What Is 8620 Steel Used For?
MetalNow · October 13, 2026
Most people assume a hard part has to start as hard steel. 8620 works the other way around. It's a low-carbon alloy that starts soft, machines easily, and only gets hard where you want it, on the surface, after the part is already cut to shape.
That's why it ends up inside so many gearboxes, drivetrains, and wear-heavy assemblies. A gear tooth has two jobs that pull in opposite directions: resist wear on the contact face, and not snap when the load spikes. One steel rarely does both well. 8620, treated right, gets close.
Here's what 8620 actually is, what it's used for, how a part goes from bar stock to finished, and how to tell whether your job needs it or something simpler.
Quick answer: 8620 is a low-alloy nickel-chromium-molybdenum steel made for carburizing, a heat treatment that hardens the surface while the core stays tough. It's used for gears, pinions, shafts, camshafts, pins, rollers, and other parts that need to resist wear on the outside and shock on the inside. If a part has to survive both sliding contact and impact, 8620 is usually on the shortlist. If you aren't going to carburize it, you probably don't need it.
What 8620 steel actually is
8620 is a low-alloy steel in the nickel-chromium-molybdenum family. The name is a code: the 86 identifies the alloy family, and the 20 means roughly 0.20 percent carbon. Its UNS number is G86200.
Element Typical range
Carbon 0.18-0.23%
Manganese 0.70-0.90%
Chromium 0.40-0.60%
Nickel 0.40-0.70%
Molybdenum 0.15-0.25%
The nickel, chromium, and molybdenum are there for hardenability, the ability of the steel to harden deeper into the part, and for core toughness after heat treatment. They're what separate 8620 from a plain low-carbon steel like 1018.
The low carbon is on purpose. With only about 0.2 percent carbon, 8620 can't be made very hard by quenching alone. That's the point. It keeps the core soft and tough, and a process called carburizing adds carbon to the surface afterward.
The idea behind 8620: a hard shell around a tough core
Carburizing means heating the part in a carbon-rich atmosphere, commonly around 1,700°F, so carbon soaks into the surface. The longer it soaks, the deeper the carbon goes. Quench the part, and the carbon-rich outer layer, called the case, hardens to somewhere around 58 to 62 HRC. The core, still low in carbon, stays much softer and tougher.
Think about what a gear tooth goes through. The face of the tooth takes constant rolling and sliding contact, which wears down soft steel fast. The base of the tooth bends with every load cycle, which cracks brittle steel. A through-hardened part would resist wear but could snap at the root. A soft part would flex fine but wear out. A case-hardened 8620 tooth handles both: hard where the contact happens, tough where the bending happens.
How an 8620 part gets made, step by step
This is the part most buying guides skip, and it explains almost every decision about the grade.
Start with soft bar stock. 8620 is usually supplied annealed or normalized, which makes it easy to machine.
Rough and finish machine, leaving a little extra. Everything with tight geometry gets cut now, while the steel is soft. Parts that must stay soft after hardening, like threads, are typically masked so the carbon can't get in.
Carburize. Time and temperature set the case depth. Case depths commonly run from about 0.020 to 0.060 inch, depending on the part and the spec.
Quench and temper. The part is usually quenched in oil, then given a low-temperature temper, commonly in the 300 to 400°F range, to relieve stress without giving up much hardness.
Finish grind or hone. The part moves a little in heat treatment, so critical surfaces get ground to final size.
Inspect. Surface hardness and case depth get checked against the drawing.
The exact numbers come from your drawing and your heat treater. Treat the ranges here as the typical picture, not a heat treat spec.
What 8620 steel is used for
Gears and pinions. This is the classic use: transmission gears, differential ring and pinion sets, spur and helical gears, and worm gears.
Shafts and splines. Output shafts, spline shafts, and drive shafts where the surface sees wear and the core carries torque.
Camshafts and cam-driven parts. Contact surfaces that need to resist wear under repeated load.
Pins, rollers, and bushings. Wear parts in heavy equipment, agricultural machinery, and industrial machines.
Clutch and ratchet components. Parts that engage hard and often.
Tooling and fixtures. Locating pins, wear plates, and bushings in production tooling.
You'll find it across automotive and motorsports drivetrains, heavy equipment, industrial gearboxes, and general power transmission. Different industries, same problem: a surface that has to last and a core that can't be brittle.
Key properties at a glance
These are typical figures. Real values depend on the condition, size, and mill, so check the mill cert for the exact chemistry. Our guide on how to read a mill certificate walks through it.
When 8620 is the right call
The surface wears and the core takes shock. This is the textbook case. If the part sees both abrasion and impact, case hardening gives you something a through-hardened or soft steel can't.
You want to machine first and harden last. Because 8620 starts soft, you can cut complex shapes, gear teeth, and splines easily, then harden the finished geometry.
You need a deeper hard case than a plain carbon steel gives you. The alloying lets 8620 build a thicker, more reliable case with a stronger core underneath than 1018 does.
Cost matters. It's usually less expensive than higher-nickel carburizing grades like 9310, and it covers most general gear and shaft work.
When 8620 isn't the right call
You aren't going to carburize it. As supplied, 8620 is a decent low-alloy steel with moderate strength, and you'd be paying for hardenability you never use. If the part isn't getting case hardened, a simpler grade usually does the job for less.
You need the whole section hard. Carburizing hardens the outer layer only. For parts that need strength all the way through, a through-hardening grade like 4140 is the better fit. Our 4130 vs 4140 guide covers that family, and you can buy 4140 steel online if that's the direction you're leaning.
You can't get it heat treated. Carburizing is a specialty process. If you don't have access to a heat treater who does it, 8620 won't deliver what it's known for.
The part has to be welded after hardening. The high-carbon case is crack-prone under weld heat. Weld before carburizing, or pick a different grade.
Distortion is a deal breaker. Any quench moves the part. If you can't leave grinding stock, a grade that can be nitrided, like 4140, distorts less.
8620 vs 1018 vs 4140
For a deeper look at the low-carbon side, see our 1018 vs 1045 guide.
Buying 8620: what to check before you order
Condition. Ask whether the bar is annealed, normalized, or as-rolled. It changes how it machines.
Size. Larger sections don't reach the same core hardness as small ones, so tell your heat treater the size you're working with.
Grinding stock. Leave extra on critical surfaces. Your heat treater can tell you how much.
8620 vs 8620H. The H grade is produced to a guaranteed hardenability band. If your drawing calls for it, make sure that's what you're buying.
The mill cert. Check the chemistry, especially nickel and molybdenum.
8620 also works well as a remnant. It's the same steel as a full bar, just shorter. For a prototype pinion, a one-off shaft, or a test piece to check your heat treat process before you commit to a full order, a remnant is a cheap way to find out. Just make sure the piece is long enough for your machining.
We carry 8620, and we ship nationwide. See how shipping works before you order.
The mistakes we see most often
Specifying 8620 for a part that won't be carburized. It's the most common one. The grade only earns its price with the right heat treatment.
Machining straight to final size. Heat treatment moves metal. Without grinding stock, you can end up with a hard part that's out of tolerance and can't be fixed.
Welding carburized surfaces. The case cracks. Weld first, or design the weld away from hardened areas.
Ordering "8620" and nothing else. Condition, size, and whether it's the H grade all matter for how it heat treats.
A quick gut-check before you order
Does the surface need to resist wear while the core handles shock? If yes, 8620 is a strong candidate.
Can you get it carburized? If not, look at other grades.
Do you need the whole part hard? If yes, consider 4140.
Will you machine before heat treat and leave grinding stock? If yes, you're set up right.