1018 Steel is a mild, low carbon steel that is machinable, weldable and useful where high-strength is not required, such as fixtures and mounting plates. It is magnetic and heat treatable.
4140 alloy steel is generally harder and stronger than carbon steel. Additionally, it provides high impact resistance, fatigue strength, and torsional strength, which makes 4140 a great choice for drive shafts, axles, and torsion bars. In terms of hardening, 4140 can be hardened using a variety of methods such as cold working, or heating and quenching.
Offers great weldability without compromising impact resistance. Often used in gears and fasteners.