Alloy 4130: A Common Choice for Automotive

4130 steel is commonly used in the automotive industry due to its excellent combination of mechanical properties and weldability.

Strength & Durability

4130 steel offers high strength and excellent durability, making it well-suited for components that need to withstand heavy loads, stress, and impact. This is particularly important in automotive parts like chassis frames, suspension components, and roll cages.


While 4130 steel is strong, it is also relatively lightweight compared to some other high-strength materials. This makes it advantageous for reducing the overall weight of a vehicle, which can improve fuel efficiency and handling.

Weldability & Machinability

4130 steel can be easily welded, which is essential for the manufacturing and repair of automotive components. Welding allows for the fabrication of complex structures and the modification of existing parts.

This type of steel is also known for its good machinability, making it easier to machine into intricate shapes and components used in automotive applications.

Corrosion & Fatigue Resistance

While not as corrosion-resistant as stainless steel, 4130 steel can still resist rust and corrosion to a reasonable extent. This is important for automotive components that are exposed to environmental conditions.

4130 steel exhibits good fatigue resistance, which is crucial for components subjected to cyclic loading, such as suspension parts and axles.

Heat Treatment

4130 steel can be heat-treated to enhance its mechanical properties further. This allows for customization to meet specific automotive requirements, such as achieving higher hardness or strength.


4130 steel is cost-effective when compared to some other high-strength materials, making it an attractive choice for various automotive components.

Common automotive applications of 4130 steel include suspension components (such as control arms and sway bars), chassis frames, roll cages, steering components, and various structural elements. Its versatility and favorable combination of properties make it a valuable material in the automotive manufacturing and performance industries.

The Five Types of Carbon Steel Round Tube

The Five Types of Carbon Steel Round Tube

When it comes to steel manufacturing, one type has the lion’s share of the market: by volume, carbon steel accounts for 90% of the steel produced each year. The increasing growth of the oil and gas industry means carbon steel tube and pipe are in constant demand, with over 50% of all steel tube and pipe being used for petrochemical production. Carbon steel’s ability to withstand corrosion and extreme environmental conditions makes it an excellent choice for parts used in oil and gas processing, from drilling to refining and transport.

Round Tube
While tube may look similar to pipe, the two shapes are used for different purposes. Pipe is used to transport substances such as oil and gas, while tube is used as a structural element. For this reason, tube is generally made to be stronger and more robust than pipe. Tube can also come in a variety of shapes such as round, square, or rectangular. When carbon steel round tube is needed, there are five types available for use:

Electric Resistance Welding (ERW)
Produced from cold-formed coil made of low carbon steel, this method uses electric resistance welding to form it into round tube. The welding itself can be done in several ways, but most often through an automated process. This means high quality ERW tube can be produced at a low manufacturing cost, making it a very popular choice for customers.
ERW tube’s affordability and versatility leads to it being used in many applications including automotive frames, supports and stands, and internal machine components.

Cold Drawn Seamless (CDS)
CDS tube starts with steel billets, heated to an extremely high temperature and pierced with machinery to create the tube’s hole. The steel is then rolled to elongate the tube and shrink its diameter, and cooled once it has been formed to the desired shape. This process results in very sturdy tube with thick walls and a smooth surface.
Because CDS tube is not only strong but aesthetically attractive, it is often used for visible automotive parts such as roll bars and frames. Other common uses include hydraulic cylinders, infrastructure columns, and boiler tubing.

Drawn-Over-Mandrel (DOM)
This type of tubing is produced through machining with the use of mandrels. A mandrel is a taper bar, used to gradually increase the diameter of a part placed on it – such as the small mandrels used by jewelers to resize and widen rings. For round tubing, steel coil is sheared and joined by welding, then finished by using mandrels. This machining creates high-quality tube with excellent levels of hardness, strength, and consistency.
DOM tube is used extensively in the automotive industry, found in parts including shock absorbers, dampeners, and seat frames. It is also regularly used in hydraulic parts such as pumps and cylinders.

