Tepelné ovlivnění ocelí při různém způsobu dělení

Abstract

Předložený článek řeší problematiku tepelného ovlivnění ocelí při dělení materiálu.

The submitted article describes the effects of a thermal separation of material on the properties of the surface layers. The separation of material is an integral part of a preparation of all final products. During cutting the surface layer of the separated material is effected, which then has an influence on the sequence of the following operations. Three methods of thermal separation of material were selected for the experiment described in the article -a method of laser, plasma and flame cutting. The temperatures for plasma cutting were 30 000°C and 20 000°C. The material selected for these three methods was a common steel 11 373, which is industrially produced and processed. The effect on the material was shown by measuring microhardness using the microhardness tester OM 20. The comparison of individual methods of material separation showed interesting results regarding the effects on the surface layer. The laser cutting showed the highest values of hardness. This was caused by a big temperature gradient between the place of cutting and the surrounding area. The laser beam (10^6 °C) had such a thermal effect on the surface layer that it created bainitic structure with the hardness of 340 HV. The effected depth was, however, very small and came to only 1mm. For plasma cutting of the tested material, two different temperatures were used. The first temperature was 30 000°C and the effect on the surface layer revealed the same depth as in the case of laser cutting - 1mm. The hardness of the surface layer, however, reached the value of 278 HV, which represents a fine pearlitic structure. When using plasma at a lower temperature, the value of hardness measured was 250 HV, which also shows a fine pearlitic structure. The last one was a method of thermal separation of material using flame . This method showed the smallest effect on the surface layer. The hardness in the place of cutting was 165 HV. The depth of the effected layer was considerably greater compared to the laser and plasma cutting and reached the value of 3mm. Hardening of the surface layer or in other words a creation of an unbalanced structure was evident only in the case of laser cutting. In other cases the surface layer was not significantly effected. One of the reasons is the type of material used. Steel 11 373 contains only a small percentage of carbon (0.17% C). Material with such small content of carbon prevents its hardening. For further studies of thermal effects on steel during material separation by laser, plasma and flame cutting, I propose using a wide range of material with a different carbon content. Also, it is possible to use machines at different power and observe the effects on the changes of the structure.