Carbon Steels
Carbon steel, also referred to as mild steel, is iron that’s been alloyed with varying levels of carbon and is best known for its strength, weldability, and heat “treatability”.
Carbon steels are categorized according to their carbon content; the amount present in a given steel grade varies, and in turn, those grades’ properties vary considerably.
Low carbon steels contain less than 0.3% carbon (by weight); common low carbon steel grades include 1018 and 1020.
Medium carbon steels contain 0.3 – 0.5% carbon; common medium carbon steel grades include 1045 and H13 tool steel.
High carbon steels contain 0.6% or more carbon; common high carbon steel grades include 17-4, 304, and 316.
Carbon steel’s mechanical properties vary slightly based on the carbon content of each grade.
| Property | Low Carbon | Medium Carbon | High Carbon |
| Yield Strength MPa | 350 | 415 | 570 |
| Tensile Strength MPa | 420 | 620 | 965 |
| Elongation at fracture | 15% | 25% | 9% |
| Hardness (Brinell) | 121 | 201 | 293 |
| Bulk Modulus GPa | 140 | 140 | 140 |
| Density g/cm³ | 7.85 | 7.85 | 7.85 |
Due to its low cost and heat treatability (which improves the alloy’s tensile strength, wear resistance, ductility, and hardness), carbon steel is used for numerous applications, including:
- Ball bearings
- Springs
- Gears
- Fasteners
- Shafts
- Wire
- Piping
Despite its widespread use, carbon steel has several disadvantages that should be considered, including poor corrosion resistance and formability. Low carbon steels, in particular, are not heat treatable, which would otherwise strengthen the alloy or improve its ductility.
Alloy Steels
Alloy steel is a type of steel made from iron, carbon, and at least one additional element to improve certain properties. By adding other elements, alloy steel can be tailored for greater hardness, strength, or corrosion resistance, making it a versatile choice for many industrial applications.
Alloy steels can be engineered with a wide variety of properties, depending on the types and amounts of elements added. Most alloy steels are valued for their:
- Durability
- Corrosion resistance
- Wear resistance
- High strength
The carbon content in alloy steel varies by type. Most alloy steels have less than 0.35% carbon by weight. Low-carbon alloy steels—ideal for welding—usually have less than 0.25% carbon. Tool steels are an exception, containing higher carbon levels, typically between 0.7% and 1.5%.
Common alloying elements in steel include boron, chromium, molybdenum, manganese, nickel, silicon, tungsten, and vanadium. Less frequently, elements like aluminum, cobalt, copper, lead, tin, titanium, or zirconium may also be added to achieve specialized properties.
Types of Alloy Steel
While alloy steels are broadly categorized into low-alloy and high-alloy steels, we can actually get a bit more granular.
Low-Alloy Steel
Low-alloy steels contain less than 8% alloying elements, which are added to improve specific mechanical properties. For example, adding molybdenum increases strength, while nickel and chromium boost corrosion resistance, toughness, and high-temperature performance.
High-strength low alloy (HSLA) steel
High-strength low-alloy (HSLA) steel, also known as micro-alloyed steel, is known for its excellent strength and resistance to atmospheric corrosion. Commonly hot-rolled or cold-rolled, HSLA steel includes various types—such as weathering, acicular ferrite, pearlite-reduced, dual-phase, control-rolled, and micro-alloyed ferrite-pearlite steel. While HSLA offers high strength, it can be more difficult to form, though elements like zirconium or calcium can be added to improve machinability.
Maraging Steel
Maraging steel is a special low-carbon alloy known for its exceptional strength, toughness, and ductility. Unlike most steels, it is hardened through the precipitation of intermetallic compounds—primarily Ni3Mo, Ni3Ti, Ni3Al, and Fe2Mo—rather than by carbon. Maraging steel is commonly used in aerospace, tooling, and high-performance equipment requiring superior durability.
Tool Steel
Tool steel refers to a group of carbon and alloy steels designed for exceptional hardness, toughness, and wear resistance—ideal for making tools, machine dies, and hand tools. These steels can perform well under high temperatures. We’ll dive deeper into tool steel in a separate section.
