What are the Different Types and Grades of Steel?

Introduction

Steel is everywhere. Many items in our daily lives, from high-rise buildings to automobile bridges, and even to everyday kitchen utensils and tableware, are inseparable from steel, a basic material. However, despite the wide application of steel, most people are not familiar with the different types and grades of steel, and it is difficult to distinguish the differences between them.

This article will introduce the main types of steel in detail, including common types such as carbon steel, alloy steel, and stainless steel. At the same time, we will also explain the specific classification standards and logic of steel grades to help you clearly understand the performance and use differences between different types of steel.

By reading this article, you will be able to more accurately identify and select steel that suits your needs, thereby improving the quality and efficiency of your project, avoiding losses or risks caused by incorrect material selection, and making you more professional and confident in your work and life.

Main Types of Steel

Based on the differences in main components, we divide steel into carbon steel, alloy steel, and stainless steel. Next, we will discuss these three types of steel.

Carbon Steel

Carbon steel is a type of steel with a carbon content between 0.05% and 2.1%, and very little content of elements other than iron and carbon. Carbon steel is the most produced of the above four types of steel.

The definition of carbon steel from the American Iron and Steel Institute (AISI) states:

• No minimum content is specified or required for chromium, cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium, zirconium, or any other element to be added to obtain a desired alloying effect;
• The specified minimum for copper does not exceed 0.40%;
• Or the specified maximum for any of the following elements does not exceed: manganese 1.65%; silicon 0.60%; and copper 0.60%.

According to the specific carbon content, carbon steel is divided into low carbon steel, medium carbon steel and high carbon steel. Generally speaking, the higher the carbon content of carbon steel, the higher its hardness and strength. However, the ductility and toughness of carbon steel with high carbon content will decrease, and the higher hardness and strength will also increase the difficulty and cost of welding. And the higher carbon content will also cause the melting point of the metal to decrease (for details, please refer to the analysis of the effect of carbon content on melting point in this article: Ultimate Guide to Melting Points of Metals.)

(Here is an additional explanation of the classic “impossible triangle” of metal materials. The triangle of metal materials refers to the strength, plasticity and stability of the material, and the main discussion is the performance limit of the material, which is a scientific problem. The impossible triangle of metal materials means that it is difficult for the material to achieve the best of these three points at the same time. Generally speaking, high-strength materials mean poor plasticity and stability, and high-plasticity materials mean poor stability of the material.)

According to the American AISI/SAE standard, the classification definitions of low carbon steel, medium carbon steel and high carbon steel are as follows:

Low Carbon Steel

Low carbon steel is also called mild steel, with a carbon content of 0.05% to 0.15%. Because of the lower carbon content, low carbon steel is relatively soft, has higher toughness and ductility, and has lower processing difficulty and cost in material forming. Common low carbon steel materials include AISI 1008, 1010, 1018, ASTM A36, etc. These low carbon steel material grades are mainly used to produce some cold-formed parts, such as bolts and rivets; welded structures such as bridge pipes, etc.;

Medium Carbon Steel

The carbon content of medium carbon steel is about 0.3-0.5%. Compared with low carbon steel, medium carbon steel can have moderate strength and ductility toughness, better cutting performance, and is not easy to stick to the knife; the hardness of the material can be increased by quenching. AISI 1045, 4130, SAE 1541, etc. are relatively common medium carbon steels, mainly used to produce transmission parts, high-strength fasteners, etc.

High Carbon Steel

The carbon content of high carbon steel is about 0.6% to 1.0%. The higher carbon content makes it harder than medium carbon steel, but high hardness generally means greater brittleness and poor toughness of the material. The material itself cannot be directly produced by cold working. It needs to be annealed first and then lightly cold worked. In addition, high carbon steel is prone to cracking during welding. It needs to be preheated first and softened to a certain extent before welding, and post-weld annealing is required to avoid cracking. AISI 1060, 1095, and 52100 are all common high carbon steel material grades. Because of their high hardness and wear resistance, they are widely used in the production of cutting tools and wear-resistant parts.

Alloy Steel

Compared with carbon steel, alloy steel adds many kinds of alloy elements on the basis of iron and carbon to improve the overall strength, corrosion resistance, high temperature and high pressure resistance, mechanical properties, etc. of the material. When the alloy content exceeds 5%, this alloy steel is called high alloy steel; when the alloy content is between 1% and 5%, this material is called low alloy steel.

Cr, Ni, Mo, V, W, etc. are all common alloying elements. The hardness and corrosion resistance of the material can be significantly improved by adding chromium (Cr); the toughness of the material can be improved by adding nickel; the strength of the material at high temperatures can be improved by adding molybdenum. Therefore, alloy steel can provide solutions for industry challenges such as structural applications, high temperature applications, and applications in corrosive environments.

