Effects of Water Jet Height and End Dipping on the Cooling Rate and Hardenability in the Jominy End Quench Test

The effects of water jet height and end dipping on cooling rate and hardenability in the Jominy end quench test were investigated to understand the Jominy test in more detail. Experimental tests were conducted under end dipping cooling condition as well as for specific water jet heights of 35, 65, and 100 mm. The thermal behavior and mechanical properties of the Jominy specimen with region were evaluated using thermocouples and hardness measurements, respectively. The effect of the water jet height on the thermal and hardness behaviors was not large; especially, the influence of water jet height was negligible when the water jet height was over 50 mm. These observations indicate that the uncertainty of the water jet height is not important during the standard Jominy end quench test. Meanwhile, during the standard Jominy test, we cannot neglect the heat flow along the radial direction of the specimen because the temperature difference between the center and surface area was not small; the maximum temperature difference was approximately 50 °C. Based on the comparative study between the standard Jominy cooling and the end dipping cooling processes, the thermal gradient along the radial direction of the specimen can be reduced with the more stable cooling condition on the Jominy end. However, the effect of temperature deviation along the radial direction of the Jominy specimen on the hardness distribution along the longitudinal direction was not large, which shows the high reliability of the Jominy end quench test.

Detailed Barkhausen noise and microscopy characterization of Jominy end-quench test sample of CF53 steel

Jominy end-quench test samples from CF53 were used for studying the relationship of microstructural changes with the magnetic Barkhausen noise (BN) response. As the Barkhausen noise method is sensitive to both stress and microstructural state, it can be applied for material characterization. This study presents observations from BN measurements with different sensors and from different locations (as-quenched and ground) on the sample surface. Detailed microstructural characterization with a scanning electron microscope and a transmission electron microscope was carried out to correlate the BN responses with the microstructural features. In addition, residual stresses were measured by X-ray diffraction. The results indicate that the ground surface displayed mainly the effect of the grinding compressive stress state, while the as-quenched surface had variations due to higher microstructure sensitivity. An important finding of the results was that the sensitivity of BN to different surface conditions varied: The BN response in the ground area was mainly generated by both the residual stress and the microstructural effect, whereas for the as-quenched surface the microstructural effect was more evident.

Thermal Shock Resistance of Si3N4/hBN Ceramic Composites

Si3N4/hBN composites were fabricated by hot isostatic pressing at 1700°C/3h with 1, 3 and 5 wt. % micro-sized or nano-sized hexagonal boron nitride particles added to silicon nitride matrix. An indentation quench test method was used for estimation of thermal shock resistance of monolithic Si3N4and Si3N4/hBN composites. Thermal shock resistance of the composites increased with the increase of size and volume of hBN particles. The critical temperature difference for the composites with micro-sized hBN was significantly higher (over 900°C) compared to the monolithic silicon nitride (580°C).

Thermal shock properties of glass-ceramics synthesized from a glass frit

In this study, the behavior of glass-ceramics synthesized from a glass frit of FFW (Final Flotation Waste) originated from the RTB Bor Company was investigated. Thermal shock resistance was monitored in order to assess the possibility of application of such waste material. Thermal shock of the samples was conducted using water quench test. Image analysis and ultrasonic measurements were used as nondestructive methods for quantification of thermal shock damage at the surface and in the bulk of the specimens. Phase composition of samples was determined by X-ray powder diffraction (XRPD). The degradation level of samples was about 43 % after 20 cycles of water quench tests. The results pointed out that glass-ceramic material exhibited good thermal shock resistance.