Low pressure carburizing (LPC) is a proven, robust case hardening process whose potential is only limited by the style and size of vacuum furnace. Today, LPC is typically used in horizontal vacuum furnaces where the opportunity to carburize large parts is limited. In this paper we present a new adaptation of the technology in large pit type vacuum furnaces, capable of opening to air at elevated temperature. This underscores the potential of LPC to carburize larger, more massive parts in a clean, effective and efficient process. The result is quality casehardened parts without the undesirable side effects of atmosphere gas carburizing such as the use of a flammable atmosphere, reduced CO and NOx emissions, no intergranular oxidation, and limited retort life. Another significant advantage is decreased process time. The case study presented here shows that eliminating furnace conditioning and increasing process temperature can significantly reduce cycle durations by nearly three times and cut utility costs in half. Under these conditions, a return on investment (ROI) is in the neighborhood of 1 – 2 years is possible, making LPC in a pit style furnace a cost-effective solution than traditional atmosphere gas carburizing technologies.

Extension of the service life for high temperature structural alloy RA602CA is the goal for the project described in this paper. The performance of alloy RA602CA and aluminized RA602CA in a gas carburization furnaces were studied for periods up to two years. Aluminizing treatments (widely used in aerospace industry, especially in turbine blade applications) were also studied in this project. Carbon has very low solubility in alumina, so aluminizing could be a good method for protecting RA602CA alloys. Microstructural development during the carburizing process is presented, and the degradation of chromium oxide as well as alumina oxides is identified. The weight gain of RA602CA compared to similar alloys is discussed.

A new technology has been introduced to the North American market as a potential replacement for conventional gas carburizing. This new approach, called Through Surface Hardening (TSH) technology, utilizes a low hardenability (LH) steel and induction hardening to create a contoured hardened pattern, similar to a traditional gas carburizing process. In this study, TSH-processed and conventional gas-carburized SAE 8620 fatigue samples were subjected to reverse torsional loading, generating comparative stress to cycle curves. This paper outlines the torsional fatigue performance and metallurgical characteristics of each process type.

Studying the gas composition of an atmosphere furnace reveals many parameters that can be used to predict metallurgical results of parts being processed. Today’s heat treaters strive for process consistency in order to eliminate variability, rework, and (in the worst case) scrap. In atmosphere heat treating, understanding control parameters and atmosphere composition provides critical insight into expected results. In this presentation, the audience will have the opportunity to observe gas compositions that would typically be found in carbon-neutral or carbon-rich atmospheres; they will also be able to see how atmospheric properties directly affect the metallurgical properties of heat treated parts. The presenter will illustrate examples of common atmospheres based on furnace types and will discuss common characteristics of improperly controlled atmospheres and how those atmospheres can lead to flawed results. Real-world examples of metallurgical results will be used to illustrate what can be expected from an “out of control” situation.

Historically, this carburizing has been performed in an endothermic gas consisting of CO 2 , CH 4 , CO, etc, but carburizing in low pressure with the proper gas mixture changes the landscape. Using C 2 H 2 , the process is no longer endothermic as C 2 H 2 is a catalytically decomposable hydrocarbon and dissociates in the presence of an iron catalyst. LPC is a recipe driven in contrast to the constant monitoring of the carbon potential in atmospheric gas carburizing, and with the wide acceptance of simulation programs, recipes are no longer created by trial and error. Introduction of nitrogen to the steel, followed by carbon with higher temperatures, can dramatically reduce cycle times and still control grain growth.

Heat treaters need an effective simulation tool to predict the carburization performance of a variety of steels. The tool is needed not only to predict the carbon profile but also to optimize the process in terms of the cycle time and the cost. CarbTool has been developed to meet these needs for gas and vacuum carburization. In this paper, CarbTool predictions were compared with industrial experimental results of four types of steels, heat treated by both gas and vacuum carburizing processes. Based on the excellent agreement of model predictions and experimental results, CarbTool may be used to predict the carbon concentration profile for a variety of alloys in both gas and vacuum carburizing processes.