Forging
When forging, heat the steel to a light yellow heat (1200°C) and hammer as long as a red glow is visible (600°C). Slightly exceeding these limits does not necessarily cause any harm, such as burning or cracking. A tricky feature of 80CrV2 is that forgings may air-harden. High forging temperatures dissolve all carbides, which then remain dissolved during the forging process. Particularly, the dissolved V results in an abrupt increase in hardenability. As a result, forgings may contain bainite and martensite despite slow air cooling. This makes them difficult to file, grind, or drill, and untempered martensite can cause delayed cracking. If no other heat treatments are performed immediately, temper the forgings to prevent this cracking.
Thermal cycle
The microstructure of forgings can be improved through a thermal cycle: cool the forgings to room temperature, reheat until magnetism disappears, and cool in air. If you cool the steel only to a black heat, you must repeat the cycle twice, as a drop to black heat is not as effective as cooling fully to room temperature.
When hardened, an as-forged microstructure containing bainite and martensite produces very small austenite grains, but they will have mixed sizes. A thermally cycled blade does not necessarily produce smaller austenite grains, but it results in a more homogeneous microstructure that behaves much more predictably during hardening
Hardening
80CrV2 steel plates are usually sold in a soft-annealed condition. Industrial soft annealing takes several hours, giving the carbides plenty of time to grow to relatively large sizes. This soft-annealed state is not suitable for fast hardening in a blacksmith’s forge because the carbides dissolve too slowly; however, it works well for furnace hardening, which allows for longer soak times. High forging temperatures dissolve these large carbides, causing them to re-precipitate as smaller particles, which allows the forged steel to be easily hardened in a forge.
Like standard high-carbon steels, 80CrV2 hardens when quenched from a non-magnetic temperature. However, due to the chromium alloying, 80CrV2 requires a slightly higher hardening temperature to achieve maximum hardness. Therefore, after the steel becomes non-magnetic, continue heating until you notice a subtle change in the glow color. The target temperature is about 840°C.
Quench the blade in oil, as quenching in water will result in cracking. Warm canola oil (about 70°C) works well. The as-quenched hardness is about 66 HRC.
Tempering
Temper the blade immediately once it has cooled to room temperature, as waiting too long may result in the cracking of untempered martensite. The best combination of hardness and toughness is achieved when the blade is tempered at 170–180°C for 1–2 hours, which produces a hardness of about 63 HRC.
If you temper by color, yellow shades are good. The furnace tempering mentioned earlier produces a yellow oxide color on the surface. However, if you temper with a torch, the time is shorter, and the temperature is higher (220-260°C), but the color is the same. Because temperature and time affect both the softening of the steel and color in a similar way, the resulting color indicates the tempering outcome quite accurately.