It is very useful for any mechanical engineer to be aware of 4130 steel properties. 4130 steel, otherwise known as Chromoly or chromium molybdenum steel alloy, is made with 0.8 to 1.1% chromium and 0.15 to 0.25% molybdenum as strengthening agents. steel properties make it a versatile metal, especially mechanical properties such as high ductility, good weldability, and the fact it can be machined easily.
Four digit AISI (American Iron and Steel Institute) numbers are used to designate alloy steels.
4130 steel sheets and coils are very hard and due to their high strength and weldability, are widely used for:
- Military aircraft
- Commercial jets
- Machine tools
- Welded tubing (especially in the oil and gas industries)
steel properties also make it ideal for fabricating car parts and machine components.
AISI 4130 steel is forged at a temperature between 950° C and 1230° C. If the temperature is at the lower end during the finishing stage, the grain of the steel alloy will be finer.
If the temperature is too low at forging it may affect the uniformity in parts of the structure creating the need for normalisation before heat treating the steel.
The reason for heat treatment is to prepare the alloy for machining and to enhance 4130 steel properties. There are four main ways to heat treat steel alloy: annealing, normalising, hardening, and tempering.
Once 4130 steel has been forged into parts, sheets or coils, it may be annealed straightaway. It will be transferred from the forge into a furnace and kept at a temperature of approximately 860° C. It will be held there for a set amount of time then furnace cooled.
The main reason to anneal 4130 steel is to prepare it for machining. The resulting structure obtained by annealing the steel alloy makes it ideal for forming simple shapes, e.g. sheets or coils.
Sometimes a speroidizing annealing process at 750° C will be needed if the temperature of cooling hasn’t been uniform across the metal which has resulted in an uneven structure.
The normalising process heats the steel to a higher temperature than annealing, typically to 900° C, but this figure can vary by 10° C either way depending on preferred production outcomes. Sometimes, normalising may take place on rolled or forged steel to condition it before heat treatment. If this is the case, say before the steel is hardened and tempered, the higher temperature value will be used, i.e. 910° C. If normalising is to be the final treatment, then 890° C would probably be used.
The process uses such a high temperature in order to create the conditions for transformation from ferrite to austenite, and is then air cooled to finish.
The objective of a hardening heat treatment is obviously to alter 4130 steel properties by increasing the hardness, but it also increases the tensile strength and brittleness of the steel. 4130 steel hardening treatment creates martensite in the alloy post-quenching.
The steel is normally austenitised to transform all micro constituents to austenite in the range 815 to 870° C.
The main purpose of tempering is to relieve stress from the metal after hardening. It also starts the process of creating the required mechanical properties. The temperature for the tempering process depends on the properties desired. In many cases, 4130 steel alloy manufacturers will experiment with different tempering temperatures to yield various results.
4130 steel properties make it straightforward to machine conventionally unless it has been significantly hardened. Annealed 4130 has a machinability rating of 72%, which is increased if further hardening takes place due to the formation of martensite.
4130 steel is easy to weld due to its low carbon content. This makes it popular in sheet, coil, or tube form as it can be used to fabricate sections of aircraft or pipework for the oil and gas industry.
Here are values for some of the main steel properties:
- Density – 7.85 g/cm3
- Hardness – 217 (Brinell scale) – 95 (Rockwell B)
- Ultimate Tensile Strength – 540 MPa
- Yield Tensile Strength – 460 MPa
- Modulus of Elasticity – 205 GPa
- Machinability – 72% (in annealed state)
4130 steel properties make it the perfect choice for automotive, aeronautic and aerospace engineering as it is tough, easily machined and weldable. When heat treated, it develops mechanical properties that make it a very strong metal, although it can lose some of its machinability.