ThePipingMart Blog Grades AISI 4042 Alloy Steel (UNS G40420) – Composition, Properties and Uses

AISI 4042 Alloy Steel (UNS G40420) – Composition, Properties and Uses

AISI 4042 Steel

AISI 4042 steel is a medium-carbon, chromium-molybdenum alloy steel that offers excellent mechanical properties and machinability. This steel is commonly used in a range of industries, from automotive to food processing. AISI 4042 Alloy Steel, also known as SAE-AISI 4042 steel, is one of the strongest types of alloys available in the market. Composed of varying amounts of carbon, manganese, silicon, and chromium, this steel exhibits excellent toughness, ductility, and strength, making it a preferred choice in various industrial applications. What sets AISI 4042 Alloy Steel apart is its ability to withstand extreme temperatures and harsh environments. UNS G40420, its more technical name, is widely used in applications such as gears, shafts, and axles, all of which require high levels of strength and durability. With these impressive properties, it’s no wonder why AISI 4042 Alloy Steel is one of the top choices in the industrial world. This post will take a comprehensive look at the uses, corrosion resistance, heat resistance, heat treatment, and machining capabilities of UNS G40420.

What Forms of AISI 4042 is Available at Piping Mart?

  • Nut
  • Bar
  • Bolt
  • Pipe
  • Screw
  • Tubing
  • Valves
  • Washers
  • Flanges
  • Fasteners
  • Electrodes
  • Stud Bolts
  • Sheet Plates
  • Pipe Fittings
  • Forged Fitting
  • Instrumentation Fittings

AISI 4042 Composition

Element Content (%)
Iron, Fe 97.93-98.55
Manganese, Mn 0.70-0.90
Carbon, C 0.40-0.45
Molybdenum, Mo 0.20-0.30
Silicon, Si 0.15-0.35
Sulfur, S 0.040
Phosphorous, P 0.035

AISI 4042 Physical Properties

Properties Metric Imperial
Density 7.85 g/cm3 0.284 lb/in³

AISI 4042 Mechanical Properties

Properties Metric Imperial
Elastic modulus 190-210 GPa 27557-30458 ksi
Bulk modulus (typical for steel) 140 GPa 20300 ksi
Shear modulus (typical for steel) 80 GPa 11600 ksi
Poisson’s ratio 0.27-0.30 0.27-0.30
Hardness, Brinell 179-229 179-229
Hardness, Knoop (converted from Brinell hardness) 226 226
Hardness, Rockwell B (converted from Brinell hardness) 93 93
Hardness, Rockwell C (converted from Brinell hardness, value below normal HRC range, for comparison purposes only) 14 14
Hardness, Vickers (converted from Brinell hardness) 214 214
Machinability (annealed and cold drawn. based on 100 machinability for AISI 1212 steel) 65 65

AISI 4042 Thermal Properties

Properties Metric Imperial
Thermal conductivity 44.5 W/mK 309 BTU in/hr.ft².°F

AISI 4042 Equivalent

  • ASTM A322
  • ASTM A331
  • ASTM A519
  • SAE J404
  • SAE J412
  • SAE J770

AISI 4042 Uses

4042 Alloy Steel is often used for automotive parts due to its high strength and its ease of machining. It can be utilized in the production of connecting rods, crankshafts, piston pins, and other components that require strength and durability. Additionally, it can also be found in applications that require wear resistance, such as valve seats and bearings. Additionally, AISI 4042 steel can be used in the food industry, where it is often used for parts that are exposed to high temperatures, such as ovens and hot plates.

AISI 4042 Uses in Industries

  • Automotive Industry
  • Construction Industry
  • Aerospace Industry
  • Oil and Gas Industry
  • Manufacturing Industry

AISI 4042 Corrosion Resistance

AISI 4042 steel has excellent corrosion resistance due to its high chromium content. The addition of molybdenum provides additional corrosion protection against acidic conditions such as those found in food processing environments. In fact, this steel is often chosen for applications that require superior corrosion protection because it resists both oxidizing and reducing acids very well.

AISI 4042 Heat Resistance

AISI 4042 has impressive heat resistance due to its combination of chromium and molybdenum content which gives it the ability to withstand temperatures up to 1000°C (1832°F). This makes it ideal for applications that involve high temperatures, such as furnace components or automotive components exposed to extreme temperatures while driving or braking.

AISI 4042 Heat Treatment

AISI 4042 is typically hardened through quenching and tempering, followed by a low-temperature tempering process. This hardening process improves the strength and wears resistance while retaining good ductility, which allows for better machinability than other alloys with similar mechanical properties.

AISI 4042 Machining

Machining AISI4042 is relatively easy since it has good cutting properties due to its low carbon content combined with its moderate hardness level after heat treatment. This makes it ideal for components where tight tolerances are required since there will be less tool chatter during cutting operations which could produce undesired results if not properly controlled. The relatively low cost associated with machining this grade makes it desirable for many applications where cost efficiency is important, but so are tight tolerances or difficult shapes that may need accurate cuts made on them without causing any damage or distortion to the material itself during machining operations.


AISI 4042 is a unique and versatile alloy steel that can be used in a wide range of applications. Its low initial cost, medium strength, and processability make it an excellent choice for many manufacturing processes. AISI 4042 has good weldability and machinability, as well as resistance to galling, stress corrosion cracking, and fatigue. The combination of these properties makes it suitable for automotive, aerospace, heavy equipment, and other demanding applications where strength and wear are essential. In conclusion, AISI 4042 is an economical solution that has become increasingly popular across a range of industries due to its ability to provide reliable results. For manufacturers looking for cost-effective ways to increase the performance of their machinery or products, AISI 4042 steel is definitely worth considering.

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