ASTM A572 Grade 50, EN 10025 S355J2, AISI 4140, AISI 4340, AISI 5160, etc. are all common alloy steel material grades.

The applications of alloy steel include structural components, high-temperature equipment, corrosive-resistant engineering, and especially the automotive industry. In automotive manufacturing, many stamping parts are produced from high-quality carbon steel and alloy steel grades such as SPCC, DC01, Q235, Q355, and S355 to ensure durability and safety. To better understand how these materials are applied in real automotive products, you can explore SHAOYI Automotive Metal Stamping Parts, where SHAOYI demonstrates the use of alloy steel in precision automotive components.

Stainless Steel

Strictly speaking, stainless steel is a branch of alloy steel. The most notable alloying feature of stainless steel is that it contains at least 11% chromium, so stainless steel can also be called high-alloy steel. In the above discussion, we mentioned that adding chromium can make the material have higher hardness and corrosion resistance. Stainless steel has at least 11% chromium content, so stainless steel is often used as a solution to corrosion challenges. For example, 304 and 316 are the two most common stainless steel materials in our industrial production. They can both provide excellent corrosion resistance and high temperature and high pressure resistance. Stainless steel is divided into the following types according to its microstructure:

Austenitic Stainless Steel

Austenitic stainless steel is the largest family of stainless steel with a face-centered cubic crystal structure. Common austenitic stainless steels are mainly 200 series stainless steel and 300 series stainless steel.

200 series stainless steel is a chromium-manganese-nickel alloy. By adding manganese (Mn) and nitrogen (N) elements to replace the relatively high-cost nickel (Ni), the stability of the austenite structure can be maintained, and the yield strength of 200 series stainless steel is 50% higher than that of 300 series stainless steel. However, the corrosion resistance of 200 series stainless steel is relatively poorer than that of 300 series stainless steel. Common 200 series stainless steel grades are 201 and 202. Due to their higher strength and lower cost, they are generally used in applications with lower requirements for corrosion resistance, such as daily stainless steel consumer products, interior decoration pipes, door and window frames, etc.

300 series stainless steel is a chromium-nickel alloy and is also our most common stainless steel material. 300 series stainless steel materials have excellent corrosion resistance, welding performance and high temperature and high pressure resistance. Common 300 series stainless steel materials include 304, 316, 321, 347, etc., which can provide solutions for high-demand industries such as marine engineering, medical equipment, pharmaceutical equipment, and chemical pipelines.

Ferritic Stainless Steels

Ferritic stainless steels Ferritic stainless steels have a body-centered cubic crystal structure and are magnetic. The chromium content is between 10.5% and 27%, but compared with austenitic stainless steel, the nickel content of ferritic stainless steel is extremely low, so the cost is also much lower. Common ferritic stainless steels are 409, 429, 430 and 446, which are often used in the production of mildly corrosive applications such as automobile exhaust pipes, construction and structural applications.

Martensitic Stainless Steels

Martensitic stainless steels have a body-centered tetragonal crystal structure and are magnetic. By adjusting the content of elements such as Cr, C, and Mo in martensitic stainless steels, they can be divided into three categories:

Stainless Steel Engineering Steels

Stainless steel engineering steels have moderate corrosion resistance and high toughness, such as 410, 420. These stainless steel materials can be used to produce turbine blades, shafts, fasteners, etc.;

Stainless Steel tool steels

Stainless steel tool steels, such as 440C, have ultra-high hardness and wear resistance and can be used to produce bearings and abrasives;

Creep-Resistant Stainless Steels

Creep-resistant stainless steels, such as 630/17-4PH, have high strength at high temperatures and are mainly used to produce aircraft engine components and nuclear power plant fasteners.

Duplex Stainless Steels

Duplex stainless steels are stainless steels that have both austenite and ferrite phases, with an ideal ratio of 50:50, but commercial alloys may have a ratio of 40:60. Duplex stainless steels contain 19%-32% chromium and up to 5% molybdenum, both of which are higher than austenitic stainless steels, but the nickel content is lower than austenitic stainless steels. The yield strength of duplex stainless steels is about twice that of austenitic stainless steels. Common duplex stainless steels include: duplex 2205 (S32205), duplex 2507 (S32750), which can be used to produce desalination equipment, submarine oil and gas pipelines, chemical storage tanks/reactors, etc.

Precipitation Hardening Stainless Steels

Precipitation hardening stainless steels can obtain higher strength through precipitation hardening. They are divided into three categories according to the crystal structure.

Martensitic Precipitation Hardening Stainless Steels

Martensitic precipitation hardening stainless steels exhibit martensitic structure at room temperature under solution annealing and precipitation hardening conditions. Due to its ultra-high strength, good corrosion resistance and formability, it is widely used in high-end fields such as aerospace, energy, and military industry.

