The main role of B in steel is to increase the hardenability of steel, thereby saving other less expensive metals, and nickel, chromium, molybdenum and the like. For this purpose, the content is generally specified in the range of 0.001% to 0.005%. It can replace 1.6% nickel, 0.3% chromium or 0.2% molybdenum. Boron molybdenum should be noted that molybdenum can prevent or reduce temper brittleness, while boron has a slight tendency to promote temper brittleness, so it cannot be used. Boron completely replaces molybdenum.
Boron is added to the medium carbon carbon steel. Since the hardenability is improved, the properties of the steel with a thickness of 20 mm or more can be greatly improved after quenching and tempering. Therefore, 40B and 40MnB steel can be used instead of 40Cr, and 20CrMnTi carburized steel can be replaced by 20Mn2TiB steel. However, since the effect of boron decreases or even disappears with the increase of carbon content in the steel, in the selection of boron-containing carburized steel, it must be considered that after the carburization of the part, the hardenability of the carburized layer will be lower than that of the core. This feature of permeability.
Spring steel is generally required to be completely hardened, and usually the spring area is not large, and it is advantageous to use boron-containing steel. The effect of boron on high-silicon spring steel fluctuates greatly, which is inconvenient to adopt.
Boron has a strong affinity with nitrogen and oxygen. The addition of 0.007% boron to the boiling steel can eliminate the aging of steel.