous cooling transformation; Microstructure characterization; Fracture behavior

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Citations

  • Yue, X. (2013). Evaluation of Heat-affected Zone Hydrogen-induced Cracking in High-strength Steels [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1374109768

    APA Style (7th edition)

  • Yue, Xin. Evaluation of Heat-affected Zone Hydrogen-induced Cracking in High-strength Steels. 2013. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1374109768.

    MLA Style (8th edition)

  • Yue, Xin. "Evaluation of Heat-affected Zone Hydrogen-induced Cracking in High-strength Steels." Doctoral dissertation, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1374109768

    Chicago Manual of Style (17th edition)

osu1374109768
1,144
© 2013, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.