Effects of Mn additions on the P embrittlement of the Fe grain boundary

Abstract

To achieve an electronic level understanding of intergranular embrittlement and its control in steel, the first principles full potential linearized augmented plane wave method and the atomic force approach are used to investigate the effect of Mn additions and P impurities on the energetics and underlying electronic properties of both the Fe grain boundary ͑GB͒ and the corresponding intergranular fracture surface ͑FS͒. The calculated binding-energy difference is ϩ0.17 eV/adatom for P in the P/Fe binary system, in agreement with its observed embrittlement potency. The Mn is also found to contribute a direct embrittling effect of ϩ0.20 eV/adatom, associated with stronger Mn-Fe chemical bonding in the FS environment. The computed binding-energy difference for P in the ͑PϩMn͒/Fe ternary system is increased to ϩ0.40 eV/adatom, consistent with experimental evidence that Mn facilitates P embrittlement in the grain boundary. The origin of the Mn enhanced P embrittlement is attributed to the strengthened in-plane P-Mn interaction, which makes the P impurity interact more isotropically with the surrounding Mn and Fe atoms in the GB and FS.

Microstructural and Fracture Behavior of Phosphorus-Containing Fe-30Mn-9Al-1Si-0.9C-0.5Mo Alloy Steel

“…As with prior understanding regarding the P embrittlement in low alloy steels [1] and Mn steels, [2,3] the study presented here has shown also that P embrittles agehardenable nominal Fe-30Mn-9Al-1Si-0.9C-0.5Mo alloys. Regardless of heat treatment regime investigated, increasing P content corresponds to a change from ductile to cleavage fracture and an increase in hardness in agehardenable Fe-Mn-Al-C steel.…”

“…Brittle cleavage fracture dominated the 0.043 and 0.07 pct P-containing alloys. A hard brittle P eutectic phase was observed in the 0.07 pct P-containing alloy.Phosphorus 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-0.9C-0.5Mo 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).…”

Development of an interatomic potential for phosphorus impurities in -iron

“…Previous ab initio calculations on iron-phosphorus [22,23,24,25] using the similarly-reliable full-potential linearized augmented plane wave method have downplayed total energy and concentrated on the role of increased electron density as indicating strengthening of the bonds at the surface relative to the grain boundary. This qualitative picture is not specific to FeP and follows from the tight-binding formalism [7].…”

Effects of Impurities on an Al Grain Boundary

“…The effects of impurities in a Fe boundary, such as P and B, 9) C, 10) Mo and Pd 11) and H, 12) have been studied in detail. Some additions on the P impurity-promoted embrittlement of the Fe boundary have also been examined, such as Mn 13) and Mo. 14) For a Ni grain boundary, the effects of H, B, P 15) and Li, He, Ca 16) have been investigated.…”