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.

The microstructure and microhardness of isothermally aged Al-0.22Zr and Al-0.32Zr alloys were investigated. Peak microhardness occurred after aging at 650K for 100 h for both alloys and decreased slightly after aging at 400 h. Nanometer-scale spherical L12-structured Al3Zr precipitates were observed using Transmission Electron Microscopy, these presented r < 7 nm at the center of dendrite branches. In the Al-0.32Zr alloy, particles increased in radius after aging at 650 K from 100 to 400 h while in the Al-0.22Zr alloy, precipitate radii remained constant in the same range. This is possibly due to solute migration to the periphery of dendritic branches, where larger particles nucleated. After aging at 700 K for 100h, there are growth instabilities at the interface of the particles. A theoretical model, used to predict particle growth by diffusion, presented good agreement with the experimental findings.

An experimental investigation was conducted using laboratory-processed low carbon Mn-Mo-Nb-Ti-B dual phase steel with additions of 0.2Cr or 0.6%Cr. This study investigates the effect of Cr additions on ferrite recrystallization and austenite formation during continuous annealing in the intercritical temperature range. It was found that moderate additions of Cr (0.2%) accelerates the ferrite recrystallization (nucleation and growth) resulting in coarse ferrite grains. An increase in Cr content up to 0.6% also accelerates the ferrite recrystallization which in addition to the presence of Cr-rich carbides facilitates the austenitization predominantly through the nucleation process resulted in finer austenite grains. Thereby, the higher Cr content increases the volume of homogenized and refined martensite in the final quenched structure.

Este trabalho teve por objetivo estudar o efeito do tratamento de nitretação por plasma e do revestimento de carbonitreto de titânio sob o aspecto de resistência ao desgaste de matrizes de conformação mecânica de elementos especiais de fixação. O enfoque principal está centrado na taxa de desgaste por abrasão, caracterizado pelo atrito de elementos interfaciais entre as superfícies da matéria-prima e da matriz. Foram utilizadas três matrizes de VF 800AT diferentes, das quais duas apresentavam desgaste excessivo antes do tratamento ou revestimento superficial, e uma apresentava problemas de fratura. As propriedades mecânicas foram avaliadas através de ensaios de estereoscopia, dureza, microdureza, rugosidade, metalografia óptica e eletrônica de varredura e controle dimensional por carta de Controle Estatístico de Processo - C.E.P.. No estado tratado por nitretação a plasma, as matrizes (com camada branca bastante reduzida) apresentaram menor resistência ao desgaste (maior taxa de desgaste), ao passo que a maior resistência ao desgaste foi das matrizes com revestimento de carbonitreto de titânio. Isto foi atribuído a excelente dureza do elemento titânio, juntamente com seu poder de aderência, em contraste com a fragilidade da camada branca formada pela nitretação a plasma .

This research studies the effects of plasma-nitriding and titanium carbonitriding mixtures on the wearing resistance of mechanical forming dies for special fixing elements manufacturing. The main focus is the abrasion wear rate, characterized by the friction between the surfaces of the raw material and die. Three different configurations were used for the VF 800AT steel dies, chosen among the ones that had shown high waste rates before coating. Industry and laboratory trials were performed to compare the wear behavior. The coated dies had better results in contrast with others. The plasma-nitriding dies (with a small white layer) showed lower wear resistance (higher wear rate) when compared with titanium carbonitriding dies. That was caused by the excellent hardness of the titanium carbonitriding and the good adherence.