TESTING 1-2-3
UNDERSTANDING PHASE TRANSFORMATIONS AND WELDING OF ULTRA-HIGH STRENGTH STEELS
New high strength steels will require knowledge of how thermal processes, such as welding, will affect mechanical properties.
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AN MCDP STAFF REPORT
glin steel is an ultra-high strength steel alloy developed at Eglin Air Force Base in Florida in the early 2000s and patented in 2009. It was developed for use in high strain rate applications, such as missile components, penetrating ordnance and armor plating. Precipitation hardened (PH) maraging stainless steel alloys also are being studied for their ultra-high strength. T ese steel alloys have the potential to make a con-
siderable impact on the market. But the eff ects of certain thermal-based processes, such as casting, heat treatment
and welding, on mechanical properties have not been studied closely for control purposes. Researchers Brett Leister, Erin Barrick and John DuPont of the Depart- ment of Materials Science and Engineering at Lehigh University, Bethlehem, Pa., set out to produce a continuous cooling diagram for Eglin steel as well as develop
ADDING IT ALL UP
“Phase Transformations and Welding of Ultra-High Strength Steels” Brett Leister, Erin Barrick and John DuPont, Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pa.
Background—Eglin steel is an ultra-high strength steel developed for use in high strain rate applications. It exhibits similar strength levels to currently used alloys, but at a reduced cost due to less expensive alloying elements.
Procedure—In order to produce a continuous cooling transforma- tion diagram to aid in mechanical property control during cast- ing, heat treatment and welding, researchers conducted thermal simulations, mechanical testing, dilatometry and heat affected zone simulations. Results and Conclusions—Cooling rates and how they affect grain structure and mechanical properties were recorded.
heat treat schedules for the PH steels. T eir work is described in the paper “Phase Transformations and Welding of Ultra-High Strength Steels,” which was presented at the Steel Founders’ Society of America’s 2013 Technical & Operating Conference.
Question How do various processing steps
aff ect the mechanical properties of Eglin steel and specifi c PH maraging stainless steels?
applications, but it has a reduced cost due to a reduction in expensive alloy- ing elements such as nickel and cobalt (Table 1). Silicon is added to Eglin steel to enhance toughness. Chro- mium provides increased strength and hardenability, molybdenum increases hardenability and nickel increases toughness. T e addition of tungsten also increases strength. Fabricating this steel through cast-
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ing, forging, fusion welding and heat treatment involves a wide range of cooling rates that can produce various microstructures and resultant proper- ties. Continuous cooling transforma- tion diagrams are helpful for control-
Jan/Feb 2014 | METAL CASTING DESIGN & PURCHASING | 41 Background Eglin steel exhibits similar
strength levels to AerMet100, AF1410 and HP9-4-30 al- loys, currently used for similar
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