Effect of austenitizing temperatures on the microstructure and mechanical properties of AISI 9254 steel

In this study, the effect of austenitizing temperatures and low-temperature isothermal heat treatment (below martensite start temperature) on the microstructure and mechanical properties of AISI 9254 high silicon spring steel has been investigated. Experimental studies show that ultra-fine carbide-free bainite, tempered martensite and carbon enriched retained austenite could be observed in isothermally heat-treated samples where the as-received sample consisted of fine pearlite. A high tensile strength of ~2060 MPa, a total elongation of ~8 %, and absorbed energy of 105 J were achieved in a commercial high-Si steel by austempering below the Ms temperature. A good combination of strength and ductility has been obtained in prolonged austempering below the martensite start temperature (225 °C) from an austenitizing temperature of 870 °C.

VOLUMETRIC CHANGES AT HEATING IN STEEL 60Si2CrV SUBJECTED TO Q&P TREATMENT

The paper presents results of the investigation of phasestructural transformations and volumetric changes that occur during heating in high-silicon spring steel 60Si2CrV subjected to Q&P(quenching and partition) treatment. Chemical composition of the steel was: 0.53 % C; 1.46 % Si; 0.44 % Mn; 0.95 % Cr; 0.10 % V; 0.016 % S; 0.013 % P. Steel samples were subjected to Q-n-P treatment as follows: a) austenitization at 880 °C; b) quenching with the cooling stop at 120, 160, 200 and 240 °C; c) subsequent holding at 220, 250 and 300 °С with duration from 10 to 3600 s; d) final cooling in water. The volumetric changes during heating were studied using an optical differential dilatometer at a heating rate of 1 K/s. As a reference, a sample of the same steel stabilized by high tempering was used. The amount of retained austenite was determined by X-ray diffraction using a diffractometer DRON-3 with Fe-radiation. It is found that on the heating curves of Q&P samples, the sections corresponding to different transformations during tempering are clearly identified. On dilatograms of the Q&P samples, dilatometric effect corresponding to the second transformation during tempering (270 – 430 °C) was found to be increased dramatically, indicating an increase in retained austenite amount compared to the quenched state as a result of Q&P treatment (as confirmed by Xray study). At the same time, value of the effect corresponding to the third transformation during tempering was found to be decreased. To obtain the maximum amount of retained austenite in 60Si2CrV steel, the partitioning temperature should be of 260 – 300 °С, while the quenching completion temperature should be of 160 – 240 °С. The amount of retained austenite rises substantially as the quenching temperature increases. Duration of the partitioning stage should be selected taking into account the extreme character of austenite dependence on the partitioning time. As a result of the work, an effective applicability of the dilatometric method for analyzing the steel structural state and choosing the optimal mode of Q&P treatment was demonstrated.

Investigation of Structure, Chemical and Phase Composition of Silicon Spring Steel Scale

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Ferrite Decarburization of High Silicon Spring Steel in Three Temperature Ranges

Surface decarburization of high silicon spring steel in ambient air was studied. The experimental results confirmed the decarburized mechanism under AC1 temperature, in the temperature range of AC1-AC3 and AC3-G. Under AC1 temperature, pearlite spheroidization and surface decarburization are carried out simultaneously and pearlite spheroidization is reinforced. Considering the oxidation loss depth, the “true ferrite decarburized depth” at 850 °C (AC3-G) is still smaller than that at 760°C (AC1-AC3). That is because an “incubation period” must pass away before ferrite decarburization occurs in the temperature range of AC3-G, and the ferrite decarburized rate is limited to being equal to the partial decarburized rate.

Analysis of Cracked Spring Washer for Sleeper-Rail Joints

The paper deals with the qualitative, quantitative, and phase analyses of particles that were found during the metallographic analysis of a cracked spring washer made of silicon spring steel 38Si7, with the aim of ruling out the client’s suspicion of possible initiation of graphitization in the course of the heat treatment. The problem is solved via metallographic analysis using light microscopy, scanning electron microscopy including EDS microanalysis of the chemical composition and EDS line analysis.