Effect of Deep Cryogenic Treatment on Corrosion Behavior of AISI H13 Die Steel

AISI H13 die steel specimens were subjected to heating at 1020 °C followed by oil quenching and double tempering at 520 °C. Subsequently, these specimens were subjected to deep cryogenic treatment at −185 °C in liquid nitrogen environment for 16 h and then subjected to soft tempering at 100 °C once the specimens attained room temperature. Thereafter, the specimens were subjected to scanning electron microscopy (SEM) analysis and electron backscatter diffraction (EBSD) analysis. The electrochemical corrosion activity was investigated in 3.5% NaCl at 23 ± 0.5 °C by evaluating the evolution of open circuit potential over time and potentiodynamic curves, and electrochemical impedance spectroscopy study was also carried out. The heat-treated specimens exhibited better resistance to corrosion through more electropositive values of open circuit potential. This could be attributed to lower grain boundary area in heat-treated specimens as compared to 16 h cryogenically treated specimen as higher grain boundary areas behave as an anode in an electrochemical cell, thereby enhancing the rate of corrosion. According to electrochemical tests, the cryogenically treated surface is more resistant to corrosion, followed by heated alloy. However, both surface modification treatments improved the corrosion behavior of the untreated alloy.

Impact of austenitizing temperature on the wear behaviour of AISI H13 steel

Austenitizing temperature is of great importance to achieve the desired properties of die steel. It governs the number of carbides dissolved in the austenitic matrix, which later transforms to martensite. This paper intends to find out the impact of austenitizing temperature on the wear behaviour of AISI H13 die steel. Austenitizing of H13 steel is done at different temperatures, i.e., 1000 °C, 1020 °C, 1040 °C, 1060 °C and then tempering is done twice at 560 °C for two hours. H13 die steel when tempered after austenitizing at 1020 °C lath martensite of large size is produced. Whereas, quite smaller lath martensitic structure has been observed in H13 die steel tempered after austenitizing at 1060 °C. Wear test investigation carried out using a pin on disc tribometer for H13 steel pins austenitized at different temperatures against D2 steel disc having 61 HRC. It is observed that the wear volume of H13 die steel exhibits an inverse linear relationship with its austenitizing temperature due to an increase in hardness. It is seen that small protective layer like patches of oxidized debris formed on the worn surface of H13 steel austenitized at 1060 °C. Whereas, no such protective layer formation is found on H13 die steel austenitized at a lower temperature. Post wear test, subsurface cross-section study shows plastic deformation of grains just beneath the worn surface along the direction of wear tracks. H13 die steel austenitized at 1060 °C with larger grains shows plastic deformation of grains up to a greater depth. Whereas, H13 die steel austenitized at 1000 °C with finer grain exhibits plastic deformation up to a lesser depth. An increase in grain boundaries of nearly twice is also found below the worn subsurface up to 80 to 100 µm depth. The present study will help to select the austenitizing temperature for H13 die steel to have better wear resistance.

Theoretical investigations into magnetorheological finishing of external cylindrical surfaces for improved performance

Fine finishing entails increased percentage contact area, less friction, and less wear. The magnetorheological finishing is a precision process to obtain the fine finishing on the workpiece surface for improved functional applications. So, the rotary rectangular core-based magnetorheological finishing process is utilized for the precise finishing of the cylindrical external surfaces. The rotary-rectangular shaped tool core tip surface provides the uniformly magnetic flux concentration that further benefit to offer the uniform fine finishing on the cylindrical work-part's external surface. In this work, a theoretical model is developed to predict the reduction in the surface asperities during the magnetorheological finishing of the external cylindrical surfaces. The rotational speed of the rectangular tool core on the rotating cylindrical work-part enhances the relative speed of active abrasives, which decreases the pitch, helix angle, and increases the helical path length. These results enhance the uniform precise finishing on the cylindrical work-parts and also enhances the process performance. For validation of the theoretical roughness model, the experiments have been performed on the cylindrical external surface of the H13 die steel workpiece. The percentage error between the experimentally obtained Ra value and theoretical Ra value is found to be −4.76% to 3.06%, which shows the good agreement between the theoretical model and experimental results. It also shows the practicality and accuracy of the present process while finishing the H13 die steel and it is useful for many industrial applications.