Stainless Steel
Stainless steel is one of the most popular and corrosion-resistant types of alloy steel worldwide. It's primarily made from iron, carbon, and key elements like nickel, chromium, and molybdenum, which make up about 11–30% of its composition. We’ll explore stainless steel in more detail in a separate section.
High-alloy Steel
High-alloy steel contains more than 8% alloying elements, offering outstanding strength and excellent resistance to corrosion. While it can be more expensive and harder to machine, its toughness and durability make it ideal for automotive, structural, chemical processing, and power generation applications.
Advanced High-Strength Steel
Advanced high-strength steel (AHSS) is commonly used in the automotive industry to reduce vehicle weight while maintaining high strength. AHSS is also easy to form with techniques like sheet metal bending and metal stamping, making it a reliable choice for complex part designs.
Tool Steels
Tool steels are hard, tough, and wear-resistant metals that won’t soften at high temperatures. Due to these properties, they’re ideal for making tools, hence their name.
Tool steels are specially engineered carbon and alloy steels known for their hardness, toughness, and resistance to wear—qualities that make them perfect for making cutting tools, dies, and hand tools. These steels keep their strength at high temperatures and are available in several categories based on their unique properties and alloy composition.
- Cold work tool steels
- Hot work tool steels
- High-speed tool steels
Tool steels usually contain 0.7–1.5% carbon by weight, but some grades can range from 0.2% up to 2.1%. Higher carbon levels increase strength and hardness, but also make the steel more brittle and harder to weld.
When cold-worked, tool steels achieve a Rockwell hardness of about 60–62 HRC, though some can reach as high as 66 HRC. Tool steels are heat treatable, and the exact treatment depends on the steel’s specific composition.
Tool steels are typically made with electric arc furnaces (EAF), but that's t the only way to fabricate tool steels.
| Fabrication Method | Description |
| Annealing | Annealing is a heat treatment process that makes steel easier to work with and less brittle. The steel is heated to a specific high temperature, held there for a set time, and then slowly cooled. This changes its internal structure, improving flexibility and workability. |
| EAF | Recycled steel scrap is melted and purified in a furnace. Alloying elements are carefully added to achieve the desired properties, while chemicals help control oxidation and remove impurities. The molten steel is then poured into large molds—called ingots—and gradually cooled for further processing. |
| Electroslag Refining (ESR) | This process melts the metal slowly and evenly, resulting in a smooth, dense, and non-porous surface. |
| Hot or Cold Drawing | This method shapes smaller or custom tools with high precision. Because these steels are not very ductile, the process uses several heating cycles up to 1000°C, but cold drawing is done in just one light pass to avoid breakage. |
| Powder Metallurgy | Metal powders are pressed and heated (sintered) until they become solid and dense, creating high-quality steel components with minimal porosity. |
Types of Tool Steels
Tool steels undergo a hardening process that’s determined by their composition, and this is how they’re commonly organized.
The table below lists key properties for each type of tool steel, as well as common grades, and a description of each type can be found below that.
| Type | Common Grades | Carbon % | Other Elements | Working Temp. | Melting Temp. |
| High-Speed Steels (HSS) | M2, M4, T1, T15 | 0.7–0.85% | Chromium, tungsten, vanadium | 1100–1300°F | 2200–2600°F |
| Cold-Work Tool Steels | O1, O2, A2, A6, D2, D3, D6 | 0.9-2% | Vanadium, tungsten, manganese, molybdenum | 400–900°F | 2200–2500°F |
| Hot-Work Tool Steels | H42, H43, H21, H26 | 0.3-0.5% | Molybdenum, tungsten | 1100–1300°F | 2300–2500°F |
| Water-Hardened Tool Steels | W1, W2, W5 | 0.6-1.4% | Vanadium, molybdenum, manganese, silicone | 400–500°F | 2500–2600°F |
| Shock-Resisting Tool Steels | S1, S2, S5, S7 | 0.5-0.6% | Tungsten, molybdenum, chromium | 600–700°F | 2700°F |
| Mold Steels | P20, P21 | 0.3-0.4% | Molybdenum | 700–800°F | 2500–2600°F |
| Special Purpose Tool Steels | F1, F2, L6, L7 | 0.7-1.25% | Tungsten, chromium, nickel, molybdenum | 700–1000°F | 2500–2600°F |
High-Speed Tool Steels
High-speed steels (HSS) stay hard even at very high temperatures, making them ideal for fast cutting and high feed rates. HSS is commonly used for cutting tools, saw blades, drills, and other tools that need to hold their edge. The addition of tungsten and vanadium provides excellent abrasion resistance.