This type is manufactured to meet the necessary requirements of hydraulic lines, including the strength to withstand the stress of containing pressurized fluids. Similar to CDS, hydraulic starts with carbon steel bars which are heated, pierced, and rolled until it results in sturdy tubes. Hydraulic tube has a very shiny and bright finish which makes it appealing for its aesthetic quality as well as its overall strength and utility.
Due to its high degree of strength, hydraulic tube can also be used for applications where tubes will be bent or fitted together.

Hot Finished
Also known as seamless tube, this type is made by piercing and rotating an extremely hot piece of carbon steel. The rotation creates the shape, and it then goes through a series of mills to reduce the tube’s diameter and wall thickness. This fairly low-cost process creates a versatile, easily machinable tube. However, hot finished tube sizing tends to be less precise than other types, and its finish looks rougher. For this reason, hot finished tube is typically found in applications where aesthetics or size variance are unimportant.
Seamless tube can be found in heavy-duty uses such as construction and drilling equipment, pillars, and wind turbine components.

Suitability of Welding Carbon Steel

Carbon steel is just as described: a steel alloy containing added carbon, with the carbon making up 0.05% to 2.0% of its weight. This percentage range means carbon steel is a sprawling category, covering many different types of steels with varying levels of carbon. Steel with any other combination of alloying elements can be included in this category, so long as they contain carbon.
Clearly the many possible chemical compositions of carbon steel make it difficult to make blanket statements about this metal. Carbon increases the hardness and strength of steel, but the percentage of carbon added creates different results with the steel’s mechanical properties. Those properties then affect how the metal reacts to further processing such as welding. It is very important to understand the exact qualities of a selected carbon steel to produce a successful weld; doing otherwise risks metal damage or a weld that may fail later during use.

Carbon Content
The most important decision before beginning a weld will be the type of steel to use. Carbon steels are organized as three basic types:
• Low carbon steels: containing less than 0.30% carbon by weight
• Medium carbon steels: containing 0.30% to 0.60% carbon by weight
• High carbon steels: containing 0.61% to 2% carbon by weight

Each of these groups will weld differently due to their carbon content. The higher the steel’s carbon level, the more prone it will be to weld cracking. Low carbon steels can be much more easily welded, which is why they are the typical choice for this process.. However, high carbon steels can be welded, provided extra care is taken with the more brittle material. Heating high carbon steel prior to the weld, as well as afterwards, will help prevent cracking. Additional filler metals may also be used with high carbon steel to create a better weld.

Carbon Equivalency
Once the type of carbon steel is selected, further determination of its weldability is done using the carbon equivalency formula. This formula examines what effect the other alloying elements besides carbon may have on a weld. The percentages of alloying elements are calculated as an additional degree of carbon – and that boosted carbon level translates into a steel considered more difficult to weld. As an example: using the formula means a medium carbon steel with no added manganese will be judged as easier to weld than the same carbon metal including manganese alloy.

Overall Chemical Composition
Even after selecting a lower carbon steel, and calculating an acceptable carbon equivalency, the overall chemical composition should still be reviewed. Some elements will just not take well to welding, even with a great deal of effort. Any amount of lead in carbon steel, for instance, will significantly raise the probability of weld cracks. Other common alloying elements such as sulfur or phosphorus can have the same effect, resulting in a weak or failed weld. While carbon steel with trace amounts of either sulfur or phosphorus can still be welded, the percentages must remain extremely low (approximately 0.05% or less) to avoid weld cracking.

Cooling Rate
The job is still not complete after creating a weld, because as it cools, cracking may develop. Carbon is again the main culprit here, due to it making the steel more brittle. With higher levels of carbon and equivalent alloys, the metal must be cooled at a slower rate to prevent cracks from occurring.
In addition to the steel’s carbon percentage, other factors must be accounted for during weld cooling. The thickness of the steel being welded will affect the cooling rate, and thinner material has a higher risk of distortion. The temperature where the weld is being performed is also important. In cold temperatures, preheating may be necessary even for lower carbon steels, while it can be performed without prior operations in warmer environments.

