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Summary
  • SS 304 contains more chromium and nickel, giving it superior durability and resistance to corrosion and rust.
  • SS 409 costs less while delivering sufficient anti-corrosion protection for most applications.
  • Stainless steel is an iron alloy that adds chromium and nickel to prevent corrosion and block rust.
  • SS 304 and SS 409 are stainless steel grades with different chromium and nickel content.

Stainless steel is an indispensable material in automotive parts, especially exhaust parts like the exhaust pipe. It retains the advantages of ordinary steel, such as structural strength and resistance to cracking. Additionally, it alleviates some of steel’s greatest weaknesses, including the iron alloy’s vulnerability to rust.

That being said, stainless steel fasteners were used on some GM platforms, which turned out to be a mistake, because stainless steel fasteners tend to be worse to gall and seize than black oxide fasteners.

Furthermore, you can’t cut stainless steel with an acetylene torch because it doesn’t oxidize the way regular steel does. When you apply the oxygen jet to red hot stainless steel it simply cools the metal rather than burning it off. For this reason, exhaust fasteners made of stainless steel can be a big problem for a mechanic.

You can’t cut stainless steel with an acetylene torch because it doesn’t oxidize the way regular steel does.

– Richard McCuistian, ASE Certified Master Automobile Technician

There are many stainless steel grades (abbreviated as SS) with different characteristics and performance. Two of the most prevalent grades are SS 304 and SS 409. Stainless steel products often cite one of the grades. So, how do the two grades differ? And what’s the superior grade for automotive applications such as exhaust parts: SS 409 vs. SS 304 stainless steel?

SS 409 vs. SS 304

At first glance, you might not see any distinction between SS 304 and SS 409. However, the two stainless steel grades have significant differences.

The following is a comparison between SS 409 vs. SS 304 steel:

Chromium and Nickel Composition

The greatest difference between SS 409 and SS 304 is their chromium and nickel content. Stainless steel gets its characteristic resistance to corrosion and rust from the amount of these two elements present in the alloy.

When it comes to chromium, SS 304 is the clear winner. It contains between 18% and 20% chromium. In comparison, the chromium content of SS 409 runs between 10.5% and 11.75% chromium.

As for nickel content, SS 304 remains in the lead. Nickel comprises anywhere between 8% and 10% of 304 stainless steel. That’s higher than the amount found in 409 stainless steel, which usually contains 0.5%.

Corrosion Resistance

We judge stainless steel grades by their efficacy at preventing corrosion and stopping rust from forming on them. SS 304 has superior corrosion resistance, thanks to its higher chromium and nickel content. It can handle harsh environmental conditions, such as highly corrosive salt used to deice roads during winter.

In contrast, you might find rust on parts made from SS 409 after some time. Usually, the iron oxide only covers the surface and hasn’t penetrated the protective layer. However, rust can still ruin the part’s appearance and it might eventually find a way through.

Additionally, corrosive substances like calcium chloride or road salt can speed up the surface corrosion of 409 stainless steel grade parts.

Magnetic Properties

Lower grade stainless steel contains iron, which is a magnetic material. If iron magnetizes, it will attract other magnetic materials and magnets of the opposite polarity. But the higher the chromium and nickel content, the less magnetic stainless steel will be. The highest grades of stainless won’t even respond to a strong magnet.

, Comparing Stainless Steel Grades: SS 409 vs. SS 304

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: The majority of stainless steels falling into the “austenitic” stainless steels category are non-magnetic due to high levels of austenite. Despite the fact that austenitic grades 304 and 316 contain iron, these materials are not magnetic. The crystal structure of the alloy determines its magnetic properties.

SS 409 is made of 90% iron, making it highly magnetic. It can attract iron sand and other magnetic materials, leading to a part covered in metallic dirt.

In comparison, SS 304 contains smaller amounts of iron. It doesn’t strongly attract magnetic materials, which helps to keep it clean.

Price Tag

Stainless steel is a pricey material. And parts made of SS 304 fetch higher price tags than those that use lower grades. You get the excellent performance you pay for, but the additional expense is a waste if you can’t take advantage of the extra protection.

If you’re looking for a budget-friendly option, SS 409 is the way to go. It’s one of the most affordable stainless steel grades available. Stay aware of its limits and avoid pushing its corrosion resistance to the utmost, and you’ll be fine.

You can also remove the surface oxidation that forms on 409 stainless steel grade. Remove the oxide with a surface steel cleaner. The cleaner formula will help protect against premature corrosion in the future.

What Is Stainless Steel?

Stainless steel is an alloy of iron and carbon that can resist corrosion and rust. It’s created by adding chromium and nickel during the steelmaking process.

Chromium plays a critical role in stainless steel. When this element comes into contact with air, it reacts and forms chromium oxide. In stainless steel, chromium oxide forms a thin layer covering the surface of the steel.

The chromium oxide texture is an anti-corrosion coating that protects against more severe oxidation. It also prevents minor impacts from damaging the stainless steel, reducing the risk of corrosion and rust.

Nickel works together with chromium to increase the corrosion resistance of stainless steel. It’s a magnetic material, and large amounts might affect the magnetism of the stainless steel.

Thus, the amount of chromium (and nickel, to a lesser extent) determines the capabilities of the stainless steel grade. The higher the chromium content, the more resistant the alloy is to oxidation and corrosion.

The Society of American Engineers (SAE) devised a standard alloy numbering system for steel grades, including stainless steel.

What Is SS 304 Stainless Steel?

Officially called SAE 304 stainless steel, SS 304 is a stainless steel grade. It’s an austenitic stainless steel with a specific crystal structure that makes it non-magnetic and highly resistant to heat that would otherwise harden it. This type of stainless steel is created by adding an element that stabilizes austenite, such as nickel.

Compared to carbon steel, SS 304 is less magnetic and less conductive. As a stainless steel, it enjoys increased resistance to corrosion. Easy to shape and highly durable, it’s no wonder that SS 304 stainless steel is one of the most widely used stainless steel grades.

All About SS 409 Stainless Steel

Also called Type 409 stainless steel, SS 409 is another stainless steel grade in the SAE steel grade system. It’s a ferritic stainless steel that resists heat and protects against oxidation and corrosion.

SS 409 has superior corrosion resistance to coated carbon steel and is roughly on par with SS 410 stainless steel. It offers less overall protection against corrosion when compared to SS 304 stainless steel. SS 409 forms a light layer of oxidized material when it comes into contact with oxygen in air or water.

However, SS 409 stainless steel has a lower production cost than SS 304, making it a more budget-friendly choice.

Originally developed to make car exhaust parts that can withstand heat and corrosion, SS 409 is now used in other applications. However, it doesn’t fit applications that emphasize looking good on the outside or require the part’s surface to remain clean.

Knowing the difference between SS 304 and SS 409 can help you pick the right replacement part for your vehicle. These stainless steel grades have different strengths and weaknesses that might suit your budget and requirements.

About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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Fred benji

This info is great but you missed the one benefit of 409 – it can be bent without the cracking that happens over time. Yes, 304 is great for tips – not so good for exhaust body. And polishing- 304 polished exhaust is a waste of time unless you are building a show car.

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