What's new
What's new

303 versus 304 stainless

cnctoolcat

Diamond
Joined
Sep 18, 2006
Location
Abingdon, VA
I am looking for info about 303 and 304 stainless steels.

303 is very machinable, while 304 is a bear -- from what I understand.

304 has better anti-corrosive properties in harsh environments, whereas 303 does better in fresh water/air applications?

Cold-rolled hardness and mechanical properties of 303 and 304 are similar, no?

Aside from the corrosion benefit, why would you spec 304 steel over 303, for parts that were going to require machining? Is 304 that much cheaper??

ToolCat
 
Apparently 304 stainless is more weldable than 303. That could be a big factor for large assemblies w/ machined parts in them.

If it doesn't need to be welded, I would think 303 would be the way to go.

From what I gather the corrosion resistance between 303 and 304 is very similar. If 303 doesn't provide adequate corrosion resistance its probably best to step up to 316 anyhow.
 
I am looking for info about 303 and 304 stainless steels.

303 is very machinable, while 304 is a bear -- from what I understand.

304 has better anti-corrosive properties in harsh environments, whereas 303 does better in fresh water/air applications?

Cold-rolled hardness and mechanical properties of 303 and 304 are similar, no?

Aside from the corrosion benefit, why would you spec 304 steel over 303, for parts that were going to require machining? Is 304 that much cheaper??

ToolCat

I machine 303,304L,316L all day long. Screw Machining. 303 is free machining as I can walk away from the machine and the chips break and fall away like steel.

304 is softer than 303 but harder than 316. it cuts a razor wire ship and doesnt like to break. long stringy birds nests all over taps and drills. Doesnt work harden as bad as 316. Can take a good chip with sharp tools.

316 is a little softer than 304 and can work harden easier. Machines nice if you dont dwell on anything and take a good size chip. Marine Grade due to rust/corrosion proof properties.

Weldability...

303 not for welding

304 is weldable

316L is weldable. I emphasize the "L" in this case. I t means it has lower carbon than straight 316. I have a customer who welds this all day and says it has to be 316L not 316. It makes a big difference I guess. He has a niche market as his skills are not easily copied. I trust his judgment on that for sure.


Some PH 400 series is harder to cut but it holds tolerance easy. Just have to go slow and keep tools sharp. Mostly medical stuff so I dont know if its weldable.

303 has sulphur added and I guess that leads to poor weldability.

Edit: Passivation is used to get any carbon or iron from the tooling/cutting oil off of the parts. They do this to prevent surface rust from forming on the Stainless.

I had a guy tell me today 440 SS will rust on his shelf in 6 months.
 
304 welds very nicely, if you need that.

Flood it, keep it as cool as possible.

Sharp tools, more aggressive feeds with conservative speeds is what I've found to be a good combo.

Sent via CNC 88HS
 
I machine 303,304L,316L all day long. Screw Machining. 303 is free machining as I can walk away from the machine and the chips break and fall away like steel.

304 is softer than 303 but harder than 316.

At Alan Steel the 304 is called machinable and the 316 is not.
Have cut a lot of 304 and a little 316. Appeared to me that 316 is more difficult to cut, hence harder.
 
In addition to the above, it seems like form taps are better in 304, and cut taps do better in 303.
 
I have seen both 304 and 304L, the L in stainless is for Low carbon, so it can be welded without danger of cracking. Use caution to weld plain 304, best to use 304L if welded. 316 to 316L, same reasons. I have even seen some sq tubes a while back printed 304/304L?
 
303 gets used a lot in the food production as parts inside machines, welding is not considered. IIRC Carpenter has a number of different 303's with different doping agents for machining purposes and part use.

304 is easily welded but if the section is thick or if you’re really worried about it then 308L filler is usually the best choice spec’ed for price.

Good luck,
Matt
 
The higher carbon in 304 gives it slightly more strength than 304L. In depth info here, even speed & feed machining data per insert material for both 304 $ 304L:

AISI 304 vs 304L Stainless Steel Properties (UNS S30403) Difference Between 304 and 304L (SS304L) - The World Material

Nice description here from the link below:

"304L alloy’s lower carbon content helps minimize/eliminate carbide precipitation during the welding process. This allows 304L stainless steel to be used in the “as-welded” state, even in severe corrosive environments.... use standard 304 stainless in the same way, it would degrade much faster at the weld joints."


What’s the Difference Between Grade 304 and 304L Stainless Steel?
 
I have seen both 304 and 304L, the L in stainless is for Low carbon, so it can be welded without danger of cracking. Use caution to weld plain 304, best to use 304L if welded. 316 to 316L, same reasons. I have even seen some sq tubes a while back printed 304/304L?
I don't think I've ever seen 304 pipe or round tube that wasnt double stamped, but that may be the result of my environment more than anything else.

Sent via CNC 88HS
 
I dont do much in stainless and usually sq tube when I do so not super familiar with all the details. How would you get plain .08% carbon 304 if it's all double labeled?
I didnt notice if 304 had a minimum carbon content, i would think so since it is claimed to be stronger due the added carbon compared to 304L?
 
Consider a 1.5" or 2" round bar. Will a horizontal band saw cut rounds off faster if 303, or 304?
Doubt it, long stringy chips aren't really an issue with a bandsaw, which is the main pain point to me with 304 vs 303.
 
Consider a 1.5" or 2" round bar. Will a horizontal band saw cut rounds off faster if 303, or 304?
In my experience 303 does saw faster than 304 or 316. It's easy to tell the difference in a manual cold saw. With the same size stock 303 takes much less down force than 304.
 
I have 1.5" bar 8' long that I'm planning to cut down. Need to drill a 1/2" hole through the center of a 12" long piece.
Doesn't appear that welding on it will be fun.
 
Just FYI: 303 round bar can develop a crack in the center (sulfur migration?). That may be an issue if you are machining a cap for a pressurized application. The crack may not propagate through the whole bar so you can't rely on testing just one part. Learned this the hard way.

RT
 
I have 1.5" bar 8' long that I'm planning to cut down. Need to drill a 1/2" hole through the center of a 12" long piece.
Doesn't appear that welding on it will be fun.
Is it 303 or 304? The hole won't be fun in 304, but the welding is a bad idea on 303. It can be welded, from a redneck perspective, but it won't be anything certifiable.
 








 
Back
Top