Abstract
The gas-carburizing capacity of heat-resisting low-nickel-chromium case-hardening steels containing molybdenum was studied by using the endothermic generator gas. The main results are as follows:(1) The case depth depends on two factors: the surface carbon content and the diffusivity of carbon.(2) The diffusion coefficient of carbon is roughly determined from the case depth, using an equation; x2=2Dt, which is necessary to be corrected according to the surface carbon content.(3) Carbide forming elements, chromium, molybdenum decrease the activity of carbon and noncarbide forming elements, nickel, silicon increase it and cobalt has little influence on it.(4) The activity of carbon has a close relation with the equilibrium phase diagram and if the diagram and the relation between dew-point and the activity of carbon are known, it is possible to show the rough dew-point equilibrium curve.(5) Addition of molybdenum increases extremely the surface carbon content and the carbon potential at a high temperature, and restrains the grain growth of austenite, so molybdenum is a useful element for the high temperature carburizing process.
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