3/9/2014 AISI 4340 Alloy Steel (UNS G43400)

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AISI 4340 Alloy Steel (UNS G43400)

Topics Covered

Introduction

Chemical Composition

Physical Properties

Mechanical Properties

Thermal Properties

Other Designations

Fabrication and Heat Treatment

Machinability

Forming

Welding

Heat Treatment

Forging

Cold Working

Annealing

Tempering

Hardening

Applications

Introduction

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.

Chemical Composition

The following table shows the chemical composition of AISI 4340 alloy steel.

Element Content (%)

Iron, Fe 95.195 - 96.33

Nickel, Ni 1.65 - 2.00

Chromium, Cr 0.700 - 0.900

Manganese, Mn 0.600 - 0.800

Carbon, C 0.370 - 0.430

Molybdenum, Mo 0.200 - 0.300

Silicon, Si 0.150 - 0.300

Sulfur, S 0.0400

Phosphorous, P 0.0350

Physical Properties

The physical properties of AISI 4340 alloy steel are given in the following table.

Properties Metric Imperial

Density 7.85 g/cm3 0.284 lb/in³

Melting point 1427°C 2600°F

Mechanical Properties

The mechanical properties of annealed AISI 4340 alloy steel are displayed in the following table.

Properties Metric Imperial

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3/9/2014 AISI 4340 Alloy Steel (UNS G43400)

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Tensile strength 745 MPa 108000 psi

Yield strength 470 MPa 68200 psi

Bulk modulus (typical for steel) 140 GPa 20300 ksi

Shear modulus (typical for steel) 80 GPa 11600 ksi

Elastic modulus190-210

GPa

27557-

30458 ksi

Poisson's ratio0.27-

0.300.27-0.30

Elongation at break 22% 22%

Reduction of area 50% 50%

Hardness, Brinell 217 217

Hardness, Knoop (converted from Brinell hardness) 240 240

Hardness, Rockwell B (converted from Brinell hardness) 95 95

Hardness, Rockwell C (converted from Brinell hardness. Value below normal HRC

range, for comparison purposes only)17 17

Hardness, Vickers (converted from Brinell hardness) 228 228

Machinability (annealed and cold drawn. Based on 100 machinability for AISI 1212

steel.)50 50

Thermal Properties

The following table outlines the thermal properties of AISI 4340 alloy steel.

Properties Metric Imperial

Thermal expansion co-efficient (20°C/68°F, specimen oil hardened, 600°C

(1110°F) temper

12.3 µm/m

°C6.83 µin/in°F

Thermal conductivity (typical steel) 44.5 W/mK309 BTU

in/hr.ft².°F

Other Designations

Other designations that are equivalent to AISI 4340 alloy steel include the following:

AMS 6359 AMS 6454 ASTM A331 (4340) ASTM A711 SAE J1397 (4340)

AMS 6409 ASTM A29 (4340) ASTM A506 (4340) ASTM A752 (4340) SAE J404 (4340)

AMS 6414 ASTM A320 (L43) ASTM A519 (4340) ASTM A829 SAE J412 (4340)

AMS 6415 ASTM A322 (4340) ASTM A646 (4340-7) MIL S-5000

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.

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Applications

AISI 4340 alloy steel is mainly used in power transmission gears and shafts, aircraft landing

gear, and other structural parts.

Date Added: Sep 7, 2012 | Updated: Jul 11, 2013

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Comments

Akhtar Aziz says:

January 16, 2014 at 2:35 AM

Thanks for all the information. I have a question for you:

We applied cadmium cyanide plating to avoid rusting of this material but after certain time,

the material started to rust. We need to know what type of coating is compatible with the

Cadmium Cyanide coating for a stronger rust protection system. Not Electro plating.

Reply

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