4140 Heat Treated

Why does 4140 need to be heat treated? Is it already heat treated? I mean is 4140 like 1035 and than when they heat treat it it becomes
4140? The guy who is supposed to be teaching me this shit isn't telling me.
HELP!!!
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4140 need not be heat treated unless you desire the properties of the hardened material, one of which is greater strength. Hardness is yet another of the features that are improved. Hardness relates to tensile strength, so the harder the material is drawn, the stronger it becomes, but at the expense of ductility.
4140 is available in a heat treated condition, and is still quite machinable, or it is available in the annealed condition, so it can be heat treated at the appropriate time, to exacting specifications.
1035 doesn't become 4140-------or anything else------not when it's heat treated. All it does is get harder, there are no chemical changes in the material. It is also borderline too low to heat treat because of its low carbon content.
4140 is what it is because of the presence of specific elements, namely carbon, manganese, phosphorus, silicon, sulfur, chromium and molybdenum, in very specific quantities to develop the desired qualities. The numbers applied to steel alloys are not random-----each one has a specific meaning, and tells you what family of alloy you are dealing with. The last two digits are the percentage of carbon in the alloy, in hundredths of a percentage point. Therefore, 4140 contains .40% carbon. The designation 41 implies that the alloy is in the chrome-molybdenum family----along with 4130, 4142, 4145, 4150 and perhaps even more.
There are some excellent stock books that can provide the chemical makeup of various alloys. I suggest you contact a steel distributor and ask about acquiring one.
Harold
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Hello 4140 doesn't have to be heat treated unless it is required , 4140 is a Chromium and Molybdenum alloy that has a Carbon content of approx. .40 % or 40/100 of 1 % and responds well to heat treat for hardening , 1035 is just common steel without the alloys and it has a carbon content of .35 or 35/100 of 1 % and could be hardened , the steel that you have in your toaster , car fenders and refrigerator is plain 1010 to 1020 steel , heat treating does not appreciably change the alloy content , I have had to weld 4140 on occasion and the extra 1/10 th of a percent carbon as opposed to 4130 can make for a real headache , probably you should get a book on metals and do some reading , really too much information to get off this site . Good Luck Phil

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I made the replacement tailspring on my taildragger aircraft out of 4140....maybe 4 years ago now. heat treated and tempered correctly (well approximately correctly) it makes a superb spring steel. temper to 180,000psi UTS for a spring.
Stealth Pilot
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What the others said about material composition. If you are just looking for the answer without delving into how it gets there, take a look at this site: http://www.matweb.com/index.asp?ckck=1 search on '4140' or '4130' or what ever, pick out a standard size that makes sense to you (say 1" round stock) take a look at the different properties when heat treated differently. The composition stays the same, the tensile, yield, and ductility are all over the map.
4140 typically comes in either annealled (softest) or normalized (somewhat harder) to allow reasonable machining and fabrication. The the final assembly is heat treated to whatever specs are needed.
One application where the 4140/4130 is not heat treated is in assemblies used for extremely cold temps (-40F). The chrome/moly allows have a MUCH higher resistance to impact (Charpy test) at these temps than mild steel. Think snowmobiles at -40F and 80 mph on a frozen lake. It's nice if the front suspension doesn't shatter on an ice ridge.
Weird Al Perkoffovic wrote:

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RoyJ sez:
"If you are just looking for the answer without delving into how it gets there, take a look at this site:

Great site, Roy ! Many thanx. BYSAIBMI
Bob Swinney

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I'll bite: what is BYSAIBMI ??
And yes, the matweb site is pretty useful.
Robert Swinney wrote:

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Betcha sweet ass I bookmarked it.
Bob Swinney

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In addition to Harold's excellent answer I would add this: for most aplications 4140 is heat treated because you can! If you only need the properties of anealed 4140, why spend the money for all the extra alloying elements? As was said in other posts, heat treating 1020 or 1035 doesn't buy much in material properties. Of course, there are always exceptions to every generalization, but the basic reason 4140 is usually heat treated is because it can be heat treated to get the desired properties. Hope this helps.
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This guy is one of the worst trolls on usenet. HIV Steve, Perkoff, ad nauseum. Just killfile him.
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Weird Al Perkoffovic wrote:

Responding to responses will let us know that you're actually listening.
Assuming you mean steel, the number just specifies the alloy. How you heat treat is is a private matter between you, your heat treating shop, and your materials engineer if you have one.
I have a book, "What Steel Shall I Use". It was written in the 1940s, before engineers were assumed to know this stuff, so it's actually in something close to english and covers all the basics. The guy goes into the meaning of the numbers, why 1050 may be as good as 4140 for you (cheaper to buy, but more expensive to heat treat reliably), and other interesting stuff.
I'd recommend getting it, but I have no idea how easy copies are to find. Instead, look for a good web site that goes into alloys and heat treating.
--

Tim Wescott
Wescott Design Services
  Click to see the full signature.
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