Effect of microstructure on hydrogen embrittlement of weld-simulated HSLA-80 and HSLA-100 steels
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Effect of Microstructure on Hydrogen Embrittlement of Weld-Simulated HSLA-80 and HSLA-100 Steels K. BANERJEE and U.K. CHATTERJEE HSLA-80 and HSLA-100 steels have been subjected to weld-simulated grain-coarsened heat-affected zone (GCHAZ) and grain-refined heat-affected zone (GRHAZ) treatments at peak temperatures of 1350 ◦C and 950 ◦C, respectively, followed by varying cooling rates to approximate the weld heat inputs of 10 to 50 kJ/cm. Subsequent slow strain rate testing in synthetic seawater has been employed to assess the hydrogen embrittlement (HE) propensity of the materials. It is indicated that in spite of an increase in strength after weld simulation, further ductility deterioration, compared to the base material under similar testing conditions, did not occur in GCHAZ HSLA-100 steel and for low heat input condition of GRHAZ HSLA-80. This has been attributed to their HE resistant microstructures. Predominant acicular ferrite or lath martensite or a combination of both imparts resistance to HE, as observed in the case of grain-coarsened HSLA-100 and for the low heat input grain-refined HSLA-80 steels. The deleterious effect of bainitic-martensitic microstructure has been reflected in the ductility values of grain-coarsened HSLA-80, which is in agreement with the observation of higher susceptibility of the as-received HSLA-100 steel having a similar structure. However, contrary to its beneficial effect in the as-received HSLA-80, an acicular ferrite structure has shown vulnerability toward HE for high heat input grain-refined HSLA-80. This has been attributed to the presence of polygonal ferrite and to the development of an HE susceptible substructure on GRHAZ weld simulation.
I. INTRODUCTION
L OW-CARBON, copper-precipitation-strengthened HSLA steels have emerged as suitable replacements for the conventional high-carbon quenched and tempered HY steels for the naval ship hull structure. The HY series of steels are vulnerable to weld cracking because of the formation of untempered martensite due to the combined action of highcarbon content and alloying elements. The possible means to obviate this difficulty is to follow stringent welding process control by preheating and postweld soaking treatments or with the reduction in carbon content to a level too low to form untempered martensite. The HSLA steels meet the property requirements at a significantly lower fabrication cost due to the elimination of preheating and postweld soaking treatments. However, as the ship hull is cathodically protected to prevent corrosion from seawater, usually by using sacrificial anode zinc, cathodic hydrogen makes its way into the material causing embrittlement. At the developmental stage of HSLA steels, Montemarano et al.[1] have certified that the fracture toughness and tearing modulus of HSLA-80 steel are comparable and in some cases much better than those of HY steels. The fracture toughness data from precracked cantilever beam stress corrosion cracking (SCC) tests at a zinc level of cathodic protection indicated immunity of t
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