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4140/4150 - Widely used general purpose alloys, low in cost. A broad range of strength and toughness is attainable through variations in heat treatment. Used for forging, tubing and fittings.AISI 4150 is notable for increased hardenability with a small tradeoff in machinability. Best strength and hardness appears in preheat-treated condition. Tailoring carbon content to bar size allows uniform physical attributes to be maintained across a variety of sizes. These are oil-hardening steel of relatively high hardenability. Their chromium content provides good hardness penetration, and the molybdenum imparts uniformity of hardness and high strength.

These grades are especially suitable for forging because they have self-scaling characteristics. They respond readily to heat treatment and are comparatively easy to machine in the heat treated condition. They resist creep in temperature up to 1000°F and maintain their properties even after long exposure at these relatively high working temperatures. 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, it is widely used and highly successful alloy steel.

The following specifications are generally applicable for 4140/42 Heat Treated Rounds: ASTM A 193, Grade B7; ASTM A 434, Grades BC and BD. A special analysis of alloy steel which is heat treated by oil-quenching and tempering to develop a balance of mechanical properties. Has every requisite for brake die service-high wear-resistance, adequate toughness, high resistance to impact, and good machinability. In addition, the bars are stress-relieved before the final gag straightening, to insure a minimum of residual stresses.

This material is also available as leaded steel. The addition of lead improves machinability without sacrificing other desirable properties, with the exception that the use of this material is not recommended for applications over 400°F, since at elevated temperature ductility is low.

To obtain values for this property, specimens were taken from large and small sections, machined oversize, heat treated and finished by grinding to 0.505 in. diameter x 0.750 in. long. The specimens were checked for hardness and were then compressed between hardened steel plates. the specimens tested showed a hardness of 269 Brinell and indicated that both small and large sections developed compressive strength in excess of 100,000 psi, adequate compressive strength to meet the maximum demand of heavy duty brake-die service.

Principal Design Features
This is a higher carbon variation of the chromium, manganese, molybdenum 4100 series of low alloy steels.

Machinability of 4150 is good in the annealed condition, or in the normalized condition. After heat treatment the alloy can be very hard and it is best to limit machining at that point to grinding.

Ductility and formability in the annealed condition is good. Forming after heat treatment is difficult.

The alloy may be welded by conventional methods. Welding the alloy in the hardened (heat treated) condition may affect the mechanical properties due to welding heat input. A post-weld heat treatment may be needed. Follow an approved weld procedure.

Heat Treatment
It is best to normalize the alloy at 1650 F before heat treatment. Then heat treat at 1500 F and water quench to harden the alloy.

Forging may be accomplished at 2200 F down to 1800 F.

Hot Working
The alloy can be hot worked in the range of 1900 F to 1600 F.

Cold Working
4150 may be cold worked by conventional methods with the alloy in the annealed condition. After heat treatment the alloy is very hard and difficult to work.

Anneal at 1650 F and slow furnace cool.

Not applicable to this alloy.

Temper at temperatures ranging from 400 F to 1200 F depending upon the hardness level desired. Higher tempering temperatures result in lower hardness values. For example tempering at 600 F gives a tensile strength of 255 ksi while tempering at 1000 F gives 170 ksi.

See "Heat Treatment" and "Tempering" -- also hardens due to cold working.
Chemical Composition
Carbon 0.48 - 0.53
Chromium 0.8 - 1.1
Iron Balance
Manganese 0.75 - 1
Molybdenum 0.15 - 0.25
Phosphorus 0.035 max
Silicon 0.15 - 0.35
Sulphur 0.04 max
Physical Properties
Density (lb / cu. in.) 0.284
Specific Gravity 7.8
Specific Heat (Btu/lb/Deg F - [32-212 Deg F]) 0.113
Melting Point (Deg F) 2600
Thermal Conductivity 23
Mean Coeff Thermal Expansion 7
Modulus of Elasticity Tension 30

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