Effect of Hot Deformation on Microstructure, Hardness and Precipitation Kinetics in a C350 Maraging Steel Modified by Titanium Addition

Abstract

Maraging steels are alloys with a good balance between strength and fracture toughness. These properties are obtained by quenching and aging treatments, where the precipitation of intermetallic compounds is promoted in a martensitic matrix. In this context, this paper aims to evaluate the effect of hot deformation on microstructure, kinetics and formation of reverted austenite in a C350 maraging steel modified by titanium addition, in order to improve the mechanical properties without addition of alloying elements. The following characterization techniques were used: optical microscopy (OM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Vickers microhardness and Dilatometry. The results showed that the deformation promoted a refinement of martensitic packages and blocks, proportional to the reduction of height and a preferred alignment towards the center of the sample. In the aging treatment, the deformation accelerated the kinetics of precipitation and formation of reverted austenite. It was also verified a reduction of the volumetric variation produced by reactions and a reduction of precipitation temperature and formation of reverted austenite in the greater deformation.

Structural Study of Undeformed and Deformed Maraging C300 Steels Using X-ray Diffraction Measurements

“…These precipitates are metastable, coherent/semi-coherent with the matrix [21] and form in the first few minutes of aging at temperatures above 723 K [16,40,54]. The same diffraction pattern is observed in the work of Freitas [44], who also studied a high Ti content maraging C300 steel. However, due to aging at 823 K, the presence of Ni 3 (Ti, Mo) observed was smaller and overlapped by reverse austenite peaks.…”

“…However, as the tendency of precipitation kinetics is to reduce with a reduction in supersaturation and nucleation site, the increase in Ni 3 (Ti, Mo) volumetric fraction was less significant between 10 and 50 h than 0 and 10 h. Increasing aging time also generates austenite in the HF condition, only. That was also verified by Guiza [7] and Freitas [44], which showed that hot forging accelerates the austenite formation.…”

“…As the increase in the aging temperature leads to an increase in the formation of stable precipitates and reversed austenite, a reduction in the fraction of metastable precipitates and an acceleration in their dissolution, at temperatures higher than 823 K it is difficult to distinguish metastable precipitates in X-ray diffraction. In addition to phase formation, the X-ray diffraction also enables to verify the influence of deformation on crystallite size, microstrain and lattice parameter [44].…”