Types of SS (Stainless Steel) Investment Castings
An investment casting part poured in 316 stainless steel.
Anyone who has picked up a new hobby or interest has experienced the sensation of finding just how deep rabbit holes can go if you start to look. As an example, I recently have been getting a friend into watching hockey. On the surface, it is a simple game - players skate around and fire a puck into the net. The team with the most goals at the end of 60 minutes wins. But, even as a casual observer, it is much more complex than that. On your first (or even multiple watches), you may wonder why a team would play without a goalie, what constitutes an offside, and what the difference is between a two and four-minute penalty. All of this without getting into teams, rivalries, defensive schemes, playoffs, farm programs, international play, and everything else that comes together to make hockey - hockey. It's been fun explaining hockey to my friend because it gives us something to talk about during intermission and, as you would expect, has helped her enjoy the game so much more because now she understands the basics and the more nuanced parts of play.
Something we hope to achieve with the blogs hosted on our website is to help our visitors unpack the wide world of investment casting into small, bite-sized chunks; something they can read in 5 or so minutes and come out better informed when they start their next casting project. In today's blog, we're going to tackle the basics of one of our most popular materials stainless steel (ss). Specifically, what makes stainless steel stainless? What are the primary categories of ss, ( 300 series, 400 series, precipitation hardening, and beyond) and what each of these categories used for. Let's get into it!
What is Stainless Steel?
The perfect place to start! Chances are, you've used or passed by stainless steel in your home today without even thinking about it. SS is super commonly used in appliances like refrigerators and dishwashers or pots and pans. But what sets it apart from say, regular steel or something like bronze? Let's talk about that.
You can think of metal composition much like ingredients in a cake - instead of flour, sugar, water, vanilla, etc., in an alloy, you'll see a mix of things like iron, molybdenum, nickel, carbon, and so on. Just like our cake, by playing around with different combinations of ingredients, you can get markedly different results by changing incorporated elements. For example, if you want to have the worst cake you've ever eaten, make the batter 60% salt.
Stainless steel is an iron-based alloy with a bare minimum of 10.5% chromium in its makeup. This chromium percentage can be as high as 30% in specific grades; more on that later. Stainless steel can include several different elements but typically contains carbon, molybdenum, nickel, silicon, manganese, nitrogen, and other trace inclusions.
What is so special about Chromium?
The inclusion of >10.5% chromium makes ss resistant to rust and corrosion. When a ss is exposed to oxygen, Chromium forms a protective, passive film that enables it to self-heal when exposed to the elements. This resistance makes it a popular choice in dozens of industries because, with simple maintenance, it can perform for years and years, where other alloys will corrode and require replacement.
Other Cool Things About Stainless Steel:
Stainless Steel is very hygienic: While it is not inherently sterile, SS doesn’t support bacterial growth and is non-porous. This makes it a go-to choice for many industries where cleanliness is king, like food processing or medical instruments.
Stainless steel is recyclable. After use, its components can be reclaimed with next to no degradation, and it is estimated that 95% of stainless is recycled at the end of its lifecycle (1.)
Types of Stainless Steel
There are five primary types of Stainless Steel used in investment casting:
300 Series (Austenitic)
400 Series (Martensitic)
Ferritic Stainless
Duplex Steel
Precipitation Hardening (PH) Stainless.
Let's go over each in a little bit more detail.
300 Series SS (Austenitic):
Is the most common and widely used type of ss. It is also the most corrosion-resistant type of stainless, with a unique FCC crystal structure stabilized by nickel. Grades like 304 and 316 dominate industries from food processing to marine engineering due to their non-magnetic nature, weldability, and superior rust resistance.
Commonly poured alloys:
Carpenter 20
CN7M
Nitronic 60
Commonly used in:
Food Processing: 304 & 316 in sinks, processing lines, kitchenware
Medical: 316 for surgical instruments, implants
Construction: Architectural panels, railings, fasteners
Marine: 316 is frequently used due to saltwater resistance
400 Series SS (Martensitic):
are high-strength, magnetic alloys that can be heat-treated (quenched and tempered) for increased hardness, making them ideal for wear-resistant applications like knives, valves, and industrial tools. Unlike austenitic grades, they can be hardened and are magnetic but offer less corrosion resistance. The term "martensitic" refers to their body-centered crystal structure formed during rapid cooling from high temperatures.
