Abstract
Screw rolling of austenitic stainless-steel billets was conducted in two- and three-high mills. Statistical research results showed that, compared to heated but not rolled conditions, both screw rolling techniques provided a decrease of grain size, variance, grain size distribution asymmetry, and excess in the billet cross-section at the stationary stage of screw rolling. At that stage, grain size distribution after two-high screw rolling is closer to normal in terms of asymmetry and excess values compared to grain-size distribution after three-high screw rolling. A strong negative correlation between strain effective values and grain-size values for the cross-section of the rolled billets at the stationary stage was revealed for both two- and three-high screw rolling.
Highlights
Grain structure and, essentially grain boundaries, clearly define steel mechanical properties.In particular, the Hall–Petch relationship connects the yield point with the grain size: σ0,2 = σ0 + Ky d− 2 (1)where σ0 is the friction stress connected with the sliding of dislocations in a monocrystal, and Ky is the material’s constant
A similar process of the grain structure changes leading to a mean grain size value decrease, and the nonuniformity of grain size values decrease along the cross-section of the billets were observed after hot two- and three-high screw rolling of the AISI 321 steel billets at the same temperature and close degrees of strain
This is clearly reflected in the grain size distribution
Summary
Essentially grain boundaries, clearly define steel mechanical properties. The Hall–Petch relationship connects the yield point with the grain size (the distance between the grain boundaries d): σ0,2 = σ0 + Ky d− 2 (1). The so-called uniform grain structure (or close to such) occurs in practice for most cases, and such a structure is considered when grain size distribution is close to normal. It could be nonuniform anisomerous, which can be introduced as a whole (sum) of several normal distributions. The structure obtained after secondary recrystallization [1]
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