engleski

HARDNESS UNIFORMITY OF VICKERS HARDNESS BLOCKS FOR THE HIGH HARDNESS RANGE

Hardness uniformity is the most important property of hardness block and depends on the quality of the starting material, process of obtaining, heat and surface treatment. All parameters must be selected very carefully to achieve homogenous microstructure with no defects. Vickers hardness blocks for the high hardness range were produced by two different processes of powder metallurgy ; conventional liquid phase sintering in hydrogen and sinter HIP. Nano powder of WC with a grain size of 150 nm with specific surface area of 2, 5 m2/g and addition of grain grow inhibitors was used as staring powder. Hardness uniformity of the produced blocks was investigated in this paper. Surface of the blocks was divided into radial and circumferential divisions forming different sections on the block surface. Hardness measurements were performed in each section with one level of the test force. Applied force was 9.807 N what corresponds to measuring method HV1. For reliable hardness measurement five indentations were measured in each section. Overall 40 indentations were performed based on which conclusions about the hardness uniformity of the Vickers hardness blocks were brought. Hardness uniformity was tested by analysis of variance, ANOVA, for single factor in to order to determine if significant hardness variations across the block surface are present. From carried research was concluded that hardness distribution on test surfaces of Vickers hardness blocks has a trend according to a process of obtaining.

Vickers hardness blocks; powder metallurgy process; hardness uniformity; surface division; ANOVA

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