ThePipingMart Blog Grades AISI – SAE 4140 Alloy Steel (UNS G41400) – Composition, Properties and Uses

AISI – SAE 4140 Alloy Steel (UNS G41400) – Composition, Properties and Uses

4140 steel

SAE 4140 steel is a type of alloy steel with a wide range of uses due to its various properties. It is composed of chromium, molybdenum, and manganese, making it one of the most versatile steels available. With excellent corrosion resistance, heat resistance, machinability, and mechanical properties, it can be used in a variety of applications, such as automotive components, construction materials, and tools. This blog post will discuss the composition, chemical and physical properties, uses corrosion resistance, heat resistance, and heat treatment of 4140 steel.

AISI – SAE 4140 Alloy Steel Composition

4140 steel contains both chromium (Cr) and molybdenum (Mo). The amount of these elements in the alloy varies depending on the grade of 4140 steel being used. For example, Grade AISI 4140 contains 0.38-0.43% Cr and 0.15-0.25% Mo while Grade AISI 4150 contains 0.47-0.53% Cr and 0.20-0.30% Mo. The addition of other elements, such as manganese, can also alter the composition of 4140 steel depending on the grade being used.

Element Content (%)
Chromium, Cr 0.80 – 1.10
Manganese, Mn 0.75 – 1.0
Carbon, C 0.380 – 0.430
Silicon, Si 0.15 – 0.30
Molybdenum, Mo 0.15 – 0.25
Sulfur, S 0.040
Phosphorous, P 0.035
Iron, Fe Balance

AISI – SAE 4140 Alloy Steel Chemical Properties

SAE 4140 steel is a chromium-molybdenum alloy beloved by many metalworkers because of its versatility and malleability. Due to its impressive chemical properties, it has been used in applications ranging from shipbuilding to the manufacture of tools. 4140 Steel has excellent strength, toughness, and hardenability values, especially when tempering and quenching are employed for further processing. Additionally, it is highly corrosion-resistant and has a large amount of wear resistance as well. This makes it ideal for uses like shafts, gears, bolts, and other parts subject to mechanical stress. As a result of all these qualities, 4140 Steel remains one of the most popular materials for metalworking today – and it doesn’t look like that popularity will be waning anytime soon!

AISI – SAE 4140 Alloy Steel Physical Properties

The chemical and physical properties vary depending on the grade being used; however, some common characteristics are high strength (up to 1600MPa), high wear resistance (due to its high abrasion resistance), good ductility and toughness (due to its low carbon content), high fatigue strength (due to its quenching process), good creep strength (at elevated temperatures), good corrosion resistance (due to its chromium content) and good weldability (due to its low carbon content).

Properties Metric Imperial
Density 7.85 g/cm3 0.284 lb/in³
Melting point 1416°C 2580°F

AISI – SAE 4140 Alloy Steel Mechanical Properties

Properties Metric Imperial
Tensile strength 655 MPa 95000 psi
Yield strength 415 MPa 60200 psi
Bulk modulus (typical for steel) 140 GPa 20300 ksi
Shear modulus (typical for steel) 80 GPa 11600 ksi
Elastic modulus 190-210 GPa 27557-30458 ksi
Poisson’s ratio 0.27-0.30 0.27-0.30
Elongation at break (in 50 mm) 25.70% 25.70%
Hardness, Brinell 197 197
Hardness, Knoop (converted from Brinell hardness) 219 219
Hardness, Rockwell B (converted from Brinell hardness) 92 92
Hardness, Rockwell C (converted from Brinell hardness. Value below normal HRC range, for comparison purposes only) 13 13
Hardness, Vickers (converted from Brinell hardness) 207 207
Machinability (based on AISI 1212 as 100 machinability) 65 65

AISI – SAE 4140 Alloy Steel Thermal Properties

Properties Metric Imperial
Thermal expansion coefficient (@ 0-100°C/32-212°F) 12.2 µm/m°C 6.78 µin/in°F
Thermal conductivity (@ 100°C) 42.6 W/mK 296 BTU in/hr.ft².°F

AISI – SAE 4140 Alloy Steel Equivalent

AMS 6349 ASTM A193 (B7, B7M) ASTM A506 (4140) ASTM A752 (4140)
AMS 6381 ASTM A194 (7, 7M) ASTM A513 ASTM A829
AMS 6382 ASTM A29 (4140) ASTM A513 (4140) SAE J1397 (4140)
AMS 6390 ASTM A320 (L7, L7M, L7D) ASTM A519 (4140) SAE J404 (4140)
AMS 6395 ASTM A322 (4140) ASTM A646 (4140) SAE J412 (4140)
AMS 6529 ASTM A331 (4140) ASTM A711

AISI – SAE 4140 Alloy Steel Uses

Due to its versatility, 4140 steel has many uses across various industries, including automotive components such as gears shafts, axles, pistons, and valves ; construction materials such as bolts, nuts, screws; tools such as chisels, punches, taps etc.; sporting goods such as golf clubs; agricultural equipment such as plows; oil rigs etc.

AISI 4140 Hardness

SAE 4140 steel is incredibly hard and durable, making it ideal to use in a variety of applications. Forged from alloying chromium and molybdenum with iron, 4140 steel undergoes heat treatment to achieve its impressive hardness levels. Rated at 42 Rockwell on the C scale, 4140 steel is tough enough to withstand heavy impacts and abrasive conditions. Beyond its superior durability and hardness, 4140 steel also offers good corrosion resistance, making it a perfect choice for machine tools and other parts used in chemically challenging environments. All these features combined make 4140 steel an excellent material for many commercial applications.

AISI 4140 Corrosion Resistance

The addition of chromium increases the corrosion resistance by forming an oxide layer that prevents further oxidation or rusting – often referred to as ‘passivation’. This makes it suitable for use in marine or corrosive environments where regular stainless steel may not be suitable due to its higher cost.

Heat Resistance

Due to its high chromium content, 4140 Steel provides excellent heat-resistant properties, which make it ideal for use at elevated temperatures or in hot working conditions. It also has very good thermal shock resistance meaning it can withstand sudden changes in temperature without cracking.

Heat Treatment

Hardening or tempering 4140 Steel involves heating it to around 860C and cooling it down in air/oil/salt bath/water quenching methods depending on desired results. This extreme heating process increases the hardness but decreases the ductility, which makes it more brittle but stronger overall. After quenching it is then tempered at lower temperatures between 150-400C depending on desired results again so that you get an optimal combination between strength & ductility. Lastly, this process also improves machinability so that your finished product doesn’t have too much friction when cutting or drilling into it with machinery.


4140 Steel is relatively easy to machine due to its low carbon content, making it softer than others. It also responds well when drilled into using standard drill bits with minimal force required making it ideal for use in precision engineering applications requiring accuracy & repeatability .


All in all, 4140 Steel is highly versatile thanks to its unique combination of properties, making it suitable for a wide range of applications from automotive components & construction materials right through to tools & sporting goods etc. Its ability to resist corrosion coupled with good thermal shock & heat resistant properties make this alloy particularly useful when working in hot/corrosive conditions while still providing good machinability when required too! So if you’re looking for a reliable, durable material, look no further than 4140 Steel!

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