Synopsis : Charpy impact value of the case hardening steel subjected to combined heat treatment with excess vacuum carburizing and subsequent induction hardening was evaluated. The purpose of this study is to clarify the effect of retained austenite and cementite on the impact property. The characteristic of combined heat treatment is that the initial microstructure can be designed easily. The initial microstructure is designed by carburizing and annealing at the hyper-eutectoid composition of 1.3 mass% C and subsequent induction heating temperature is chosen between A cm and A 1 to obtain different amounts of retained austenite and cementite. The impact value improves by the induction hardening with increasing heating temperature and the tempering. The steel treated at the low heating temperature shows intra-granular fracture irrespective of the presence of pro-eutectoid cementite. As the heating temperature increases, the formation of C solid solution progresses by the decomposition of cementite and increased retained austenite transforms into the deformation-induced martensite by the impact energy, thereby increases intra-granular strength. Hence critical fracture strength transits to grain boundary strength and showed inter-granular fracture at the interface of cementite and matrix in this study. The impact value showed the correlation with the amounts of retained austenite before the test and the decrement in retained austenite before and after the test. The effect of retained austenite is due to the plastic deformation of austenite, the increase of the compressive residual stress generated by deformation-induced martensite transformation, and the consumption of the impact energy as the driving force for deformation-induced martensite transformation.
Friction property of the case hardening steel subjected to excess vacuum carburizing and subsequent severe plastic deformation and induction hardening was evaluated by the traction test. The purpose of this study is to clarify the effect of fine microstructure on the friction property, focusing on the interaction between the fine microstructure and the lubricating oil additives. The vacuum carburizing treatment is performed at the hyper-eutectoid composition of 1.0 mass% C. Subsequently, the carburized surface was formed the white layer by the surface-nanostructured wearing (SNW) process, and the specimen having the initial microstructure was subjected to induction hardening. The microstructure of the condition with SNW was finer compared to that with SNW-less. According to the traction test, traction coefficient (μ) in the specimen having the fine microstructure on the rolling contact surface decreased. Therefore, it was found that the decrease of μ could be achieved by the application of high-density lattice defects (grain boundaries in this study). After the test, the rolling contact surface of the specimen with fine microstructure became smooth, and the surface showed high reactivity with the lubricating oil additives and formed the compound film of Fe-O-P system having a fine, spherical morphology. The surface roughness was improved by the presence of the wear particles on the surface. Therefore, it was thought that the μ was decreased because the transition to a mild friction condition was caused due to the dispersion of the contact pressure.
In this paper, we propose a new localization and mapping method using the gridded map and range scan data only. The proposed method is applied to the autonomous wheelchair system. In this method we applied Particle Swarm Optimization (PSO) with appropriate initial values to estimate displacements of position and orientation of the wheelchair. We compared a conventional method that used cross correlation from a previous scan data and a current scan data and our method in some experiments. The experimental results in four situations show the high accuracy estimation and high processing speed of our method.
The Charpy impact value of case hardening steel subjected to combined heat treatment with excess vacuum carburizing and subsequent induction hardening was evaluated. The purpose of this study is to clarify the relation between the crack propagation behavior and the microstructure in steels having different amounts of retained austenite and cementite. The vacuum carburizing treatment is performed at the hyper-eutectoid composition of 1.3 mass% C. Three different heating temperatures were chosen for induction hardening in the two-phase (austenite, cementite) region between A cm and A 1 to obtain different amounts of retained austenite and cementite. Decreasing the induction heating temperature from 1 143 K to 1 043 K, increased crack propagation resistance by around 30% on average in both the quenched-only and the quenched-and-tempered specimens. The high crack propagation resistance of the samples with the low induction heating temperature was caused by the arrest effect of undissolved θ. By contrast, in the sub-zero treated specimens, crack propagation resistance showed an almost constant value irrespective of the induction heating temperature. That constant propagation resistance was attributed to the repeated bending and branching occurring during crack propagation.
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