DEVELOPMENT OF WELDING PROCEDURES ANDFILLER MATERIALS FOR JOINING HIGH STRENGTH LOW ALLOY STEELS.
Report for Jun 63-Jun 64,
TRW ELECTROMECHANICAL DIV THOMPSON RAMO WOOLDRIDGE INC CLEVELAND OHIO
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A research program was conducted to develop welding procedures and filler materials for joining a martensitic and a bainitic steel having yield strengths of 180 to 200 ksi with adequate ductility and fracture toughness. The steels selected for this work were HP 9-4-20, a martensitic steel developed by Republic Steel Company, and AMS 6435 austempered to produce a bainitic structure. Welding procedures were developed for gas tungsten-arc TIG and gas metal arc MIG welding HP 9-4-20 plate and sheet material using filler wires of essentially matching compositions. Minor porosity was observed in all welds. In some cases, particularly at the higher welding speeds, intolerable porosity was encountered. The minor porosity might be eliminated in future work by adding discrete amounts of deoxidizers such as titanium and aluminum to the filler wire. Procedures were developed for making MIG and TIG welds in AMS 6435 plate material which was austempered at 575 F. Welds made at 4 ipm with a 575 F preheat and post heat for 2 hours met the 180 ksi yield strength requirement. In no instance did the AMS 6435 weld joints meet the basic yield strength requirement because of a serious loss in heat affected zone strength due to overtempering. In addition to the poor joint properties, the fracture toughness, KIC, was considerably less than that considered necessary for good resistance to brittle failure.