Part 4 of our tool-steel presentation is a continuation of the effects of individual alloying elements on the tool-steel chemistries and heat-treated metallurgy. If you collect these articles, it will be almost like you will be connecting a “mini” book on tool steels and its heat treatment.
1. The alloying element of nickel is not a carbide former and does not react with carbon to form any carbides of any description. Nickel will tend to stabilize the austenite phase, which is the high-temperature region and sometimes known as the hardening temperature zone. It will promote a high degree of toughness when it combines with chromium, and it is added to promote toughness or impact strength. It will also tend to reduce the steel's hardening temperature and is found in oil-hardening steels rather than air-hardening steel.
2. However, (depending on the amount of nickel present) nickel can – and does – promote the formation of retained austenite.
3. Nickel has little (if any) effect on the tempering of the tool steel.
4. It is usually found in quantities up to and around 3.0-4.25% on some of the alloy case-hardening steels.
The alloying element of vanadium has two main functions in tool steels:
1. As a grain refiner that will resist to some extent grain growth in the tool steels that is caused by either (or both) too high an austenitizing temperature or holding for too long at the appropriate austenitizing temperature.
2. It is also considered a stabilizer of carbide formation at high austenitizing temperatures.
Vanadium will have somewhat of a stabilizing effect on the martensitic formation. This element tends to make the tempering of the steel difficult. The cycle times on tempering tend to be longer and require multiple tempering such as double temper or even triple temper.
Vanadium will very strongly influence the hardenability of the steel and has a strong effect on secondary hardening. Vanadium is also used to promote a fine grain in tool steels and will combine with carbon to form very hard vanadium carbide particles, especially in high-speed steels.