AISI SAE ASTM 4140 Alloy Steel

AISI 4130 Steel | 25CrMo4 | 1.7218 | 708A25 | SCM430

What is 4130 Steel?

AISI 4140 steel is a low alloy steel containing chromium, molybdenum, and manganese. It is widely used across numerous industries and is an excellent material choice due to its toughness, high fatigue strength, and abrasion and impact resistance. Not many grades can match the versatility and usefulness of 4140.

4140 Grade Designation

When discussing AISI 4140, it is important to understand what the grade number means:

Number	Meaning
4	Designates that 4140 steel is molybdenum steel, indicating that it possesses higher amounts of molybdenum than other steels, such as the 1xxx series.
1	Designates that 4140 steel has additions of chromium as well; more so than 46xx steel for example.
40	Used to differentiate 4140 Steel from other steels in the 41xx series.

How is 4140 Steel Made?

AISI 4140 is made by placing iron, carbon, and other alloying elements into an electric furnace or oxygen furnace. The major alloying elements added to AISI 4140 are:

• Chromium
• Manganese
• Molybdenum

Once the iron, carbon, and other alloying elements have been mixed together in liquid form, it is allowed to cool. The steel may then be annealed; possibly several times.

After the annealing is complete, the steel is heated to a molten phase again so that it can be poured into the desired form and can either be hot worked or cold worked through rollers or other tools to reach the desired thickness. Of course, there are other special operations that can be added to this to reduce mill scale or improve mechanical properties.

SAE AISI 4140 Alloy Steel

SAE 4140 (AISI 4140 steel) is a Cr-Mo series (Chrome molybdenum series) low alloy steel, this material has high strength and hardenability, good toughness, small deformation during quenching, high creep strength and long-lasting strength at high temperature.

4140 Steel Uses

AISI SAE 4140 alloy steel can be made into round steel bar, flat & square steel bar, steel plate, steel tube, and has many uses in the aerospace, oil and gas and automotive industries, typical uses are thin-walled pressure vessels, forged gears and shafts (Motor shafts, pump shafts, hydraulic shafts, etc.), spindles (lathe spindles, milling spindles, etc.), collars, clamps, high strength bolts, valve bonnet, screws, nuts, worms, collets, torsion bars and various carburized parts.

Datasheet & Specification

Below are 4140 alloy steel datasheets including chemical composition, properties and equivalent chart, etc.

AISI SAE 4140 Chemical Composition

The table below lists AISI 4140 chemical composition.

	AISI SAE 4140 Chemical Composition (%)
Steel (UNS)	C	Si	Mn	P (≤)	S (≤)	Cr	Mo	Ni
4140 (G41400)	0.38-0.43	0.15-0.35	0.75-1.00	0.035	0.040	0.80-1.10	0.15-0.25	–

AISI 4140 Steel Mechanical Properties

Material 4140 mechanical properties are given in the table below.

Steel	Tensile strength (Mpa)	Yield strength (Mpa)	Elongation in 50 mm, %	Reduction in area, %	Hardness (HB)	Sample diameter	Conditions
AISI 4140	1020	655	17.7	46.8	302	25.4mm (1 inch)	Normalized at 870 °C
	655	414	25.7	56.9	197		Annealed at 815 °C
	1075	986	15.5	56.9	311		Water quenched from 845 °C & tempered at 540 °C

SAE 4140 Physical Properties

Notes: 10^-6/K = 10^-6.K^-1 = (µm/m)/°C

Material 4140 coefficients of linear thermal expansion
Temperature (°C)	Value (10-6/K)	Treatment or condition
20-100	12.2	Oil hardened, tempered
20-200	12.6
20-400	13.6
20-600	14.5

4140 thermal conductivity
Value (W/m·K)	Temperature (°C)	Treatment or condition
42.7	100	Hardened & tempered
42.3	200
37.7	400
33.1	600

AISI / SAE 4140 Specific Heat
Value (J/Kg·K)	Temperature (°C)	Treatment or condition
473	20-200	Hardened & tempered
519	20-400
561	20-600

Mateiral 4140 Electrical Resistivity
Value (μΩ· m)	Temperature (°C)	Treatment or condition
0.22	20	Hardened & tempered
0.26	100
0.33	200
0.48	400
0.65	600

Material 4140 Steel Heat Treatment

The following table shows AISI 4140 steel heat treatment, rockwell hardness.

Material 4140 Heat Treat	Temperature (℃)	4140 steel hardness	Cooling/Agent
Normalizing	870	302 HB	Air
Annealing	790-845	197 HB	Furnace cooling
Quenching	830-845		Oil
Tempering (2 hour)	205	58 HRC	Oil hardening
	260	54 HRC
	315	50 HRC
	370	47 HRC
	425	45 HRC
	480	40 HRC
	540	35 HRC
	595	33 HRC
	650	28 HRC

Normalizing

4140 alloy steel is typically normalized at 870 °C (1600℉), and should be cooled at a specified temperature in still air.

Spheroidizing Annealing

For spheroidizing annealing of 4140 alloy steel, it needs heat treated to 749 °C (1380 °F), followed by slowly cooling to 666 °C (1230 °F) at a rate of 6 °C (10 °F)/hour, or rapid cooling to 675 °C for isothermal annealing.

Full Annealing

Heat treatment to 845 °C, slow cooling from 755 °C at a rate of 14 °C (25 °F)/hour to 665 °C, or rapid cooling to 675 °C for 5 hours isothermal annealing.

Tempering

Tempering temperature of 4140 alloy steel can be from 204-649 °C (400-1200°F) after normalizing and oil quenching, and the corresponding Rockwell hardness can be obtained.

Forging

Material 4140 forging temperature is about 1232 °C (2250 °F).

Welding of 4140 Steel

All common arc welding processes, such as (SAW, SMAW, FCAW, GMAW, GTAW) can be used to weld 4140 alloy steel, but in order to prevent cracking, it must be preheated to 170-350 °C (350-650 °F) before welding, preheating interpass temperature depends on the section thickness of the steel.

Equivalent Material

AISI 4140 equivalent material is listed in the table below.

AISI 4140 equivalent
USA		European Union		China		Japan		ISO
Standard	Grade (UNS)	Standard	Grade (Steel Number)	Standard	Grade	Standard	Grade	Standard	Grade
AISI SAE; ASTM A29/A29M	4140 (G41400)	EN 10083-3	42CrMo4 (1.7225)	GB/T 3077	42CrMo	JISG 4105	SCM440