What Are Steel Grades: A Guide to Types and Applications

Steel is often hailed as one of the most versatile and essential materials worldwide. While it’s primarily composed of iron (Fe) and carbon (C), today’s steel is far more intricate than this simple combination suggests. Its properties and strengths vary greatly depending on factors like carbon concentration, the presence of other elements, and manufacturing processes, making it suitable for an incredibly diverse array of uses.

Contrary to popular belief, steel isn’t just a one-size-fits-all material. There are over 3,500 different grades of steel. These grades are determined by analyzing the amount of carbon present and other alloying elements and production methods used.

Steel Grading Systems

Steel grading systems allow us to categorize steel varieties based on their use case. For example, the rate at which steel is cooled by steel manufacturers might affect its molecular strength. The time they can maintain steel at critical temperatures throughout the cooling process is also essential. Depending on the heat-treatment technique, two steel sheets with the same alloy content can have various grades.

ASTM Grading System

The ASTM Grading System categorizes steel based on a letter prefix denoting its general category, such as “A” for iron-based alloys and steel materials. Additionally, each metal is assigned a sequentially allocated number that reflects its unique qualities. This system takes into account factors like the rate of cooling during manufacturing and the maintenance of critical temperatures throughout the cooling process. Thus, steel sheets with the same alloy content may receive different grades depending on the heat-treatment technique applied.

SAE Grading System

In contrast to the ASTM system, the SAE Grading System utilizes a four-digit number for classification. The first two digits indicate the steel type and alloying element concentration, while the latter two digits specify the metal’s carbon concentration. This system provides a detailed breakdown of steel properties, making it useful for various applications.

What Is the Best Grade of Steel?

Choosing the best steel grade depends on the project’s specific needs, including application requirements, desired mechanical and physical properties, and budget considerations. While there isn’t a universal “best” grade of steel suitable for all situations, certain grades within each category are frequently recognized for their exceptional qualities and widespread use.

Prominent steel grades in each category are as follows:

  • Carbon Steels: Widely recognized grades include A36, known for its good weldability and machinability; A529 and A572, noted for their strength and toughness; and 1020, 1045, and 4130, valued for their versatility and balance of properties.
  • Alloy Steels: Popular choices like 4140 and 4150 are praised for their excellent strength and toughness; 4340 is renowned for its high strength and deep hardenability; 9310 is notable for its strength and wear resistance; and 52100 is well-regarded for its wear resistance and strength, especially in bearings.
  • Stainless Steels: Key grades such as 304 and 316 are celebrated for their corrosion resistance and versatility, making them staples in food processing and medical equipment; 410 and 420 are valued for their hardness and resistance to wear, often used in cutlery and surgical tools.
  • Tool Steels: Distinguished grades include D2, known for its high wear resistance; H13, which offers excellent toughness and resistance to thermal fatigue; and M2, a high-speed steel with a good balance of wear resistance and toughness, often used in cutting tools.

4 Major Types Of Steel

Steel is categorized into various types depending on its composition.  These include carbon steel, stainless steel, alloy steel, and tool steel. 

  1. Carbon Steels

Carbon steels, mainly iron and carbon, are the most basic steel variety. This category is renowned for its exceptional durability and cost-effectiveness. 

There are three main subclasses of carbon steels:

  • Low Carbon Steels: Also known as mild steels, these contain a small percentage of carbon (usually less than 0.25%). Their low carbon content renders them soft and flexible, making them ideal for use in sheet metal, wire, and car body parts due to their easy shaping and welding capabilities.
  • Medium Carbon Steels: With a carbon content ranging from 0.25% to 0.5%, medium carbon steels offer a good balance between strength and pliability. They are frequently utilized in making shafts, gears, and rail tracks, where a mix of robustness and flexibility is essential.
  • High Carbon Steels: These steels have a higher carbon percentage ranging from 0.5% to 1.25% and are celebrated for their hardness and resistance to wear. High carbon steels are typically used to manufacture cutting tools, springs, and other parts that demand high resistance to wear and abrasion.
  1. Alloy Steels

Alloy steels are produced by adding alloying elements such as nickel, copper, chromium, and aluminum to the base steel composition. Incorporating these elements significantly improves the steel’s properties, including its strength, ductility, resistance to corrosion, and ease of machining. Common applications include automotive parts, construction materials, pipelines, and tools, showcasing their versatility and critical role in various sectors.

  1. Stainless Steels

Stainless steels are primarily made with an 11-12% chromium content, along with additional elements such as nickel, silicon, manganese, and carbon. This composition gives them notable corrosion resistance, making them perfectly suited for outdoor construction, where they can withstand harsh weather conditions. 

Their corrosion-resistant properties also make them ideal for electrical equipment. A popular choice in this category is 304 Stainless Steel, known for its durability and effectiveness in protecting electrical components from environmental damage.

Apart from their application in construction and electrical industries, stainless steels are highly valued for their hygienic qualities. They are commonly used in the production of medical equipment, piping, cutting tools, and food processing equipment, demonstrating their wide-ranging utility and significance in sectors requiring high cleanliness and corrosion resistance standards.

  1. Tool Steels

As the name suggests, tool steels are engineered to create high-speed tools, which generate significant heat during use. Their ability to endure high temperatures and resist wear makes them particularly valuable in tool manufacturing. Key elements in the composition of tool steels include tungsten, chromium, and vanadium, each contributing to the material’s durability and resistance to wear and heat.

Steel Classifications

In addition to the four primary categories, steel can be categorized or graded according to various factors, such as:

Composition: This involves specific types like carbon, alloy, stainless steel, etc., based on the elements incorporated into the steel.

Finishing Method: Methods like hot rolling, cold rolling, and cold finishing impact the steel’s surface finish and dimensional precision.

Production Method: The manufacturing technique, whether it’s electric furnace production or continuous casting, affects the steel’s attributes and quality.

Microstructure: The internal configuration of the steel, including ferritic, pearlitic, martensitic, etc., influences its properties and suitability for different applications.

Physical Strength: Classified by strength according to American Society for Testing and Materials (ASTM) standards, which determines its appropriateness for various uses.

De-oxidation Process: Steel production can involve full deoxidation (killed) or partial deoxidation (semi-killed), affecting its characteristics and performance.

Heat Treatment: Treatments such as annealing and tempering alter the steel’s properties to better suit specific applications.

Quality Nomenclature: Steel is also graded by quality types, such as commercial, pressure vessel, and drawing quality, which indicate its compliance with specific standards and intended applications.

FastMetals: Quality Steel for Every Project

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Trust FastMetals for all your metal supply needs and ensure your projects are built to last with the best grades of steel.