DCCT DIAGRAM OF A CASE-HARDENING STEEL 20MnCrS5

Grade 20MnCrS5 is a structural alloy steel for surface hardening. Despite the low carbon content, it exhibits good wear resistance after hardening. The material can be hardened to a depth of about 40 mm. Sulphur in the content of 0.020 - 0.040 % improves lubricant function during cold processing. The material is commonly used for the production of moderately stressed parts of motor vehicles and machine parts intended for cementation with higher strength in the core (e.g. transmission gears, axles, pinions and camshafts). Continuous cooling transformation diagram of steel grade 20MnCrS5 was constructed after the compressive true strain of 0.35 with the strain rate of1 s(-1). Based on the experimentally determined value of A(c3) = 829 degrees C, the austenitization temperature of the dilatometric samples was chosen to be 880 degrees C. Samples cooled at a constant nominal rate of 0.1-35 degrees C center dot s(-1) were subjected to structural analyses (optical and scanning microscopy) as well as hardness measurements. Even at the highest applied cooling rate, trace amounts of ferrite were detected. Martensite and bainite appeared in the structure after cooling at a rate of at least 0.7 degrees C center dot s(-1). Continuous cooling transformation diagrams are valuable from the point of view of optimizing the cooling regimes after hot bulk forming and/or at the heat treatment of the final products.