Buyers Guide To Carbon Steel

¬¬¬¬Six Questions when Buying Carbon Steel

Carbon steel is a widely used material, found in items from structural steel to kitchen knives. However, these industries do not necessarily use the same grade of steel. At its most basic, this metal group is made up of any steel alloy with added carbon. The carbon percentage will usually be somewhere between 0.05% to 2.0% of the metal’s overall weight.
In any chemical composition, a range of 0.05 to 2.0 is a significant margin. Steel is no different: when it comes to formulating steel alloys, the variance in carbon percentage has a transformational effect on the produced metal. Carbon strengthens and hardens the steel, but decreases its ductility. That means the higher the carbon percentage, the less flexible the steel becomes. A high-carbon steel grade put under high or repeated stress would be more brittle and liable to crack. A grade of steel with lower carbon content will be more ductile, but not nearly as strong.
So before starting a project with carbon steel, you should carefully consider the grade you select. It can make a big difference in the end result’s success. Reviewing these six questions beforehand can help in making your choice:

1. Will the carbon steel be machined?
Machining is a process where the parts and shapes are cut from the metal. Because lower carbon grades are relatively softer steel, they are more easily and efficiently machined. A high carbon grade can be used, provided the alloy’s chemical composition includes sulfur which improves the steel’s machinability. Without sulfur, the hardness of high carbon steel will result in major wear of the cutting tools.

2. Will the carbon steel be welded?
In general, the same grades of lower carbon steel more suited for machining can be more easily welded as well. High carbon steels can be used, but often require additional treatments before and after welding. And in contrast to machining, the steels grades containing sulfur are not recommended for use in welding. The sulfur in these alloys will have a higher risk of developing cracks at the weld join.

3. Does the carbon steel need to be heat-treatable?
When it comes to heat, a good rule of thumb is 0.3. Steels with a carbon content of 0.3% or higher can be heat treated easily. This is due to the carbon itself, which helps the formation of martensite crystallization within the steel, reinforcing its hardness and strength. Grades of lower carbon steels lack the carbon necessary for martensite formation, making heat treatments unsuccessful.

4. Does the carbon steel need good formability?
Due to the wide margin of carbon percentages across grades, it can be difficult to say which grades might be more formable than others. The selected grade is often dependent on the shape: rolled sheet requires a much more ductile type of steel, but forming pieces such as angle and beam can involve a wider grade range. Overall, the more ductile carbon steels – meaning, lower carbon grades – are much easier to form.

5. Does the carbon steel need high corrosion resistance?
Because steel’s main element is iron, it is vulnerable to oxidation leading to corrosion. This is an accepted fact that when using any grade of carbon steel, it will develop a certain amount of rust. In applications where corrosion resistance is a high priority, it may be better to consider using another material such as stainless steel instead. To minimize corrosion of carbon steels, they can be coated to create a barrier between the metal and its environment. This can go from involved processes such as galvanization or plating the metal to simply applying a coat of paint.

6. How strong a carbon steel is needed?
The steel’s application is crucial to deciding the strength needed for your metal. High carbon steel is incredibly strong, but if intended to be used for making small parts such as nuts and bolts, your needs would be better served by low carbon steel’s machinability. But while low carbon steel is more formable, it would be worth the greater effort when making tools to use high carbon steel for its hardness and durability. While it may be tempting to select the hardest and strongest material available, its actual use should be an important factor in selecting the right carbon steel.

The Differences between Carbon and Stainless Steels

In all likelihood, if someone were asked the difference between carbon and stainless steel, the answer would involve appearance: one is dull and one is shiny. That might sound simple, but it’s also true! While the finish of each steel is the most obvious difference, there are other, more significant ways they differ. Learning more about the characteristics of each steel type will help determine which steel is most appropriate for a project.

Corrosion Resistance
The most significant difference between the two is the high degree of corrosion resistance found in stainless steel. Both types of steel are vulnerable to corrosion due to their iron content, which reacts with oxygen to form rust. However, the addition of chromium in stainless steel alloy provides much more protection against corrosion. The chromium in stainless steel reacts more quickly with oxygen than iron, and the resulting chromium oxide forms a protective layer on the surface of the metal. The chromium oxide prevents further oxygen interaction with the metal, effectively stopping any continued corrosion.
Carbon steel alloys may also contain chromium, but not in the amounts found in stainless steel. This means carbon steel is vulnerable to the corrosive effects of rust, which leads to damaged metal unless regularly maintained. So in situations where corrosion resistance is a big concern, stainless steel will be the best choice.

