Change of Geometric Accuracy of Structural Steels after Carburizing in Gas

Abstract

Nowadays, carburizing at low pressure or vacuum carburizing is often used, which is a modification of carburizing in gas, while carburization is performed at pressures well below the level of atmospheric pressure (101 kPa). The advantage of this process is that no internal oxidation occurs; carburizing has a higher rate and uniformity of carburization, good reproducibility of the process and lower deformation. Carburizing is mainly used for parts subjected to abrasion (eg gears). However, even with this process, the geometric accuracy and surface texture of the parts change. The changes of geometric accuracy of ground samples from carbon steel C45, low-alloy Mn-Cr carburizing steel 16MnCr5 and medium-alloyed Ni-Cr carburizing steel 14NiCr14, which were vacuum-carburized in a CO/CH4 atmosphere, were evaluated in this work. Geometric accuracy was evaluated by measurement using a 3D coordinate measuring machine, surface texture using a coherent correlation interferometer. After the carburizing process, changes in the dimensions of the samples were found in all steels. For C45 steel, the sample dimensions were reduced by 0.028 mm ± 0.004 mm, the surface roughness expressed by the parameter Ra decreased by 0.28 µm, which is 20%. In case of carburizing steels there was an increase in the dimensions of the samples, especially in the case of 14NiCr14 steel and a smaller difference in surface roughness. The same parameters of the carburizing process lead to different behaviour of carburized parts in different steels, in terms of changes in dimensions and surface texture.