Integral quench furnaces combine the benefits of low-pressure vacuum carburizing (LPC) with atmosphere oil quenching. This paper discusses key milestones in the development of integral quench furnaces and the advantages they provide in annealing, normalizing, and hardening applications.

Dew point (DP) is a function of the furnace atmosphere composition. In a metal processing furnace, maintaining appropriate atmosphere composition is critical to achieving the desired gas/metal reactions and quality and consistency of the treated product. Continuous measurement of DP is always challenging because of particulates and vapor-phase contaminants in sampled gas stream which can potentially accumulate in filtering systems and on sensors. The DP measurement can also be affected by temperature variations within the sampling unit. Thus, DP readings can drift significantly, necessitating frequent cleaning, recalibration, and sensor replacement. Air Products has developed a DP monitoring system that addresses these issues and based on long-term testing at a customer site, drifts/changes of DP readings on calibration gas were not observed after more than one year of operation, without any maintenance. The contamination and drift issues have been mitigated by incorporating an automated self-cleaning and sensor calibration process after pre-set measurement periods. Temperature control of the sensor and the sampling system are also essential to maintain consistency, and can be achieved via various design features. Drifts/changes in DP that are reported through local monitoring/alarms or remotely through cloud server access can also help to address furnace operational issues quickly and efficiently.

In the continuing effort to improve the quality and consistency of gas produced from an endothermic gas generator, several enhancements have been developed and implemented to diagnose abnormal operating conditions. Typically the variables monitored, controlled, and alarmed on gas generators were limited to the temperature of the heating chamber and the dew point of the gas being generated. As instrumentation has evolved, additional monitoring has been implemented, reducing the instances of sending “bad” endothermic gas into a process critical furnace. The new diagnostic tools allow predictive maintenance to be applied to endothermic gas generators.

The atmospheres used in a brazing furnace play a critical role in the final quality and metallurgical properties of the brazed component. Typically, exothermic, dissociated ammonia and nitrogen/hydrogen atmospheres are used for brazing mild steel, alloy steel and stainless steel components. The atmosphere composition, flow rates, pressures, and dew point are some of the key variables control final quality. Almost all brazing companies have quality issues that directly result from improper atmosphere application and control. Common problems include oxidation, flashing, inadequate braze flow, sooting, decarburization and carbon pickup. This troubleshooting presentation reviews years of field experience with nitrogen and hydrogen based atmosphere systems. It will help the heat treater or the brazing production engineer to identify these problems and apply appropriate corrective action.

Microstructural examination of a nitrided part is the most commonly used method for evaluating nitriding material and process performance. Microstructural evaluation also helps to validate that the process ran as intended and produced the desired nitrided case characteristics. However, sample preparation is often complicated by the partial or complete breakaway of the compound layer and may affect the accuracy of the conclusions made. A set of experiments was performed to evaluate the effect of two saw cutting methods, the use of metal foil for sample mounting, and the use of Ni plating before cutting. Microstructures of 12 experimental conditions were analyzed. Recommendations were made for the nitrided sample preparation best practice to analyze compound layer uniformity and thickness.

Nitrogen (N 2 ) atmospheres with different, not always optimized levels of reducing and carburizing gases are often used to prevent decarburizing and oxidation of steel parts during annealing in continuous furnaces. The type and concentration of these additives in N 2 should correlate to the extent of air leakage into furnace, entrainment of air with loaded parts, steel composition, and complex reaction kinetics in the gradients of oxygen (O 2 ) and temperature existing between the entrance and hot zones of the furnace. This study explores the effect of small, 0.1 vol.% - 0.4 vol.% propane (C 3 H 8 ) additions on composition of air-contaminated N 2 atmosphere in the temperature range of 500°C - 860°C. Microstructures are presented for AISI 1045 steel exposed to the atmospheres produced. Atmosphere compositions compared include those produced by a new type of plasma activated, in-situ reformer for N 2 -diluted C 3 H 8 . The latter method extends the atmosphere protection to the lower range of annealing temperatures. Present results may assist heat treaters in optimizing their neutral hardening operations.

Plasma nitriding is a thermochemical surface heat treatment of steel components to produce nitride layers which increase wear-, corrosion- and fatigue resistance. Research into plasma nitriding lately showed that there is a significant and characteristic amount of ammonia formed off the process gases nitrogen and hydrogen. This research paper is aimed to analyze the influence of plasma treatment parameters, such as pressure, voltage, temperature and nitrogen to hydrogen ratio on the atmosphere and the formation of ammonia during plasma nitriding. The ammonia content is measured in the exhaust gas. By correlating the measured ammonia with the treatment parameters and modeling the nitriding process, the ammonia content can then be predicted. Further a plasma nitriding potential, comparable to the gas nitriding potential, based on ammonia content is calculated and its practicability as process control parameter is shown by correlating the potential with the nitriding results, e.g. the formation of ε and γ’ nitride phases.

Late research projects show that retained austenite, if stabilized by nitrogen, has a positive influence on the fatigue strength of work pieces. The combined diffusion profile of carbon and nitrogen applied in a carbonitriding process plays the major role, besides the process temperature. Yet today, only the carbon potential is somehow controlled and even this is not easy to achieve. This paper will present a new system able to measure and control both, the carbon potential and the nitrogen potential independently. The knowledge of the activities of nitrogen and carbon in iron and the effect of alloying elements on such activities as well as the solubilities offers an easy to use method to apply the potentials on real steels.

Atmospheric pressure carburizing and neutral carbon potential annealing in nitrogen containing small additions of hydrocarbon gases can offer cost and steel surface quality alternatives to the comparable, endothermic atmosphere or vacuum operations. An experimental program was conducted for refining real-time process control methods in carburizing of AISI 8620 steel under N 2 -C 3 H 8 blends containing from 1 to 4 vol% of propane at 900°C and 930°C. Multiple types of gas analyzers were used to monitor residual concentrations of H 2 , CO, CO 2 , H 2 O, O 2 , CH 4 , C 3 H 8 , and other hydrocarbons inside furnace. A modified shim stock technique and the conventional oxygen probe (mV) were additionally evaluated for correlation with gas analysis and diffusional modeling using measured carbon mass flux values (g/cm 2 /s). Results of this evaluation work are presented.

Automation can be many different things across many different industries so it’s hard to have one definition to cover it in its entirety. In heat treating, automation is approached in categories. The types of processes and equipment may only have certain capabilities when it comes to mechanically automating a process forcing heat treaters to look at non-traditional types of automation. Many heat treaters need flexible equipment when it comes to processes and load sizes because of economic pressures and competition, costs and capital are being scrutinized. Does it take significant capital to automate a process? In the world of heat treating it doesn’t have to.