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AISI 4340 Alloy Steel (UNS G43400)

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AISI 4340 Alloy Steel (UNS G43400)

Alloy steels are designated by AISI four-digit numbers. They comprise different kinds of steels having composition exceeding the limitations of B, C, Mn, Mo, Ni, Si, Cr, and Va set for carbon steels.

AISI 4340 alloy steel is a heat treatable and low alloy steel containing chromium, nickel and molybdenum. It has high toughness and strength in the heat treated condition.

Fabrication and heat treatment

Machinability: AISI 4340 alloy steel can be machined using all conventional techniques. Machining process can be performed in the annealed or normalized and tempered conditions.

Forming: AISI 4340 alloy steel has good ductility and formability in the annealed condition. It can be bent or formed by pressing or spinning in the annealed state.

Welding: AISI 4340 alloy steel can be welded using fusion or resistance welding methods. Preheat and post heat weld procedures are followed while welding this steel by established methods.

Heat Treatment: AISI 4340 alloy steel is heat treated at 830°C (1525°F) followed by quenching in oil.

Forging: AISI 4340 alloy steel is forged at 427 to 1233°C (1800 to 2250°F).

Cold Working: AISI 4340 alloy steel can be cold worked using all conventional methods in the annealed condition. It has high ductility.

Annealing: AISI 4340 alloy steel is annealed at 844°C (1550°F) followed by cooling the furnace.

Tempering: AISI 4340 alloy steel should be in the heat treated or normalized and heat treated condition before tempering. Tempering temperatures depend upon the desired strength level.

Hardening: AISI 4340 alloy steel can be hardened by cold working or heat treatment.

Applications: AISI 4340 alloy steel is mainly used in power transmission gears and shafts, aircraft landing gear, and other structural parts.