In gas carburizing, the source of carbon is a carbon-rich furnace atmosphere produced either from gaseous hydrocarbons or from vaporized hydrocarbon liquids. Using theoretical steps with anticipated process variable inputs allows for the prediction of the carbon available to the steel surface; diffusion can be simulated. Inputs captured during a real-time run can predict the carbon buildup in a part. The simulation and real-time data can be matched up to compare metallurgical results. We will cover principles of atmosphere carburizing, including sensor and control technology. We will discuss the analysis of input variables associated with carburizing applications and understanding the effects the atmosphere, temperature and time have on results. We will look at information using three-gas analysis as opposed to analysis using oxygen probes and review what an atmosphere would look like during a carburizing run. We will review real world scenarios with actual data that allow for a comparison of simulation versus calculated carbon transfer and diffusion against metallurgical lab results.

This paper investigates the effects of process time and temperature during plasma nitriding on the wear and fatigue properties of AISI 4330 steels. Nitriding, a thermochemical treatment involving nitrogen deposition and diffusion into metallic materials, has been widely used to enhance surface properties, wear resistance, fatigue strength, corrosion resistance, and friction characteristics of dynamically loaded components. The plasma nitriding process is conducted in a vacuum chamber where the specimen acts as a cathode, with high voltage (300-1000 V) applied between the cathode and the vessel (anode) at gas pressures of 1-13 mbar, creating an abnormal glow discharge that envelops the specimen. The process typically begins with hydrogen-atmosphere cleaning and pre-heating, followed by nitrogen introduction to initiate and maintain the nitriding action. Performance improvements were evaluated using pin-on-disk wear testing and rotating and bending fatigue testing methodologies.

This study examines the critical but often overlooked role of surface roughness in gaseous nitriding processes. While nitriding technology fundamentally relies on gas-solid interactions through multiple stages—including ammonia diffusion to the metal surface, dissociation reactions, nitrogen transfer, and bulk diffusion—the authors highlight how surface conditions significantly impact treatment outcomes, particularly at the relatively low processing temperatures (380-590°C) where surface reactions become rate-limiting. The research investigates how surface roughness affects the gas-metal contact area and consequently influences nitrogen uptake kinetics, challenging the traditional assumption that nitriding produces negligible changes in surface morphology. Working with commercial furnaces that use nitriding potential as the primary process control parameter, the researchers correlate various surface finishes with nitrogen absorption rates, ammonia dissociation, and atmosphere activity. The ultimate goal is to incorporate surface roughness—a specification widely used in metalworking industries—as a formal parameter in control systems, thereby enhancing process predictability and meeting increasingly stringent industrial standards for surface quality in nitrided components.