304 vs. 347 Stainless Steel: What's the difference?

Before we pit 304 and 347 against each other, let's make sure we're all on the same page about what stainless steel actually is. At its core, stainless steel is an alloy—a mix of iron and other elements—that resists rust and corrosion. The magic ingredient here is chromium. Add at least 10.5% chromium to iron, and you get a thin, invisible layer of chromium oxide on the surface. This layer acts like a shield, repairing itself if scratched, which is why stainless steel stays "stainless."

But chromium alone isn't enough to make every stainless steel unique. Manufacturers tweak the recipe by adding other elements—nickel, carbon, manganese, and sometimes more exotic metals like niobium—to fine-tune properties like strength, flexibility, and resistance to heat or chemicals. That's where 304 and 347 come in: they're both part of the "austenitic" family of stainless steels (known for their ductility and non-magnetic properties), but their extra ingredients make them suited for very different jobs.

Think of stainless steel grades as baking recipes. Both 304 and 347 start with a base of iron, but their "spices" change everything. Let's break down their key ingredients:

304 Stainless Steel: The "All-Purpose" Mix

304 is often called the "workhorse" of stainless steels, and for good reason. Its recipe is simple but effective: roughly 18% chromium and 8% nickel (hence the nickname "18-8 stainless"). This combo gives it excellent corrosion resistance and makes it easy to form into sheets, pipes, or wires. It also contains small amounts of carbon (usually less than 0.08%) and manganese, which help with strength and (that's "workability" for those who don't speak metallurgy jargon).

You've probably interacted with 304 today without realizing it. It's in your kitchen appliances (think refrigerators, dishwashers), food processing equipment, surgical tools, and even the stainless steel railing on your office stairs. It's affordable, reliable, and handles everyday wear and tear like a champ.

347 Stainless Steel: The "High-Temp Specialist"

347 takes the 304 recipe and adds a secret weapon: niobium (sometimes called columbium, but let's stick with niobium for simplicity). Niobium is a rare earth metal that might sound fancy, but its job is straightforward: it "stabilizes" the steel against a common problem in high-heat environments called "carbide precipitation."

Here's the quick version: when stainless steel with carbon is heated to high temperatures (say, 800–1500°F/425–815°C), carbon can team up with chromium to form chromium carbides. These carbides tend to gather at the "grain boundaries" of the metal (the tiny seams between metal crystals), leaving the surrounding areas short on chromium. Without enough chromium, that protective oxide layer we talked about earlier breaks down, making the steel vulnerable to corrosion. This is called "intergranular corrosion," and it's a big issue in high-heat applications.

Niobium in 347 solves this by bonding with carbon first, forming niobium carbides instead of chromium carbides. That way, chromium stays where it belongs—protecting the steel. 347 also has slightly more chromium (around 17–19%) and nickel (9–13%) than 304, and its carbon content is capped at 0.08% as well. The result? A steel that laughs in the face of high temperatures.

Okay, so their recipes are different—but how does that translate to real-world performance? Let's compare their mechanical properties, which is just a fancy way of saying "how strong, stretchy, and tough they are."

Tensile Strength: How Much Pull Can They Take?

Tensile strength is the maximum stress a material can handle before breaking. 304 has a tensile strength of about 515 MPa (megapascals), while 347 comes in slightly higher at around 550 MPa. That might not sound like a huge difference, but in high-pressure applications—like pressure tubes in a power plant—every MPa counts.

Yield Strength: When Do They Start to Bend?

Yield strength is the point where the material stops springing back and starts to deform permanently. 304 yields at about 205 MPa, while 347 is a bit stiffer, yielding at around 240 MPa. Again, not a massive gap, but if you need a part that stays rigid under stress (like a structural bracket in aerospace), 347 might have the edge.

Ductility: Can They Stretch Without Breaking?

Ductility is how much a material can stretch before snapping. 304 is highly ductile, with an elongation (stretch before breaking) of around 40%. 347 is still ductile but slightly less so, at about 35%. This means 304 is easier to bend, shape, or form into complex parts—think of it like comparing a rubber band (304) to a slightly stiffer rubber band (347).

Hardness: How Resistant to Dents?

On the Brinell hardness scale (which measures how easily a material is indented), 304 scores around 92, while 347 is a touch harder at 95. Again, similar, but 347 might hold up better to abrasion in rough environments.

Overall, their mechanical properties are pretty close. The real differences show up when you throw heat, corrosion, or extreme pressure into the mix.

Both 304 and 347 are known for corrosion resistance, but their Achilles' heels are different.

304: Great for Everyday, but Not Perfect

304 is excellent at resisting general corrosion—think rain, humidity, or exposure to mild chemicals. That's why it's used in food processing (acids from fruits and veggies), coastal architecture (salt spray), and medical equipment (sterile environments). But remember that intergranular corrosion issue we mentioned? If 304 is heated to that 800–1500°F range (say, during welding or in a high-temperature industrial process), it becomes vulnerable. For example, if you weld a 304 pipe and don't cool it properly, the heat-affected zone might start to corrode from the inside out over time.

