Welding of ASTM A709 50CR Using Austenitic Filler Wires With Varying Heat Inputs and Maximum Interpass Temperatures

About the report:

ASTM A709 Grade 50CR, also known as ASTM A1010, is a structural steel developed to address the corrosion issues associated with the use of traditional weathering steels, especially in environments involving combined prolonged wetness and chlorine salts. The fabrication of bridge girders from Grade 50CR has largely relied on the use of 309L solid filler wire with heat inputs up to 55 kJ/in and maximum interpass temperatures up to 450 °Ffor 1 in thick plate. The purpose of this project was to determine if higher heat inputs could be used when welding 50CR and to evaluate several filler wire materials that could be used during plate girder fabrication. Three groups of50CR plates were used in this study: sixteen 1/2-inch thick welded 50CR plates, twelve 1 in thick welded 50CR plates, and two welded AWS D1.5 prequalification record (PQR) plates. The testing performed in this study revealed the following:

• The ductile to brittle transition temperature (DBTT) of the 50CR base plate was measured to be -40 °F.
• A range of austenitic stainless steel filler wires can be used to successfully weld 50CR. In this study, 309LC (metal cored wire), 309LSi (Si added for flowability and appearance), and 316L (Mo added for enhanced corrosion resistance) were found to be viable alternatives to the incumbent filler wire, 309L.
• Use of 309L filler wires for 1/2 in plates results in submerged arc welds (SAW) which are borderline with respect to impact energy at the high heat input level of 75 kJ/in, over the temperature range investigated. Lower heat inputs (e.g., 55 kJ/in previously shown effective) are recommended. Similar results were obtained for welds in 1/2 in plates produced with 309LSi and 316L.
• Heat inputs of up to 75 kJ/in at all interpass temperatures explored (up to 450 °F) can be used to weld 1/2-inch plates with 309LC filler wire. The enhanced toughness and low DBTT of welds in 1/2 in plates formed using 309LC filler wire appears to be due to the mitigation of large, aligned d-ferrite grain formation during solidification. Such large, aligned grains otherwise serve as preferred crack paths in welds.
• Heat inputs of 90 kJ/in and interpass temperatures of up to 450 °F can be used for all four of the filler wires investigated (309L, 309LC, 309LSi, and 316L) for 1 in thick plate.

It is recommended that when 50CR is considered for bridges in specific corrosive environments due to its corrosion resistance, improved mechanical properties, and lifetime cost, the aforementioned findings be incorporated in the guidance documents. The availability of alternatives to the conventional solid 309L filler wire currently used to weld 50CR allows more vendors, eliminating the requirement for sole source justification and opening broader possibilities to satisfy Buy America requirements for federally funded bridge projects. Finally, 309LC (metal-cored filler wire) outperformed the solid filler wires examined in this study with respect to production (higher deposition rates and fewer required passes) and mechanical properties (especially impact toughness) of the resulting welds.

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