Steel has been around in various forms for thousands of years, but it had always been in limited supply until the invention of the Bessemer process, which enabled mass production, it basically invented the commercial method for steel production.
The various methods of making steel, like electric arc furnaces, oxygen converters, and precision alloying, have led to the production of different kinds of steel with varying properties and compositions. There are low-carbon steels like the 1018 steel, and other steels with a high carbon composition.
When choosing alloy steel for high-performance use, 4140 and 4130 steel are among the top choices. Though they’re low alloy steels and also low carbon steels made from iron, carbon, chromium, and molybdenum, the difference in their carbon content, mechanical properties, and how they respond to heat treatment means they’re used in very different applications.
This article focuses on Alloy steel, highlighting the difference between the 4140 and the 4130 steel. This article also provides a side-by-side comparison, breaking down both chromoly steel types for comparison purposes, with special focus on their great workability, cost, and how well they withstand stress, temperature, and load.
Introduction to Alloy Steel
Alloy steel is the mixture (alloying) of other elements with carbon to get a desired quality or mechanical property. Some of these elements may usually include hardening and strengthening agents like nickel. These elements are added in varying quantities depending on the mechanical properties being sought. This means that the specific combination and proportion of these elements determine the application of the alloyed steel.
Usually, the properties sought after in alloyed steel include strength, hardness, toughness, wear resistance, weldability, and flexibility. The varying properties of Alloyed metal have made it the desired and recommended steel for High-performance use
Alloy steel is generally divided into Low and High Alloy steel. The low steel has a small amount of alloying elements, it is usually less than 5%. The High alloy Steel has a higher percentage of alloying materials, which is usually more than 5%
Chemical Composition and Content
Alloy steel is mainly made up of Iron and Carbon – which are the base elements- and the alloying elements.
The alloying elements may include: Chromium, Molybdenum, Nickel, Manganese, vanadium, Silicon, all depending on the specific and desired application.
The composition of Alloyed steel, therefore, includes:
Carbon
Iron
Chromium
Molybdenum
Nickel
Manganese
Vanadium
Silicon
Each of these elements has its own mechanical properties. These properties are however, not exclusive, meaning two elements can share the same properties and may not share another. Chromium is known to enhance hardness, toughness, and wear resistance.
It significantly improves corrosion resistance. This is why it is a key component in stainless steel. While manganese improves hardness and tensile strength. It also deoxidizes the steel and reduces brittleness, enhancing the steel’s ability to withstand impact.
As mentioned earlier, Alloy Steel has varying degrees of properties ranging from strength to flexibility and weldability. Consequently they are put to different uses. For example, the kind of steel needed for building bridges will be different from that needed to build a bicycle. The quality of Strength may be prioritized over flexibility when it comes to bridge building.
To fully recognize these varying qualities in their varying degrees, varying organizations have come up with systems. The Society of Automotive Engineers and the American Iron and Steel Institute created a numbering system.
Hence the 4140 steel and the 4130 steel.
4140 Steel
In a 4140 steel, the figure 41 means it has Chromium and molybdenum, the figure 40 shows the carbon content of the steel, which is about 0.40% carbon. The 4140 steel is a low-alloyed steel. It is renowed for its superior strength.
4130 steel
Just like it is for the 4140, the figure 41 means the steel has chromium and Molybdenum. The figure 30 also indicates the carbon content of the steel which in this case is about 0.30%. 4130 steel is a chromoly steel with low carbon content, making it easier to weld, form, and machine.
The 4130 steel and 4140 steel: A Comparative Analysis
This is the main bane of this article. The focus will be on the chemical composition, Mechanical properties, their heat treatment, and their most suitable application
um and Molybdenum. The figure 30 also indicates the carbon content of the steel which in this case is about 0.30%. 4130 steel is a chromoly steel with low carbon content, making it easier to weld, form, and machine.
