It is required by developed countries and ISO that Charpy impact machines have been calibrated annually with reference test
pieces which coefficient of variations is within 5%. Developed countries use 40CrNiMo steel, which is made by special manufacture processes for very pure and very uniform as raw material to produce reference test pieces. The high cost embarrasses developing countries to use this kind of reference test pieces widely. A production method of low cost reference test piece which coefficient of variation is within 3% by hot rolled low carbon steel sheet is developed. The test pieces have used in Baoshan Iron & Steel Co. Ltd., laboratories and have showed efficiency on finding problems for impact machines, however attestation of validity on this reference test piece for
calibration Charpy impact machines in large number of laboratories is needed. In 2001, CNACL national laboratory ability on Charpy impact validation campaign not only prove the validity of the low cost reference test piece, but also attest indirectly that it is necessary to calibrate Charpy impact machines by reference test pieces annually. At the same time, it is foud that to calibrate impact machine is necessary to use at least two reference test piece with same reference energy range.