Abstract
Convetional technology is mainly used for processing parts where high hardness, although conventional treatment of tool steels is ordinarily used in industrial practice, engineers continue to seek new procedures to rid tool steels of objectionable primary sharp-edged chromium carbides, which impair toughness. Fortunately, research into metal forming yielded new methods of modifying the microstructure of hypereutectoid steels. Using these methods, mechanical properties can be improved by virtue of eliminating objectionable sharp-edged carbides. These carbides resist dissolution and their size and shape make them undesirable microstructural constituents. Although they do improve wear resistance of the matrix, they also impair toughness and may act as stress concentrators. The microstructures produced by a sequence involving semi-solid processing and subsequent forming operations were different from conventional semi-solid-processed microstructures. In the former microstructures, the prior carbide network was broken up, dispersed, and became a strengthening constituent. Brittleness which plagues materials with prominent carbide networks was thus removed.The experimental material used in this study was X210Cr12 tool steel. Two semi-solid processing temperatures were used: 1240°C and 1260°C. There were two holding times: 30 minutes and 60 minutes. Another variable was the number of reductions. The resulting microstructures were examined with respect to individual sequences and reductions applied. Detailed microstructure analysis was carried out using a scanning electron microscope (SEM). Chemical compositions of carbides were determined by means of EDS (Energy Dispersive X-ray Spectroscopy). Microhardness was measured in order to gather comprehensive materials data. The purpose of the study was to identify trends, if any, in microstructural property evolution in response to the above-described processing sequence.
Highlights
Unconventional treatment of material by heating to the semi-solid state has been known since the 1970s
It was clear that the temperature was too low and failed to cause dissolution of all primary chromium carbides
The last reduction resulted in notable elongation of austenite grains and alignment of the ledeburite network with the deformation direction
Summary
Unconventional treatment of material by heating to the semi-solid state has been known since the 1970s. At that time, it was primarily used for low-melting materials. It was primarily used for low-melting materials Most often, they were aluminium and magnesium alloys [1, 3]. The process was adopted for higher-melting materials, typically steels [2,3,4]. For the desired microstructure to be obtained, a liquid fraction interval of 10%-60% must be maintained. Microstructures produced by semi-solid processing typically consist of polyhedral austenite grains embedded in a ledeburite network. In terms of the effect of the network on mechanical
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