Boron is a small intermediate element added to improve hardenability. It is most effective in low and medium carbon steels (<0.40%). Boron increases the strength of heat treated steels in the quenched and tempered state. Boron steels can be directly quenched and hot worked to obtain a high strength product. Boron steels are generally used in applications subject to wear.
Qualities
20MnB4, 33MnCrB5-2, SAE 51B60, ZF 6, ZF 7, ZF 7B