Guidelines for Hardness Testing of Thin Hardened Surface Layers
NOT PERMITTED
the use of the following instruments for measuring the hardness of thin hardened layers
To obtain reliable hardness results on steel and cast iron parts with surface layers 0.01–0.6 mm deep, hardened by various methods, the following must not be used for measurements:
Any portable electronic dynamic (rebound, Leeb) hardness testers
TD-42, TDM-2, TVM-500, TEMP-2,
TEMP-4, etc.
Bench-top Rockwell (HRC, HRB) hardness testers
Bench-top superficial Rockwell (HR30N, HR45N) testers with loads above 15 kgf
TK-2, etc.
ITR, 2143 TRS-M, etc.
Bench-top Brinell (HB) hardness testers
TSh-2, etc.
Portable Poldi and Shore hardness testers
TSh-2, etc.
PERMITTED
the use of the following instruments for measuring the hardness of thin hardened layers
Any portable electronic ultrasonic (UCI) hardness testers
TM-40, TKR-45, UIT TKM-459, T-U2, etc.
Portable Vickers hardness testers
TPP-2,
TVP-5012, etc.
Bench-top Vickers hardness testers with a load of 5–10 kgf. A 30 kgf load is not permitted, as it punches through the layer.
TP, TP-2,
TP7r-1,
IT 5010-01, etc.
Bench-top microhardness testers — the drawing must specify the hardness requirement as HV0.05 (50 gf load) or HV0.1 (100 gf load)
PMT-3, etc.
SURFACE PREPARATION FOR HARDNESS TESTING
To obtain a reliable result, carbon deposits and the magnetite oxide film must be completely removed from the surface of the tested part or specimen at the measurement point, down to the base metal (to a bright metallic finish).
The cleaning method must not remove the upper part of the hardened layer.
Usually, manual cleaning with abrasive paper (emery cloth) of various grit sizes is sufficient.
The use of low-speed grinders and similar tools with discs of suitable grit is permitted.
When measuring hardness directly on parts with a portable ultrasonic hardness tester, the surface roughness must be no greater than Ra 0.8 µm.
When testing specimens and small parts on bench-top hardness testers, the roughness must comply with the standards (GOST, DSTU) for the specific test method.