One of the most important indicators of any metal is the hardness which characterizes its ability to resist penetration into it of other body having bigger hardness. Steel is not an exception.
Instruction
1. Durability became closely connected with its such characteristics as wear resistance, durability and so forth. There are many ways of determination of hardness of metals. One of them – Brinell's method when the steel ball is pressed into the surface of metal (steel) by means of a special press (Brinell's press). Upon termination of impact of a ball on a metal surface by means of a special magnifying glass the measurement of diameter of a hole is made. On the basis of these tables attached to a press the hardness of NOT steel is defined.
2. The following method – Rockwell's method - assumes cave-in in a steel surface of a diamond cone with a corner of 1200 at top. Cave-in is carried out with preliminary loading of 10 kg in the beginning, and then full – from 60 to 150 kg. For this purpose also the special press is used.
3. When using this method it is necessary to observe some requirements. So, on the studied surface there should not be a scale, cracks and hollows. Impact on a surface is strictly perpendicular. For determination of value of durability special tables are also used. There is an accurate dependence – the steel, the less depth of penetration into it at cave-in is more solid and, therefore, the higher value of hardness.
4. The Vikkersa method in which for cave-in the tetrahedral diamond pyramid with a corner at top of 1360 is used is similar to Rockwell's method. Here upon termination of loading the print diagonal is measured. For staly influence time - 10-15 sec. At the same time the effort has to be made strictly perpendicular to a surface with smooth increase. The surface of a prototype can have roughness no more than 0.16 microns, and distance between the center of a print and edge of a sample or next print – not less than 2.5 lengths of diagonal of a print.
5. Hardness of steel is defined also by method of a shock print by means of the hard-alloy conic indenter or a steel sphere. The technique of measurement of hardness on Shora belongs to indirect methods. In it it is used baizes of a certain weight with a diamond tip, vertically falling from a certain height on a test surface. Rebound height quickly is characteristic of hardness which is measured in conventional units.