Evaluation of Heat-Affected Zone Hydrogen-Induced Cracking in Navy Steels The implant test was conducted on HY-100, HSLA-100, and HSLA-65, plus the hydrogen-induced cracking susceptibility was quantitatively evaluated The implant test was conducted on HY-100, HSLA-100, and HSLA-65 to evaluate their susceptibility to heat-affected zone (HAZ) hydrogen-induced cracking (HIC). The stress vs. time to failure curve was plotted, and the normalized critical stress ratio (NCSR) and embrittlement index for each steel were determined, which can be used to quantitatively evaluate HIC susceptibility. The coarse-grained HAZ (CGHAZ) microstructure of the three steels was characterized by means of optical and transmission electron microscopy. In addition, SEM fractography was conducted to study the HIC fracture behavior. Intergranular (IG), quasi-cleavage (QC), and microvoid coalescence (MVC) fracture modes were found to occur sequentially during the crack initiation and propagation process. The fracture behavior observed in the present investigation is in good agreement with Beachem’s model. It can be concluded based on the implant test results that, among the three steels, HY-100 is the most susceptible to HAZ HIC while HSLA-100 and HSLA-65 exhibit good resistance. The difference in the HIC susceptibility JANUARY 2013, VOL. 92 20-s WELDING RESEARCH of the three steels is further explained by combining the microstructure characterization of the CGHAZ and fracture behavior. These results can serve as a benchmark for the future development of high-performance Navy steels. Introduction ABSTRACT Ship structures are subject to a complex dynamic loading during service that is superimposed on residual stress present as a result of fitup and fabrication. Therefore, high-performance steels for ship structure applications have been a constant goal pursued by the United States Navy. In order to meet the requirement for good combination of high strength and low-temperature fracture toughness, high-yield-strength steels (HY series) and high-strength, low-alloy steels (HSLA series) have been under development by the Navy for the last 50 years. Among them, HY-100, HSLA-100, and HSLA-65 are used extensively in surface ship and submarine construction today, and they will continue to be the principal structural materials in the foreseeable future (Refs. 1–3). Navy shipbuilding has been heavily reliant on welding as a fabrication technique, and it has been of great practical importance to conduct weldability testing of steels. Among various weldability issues of high-strength steels, hydrogen-induced cracking (HIC) (also referred as cold cracking) in the heat-affected zone (HAZ) following welding is of concern (Refs. 4–6), and thereby it is important to evaluate the naval steels’ susceptibility to HAZ HIC. Within the HAZ, the coarsegrained HAZ (CGHAZ) is the most susceptible to formation of untempered martensite with coarse grain size (Refs. 7, 8), and therefore potentially the most susceptible to HIC (Ref. 9). Based on the strong microstructure influence on HIC, CCT diagrams for the CGHAZ of HY- 100, HSLA-100, and HSLA-65 have been constructed, as described in an earlier publication (Ref. 10). In parallel with that study, the susceptibility to HIC has been evaluated for the same three steels. In the present investigation, the implant test is used to evaluate susceptibility to HIC. The microstructure of the weld CGHAZ from this test is characterized, and fractography is conducted to illustrate the HIC fracture behavior. The HIC test experimental results will be used to develop a weldability database of current Navy steels, which can serve as a benchmark for the future development of highperformance steels. Materials and Experimental Procedure HY-100, HSLA-100, and HSLA-65 were provided in the form of rolled plate by the Naval Surface Warfare Center, Carderock Division, West Bethesda, Md. Table 1 summarizes the chemical compositions of the three steels used in this investigation. The steel plates were machined into the implant specimens, whose dimensions are listed in Table 2. The implant test used in the present investigation was first developed by Henri Granjon at the Institut de Soudure (French Welding Institute) (Ref. 11). In the implant test, a cylindrical sample with a 0.5-in.- (12.7-mm-) long 10-32 UNF thread on one end is inserted into a clearance hole in the center of the specimen plate. The other end with a 0.5-in.- (12.7- mm-) long 1/4-20 UNC thread is inserted into a threaded connection rod of the loading system so that it is possible to apply a tensile load on the specimen after welding. A weld bead was then deposited on the top surface of the specimen plate directly over the threaded sample and hole, creating a HAZ in the 10-32 UNF thread region, as shown in Fig. 1. The thread serves to create a stress concentration in the HAZ region, thereby causing HIC to occur in the HAZ instead of the fusion zone. Two minutes after completion of welding, the sample is loaded in tension when the temperature of the weld assembly is in the range of 100°–150°C. The tensile load is provided by The Ohio State University Modified Implant Testing System (OSU-MITS), as shown in Fig. 2, which was specially designed and built to BY X. YUE AND J. C. LIPPOLD KEYWORDS Implant Test Hydrogen-Induced Cracking CGHAZ Microstructure Fracture Behavior HSLA-100 HY-100 HSLA-65 X. YUE (yuexinosu@gmail.com) and J. C. LIPPOLD are with the Welding Engineering Program at The Ohio State University, Columbus, Ohio. Based on a paper presented at FABTECH 2012 in Las Vegas, Nev., November 12–14, 2012.
Welding Journal | January 2013
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