Hardness testing

Determination of metal hardness is carried out as part of the work to determine the service life of equipment, for example, the service life of the main elements of boilers, turbines and pipelines of thermal power plants. Hardness testing, as a rule, is carried out in combination with other non-destructive testing methods to form a complete picture of the object.

To conduct this type of study, one-way access to the control object is sufficient. The equipment is compact, which means that it is possible to carry out control in conditions of limited access. 

There are several scales (methods of measurement) for measuring hardness:

• Brinell method – hardness is determined by the diameter of the imprint left by a metal ball pressed into the surface. Hardness is calculated as the ratio of the force applied to the ball to the imprint area (moreover, the imprint area is taken as the area of ​​a part of the sphere, and not as the area of ​​a circle (Meyer hardness)); the unit of hardness according to Brinell is MPa (kg-s/mm²).
• Rockwell method – hardness is determined by the relative depth of indentation of a metal ball or diamond cone into the surface of the material being tested. The hardness determined by this method is dimensionless and is designated HR, HRB, HRC and HRA; hardness is calculated by the formula HR = 100 (130) – kd , where d  is the indentation depth of the tip after removal of the main load, and k  is the coefficient. Thus, the maximum Rockwell hardness on the A and C scales is 100 units, and on the B scale – 130 units.
• Vickers method – hardness is determined by the area of ​​the imprint left by a tetrahedral diamond pyramid pressed into the surface. Hardness is calculated as the ratio of the load applied to the pyramid to the area of ​​the imprint (moreover, the imprint area is taken as the area of ​​a part of the surface of the pyramid, and not as the area of ​​the rhombus); dimensionality of Vickers hardness units kg-s/mm². The hardness determined by this method is designated HV.