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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

 

April, 2011

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