The carburization of steel parts changes the chemical composition in the surface. According to the change of chemical composition a change in density occurs. If the change in density is distributed in an asymmetrical way, distortion can not be avoided.In order to find out the effects of specifying factors on distortion, several finite element simulations of asymmetrically carburized 20MnCr5 discs were carried out. All simulated activities during the carburizing process occur at austenitization temperature. First, an analysis with several geometries -with changed radii and changed thicknesses -shows, that the influence of the partial carburization on distortion decreases exponentially with increasing thickness of the disc. Second, an analysis with four different carbon profiles shows, that a change in carbon profile leads to different distortion behaviour.In order to check the quality of the calculated results, the distortion of a partially carburized and afterwards oil-quenched disc was measured by coordinate measurements. This result was compared with the simulated distortion and shows a good agreement.
This paper presents an ultrasonic method to measure the movement of workpiece surfaces during quenching processes in liquids in order to estimate the time-dependent in-process distortion of the workpiece. The movement is determined by the time-of-flight of the ultrasonic signals from the transducer to the surface and back again (impuls-echo-method). As the simulation of quenching processes depends on several assumptions of the model parameters and almost no experimental intermediate geometry data for quenching processes exist, the in-process-measurements of the surface movement can be used to improve the simulation models and also to extend the knowledge about model parameters. The paper shows an analysis of the ultrasonic data for measurements on cylindrical discs of 20MnCr5 steel and compares the ultrasonic in-process results with simulated data. Additionally, coordinate measurements carried out before and after the heat treatment are presented as a reference and the uncertainty of the ultrasonic measurements is discussed.
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