Types of Steel

The four major steel types are carbon steel, stainless steel, tool steel and alloy steel. All steels are made of iron and carbon. Specialized steels include small amounts of chromium, magnesium, zinc or other metals.

Carbon steel is the most common type of steel, making up 90% of steel production, and can be easily welded or machined. It typically has a carbon content from 0.05-2.1% by weight and has three different categories:

• Low carbon steel has up to 0.3% carbon content. It is low cost and easy to form, making it suitable for machinery, pipes, wires and structural components.
• Medium carbon steel has 0.31-0.6% carbon and 0.31-1.6% magnesium. It has higher strength but lower ductility, making it harder to form. It is used in gears, cranks and machinery parts.
• High carbon steel has 0.61-1.50% carbon and 0.31-0.9% magnesium. It is tougher and harder than other steels but more difficult to form or weld and is used in steel plates and bars.

Stainless steel is an alloy known for having 10-20% chromium, which protects the metal from oxidation and corrosion, making it suitable for sheet metal and outdoor construction. The chromium gives stainless steel its sheen and makes it popular in kitchenware. Stainless steel has several classes based on their metallurgical structure, including the following:

• Austenic alloys are non-magnetic and the most common stainless steels, often used in kitchen appliances.
• Ferritic alloys are magnetic and less expensive than most stainless steels.
• Martensitic alloys have greater strength but less resistance to oxidation than most stainless steels and are used in pliers, cutlery and medical instruments.

Alloy steel combines steel with such metals as nickel, copper or aluminum. Alloy steels can be more expensive than other types and are often used in girders, rails, rods and pipelines.

Tool steels are types of carbon steel and alloy steel that contain cobalt, molybdenum, tungsten and vanadium for hardness and abrasion resistance. These are the major grades of tool steel:

• Water-hardening tool steels have high hardness and lower cost but tend to be brittle and unsuited for high temperatures. Common uses include drills and cutlery.
• Air-hardening tool steels have high wear-resistance and are used in many types of dies.
• Cold-working or D-type tool steels have higher carbon and chromium compared to other tool steels and are often used in cutters, burnishing tools and wood-working tools.
• Oil-hardening tools steels have high toughness and abrasion resistance and are frequently used in bushings and gauges.
• Shock-resisting tool steels are effective at low and high temperatures but are less corrosion resistant. They are often used in chisels, breaker hammers and pneumatic tools.
• High-speed tool steels retain their hardness at high temperatures, making them suitable for saw blades, drill bits and router bits.

Steel grading is a system for categorizing varieties of steel and materials based on their properties. The American Society of Testing (ASTM) grading system assigns the metals a classification letter based on the following:

• A represents ferrous metals and products such as iron and steel materials
• B represents nonferrous metals and products such as coatings
• C represents ceramic, concrete and masonry materials.
• F represents end-use materials and products such as bolts

The letter is followed by a 1-3 digit reference number, such as A572 steel, a high-strength, low alloy structural steel that is popular in construction.

Metric standards will be followed by the letter M. Updated standards will have a two-digit number representing the year of updating, such as 99 for 1999. For example, in ASTM A 582M-95, the M represents the metric system and the 95 represents 1995 as the year of its most recent update.

Grades are indicated by numbers that represent the metal properties. For example, A572 steel is available in five different grades, 42, 50, 55, 60 and 65, with the grade number representing the different yield strengths.

The Society of Automotive Engineers (SAE) uses a four-digit classification for steel types. The first digit indicates a type of carbon steel alloy. The remaining digits indicate the percentage concentration of other elements. For example, SAE 5130 is a chromium steel alloy with 1% chromium and 0.30% carbon.

The construction industry uses about 50% of the world’s steel. Steel is a popular building material for its strength, low cost and ability to bind to concrete.

Galvanized steel is carbon steel coated in zinc to reduce corrosion. It is used in large structural pieces as well as railings, fences and gutter systems.

The following are steel products used in building and construction.

• Structural steels are used for framing buildings.
• Reinforcing bars such as rebar add tensile strength to concrete.
• Steel pipes are frequently used in plumbing, as railings on construction sites and to provide support for construction piling.
• Steel sheet products are found in roofing, ceiling and walls.
• Steel plate is frequently used in construction and mining equipment and many types of machinery.
• Steel rods are used for reinforcement at construction sites.
• Non-structural steels are used in ductwork and heating and cooling equipment.

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