Since the early 1900s, stainless steel has been a fixture in our everyday lives. This alloy can be found everywhere, from watches to skyscrapers and aircraft. Its strength, corrosion resistance, and affordability make it an appealing choice for many projects. Even better, stainless steel is fully recyclable! The alloying elements used in its chemical composition can be extracted from melted stainless steel, and then reused with no degradation in their performance.
Having learned of its valuable properties, it is little wonder that so many different industries rely upon using stainless steel. With a wide range of grades and alloys available on the market, a manufacturer can be sure to find a type of stainless steel to suit their needs. Here are five of the most common uses of this metal alloy:
Construction
Modern construction is largely dependent on stainless steel due to its strength, flexibility, and resistance to corrosion. Its durability makes it a good choice for both interior and exterior use. Skyscrapers and commercial buildings often have frames and exterior cladding made of stainless steel. Its durability means less time and expense can be spent on maintenance, since the metal remains rust-free.
Energy and Heavy Industry
The oil, gas, and chemical industries present a great challenge to construction. These industries typically operate in environments which involve high temperatures and corrosive, toxic substances. Specialized grades of stainless steel have been developed for these industries, designed for enhanced corrosion resistance and able to handle extreme ranges of temperature. These “super-steel” grades are used for storage tanks, pipework, and valves.
Crude oil is an extremely corrosive substance, so stainless steel is invaluable in the construction of offshore rigs and drilling components. Stainless steel can also be found making up the equipment for renewable energy sources such as wind or hydro power. Its resistance to developing rust allows it to withstand the corrosive effects of seawater and varying temperatures.
Automotive and Transportation
Stainless steel has long been an integral part of automotive manufacturing, although mainly used in the past for exhaust systems and trim. With the rise of environmental concerns, more auto makers are expanding their use of stainless steel in structural components due to its recyclability.
The transportation and shipping industries are highly reliant on stainless steel, from shipping containers to tanker trucks. Transporting chemicals and other substances requires strong, non-reactive metals like stainless steel. Its strength also allows for thinner containers, which saves on fuel costs. Its corrosion resistance then requires less maintenance and easier cleaning of those containers and other transport equipment.
Medical Instruments
The production of medical instruments has involved stainless steel for well over a century. While bacteria can form on its surface, its natural corrosion resistance means a stainless steel tool is unlikely to have cracks or grooves where the bacteria can harbor itself. This makes for easy and thorough sterilization of stainless steel medical tools. The stainless steel instruments can be sterilized and reused for many cycles before they will show enough wear to be discarded.
Food Production and Catering
When it comes to cooking, once again stainless steel’s durability and corrosion resistance play key roles. Many foods such as tomatoes are highly acidic, leading to corrosion and discoloration of aluminum or copper cookware. The more reactive a metal, the more it can potentially affect a food’s flavor, often for the worse. Stainless steel is an ideal material for food production and storage because it has strong corrosion resistance, which means the metal does not react to its environment or the substances stored inside it. This durability means less waste; knives, cutlery, and cookware can be used for many years before showing excessive wear.
Stainless steel is an even more important material in commercial food production. As in the medical industry, equipment sterilization is the utmost priority, and stainless steel can hold up to cleaning cycles involving high temperatures and strong anti-bacterial products. Its non-porous surface means bacteria are unable to hide away during cleaning, and lowers the chances of carrying over any germs between food production batches.
Category: Stainless Steel
The Basics of Welding Stainless Steel
Cracking, spatter, incomplete fusion: just a few of the many pitfalls you may face when attempting a weld. While no approach is completely foolproof, your chances of a successful weld are much better once you have a good understanding of the basics. It is also important to tailor your methods to your choice of material; what works best for one type of stainless steel may not be as helpful with another. In this case, we’ll examine a few of the most popular methods of stainless steel welding.
The Material
There are many different grades of stainless steel, but they all have at least one alloying element in common: chromium. The addition of chromium is what makes steel ‘stainless’, with its characteristic shine and boosted corrosion resistance. However, adding chromium to the steel’s chemical composition – along with other elements such as molybdenum, silicon, or manganese – affect how the metal will react to heat. These elements lower the thermal conductivity of stainless steel, which means heat will not spread as easily through the material. This lack of efficient conductivity requires a stronger heat input, but higher temperatures or an extended welding time increases the chances of a burn-through or other heat-related faults. Whatever process you use for welding stainless steel, it will be a matter of balancing necessary heat input vs the potential for heat damage.
