D. Mohan Lal

Cryogenic treatment to augment wear resistance of tool and die steels

Cryogenic treatment is a supplementary process to conventional heat treatment process in steels. It is an inexpensive one time permanent treatment affecting the entire section of the component unlike coatings. Though the benefits have been reported widely, there are issues debated upon, in respect of the treatment parameters, extent of benefits experienced in different materials, underlying mechanism and pretreatment conditions. A study on the improvement in wear resistance and the significance of treatment parameters in different materials has been made. It is found that cryogenic treatment imparts nearly 110% improvement in tool life. It is even superior to TiN coatings. The underlying mechanism is essentially an isothermal process.

Experimental Investigation on the Thermal Conductivity and Viscosity of Silver-Deionized Water Nanofluid

Abstract This article presents an experimental investigation where the thermal conductivity and viscosity of silver-deionized water nanofluid is measured and studied. The mixture consists of silver nanoparticles of 0.3, 0.6, and 0.9% of volume concentrations and studied for temperatures between 50°C and 90°C. The transient hot-wire apparatus and Cannon-Fenske viscometer are used to measure the thermal conductivity and kinematic viscosity of nanofluid, respectively. The thermal conductivity increases with the increase in temperature and particle concentrations. A minimum and maximum enhancement of 27% at 0.3 vol% and 80% at 0.9 vol% are observed at an average temperature of 70°C. The viscosity decreases with the increase in temperature and increases with the increase in particle concentrations. The effect of Brownian motion and thermophoresis on the thermo-physical properties is discussed. Thus, an experimental correlation for thermal conductivity and viscosity, which relates the volume concentration and temperature, is developed, and the proposed correlation is found to be in good agreement with the experimental results.

Deep Cryogenic Treatment Improves Wear Resistance of En 31 Steel

Cryogenic treatment is an inexpensive supplementary process to conventional heat treatment, which improves the tribological properties of steels. A study has been made on the effect of cryogenic treatment on En 31 steels done at different stages of heat treatment. It is observed that through cryogenic treatment the wear can be decreased by a maximum of 75% depending on the service conditions. Scanning electron microscopy (SEM) study was also conducted to identify the possible mechanism which augments the improvement in wear resistance (WR) in cryogenically treated En 31 steels. Based on the study it is also confirmed that the cryogenic treatment should be done before tempering immediately after quench hardening to obtain maximum benefits.

Measurement of Thermo Physical Properties of Metallic Nanofluids for High Temperature Applications

This article presents the measurement of thermal conductivity and viscosity of nanofluids experimentally. Silver nanoparticles dispersed in water with volume concentrations of 0.3, 0.4, 0.6, 0.8, 0.9, and 1.2 vol% are used in the present study. A transient hot-wire apparatus is used for measuring the thermal conductivity of nanofluids and a Cannon-Fenske viscometer is used to measure the kinematic viscosity of nanofluids. The data are collected for temperatures ranging from 50 to 90°C. The results have shown an increase in the measured thermal conductivity and viscosity of nanofluids as the particle concentrations increase, and the values are higher than the values of the base liquids. The minimum enhancement of 27% for 0.3 vol% and a maximum enhancement of 115% for 1.2 vol% are observed at an average temperature of 70°C when compared with pure water for the same temperature. Further, the thermal conductivity of nanofluids increases with the increase in nanofluid temperatures and, conversely, the viscosity of nanofluids decreases with the increase in temperature of nanofluids. An experimental correlation is developed based on the experimental data for thermal conductivity and viscosity that relates the particle volume concentration and nanofluid temperature.

A numerical model for thermal mapping in a hermetically sealed reciprocating refrigerant compressor

In a refrigerant compressor, improvement in performance such as reduction of various electrical and mechanical losses, reduction of gas leakage, better lubrication, reduction of suction gas heating etc. can be achieved by maintaining a low temperature rise inside the compressor. Proper selection and location of an internal over load protector relay, estimation of heat transfer coefficient and winding insulation coefficient are also vital in enhancing the performance. In this context it is necessary to understand the temperature distribution inside a compressor for an optimal design. In this paper, a numerical model has been created and a heat transfer analysis for a hermetically sealed reciprocating refrigerant compressor is presented. The temperature distribution inside the compressor has been obtained taking into consideration the various heat sources and sinks and compared with experimental results. The maximum temperature was observed at the rotor which was 427.5 K. The deviation of the predicted rotor temperature from that of experimental value is 5.5% only. A good agreement was found between experimental results and that predicted in the numerical analysis.

Enhancing the Wear Resistance of 100Cr6 Bearing Steel Using Cryogenic Treatment

The purpose of this study is to examine the effect of cryogenic treatment on the enhancement of the wear resistance of 100Cr6 bearing steel. The study also aims to reveal the underlying mechanisms responsible for the enhancement of wear resistance by deep cryogenic treatment (DCT) at −185°C. The wear behavior was assessed by a reciprocatory friction and wear monitor under varying normal loads (ASTM International, Annual Book of Standards, 1996). It was found that the wear resistance was increased by 37% due to DCT when compared with that of conventional heat treatment (CHT). A scanning electron microscopy (SEM) study was also conducted to identify the possible mechanism that augments the improvement in the wear resistance of cryogenically treated 100Cr6 bearing steels. The microstructural study suggests that the improvement in the wear resistance is attributed to the conversion of the retained austenite into martensite, along with the precipitation and distribution of the carbides brought in by the cryogenic treatment. The differential scanning calorimeter (DSC) analysis conducted on the bearing steel samples showed that the DCT mainly enhances the destabilization of martensite by activating carbon clustering and transition carbide precipitation. Deep cryogenic treatment demonstrated more improvement in the wear resistance and hardness compared with conventional heat treatment.

