The effect of molybdenum on interphase precipitation and microstructures in microalloyed steels containing titanium and vanadium

Abstract

Despite much research into steels strengthened through interphase precitation, there remains much that is not clear, such as the role of a range of elements, particularly Mo, in the interphase precipitation process. Four steels were manufactured with identical composition, but with variations in Ti, V, Mo and N content to investigate the effect of composition on interphase precipitation. Alloys were rapidly cooled from the single austenite phase field and isothermally transformed at 630°C and 650°C for 90min. The addition of Mo was found to significantly reduce the austenite to ferrite transformation kinetics, particularly for the V steel. Interphase precipitation was observed in all alloys at both transformation temperatures. For the Ti bearing steel, the two types of precipitate were observed throughout the sample, namely TiC (finer) and Ti2C (coarser), while for the V bearing steels, VC (finer) and V4C3 (coarser) were observed. Where Mo was present in the alloy, it was found dissolved in all carbide types. The (Ti,Mo)C and (V,Mo)C formed by classical planer interphase precipitation (PIP) while the (Ti,Mo)2C and (V,Mo)4C3, that had a much wider row spacing, formed through curved interphase precipitation (CIP). Each adopted one variant of the Baker-Nutting orientation relationship. The Ti-microalloyed steels exhibited the smallest precipitates of all the steels, which were approximately the same size irrespective of whether Mo was present in the alloy and irrespective of the transformation temperature. However, the addition of Mo to the V bearing steels resulted in a significant increase in precipitate volume fraction and a reduction in precipitate size. The mechanisms of interphase precipitation leading to the coincident production of two different precipitate types is considered and the role of Mo on the interphase precipitation process is discussed. The resultant effect on strength is considered.

Observing hydrogen in steel using cryogenic atom probe tomography: A simplified approach

“…A ferritic steel designed to incorporate a high number density of V-Mo-Nb transition metal carbides was used in this study (as per [24]) with the nominal chemical composition given in Table 1. The material sheet was manufactured in a continuous production from 980°C, hot rolling and then coiling at 650°C, which typically allows the formation of high-density carbide precipitates [32]. The yield strength, tensile strength, stiffness and Poisson ratio for the as-received material were 820 and 897 MPa, 200 GPa and 0.3 respectively.…”

Effect of Molybdenum on the Impact Toughness of Heat-Affected Zone in High-Strength Low-Alloy Steel

“…The migration and growth of prior austenite grain after the high-temperature welding thermal cycle in the HAZ can be inhibited by a large number of fine carbides and nitrides [ 16 , 17 ]. As a well-known microalloying addition, Nb, V, Ti, and Mo could refine the grain size and provide fine carbonitride precipitates, which facilitate superior mechanical properties [ 18 , 19 , 20 , 21 ]. Gómez et al reported that the addition of Nb in steel was beneficial for retarding the static recrystallization of austenite and achieving fine ultimate microstructures [ 22 ].…”

The Impact of Interphase Precipitation on the Mechanical Behavior of Fire-Resistant Steels at an Elevated Temperature

“…Studies have shown that a number of precipitate-forming elements can form interphase precipitation, such as carbonitrides of Ti, Nb, V, Mo, Cr, etc. [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. There have been two main approaches to obtain interphase precipitation up to now.…”