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The quality of cutting of low-carbon and stainless steel by beams of fiber and CO 2 lasers with oxygen or nitrogen being used as a process gas is compared. The cut surface roughness for sheets from 3 to 10 mm thick is determined. Domains of optimal (in terms of the minimum roughness criterion) application of lasers of various types in the space of dimensionless parameters (Peclet number and dimensionless power) are found. It is demonstrated that the CO 2 laser is more effective for laser-oxygen cutting, while the fiber laser is more beneficial for cutting with the use of a neutral gas.

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The microstructure of WC/Co hard alloys after surface laser treatment is studied. It is established that during the laser treatment of the hard alloys, the chemical interaction between the components of the WC/Co powder mixture occurs in the samples' surface according to the reaction 3Coz3WCR(Co; W) 3 Cz2C. High cooling rate during the laser treatment allows preserving the products of this reaction, i.e. graphite inclusions and complex carbide (Co; W) 3 C to room temperature.

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The fiber and CO 2 laser were compared from the viewpoint of two laser-cutting methods: the oxygen-assisted cutting of lowcarbon steel and fusion cutting of stainless steel with a neutral assistant gas. The absorbed laser energy was measured in respect to the unit of the removed material volume at the cutting parameters correlating to the minimal roughness of the cut surface. This value equals to 11…13 J/mm 3 both for the fiber and 2 lasers. During the fiber-laser cutting, the minimal roughness is reached at the Peclet number 0.35…0.4, at the CO 2 -laser cutting -at 0.45…0.55. At the fusion cutting of stainless steel, the minimal roughness is reached at the maximal cutting speed. The maximal cutting speed has the higher value in the fiber-laser case at the same laser power. The paper discusses the potentiality of the method of absorbed laser energy measurement by the value difference at the cut channel inlet and outlet. NomenclatureW laser power V cutting speed t sheet thickness

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