Influence of Tempering Time on the Behavior of Large Carbides’ Coarsening in AISI H13 Steel

Abstract

The mechanical properties, microstructures and precipitation behaviors in AISI (American Iron and Steel Institute) H13 steel tempered at 863 K for 0.5, 2, 4, 10 and 20 h were investigated. The values for H13 tempered for 2–4 h resulted in die steel that reached the desired properties as specified in NADCA (North American Die Casting Association) #207-2016. The cubic Ostwald ripening model was applied to simulate the coarsening of the large carbides, which were mainly M23C6 and M3C, as determined from FactSage predictions as well as measurements with transmission electron microscopy (TEM). TEM revealed that the equivalent circle radius (ECR) decreased during 0.5–2 h, because of the nucleation of many new precipitates. According to the Ashby-Orowan modified precipitation strengthening model, this decrease in ECR leads to an increase in the contribution of precipitates to yield strength. Between 2 and 4 h tempering, the ECR of large carbides increases sharply but then increases asymptotically from 4 to 20 h, which obeys the calculated Ostwald ripening rate for cementite and M23C6 in H13 after 863 K tempering. This observation for the Ostwald ripening of M23C6 is in agreement with experimental data for other steels in the literature.

Effect of Different Post-Processing Thermal Treatments on the Fracture Toughness and Tempering Resistance of Additively Manufactured H13 Hot-Work Tool Steel

“…The hardness of ABT decreased to 460 HV1 after 40 h, while that of QT decreased to 425 HV1, confirming the higher tempering resistance after direct tempering from the AB condition. The results of the softening behavior of a wrought hotwork tool steel, initially quenched and tempered followed by soaking at 600 °C, agree well with the behavior of the QT sample in this work (i.e., ~420 HV after 25 h of soaking) [5,23]. Clearly, the improved temper resistance in ABT must be directly correlated to the higher tempering temperature used for ABT (625 °C) than for the QT sample (600 °C) and the higher thermal stability induced.…”

Effect of Grain Size and Cooling Rate on the Martensite Start Temperature of Stainless Steel

“…Figure 1 shows the equilibrium phase diagram of the stainless steel calculated using the thermodynamic software FactSage 7.1. [ 27 ] The austenite started to form at 720 °C and completely austenitized at 850 °C. Therefore, the austenitizing temperature rang in the current study was chosen to be 900–1200 °C.…”

Cryogenic Treatment of Martensitic Steels: Microstructural Fundamentals and Implications for Mechanical Properties and Wear and Corrosion Performance

“…Variations in wear rate due to the application of cryogenic treatment could be attributed to the combined effects of greater RA-to-martensite transformation (although the extent of this can only be roughly estimated due to the 'distortion' caused by hightemperature tempering used in treatment sequences), more pronounced carbide precipitation, and martensite refinement [334]. As harder and finer martensite forms, along with a higher number and population density of nano-sized precipitates, the wear resistance of hot work tool steels is generally improved through CT.…”