Chemical Composition
The content of a steel would determine how it would react under certain conditions, dictating what applications it would be put to. The exact content of these elements is described in the table below.
| ELEMENTS | 4140 Steel | 4130 Steel |
| Iron | 96.785 - 97.77 % | 97.03 – 98.22% |
| Carbon | 0.380 - 0.430 % | 0.280 – 0.330% |
| Manganese | 0.75 - 1.0 % | 0.15 – 0.30% |
| Chromium | 0.80 - 1.10 % | 0.80 – 1.10% |
| Phosphorus | ≤ 0.035 % | |
| Silicon | 0.15 - 0.30 % | 0.15 – 0.30 |
| Sulphur | ≤ 0.040 % | |
| Molybdenum mo | 0.15 - 0.25 % | 0.15 – 0.25% |
The 4140’s higher carbon content results in better hardness, tensile strength, and maximum stress capacity, while the 4130 steel offers more flexibility and excellent ductility in cold forming and welding.
Mechanical Properties
The mechanical properties of any steel generally describe how the steel will behave under different condition of force. This helps designers, builders and engineers understand how steel will perform in real life conditions by this they can decide what kind of steel to use.
Mechanical properties include yield strength, tensile strength, ductility, hardness, toughness, and creep resistance. The table below compares the mechanical properties of the 4140 and 4130 steel.
| Mechanical Property | 4140 Steel | 4130 Steel |
| Tensile Strength(ultimate) | 655 MPa | 560 MPa |
| (Tensile) Yield Strength | 415 MPa | 460 MPa |
| Brinell Hardness | 197 | 217 |
| Elongation at break | 25.7 % | 21.50% |
| Modulus of Elasticity | 205 GPa | 190-210 GPa |
Physical Properties
The Physical properties of steel refers to thier basic characteristics, as opposed to the mechanical properties which describes how the steel reacts to force or stress, the physical property merely describes what the material is.
The physical properties of steel include:
Density
Melting Point
Thermal conductivity
fatigue Strength
Specific Heat Capacity
Electrical Conductivity
Magnetic Properties
The table below displays the physical properties of 4140 v 4130 Steel
| Physical Property | 4140 Steel | 4130 Steel |
| Density | 7.85 g/cm³ | 7.85 g/cm³ |
| Melting point | 1416 °C (2580°F) | 1432 °C (2610°F) |
| Thermal Conductivity | 42.6 W/m.k | 46.6 w/ M.k |
| Specific Heat capacity | 477 J/kg·K | 475 J/KG.K |
| Electrical conductivity | low | low |
| Magnetism | ferromagnetic | ferromagnetic |
Weldability and Machinability of 4140 and 4130 steel
Other properties of the 4140 and 4130 steel are weldability and machinability. The weldability of a steel refers to how easily the steel can be welded without cracking or weakening. The machinability, on the other hand, refers to how efficiently the steel can be cut, shaped, or finished with tools
Both the 4140 and 4130 steels are pretty machinable; the 4140 steel is, however, far less machinable than the 4130. In other words, the 4130 is readily machinable. For weldability, the 4130 steel also ranks higher than the 4140 steel. Successfully welding a 4140 steel requires preheat and post-weld heat treatment; failure to do this may lead to the cracking of the steel
The TIG, MIG, and stick welding methods can be used for both kinds of steel. However, conventional methods also work for 4130.
The Heat Treatment Process of 4130 and 4140 Steel
The heat treatment of steel is simply a controlled way of changing the internal structure of the steel. It is done in 3 simple steps. The steel is heated to a certain temperature, typically between 1450 and 1700 degrees Fahrenheit, depending on the results desired. It is held at that temperature for a while, and then it is cooled down
Steel can be cooled by air, oil, or water, and it can either be cooled quickly or slowly. Each variation in the process affects the properties of the steel as it causes the rearrangement of atoms in the steel, and changes the characteristics of the steel.
Before the specific process of heat treatment for the 4140 and the 4130 is considered, it is important to briefly consider the various types of heat treatments.
Annealing
The following steps will guide you on the annealing process of the 4041 steel: Heat up the steel to 800–850°C (1470–1560°F). Hold it for 1 hour per inch of thickness. Then cool it slowly in the furnace at a rate of 10–20°C/hour to 500°C. The final step is to air cool.
