Mr. Mark, the formula for performance improvement does not come from metallurgical textbooks, I have derived it from so called Hall-Petch relation to provide simple answer to your question. Please keep in mind that my formula is simplified and may be even oversimplified. The consequence is that the formula may work with different accuracy/applicability for strength, toughness or hardness.
The Hall-Petch relation describes the grain-boundary strengthening method that uses grain boundaries as pinning points which impede dislocation movement. The smaller grain is stronger because in the larger grain, a dislocation can travel without being stopped by a grain boundary.
The Hall-Petch relation does not consider so-called twin boundaries within the grains, but despite all possible imperfections it is one the most universal relations in mechanical metallurgy. It says, that over wide range of grain sizes the typical mechanical properties increase with the reciprocal root of the grain size.
Your P50 seems to be very fast speed quenching oil with low viscosity. Its quenching power almost approaches that of water or some water solutions. High initial cooling rate is important to get full hardness, but slower cooling is necessary when martensite is formed because stress needs some time to equalize.
What concerns oil quenching I have found several useful information in the attached paper.
Oil Quenching Tech.pdf (Size: 986.41 KB / Downloads: 3)
Jan
The Hall-Petch relation describes the grain-boundary strengthening method that uses grain boundaries as pinning points which impede dislocation movement. The smaller grain is stronger because in the larger grain, a dislocation can travel without being stopped by a grain boundary.
The Hall-Petch relation does not consider so-called twin boundaries within the grains, but despite all possible imperfections it is one the most universal relations in mechanical metallurgy. It says, that over wide range of grain sizes the typical mechanical properties increase with the reciprocal root of the grain size.
Your P50 seems to be very fast speed quenching oil with low viscosity. Its quenching power almost approaches that of water or some water solutions. High initial cooling rate is important to get full hardness, but slower cooling is necessary when martensite is formed because stress needs some time to equalize.
What concerns oil quenching I have found several useful information in the attached paper.
Oil Quenching Tech.pdf (Size: 986.41 KB / Downloads: 3)
Jan