Abstract
In the present study, microstructure, hardness, and abrasion resistance of a heat-treated high carbon-high chromium steel (FMU-11) used in the cement mills were investigated. To investigate the best heat-treating cycle for the FMU-11 steel, three sets of samples were heat treated. The first set was tempered two times, the second set was re-hardened, and the third set was cryogenically heat treated. These samples were then compared with the conventionally heat-treated samples. The samples' microstructure was studied using an optical microscope, where traditional black and white etching, as well as color etching, were used. Scanning electron microscopy (SEM) was applied for higher magnification studies and in-depth analysis of the chemical composition. The mechanical properties were investigated by measuring the hardness and the wear resistance for the samples heat-treated in different cycles. The results showed that the cryogenic treatment and double-tempered samples had the highest hardness and wear resistance. In addition, the results showed that the re-hardening operation caused the carbides to be finely separated and evenly distributed in the steel matrix. The wear test results illustrated that the wear mechanism could be the delamination wear and the abrasive wear combined.
Highlights
A milling system is one of the most widely used machines for reducing the granular sizes in cement production
The small carbides and martensite needles were clearly seen after this heat treatment
Based on the amount of carbon and chromium in this steel, the type of carbides could be determined with the ratio of chromium to carbon
Summary
A milling system is one of the most widely used machines for reducing the granular sizes in cement production. A new type of steel called high carbon-high chromium steel (FMU-11) has been used in the production of cement mill floor liners. This steel contains 1.4-1.6% carbon and 11-13% chromium. This type of chemical composition provides good abrasion resistance, and if a suitable heat treatment cycle is applied to obtain a tempered martensite structure with a minimum amount of retained austenite and uniform distribution of carbides in the steel matrix [3]. Chromium up to 13.0% can be solved in the austenite, so if the chromium separates and its concentration increases in the separated areas, the possibility of forming carbides increases, and as a result, the impact resistance can be reduced [4]. There is a fourth carbide in the system, Cr3C2, that essentially does not dissolve Fe and is of minor importance for this type of steel [5]
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