Role of annealing twins for grain refinement in controlled rolling of low carbon microalloyed steel.

Abstract

SynopsisA 0.1 %C-1.35%Mn-0.03%Nb steel was hot rolled in a single pass up to 83 % reduction in thickness at a temperature between 790 °C and 1 050 °C and the deformation state of austenite was examined metallographically in detail. It was found that annealing twins were formed abundantly in the austenite during heating before rolling, or during recrystallization in a high temperature. Rolling at a temperature below the recrystallization temperature of austenite resulted in a severe deformation of these annealing twins. At the same time, a heavy local deformation was introduced into the regions near boundaries of these annealing twins, and also near austenite grain boundaries. Such a local concentration of deformation was found to enhance the formation of ferrite nuclei in these regions during the subsequent ferrite-pearlite transformation. It was suggested that this effect was most essential in the grain refinement of control-rolled steel.

Nucleation of Proeutectoid Ferrite on Complex Precipitates in Austenite

“…This implies that plastic accommodation in austenite itself does not promote intragranular ferrite transformation significantly. Since it is known that deformation bands as well as deformed annealing twin boundaries act as preferential nucleation sites within the austenite grain, 19,20) the increase in ferrite nucleation at MnS by hot rolling should be less than the observed increase in intragranular ferrite in Fig. 12(a).…”

Factors Affecting Texture Memory Appearing through α→γ→α Transformation in IF Steels

“…transformation in deep-drawable cold-rolled sheet steels. 1,2) On the other hand, it has been observed that the initial texture hardly changes in microalloyed low-carbon steels with a considerable amount of Mn such as 0.09 mass%C-0.62 mass%Mn-0.03 mass%Nb, 3) 0.1 mass%C-1.35 mass%Mn-0.03 mass%Nb 4) and 0.19 mass%C-1.35 mass% Mn-0.06 mass%Nb 5) controlled-rolled sheet steels, in which martensitic transformation took place during cooling. In these studies, the mechanism was not discussed.…”

Transformation behaviour of austenite after thermomechanical treatment

“…8 It could explain the common tendency, shown in Figures 4.12, 4.17 and 8.2, that the acceleration of transformation is pronounced even with a small amount of deformation in which the increases in the above-mentioned y interfacial surfaces are still gradual. It elevates the A r3> temperature ( 0.11 % C 0.26% Si-1.36% Mn-0.05% Nb -0.04% V-0.004% N Reheated at 1250° C, finish-rolled at temperatures below 800° C and aircooled 13-mm thick plate.…”