Boron microalloying effect
Boron microalloying effect: Boron is added in small amounts to protect austenitic grain boundaries, prevent ferrite formation, and increase hardenability.
Physico-Chemical Effect Mechanism
Boron reacts with the iron-oxygen mixture at austenite grain boundaries, which blocks ferrite formation. This prevents the occurrence of nucleation and improves the crystal structure of the weld.
Metallurgical Relevance & Welding Risks
The boron microalloying effect increases the hardenability and strength of the weld. However, too high a boron content can contaminate the microstructure, leading to pores and cracks. Additionally, excessive boron can reduce the toughness of the steel.
Shop Practice & Instructions
Use boron in small amounts (about 0.01 to 0.05%) for alloying. The exact amount depends on the steel used and the welding process. Monitor the temperature during cooling to ensure optimal processing.