Adding chromium as an alloying element in stainless steel not only boosts corrosion resistance, it is also the source of the metal’s distinctive shine. Carbon steel naturally has a flatter finish, and its vulnerability to corrosion leads to tarnishing and other discoloration. It can be sanded to smooth the metal and produce more shine, but unless some type of coating is applied to the polished carbon steel, the same rust and discoloration will develop.
Stainless steel, on the other hand, has a natural luster which polishing can increase to a mirror shine. Polishing also provides even more corrosion resistance to the metal, without the need for an additional protective coat. This is because any existing irregularities are sanded down during polishing, so corrosive particles are less likely to cling to the metal’s surface. For projects where aesthetics is an important factor, stainless steel may be preferable over polished or painted carbon steel.

Mechanical Properties
Both carbon and stainless steels are produced in multiple types and grades, so it can be difficult to make a clear distinction between the two kinds of steel. In general, stainless steels tend to be more ductile, while carbon steels have greater tensile strength. This is due to the carbon alloying percentage found in carbon steels. Carbon makes steel harder, to the point of becoming very strong and brittle with high-carbon steels.
However due to the variety of available carbon and stainless steels, these properties may not apply across the board. A low-carbon steel can be more ductile than certain types of martensitic stainless steel. Some stainless steel grades will be harder and with greater tensile strength than a low-carbon steel. Ultimately, the mechanical properties of any kind of steel should be considered for its specific use in a project.

As a general rule, stainless steel will be more expensive than carbon steel due to its alloying elements. Carbon steel may contain other elements, but is mainly made up of iron and carbon which are fairly affordable. Stainless steel is created with the addition of chromium, and also has higher amounts of alloying elements such as nickel and manganese. Each additional element to the stainless steel’s chemical composition increases the cost. For a lower budget project where aesthetics is a lesser priority, carbon steel will be the best way to go.

Selecting Tool Steel Grades

When it comes to industrial machinery such as drills, dies and cutting tools, tool steel is the favored choice. As you can tell by the name, it’s designed for this very purpose. High amounts of carbon and other alloying elements gives tool steel enhanced hardness and strength, qualities which allow it to weather the repeated stresses of manufacturing. But while all tool steel is tough, selecting the right grade of tool steel is important to ensuring you have the type best suited for the job. A good starting point is to first determine the exact purpose of the tool steel you plan to use:

1. Will it be doing work at low temperatures?
2. Will be doing work at high temperatures?
3. Do you intend to use it at high speeds?
4. Will the tool steel be involved in repeated impacts?
5. Will it be used for plastic molding?
6. What is your budget?

Low Temperature Work
For work performed at very low temperatures, the tool steel group known as cold work steel best fits the bill. All tool steels are very hard, but extreme hardness tends to be accompanied by increased risk of cracking. With extreme cold, metal can become even more brittle. So cold work steels are carefully quenched, using methods that allow the steel to retain some degree of flexibility. Quenching in oil (O-series), air (A-series), or adjusting the chemical composition to include more chromium (D-series) produces cold work steel that can perform well in low temperatures. While these cold work steels are pricier than water-hardened types, the mechanical benefits justify the higher cost.

High Temperature Work
Whatever the type of steel, any prolonged exposure to high temperatures will begin to affect its mechanical properties. As the temperature climbs, the atoms in the steel will increase their movement, creating structural changes within the metal. Because tools steels are already heat-treated prior to use, the application of more heat makes them even more vulnerable to structural changes. At worst, it can affect the steel’s crystal structure to the point of reversing the initial heat treatment. To avoid this, hot work steels are formulated with lower carbon and higher alloying content. The increased amount of molybdenum and tungsten produces a steel that can retain its hardness and wear resistance at extreme high temperatures.

