Investigation of heat-affected zone cracking in welded joints of modified HY-80 steel.
Henry, Eugene M.
Clark, John R.
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Heat-affected zone cracking in the welding of modified HY-80 steel (thicknesses greater than 1-1/4")has been a serious and costly problem in the nuclear submarine construction program. Welded joints fabricated with a normal heat input, some with a preheating temperature of 150 F, some with no preheating, were examined microscopically and hardness, impact strength, and tensile strength measured. In these investigations attention was focused primarily on the heat-affected zone. X-ray diffractometer tests were made to determine the presence of retained austenite in both the heat-affected zone and in the weld deposit. The specimens were fabricated by Mare Island Naval Shipyard under good shop conditions. In welds made without preheating a considerable portion of the heat-affected zone, particularly the portion adjacent to the outer weld passes, showed low notch toughness, high hardness, and in a tensile test did not deform to any appreciable extent without cracking. In fact, the mechanical properties in this area are not greatly different from those of fully hardened base plate, and microscopic examination of this area revealed a high percentage of untempered martinsite. Spontaneous "delayed" cracking was observed in all incomplete welds which were fabricated without preheating. This cracking occurred both in the heat affected zone and in the weld deposit. Joints welded with a preheating temperature of 150 F showed somewhat better mechanical properties and considerably less cracking in the heat affected zone. However, tensile tests of thee welds, with the heat affected zone oriented longitudinally with the specimen, revealed that cracks can and do occur in this zone with negligible elongation.
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