Effect of Carbon and Nitrogen on Work-hardening Behavior in Metastable Austenitic Stainless Steel

Abstract

The effects of C and N on the work-hardening behaviors were compared in metastable austenitic steels in which varied amounts of C and N were separately added (Fe-18%Cr-8%Ni-(C,N) alloys). Although both C and N suppressed deformation-induced martensitic transformation during tensile deformation due to their austenite-stabilizing effect, they enhanced the work hardening of the steels. Comparison of C-added and N-added steels revealed that C addition more increased the work-hardening rate than N addition. In order to clarify the reason of the more significant effect of C, the individual hardness of deformed austenite and deformation-induced martensite (DIM) were measured in cold-rolled C-added and N-added steels by using a nano-indentation tester. The nanohardness of deformed austenite increased with increasing the thickness reduction and amount of added C and N. However, there is little difference between C-added and N-added steels in the hardening behavior of austenite, meaning that the difference in work-hardening rate of metastable austenitic steel between C-added and N-added steels is not derived from the hardness of deformed austenite but that of DIM. The nanohardness of DIM was significantly higher in the C-added steel than N-added steel, and thus, the main factor affecting the higher work hardening of 0.1C steel should be considered to be the higher hardness of C-containing DIM. In addition, in C-added steels, an excellent strength-ductility balance was achieved compared with N-added steel because the hard DIM is gradually formed until the later stage of deformation, meaning that pronounced TRIP effect was obtained in C-added steels than N-added steels.

Profilometry‐Based Inverse Finite Element Method Indentation Plastometry

“…The exact behavior depends on several factors, including the temperature (because the thermodynamic driving force for martensite formation is greater at lower temperature) and the stacking fault energy, with a low value facilitating the cross-slip that can be involved in the phase transformation. [48][49][50][51] The composition is important, including the carbon and nitrogen levels. High levels of these tend to retard martensite formation, although very low levels of carbon lead to a reduction in the hardness of the martensite.…”

Effect of Relatively Low Levels of Porosity on the Plasticity of Metals and Implications for Profilometry‐Based Indentation Plastometry

“…However, if the plasticity has an associated volume change, then this may not be the case. For example, TCA has been reported [7][8][9][10] in metastable austenitic stainless steels, in which plasticity commonly involves the formation of martensite, that is, a phase change (with an associated volume change) takes place. The presence of porosity, which might be expected to be raised during plastic deformation by a tensile hydrostatic stress and decreased by a compressive one, could therefore lead to a TCA effect.…”

Tensile-Compressive Asymmetry in Extruded Az31b Rod and its Effect on Profilometry-Based Indentation Plastometry (Pip)

“…Another instance is when the plasticity involves a phase change, since in most cases this will be accompanied by a volume change. For example, in certain metastable austenitic stainless steels, it is common for plasticity to stimulate martensite formation, raising the hardness (and hence the work hardening rate) appreciably [4][5][6][7]. For a positive volume changeie the new phase being less dense than the parent region, its formation should be promoted by a tensile hydrostatic stress and inhibited by a compressive one.…”