Previous studies have pointed out the need to properly characterize industrial quenching processes to account for the inherent heterogeneities of the process. This study focuses on the identification of thermal boundary conditions of a hollow cylinder quenched by immersion in mineralized oil previously subjected to a predefined air transfer step. The test specimen is instrumented with in-body thermocouples at multiple locations along the radial and azimuthal direction thus mapping the outer and inner surfaces of the hollow cylinder. Based on the experimentally acquired datasets, characteristic points of physical significance during the cooling regimes after immersion are identified to produce time dependent analytical cooling curves. An inverse identification method is applied to estimate heat flux and temperature dependent heat transfer coefficients at locations of interest in both inner bore and outer surfaces. Results demonstrate the non-homogeneous cooling of the specimen during the quenching process before immersion (air transfer) and after immersion in the quenchant, hence confirming the importance of accounting for the influence of the industrial environment. The results are also compared with previous characterization data obtained with a plate probe for the same facilities thus capturing the influence of probe geometry on the identification of thermal boundary conditions.

As a result of research conducted by the Department of Materials Science and Metallurgy at the University of Cambridge and tests conducted in the calibration laboratory at CCPI Europe Ltd, a new mineral insulated (MI) thermocouple cable has been developed for sensor manufacturing. The use of both type K and type N base metal thermocouple combinations under operational conditions during extended and/or high temperature conditions have historically been shown to have a limited life operation. The test results on mineral insulated cable show that conventional type K mineral insulated thermocouple designs can maintain calibration limits and stay within IEC 60584 -1: 2013 class 1 and ASTM E230 special tolerances for a limited number of operations. However, when compared to the type K sensors, manufactured from the new designed mineral insulated cable, these new designs have been shown to maintain calibration values to meet both IEC 60584 -1: 2013 class 1 and ASTM E230 special tolerances for up to five times longer. This new mineral insulated cable can allow type K and N thermocouples to work longer and at higher temperatures with significantly reduced drift, offering greater measurement confidence. This paper will discuss how the new design will offer the opportunity for type K and type N MI thermocouples to work for longer and at higher temperatures under both continuous and cycling conditions with significantly reduced drift, giving increased confidence in measurement capability.

Dilatometry test systems are commonly used for characterizing the transformation behavior in steels and induction heating is commonly the heating source. In these systems, the steel test article is assumed to have a uniform temperature throughout the sample. This is a good assumption for slow heating rates with small samples, however, for induction hardening cycles this may or may not be accurate. Using computer models, it is possible to predict the temperature dynamics of the sample, both radially and axially, during the thermal processing cycle (heating and cooling). O1 tool steel was utilized to characterize and model heating and cooling temperature gradients. Specimens instrumented with multiple thermocouples were induction heated and gas quenched. The test data and geometry were evaluated with 1- D and 2-D models to characterize transient temperature gradients. The goal of the modeling is to better characterize temperature corrections required when rapid heating and cooling processes are used to determine transformation behavior in induction hardenable steels.

The most common probe used for cooling curve analysis of quenchants is a 12.5 mm diameter x 60 mm Inconel 600 cylindrical probe with a Type K thermocouple inserted into the geometric center. The time-temperature cooling curve is obtained at this position and is the basis for national and international standards including ASTM D6200, D6482, D6549, ISO 9950 and others. However, greater insight into the quenching process would be possible if a better profile were available for the uniformity and wetting kinematics of the quenching process. An alternative probe design, proposed by Prof. H.M. Tensi and his colleagues, utilizes a cylindrical 15 mm diameter x 45 mm flat-bottom shape with four thermocouples. One thermocouple is inserted to the geometric center of the probe at 22.5 mm from the bottom. The remaining three thermocouples are located 2 mm below the surface of the probe at 2 mm, at 15 mm, and at 30 mm from the bottom. This alternative probe design was used to characterize the usual centerline cooling curve properties as well as rewetting properties of two vegetable oils, palm oil and canola oil, a commercial fast petroleum oil quenchant, and a conventional petroleum oil quenchant. The probe construction, use, and quenching characterization results are reviewed in this paper.

Accurate simulation of phase transformation during quenching of steels requires comprehensive knowledge of thermal and physical properties of the material. In cases when reliable material data are not available they can be obtained by a two-stage inverse method proposed in the paper. It includes a Jominy test of a specimen with thermocouples. At the first stage, we obtain TTT diagrams by means of analyzing cooling curves for several regions of the specimen obtained from experimental results. The second stage includes correction of material thermo-physical properties, i.e. the thermal conductivity and specific heat for each phase as well as estimation of the latent heat for each phase transformation. Parameters fitting is carried out iteratively by comparing FEM simulation and experimental results. Varying of parameters is performed with evolutionary methods of multi-parameter optimization. The developed method is implemented in QForm commercial software.

The effect of probe geometry on the re-wetting behavior and heat extraction of cylindrical probes during forced convective quenching in laboratory-scale equipment was studied. Flat-end and hemispherical-end cylindrical probes made of AISI 304 stainless steel and instrumented with type-K thermocouples were considered. Two free-stream velocities (0.2 and 0.6 m/s) and two initial probe temperatures (850 and 950°C) were studied. The quench medium was water at 60°C. The inverse boiling curves and videos obtained showed that the vapor film stage lasts longer when using flat-end probes. This delay in the start of re-wetting shifted the cooling curves to the right and favored the probe surface to reach lower temperatures before the start of re-wetting which resulted in slightly higher values of the wetting front velocity. It is shown that the hydrodynamics of the flow around the probe end is responsible for the differences observed between the two geometries.

Energy Savings through Steady State Control Modern heat treat companies are faced with challenges trying to balance work-flow, processing time, and production/energy costs. Unnecessarily long processing times induce extra costs when an automated process cannot tell the true temperature of a load and the engineer must increase soak times to accommodate. These increased soak times use more energy and increase overall production costs. Typically, control or load thermocouples in an oven or furnace only show the wall temperature, and normally only parts of the load. However, the real interest is in what temperature the load actually has reached inside and when is the temperature uniform throughout the whole work piece. Normally, to accommodate for this lack of knowledge in a ramp/soak program, the dwell-time is extended to ensure that the temperature is uniform without truly knowing. Instead, using a method for predicting load uniformity, or Steady State Control, would save time, energy, and, most importantly, money.