No. 45 steel, is the name for GB, JIS called: S45C, ASTM called 1045,080M46, DIN called: C45
No. 45 high-quality carbon steel for structural steel, high hardness cutting process, the mold used to do template, shoot the child, guide posts, etc., subject to heat treatment.

45 # steel is widely used in machinery manufacturing, good mechanical properties of this steel. But this is a medium carbon steel, hardened performance is not good, 45 steel can be hardened to HRC42 ~ 46. So if you need to surface hardness, but also hopes to play 45 # steel superior mechanical properties, often 45 # steel surface carburizing, so you can get the required surface hardness.