Atomic-scale characterization of prior austenite grain boundaries in Fe-Mn-based maraging steel using site-specific atom probe tomography

作者：Moszner F; Gerstl S S A; Uggowitzer P J; Loeffler J F

来源：Acta Materialia, 2014, 73: 215-226.

DOI：10.1016/j.actamat.2014.04.009

• Atom probe tomography
• Precipitation
• Mechanical behavior
• Grain boundary embrittlement
• Fe-Mn maraging steels

The embrittlement and de-embrittlement behavior of an Fe-10Mn-1Pd (wt.%) maraging steel upon isothermal aging at 500 C is related to microstructural changes at prior austenite grain boundaries (PAGBs). Site-specific atom probe tomography measurements were performed to analyze the local chemistry of the PAGBs. Tensile tests and hardness measurements were conducted of the ternary alloy and of a binary non-hardenable Fe-10Mn alloy for comparison. Isothermal aging of the binary steel led to a decrease in strength along with a considerable increase in uniform elongation. The Pd-containing alloy, on the other hand, showed significant age-hardening, and an embrittlement and de-embrittlement transition was revealed. Ductile behavior was observed in the initial as-quenched and over-aged states, but there was zero tensile elongation in the intermediate under- and peak-aged regions, where intergranular fracture along the PAGBs occurred. In the brittle peak-aged state a large number of small nanometer-sized particles rich in Mn and Pd formed inside the grains and decorated the PAGBs. The precipitates grew in size on prolonged aging. Mn segregation to the PAGBs was revealed; the Mn concentration level at the boundaries varied with aging time and was highest in the peak-aged condition. Embrittlement and de-embrittlement mechanisms are discussed and compared to these observations.

• 出版日期2014-7