Representative martensitic precipitation hardening stainless steel material grades include:

17-4 PH (UNS S17400), because of its high strength and excellent fatigue resistance, it is mainly used to make engine brackets and landing gear components;

15-5 PH (UNS S15500), because of its excellent high-temperature oxidation resistance, it is widely used to make rocket engine casings and satellite brackets;

Custom 450 (UNS S45000) has excellent characteristics such as radiation resistance and stress corrosion resistance, and is used to make nuclear reactor control rod drive mechanisms;

Custom 465 (UNS S46500), with strength similar to titanium alloys and lower cost, is often used to make aircraft fasteners and door hinges.

Semi-Austenitic Precipitation Hardening Stainless Steel

Semi-austenitic precipitation hardening stainless steel is initially austenitic in the solution annealed state for ease of manufacturing, but then transforms to martensite to provide higher strength and precipitation hardening. Due to its multi-stage adjustable mechanical properties, it is widely used in aerospace, precision instruments and high-end industrial fields.

Representative semi-austenitic precipitation hardening stainless steels include:

17-7 PH (UNS S17700) is not magnetic, but has high strength and fatigue resistance, and is often used as a material solution for aircraft structural parts;

15-7 PH (UNS S15700) has excellent resistance to stress corrosion cracking and can be used to manufacture rocket fuel tanks for spacecraft;

AM-350 (UNS S35000) has high hardness and is resistant to ablation, making it an ideal material for making firearm firing pins and missile seeker housings;

AM-355 (UNS S35500) is used to make corrosion-resistant pump shafts for chemical valves because of its high hardness, but it should be noted that AM-355 itself has poor corrosion resistance, so it is generally used for mildly corrosive applications.

Austenitic Precipitation Hardening Stainless Steel

Austenitic precipitation hardening stainless steel is austenitic at room temperature under solution annealing and precipitation hardening conditions. With its high temperature strength, corrosion resistance and non-magnetic properties, austenitic precipitation hardening stainless steel is widely used in aerospace, energy and high-end industrial fields.

Representative alloys include:

A-286 (UNS S66286) has high resistance to high temperature oxidation and can be used to make jet engine parts such as turbine disks, bolts, and combustion chamber liners;

Discalloy (UNS S66220) is resistant to hydrogen sulfide corrosion and has high strength, and is the project material for the production of deep well drilling tools.

(Please note that the increase in numbers for the 200 series, 300 series, and 400 series mentioned above does not represent a progressive relationship in performance, and the stainless steel models in the same series, such as 304 and 316, cannot represent a simple performance improvement.)

Other Steel Types

In addition to the above classification of steel types by material, steel types can also be classified according to different dimensions:

By form: profiles, plates, pipes, wires, strips, bars;

Finishing method: hot-rolled steel, cold-rolled steel, forged steel, cast steel;

International standards: ASTM, DIN, EN, GOST, JIS, etc.;

Heat treatment: normalizing, tempering, annealing, quenching;

Application: structural steel, tool steel;

Deoxidation Degree: Rimmed Steel, Killed Steel, Semi-killed Steel

In the above section, we have learned about the types of steel. Next, we will elaborate on the steel grades of different types of steel.

Steel Grade Standards

Before introducing specific material steel grades, we must first understand a concept, that is, steel grade standards. Each country has different steel grade standards. The following are relatively common international material standard types:

For alloys in general (including steel), unified numbering system (UNS) of ASTM International and the Society of Automotive Engineers (SAE).

American steel grades : AISI/SAE steel grades standard

British Standards

International Organization for Standardization (ISO)

European：EN standards

Japanese : Japanese Industrial Standards (JIS) standard and NK standard

Germany : DIN standard

China : GB standard

Russia : GOST standard

France : AFNOR standard

Steel Material Grade Numbering Systems

In the introduction of the above steel material types, there are some examples of material steel grades. We will find that different materials belong to different material grade coding systems in different standards. In this part, we will use the American steel standard as an example to explain the classification logic of these material grade numbering systems.

Carbon Steel And Alloy Steel Numbering Systems

In the SAE/AISI numbering system, the material grade of carbon steel and alloy steel is generally represented by four digits.

The first digit indicates the main alloying element type of the material;

The second digit indicates the highest grade (tg) element;

The last two digits indicate the carbon content, expressed as a percentage of weight (basis point).

Below are two tables about the meaning of carbon steel and alloy steel number numbers for reference.

