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Materials

Classification of Steel 201

Classification of Steel introduces users to steel designations systems, particularly AISI-SAE and UNS methods. This class describes classifications for plain carbon, alloy, high-strength low alloy, stainless, and tool steels, with a focus on AISI-SAE designations. There are many different types of steels, each having unique chemical contents and properties. Manufacturers distinguish between these metals by a numerical designation. In the AISI-SAE system, this number indicates the family of steel and the steel's carbon content. Some designations also describe the metal's intended use or special properties.

Because composition and processing methods determine a metal's properties, understanding steel classification is critical to choosing the best material for an application. After this class, users will be able to distinguish between major types of steel classifications and describe the nomenclature used to identify various grades of steel.

Difficulty Intermediate
Format Online
Number of Lessons 17
Language English

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The Importance of Steel Classification
Key Variables
AISI-SAE System
Unified Numbering System
Steel Review
Types of Steel
Plain Carbon Steel
Types of Plain Carbon Steel
Plain Carbon Steel Classification
Grades of Plain Carbon Steel
Plain Carbon Steel Review
Alloy Steel
Alloy Steel Classification
HSLA and Stainless Steel Classifications
Tool Steel Classification
Steel Classification Review
Understanding Steel Classification Systems

Describe the importance of steel classification.
Identify the variables that determine the properties of a steel.
Describe the AISI-SAE classification system.
Describe the Unified Numbering System.
Describe the main categories of steel.
Define plain carbon steel.
Describe the main categories of plain carbon steel.
Describe the classification of plain carbon steel.
Identify the main AISI-SAE grades of carbon steel.
Describe AISI-SAE alloy steel classification.
Describe AISI-SAE alloy steel classification.
Describe HSLA and stainless steel classifications.
Describe tool steel classification.

Vocabulary Term

Definition

AISI-SAE

The most common classification in the United States for plain carbon steels and alloy steels. American Iron and Steel Institute (AISI) is an association responsible for setting standards and creating numbering systems for various ferrous metals, and the Society of Automotive Engineers (SAE) writes specifications and other data used in a broad range of industries.

AISI-SAE designations

A steel classification system developed by the American Iron and Steel Institute (AISI) and the Society of Automotive Engineers (SAE). AISI-SAE designations are usually four-digit numbers based on a steel's contents.

alloy steel

Steel that contains added materials that change the property of the metal. Common alloy elements include chromium, manganese, molybdenum, and nickel.

alloy steels

Steel that contains added materials that change the property of the metal. Common alloying elements include chromium, manganese, molybdenum, and nickel.

carbon

A common, non-metalic element that is combined with iron to create steel. Carbon content typically increases hardness in metal.

corrosion resistance

The ability of a material to resist deterioration and chemical breakdown due to surface exposure in a particular environment. Alloying chromium with steel can increase the metal's corrosion resistance.

deoxidation

A process that removes or reduces the oxygen in molten steel. Deoxidation prevents the metal from oxidizing as it solidifies.

ductility

The measure of a material's ability to be drawn, stretched, or formed without fracturing. Ductility is a mechanical property.

free-machining steels

A particular grade of steel that has small amounts of additional alloying elements to improve machinability. 11xx and 12xx grades are free machining steels.

hardenability

The ability of a metal to be hardened by heat treatment processes. Steels have varying degrees of hardenability.

hardness

The measure of a material's ability to resist penetration, indentation, and scratching. Hardness is a mechanical property.

heat treatment

Controlled heating and cooling processes used to change the structure of a material and alter its physical and mechanical properties. Annealing, quenching, and tempering are heat treatments.

high-carbon steels

A plain carbon steel that contains more than 0.6% carbon. High-carbon steels are extremely strong and hard.

high-strength low-alloy steels

HSLA. A type of steel that contains low levels of carbon and alloying elements. High-strength low-alloy steel exhibits good strength and is relatively inexpensive.

HSLA

High-strength low-alloy steel. A type of steel that contains low levels of carbon and alloying elements. HSLA steel exhibits good strength and is relatively inexpensive.

iron

A silver-white, metallic element that is highly magnetic. Iron is alloyed with carbon to make steel.

low-carbon steels

A plain carbon steel that contains less than 0.3% carbon. Low-carbon steels are generally tough, ductile, and easily welded.

mechanical properties

A characteristic that describes how a material reacts when subjected to a force that attempts to stretch, compress, bend, dent, scratch, or break it. Tensile strength, hardness, and ductility are mechanical properties.

medium-carbon steels

A plain carbon steel that contains between 0.3% and 0.6% carbon. Medium-carbon steels are strong, hard, and not as easily welded as low-carbon steels.

physical properties

A characteristic that describes a material's volumetric, thermal, electrical, and magnetic characteristics. Physical properties are a collection of characteristics that describe how a material responds to forces other than mechanical forces.

plain carbon steels

Steel that contains less than 3% of elements other than iron and carbon. Plain carbon steel is considered the most "pure" form of steel.

stainless steels

A type of alloy steel that contains a large percentage of chromium. Stainless steel exhibits excellent corrosion resistance.

stainless steels

A type of alloy steel that contains a large percentage of chromium. Stainless steels exhibit excellent corrosion resistance.

steel

A ferrous metal consisting of iron and carbon, usually with small amounts of manganese, phosphorus, sulfur, and silicon. Steels are classified using AISI-SAE numerical designations.

tool steels

A specialized type of alloy steel that has excellent strength, toughness, and wear resistance. Tool steels are used in cutting tools, punches, and other industrial tooling.

Unified Numbering System

UNS. A common classification system that is used for both ferrous and nonferrous metals. UNS identifications include a prefix followed by five digits.

yield strength

The maximum stress a material can withstand before being plastically deformed. Yield strength is also called the elastic limit.