The Processes
There are several different methods of welding stainless steel, but most welders use one of these three types. There are other factors that can be considered in more detailed, but generally the selection depends upon the material’s thickness:
1. Tungsten Inert Gas (TIG) welding
This process is one of the most commonly used for welding stainless steel. TIG welding, often referred to as tungsten gas arc welding, creates a low heat input which makes it the best choice for thinner materials. The heat is generated using electricity, which powers an electric arc between the tungsten electrode and the base metal. An inert gas such as argon creates a sheathing environment around the electrode, protecting and cooling the tungsten. This dampening effect helps to keep a relatively low heat input, as well as creating less smoke and oxidation.
Low heat input means TIG welding is ideal for thin stainless steels or precision welds on critical joints. Its concentrated heat allows for a narrow fusion zone, which calls for a high degree of control over the welding process. After completion, a TIG-produced join requires little to no post-weld finishing.
2. Metal Inert Gas (MIG) welding
Also known as gas metal arc welding, MIG uses electricity to melt and join metal during a weld. However, unlike TIG welding, MIG requires the use of both an inert shielding gas and a solid wire electrode. This filler metal wire is continuously fed during the welding to create the arc between the electrode and base metal.
Due to the higher heat during the weld, MIG is best selected when welding thicker widths of stainless steel or steel plate. It can be adapted for semi-automatic welding processes, since the continuous wire feed allows for long joins. It also produces little spatter and easy cleanup after processing.
3. Resistance welding (RW)
TIG relies upon a welding operator and MIG can be done manually or through automation, but for manufacturers who require a highly automated process, resistance welding is key. The method involves an electrical current run through weld electrodes, which apply force to the pieces being joined (the “resistance” part of the process). This force is converted to heat, and the resulting heat melts the metal enough to join it together. When completed successfully, the molten metal at the point of contact will form a rounded weld, known as a “nugget”.
Unlike the other two processes, RW has a steep initial cost of equipment setup and requires a high amount of power. This means it has little portability and cannot be used in the field like TIG and MIG welding. However, for manufacturing purposes, resistance welding is ideal. It is fast, reliable, requires no filler metals or other materials, and is excellent for sheet metal applications. Stainless steel can get up to weld temperature very quickly using the RW method, so welding can be completed within a few milliseconds.
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.
Appearance
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.
Cost
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.
Ten Differences between Aluminum and Steel
At first glance, aluminum and stainless steel may appear similar: both a silvery gray, softly shiny, and used to make many of the same products. Many food service and kitchenware items, for instance, are made available from a manufacturer in both types of metals. What separates these two, other than price?
1. Thermal Conductivity
Aluminum is a metal with a high degree of thermal conductivity. What that means in real terms is that a water will boil more quickly in a stockpot than one made of stainless steel. However, aluminum also cools more quickly than stainless, so stainless will help keep a pot of soup warm longer.
2. Thermal Properties
Its lower degree of thermal conductivity means stainless steel is much more resilient to use in high temperatures. Aluminum will begin to soften around 400 degrees Fahrenheit; meanwhile, stainless steel can function well at temperatures up to 800 degrees. Some stainless steel grades can withstand temperatures nearly double that for short periods of work, up to 1500 degrees.
3. Strength
Both metals are quite strong and durable, but stainless steel more so than aluminum.
4. Strength to Weight Ratio
Stainless steel is very strong, but at the cost of a heavier weight. While aluminum is not as strong, manufacturing with this metal will result in an item nearly one third the weight of a steel part. This incredible strength to weight ratio makes aluminum very attractive to manufacturers, especially in the aerospace industry.
5. Welding
Most grades of stainless steel are relatively simple to weld, while aluminum’s high thermal conductivity makes it a more difficult task. However, both are among the most popular types of metals used in welding.
6. Electrical Conductivity
Aluminum has the distinct advantage over stainless steel here, with it being an excellent conductor of electricity. Stainless steel does not conduct electricity well in comparison to other metals.
7. Workability
Pure aluminum is a very soft and malleable metal, and even after alloying, it is easy to cut and form. Due to its strength and hardness, stainless steel takes effort to form into shape.
8. Corrosion Resistance
Both metals are known for excellent corrosion resistance. Chromium is one of the principal alloying agents in stainless steel, and boosts the corrosion resistance of the steel alloy. Aluminum is naturally resistant to corrosion on its own, although it is more vulnerable to damage from highly basic or acidic exposure.
9. Cost
In general, a part made of aluminum will be more affordable than the same item made of stainless steel.
10. Reaction to Foods
Consumers have the choice between aluminum and stainless steel cookware, and often make the decision to purchase aluminum based on price. However, aluminum is a more reactive compound than stainless steel. Acidic foods such as tomato sauces can leave aluminum damaged or with unsightly marks, while other foods like eggs can discolor if cooked or stored in aluminum. While both metals produce high-quality items, choosing stainless steel may be worth some additional money for non-reactive cookware.
