Maraging Steel (Introduction)

MARAGING STEEL (INTRODUCTION)

Maraging Steel (Introduction) Maraging Steel

What is maraging steel?

Maraging steel is an extra-low carbon content steel that boasts of exceptional material strength and toughness. The term ‘maraging’ refers to the strengthening mechanisms; ‘mar’ refers to martensite, and ‘aging’ refers to a heat treatment called age hardening. Maraging steel is forged by a martensitic transformation followed by subsequent age hardening. The resulting microstructure consists of many micro precipitates embedded within the martensite lathes.

Compare this to what martensite looks like in general:

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Taken from this source.

What is Age Hardening?

Age hardening is a heat treatment process that causes solid precipitates to form within the martensitic matrix. These precipitates are as small as several nanometers, and function as an obstacle against dislocation movement that contribute to the materials’ superior properties2.

Grades of maraging steel

Maraging steel comes in different grades (250, 300, 350 grade). This grade number refers to the maximum achievable yield strength (in ksi), and this is often dependent on the initial composition, alloy content, and the thermo-processes. The commonality (for the most part) of these different grades are that all maraging steels typically contain 18% Nickel. The other alloying elements (such as Cobalt or Titanium) are variable.

Chemistry of 350 grade maraging steel

C Si Mn Ni Co Mo Ti Al Fe < 0.03% < 0.10% < 0.10% 18.50% 12.00% 4.80% 1.40% 0.10% Remainde r

Source

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Maraging steel applications

One of many advantages that maraging steel have is their malleability. Maraging steels are highly sought in applications that require precise and specific geometries and demand operation at high loads. Examples of such applications are:

1. Rocket motor casings. These casings need to be comprised of material that can be molded according to specified design, and demand the ability to contain the highly pressurized inner contents. 2. Takeoff and landing gear in aircraft. These components are often susceptible to high stresses and malleability is also important here. 3. Fencing blades. Fracture resistance makes maraging steel an attractive choice in the sport of fencing. This reduces the risk of fencing related injuries.

Process-structure-property (PSP) linkage of maraging steel

We are interested in PSP linkages of a 350 grade maraging steel. We are interested in studying the effects of different aging temperature and time. 350 grade annealed maraging steel were received, then quenched at 830C for 1.5 hours. Post-quenching, different aging temperatures and time were used for heat treatment. A total of 18 samples were obtained with the following heat treatments:

Sam1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ple No. Agin0.5 6 30 60 300 600 0.5 6 30 60 300 600 0.5 6 30 60 300 600 g Ti me ( min utes ) Agin 430 500 570 g Te mp. (Cel cius )

Nano-indentation will be performed to obtain mechanical properties of each sample. Imaging techniques such as scanning electron microscopy will be used and then 2 point statistics will be performed for rigorous microstructure quantification. The complete collection of these data will be used to create our PSP linkage of 350 grade maraging steel.

References

1 Hall, A. M., and C. J. Slunder. “The metallurgy, behaviour and applications of 18 Ni maraging

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steel.” NASA, SP-5051 (1968).

2 Designing Ultrahigh Strength Steels with Good Ductility by Combining Transformation Induced Plasticity and Martensite Aging

Misc. Resources

Maraging Steel Data Sheet

Maraging Steel Spec. Sheet

Matweb Database

Dierk Raabe on Maraging Steels

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