The Effect of Primary Ferrite on Bainitic Transformation, Microstructure, and Properties of Low Carbon Bainitic Steel
- PDF / 3,562,364 Bytes
- 9 Pages / 594 x 792 pts Page_size
- 65 Downloads / 233 Views
621.762.8:546.56-121:620.17
THE EFFECT OF PRIMARY FERRITE ON BAINITIC TRANSFORMATION, MICROSTRUCTURE, AND PROPERTIES OF LOW CARBON BAINITIC STEEL Man Liu,1 Guang Xu,1 Junyu Tian,1 Zhenye Chen,2 and Ziliu Xiong2 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 11 – 20, May, 2020.
The effects of primary ferrite on bainitic transformation, microstructure, and properties of low carbon bainitic steel Fe – 0.22C – 2.01Si – 2.20Mn – 0.22Mo are investigated by metallographic and dilatometric methods. It is found that the effect of primary ferrite on subsequent bainite formation appears as a change in the ratio of two competing processes: advance of the austenite–ferrite interface and its retardation due to retained austenite stability.
Key words: primary ferrite, bainitic transformation, retained austenite, microstructure, mechanical properties.
In summarizing published data it may be concluded that the majority of research is concentrated on studying bainitic transformation in a steel of entirely austenitic structure. Numerous studies have been devoted to the characteristics of bainite formed in a two-phase austenite–ferrite structure [24, 25]. As a first transformation product of austenite during cooling hypereutectoid ferrite has a strong effect on subsequent austenite transformation products. It has been shown in [24] that a small volumetric proportion of primary ferrite (less than 10%) stimulates subsequent bainitic transformation due to more intense nucleus formation in medium-carbon steels (0.478 – 0.490 wt.% C). However, an opposite result has been obtained in [25] in which the effect of primary ferrite (about 51 vol.%) on the kinetics of bainitic transformation in low-carbon (0.155 wt.% C) and medium carbon (0.319 wt.% C) steels was studied. The authors confirm that formation of primary ferrite suppresses subsequent bainitic transformation. Therefore, so far the effect of primary ferrite on bainitic transformation is unexplained. The present work is to study the effect of primary ferrite on bainitic transformation in low-carbon steel Fe – 0.22C – 2.01Si – 2.20Mn – 0.22Mo (wt.%).
INTRODUCTION Bainitic steels are used extensively in industry [1 – 5]. Many studies of the effect of alloying elements [6 – 11], heat treatment [12 – 17], and deformation on the nature of bainite transformation are well known. For example, alloying with niobium slows down bainitic transformation, but molybdenum facilitates it [6]. With addition of chromium there is an increase in low-carbon bainitic steel tensile strength due to an increase in the amount of bainite [10]. It has been confirmed in [12] that two-stage treatment accelerates bainitic transformation. An increase in ductility and toughness is achieved due to quenching for bainite and Q&P-heat treatment of medium-carbon Mn – Si – Cr-steel with strength of 1700 MPa [13]. A finer bainite microstructure is obtained in a specimen after thermal annealing at a temperature below the Ms compared with annealing at a temperature above the Ms [14]. In addition
Data Loading...
