Effects of Grain Size on Mechanical Properties and Work‐Hardening Behavior of AISI 304 Austenitic Stainless Steel

Abstract

Grain size effects on the properties of AISI 304 austenitic stainless steel are studied. Yield stress (YS) and ultimate tensile strength (UTS) increased with decreasing grain size (Hall–Petch law) while the difference between YS and UTS decreased. Three distinct stages for work‐hardening rate are identified: I) initial rapid fall until reaching a minimum value, II) subsequent rise to a maximum due to the transformation‐induced plasticity (TRIP) effect, which is found to enhance by increasing grain size, and III) final fall until the onset of necking. More in‐depth analysis on the mechanical stability of austenite reveals that for below‐average grain size of ≈50 μm, by decreasing grain size, the TRIP effect diminishes; whereas for grain size larger than ≈50 μm, by increasing grain size, the TRIP effect becomes less pronounced. Due to the strong TRIP effect, high incremental work‐hardening exponents (n‐values of higher than 0.8) and low‐yield ratios (smaller than 0.5) are observed. It is also found that when the average grain size increases, the tensile toughness and the size and depth of dimples increase. The latter is responsible for the tardiness of the microcavity coalescence, which is indicative of high ductility of this austenitic alloy.

Deformation-induced martensite in austenitic stainless steels: A review

“…The obtained grain refinement in AISI 304 stainless steel by the reversion of martensite can significantly enhance the yield stress and tensile strength of the material at the cost of total elongation (Fig. 13a) [106,121,[204][205][206]. However, its effect on the yield stress is much more pronounced, which is related to the dependency of the ultimate tensile strength (UTS) on the TRIP effect and the grain size, and intercorrelation of these latter, as discussed before.…”

“…The amount of deformation-induced martensite depends on the chemical composition [2,116,117], initial grain size [73,85,[117][118][119][120][121][122][123][124][125][126][127][128], deformation temperature [56,57,[129][130][131][132][133][134][135], strain rate [57,[136][137][138][139][140][141][142], stress state and strain state [57,137,[143][144][145][146][147][148][149], strain [150][151][152], applied magnetic field [153], etc. Among these parameters, the chemical composition and initial grain size of the austenite phase can be classified as the material factors while the rest of parameters are deform...…”

“…In a more recent study [118], the mechanical stability of austenite phase in Fe-16Cr-10Ni alloy was found to be independent of its grain size. Recently, it has been shown that below average grain size of ~ 50 μm, by decreasing the grain size, the mechanical stability of austenite phase in AISI 304 stainless steel increased, whereas for a sample with a grain size larger than ~ 50 μm, a higher mechanical stability of austenite was observed [121]. For tensile straining of a 204Cu stainless steel [85], an anomalous dependence of the rate of the formation of strain-induced martensite on the grain size was observed as shown in Fig.…”

“…13c. The lower Hall-Petch slope for the UTS (166 MPa.μm 0.5 ) compared to that of YS (391 MPa.μm 0.5 ) implies a lower grain size dependency for the former due to the TRIP effect [121].…”

On the origin of the high tensile strength and ductility of additively manufactured 316L stainless steel: Multiscale investigation

“…One can assume that the dislocation cell structure formed in the as-built 316L tend to stabilize the austenitic phase of the AM steel and thus inhibit the strain-induced martensite transformation. Moreover, It is well established that the austenite stability is strongly related to the chemical composition (especially carbon and manganese) [55] but also to grain size [56]. Naghizadeh et al [56] showed that below average grain size of ≈50 m, the tendency to martensitic transformation diminishes by decreasing grain size.…”