Austempering and Bainitic Transformation Kinetics of AISI 52100

AISI 52100 is a high carbon alloy steel typically used in bearings. One hardening heat treatment method for AISI 52100 is austempering, in which the steel is heated to above austenitizing temperature, cooled to just above martensite starting (Ms) temperature in quench media (typically molten salt), held at that temperature until the transformation to bainite is completed and then cooled further to room temperature. Different austempering temperatures and holding times will develop different bainite percentages in the steel and result in different mechanical properties. In the present work, the bainitic transformation kinetics of AISI 52100 were investigated through experiments and simulation. Molten salt austempering trials of AISI 52100 were conducted at selected austempering temperatures and holding times. The austempered samples were characterized and the bainitic transformation kinetics were analyzed by Avrami equations using measured hardness data. The CHTE quench probe was used to measure the cooling curves in the molten salt from austenitizing temperature to the selected austempering temperatures. The heat transfer coefficient (HTC) was calculated with the measured cooling rates and used to calculate the bainitic transformation kinetics via DANTE software. The experimental results were compared with the calculated results and they had good agreement.

Effect of Part Size on Surface Heat Flux during Immersion Quenching

In this paper, the effect of quench probe diameter on the heat transfer rate during immersion quenching of stainless steel (SS) probes in still water has bee studied. Quench probes of different diameters with an aspect ratio of 2.5 were prepared from SS. These probes were heated to 850 °C and then quenched in water. Time-temperature data were recorded during quenching. The surface heat flux and temperature were estimated based on the inverse heat conduction (IHC) method. The results of the computation showed that the different cooling regimes during quenching in water were significantly affected by the diameter of the quench probes. The peak heat flux was higher for the probe having larger diameter followed by the next larger diameter probes.

Minimizing Sampling Loss in Trace Gas Emission Measurements for Aircraft Engines by Using a Chemical Quick-Quench Probe

This paper describes the development and testing of a gas sampling probe that quenches chemical reactions by using supersonic expansion and helium dilution. Gas sampling probes are required for accurate measurement of exhaust emissions species, which is critical to determine the performance of an aircraft engine. The probe was designed through rounds of computational modeling and laboratory testing and was subsequently manufactured and then tested at the University of Tennessee Space Institute behind a General Electric J85 turbojet engine at different power settings: idle, maximum military, and afterburning. The experimental test results demonstrated that the chemical quick-quench (CQQ) probe suppressed the oxidation of carbon monoxide (CO) inside the probe system and preserved more CO at afterburning conditions. In addition, the CQQ probe prevented hydrocarbons from being partially oxidized to form CO at idle powers and measured higher hydrocarbons and lower CO emission compared with a conventional probe at that low power condition. The CQQ probe also suppressed nitrogen dioxide (NO2) to nitric oxide (NO) conversion through all engine power settings. These data strongly support the conclusion that the CQQ probe is able to quench unwanted chemical reactions inside the probe for all engine power levels.

Minimizing Sampling Loss in Trace Gas Emission Measurements for Aircraft Engines by Using a Chemical Quick-Quench Probe

This paper describes the development and testing of a gas sampling probe that quenches chemical reactions by using supersonic expansion and helium dilution. Gas sampling probes are required for accurate measurement of exhaust emissions species, which is critical to determine the performance of an aircraft engine. The probe was designed through rounds of computational modeling and laboratory testing, and was subsequently manufactured and then tested at the University of Tennessee Space Institute (UTSI) behind a General Electric J85 turbojet engine at different power settings: idle, maximum military and afterburning. The experimental test results demonstrated that the Chemical Quick-Quench (CQQ) probe suppressed the oxidation of carbon monoxide (CO) inside the probe system and preserved more CO at afterburning conditions. In addition, the CQQ probe prevented hydrocarbons from being partially-oxidized to form CO at idle powers, and measured higher hydrocarbons and lower CO emission compared to a conventional probe at that low power condition. The CQQ probe also suppressed nitrogen dioxide (NO2) to nitric oxide (NO) conversion through all engine power settings. These data strongly support the conclusion that the CQQ probe is able to quench unwanted chemical reactions inside the probe for all engine power levels.

Design of a Jet-Stirred Gas Generator for Studies of High Temperature Mixing and Combustion

A high-temperature Jet-Stirred Gas Generator (JSGG) has been designed to investigate the characteristics of combustion in the mixing layer between a flow of air and a mainstream flow of rich combustion products. The design goal is delivery of a near-equilibrium, spatially-uniform flow of combustion products for a range of Mach numbers in the test section between 0.1–0.7, pressures of 1–10 atm, and equivalence ratios of 0.5–2.0. In this paper we describe the reactor design, as well as the numerical and experimental evaluation of its operation. The FLUENT turbulent flow code was used together with a reduced chemical kinetic model for propane-air oxidation to verify the attainment of well-mixed, near-equilibrium conditions. Experiments were performed using flow sampling at the inlet of the test section by means of an optimized aerodynamic-quench probe. Both the experiments and the calculated results indicate achievement of the design goals.