Hot-rolled (HR) 42CrMo bars are produced by heating billets to a high temperature (1100-1250°C) and passing them through a series of rolling stands to achieve the final diameter. Key specifications include:
Standards: Supplied as per standards like EN 10083-3, ASTM A29, etc., often in the "+A" (annealed), "+N" (normalized), or "+QT" (quenched & tempered) condition even though the forming process is hot rolling.
Surface: Characterized by a dark, oxidized mill scale layer, which must be removed (by pickling, blasting, or machining) for most applications. Some surface decarburization (loss of carbon) is always present and must be machined away if the surface properties are critical.
Dimensional Tolerances: Governed by standards like EN 10060 (for HR rounds) or ASTM A29. Tolerances are relatively wide (e.g., ±0.8-1.5% of diameter, depending on size) compared to cold-finished bars.
Straightness: Commercial straightness tolerances apply; HR bars are not perfectly straight.
Applications: Used for components that will undergo significant machining, forging, or subsequent heat treatment where the as-rolled surface and tolerances are not final.