On the crystallographic characteristics of nanobainitic steel

Abstract

This study aims to elucidate the crystallographic characteristics of bainite transformed in a temperature range of 200-350°C, where a nanobainitic structure is formed. The microstructure, consisting of bainitic ferrite laths and retained austenite, became significantly refined and its crystallographic arrangement changed with a decrease in the phase transformation temperature. At 200-250°C, the bainite packets mostly consisted of one or more blocks (i.e. bainitic ferrite laths and retained austenite lamellae) with different orientations, having a common habit plane. Some of the bainitic laths formed in this temperature range were composed of small segments with similar orientations, while others displayed a ragged morphology with small protrusions, suggesting face-to-face and face-to-edge sympathetic nucleation, respectively. At 300-350°C, the latter nucleation mechanism appeared to be dominant, as bainite packets mostly consisted of two sets of bainitic ferrite laths with similar orientations and inclined to each other (i.e. having different habit planes). In general, all rational orientation relationships (ORs) ranging from Kurdjumov-Sachs (K-S) through to Nishiyama-Wassermann (N-W) were observed within the transformation temperature range. The N-W OR was dominant at 350°C and progressively changed towards the K-S OR, which was prevalent at 200°C. The five-parameter crystallographic approach was used to statistically measure the habit plane distributions for both bainitic ferrite and retained austenite, which were generally found to be irrational and exhibited a significant anisotropy. The bainitic ferrite interface plane distribution displayed a wide peak spreading from (101) to (535). The retained austenite revealed a maximum at the (111) orientation, extending towards the (554).

Morphological and Crystallographic Characteristics of α Structure in a Low-Carbon Iron–Nickel Alloy

“…It is probable that this effect is a consequence of the change of the transformation temperature. This confirms Beladi's idea that the phase transformation temperature has a significant effect on the OR between the parent phase and the daughter phase [6]. The OR of LM was mainly K-S OR, since the specimen in our study was composed of low-carbon high alloy.…”

“…Abundant work has been conducted to introduce some crystallographic terminologies considering γ to α phase transformation in carbon steels. Table 1 presents various possible orientation relationships (ORs) between the γ parent phase and the α daughter phase [6], that is, Kurdjumov-Sachs (K-S) OR, Nishiyama-Wassermann (N-W) OR, Greninger-Troiano (G-T) OR, and Pitsch OR. In the manuscript, we will only consider the crystallographic orientation variants from a certain prior austenite crystal that are based on K-S ORs.…”

“…Table 1. Ideal orientation relationships between γ structure (parent austenite) and α structure (daughter bainite/martensite) [6]. The features of both martensitic microstructure and bainitic microstructure have been deeply explored in recent years [11][12][13][14].…”

Reformation Behavior of Austenite in 2205 Duplex Stainless Steel with Rapid Heat Treatment

“…The results showed that misorientation angles mainly distributed between 42° and 47° within the isothermal temperature range, typically shown in Figure a. It was reported that the ideal misorientation angles for K‐S and N‐W OR between ferrite and austenite were 43° and 46°, respectively . Thus, in the present work, misorientation angles at 43° ± 1° and 46° ± 1° were determined as the ones corresponded to type K‐S boundary and type N‐W boundary, respectively.…”

The Nitrocarburising Response of Low Temperature Bainite Steel

“…In all of these applications, there is potential for improved performance by enhancing the surface properties. There have been studies of microstructure and property relationships [1][2][3][4], crystallography [5,6], wear behavior [7,8], and thermal tempering [9,10] of nano-bainitic steels (henceforth termed low temperature bainite) but it has been no attempt to enhance its surface properties.…”