Abstract: The relationship between variation of friction coefficient of steel GCr15 against the hard alloy YG8 and the normal load and sliding speed under dry sliding condition was studied in this paper. The results show that the friction coefficient of the steel in dry sliding friction decreases with increment of load and speed. On the basis of changes of wear surface and surface temperature calculation it was considered that the flash temperature increases with an increment of load and/or speed. This results in the partial melting of the frictional surfaces, i. e. the boundary lubrication is formed, therefore, the friction coefficient decreases. And, there is a decrease in the difference of friction coefficient between different microstructures under the condition of higher load and/or speed.