The full transcript for the video is below. In this video we are trying to answer the following questions. What is martensititc stainless steel? What grades or types would be considered martensitic? Can you heat treat martensitic stainless steels? What is the difference between martensitic and austenitic stainless steels?
Today’s video is the first on Martensitic stainless steels and we hope you find useful. Martensitic stainless can be hardened by conventional heat treatments. You may be familiar with heat treating carbon and alloy steels. If not, in very simplified terms you heat the material up to a temperature where the structure becomes austenitic and then cool at a rate fast enough and “presto” martensite is the resulting structure. Cool slower and the steel structure would become ferrite and iron carbides. With the faster cooling, the carbon atoms do not have time to form the carbides and become “stuck”.
Martensite is considerably harder, stronger, and more brittle than the other structures we have touched on in previous videos, the austenite and ferrite types. Hardness achieved goes up with increasing carbon content of the alloy. Here in part one we will be discussing alloys with a carbon content of .15 % and less which yield a hardness of 45 Rockwell C and below depending on the amount of carbon.
At their maximum hardness, these alloys are also at their most resistant to general corrosion but tend to be brittle. To get the combination of corrosion performance and useful strength and hardness, the material is again heated to create a “tempered” martensitic final structure. Lose the brittleness without sacrificing too much hardness and corrosion resistance.
These Martensitic stainless types also lose toughness in impact at temperatures of 0-100 F depending on the type and heat treatment.
Wow… so now we are balancing the hardness, strength and corrosion performance we need. Sounds complicated and it is Glad we’re not doing that here. Just the basics…
Anyway, let’s get into some of the types in this category
Type 410 at 11.5 to 13.5 has a carbon maximum of .15%. Depending on the actual carbon content, the maximum hardness it can achieve varies from the low 30’s to low 40’s Rc. Various specifications restrict the chemistry or require a range of hardness in standard tests to assure the higher hardness version when needed. AMS 5612 for aircraft applications is one that requires the higher hardness in standard test.
Type 403 is a very similar chemistry and is known as “turbine quality”… originally used for steam turbine blade, valves, and other component applications where strength and oxidation corrosion at operating temperatures above 800 F
Type 416 has the same .15% maximum carbon and Chromium at 12% to 14% but has Sulfur added to improve machinability. Often it has lower actual carbon content and typically is used at lower hardness than 410. Sulfur has negative effects on toughness and corrosion resistance. This grade is used where the added machinability offsets a loss in corrosion performance and mechanical properties. 416 is used in a wide variety of applications such as screw machine parts.
As we have said before, specifications often restrict the chemical composition further and add requirements for the material far beyond just the chemistry.
Stay tuned for part 2…. higher carbon and higher hardness martensitic stainless steels. This is Michael Michlin Metals. Out.