For all you metallurgists.. which is better and what's the diff ?

[debatethis]

I'm looking at an aftermarket rotor and have seen a couple of different options. One is made of 420 stainless steel and the other is made of 340 stainless. I know general assumption is  "bigger number must be better" but I'd like to know from you machinists and metallurgists that know for fact. What is the difference and which is going to be better for a rear brake rotor ?

[UncleRico]

What you need is an Alchemist. Luckily for your I renewed my subscription to Alchemist Monthly.

I'm more familiar with 304 and 316 stainless, but I'll give it a whirl and tell you what I know.

The number in your case 420 and 340, is the molly compound and make up of the metal. The higher is NOT necessarily better. It depends on your application.

Grade 420 stainless steel is a higher carbon version of 410; like most non-stainless steels it can be hardened by heat treatment. It contains a minimum of 12 per cent chromium, just sufficient to give corrosion resistance properties. It has good ductility in the annealed condition but is capable of being hardened up to Rockwell Hardness 50HRC, the highest hardness of the 12 per cent chromium grades. Its best corrosion resistance is achieved when the metal is hardened and surface ground or polished.

Related grades to 420 are high carbon high hardness martensitic stainless steels such as the 440 series (see Atlas Steels Datasheet on this series of grades) and also variations to 420 containing molybdenum (for increased corrosion resistance), sulphur (for increased machinability) or vanadium (for higher hardness). A slightly higher carbon version of 420 is the non-standard grade 420C.

Martensitic stainless steels are optimised for high hardness, and other properties are to some degree compromised. Fabrication must be by methods that allow for poor weldability and usually also allow for a final harden and temper heat treatment. Corrosion resistance is lower than the common austenitic grades, and their useful operating temperature range is limited by their loss of ductility at sub-zero temperatures and loss of strength by over-tempering at elevated temperatures.


As for 340, I've never heard of that. Are you sure you're not confusing it with another number, perhaps a Nickel Stell alloy?

[ananomaly]

Rico...You must have stayed at a Holiday Inn express last night!!! BraveOhOhOhOh :Clap.gif :ThumbsUp.gif

[eldiablo64]

LMAO

[debatethis]

here's one

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=002&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=120042759046&rd=1,1


here's the other

http://cgi.ebay.com/ebaymotors/POLARIS-PREDATOR-CUSTOM-REAR-ROTOR-FREE-SHIPPING_W0QQitemZ160042890674QQihZ006QQcategoryZ35592QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

I asked the guy about the second one and he said they are 307 stainless steel (made a mistake about the 340) .

So regardless of price and other things, which grade stainless would perform better for a rear brake rotor application ?

[UncleRico]

Honestly, we need 450rCrazy to weigh in on this topic.

He's the brake master. He designs brakes for dragsters. He'd be able to tell you which is best.

307 doesn't ring a bell either. (I think I remember hearing 307 in relation to Nickel alloys, but don't hold me to that)

I can tell you that 304 is better than 316, qualitywise when it comes to stainless, but I would imagine you would want to research the temperature and hardness factors of each metal to make the right decision when it comes to brakes.

[450rcrazy]

well I brought out my mil-spec book on metal alloys no such luck finding 340 or 307 stainless.but I do know there is a 347 stainless witch handels high heat up to 1650f intermitantly does not harden and is corrosion resistant .420 stainless is a high strength stainless steel heat treatable (hardenable) but is magnetic witch also means it will rust not as bad as plain steel but  none the less will rust .If I had to choose between the two I would choose 420 becouse the additional hardness will allow for longer wear expecially becouse we basicaly grind dirt and mud into the surfaces. 420 however will be more prone to warpage but you probably wont notice it becouse atvs are equiped normally with floating calipers witch will follow the rotor side to side you being none the wiser.Hope this helps.Rico I didn't know you knew materials that well I am impressed.

[debatethis]

I really appreciate all the help guys.


Cain

[UncleRico]

Rico I didn't know you knew materials that well I am impressed.

"Yeah, I'm like the retarded guy from RAINMAN".


"STOP MAKING FUN OF TOM CRUISE!!!"

[450rcrazy]

"STOP MAKING FUN OF TOM CRUISE!!!"

how can anyone not make fun of TOM CRUISE hell even the scientologists are embarrased. I dont think John Travolta will even look at him much less talk to him anymore. 2:L