Chromium Affinity
Chromium affinity describes the strong binding of chromium to oxygen and carbon. This leads to stable oxide layers on the surface and the formation of carbides in the interior, which increases hardness and corrosion resistance.
Physical-Chemical Mechanism of Action
Chromium has a high affinity for oxygen and carbon. Under normal conditions, it forms a thin, stabilized oxide layer on the surface that prevents corrosion. Inside the material, chromium reacts with carbon to form carbides, which increase hardness.
Metallurgical Relevance & Risks in Welding
High chromium affinity can cause problems if the material is not welded correctly. Too fast cooling leads to glass-hard martensite, which increases hardness but also reduces fracture toughness. Too slow cooling results in a coarse grain structure, reducing toughness and deformation capability. Additionally, corrosion can persist or even worsen if the oxide layer is not fully formed.
Workshop Practice & Action Guidelines
To optimally utilize chromium affinity, it is important to treat the material in a shielded environment or under shielding gas (such as argon) during welding. Cooling steps should be controlled: too fast cooling can lead to glass-hard martensite (t8/5 < 5 s), while too slow cooling results in a coarse grain structure and reduced toughness (t8/5 > 25 s). The weld should be thoroughly cleaned after the process to ensure that no corrosion persists.