What’s up guys? This is Michael with Michael Talks Metal back for another session on some metal! Thanks for watching, let’s do this!

Topic for this video is a category of alloy steels that achieve very high strength levels with a simple heat treatment after the manufacture of the part. These alloys are called “Maraging” steels. MAR from martensite and AGEING for how they develop  strength.

Conventional steel alloys  like 4340 ,that can achieve comparable strength levels have a minimum carbon content of point 4 % and require a high temperature austenitizing step followed by rapid quenching and then a final tempering to develop their strength. Needless to say, this process can be very troublesome in many part configurations. With these carbon levels any welding requirement can be very problematic.

Maraging steels simplify the heat treatment since they require only a single step  low temperature heat treatment with no drastic “Quench”

This “Maraging” category of steel has low carbon content which lends greater toughness at high strength levels as compared to the higher carbon alloy steels at similar strength levels. Weldability is also much improved owing to the lower carbon.

They are highly alloyed steels where the major elements Nickel, Cobalt, and Molybdenum allow the formation of a stable martensitic structure in the annealed condition and the minor elements Titanium and Aluminum can strengthen the microstructure when it receives the ageing heat treatment after parts are manufactured.

Typical applications  involve high strength levels and often failure critical components where toughness is important.

These three alloys of the most common type are premium remelt aircraft quality steels conforming to AMS2300  cleanliness. All are point 03 % maximum Carbon, point 010 % Sulfur, and point 010% maximum Phosphorus.

The three alloys are in order of increasing strength after aging and the UNS designation defines the chemistry

Maraging 200,  UNS K92810 has 17 to 19 % Nickel, 8 to 9 % Cobalt, 3 to 3.5% Molybdenum, point 15 to point 2% Titanium and point 05 to point 15% Aluminum.

Maraging 250 ,  UNS K92890 has 17 to 19 % Nickel, 7 to 8.5% Cobalt, 4.6 to 5.2 % Molybdenum, point 3 to point 5% Titanium, and point 05 to point 15% Aluminum.

Maraging 300, UNS K93120 has 18 to 19% Nickel, 8.5 to 9.5% Cobalt, 4.6 to 5.2% Molybdenum, point 5 to point 8% Titanium, and point 05 to point 15% Aluminum.

Maximum hardness in the annealed for all three is 321 BHN ( 34 Rockwell C).

Annealing is typically at 1500 to 1700 degrees F  and would be performed by the producing steel mill.

Ageing is typically performed   at 900 degrees F for 6 hours after manufacture of parts.

Common specifications for Maraging steels are AMS 6512, AMS 6514, MIL-S-46850, and MIL- S-13881.  Requirements within specs and for parts are extremely important in these high strength steels.


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