In steelmaking, copper is an element that must be carefully controlled. Although copper itself is a valuable metal with excellent properties, excessive copper in steel can cause serious problems during high-temperature processing.
At elevated temperatures, iron tends to oxidize preferentially, while copper—with its relatively low melting point of 1083°C—remains unoxidized and becomes enriched beneath the oxide scale. This copper-enriched layer can form low-melting-point alloys or segregate along the austenite (γ-phase) grain boundaries once its solubility limit is exceeded. As a result, the billet or hot-rolled slab may experience hot shortness or surface cracking, a phenomenon commonly known as “copper brittleness.” This significantly reduces the hot workability and yield of steel.
However, copper is not purely detrimental. When added in a controlled amount, it can remarkably enhance the strength, corrosion resistance, and weldability of steel. For this reason, copper-containing steels are widely used in shipbuilding steel, pressure vessel steel, oil pipeline steel, structural steel, and weathering steel.
In corrosion-resistant steels, the copper content is typically controlled within 0.2%–0.4%, effectively improving atmospheric corrosion resistance. The precipitation of ε-Cu particles provides precipitation strengthening and helps to impede fatigue crack propagation, thereby enhancing fatigue strength.
In high-strength pipeline steels (grade X80 and above), the American API standard recommends adding copper to improve mechanical and anti-corrosion properties. Similarly, martensitic antibacterial stainless steels and weathering steels often use copper as an essential alloying element.
Beyond steelmaking, copper remains a critical industrial metal. Its electrical conductivity ranks second only to silver, making it indispensable in the electrical industry. Its excellent corrosion resistance also makes it suitable for electroplating and cladding—for instance, a thin copper layer is often plated on steel before chromium coating to improve adhesion and corrosion protection.
In summary, copper acts as a double-edged sword in steelmaking. When properly controlled, it can strengthen and protect steel; when excessive, it can cause hot brittleness and cracking. Therefore, maintaining an optimal copper content in steel is crucial for ensuring product quality and production stability.