First Digit of SAE/AISI Carbon and Alloy Steel Grade

Second Digit of SAE/AISI Carbon and Alloy Steel Grade

Stainless Steel Numbering Systems

Unlike the 4-digit numbers of carbon steel and alloy steel (such as 1045, 4140, etc.), stainless steel numbers generally consist of 3 digits (such as 304, 316, etc.). The first digit of the stainless steel number is used to indicate the stainless steel series. The following 2 digits do not represent specific performance differences or composition differences, and have no special meaning. Instead, they are a historical steel number code used to distinguish different stainless steel materials. In addition to the three digits, the stainless steel number may be followed by some special letter suffixes to indicate that the performance of the material has been improved in some aspect.

Common Stainless Steel Series:

100 Series:

Type 102;

200 Series – austenitic chromium-nickel-manganese alloys:

Type 201;

300 Series – austenitic chromium-nickel alloys:

Type 304, Type 309, Type 310, Type 316, Type 321, Type 321, Type 347, etc.;

400 Series – ferritic and martensitic chromium alloys:

Type 409, Type 410, Type 416, Type 420, Type 430, Type 439, Type 440, etc.;

900 Series – austenitic chromium-molybdenum alloys:

Type 904

Common Stainless Steel Grades With Letter Suffix Meanings

(Attached is the chemical composition table of each steel grade to facilitate comparison of composition differences)

L: L stands for low Carbon, lower carbon content can effectively improve weldability and reduce intergranular corrosion. Common stainless steel grades include 304L, 316L, and 317L;

S: S is another form of low carbon. S is often found after the steel grade of high chromium-nickel austenitic steel. Common stainless steel grades include 309S and 310S.

N: N means the addition of nitrogen (N), which can effectively improve the strength of the material. Common stainless steel grades include 304N and 316N;

LN: Indicates the addition of nitrogen (N) on the basis of low carbon, which can enhance the strength of the material and improve corrosion resistance. Common steel grades include 201LN, 304LN, 316LN, 347LN;

LM: Indicates that more molybdenum (M) is added on the basis of low carbon, which can effectively improve the material’s resistance to pitting and crevice corrosion (especially in chlorine-containing environments, such as seawater or chemical media). Common steel grades include 317LM;

LMN: indicates a lower carbon content, with the addition of nitrogen (N) and molybdenum (M). The most common stainless steel grade is 317LMN. Nitrogen solid solution strengthening increases the yield strength of 317LMN by about 20-30% compared to 317L, making it suitable for high-pressure equipment. The combination of low carbon + nitrogen reduces the risk of sensitization in the heat-affected zone of welding, and no annealing is required after welding;

H: H stands for High Temperature Service, indicating that this material has been specifically improved for high temperature environments. Common stainless steel grades include: TP304H, TP309H, TP310H, TP316H, TP321H, TP347H, TP348H;

Ti: Indicates that titanium (Ti) is added to this material. It can improve the stability of stainless steel materials at high temperatures and avoid intergranular corrosion. Common stainless steel grades: 316Ti.

Cb: Indicates that niobium (Cb) is added to the material. The purpose of adding this material is to prevent intergranular corrosion at high temperatures. Niobium can form niobium carbide before chromium and carbon, preventing the loss of chromium content at high temperatures from causing a decrease in material strength. Common stainless steel grades include TP309Cb and TP310Cb.

Common Steel Material Grades

Common Carbon Steel Grades:

ASTM, AISI, SAE:

ASTM A36, AISI/SAE 1018, 1020, 1045, ASTM A53 Gr. A/B, ASTM A106 Gr. A/B/C;

JIS:

SS330, SS400, SS490, S10C, S20C, S45C, STKM 11A, STKM 13A;

EN:

EN 10025-2 S235JR, S275JR, S355JR;

EN 10083-2 C22, C35, C45;

EN 10216-2 P235GH;

EN 10210 S275J2H, S355J2H;

GB：

Q195、Q215、Q235、Q255、Q275

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Common Alloy Steel Grades:

ASTM, AISI, SAE:

AISI/SAE 4140, 4340, AISI/SAE 8620, ASTM A182 F11, F22, ASTM A387 Gr. 11, Gr. 22;

JIS:

SCM415, SCM420, SCM440, SNCM220, SNCM420, SNCM439, STB 410, STBA 20, STBA 22;

EN:

EN 10083-3 34CrMo4, 42CrMo4;

EN 10083-3 31CrMoV9, 34CrNiMo6;

EN 10084 16MnCr5, 20MnCr5;

EN 10216-2 13CrMo4-5, 10CrMo9-10;

Common Stainless Steel Grades:

ASTM, AISI, SAE:

AISI 304, 304L, 316, 316L, 410, 430, 2205, 17-4 PH;

JIS:

SUS 304, SUS 304L, SUS 316, SUS 316L, SUS 410, SUS 430, SUS 329J3L, SUS 329J4L, SUS 630;

EN:

EN 10088-2 / 3 1.4301, 1.4307, 1.4401, 1.4404, 1.4006, 1.4016, 1.4462, 1.4542.

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