High-speed steels can be further sorted into the following sub-types, based on the additional alloying elements.
Molybdenum-based (M)
Molybdenum-based high-speed steels harden at lower temperatures and aren't as hard as tungsten-based types, but they offer improved durability and toughness. Depending on the grade, the molybdenum content ranges from 5 - 10%.
Tungsten-based (T)
This property allows HSS to stay hard at high temperatures, ensuring precision machining even when cutting the hardest materials. Depending on the grade, the tungsten content ranges from 12 - 18%.
Cold-Work Tool Steels
This group includes three main sub-types (detailed below), all of which offer moderate hardness, excellent wear resistance, and reliable hardenability. They are ideal for producing larger parts or components that must be hardened with minimal distortion.
High Carbon and Chromium (D)
These steels are also air-hardening, making them a top choice for long production runs that require reliable performance and consistent hardness. All grades have approximately the same amount of carbon and chromium contents (see above table).
Oil Hardening (O)
These steels are strong, abrasion-resistant, and ideal for manufacturing thread-cutting chasers, arbors, bushings, and die blanking tools. In addition to a roughly 1% carbon content, the other key alloying element is manganese.
Air Hardening (A)
These steels are air-cooled, offer low distortion (especially grade A6), and are both tough and easy to machine. They’re commonly used in arbors, blanking dies, and die bending applications. Alongside the 0.95-1.1% carbon content, these steels have approximately 5% chromium.
Hot-Work Tool Steels
Used to make lots of tools other than cutters, H-grade boasts the ability to work well in high temperatures for long stretches at a time. It’s low carbon with a good amount of alloying metals in it. There are three types in this category:
Chromium-based (H1-H19)
These steels come with a 5% chromium content and are commonly used for cold heading die casings and for hot extrusion processes involving magnesium and aluminum.
Tungsten-based (H20-H39)
These steels are often chosen for cold heading die casings and for hot extrusion processes with magnesium and aluminum, thanks to their strong performance and reliability. Tungsten comprises anywhere from 9-12% of the grade's composition.
Molybdenum-based (H40-H59)
These steels are frequently used in cold heading die casings and hot extrusion processes for magnesium and aluminum due to their strength and reliability. Molybdenum makes up 1-2% of the material's composition.
Water-Hardened Tool Steels
This high-carbon tool steel has lower hardenability and requires water quenching, which can make it more prone to cracking or warping. It's an affordable choice with limited heat resistance and is mainly used for basic tools like reamers, embossing tools, and cutting blades.
Shock-Resisting Tool Steels
This steel is built for high-stress, low-temperature environments. It offers excellent impact toughness, moderate heat resistance, and lower abrasion resistance. Common applications include chisels, collets, and shearing blades.
Mold Tool Steels
This type of steel is primarily used to create molds for manufacturing plastic products and parts. is primarily used to create molds for manufacturing plastic products and parts.
Special Purpose Tool Steels
These tool steels are premium materials—best reserved for applications where no other steel performs as well. With minimal alloying and little required treatment, they’re highly specialized. Special-purpose tool steels come in two main categories, which we describe below.
Low alloy
This tough steel is commonly used to make bearings, clutch plates, rollers, wrenches, cams, and collets.
Carbon- and tungsten-based (F)
This group of steels is water-hardening, offering high wear resistance but limited shock resistance and poor performance at high temperatures. They are commonly used for paper-cutting blades, broaches, burnishing tools, and plug gauges.
Stainless Steel
Stainless steel is best known for its strength, corrosion resistance, and aesthetic appearance. Its most defining feature, a minimum chromium content of 10.5%, which creates a chromium oxide layer that protects against oxidation and improves its strength and durability.
While stainless steel is a universal metal, naming conventions are not. Here are the different names for stainless steel standards that are used around the world.
