Alloy Steel
Medium and high-carbon alloy steels (4140, 4340, 8620) with enhanced strength and hardenability. Used for gears, shafts, and high-stress structural components.
About Alloy Steel
Alloy steels incorporate additional alloying elements (chromium, molybdenum, nickel, vanadium) beyond carbon to achieve enhanced strength, hardenability, and wear resistance. These steels bridge the gap between mild steel and tool steel, offering high performance at moderate cost.
FabRapid machines the most common alloy steel grades: 4140 (the general-purpose workhorse), 4340 (ultra-high-strength), and 8620 (case-hardening grade). All can be heat treated to achieve specific hardness and mechanical properties tailored to the application.
Alloy steels are essential for power transmission components (gears, shafts, axles), high-stress fasteners, oil and gas downhole tools, and any application where the strength of mild steel is insufficient but the cost and difficulty of machining tool steel is unwarranted.
Material Properties
Available Alloy Grades
4140
Chrome-moly alloy with excellent toughness and fatigue resistance. Can be through-hardened to 28-32 HRC (Q&T) or 54-59 HRC (oil-quenched).
Shafts, gears, bolts, spindles, hydraulic cylinders
4340
Nickel-chrome-moly alloy with the highest toughness and strength of common alloy steels. Tensile strength up to 1860 MPa when heat treated.
Landing gear, crankshafts, connecting rods, power transmission shafts
8620
Low-carbon alloy designed for case-hardening (carburizing). Creates a hard, wear-resistant surface with a tough core.
Gears, pinions, camshafts, worm gears, ring gears
Compatible Manufacturing Processes
Alloy Steel can be processed using these manufacturing methods.
Available Surface Finishes
Surface treatments compatible with Alloy Steel.
Common Applications
Design Guidelines for Alloy Steel
Specify pre-hardened 4140 (28-32 HRC) when possible — machines much easier than fully hardened
For case-hardened parts (8620), allow grinding stock on critical surfaces to remove any heat treatment distortion
Design generous fillets on shaft transitions — alloy steels are susceptible to fatigue failures at stress concentrations
Specify required heat treatment and hardness range on the drawing (e.g., "4340 Q&T to 38-42 HRC")
Alloy Steel FAQ
4340 contains nickel (1.65-2.00%) which 4140 lacks, giving it superior toughness and hardenability. 4340 can achieve higher hardness while maintaining impact resistance, making it preferred for critical applications like aircraft landing gear. 4140 is more cost-effective and sufficient for most industrial shafts and gears.
Use 8620 when you need a hard, wear-resistant surface (60+ HRC) combined with a tough, impact-resistant core. This is achieved through case-hardening (carburizing). 4140 is better when uniform through-hardness is needed. Gears are the classic 8620 application.
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