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The influence of tempering process for properties of boron steel
Doležal, Luděk ; Kubíček, Jaroslav (referee) ; Slováček, Marek (advisor)
This bachelor thesis deals with the problem of the occurrence of residual austenite in the crossbar of a harvester forestry tracks during tempering after a longer period of time. The chosen material is boron steel 27MnCrB5-2. The experiment is carried out by comparing three samples, the first is tempered immediately after quenching, the second is tempered 48 hours after quenching and the third is not tempered. According to preliminary calculations of cooling rates and Mf temperature, the presence of residual austenite is unlikely. On all metallographic smears, an identical martensitic-bainitic structure can be observed by optical microscopy. On a scanning microscope, both tempered materials show lower bainite with carbides within the ferritic lamellae. Only the quenched sample has carbides that are difficult to distinguish from the martensitic structure, but no evidence of residual austenite. Based on the hardness measurements, the quenched crossbar has the highest hardness. According to the corresponding curve in the CCT diagram, the hardness corresponds to the bainitic structure. The occurrence of residual austenite was definitely ruled out by X-ray diffraction at less than 2% resolution of the equipment used
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Materials change of parts for harvester chain production
Houdek, Radim ; Kubíček, Jaroslav (referee) ; Sigmund, Marian (advisor)
The work is focused on the track element, namely the replacement of the crossbar material from steel 27MnCrB5-2 to steel 30MnB5 from which the other parts of the cell, the cubes, and the bar are made and welded by the GMAW method. Changing the material and omitting the preheating phase would reduce the production time of the cell by approximately half the time. The theoretical preheating temperature calculated according to the relevant standard for both steels exceeded 200 ° C. Test specimens imitating the weld between the crossbar and the cube were welded on which a qualitative evaluation was performed. These were weldments of 30MnB5 steel with preheating (sample 10), 30MnB5 steel without preheating (sample 11) and 27MnCrB5-2 steel with preheating (sample 9). In terms of macrostructure, non-penetrations were found on all samples. Martensitic structure was found in all areas by microstructural observation. When measuring the hardness according to the Vickers method, approximately the same hardness profile was obtained in all weld areas of samples 10 and 11. The highest value reached 450 HV1 and exceeds the maximum hardness recommended by the standard. Due to very similar test results for 30MnB5 steel weldments with and without preheating, it is possible not to perform preheating. However, the results may be skewed by the relatively small size of the test specimens. For a reliable evaluation and final decision, it is necessary to perform tests on a real crossbar after complete production.
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Optimalisation of heat treeatment of steel - 27MnCrB5-2
Černín, Jiří ; Němec, Karel (referee) ; Věchet, Stanislav (advisor)
This bachelor’s thesis deal with heat treatment of bor steel, 27MnCrB5-2. The work contains assessment and further proposal of new suitable form fot heat treatment. With request for the most possible hardness and preservation optimal scale of tenacity and reasonable price. Teoretical part describes basic information about heat treatment. In the practical part was investigate sttructure, hardness and chemical composition of six samples.
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Materials change of parts for harvester chain production
Houdek, Radim ; Kubíček, Jaroslav (referee) ; Sigmund, Marian (advisor)
The work is focused on the track element, namely the replacement of the crossbar material from steel 27MnCrB5-2 to steel 30MnB5 from which the other parts of the cell, the cubes, and the bar are made and welded by the GMAW method. Changing the material and omitting the preheating phase would reduce the production time of the cell by approximately half the time. The theoretical preheating temperature calculated according to the relevant standard for both steels exceeded 200 ° C. Test specimens imitating the weld between the crossbar and the cube were welded on which a qualitative evaluation was performed. These were weldments of 30MnB5 steel with preheating (sample 10), 30MnB5 steel without preheating (sample 11) and 27MnCrB5-2 steel with preheating (sample 9). In terms of macrostructure, non-penetrations were found on all samples. Martensitic structure was found in all areas by microstructural observation. When measuring the hardness according to the Vickers method, approximately the same hardness profile was obtained in all weld areas of samples 10 and 11. The highest value reached 450 HV1 and exceeds the maximum hardness recommended by the standard. Due to very similar test results for 30MnB5 steel weldments with and without preheating, it is possible not to perform preheating. However, the results may be skewed by the relatively small size of the test specimens. For a reliable evaluation and final decision, it is necessary to perform tests on a real crossbar after complete production.
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Optimalisation of heat treeatment of steel - 27MnCrB5-2
Černín, Jiří ; Němec, Karel (referee) ; Věchet, Stanislav (advisor)
This bachelor’s thesis deal with heat treatment of bor steel, 27MnCrB5-2. The work contains assessment and further proposal of new suitable form fot heat treatment. With request for the most possible hardness and preservation optimal scale of tenacity and reasonable price. Teoretical part describes basic information about heat treatment. In the practical part was investigate sttructure, hardness and chemical composition of six samples.
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