Overview of JIS G 4051 Carbon Steels for Machine Structural Use

JIS G 4051 is a Japanese Industrial Standard that specifies carbon steels used for machine structural purposes. These steels are commonly used in automotive parts, machinery components, and tools that require reliable strength and machinability.
Key Grades Under JIS G 4051
S15C – Low carbon, good for cold forming
S35C – Medium carbon, suitable for shafts, bolts
S45C – Most commonly used; balanced strength and machinability
S55C – High carbon content, used in applications demanding higher hardness
Characteristics
Good machinability
Moderate weldability (depending on carbon content)
Commonly available in hot-rolled or cold-drawn forms
Can be heat-treated for increased hardness and mechanical performance
Typical Applications
Shafts, axles, gears, pins, bolts, and general mechanical parts
JIS G 4051 steels are widely adopted across Asia and are often cross-referenced with other standards like AISI/SAE or DIN. For example, S45C ≈ AISI 1045.