There are three types of hardness testing standards for pit furnaces, namely Vickers, Rockwell and Surface Rockwell. According to the same heat treatment method, the hardness test method of the surface quenching and tempering heat treatment furnace and the chemical heat treatment furnace is also different.
The main technical parameters of the chemically heat treated workpiece are the hardened layer depth and the surface hardness. The depth of the hardened layer is still to be measured with a Vickers hardness tester. Detect the distance from the surface of the workpiece to the point where the hardness drops to 50 HRC. This is the effective hardening depth.
Chemical heat treatment is the atomization of the surface of a workpiece into one or several chemical elements, thereby changing the chemical composition, organization and properties of the surface of the workpiece. After quenching and low temperature tempering, the surface of the workpiece has high hardness, wear resistance and contact fatigue strength, and the core of the workpiece has high toughness.
The surface hardness test of the chemically heat treated workpiece is similar to the hardness test of the surface hardened heat treatment workpiece, and can be detected by a Vickers hardness tester, a surface Rockwell hardness tester or a Rockwell hardness tester, except that the thickness of the nitriding thickness is thin, generally not larger than 0.7mm, then you can no longer use the Rockwell hardness tester.
If the local hardness of the part is high, the local quenching heat treatment can be performed by means of induction heating. Such parts are usually marked with the local quenching heat treatment position and local hardness value on the drawing. The hardness test of the part is to be carried out in the designated area. The hardness tester can use the Rockwell hardness tester to test the HRC hardness value. If the heat treatment hardened layer is shallow, the surface hardness tester can be used to test the HRN hardness value.
The surface quenching and tempering heat treatment of the pit furnace is usually carried out by means of induction heating or flame heating. The main technical parameters are surface hardness, local hardness and effective hardened layer depth. The hardness test may be performed by a Vickers hardness tester or a Rockwell or surface Rockwell hardness tester. The choice of test force (scale) is related to the effective hardened layer depth and the surface hardness of the workpiece. There are three hardness testers involved here.
The Vickers hardness tester is an important means to test the surface hardness of heat-treated workpieces. It can be used to test the surface hardened layer as thin as 0.05mm thick with a test force of 0.5-100kg. Its precision is the highest, and the hardness of the surface of the workpiece can be distinguished. difference. In addition, the effective hardened layer depth is also detected by a Vickers hardness tester. Therefore, it is necessary to equip a unit for surface heat treatment or a large number of surface heat treatment workpieces with a Vickers hardness tester.
The surface Rockwell hardness tester is also very suitable for testing the hardness of surface hardened workpieces. The surface Rockwell hardness tester has three scales to choose from. Various surface hardened workpieces with effective hardening depths in excess of 0.1 mm can be tested. Although the accuracy of the surface Rockwell hardness tester is not as high as the Vickers hardness tester, it has been able to meet the requirements as a means of quality management and inspection of the heat treatment plant. Moreover, it has the characteristics of simple operation, convenient use, low price, rapid measurement, and direct reading of hardness value. The surface Rockwell hardness tester can be used for rapid and non-destructive part-by-piece inspection of batch surface heat treatment workpieces. This is important for metalworking and mechanical manufacturing plants.
When the heat treatment hardened layer on the surface of the pit furnace is thick, a Rockwell hardness tester can also be used. When the thickness of the hardened layer is 0.4 to 0.8 mm, the HRA scale can be used, and when the thickness of the hardened layer exceeds 0.8 mm, the HRC scale can be used.
Vickers, Rockwell and Surface Rockwell hardness values can be easily converted to each other and converted to standard, drawing or user-required hardness values. The corresponding conversion tables are given in the international standard ISO, the American standard ASTM and the Chinese standard GB/T.
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