44130 has a carbon content of .28-.33%, manganese of 0.70-0.85%, phosphorus at 0.035%. 4130 also contains chromium and molybdenum, which are both used in the quench and temper process to provide 4130 with its strength and toughness. 4150 has a carbon content of .28-.33%, manganese at 0.70-0.85%, phosphorus at 0.035%. 4150 also contains sulfur, which 4130 does not contain. 4150 is used for applications that need a high strength and low weight such as in aircraft parts, gears and shafts. 4150 has greater toughness than 4130 so it can be used to make parts that require a higher level of toughness.
