Introduction to the SAE-AISI Designation System
Abstract
This article explains the standardized SAE-AISI designation system for carbon and alloy steels. The system primarily uses a four-digit numerical code to identify different steel grades based on their chemical composition. The first digit indicates the main alloying element, the second digit shows the concentration of major elements, and the last two digits represent carbon content. The article details various steel categories, their classifications, and additional letter designations used to indicate special characteristics, providing essential information for engineers and materials specialists.
Introduction to Steel Classification
Understanding the Four-Digit System
The SAE designation system uses a straightforward four-digit numbering scheme, with some alloy steels using five digits (51XXX; 52XXX). The system's structure is as follows:
Carbon Steel Classifications
- 10xx series: Plain carbon steels (1.00% Mn maximum)
- 11xx series: Resulfurized carbon steels
- 12xx series: Resulfurized and rephosphorized carbon steels
- 15xx series: Non-resulfurized high-manganese carbon steels (up to 1.65%)
Alloy Steel Classifications
The first digit indicates the primary alloying element:
- 2xxx: Nickel steels
- 3xxx: Nickel-chromium steels
- 4xxx: Molybdenum steels
- 5xxx: Chromium steels
- 6xxx: Chromium-vanadium steels
- 7xxx: Tungsten-chromium steels
- 9xxx: Silicon-manganese steels
Additional Designations
Special letter designations provide further classification:
- B: Indicates boron content (0.0005-0.003%)
- L: Indicates lead content (0.15-0.35%)
- M: Designates merchant quality steel
- E: Indicates electric-furnace steel
- H: Indicates hardenability requirements
For example, SAE 5130 represents a chromium steel alloy containing 1% chromium and 0.30% carbon.
Table 1: The SAE/AISI steel numbering designation system
| Carbon steels | 10XX | Plain carbon, Mn 1.00% max |
| 11XX | Resulfurized free machining | |
| 12XX | Resulfurized/rephosphorized free machining | |
| 15XX | Plain carbon, Mn 1.00-1.65% | |
| Manganese steels | 13XX | Mn 1.75% |
| Nickel steels | 23XX | Ni 3.50% |
| 25XX | Ni 5.00% | |
| Nickel-chromium steels | 31XX | Ni 1.25%, Cr 0.65-0.80% |
| 32XX | Ni 1.75%, Cr 1.07% | |
| 33XX | Ni 3.50%, Cr 1.50-1.57% | |
| 34XX | Ni 3.00%, Cr 0.77% | |
| Molybdenum steels | 40XX | Mo 0.20-0.25% |
| 44XX | Mo 0.40-0.52% | |
| Chromium-molybdenum steels | 41XX | Cr 0.50-0.95%, Mo 0.12-0.30% |
| Nickel-chromium-molybdenum steels | 43XX | Ni 1.82%, Cr 0.50-0.80%, Mo 0.25% |
| 47XX | Ni 1.05%, Cr 0.45%, Mo 0.20-0.35% | |
| Nickel-molybdenum steels | 46XX | Ni 0.85-1.82%, Mo 0.20-0.25% |
| 48XX | Ni 3.50%, Mo 0.25% | |
| Chromium steels | 50XX | Cr 0.27-0.65% |
| 51XX | Cr 0.80-1.05% | |
| 50XXX | Cr 0.50%, C 1.00% min | |
| 51XXX | Cr 1.02%, C 1.00% min | |
| 52XXX | Cr 1.45%, C 1.00% min | |
| Chromium-vanadium steels | 61XX | Cr 0.60-0.95%, V 0.10-0.015% |
| Tungsten-chromium steels | 72XX | W 1.75%, Cr 0.75% |
| Nickel-chromium-molybdenum steels | 81XX | Ni 0.30%, Cr 0.40%, Mo 0.12% |
| 86XX | Ni 0.55%, Cr 0.50%, Mo 0.20% | |
| 87XX | Ni 0.55%, Cr 0.50%, Mo 0.25% | |
| 88XX | Ni 0.55%, Cr 0.50%, Mo 0.35% | |
| Silicon-manganese steels | 92XX | Si 1.40-2.00%, Mn 0.65-0.85%, Cr 0-0.65% |
| Nickel-chromium-molybdenum steels | 93XX | Ni 3.25%, Cr 1.20%, Mo 0.12% |
| 94XX | Ni 0.45%, Cr 0.40%, Mo 0.12% | |
| 97XX | Ni 0.55%, Cr 0.20%, Mo 0.20% | |
| 98XX | Ni 1.00%, Cr 0.80%, Mo 0.25% |
Click on the link to see a list of AISI-SAE standards the following material categories
- Group of standards for structural and constructional steels
- Group of standards for stainless and heat resisting steels
- Group of standards for steel castings
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