Stainless steel 304 vs 316

Good review, just a couple of comments-

Your description of the differences between the two omits the main purpose of the molybdenum in 316. That vital 2-3% is there to reduce the likelihood of pitting and, because the two take place using the same mechanism, crevice corrosion.

You say there is a difference in 'stress resistance' between the two. Not sure I understand this. Without looking it up I don't think their strength or fatigue resistance differs a great deal.

Magnetism is never strong for either and mostly non-existent. It occurs due to ferrite retention, which is more likely with lower levels of nickel. It has been noted that swarf from drilling or turning either of them can be magnetic, due to the probable heating to above the austenitising temperature.

General interest: it is just over 100 years since stainless steel was discovered (1913). Apparently it was entirely accidental when the discoverer was trying to do something else. Chromium was added to iron and it was found later that the solid metal had not rusted, whereas the other samples had.
 
After a quick read I have two comments.

Quite a lot of jargon in the furnace section.

Resistance to Corrosion
304 stainless steel also known as A2 stainless steel is resistant to corrosion however 316 stainless steel also known as A4 stainless steel provides a higher degree of corrosion because ... should be corrosion resistance because ...
 
Thanks guys, edited some points and will look into others this week.

I will be completing the magnetism this week hopefully and yes you are right both can have a certain degree of magnetism and usually non existent.
 
I would sum it up by saying 316 is marine grade 304 isn't. Out of interest I wanted two deck fittings to hold twin twistle rig poles, I got quotes from marine fabricatiors of around £200. Kitchen manufactures who use stainles use 316 so I visited one with the drawing - £70 total for both fittings.
 
A few pedantic comments to add.

Not all electric arc furnaces use only scrap. Some charge iron ore to an initial melt made with scrap. Some use up to 75% ore. While these are minority, could say that they " 'mostly' use cold scrap metal..."

The section on basic oxygen steel making is good, but I wonder if it might be about 50% of them bottom blown these days as opposed to lance top blown?

Not all pig iron is made in the blast furnace system. Some is produced from electric arc melters.

Stainless.
There's many grades, could mention that, as there's an uninformed impression that "stainless is stainless" - that the term refers to a grade as opposed to a family of grades, with 304 and 316 being two of the most commonly encountered by for example marine users.

The wording about durability of stainless versus carbon steel seems to imply that its impossible to get carbon to last. Galvanized carbon steel has a life expectancy of over 100 years in some environments. A way to put this might be to say that "...stainless is self protecting, requires no protective coatings..." or similar?

"Each of these types of stainless have there pros and cons..." spelling: "their"

The question of magnetism raises many myths. I wonder if its better to stress that this is NOT a definitive test for grade of SS, and is unreliable.
 
KellysEye said:
I would sum it up by saying 316 is marine grade 304 isn't. Out of interest I wanted two deck fittings to hold twin twistle rig poles, I got quotes from marine fabricatiors of around £200. Kitchen manufactures who use stainles use 316 so I visited one with the drawing - £70 total for both fittings.
Click to expand...

Result!
 
JClarkes said:
I just spent the last few days writing a blog on the differences in stainless steel A2 vs A4 if anyone is interested.

Just need to complete the magnetism part at the end. Should I add anything to it?

http://www.jclarkemarine.com/blogs/news
Click to expand...

I dont know what you intended saying about magnetism but the previous heading, " 5. What chemicals are used in Stainless steel? " jarred the nerves a bit.

I would use "chemicals" to mean chemical compounds. Your heading should really be "5. What alloying elements are in stainless steel"
 
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