Hydrogen Sources
The main pathways for hydrogen to enter liquid steel include: Rust on the surface of scrap steel (xFeO·yFe₃O₄·2H₂O); Hydrogen present in ferroalloys; Moisture contained in carburizers, deoxidizers, mulching materials, insulation materials, slagging agents (Ca(OH)₂), bitumen, and tar; Undried ladles, tundishes, and injection pipes; Spray coatings applied to ingot molds; Water seepage from molds and atmospheric moisture interacting with molten steel or slag, subsequently dissolving into the steel.
Hydrogen Forms
In steel, hydrogen exists primarily in its atomic form. At high temperatures, hydrogen atoms readily combine to form hydrogen molecules. Due to its high reactivity, atomic hydrogen naturally tends to form molecular hydrogen, which is released gradually.
Hydrogen Effects
When the hydrogen content in cast iron exceeds 2 ppm, it increases the likelihood of porosity or general porosity, which in turn leads to iron embrittlement. Hydrogen embrittlement is particularly prevalent in martensitic steel, while it is less significant in ferritic steel. Moreover, hydrogen embrittlement tends to intensify with increased hardness and carbon content.
Conversely, hydrogen can enhance the permeability of steel but also increases coercivity and iron loss.