High Speed Work
Tool steel used at high speeds are put under a great deal of pressure. High speed tool usage leads to increased friction, which means the steel will be exposed to both heavy wear and high temperatures. This means a metal must possess the durability of hot work steel, and even more resiliency to hold up to the friction. High speed tool steels typically include tungsten, chromium, and vanadium as their alloying elements to produce a very hard steel. This protects it against the pressure and abrasion of high speed work, while its hardness allows it to retain a sharp cutting edge during use.

High Impact Work
To undergo repeated major impacts, the necessary grade of tool steel must have a high degree of shock resistance. Tool steel is prized for its hardness, but that hardness means the metal can crack, chip, or lose its shape with impact. Shock resistant tool steels generally have a lower carbon content along with alloys such as silicon, sacrificing some hardness to give it more ductility and tensile strength. However, this does come at the cost of lower wear resistance. This means high impact tool steels are best suited for impacts only, rather than machinery that will experience more friction and wear.

Plastic Molding Work
The tool steels used for plastic molding are known as the P-series, or special purpose steels. These are much softer than the other types of tool steel due to alloying elements such as nickel, which impedes hardening during the forging process. While the hardness is decreased, P-series tool steel possesses enough malleability to allow it to be shaped into a variety of molding dies. After being heat treated, the tool steel molds can be used to produce plastic items. Theis grade of tool steels are rarely used for any other purpose, because the lengthy and complex manufacturing process makes it more costly to produce.

Cost of Tool Steel
As you can see, the more specialized the task of a tool steel, the more you should prepare yourself to spend. The price tag is well worth it: purchasing the right type of tool steel means it will perform better for its intended work and will last longer while doing it. Choosing the wrong type of tool steel can result in more frequent repairs or even replacements, both requiring an additional cost. However, for general usage not involving any extreme conditions, W-series tool steel will perform well. Due to being water quenched, these steels are the least expensive of all tool steels to produce or purchase. Hand tools, springs, and other small steel goods are typically made of this grade of tool steel.

Hot Rolled Steel Grades

When it comes to steelmaking, production can be divided into two basic groups: cold rolled and hot rolled steel. In earlier eras, molten steel was cast into blocks known as ingots. These ingots were convenient to stack and ship, and could be melted back down when needed for use. In current times, steel manufacturing is done on a massive and continuous scale. To make this process more efficient, manufactured steel is produced to be as close to a finished product as possible.
Newly forged steel emerges as a continuous slab of red-hot metal, which is then fed into a series of mills. The process is similar to a home pasta maker: with each consecutive rolling, you will end up with a thinner and thinner result. As the steel progresses through the mills, the metal remains hot enough to stretch and thin out into a long strip. Once rolled out to the desired thickness, it can be cut into shapes such as bars, or thinned enough to be rolled into coil.

Most Popular Grades
Hot rolled steel is available in several different grades, which are the standards set for a steel type. Generally, steels in North America conform to the standards set by the American Society for Testing and Materials (ASTM), or those set by the Society of Automotive Engineers (SAE). ASTM steel grades always begin with an “A”, which is the letter assigned to ferrous metals. SAE steel grades use a four-digit number for identification.

A36 Hot Rolled Steel
One of the most popular grades of hot rolled steel, A36 is a low carbon steel alloy. The low percentage of carbon within A36 steel means it is highly versatile: it can easily be formed, machined, or welded.
The low amounts of other alloying elements such as nickel and chromium make A36 steel just average in corrosion resistance, but also keeps the price relatively low. For this reason, it is widely used in applications where cosmetic appearance is not a priority. You will often find A36 hot rolled steel used for heavy duty construction and equipment manufacturing.
Common applications include:
• Bridge and building construction
• Automotive frames and trailers
• Agriculture equipment
• Oil and gas equipment

1018 Hot Rolled Steel Bar
Another popular choice of hot rolled steel is 1018, which is a similar grade to A36. A36 is often the top choice in manufacturing, but 1018 will be selected if the application calls for bar or strip steel. It is even lower in carbon percentage than A36, and this low carbon in 1018 allows for excellent formability. The low carbon level also allows 1018 to be a fairly ductile type of steel which can be easily bent and machined.
Common applications include:
• Gears
• Pins and studs
• Steel bar in square, rounded square, hexagonal and other shapes

