Microalloyed steel

About: Microalloyed steel is a research topic. Over the lifetime, 2183 publications have been published within this topic receiving 33586 citations.

Hot-working in the γ + α region of TRIP-aided microalloyed steel

Abstract: Purpose: The aim of the paper is to investigate the influence of hot-working in the γ+α range and isothermal holding temperature in a bainitic range on a stability of retained austenite in a TRIP-aided microalloyed steel. Design/methodology/approach: The thermomechanical processing in the γ+α range to obtain multiphase structures with the retained austenite in a microalloyed steel was realized. It consisted of plastic deformation of specimens at 750°C or 780°C, oil cooling and isothermal holding in a bainitic region. Degree of deformation was 28 or 50%. To reveal the multiphase structure optical and transmission electron microscopy were used. X-ray diffraction method was employed to determine a volume fraction of retained austenite. Findings: It was found that hot-working in the two-phase region influences essentially a multiphase structure of investigated steel. The ferrite fraction is comparable for heat-treated and thermo-mechanically processed specimens but the ferrite grain size is twice smaller in a case of plastically-deformed specimens. The optimum isothermal holding temperature in a bainitic range is 300°C, independent on austenitizing temperature. The specimens forged in the γ+α range and isothermally held at this temperature made it possible to obtain about 10% of retained austenite. Research limitations/implications: Investigations concerning the influence of isothermal holding time in a bainitic range on the stability of retained austenite should be carried out. Practical implications: The established conditions of the thermomechanical processing can be useful in a development of the hot-rolling technology for TRIP-aided microalloyed steels. Originality/value: The realized thermomechanical processing enabled to obtain about 10% fraction of retained austenite in a steel containing 0.5% Si.

Effect of prior-austenite grain size and transformation temperature on nodule size of microalloyed hypereutectoid steels

Abstract: The effect of prior-austenite grain size and transformation temperature on nodule size and colony size of hypereutectoid steels containing 1 pct carbon with different levels of vanadium and silicon was investigated. Specimens of the various steels were thermally processed at various temperatures ranging from 900 °C to 1200 °C and transferred to salt bath conditions at 550 °C, 580 °C, and 620 °C to examine the structural evolution of pearlite. The heat-treatment work showed that for only the hypereutectoid steel without vanadium there was a continuous grain boundary cementite network, the thickness of which increased with increasing reheat temperature. Analysis of the thermally processed hypereutectoid steels also indicated that the prior-austenite grain size and transformation temperature controlled the nodule size, while the colony size was dependent on the latter only.

Surface characteristics analysis of nitrocarburized (Tenifer) and carbonitrided industrial steel AISI 02 types

Abstract: Generally, tool steels for cold work are obtained by rolling and forging processes. They are treated to have a structure conferring to the material a high toughness limit in terms of wear resistance and endurance. The objective of this study is the thermochemical heat treatment of industrial steel blades made of AISI 02 types, intended for polymer crushing. The effects of nitrocarburizing (Tenifer) and gaseous carbonitriding processes on surface characteristics are considered. These surface treatments increase the usefulness of properties, that is, fatigue strength, wear and corrosion resistance of this microalloyed steel. The influence of treatment duration and the thickness of the layers on surface properties are investigated. The analysis and characterization are carried out using physical analysis [optical microscopy, scanning electron microscopy, X-ray diffraction and glow discharge optical emission spectroscopy (GDOES) techniques] and mechanical measurements (microhardness, weight loss and residual stresses) of treated material. The results are intended to contribute in defining and optimizing the adequate choice of treatments for this type of steel in industrial conditions.