Key Engineering Materials Vol. 647

Abstract: Selecting and correctly heat treating an appropriate tool steel for production a die is not a simple task. This paper points out defects which are encountered most frequently in dies when a poor-quality material or an inadequate heat treating schedule was selected or when the prescribed heat treating schedule was not followed. The most common deficiencies in semi-finished products from tool steels for die making include carbide banding and non-uniform microstructure with substantial variance in grain size. Incorrect tempering parameters are often used and the materials are thus treated in the region of temper brittleness. Cases of the above kind have been investigated by the laboratory at COMTES FHT a.s. in recent years and their summary is given in the text below.

Abstract: This contribution deals with the analysis of causes of a breakdown of a turbine rotor where stage 13 completely broke off. Microstructure and fractographic analyses showed that a dominant cause of the breakdown was stress corrosion cracking caused by impurities in the steam.

Abstract: Safe operation of the machinery depends on quality of the individual machine parts. These are controlled by different non-destructive methods not only at the end of the production but also during it. In large quantity series production it is necessary to ensure the fastest control method possible. Shafts may bend during production due to the heat treatment and they need to be straightened by mechanical methods. Shafts straightening may cause cracks formation which is unacceptable from the point of view of the part operation. Therefore crack detection system QASS CiS.01 is used to reveal them on the basis of the magnitude of energy response. The results obtained from the detector were controlled using metallography and its function was successfully confirmed. It is not possible to determine relation between energy value and cracks length from carried out metallographic observation and values measured by the detector.

Abstract: The paper discusses the problem of recurrent corrosion of casing of metal detectors used in food industry. The detector casing is fabricated by welding sheets of X5CrNi18-10 stainless steel. The detectors in service suffered non-uniform spot corrosion. The likely cause of the corrosion attack was the accumulated contamination of the detector surface with cleaning and disinfecting agents containing chlorine. The sheet surfaces of the original detectors were shot-blasted. After the sheet finishing process was changed to grinding and minor design changes were made, the corrosion resistance of the detector casing improved. The enhanced corrosion resistance of the detectors with ground surfaces was confirmed by salt spray tests. The use of the modified detectors then led to a lower number of complaints about the devices.