1011 Hot Rolled Sheet and Plate
SAE 1011 is a strong, low-alloy form of hot rolled steel. Its low percentages of carbon and other alloying elements means this steel grade is very hard and strong, while remaining easy to drill, form and weld. 1011 is strong and durable, but can be vulnerable to corrosion with its low alloying percentages. Exposed to the elements, the iron content of 1011 will begin to discolor, corrode, and roughen its surface. For added corrosion protection, an outer layer is often applied to the steel’s surface, through painting or processing such as galvanization.
Common applications include:
• Building and roofing construction
• Shipping containers
• Automotive parts
• Heavy equipment

A36 Steel: A Grade Guide

The global market for structural steel is enormous, valued at 100 billion dollars USD yearly. It’s easy to see why steel is such an appealing choice for construction due to its qualities: high strength, toughness, formability and ease in welding. And among the many types of structural steels, grade A36 stands above the crowd.

Key Attributes of A36 Steel

A36 is a low carbon steel, which means its composition contains less than 0.3% carbon by weight. At its most basic, steel is formed when alloying iron with carbon. Carbon grants more strength and hardness to the alloyed metal in comparison to pure iron. However, as the percentage of carbon in the steel grows larger, the hardness can become brittle. That same hardness also produces steel with lower ductility and less workability.

In contrast, low carbon steels like A36 are relatively soft and not quite as strong compared to other steels. But their greatest attribute is ductility: that same softness means low carbon steel is much more formable and malleable. This makes low carbon steel an excellent choice for machining and welding. So it’s not surprising to learn that this category is the most widely used type of carbon steel – and A36 is the most utilized type of low carbon steel.

A36 steel is unique in its grading: unlike many other steels whose number is determined by their chemical composition, A36 is designated by its mechanical properties. What this means is that most grades have alloys that must be added in specific percentages in order to qualify as that steel type; meanwhile, A36 steel must meet the set mechanical standards for its grade. So while it does need to conform to certain chemical composition standards, the most important characteristic of A36 steel as established by ASTM International is its yield strength. In order to be graded as A36, the steel must meet a minimum yield strength requirement of 36,000 pounds per square inch. The metal must be able to withstand that amount of pressure with only 0.2% or less deviation to its shape under stress.

A36 is also a relatively ductile steel, able to elongate to around 20% of its original length during tensile testing. Along with its yield strength, this ductility gives A36 steel a high degree of impact strength at room temperature. This toughness helps prevent the metal from fracture and other damage.

Uses for A36 Steel

As you might tell from its attributes, A36 is quite a versatile material. It comes in a variety of shapes suited for riveted, bolted, and welded construction. Many of these shapes are designed for structural applications such as bridges and buildings. Wide flange beams (shaped like an “H”) are used as columns or beams. Tee bars (formed in a “T” shape) can be found used as beams or bracing. Angles are generally used as bracing or finishing elements. However, its uses are not limited to large construction projects. The versatility of A36 steel lends itself to other uses such as ship building, heavy equipment manufacturing, and automotive parts.  Whatever its purpose, it’s clear why grade A36 steel is so popular: tough, strong, easily welded…and all this at a relatively low cost!

What is a Ferrous Metal?

When classifying metals, focusing on a particular property is most often used as a way to divide them into two groups. Is this metal ductile or non-ductile? Is it magnetic or not?

When it comes to ferrous metals, one basic quality determines the groups: whether the metal contains iron. If iron makes up a large percentage of its composition, the metal is considered to be ferrous. If it contains no iron, or just trace amounts of it, it will be labeled a non-ferrous metal.

Beyond that, it becomes more difficult to apply general labels on the groups and the metals’ properties. While ferrous metals can range from iron itself to stainless steel, the alloying elements greatly affect the metal’s characteristics. For example, most ferrous metals are magnetic. But austenitic stainless steel is not, due to the high levels of nickel added to the steel for alloying. The nickel allows the steel to form in a crystal structure that is mostly austenite – and austenite is not magnetic.

