Metal · Material guide
Custom alloy steel parts from independent machine shops
Alloy steels like 4140 and 4340 add chromium and molybdenum to plain carbon steel for far higher strength and fatigue life, and they can be heat treated to a target hardness. Upload a drawing and hear back from shops that machine and treat chromoly every day.
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Grades
Alloy steel grades shops run most
The grade sets strength, hardenability, and how it responds to heat treatment. These are the ones you will see quoted.
4140
The workhorse chromoly. Strong, tough, and readily heat treated to a target hardness. Machines well in the annealed or pre-hard condition and is stocked everywhere in bar and plate.
Best for Shafts, gears, tooling, structural and pressure parts
4340
A nickel-chromium-molybdenum steel with higher strength and much better fatigue and impact toughness than 4140, especially in thick sections. Costs more.
Best for Highly stressed shafts, landing gear, gears
4130 chromoly
A lower-carbon chromoly prized for weldability and toughness at moderate strength. The tubing alloy for roll cages, frames, and aerospace structure.
Best for Welded tube frames, roll cages, brackets
8620
A case-hardening alloy steel. Left soft and tough in the core, then carburized to a hard wear surface. The standard for gears and bearing races.
Best for Gears, pins, bearing races, wear parts
Pre-hard (4140 PH)
Supplied already heat treated to roughly 28-32 HRC so parts are strong as-machined with no post-heat-treat distortion or scale.
Best for Mold bases, fixtures, parts needing no post-treat
Specs
Material properties
Representative values for 4140 in the quenched-and-tempered condition. Exact numbers depend on grade and heat treatment.
| Property | Typical value |
|---|---|
| Density | 7.85 g/cm³ (0.284 lb/in³) |
| Tensile strength (4140 Q&T) | ~150 ksi (1030 MPa) |
| Yield strength (4140 Q&T) | ~130 ksi (900 MPa) |
| Hardness range (heat treated) | ~28-55 HRC depending on temper |
| Max service temp | ~400 °C (750 °F) before tempering back |
| Machinability | Good annealed; harder after heat treat |
| Corrosion resistance | Poor; will rust, needs oil, coating, or plating |
| Weldability | 4130 good; 4140/4340 need preheat and post-weld heat |
Alloy steels are usually machined soft, then heat treated to final hardness. Note the target hardness and whether the shop should coordinate treatment.
Stock
Forms we machine it from
Round bar
Turned shafts, pins, and cylindrical parts.
Plate & block
Milled and 5-axis parts machined from solid.
Tube
DOM and seamless tube for frames and structure.
Processes
Manufacturing methods for alloy steel
The right process depends on part geometry, tolerances, and production volume.
Finishing
Finishes for alloy steel
Alloy steel rusts, so most parts get a coating or plating unless they run in oil.
Black oxide
A thin conversion coating that adds mild corrosion resistance and a black finish without changing dimensions.
Zinc / nickel plating
Electroplated corrosion protection for fasteners and exposed parts. Nickel is harder and more durable.
Nitriding
A surface hardening treatment that adds wear and fatigue resistance with minimal distortion, common on shafts and gears.
Powder coat / paint
A durable colored coating for structural and cosmetic parts. Mask threads and bearing fits.
Oil / as-machined
Bare parts shipped oiled for short-term rust protection, fine for parts that run in a lubricated assembly.
Specify the target hardness and the finish or plating on your drawing, and mask any bearing fits or threads.
Applications
Where alloy steel parts are used
Alloy steel is the default when a part needs strength, fatigue life, and hardness at reasonable cost.
Compare
Alloy Steel vs other materials
How alloy steel compares to the other metals shops quote most.
Alloy Steel vs Carbon Steel
Carbon Steel →- Alloy steel is stronger, tougher, and hardens deeper thanks to its chromium and molybdenum
- Plain carbon steel (1018, 1045) is cheaper and fine for lower-stress parts
- Both rust and need a coating; alloy steel justifies its cost on stressed or heat-treated parts
Choose alloy steel for stressed, fatigue-loaded, or heat-treated parts. Choose carbon steel for general low-stress work at lowest cost.
Alloy Steel vs Stainless Steel
Stainless Steel →- Stainless resists corrosion without a coating; alloy steel must be plated or oiled
- Alloy steel reaches higher strength and hardness per dollar and machines more predictably
- Stainless is the choice for hygiene and wet or chemical environments
Choose alloy steel for maximum strength at low cost in dry or coated service. Choose stainless when corrosion resistance is the priority.
Questions
Frequently asked questions
4140 is the all-around chromoly: strong, tough, readily heat treated, and inexpensive. 4340 adds nickel for higher strength and much better fatigue and impact toughness, especially in thick sections, at a higher price. Use 4140 for most shafts and tooling and 4340 for the most highly stressed parts like landing gear and heavy shafts.
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Get alloy steel part quotes
Upload a drawing once and compare quotes from independent shops that machine and heat-treat 4140, 4340, and 4130.
STEP · STL · IGES · DWG · DXF · PDF · and more
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