ASTM A29 4130 Steel

A29 vs. A519 — Product Form Governs

The material grade (4130) is the same in both standards, but the product standard governs the product form and testing requirements:

- ASTM A29: Bar (round bar, square bar, hexagonal bar) — used as machining stock, shafting, and raw material for machined parts.
- ASTM A519: Seamless tubing — hollow circular cross-section for structural and mechanical tube applications.

The two products are not interchangeable. A purchase order referencing 'ASTM A29 4130' will produce bar, not tube.

When A29 4130 Bar Is Specified

4130 bar to ASTM A29 is used for: machined aerospace components (brackets, fittings, pins), round bar for turning into shafts or spindles, and square/hex bar for machined tooling applications. The MTC for A29 bar documents chemical analysis and mechanical properties per the standard.

Using 4130 Bar and Tube Together

Many assemblies combine both forms: a tubular link with machined bar ends, a frame with turned bosses, a shaft with a tubular spacer. The bar is ordered to the bar standards and the tube to ASTM A519, each with its own certificate.

For the parts to work together, match the conditions as well as the grade. If a welded assembly uses normalized tube, the bar fittings should be in a compatible condition so that the weld and both heat-affected zones behave similarly. If the whole assembly will be heat treated after welding, both can start annealed. State the condition for each item on the order, and keep the two certificates together in the job record.

Bar is dimensioned by diameter and is solid; if you intend to bore it out, compare the cost with starting from tube, as discussed under 4130 hollow tubing. The tube standard is described under ASTM A519 4130 tubing.