So although it can be difficult to generalize about all ferrous metals as a group, there are some general characteristics that can be made about them. Ferrous metals are very hard and strong, especially in comparison to non-ferrous ones such as tin or copper. They’re vulnerable to rust due to their high percentage of iron, unless given corrosion resistance through alloying elements or protective coatings. And they’re usually (but not always) magnetic, which makes them very useful for motor and electrical applications.

The most common categories of ferrous metals include:

  • Carbon steel: there’s certainly no question of this being a ferrous metal, with over 90% of its composition being made up of iron. It is very hard and can keep a sharp edge, making it well-suited for mechanical uses such as drill bits and blades.
  • Cast iron: this metal is exceptionally hard due to its high levels of carbon, but the carbon also makes it quite brittle. For this reason, cast iron is now primarily used for smaller machine components or cookware.
  • Stainless steel: the most commonly used type of ferrous metals, especially for consumer goods. The addition of chromium is what makes a steel stainless, and gives it good corrosion resistance. And it’s magnetic, which is why you can stick magnetics on your refrigerator.
  • Alloy steel: the properties of this group of ferrous metals can vary much more widely than the others, since the alloy is specifically formulated for a particular purpose. So while alloy steels are ferrous, the added elements allows the metal to be tailored for more strength, ductility, hardness or other property.

Decoding Steel by its Numbers

Like any other field of expertise, the steel industry has its own jargon – one that may be confusing upon first encounter. Why are they assigned four-digit codes? What’s the difference between Alloy 4130 and 4140?

Steel is sorted into four main categories as set by the AISI (American Iron and Steel Institute):

Being steel, these contain the same two basic elements of iron and carbon. Determining their category depends on the percentage of carbon and other alloys added to the iron, which changes the properties of the finished metal.

Within each category, steel can then be classified according to type. This usually includes several of the descriptive factors below:

  • Composition: the main categories of carbon, alloy, stainless, and tool steel.
  • Microstructure: these are the subcategories of composition. For instance, stainless steel can be classed as ferritic, austenitic, martensitic, and duplex steels.
  • Method of production: two methods account for almost all modern steel production, known as EAF (electric air furnace), and BOS (basic oxygen steelmaking).
  • Form/Shape: also known as primary forming, creating shapes such as plate or bars.
  • Method of finish: this is referred to as secondary forming, the techniques which give the final product its properties and finish. This can include processes such as hot and cold rolling, tempering, or galvanizing.
  • Physical strength: using ASTM (American Society for Testing and Materials) standards, the designation typically includes a letter prefix and assigned number.

There are two primary numbering systems used to classify metals, so steel descriptions typically will include both. Along with AISI, the numbering system set by SAE (Society of Automotive Engineers) is most used in the metals industry. For the most part, SAE has adapted their system to align with the classifications set by AISI, so that specifications are standardized for steel.

So with this information, consumers have the ability to recognize the category and classification of a steel item. In the four digit code system, the first number will determine the type:

Starting with 1: Carbon steel

2: Nickel steel

3: Nickel-chromium steel

4: Molybdenum steel

5: Chromium steel

6: Chromium-vanadium steel

7: Tungsten-chromium steel

8: Nickel-chromium-molybdenum steel

9: Silicon-manganese steel and other SAE grades

The following numbers then give additional detail to the specific type of steel. In most cases, the second digit indicates the percentage of alloying element. The last two digits are the percentage of carbon concentration within the steel.

So using the example of 4130 vs 4140 steel: both start with a 4, so they are molybdenum steels – with the concentration of molybdenum being 1%. The difference between the two is that 4130 has a carbon percentage of roughly 0.30%, while 4140 contains 0.40 percent carbon. Because of its lower carbon percentage, 4130 would be more easily machined and weldable than 4140. However, the higher degree of carbon in 4140 alloy gives it greater hardness and strength than 4130. Armed with this knowledge, this may better help you choose the right type of steel for your needs.