Effect of Cryogenic Treatment on the Microstructure and Wear Resistance of X45Cr9Si3 and X53Cr22Mn9Ni4N Valve Steels

The effect of cryogenic treatment on the microstructure and wear resistance of X45Cr9Si3 and X53Cr22Mn9Ni4N valve steels is investigated by conducting an optical and scanning electron microscopy (SEM) study and reciprocating wear test (ASTM standard G-133). The materials are subjected to shallow (193 K) and deep cryogenic treatment (85 K), and the microstructure and wear resistance are compared with those of conventional heat treatment. The wear test data show that for a maximum load of 30 N and 5 Hz frequency, the wear resistance of the X45Cr9Si3 and X53Cr22Mn9Ni4N improved by 15.2 and 10.3%, respectively, due to shallow cryogenic treatment (SCT) and 42.39 and 22.08%, respectively, due to deep cryogenic treatment (DCT) compared to that of the conventional heat treatment. The enhancement in the wear resistance of the X45Cr9Si3 and X53Cr22Mn9Ni4N valve steels observed through the optimized DCT was 46.51 and 27.8%, respectively, compared to the samples without cryogenic treatment. The microstructural study clearly proves that the full elimination of the retained austenite was not achieved in the SCT and DCT specimens. However, there was a reduction in the amount of retained austenite when compared to conventional heat treatment (CHT) specimens. After studying the metallurgy of the cryogenically processed valve steels, it was concluded that the formation of fine carbides dispersed in the tempered martensite structure was the main reason for the enhancement of wear resistance along with the retained austenite transformation.

Optimization of the Cryogenic Treatment Process for En 52 Valve Steel Using the Grey-Taguchi Method

This study investigated the optimization of the deep cryogenic treatment for En 52 valve steel using the Taguchi method in combination with the Grey relational analysis. The factors considered for the optimization are the cooling rate, soaking temperature, soaking period, and tempering temperature, each at three different levels. The mechanical properties such as the tensile strength, hardness, and wear resistance were selected as the quality targets. Nine experimental runs based on L 9 (34) orthogonal array of the Taguchi method were performed. An optimal parameter combination of the deep cryogenic treatment was obtained via the Grey relational analysis. The analysis of variance is applied to identify the most influential factor and it is found that the soaking period is the most influential factor for the deep cryogenic treatment of En 52 valve steel. A confirmation experiment is performed to verify the optimal result. The results of the confirmation tests prove that the tensile strength, hardness, and ...This study investigated the optimization of the deep cryogenic treatment for En 52 valve steel using the Taguchi method in combination with the Grey relational analysis. The factors considered for the optimization are the cooling rate, soaking temperature, soaking period, and tempering temperature, each at three different levels. The mechanical properties such as the tensile strength, hardness, and wear resistance were selected as the quality targets. Nine experimental runs based on L 9 (34) orthogonal array of the Taguchi method were performed. An optimal parameter combination of the deep cryogenic treatment was obtained via the Grey relational analysis. The analysis of variance is applied to identify the most influential factor and it is found that the soaking period is the most influential factor for the deep cryogenic treatment of En 52 valve steel. A confirmation experiment is performed to verify the optimal result. The results of the confirmation tests prove that the tensile strength, hardness, and wear resistance of the deep cryotreated En 52 valve steel samples improved simultaneously through the optimal combination of the deep cryogenic treatment parameters obtained from the proposed method. The improvement in the tensile strength, hardness, and wear resistance of the deep cryotreated samples at the optimized treatment condition on the samples without deep cryogenic treatment is 7.84, 11.16, and 46.51%, respectively. Through the deep cryogenic treatment the wear resistance of the En 52 valve steel has improved more compared to the other responses.

Optimization of Deep Cryogenic Treatment Process for 100Cr6 Bearing Steel Using the Grey-Taguchi Method

This article presents a method for optimizing the deep cryogenic treatment (DCT) process parameters for 100Cr6 bearing steel, based on the Taguchi method with Grey relational analysis. The DCT parameters considered for the optimization included the cooling rate, soaking temperature, soaking time, and tempering temperature, with the quality targets of dimensional stability, wear resistance, and hardness. As per the Grey-Taguchi technique, nine experimental trials based on the L9 (34) orthogonal array were conducted. The optimum parameters for 100Cr6 bearing steel were arrived at based on Grey relational analysis. Analysis of variance (ANOVA) was performed and soaking temperature was identified as the most influential factor in deep cryogenic treatment of 100Cr6 bearing steel. The improvement in dimensional stability, wear resistance, and hardness of the deep cryotreated samples under optimized treatment conditions was 13.77, 49.02, and 19.35%, respectively. A microstructural examination was carried out to identify the possible mechanism of cryogenic treatment in improving the properties of the 100Cr6 bearing steel. A confirmation test was subsequently conducted to validate the test results.

Influence of cryogenic treatment on the wear characteristics of 100Cr6 bearing steel

A series of reciprocating wear tests were performed on the deep cryogenically treated and conventionally heat-treated samples of 100Cr6 bearing steel to study the wear resistance. The worn surfaces as well as the wear debris were analyzed by scanning electron microscopy. The improvement in wear resistance of the deep cryogenically treated samples ranges from 49% to 52%. This significant improvement in wear resistance can be attributed to finer carbide precipitation in the tempered martensitic matrix and the transformation of retained austenite into martensite. X-ray diffraction analysis shows that the volume fraction of retained austenite in the conventionally heat-treated samples is 14% and that of the deep cryogenically treated samples is only 3%.