Steel is a combination metal of iron and carbon and is the most popular metal alloy used today. Its use is so extensive that virtually all industries utilize steel in some way or the other. Aside from being one of the commonest metals, steel is also one of the most versatile in use today. In this steel guide, we will examine some of these properties. We will also consider the different grades and applications of steel, as well as factors to consider when choosing the right type of steel for custom part prototyping and manufacturing.
Properties of Steel
Chemical properties of steel
Steel is an alloy of iron and carbon. The carbon content of steel usually doesn’t exceed 1.5%, meaning the bulk of steel is iron. Aside from carbon, there are other metals that can be found in steel. Some of these metals, like manganese and phosphorous, are added to target and improve certain properties. Some other metals in steel are only there incidentally and are known as trace or residual elements. Examples of residual elements are silicon, copper, nickel, tin, and molybdenum.
While iron makes up most of the steel alloy, the other metals it contains can significantly affect its properties. For instance, iron itself is soft with little industrial use as an engineering material. The addition of carbon helps strengthen and harden steel, making it far more useful as an engineering material.
Physical properties of steel
Steel has a high melting point of about 1510C. That is very high, even relative to other metals. For further emphasis, consider the melting points of bronze and copper, which are 1040C and 1083C, respectively.
Steel is also a very dense metal, having a density of 7850kg/m3, about eight times that of water. Steel is harder than iron (Cast iron vs steel). Hardness, as a property, is usually a critical factor in many CNC machined components. If metal is too hard, its machinability will suffer, and it will be difficult to work with. However, some metals need to be very hard because of what they will be used for, like with CNC cutting tools. There are different grades of steel, and they usually vary in their hardness.
Iron is more brittle than steel. Industrially, many materials need to be elongated before use. A brittle material will break apart when elongated. Again, the grade of steel determines its elongation properties. Low-carbon steels elongate far more than high-carbon steel.
The physical and chemical properties dictate the uses of steel.
Different grades and uses of steel
One common property of most alloys is the presence of different grades. This is because alloys are combinations of more than one component, and varying the composition of individual constituents may affect their properties.
For steel, there are more than 3500 grades. But all types of steel fall into four broad categories: carbon, alloy, stainless, and tool steel. This grading system is on the basis of the chemical composition of the steel. The variations in chemical composition are largely responsible for many of the observed variations in the physical properties of the different grades. By implication, this affects the way their used in rapid prototyping and custom parts manufacturing.
Let us briefly examine these grades.
Carbon steel
Carbon steel is responsible for about 90% of total steel production today. The carbon range of carbon steel is between 0.04% and 1.5%. We have established that many different elements can be added to iron when forming steel. Carbon steel relies mainly on carbon to determine its properties.
There are three types of carbon steel, depending on the amount of carbon added when forming the steel. They are:
- Mild carbon steel: also known as low-carbon steel, this type of steel contains 0.04% to 0.3% of carbon. This is usually present in rail components, like couplings, axles, gears, etc.
- Medium carbon steel: contains between 0.3% and 0.6% of carbon. This is present in CNC cutting tools and many machine parts.
- High carbon steel: contains between 0.6 and 1.4% of carbon. This grade is of use in pistons, cylinders, rapid tooling, die casting, and railways.
Increasing the carbon content affects some of the properties of carbon steel, including a decrease in the ductility and weldability of the steel. This also explains the better elongation properties of low-carbon steel relative to high-carbon steel. In rapid prototyping, the high flexibility of the metal in use is typically an advantage.
On the other hand, increasing the carbon content increases the strength and hardness of the steel. This is also another essential steel property to consider in rapid prototyping.
Nowadays, many manufacturers in the machining industry use a type of carbon steel known as free-machining steel. This type of steel contains additional elements like sulfur and phosphorous that have been subjected to different treatments. The benefit is better machinability of steel with no significant decrease in other desirable qualities.
Alloy steel
As the name suggests, this steel grade contains certain alloying elements in different proportions to improve certain characteristics of the steel. The targeted properties are weldability, machinability, hardness, durability, corrosion and heat resistance, ductility, etc. Common alloying elements are manganese, aluminum, copper, vanadium, titanium, nickel, silicon, and chromium. Alloy steels can be further grouped into low alloy and high alloy. The former contains between 1% and 5% of alloying elements, while the latter has about 5-50% of alloying elements present.
