Part 3 will focus on specific groups of tool steels. This particular presentation will focus on the A series of tool steels. The A series is that group of tool steels that can transform from austenite simply by heating up into the austenite region for that particular tool steel group and cooling in air. The air can be moving or still. It must be dry, however, or there is a risk of crack propagation occurring.
It can be seen that the A series ranging from A1 up to A6 has an approximate
carbon content at 0.7-1% and a chromium content of approximately 1-5%. There is
also a molybdenum addition (on average) of 1-1.25%. From A6 up to A10, the
carbon content can range from 0.7-2.25%. Molybdenum will range from 1.25-5%, and
chromium from 5-5.25%.
It is within this section of the A-series tool steels that we begin to see the
addition of nickel (1.50-1.80%). Vanadium also starts to make an appearance from
1% up to 4.75%. We can also see tungsten making an appearance of 1-1.25%.
The addition of the elements vanadium and tungsten and the increase in chromium and in molybdenum begins to suggest that their interaction with carbon
will initiate widely dispersed complex-carbide formations. The finely dispersed
carbides give rise to high wear resistance and higher hardness values than
would be normally expected with the air hards A1-A6.
The nickel that is added to A9 and A10 is not a carbide former, but it will
improve the impact strength. The nickel can also propagate retained austenite
if the correct austenitizing temperature is not carefully chosen and the
cooling rate is not correct.
Next time we will discuss the impact of these alloying elements on
Tool Steels (part 3)
By David Pye
David Pye is the owner and operator of Pye Metallurgical International Consulting, Saint Anne's on Sea, Lancashire, U.K. He has 25 years of practical experience in captive and commercial heat treatment, metallurgical laboratory operation and industrial furnace sales. He also has teaching experience on a very wide range of heat-treatment and metallurgical subjects.
He can be reached at firstname.lastname@example.org.
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