347: The Corrosion Champ in High Heat

Thanks to niobium, 347 is practically immune to intergranular corrosion, even after heating. That makes it a star in environments where heat and corrosion team up—like heat exchanger tubes in a petrochemical plant, where hot, corrosive fluids flow through metal pipes. It also holds up well in high-pressure systems, like the pressure tubes that carry steam in power plants. Even in marine environments, where saltwater is relentless, 347 outperforms 304 over time.

But here's the catch: 304 is still better in low-heat, everyday scenarios. It's more affordable and easier to work with, so there's no need to overengineer with 347 if you're just making a kitchen sink.

Let's talk about high temperatures—the kind that would make a regular metal sweat. This is where 347 really shines.

304: Starts to Struggle Above 800°F

304 handles moderate heat well. It's fine in ovens, car exhaust systems, or hot water tanks. But above 800°F (425°C), its strength starts to ｄｒｏｐ, and as we discussed, that carbide precipitation becomes a risk. At 1600°F (870°C), it's no longer reliable for structural use—think of it like trying to use a plastic ruler to prop up a bookshelf in a sauna.

347: Built for the Heat

347, on the other hand, laughs at high temperatures. It can handle continuous use up to 1600°F (870°C) and short bursts up to 1900°F (1038°C). Why? Because niobium stabilizes its structure, preventing the grain boundaries from weakening. This makes it ideal for applications like aerospace components (jet engines get incredibly hot), furnace parts, and heat efficiency tubes in power plants, where maximizing heat transfer without sacrificing durability is key.

Imagine a heat exchanger tube in a coal-fired power plant: it's constantly exposed to superheated steam at 1000°F. 304 might last a few years before developing cracks, but 347 could keep going for decades. That's why industries like power plants & aerospace rely on 347 for critical high-heat parts.

Let's get practical. When should you reach for 304, and when is 347 the way to go?

304 Stainless Steel: The Everyday Hero

304 is everywhere because it's affordable, versatile, and good enough for most jobs. You'll find it in:

• Kitchen gear: Sinks, utensils, appliances, and food storage containers (it's food-safe!)
• Architecture: Handrails, facades, and decorative trim (it looks good and resists weathering)
• Medical equipment: Surgical tools, hospital beds, and MRI machines (easy to sterilize)
• Low-temperature industrial parts: Pipes for cold water, HVAC systems, and non-critical structural components

347 Stainless Steel: The High-Performance Specialist

347 is the go-to when "good enough" isn't enough—especially in high-heat, high-pressure, or corrosive environments. Common uses include:

• Heat exchanger tubes: In petrochemical facilities and power plants, where fluids are heated or cooled under extreme conditions
• Pressure tubes: Carrying steam, oil, or gas in pipelines and industrial systems where failure could be catastrophic
• Aerospace components: Jet engine parts, exhaust systems, and structural elements that face high temperatures and stress
• Marine & ship-building: Saltwater-resistant parts like propeller shafts and hull components
• Nuclear power: Some nuclear reactors use 347 for its radiation resistance and high-temperature stability (though specialized grades like RCC-M Section II nuclear tube are often used here too)

One quick note: 347 costs more than 304—sometimes 20–30% more—because of the niobium. So unless you need its high-heat or corrosion-resistance superpowers, 304 is the smarter budget choice.

At the end of the day, the choice between 304 and 347 comes down to your needs. Ask yourself these questions:

Do you need high-temperature resistance?

If your project involves heat above 800°F—like a heat exchanger tube or a jet engine part—go with 347. The niobium will keep it strong and corrosion-resistant.

Is corrosion a major concern, especially after welding or heating?

347's niobium stabilizes it against intergranular corrosion, making it better for welded parts or high-heat industrial systems. 304 works if you're sticking to room temperature.

What's your budget?

304 is cheaper and works for most everyday applications. Only splurge on 347 if you truly need its high-performance features.

How important is ductility?

If you need to bend, shape, or form the steel into complex parts (like decorative metalwork), 304's higher ductility makes it easier to work with.

Think of it like choosing between a sedan and a sports car. A sedan (304) is great for commuting, grocery runs, and everyday life—it's reliable and affordable. A sports car (347) is faster, stronger, and built for extreme conditions, but you'll pay more and it's overkill for trips to the mall.

304 and 347 stainless steel might look similar on paper, but their differences are all about specialization. 304 is the people's steel—versatile, affordable, and ready for whatever life throws at it. 347 is the expert, called in when the going gets tough: high heat, high pressure, and corrosive environments where failure isn't an option.

Whether you're building a kitchen, a power plant, or a spaceship, understanding these differences helps you pick the right material for the job. And remember: when in doubt, talk to a materials engineer or supplier. They can help you weigh factors like cost, performance, and longevity to make the best choice.

At the end of the day, both 304 and 347 are testaments to human ingenuity—turning simple elements into materials that build our world, one tube, pipe, or bracket at a time.