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The boronizing is a thermochemical process in which the boron atoms are introduced into the steel surfaces. This study evaluates the fracture toughness of boride layers developed by powder boronizing of high-chromium steels Sleipner, K 190, Royalloy, Sverker 21 and Sverker 3. The process was carried out at 1323 K, for 10 h, and in solid Durborid powder mixture. First of all, the microscopic and EDS analysis to investigate a chemical composition of boride layers were realized. Subsequently, the Vickers microhardness tester was used to generate the microcracks in borides. The load of 2 N was used for indentation. The microhardness of Fe2B phase ranged between 1551 HV0.2 and 1726 HV0.2. For the FeB phase, the microhardness ranged between 1974 HV0.2 and 2277 HV0.2. For quantification of the fracture toughness, the Palmqvist method was used, when the values of length of the microcracks that appeared in the corners of the indentations were analyzed. The fracture toughness of the FeB phase was lower compared to the Fe2B phase. The fracture toughness ranged between 1.98 MPa·m1/2 and 2.58 MPa·m1/2 for the FeB phase and between 3.87 MPa·m1/2 and 4.50 MPa·m1/2 for the Fe2B phase. It was found that the chemical composition of the steel does not have a significant effect on the values of the fracture toughness.
Keywords: Boronizing, boride layers, steel, microhardness, fracture toughness© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.