4140 Steel??

Cabro32

Cabro32

Active User
Registered
Joined
Aug 24, 2013
Messages
29
So Wednesday I go to the local steel supplier and ask for a 2' long piece of 1 1/8" 4140 round rod. The supplier said, I don't have any in stock, but cold roll is the same thing. That's when I should have walked away, but having been told he was a stand up guy I didn't. He said he had a truck coming in tomorrow and could order the 4140 today. Since this was my first ever purchase of 4140 I said ok.
So Thursday I get a call to go pickup the order. It was painted a couple colors and cost $53.33 I get it home and put it in the lathe and hit it with 150 grit sand paper. The paint came off and the bar had a thick coat of rust on it. Just about then my son-in-law arrives with a 2' long piece of 3" 4140 round rod he picked up in the next town. It was marked 4140 and was nice and shiny and he paid $42.50.

The 3" 4140 when hit with a hammer had a nice ring to it and the 1 1/8" 4140 had a thud to it when it was hit with a hammer.

The 3" inch 4140 when filed barely made a mark while the rusty 4140 was much softer.

Obviously he took one look at me and new I just fell off the turnip truck on the way into town. Long winded story to get to the question. Does 4140 rust as bad as cold roll or does it stay shiny?
 
Exact_metals has 12" 1" OD 4130 for $7, they ship as many as you want for $5. Prices for 6061, 1018 and 12L14 are also very good.
 
Your comparing a couple of different things. "Cold Rolled" doesn't tell you what kind of steel it is, only how it is made. All 4140 isn't "cold rolled" or "hot rolled". It can be found both ways, within certain size limits. What most people are used to seeing as "cold rolled" is made that way, and usually is a low carbon steel, such as 1018 or 1020. They are not all that hard, and cannot be through-hardended. And yes, they will rust, like all steels. What you are probably seeing as a rusty bar is a hot rolled product, and all that means is that it is formed at temperatures that are high enough to oxidize the surface and form a scale. A little weather, and that dark gray/black scale will most definitely rust. And it could be a low carbon steel as well for all you know. Except for the file hardness test.

To answer your question, though......both will rust. Hot rolled comes pre-rusted. Neither will stay shiny unless you protect the surface from moisture and air.
 
Your supplier may be a "stand up guy", but if he says 4140 and "cold rolled" are the same thing he doesn't know what he's talking about. As Tony said, any kind of steel (including 4140) may be cold rolled, but 4140 specifies a specific alloy with precisely controlled amounts of chromium, molybdenum, and carbon. When people talk of generic "cold rolled" steel it's usually 1018, which is not nearly as strong as 4140. Cold rolled steel will generally have a better finish and better mechanical properties than the same composition steel in hot rolled form.

The difference in the two bars you got (assuming both really are 4140) may be in the temper; your son in law's piece may be hardened to some extent while yours may be annealed or normalized.

Both will rust, but often hardened steel forms a thin oxide layer that slows (but does not eliminate) further rusting.
 
FanMan said:
Your supplier may be a "stand up guy", but if he says 4140 and "cold rolled" are the same thing he doesn't know what he's talking about. As Tony said, any kind of steel (including 4140) may be cold rolled, but 4140 specifies a specific alloy with precisely controlled amounts of chromium, molybdenum, and carbon. When people talk of generic "cold rolled" steel it's usually 1018, which is not nearly as strong as 4140. Cold rolled steel will generally have a better finish and better mechanical properties than the same composition steel in hot rolled form.

The difference in the two bars you got (assuming both really are 4140) may be in the temper; your son in law's piece may be hardened to some extent while yours may be annealed or normalized.

Both will rust, but often hardened steel forms a thin oxide layer that slows (but does not eliminate) further rusting.
Click to expand...

There are also different 4140's I have some 4140, 4140 firmex and 4140ht which is heat treated and harder that heck. Machines very nice with carbide but is prehardened for different jobs. Exact metal sells 4140ht also just depends on your needs. I'm making large vee block from a 2x4x10" block of 4140ht it will make a nice set when I'm done.


Todd
 
One other thing worth noting -and this is where the "suspicious" salesman might actually be speaking words of wisdom and not words of deceit... 4140 in a normal condition that's not been hardened, is no stronger than 1018. As a matter of fact, in the unhardened condition, 1018 has slightly higher tensile and yield strengths.

The situation changes dramatically when you begin to heat-treat the materials. Heat treated 1018 does not provide additional strength in the material and it only makes the surface a little scratch resistant if the proper techniques were used to heat treat it.

4140 on the other hand, can triple in yield and tensile strength using very rudimentary heat treating techniques.

The overall yield strength of 1018 is around 70,000 PSI.
Depending on the level of heat treating, 4140 can range from about 60,000 PSI to (roughly) 90,000 PSI at 25 Rockwell and up to 190,000 PSI at/around Rockwell 50. (These are all approximate numbers off the top of my head).

The salesman is right in one respect... If you're talking about untreated metals, 1018 and 4140 are about the same.

Ray
 
Thanks all for taking the time to set me straight. I really learned alot.
Joe
 
Alro Chart2.jpgAlro Chart1.jpg[Colorcode.jpgATTACH]68670[/ATTACH]

Here are a few color charts for steel in your area can't find one for Edgecomb Steel if I find my book I'll copy it and specs for 4140. Maybe this will help if it's coded paint color.

Todd

Alro Chart1.jpg Alro Chart2.jpg Colorcode.jpg
 

Attachments

  • Colorcode.pdf
    33.7 KB · Views: 30
What about using a GRD 8 bolt for 4140 turning stock.
I use high quality stuff like Unbrako and is cost effective ,

Yes I know sizes are limited but size for size its cost effective.
Plus factor is that i can get get GRd 8 bolts from a lot more places than I can get 4140 stock from

Ozwelder
 
You must log in or register to reply here.
Back
Top