ASTM A29/A29M — Standard Specification for General Requirements for Steel Bars, Carbon and Alloy, Hot-Wrought
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Scope
General requirements and the chemical composition tables for hot-wrought carbon and alloy steel bars designated by SAE/AISI number (10xx, 11xx, 12xx, 13xx, 15xx, 40xx, 41xx, 43xx, 46xx, 47xx, 48xx, 50xx, 51xx, 61xx, 81xx, 86xx, 87xx, 88xx, 92xx, 93xx, 94xx) and UNS number. It does not give mechanical properties — those come from the ordering condition, ASTM A108 (cold-finished), A434 (Q&T alloy bar), A322 (alloy bar) or the customer specification. Also defines H-band hardenability referencing SAE J1268.
Grades covered by ASTM A29
| Grade | No. | Type | C % | Yield MPa | Tensile MPa | Nearest equivalents |
|---|---|---|---|---|---|---|
| SAE 1010 | 1.0301 | Low-carbon steel for cold forming, welding and case hardening | 0.08 – 0.13 | 180 | 325 | C10, S10C, 1008 |
| 1018 | G10180 | Low-carbon steel, cold-finished bar (case-hardenable) | 0.15 – 0.2 | ≈ 370 | ≈ 440 | C15 / C15E, S235JRC / C22, S15C / S17C / S20C |
| 1045 | G10450 | Medium-carbon steel, hardenable | 0.43 – 0.5 | ≈ 310 | ≈ 565 | C45, S45C, 45 |
| 1095 | G10950 | High-carbon steel (spring / knife / blade steel) | 0.9 – 1.03 | ≈ 380 | ≈ 650 | C100S, C90S / C98S, SK95 (SK4) |
| 4130 | G41300 | Chromium-molybdenum low-alloy steel, weldable (chromoly) | 0.28 – 0.33 | ≈ 360 | ≈ 560 | 25CrMo4, 30CrMo4, SCM430 |
| 4140 | G41400 | Chromium-molybdenum low-alloy steel (chromoly) | 0.38 – 0.43 | ≈ 415 | ≈ 655 | 42CrMo4, SCM440, 42CrMo |
| 4340 | G43400 | Nickel-chromium-molybdenum low-alloy steel, deep hardening | 0.38 – 0.43 | ≈ 470 | ≈ 745 | 34CrNiMo6, 36CrNiMo4, SNCM439 |
| 8620 | G86200 | Nickel-chromium-molybdenum case-hardening steel | 0.18 – 0.23 | ≈ 385 | ≈ 540 | 20NiCrMo2-2, SNCM220, 20CrNiMo |
Revision history and superseded standards
| Year | Change |
|---|---|
| 1920s | SAE numbering system established; A29 codifies chemistry for ASTM buyers |
| 2020 | A29/A29M-20 — current |
Where to buy the standard
The full text is copyrighted by ASTM International and is not reproduced here. Purchase the current edition from ASTM International or your national standards body. The values on this site are the normative limits as published; the standard's own tables, notes and test methods govern.
Related standards
A29 sets the rules, the SAE number sets the steel
ASTM A29 is the general requirements specification for hot-wrought carbon, alloy and free-machining steel bars. It does not define 1045 or 4140; it defines what a bar of any of them must satisfy — permitted variations in dimension, straightness, surface condition, the heat analysis and product analysis tolerances, the marking, and how the material is tested and certified.
The alloy itself comes from the SAE/AISI four-digit system, which A29 tabulates. The first digit is the alloy family (1 carbon, 4 molybdenum-bearing, 5 chromium, 8 nickel-chromium-molybdenum), the second usually the concentration of the principal alloy, and the last two the carbon content in hundredths of a per cent. 4140 is a chromium-molybdenum steel with 0.40 % carbon; 1045 is plain carbon with 0.45 %.
Where A29 stops and the product specifications start
A29 covers the bar as a semi-finished product. What happens to it afterwards belongs to other documents. A108 covers cold-finished bar, where the drawing or turning operation changes the mechanical properties and the tolerance class. A576 covers hot-wrought special-quality bar. A311 covers stress-relieved cold-drawn bar where straightness under machining matters. A322 narrows A29 to the alloy grades specifically.
None of these guarantee a hardness or a tensile strength unless the order says so. A bar ordered to A29 and 4140 arrives as-rolled; 4140 in a heat-treated condition is a separate line on the order, with the condition and the section size both stated, because hardenability runs out with diameter.
Heat analysis, product analysis and why they differ
Two chemical analyses appear on a bar certificate and they are not the same thing. The heat analysis is taken from the ladle and represents the cast; it is what the grade limits apply to. The product analysis is taken from the finished bar and is allowed to deviate from the heat analysis by tabulated amounts, because segregation during solidification is a physical fact rather than a defect.
A29 publishes those permitted deviations. A carbon result a few hundredths above the grade maximum on a product analysis is conforming if it falls inside the A29 tolerance, and rejecting it as off-grade is a common and expensive error.
A29 = general requirements; the SAE number = the alloy.
Cold-finished bar adds A108; special quality adds A576.
As-rolled unless the order names a heat-treated condition.
Product analysis may legitimately fall outside the grade limits within A29 tolerance.
faq.h
What is ASTM A29?
The general requirements specification for hot-wrought carbon, alloy and free-machining steel bars. It sets dimensional tolerance, surface condition, analysis tolerance, marking and testing for bar; the alloy itself is named by an SAE/AISI number that A29 tabulates.
How do I read an AISI four-digit number?
First digit is the alloy family — 1 carbon, 4 molybdenum-bearing, 5 chromium, 8 nickel-chromium-molybdenum. The second usually indicates the principal alloy content. The last two are carbon in hundredths of a per cent, so 4140 is a chromium-molybdenum steel at 0.40 % C.
What is the difference between A29 and A108?
A29 covers hot-wrought bar as it leaves the mill; A108 covers cold-finished bar, which has been drawn, turned or ground afterwards. Cold finishing raises strength, tightens tolerance and introduces residual stress, so the two are different products at the same grade.
Does A29 guarantee a hardness or tensile strength?
No. Bar to A29 is supplied as-rolled unless the order states a heat-treated condition. Where a mechanical property is required it must be specified with the section size, because through-hardening depends on diameter.
Why does the product analysis differ from the heat analysis?
Segregation during solidification. The heat analysis comes from the ladle and is what the grade limits apply to; the product analysis comes from the finished bar and is allowed to deviate by amounts tabulated in A29. A result outside the grade limit but inside the A29 tolerance is conforming.