# 4340 steel machinability



## bearcar1 (Dec 18, 2009)

A friend of mine has offered me a lump of 4340 alloy steel that has been annealed. I am a bit skeptical about accepting his offer for fear of being stuck with a piece that is gnarly and as tough as one of the mother-in-law's steaks. :big: From the little bit that I have been able to find by doing an internet search it is vague to say the least. What kind of finish can one expect from this alloy when turning in the lathe and does it require the use of carbide cutters etc.? If it will machine without a lot of 'hubbub' I'll take my friend up on his offer. 

BC1
Jim


----------



## joeby (Dec 18, 2009)

4340 isn't bad to machine, it is a little different than mild steel or low carbon. You'll have to adjust your speeds a little, (run slower) but it will give you a nice finish.

 I have a good bit of 4140 and 4340 pre-hardened material and I rather like working with it. It is plenty tough enough to be used for making the odd piece of tooling that you might need around the shop. I think the 4140 that I have is around 34 Rc.

 I wouldn't pass it up.

Kevin


----------



## bearcar1 (Dec 18, 2009)

Thanks for that information Kevin. The pieces that I am being offered are round stock and I was thinking "flywheel material". What kind of finish can be had with this, high luster or rather dull sheen? and how easily does the stuff work harden? I am asking all of these questions because I had gotten a length of steel bar fro this fellow once before and it was some gawd (sic) awful stuff I have ever encountered and do not wish to make the same mistake again.

BC1
Jim


----------



## joeby (Dec 18, 2009)

Jim,

 The finish you get will depend on a few details such as HSS or carbide tools, speeds, feeds, coolant or not, etc. :

 Machining with HSS, I usually get a finish that is sort of a dull gray, but void of the torn up appearance of mild steel. Carbide, with speed to suit, will almost shine after taking a finish pass.

 You can expect some work hardening, but it has never really caused me problems except for break-through when drilling. The fine edge of the slug just before the drill goes through a part can get hard enough to give the drill a beating.

 Watch your speeds and feed enough to take a reasonable chip and you should be fine. When drilling through holes, ease up on the feed just as the drill is starting through the backside and you shouldn't have trouble.

 Keep in mind that the pressure exerted on the tool to get it to cut is going to be higher than it would be with mild steel. The smaller lathes and mills may not be rigid enough for cutting under those conditions. 

 Do you have any idea what the piece was that you had trouble with?

Kevin


----------



## cobra428 (Dec 18, 2009)

Jim
Look here, they tell you all you want to know

http://www.mcmaster.com/#steel/=4zocwj

Tony

Post Post Mcmaster Carr is a wealth of info go to metals and pick what you want and they will tell you all about it


----------



## bearcar1 (Dec 18, 2009)

Thanks again Kevin, I do not know what type of steel I got the first time but I have an idea it was more of this same stuff.

Ton', hey thanks for reminding me of McMaster, I had used their catalog many times in the past for researching different types of materials.

I think that I will pass on my friends offer. The more I am finding out here the more I am thinking that I would really rather not have the headaches this stuff may/may not present.

BC1
Jim


----------