Classes of Stainless Steel
When it comes to steel types, stainless is a broad category. Any ferrous alloy containing at least 10.5% chromium can call itself stainless steel. While additional alloying elements may be included, chromium is the significant ingredient in transforming a steel into “stainless”. Chromium boosts the corrosion resistance, durability, and strength of steel. It also results in a distinctive shine and boosts the metal’s stain-resistant properties – which is where we get its name.
So we see that all steels within the stainless family share one common alloy in chromium. What then separates them into classes are the other alloying elements, such as molybdenum or nickel. The different chemical compositions affect the steel’s crystal structure, which is how they are divided into 5 basic classes:
- Austenitic stainless steel
- Ferritic stainless steel
- Martensitic stainless steel
- Duplex (ferritic-austenitic) stainless steel
- Precipitation-hardening (PH) stainless steel
Austenitic stainless steel
The most popular grades of stainless steel come from this group, which are alloyed with high levels of chromium, molybdenum, and nickel. This gives the metal a superior degree of corrosion resistance and malleability, along with excellent weldability. While this class of stainless steels cannot be hardened through heat processing, and are prone to cracking under heat, they can be successfully hardened through cold working. Another asset is its strength against corrosive elements, which means austenitic steel is used in varied applications from marine and aerospace environments to chemical and food processing.
Ferritic stainless steel
These steels are best known for having low levels of carbon, making them a more iron-centric (ferritic) type of steel. It contains high levels of chromium and nickel, and like austenitic stainless, is strengthened through work hardening or cold working. It may not be as strong or hard as austenitic steel, but ferritic stainless is very resistant to stress-induced corrosion cracking. This makes it a popular choice for any components encountering corrosive substances or environments, such as industrial or automotive parts.
Martensitic stainless steel
Martensitic steels make up the hardest class of stainless steel, with a high level of carbon content alloyed mainly with chromium. However, that high degree of hardness also limits its use, since it can be brittle and less tough than the other classes of stainless steel. This means martensitic steel use is reserved for parts requiring great tensile strength and impact resistance, without being exposed to corrosive elements. Surgical instruments, valves, and pumps are often made of these steels.
Duplex (ferritic-austenitic) steel
Also known as ferritic-austenitic stainless steels, duplex is engineered to combine the best properties of both classes. They are alloyed with over 20% chromium and 5% nickel, boosting their yield strength and corrosion resistance. It also has approximately double the overall strength compared to ordinary austenitic stainless steel, while still being less expensive than austenitic due to the lower amount of nickel. With these qualities, duplex is heavily used in the oil industry, especially for underwater oil and chemical processing. It has the toughness to stand up to the corrosion caused by chloride and other elements.
PH (precipitation hardening) stainless steel
Steels in this class are notable for including aluminum, copper, and titanium among their alloying elements. When these steels are heat treated, the aluminum and other alloys form precipitates within the metal, reinforcing its crystal microstructure. This natural precipitation-hardening means that after its forging, it requires just a single low-temperature hardening to be ready for use. PH steel ranks highest in tensile strength among all stainless steel classes, which makes it well suited for the stresses of industrial use. Turbines, nuclear power plants, and aerospace components often make use of this class of steel.
Grade 304 vs 316
Grade 304 vs 316: The Differences between Stainless Steels
304 Stainless Steel versus 316 Stainless Steel: to the average layperson, these will appear to be very similar materials. They both fall into the 300 Series class, made up of austenitic chromium-nickel alloys. They’re the same grayish-silver color, with a bright and lustrous shine. Neither type can be hardened through heat treatments, but can be work-hardened.
But as those with more knowledge of these steels realize, it’s the small details between the two grades that make for crucial differences. Knowing more about these difference can provide consumers with better insight into the right type of steel for their use.
300 Series Steel
The steels within the austenitic class are generally alloyed with three main elements: chromium, nickel, and molybdenum. They’re known as low-carbon steels, with less than 0.8% carbon making up their chemical composition. Alloying with chromium increases the strength, hardness, and corrosion resistance of iron. Nickel also boosts the metal’s strength and hardness, while helping to prevent against loss of ductility and toughness.
However, it’s the addition of molybdenum that is one of the most significant differences between the 304 and 316 grades. Grade 304 stainless steel contains 18% nickel and 8% chromium, while 316 has 16% chromium, 10% nickel, and 2% molybdenum. Like the other alloying elements nickel and chromium, molybdenum is used to strengthen and toughen steel. But its biggest asset in 316 stainless steel is in the prevention against chloride corrosion.
