Vliv chemického složení na rozpadové diagramy nízkolegovaných mangan-chromových ocelí

Abstract

Low-alloy construction steels of the type 16MnCrS5 and 20MnCrs5 are intended for chemical-thermal treatment by cementing the surface layer. By carburizing the surface layer, a highly hard and abrasion-resistant layer is obtained after clouding, while the toughness of the core of the product is preserved. These steels are commonly used for the production of moderately stressed motor vehicle components and machine parts (e.g. gearboxes, pinions, camshafts and overrunning clutch). By controlled rolling and cooling, the effort is to achieve a well-machinable structure without cloudy components. On the basis of dilatometry, three DARA diagrams of these steels differing from each other in the content of carbon, manganese, chromium, nickel, molybdenum and nitrogen were constructed. The transformation diagrams were constructed under comparable austenitizing conditions of 880 °C, after an actual compression strain of 0.30. The samples were cooled at constant rates of nominally 0.1-35 °C/s and subsequently subjected to structural study (optical and scanning microscopy) and hardness measurements. Transformation diagrams provide very valuable information in the optimization of controlled cooling in operating conditions after rolling and for heat treatment of final products.