- International Organization for Standardization (ISO) 15510
- European Standard (EN)
- German Standard (DIN)
- Chinese National Standard (GB)
- British Standard (BS)
- Japanese International Standard (JIS)
Stainless steel grades are made by combining chromium and nickel, in varying amounts, to medium and/or low-carbon steels; they are then categorized by their micro, or crystal, structure and composition. The three main crystalline structure groups are austenitic, ferritic, and martensitic.
| Austenitic | Ferritic | Martensitic | |
| Composition | Minimum of 16% chromium and 6-8% nickel | High chromium content of 10.5% to 30%, low carbon, minimal or no nickel | 12% - 18% chromium and high carbon content (0.1 – 1.2%) |
| Microstructure | Face-centered cubic (FCC) structure – similar to high-temperature phase of iron (austenite) | Body-centered cubic (BCC) structure – similar to pure iron (ferrite) | Body-centered tetragonal (BCT) structure |
| Grades | 201, 202, 205, 301, 302, 303, 304, 305, 308, 309, 310, 314, 316, 317, 321, 330, 347, 348, 384 | 430, 434, 409, 439, 444 | 403, 410, 414, 431, 422, 420, 416, 440 |
Austenitic Stainless Steel
Of the stainless steel types, austenitic is the most common in terms of the number of relevant grades. As a material family, austenitic stainless steels are best known for their corrosion resistance, excellent ductility, and strength in high-temperature environments.
These stainless steels are primarily composed of iron, with chromium and nickel acting as the main alloying agents.
Due to its strength and corrosion resistance, austenitic stainless steels are used across many industries and in numerous applications, including:
- Implants, prostheses, and general hospital equipment
- Boiler tubes and heat exchangers for power generation
- Aircraft exhaust systems, turbine blades, coolant tubing, landing gear components
These are the typical mechanical and chemical properties for the most common austenitic stainless steels:
| Mechanical Property | Typical Values |
| Yield Strength MPa | 205-215 |
| Tensile Strength MPa | 505-520 |
| Elongation at fracture | 40-70% |
| Hardness (Brinell) | 201-217 |
| Bulk Modulus GPa | ~160 |
| Density g/cm³ | 8.00 |
| Chemical Property | Typical Values |
| Carbon | <0.08% |
| Nickel | 8-22% |
| Chromium | 16-26% |
| Heat tolerance | 870 – 925 °C |
| Acid tolerance | Moderate |
| Chloride tolerance | Low |
Ferritic Stainless Steel
The ferritic branch of the stainless steel family is characterized by its high chromium content, which is typically 10.5% to 30%. This amount of chromium gives ferritic stainless steels fantastic corrosion resistance and thermal conductivity.
Ferritic stainless steels are commonly used in applications that require durability and resistance to corrosion and high temperatures, including:
- Heat exchangers
- Boiler tubing
- Chemical processing equipment
- Structural components
The typical mechanical and chemical properties for ferritic stainless steels are shown in the following tables.
| Mechanical Property | Typical Values |
| Yield Strength MPa | 205-275 |
| Tensile Strength MPa | 415-450 |
| Elongation at fracture | 22% |
| Hardness (Brinell) | 72 |
| Bulk Modulus GPa | 220 |
| Density g/cm³ | 7,700 |
| Chemical Property | Typical Value |
| Carbon | 0.12% |
| Nickel | 0-0.5% |
| Chromium | 10.5-30% |
| Manganese and Silicon | Max 1.0% |
| Heat Tolerance | 815 – 817 °C |
| Acid Tolerance | Moderate |
| Chloride Tolerance | Low |
Martensitic Stainless Steel
Like other grades, martensitic stainless steel is known for its hardness, corrosion resistance, and strength. It can be further hardened and strengthened through heating and aging processes.
Martensitic stainless steels are commonly used in applications that require strength, hardness, and corrosion resistance, including:
- Bushings
- Bearings
- Valves
- Fasteners
- Surgical instruments
These are the mechanical properties of martensitic stainless steels, broadly speaking.
| Mechanical Property | Typical Values |
| Yield Strength MPa | 205-275 |
| Tensile Strength MPa | 415-450 |
| Elongation at fracture | 22% |
| Hardness (Brinell) | 72 |
| Bulk Modulus GPa | 220 |
| Density g/cm³ | 7,700 |
