High Silicon Austempered steels (AHSS) are materials of great interest due to their excellent combination of high strength, ductility, toughness, and limited costs. These steel grades are characterized by a microstructure consisting of ferrite and bainite, accompanied by a high quantity retained austenite (RA). The aim of this study is to analyze the effect of an innovative heat treatment, consisting of intercritical annealing at 780 °C and austempering at 400 °C for 30 min, on the microstructure and mechanical properties of a novel high silicon steel (0.43C-3.26Si-2.72Mn wt.%). The microstructure was characterized by optical and electron microscopy and XRD analysis. Hardness and tensile tests were performed. A multiphase ferritic-martensitic microstructure was obtained. A hardness of 426 HV and a tensile strength of 1650 MPa were measured, with an elongation of 4.5%. The results were compared with those ones obtained with annealing and Q&T treatments.

A novel high silicon austempered (AHS) steel has been studied in this work. The effect of different austenitizing temperatures, in full austenitic and biphasic regime, on the final microstructure was investigated. Specimens were austenitized at 780 °C, 830 °C, 850 °C and 900 °C for 30 min and held isothermally at 350 °C for 30 min. A second heat treatment route was performed which consisted of austenitizing at 900 °C for 30 min and austempering at 300 °C, 350 °C and 400 °C for 30 min. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) have been used to evaluate the microstructural evolution. These techniques revealed that the microstructures were composed of carbide-free bainite, ferrite, martensite and retained austenite (RA) in different volume fractions (Vγ). An aqueous borate buffer solution with 0.3 M H3BO3 and 0.075 M Na2B4O7∂10H2O (pH = 8.4) was used for corrosion tests in order to evaluate the influence of the different volume fractions of retained austenite on the corrosion properties of the specimens. The results showed that when increasing the austenitization temperatures, the volume fractions of retained austenite reached a maximum value at 850 °C, and decrease at higher temperatures. The corrosion properties were investigated after 30 min and 24 h immersion by means of potentiodynamic polarization (after 30 min) and electrochemical impedance spectroscopy (after both 30 min and 24 h) tests. The corrosion resistance of the samples increased with increases in the volume fraction of retained austenite due to lower amounts of residual stresses.

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It is proposed to study technological processes of metal ware production as a consequence of macroscopic, microscopic and submicroscopic building typical for an initiate structure, transformed by phases or structurally. It makes possible to use the technological heredity theory in order to predict product quality. This approach is shown on the example of continuous method of deformational nanostructuring. It allowed to formulate the basics of the assessment strategy of various multistage processes of material processing in terms of achieving the required set of properties.

This paper examines the mechanical properties of high-strength (1,770 MPa) 7-wire prestressing strands and how they tend to change under thermo-mechanical treatment involving short-term induction tempering under high tension. The change dynamics of the following properties was monitored for 12.5 mm strands: tensile strength, yield strength, full elongation at maximum tension force and modulus of elasticity in the temperature range from 360 to 400 °С, the process speed range from 50 to 65 m/min, and at the tension force of 64 kN. The authors found a quantitative increase of the mechanical properties of prestressing strands for all the studied regimes of thermo-mechanical treatment. Thermo-mechanical treatment resulted in a significant growth in yield strength -from 28 to 36%, and in full elongation at maximum tension force, which demonstrated a higher than double growth. The paper shows how the temperature and rate of thermo-mechanical processing influence the mechanical properties of prestressing strands and their change dynamics.