Moderate levels of corrosion resistance, high hardenability and machinability, poor formability and can be welded with caution. Here's a closer look at the martensitic family of stainless steel.
Today there are roughly 200 different grades of stainless steel, all of which fall within one of the five families of stainless steel:
- Precipitation Hardening
In a previous blog, we explored austenitic stainless steels, detailing where to use some common grades and why. Here, the focus is on martensitic stainless steels.
All stainless steels are iron-based alloys containing at least 10.5% chromium. The rest of the makeup is defined by various alloying elements, which control the microstructure of the alloy. For martensitic stainless steels, that make up includes carbon and iron.
Characteristics: Moderate levels of corrosion resistance, high hardenability and machinability, poor formability and can be welded with caution. Can be heat treated to provide a range of mechanical properties.
Now let’s take a closer look at three martensitic grades to see which are best suited for what applications—and why.
Where to use it: Valve and pump parts, fasteners, cutlery, turbine parts and bushings.
Why: This heat-treatable grade is ideally suited for use in environments where corrosion is not severe. This includes air, fresh water and with some chemicals and food acids. A quenched and double tempered variation is used for parts in hydrogen sulfide service.
Where to use it: Pump shafts, valve components and automatic screw machine parts.
Why: This is considered a ”free-machining variation” of 410 that features useful corrosion resistance to natural food acids, basic salts, water and most atmospheres.
Where to use it: Steam turbines as blading and bolting material.
Why: This grade is designed for service temperatures up to 1200 F° and features a good combination of strength and toughness.
Where to use it: Ball or roller bearings
Why: This high carbon chromium steel can attain the highest hardness (Rockwell C60) of any standard stainless grade. In the hardened and stress relieved condition, 440 C has maximum hardness and its strength, corrosion resistance and abrasion resistance are all considered high.
The variation 440 A features lower levels of carbon (.60), resulting in lower hardness, but greater toughness in the hardened condition.