While there are many materials which are tough and long-lasting and others which are malleable it is difficult to find materials which have all of these characteristics. This is why maraging steel is so important in the world of mechanical engineering and why it plays a major role in our everyday lives.
What is Maraging Steel?
Maraging steels are generally ultra strong iron-nickel alloys of high toughness and relatively high levels of ductility. Contrary to other strong alloys, maraging steel doesn’t contain any carbon molecules as this would have a negative impact on their malleability. Instead, they are enriched with substances such as titanium, molybdenum, aluminium, and cobalt. Then the material is treated with heat at around 820 degrees Celsius for half an hour, cooled and heated again at 500 degrees Celsius for 3 hours and then left to cool at room temperature for hardening purposes. There are also alternative heating processes followed using different temperatures to achieve other kinds of precipitation of inter-metallic compounds.
Maraging steels are categorised in grades and are separated by different compositions in their nickel and the aforementioned secondary components. In general, the nickel percentage ranges from 15% to 25%. Cobalt percentage ranges from 5% to 15%, molybdenum from 2% to 7%, titanium from 0.1% to 2%, and aluminium from 0.05% to 0.2%. In some cases chromium is also added, further increasing the harden-ability of the steel during the heat treatment as well as offering stainless steel corrosion resistance properties to the final product.
Unique Properties of Maraging Steel
- Starting with the high strength of the maraging steel, depending on the grade it ranges from 1500 (grade 200) to 2400 (grade 350) of MPa of yield strength. This is about seven times greater than a typical construction steel of the highest S355 grade.
- The tensile strength of maraging steel is 2450 MPa while that of the S355 steel is only 470 MPa, meaning that it can withstand very strong tensile forces without being permanently deformed.
- Maraging steel is very strong yet very ductile/malleable, and these two characteristics are very hard to combine and also very useful in practice. This means that maraging steel can be easily formed and rolled into shape without cracks and fractures forming on its surface or body.
- Another unique property of maraging steels is their very good weldability which basically means that it can be easily joined with other metals achieving a good level of integration on the welding points.
- Adding chromium, cadmium, or with phosphating makes maraging steel exceptionally resistant to corrosion from a wide spectrum of elements. Even when untreated, maraging steel retains corrosion resistance properties thanks to the relatively high nickel concentration.
- Maraging steels are generally stable in their physical properties and do not demonstrate significant thermal expansion or dimension change after hardening treatment. This makes it possible to machine the piece to its final dimensions before performing the heat treatment procedure.
Common Uses of Maraging Steel
Thanks to the unique properties of maraging steel, combining high tensile strength with ductility, it is extensively used in aerospace applications like wing fittings, various tools that are made to be durable, fastener components that are made to hold elements reliably, and machinery parts that are built to last. Especially on applications that are fuel-critical such as rockets and missiles where the weight to power/propulsion ratio is a key consideration, maraging steel is preferred as it can be rolled to thin sheets and retain its strength even at temperatures as high as 400 degrees Celsius.
The physical properties stability makes maraging steel perfect for machinery that interchanges between cold and hot quickly, so it is used for engine crankshafts, weapon firing pins, gearboxes, and gas centrifuge units. Due to the material’s high resistance to breakage maraging steel is also used in fencing sports to avoid accidents, golf club heads, and bicycle frames. Finally, and because crack propagation is very slow, it is used in applications where visual inspections are frequently performed and parts are able to serve in emergency situations allowing the time for their replacement.