Acetylene Flow Rate as a Crucial Parameter of Vacuum Carburizing Process of Modern Tool Steels

Abstract

Carburizing is one of the most popular and wide used thermo-chemical treatment methods of surface modification of tool steels. It is a process based on carbon diffusive enrichment of the surface material and is applied for elements that are supposed to present higher hardness and wear resistance sustaining core ductility. Typical elements submitted to carburizing process are gears, shafts, pins and bearing elements. In the last years, more and more popular, especially in highly advanced treatment procedures used in the aerospace industry is vacuum carburizing. It is a process based on chemical treatment of the surface in lower pressure, providing much higher uniformity of carburized layer, lower process cost and much lesser negative impact on environment to compare with conventional carburizing methods, as for example gas carburizing in Endo atmosphere. Unfortunately, aerospace industry requires much more detailed description of the phenomena linked to this process method and the literature background shows lack of tests that could confirm fulfilment of all needed requirements and to understand the process itself in much deeper meaning. In the presented paper, authors focused their research on acetylene flow impact on carburized layer characteristic. This is one of the most crucial parameters concerning homogeneity and uniformity of carburized layer properties. That is why, specific process methodology have been planned based on different acetylene flow values, and the surface layer of the steel gears have been investigated in meaning to impact on any possible change in potential properties of the final product.

Modeling and Simulation of Vacuum Low Pressure Carburizing Process in Gear Steel

“…It was shown that acetylene flow is necessary for the control of diffusion and transfer coefficients. Acetylene flow is one of the most critical parameters affecting the uniformity of the carburized layer properties [23]. Semenov et al determined the parametric expressions of the carbon potential and mass transfer coefficient in the low-pressure carburizing process based on experimental data on the formation of saturated carbon layers in vacuum carburizing.…”

Enhanced Toughness of High‐Temperature Carburizing Gear Steel via Refining Twin Martensite and Retained Austenite by Nb Microalloying

“…Nb microalloying has been widely recognized as the best way to develop the steel for high‐temperature carburizing due to the pinning effect of niobium precipitates on austenite growth. [ 9 ] An et al [ 10 ] investigated the austenite grain coarsening behavior of Nb–Ti microalloying 18CrNiMo7‐6 gear steel during high‐temperature pseudocarburizing (without carburizing atmosphere). It was indicated that Nb–Ti microalloying had an obvious advantage in restraining austenite grain growth.…”