Commonly Poured Alloys:
410 Stainless
416 Stainless
440C
CA6NM
Commonly used in:
Cutlery & Blades: Kitchen knives, surgical scalpels, hunting knives
Aerospace and Power Generation: Turbine Blades & Fasteners:
Valve Components & Pump Shafts: Oil & gas, water treatment, and industrial systems
Ferritic Stainless Steel:
are magnetic, corrosion-resistant alloys with a body-centered cubic crystal structure. They are composed mainly of chromium (10.5–30%) and little to no nickel. Known for their moderate strength, good ductility, and cost-effectiveness, they are widely used in automotive, appliance, and industrial applications where high corrosion resistance is not the primary requirement. Ferritic SS Cannot be hardened by quenching (unlike martensitic steels) and, while not as corrosion-resistant as austenitic steels, ferritic grades offer better stress corrosion cracking resistance at a lower price point.
Commonly Poured Alloys:
409 Stainless
430 Stainless
434 Stainless
439 Stainless
Commonly Used In:
Automotive: exhaust systems, heat shields, mufflers
Industrial Use: Furnace parts, heat exchangers, incinerators
Architecture & Construction: Wall cladding, roofing and rainwater systems, elevator panels
Duplex Steel
Duplex stainless steels are high-strength, corrosion-resistant alloys that combine the best properties of austenitic and ferritic stainless. Its name comes from its two-phase microstructure (~50% austenite + ~50% ferrite), giving it unique advantages over traditional stainless grades.
Some Advantages of Duplex:
✅ Better chloride resistance than 316 stainless (Great for marine applications)
✅ 2x stronger than 304/316 austenitic steels, allowing lighter, thinner designs.
✅ Good resistance to stress corrosion cracking (unlike austenitic steels).
✅ Cost-effective alternative to high-nickel alloys
✅ Magnetic (due to ferrite content duplex steels are at least partially magnetic)
Commonly Poured Alloys:
2205
2507
2304
Zeron 100
Commonly Used In:
Marine Industry: Offshore platforms, subsea equipment, desalination plants
Petrochemical: Chemical processing, marine, oil & gas piping, pressure vessels
Precipitation Hardening (PH) Stainless Steel
Are high-strength, corrosion-resistant alloys that can be hardened to exceptional strength levels through a specialized heat treatment process called precipitation hardening (or age hardening). These steels combine the best properties of martensitic and austenitic grades—offering ultra-high strength, good corrosion resistance, and excellent toughness.
What makes PH stand out?
✅ Extremely high strength-to-weight ratio (stronger than titanium in some cases).
✅ Good corrosion resistance (better than martensitic, near 304 stainless).
✅ Can be heat-treated after machining/welding for precise strength control.
Commonly Poured Alloys:
15-5 PH
17-4 PH
25-5 PH
Commonly Used In:
Aerospace: Landing gear parts, structural fittings, shafts
Marine: Pump shafts, valve parts, propeller shafts
Medical: Orthopedic implants, surgical tools, dental drills
Defense & Firearms: Gun barrels, bolt components, triggers, fasteners
Conclusion:
We began this blog by talking about hockey and the rabbit holes you can go down as soon as you look past the game on a surface level. A quick readthrough of this article will show you just how wide the world of stainless steel can be!
In this whirlwind blog, we talked about the basics of stainless steel, briefly introduced categories, talked about the strengths of each category, some frequently poured alloys, and common usage scenarios. We tried to keep things brief, but each grade of stainless steel could warrant its own discussion if you really wanted to nerd out with us!
Ultimately, if you're looking to utilize stainless steel in your next casting project, it is a good idea to look at all of the nuances of your project before settling on a material and grade. There is a ton to choose from!
At IPC, we have expert engineers and metallurgists standing by who are able to help you pick the perfect alloy for any application. If you'd like to learn more about our material selection, or kick off your investment casting project, contact us today!
Sources:
"Recycling," World Stainless, accessed May 30, 2025, https://worldstainless.org/sustainability/environment/recycling/.