Alloy steels are primarily used in the manufacture of automobile components, aerospace, and motor parts.
Stainless steel
This is perhaps the most relevant grade of steel in steel CNC machining. And as you already know, it also has widespread use in many household items. The name “stainless” comes from its high resistance to corrosion and many other chemical reactions.
CNC stainless steel generally contains high amounts of chromium (up to 20%) and nickel. Its extensive use in steel CNC machining may be due to its ability to resist corrosion – about 200 times more than mild steel. Stainless steel is also resistant to oxidation. This property is due to the formation of a chromium film on the stainless steel surface. Better corrosion-resistant properties give stainless steel an edge over carbon steel in CNC machining. Aside from corrosion resistance, stainless steel has good formability and high tensile strength.
There are three types of stainless steel in terms of crystalline structure, namely:
Austenitic
This type of stainless steel is rich in chromium and nickel. The steel composition is about 18% chromium and 8% nickel. The carbon content is generally minimal – about 0.8%. While they have excellent corrosion resistance, they are not very heat-treatable and also not magnetic. Industrially, austenitic steel is vital in manufacturing pump shafts, sheathing, and many components like screws, bolts, etc. This stainless steel type is also common in many household equipment.
Ferritic
This type of stainless steel contains between 12% and 18% chromium, trace amounts of nickel, and about 0.1% carbon. There may also be other alloying elements, like titanium, molybdenum, and aluminum. Ferritic stainless steel also has excellent corrosion resistance properties, informing its use in many forming and pressing industrial operations. Ferritic stainless steel cannot be heat-treated but can be cold-worked.
Martensitic
The steel composition of this type contains 11-17% chromium, 0.12-0.35% nickel, and about 1.2% carbon. They are magnetic and heat-treatable. Martensitic steel is the first steel type to be developed. Its use industrially today is in manufacturing many CNC equipment, like cutting tools, and engineering equipment, like hydraulic pumps, valves, steam pumps, etc.
Tool steel
The last group of steels is tool steels and it contains many different carbon and alloy elements. Some of these elements are tungsten, vanadium, cobalt, and molybdenum, and they are usually present in varying proportions. Adding these elements improves the heat resistance and durability of steel, which makes them suitable in the manufacture of many curing and drilling tools in steel CNC machining. Tool steel is also an important metal in injection molds and pressing tools. However, the weldability of tool steel is very low.
Applications of steel
There are many applications and uses of steel in several different industries globally, even though our primary concern is on the CNC machining and rapid prototyping industry. Some of the areas where steel can be used include:
Industrial components
Steel is the go-to metal in many industries around the world. This is due to many of its properties, which are generally desirable when dealing with metals in industries. In rapid tooling and custom parts manufacturing, for instance, high resistance to corrosion means the steel components can last longer and also give a maximum effect for longer periods. The kind of steel most employed for machining purposes is CNC stainless steel. It is noteworthy that there are even still different grades of stainless steel. Storage tanks, machines, and protective equipment are just a few of the industrial applications of steel.
Automobiles
One of the primary metals involved in the manufacture of automobiles is steel. This isn’t surprising, considering the lightweight nature and easy formability of steel. Today, many automobiles use advanced high-strength steel (AHSS), which is steel with yield levels higher than 80 psi. Usually, AHSS relies on retained austenite in a martensite matrix and may also contain ferrite. With AHSS, there’s better formability, and the steel still retains its strength and other desirable properties.
While most popular in cars and automobiles, steel is also relevant in the aerospace and marine industries. Steel’s lightweight and corrosion-resistant properties justify its use in airplanes and ships, respectively. The railway industry is not left behind, as wheels, axles, bearings, rail lines, etc., all contain steel.
Energy
The primary property leveraged here is steel’s fantastic durability. Virtually all energy-producing and distributing sectors use steel in one way or the other. Typically, high-strength, carbon, stainless, and alloy steels are used for manufacturing many energy production components. Also, transformers usually have a magnetic steel core and steel-reinforced cables. Generators and motors of these heavy machines also require the use of steel.
Packaging
Steel is fully recyclable, and therefore, eco-friendly. This is one of the primary reasons for its use in the packaging industry. Well, that and being able to resist corrosion and protect the goods and products from external environmental elements. The type of steel most implicated as a packaging material is low-carbon steel, probably because of its ease of machining.