Molybdenum: The Difference Maker
The boosted percentage of nickel, along with the inclusion of molybdenum, means that 316 has better chemical resistance when compared to 304 steel. The most significant corrosion protection it offers is against chlorides. In applications where the steel will be exposed to salts or seawater, 316 steel outperforms other Series 300 steels in resisting the development of pits and crevices. This is also why 316 is known as “marine grade” steel.
That’s not to say that Grade 304 isn’t strong and resistant to general corrosion on its own merits. In fact, its overall attributes and reliable performance is why 304 steel is the most widely used of all stainless steels. One other great advantage is its cost: by containing less nickel, along with no molybdenum, Grade 304 is a more affordable choice of material. So as long as the steel will be used with milder acids only, and have little to no contact to salt, it will save a bit of money to construct items out of 304. For applications that include exposure to chlorides and powerful corrosives, 316 with its added molybdenum would be the better choice.
When it comes to formability and welding, molybdenum comes into play again. Formability refers to a metal’s ability to be formed into a particular shape without incurring damage. While 316 is regularly used to form metal parts and structures, the hardness coming from molybdenum means forming requires more effort than compared to 304. The same goes for welding; both grades are commonly welded austenitic steels, but 304 is generally more easily weldable.
Advantages and Applications of Grade 304 Stainless Steel
With its good formability, resistance against heat and corrosion, and affordability, it’s understandable that 304 is the most popular of all stainless steels. It’s a reliable and versatile alloy, and readily welded by all common methods.
Some of the most common applications of Grade 304 steel include:
• Kitchen equipment and cookware
• Cutlery and flatware
• Appliances such as refrigerators and dishwashers
• Piping and fasteners
• Equipment used in dairy, brewing, and pharmaceutical production
Advantages and Applications of Grade 316 Stainless Steel
While it does come at a higher cost, when an application requires protection against severe corrosion, 316 will be the recommended choice. Its strength and durability are a necessity for usage in harsh environments, including underwater. In some cases, 316 may last many times longer than a part made of 304 – giving extended usage life to your parts and structures.
Some of the most common applications of Grade 316 include:
• Marine vessels and structures in marine environments
• Chemical processing and storage equipment
• Medical devices
• Textile, pulp, and paper manufacturing
• Jet engine parts
Common Metals That Don’t Rust
When it comes to protecting and maintaining metal, the most constant battle encountered will be against rust. Rust compromises a metal’s chemical characteristics, eventually leading to its disintegration. And even if it doesn’t progress to a destructive point, it’s just not very appealing on an aesthetic level. The distinctive orange-brown of rust forming on metal can make it look old and shabby long before its time. So one of the best solutions to this problem is to eliminate it from the start: choosing a metal that won’t rust.
Common rust-free metals include:
- Aluminum
- Stainless steel
- Red metals (copper, brass, and bronze)
- Galvanized steel
Aluminum
Aluminum and aluminum alloys cannot rust because they contain no to very little iron, and ‘true’ rust is made up of iron oxide. That doesn’t make aluminum indestructible, since it can still oxidize when exposed to water. But unlike iron oxide which will wear away at the underlying metal, the forming of aluminum oxide actually becomes a protective barrier. Once it develops on the aluminum’s surface, the oxide layer will be quite resistant to any additional corrosion.
Stainless steel
Most grades of stainless steel include at least some amount of iron, the element which leads to rust. However, the other alloying elements – particularly chromium – lends it protection to the material. Chromium tends to oxidize very quickly and like aluminum, the resulting oxide then forms a barrier against rust. With this chromium oxide layer in place, oxygen is no longer able to reach and react to the metal underneath. Other alloying elements in stainless steel such as nickel and molybdenum provide resistant to rust development.
Copper, brass, and bronze
Collectively known to as “red metals”, these metals can oxidize without rusting since they contain virtually no iron. Copper is very slow to react to oxygen and other environmental factors, but once corrosion does occur it will gradually turn the bright reddish metal to a verdigris green patina. Brass and bronze are copper alloys, with the dual benefits of copper’s own corrosion resistance and the rust-free properties of alloying elements. Both brass and bronze are even more resistant to corrosion than pure copper.
Galvanized steel
Unlike the other three types mentioned, galvanized steel relies upon the application of a physical barrier to prevent rust. Carbon steel is galvanized after being coated with a thin layer of zinc. After bonding with the surface, any oxidation which does occur becomes zinc oxide. A zinc layer exposed to water will become zinc carbonate, which is water-insoluble and puts a stop to any further chemical reactions. More importantly, whatever oxidation that takes place will affect the wear of the zinc before reaching the steel underneath.
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):
- Carbon steel
- Alloy steel
- Stainless steel
- Tool steel
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.