Alloy steel adds chromium, molybdenum and nickel to carbon steel so it can be hardened deep and still stay tough. It's what shafts, pins, gears, spindles and oilfield parts are made from when mild steel would bend or wear. We source alloy bar, plate and tube for Texas machine shops, oilfield fabricators and equipment builders, saw cut to your lengths.
What shops use alloy steel for
Machine shops buy 4140 more than any other alloy grade. Annealed 4140 machines easily and gets heat treated after. Pre-hardened 4140, supplied quenched and tempered to roughly 28–32 HRC, skips the heat-treat step and still machines, which is why it shows up in shafts, spindles and fixtures. 4340 adds nickel for more toughness in big sections, the choice for heavily loaded shafts and landing-gear-type parts. 8620 is a carburizing grade: soft core, case-hardened skin, the standard for gears and cams. 4130 chromoly tube is the go-to for roll cages, race frames and lightweight welded structures.
Oilfield shops use 4140 and 4130 for subs, crossovers and pressure-side parts, often with hardness limits set by the customer. Say the hardness range on the RFQ; it decides whether you need annealed or pre-hard.
Common alloy steel grades
| Grade | Key traits | Typical uses |
|---|---|---|
| 4130 | Chromoly, weldable, good strength-to-weight | Roll cages, frames, aircraft-style tube, brackets |
| 4140 annealed | Soft for machining, heat treated afterward | Shafts, pins, tooling, oilfield parts |
| 4140 pre-hard | Quenched and tempered, about 28–32 HRC, machinable as supplied | Spindles, fixtures, shafts that skip heat treat |
| 4340 | Nickel-chromium-moly, deep hardening, very tough | Heavy shafts, axles, high-stress parts |
| 8620 | Low-carbon carburizing grade, tough core, hard case | Gears, cams, pins, wear parts |
Forms available
Most alloy steel is bought as round bar, either hot rolled, cold drawn, or turned, ground and polished for shafting that's close to size. Plate and flat bar in 4140 cover blocks, base plates and fixture stock. 4130 comes as round tube in thin walls for fabrication, plus sheet and plate. Hollow bar and heavy-wall mechanical tubing save material on sleeves and bushings when you'd otherwise bore out a solid. We quote alloy by the piece, so you can order one 4" slug or a full bar.
Typical alloy steel size ranges
| Form | Commonly available range |
|---|---|
| 4140 and 4340 round bar | 1/4" to 12" diameter and larger in hot rolled; random lengths around 12' to 20' |
| 8620 round bar | 1/2" to about 8" diameter |
| 4140 plate and flat | 1/4" to 6" thick, cut to size from larger plate |
| 4130 round tube | 1/4" to 3" OD, 0.028" to 0.250" wall |
| 4130 sheet and plate | 0.020" to 1/2" thick |
Commonly available ranges. Ask for anything outside them.
Cutting options for alloy steel
Bar and tube get saw cut to length, the standard method for alloy. Pre-hard 4140 saws slower than mild steel but cuts cleanly. Plate blanks can be waterjet cut when you don't want a heat-affected edge, which matters on pre-hard and on parts that get machined to the line. Plasma is fine for rough blanks with machining stock on every edge, but it leaves a hardened zone that dulls tools. Leave cleanup allowance on anything that gets finished.
Certs and heat numbers
Alloy steel is where certs matter most outside of aerospace. An MTR confirms the chemistry, the condition (annealed or quenched and tempered) and, for pre-hard, the hardness. Oilfield and hydraulic customers often ask for traceability from heat number to finished part. Tell us on the RFQ and we can get mill certs and ask for the heat number to be carried onto each cut piece.