Abstract
The characteristics of elongated MnS have a critical effect on fatigue anisotropy and all mechanical anisotropies. A comparative investigation of nonmetallic inclusions in both stainless steels and tool steels has been carried out in this study. The inclusion characteristics were investigated using electrolytic extraction (EE) followed by scanning electron microscopy combined with energy-dispersive spectroscopy (SEM-EDS). Overall, three types of MnS inclusions (type I (regular), type II (irregular) and type III (Rod)) were found in tool steels in as-cast samples, which had not been heat-treated. Furthermore, three types of MnS inclusions (Rod-like sulfide (RS), Plate-like sulfide (PS) and Oxysulfide (OS)) were found in samples taken after rolling. Based on the breakability of the elongated MnS, three types of inclusions, Type UU, UB and BB, where U represents the undamaged or unbroken edge of an inclusion and B represents the fragment or broken edge of an inclusion, were studied in both stainless steels and tool steels both before and after additional heat treatment. The effect of heat treatment and dissolving the metal layer during the EE process is also discussed. The results show that both processes have a limited effect on the breakability of inclusions in steels with carbon contents <0.42 mass%.
Highlights
The results show that both processes have a limited effect on the breakability of inclusions in steels with carbon contents
The electrolytic extraction method can successfully be applied for stainless steels containing less than 0.1 mass% carbon and for tool steels containing 0.15 mass% C
For tool steels containing more than 0.15% C, carbides were extracted from the steel matrix during the electrolytic extraction (EE) process and they covered other inclusions
Summary
In this study, the purpose of the heat treatment was to dissolve the carbides in the metal matrix to enable better conditions to determine the inclusion characteristics. This is due to the fact that in a tool steel with a high carbon content, the MnS inclusions are all covered by carbides after applying the EE process to a steel sample. After being heated for the desired time, the samples were rapidly cooled (quenching in cold water) to avoid other carbides (such as cementite) precipitating. A 5 min heat treatment time was used for the rolled 13HMF steel sample in order to be able to compare the results from the inclusion characterization. Different holding times at 900 ◦ C were applied for the rolled 42CrMo4 and 3R65 steel samples
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