Microstructural and Fracture Behavior of Phosphorus-Containing Fe-30Mn-9Al-1Si-0.9C-0.5Mo Alloy Steel
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hosphorus embrittlement in low alloy steel[1] and Mn steels,[2,3] steels with 10 pct or more Mn content, is well known, but microstructure and fracture behavior across a broad range of phosphorus levels have not been reported regarding its effect in Fe-30Mn-9Al-1Si-0.9C0.5Mo alloys. Nominal Fe-30Mn-9Al-1Si-0.9C-0.5Mo alloys are fully austenitic or are duplex (c and a) after solution treatment at 1273 K (1000 °C).[4] Ferrite volume fraction reduction is known to occur when phosphorus (P) content is reduced,[4] the solution treatment temperature is increased to 1323 K (1050 °C),[5] and Si content is maintained at a nominal 1 pct content. FeMn-Al-C steels age harden by spinodal decomposition with corresponding decreases in ductility and toughness.[4,6] As the amount of aging increases (both in time and temperature), the propensity of cleavage fracture also increases,[7,8] thus cleavage fracture becomes the dominant fracture mode in aged material. Cleavage fracture is also associated with heterogeneous precipitation along c grain boundaries.[9] What is not fully known is the effect P has regarding dynamic impact toughness,
RYAN A. HOWELL, US Army Officer, is with the Army Research Lab, Weapons and Materials, United States Army, Aberdeen Proving Ground, MD 21005. Contact e-mail: [email protected] DAVID C. VAN AKEN, Metallurgical Professor, is with the Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, MO 65409. Manuscript submitted November 3, 2014. Article published online May 28, 2015 METALLURGICAL AND MATERIALS TRANSACTIONS A
hardness, fracture surface characteristics, and microstructure of cast Fe-Mn-Al-C alloys. Prior CVNE experimental results revealed structure property differences between two nominal Fe-30Mn9Al-1Si-0.9C-0.5Mo alloys with differing P content.[10] A 0.043 pct P-containing alloy exhibited an 80 pct reduction in room temperature CVNE to 13.6 J/cm2 compared to a 0.006 pct P-containing alloy with a CVNE value of 73 J/cm2. The fracture mode changed from microvoid coalescence for the 0.006 pct P-containing alloy to cleavage fracture for the 0.043 pct P-containing alloy. The research presented for this communication provides additional observations regarding the structure property effects due to varying concentrations of P in nominal Fe-30Mn-9Al-1Si-0.9C0.5Mo steels. Cast plate specimens were produced from high purity induction Fe, Al, ferrosilicon, ferromolybdenum, and electrolytic Mn or ferromanganese in an induction furnace under argon cover. Alloys were cast into olivine phenolic no-bake sand molds and poured without filtering with 100 K (100 °C) superheat. A low density coagulant was utilized for deslagging. Chemical analysis after dissolution in perchloric acid was conducted using ion-coupled plasma spectrometry except for Mn and Al. Those elements were measured by wavelength dispersive spectrometry (Table I). ASTM E 23 Type-A V-notch Charpy test samples of each alloy were produced from the cast plates and prepared for two testing categories. The
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