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 heat-treating parameters.