Domestic appliances
We don’t think we need to say much about this. This is the most widespread use of steel today. Forks, knives, spoons, pots, ovens, refrigerator components, etc., require steel for their production. The type of steel that will be used depends on the type of product that needs to be made.
Pros and Cons
Pros
- Steel is present in several different grades and can meet many manufacturing demands and requirements
- Very resistant to corrosion
- Steel is usually lightweight and easily machinable
- Extremely durable
Cons
- Steel may become very brittle and break apart upon exceeding certain limits
- Many grades of steel are not heat-treatable
RapidDirect’s CNC Machining Metals
CNC machining usually involves using metal alloys, and CNC machining steel is one of the best metal alloys there is for various machining purposes. Aside from its good machinability, it has good corrosion resistance properties and electrical conductivity, making it one of the choice metals for CNC machining.
At RapidDirect, we offer several steel types for your various machining and sheet fabrication needs. Our team of experts is also ready and willing to assist you with steel CNC machining needs and materials like CNC stainless steel. You can upload your design file and receive an instant quote, as well as DfM feedback.
In simple terms – we have you covered! Visit us today.
How to choose the right steel grade for custom parts manufacturing
There are many steel grades and types, usually with differing properties and characteristics. It may, therefore, be a bother for custom parts manufacturers to decide on the best for manufacturing purposes. Luckily, some pointers will help guide your choice, and we have some of them below.
Operating environment
The kind of environment the steel part will be exposed to is a critical factor to consider before deciding on the steel grade to use. Custom parts manufacturing occurs in various environments, depending on the part to be manufactured. Some steel grades will break down under conditions of high temperature and stress. The pH of the environment may also interfere with the ability of the steel grade. As such, consider all of the environmental factors and parameters before you choose a steel grade.
Corrosion resistance
Resistance to corrosion is a desirable quality and property for all types of parts and in all industries. Steel, generally, is resistant to corrosion, but the different grades have slight variations in their level of resistance. However, with some parts, resistance to corrosion must be at the highest possible. Examples of these parts are marine components, especially those in saltwater.
CNC stainless steel is the most resistant of all steel grades. The level of resistance usually increases with increasing chromium amounts.
Mechanical properties
Ductility, strength, and hardness are some of the most relevant factors to consider when choosing a steel grade for custom parts manufacturing. The presence of nickel, and in a high percentage, signify hard and ductile steel. CNC stainless steel, again, is the best steel with these properties. However, even the different types of stainless steel have different proportions of these elements. Hardness is also important with cutting and drilling parts.
Machinability
Machinability is the ease with which one can modify a particular material. It is a desirable feature with steel, even though it is usually at the expense of hardness. However, there are steel grades currently that are very machinable with no significant compromise in the other desirable qualities of the steel in use. Note, though, that certain steel types do not need to be machined before use. This type of steel is particularly useful when manufacturing heavily altered materials, like reinforced bars.
Cost
All of the properties and features here have to be considered in view of cost. There is absolutely no sense in going for steel grades that cost too much when there are cheaper, similarly effective grades. This isn’t to say you should not prioritize quality but do so in relation to cost. If finance is a problem, as is the case in most startups and small businesses, then cheaper options will do just fine. The only problem is there is no guarantee of their quality and you may end up spending more on maintenance costs than investing in a high-grade, relatively expensive product at the start. If finances will not be much of an issue, then high-grade stainless steel, like austenitic steel, is one excellent grade to invest in.
Purpose of the product
Different products require different manufacturing conditions, and in the same vein, different steel grades. Before choosing a steel grade, be sure of the purposes the final product will serve. Products that will do more cutting and drilling will likely need the toughest grades of steel. Marine parts will need to be very corrosion-resistant. Also, aerospace components and parts need to be very lightweight.
Conclusion
Steel is the most widely used metal alloy in industries today, and for good reasons too. It has several desirable properties and qualities that justify its widespread use. Then, there’s the fact of it being versatile, lending itself to use for several different purposes. But, like most other metal alloys, it has different grades. CNC stainless steel is perhaps the best grade for machining, parts manufacturing, and rapid tooling purposes. However, it is still critical to evaluate all of the available grades to be able to make the best choice in steel grade selection.
