For sale is ___ lbs of tool steel bars. I got them from a factory (for free) and the owner told me that it was 4140. He had no reason to lie since I did not pay him, so I assume that it is what it is.

WORKABILITY - Alloy C4140 is an oil-hardening steel of relatively high hardenability. Its chromium content provides good hardness penetration, and the molybdenum imparts uniformity of hardness and high strength. C4140 responds well to heat-treatment and is comparatively easily machined in the heat-treated condition. With a combination of such highly desirable properties as good strength and wear resistance, excellent toughness, coupled with good ductility, and the ability to resist stress at elevated temperatures.

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Alloy Steels 4140

Related Metals: Folder
Finkl 4140(tm)
Maxell Tooling Alloy(tm)
Specifications: AISI 4140
AMS 6349
AMS 6381
AMS 6382
AMS 6390
AMS 6395
AMS 6529
ASTM A193 (B7, B7M)
ASTM A194 (7, 7M)
ASTM A29 (4140)
ASTM A320 (L7, L7M, L7D)
ASTM A322 (4140)
ASTM A331 (4140)
ASTM A506 (4140)
ASTM A513 (4140)
ASTM A519 (4140)
ASTM A646 (4140)
ASTM A752 (4140)
SAE J1397 (4140)
SAE J404 (4140)
SAE J412 (4140)
UNS G41400

Chemistry Data


0.38 - 0.43


0.8 - 1.1




0.75 - 1


0.15 - 0.25


0.035 max


0.15 - 0.35


0.04 max

General Information

Principal Design Features

This is one of the chromium, molybdenum, manganese low alloy steels noted for toughness, good torsional strength and good fatigue strength.


4140 is used in a tremendous variety of applications, too numerous to mention here.


Machinability of this alloy is good in the annealed condition. In the heat treated and quenched condition machining is best limited to finish grinding.


As with all the low alloy steels forming may be done by conventional methods with the alloy in the annealed condition. These alloys have good ductility, but are tougher than plain carbon steel and thus usually require more force, or pressure, for forming.


Weldable by all of the conventional methods. Note that welding with the alloy in the heat treated condition will affect the mechanical properties and a post weld heat treatment may be needed.

Heat Treatment

This alloy is hardened by heating to 1550 F and quenching in oil. It is best to normalize the alloy by heating at 1675 F for a long enough time to permit thorough heating, followed by air cooling, prior to the hardening treatment.


4140 may be forged at 2200 F down to 1700 F.

Hot Working

Hot working, if required, may be done in the range of 1900 F to 1500 F.

Cold Working

The alloy readily cold works in the annealed condition by conventional methods.


Annealing is done at 1600 F followed by slow furnace cooling.


Not applicable to this alloy.


Tempering temperatures range from 400 F to 1200 F depending upon the hardness level desired. The lower the tempering temperature the greater the hardness of the alloy. For example tempering at 600 F gives a tensile strength of 225 ksi while tempering at 1000 F will give 130 ksi.


Hardens by cold working, or heating and quenching - also see "Heat Treatment" and "Tempering".

Physical Data

Density (lb / cu. in.)


Specific Gravity


Specific Heat (Btu/lb/Deg F - [32-212 Deg F])


Melting Point (Deg F)


Thermal Conductivity


Mean Coeff Thermal Expansion


Modulus of Elasticity Tension


Mechanical Data

MSO currently has no data available for this grade.

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