The timing and temperature are a bit different for the 4130 steel. The steel material is first heated to 760–790°C (1400–1450°F), and it is then held for 1 hour per inch of thickness. It is similarly cooled slowly in the furnace, but to 400–500°C, and then air-cooled.
Normalizing
This process refines the grain structure of the steel; it balances the strength and toughness of the steel. This is done by cooling the steel with air after it has been heated.
To normalize a 4140 steel, Heat to 870–925°C (1600–1700°F), hold for 1 hour per inch, and then air cool. The process for the 4130 is this, Heat to 870–900°C (1600–1650°F), hold for 1 hour per inch then air cool.
Hardening
This process makes the steel harder and stronger. This is done by rapidly cooling the steel after heating
The hardening process for the 4140 is to heat the steel material to 830–870°C (1525–1600°F), hold it for at least 30 minutes after reaching temperature, and then quench in oil. It is a bit different for the 4130, the steel is heated to 775–815°C (1425–1500°F), it is also held at that temprature for about 30 minutes, and then it is quenched in oil.
Tempering
Steel becomes brittle after going through the hardening process as explained above; tempering the steel helps to reduce the brittleness. This process involves reheating hardened steel to a lower temperature. The ideal tempering temperature ranges between 205°C and 650°C.
Tempering a 4140 steel involves heating the steel to 200–650°C (400–1200°F), depending on desired properties, holding it there for 1 hour per inch of thickness, and then air cooling it. Tempering the 4130 involves heating the steel to 400–650°C (750–1200°F), holding the same temperature for 1 hour per inch. and then air-cooling it.
Case hardening
This process allows for the outer layer of the steel to be hardened while the inner core is soft. The process is the same for both the 4140 and 4130 steel, it entails Carburizing or Nitriding. The nitriding temperature is 500–550°C (930–1020°F).
4140 steel responds exceptionally well to quenching and tempering, enabling it to reach higher Rockwell hardness levels post-heat treatment. The 4130 steel, while heat-treated for moderate strength gains, shines best when cold worked and used in an annealed condition for welding.
Hot Rolled vs Cold Drawn Steel
Steel is said to be hot rolled when it is shaped at a high temperature, because its temperature is high, it is a lot easier to shape and form. This however, makes the final product less precise. It has a rougher surface finish, and the dimension is less accurate.
A cold-drawn steel, otherwise called a cold finished steel, is drawn or formed at room temperature, after the steel has cooled. Cold drawn steel has a smoother surface finish and higher dimensional accuracy compared to hot rolled steel.
Both hot rolled and cold drawn steel can be used for 4140 and 4130 steel, depending on the application and requirements.
Structural applications and Industries
| Industry | 4140 Steel | 4130 Steel |
| Automotive | Drive shafts, gears, axles | Roll cages, chassis |
| Aerospace | Landing gear, structural links | Tubular airframes |
| Oil & Gas industries | Drill collars, tool joints | Tubular systems |
| Construction | High-load structural components | Lightweight frames |
| Manufacturing | Dies, molds, complex shapes | Low-stress machine parts |
Industry Requirements and Standards
The Society of Automotive Engineers (SAE) and the American Iron and Steel Institute (AISI) are a few of the bodies that govern the production and use of steel. They set the standards and requirements for steel production.
Other industry standards are:
Material Test Reports: This is verifying and confirming the chemical and mechanical compositions and properties of the steel
Heat treatment certification
Tracing every piece of material to its production batch and to the factory where it was made
Final Considerations
The 4140 and the 4130 steels are strong and dependable materials; they each have their unique strengths. The 4130 steel has excellent weldability and is quite machinable, the 4140 has greater strength and better wear resistance. This is the clear choice when toughness and durability are at stake.
It is clear that choosing between the two is not just trying to decide which is stronger, it is about which steel best suits the requirement and intended use. Understanding the differences between these two kinds of steel is paramount to the correct and perfect application. Choosing steel is not about what the steel can do, it is about what the steel is needed for