4130 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 of 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. 4150 is also corrosion resistant compared to 4130 which makes 4150 less susceptible to rusting after fabrication into parts. 4340 has a carbon content of .38-.43%, manganese of 0.70-0.85%, phosphorus at .035%. 4340 also contains sulfur, which 4130 does not contain. 4340 is used for applications that need a high strength and wear resistance such as in aircraft parts, gears and shafts. 4340 has greater toughness than 4130 so it can be used to make parts that require a higher level of toughness. 4340 is also corrosion resistant compared to 4130 which makes 4150 less susceptible to rusting after fabrication into parts.
