Is chrome-moly considered alloy steel?

[Cowbell]

....from the perspective of speeds and feeds, that is? Or is it considered free machining?

[ViperTX]

....hmmmmm....no lead....then it's not free machining.......

[Mcgyver]

it can be both at the same time. chrome moly's is steel with chromium & molybdenum added, ie 4130, 4140. it is available as free machining with lead, ie 41L40. in one sense steels are all alloys, but chrome moly is commonly referred to as alloy steel

[Cowbell]

So basically - take it slow on a baby mill

[ViperTX]

...look it up in the machinist handbook.....or do a search on the internet....

[NC Cams]

Chrome moly IS an alloy steel.

4140 is NOt free machining
41L40 or 4140 +Al + Ca is free machining

Assume it isn't unless it is SPECIFICALLY sold as free machining.

ViperTX's reply is a bit curt but direct and to the point and spot on at that. Many questions are posed that are readily found in the Machinist's Handbook. That's where many of us got our knowledge from BI (before internet).

Hmmmm Reminds me of a time when I asked an engineering mgr a similar question. He took me over to the library and showed me how to find the Handbook. Never made that mistake again - that is to ask him w/o looking for it in Handbook first....

[Geof]

No "one sense" (see post 2) about it; all steels are alloys. But really they should be called iron alloys not steel alloys because the major constituent is iron.

[NC Cams]

I take exception with Geoff for the following reason (re: steel actually being an iron alloy).

Yes, the prime constituent of steel is iron but, TECHNICALLY, it is the level of the iron content in the alloy that determines if it is IRON or STEEL.

As your percentage of iron drops to a certain level (can't recall but do recall the tirade about it from a metallurgy professor in college), the alloy changes TECHNICALLY from iron to steel.

You can add alloy (take chrome, manganese, moly, carbon, nickel, whatever, for example) and add it to a blob of iron or steel in relatively equivalent amounts.

However, the iron content drops as a perctentage of the TOTAL as you add alloy elements. At a certain point, you transition from iron to steel. Yes iron is still there but the grain structure now assumes a different form due to the molecular interaction of the alloys upon each other.

Moreover, as you continue to add more and more alloy, you can transition from a martensitic alloy to an austenitic alloy. Both still contain iron yet martensitic alloys are typically magnetic while austenitic alloys are non magnetic.

Hmmm, iron bearing alloys being non-magnetic. Interesting concept. Still can't explain why but it is so.

Point is this, you run the risk of becoming misinformed and/or give folks the impression of ignorance (much different from stupid) if you try to oversimplify things - especially when you start working with alloys (iron or steel). I probably know enough to be dangerous but I still rely on handbooks to keep me on the straight and narrow.

Moreover, if you try to contact a steel company and start asking for iron info and/or can't keep steel straight from iron, you tend to get a short shift if/when you come across as being ill-informed. If you're going to play in the industry, it behooves you to learn the language and speak it properly.

[RonStewart]

well i take exception with NC Cams, Geoff is correct - steel is an alloy of iron. The percent of iron content does not determine what is called steel or iron, it is actually the percentage of carbon and silicon. Low carbon steels ie SAE 1010 have a larger content of "iron" than cast iron has.

[miljnor]

I like to aurgue for no reason as well!

Sooo. NC cams is for the most part right, you might have a point about the carbon silicon, but at this point your just being argumentative (got to love that ).

Sure all steel (for the most part) is Iron but like NC said if you try to get information or try to purchase 4130 iron(an example nothing more) people ma look at you a bit different!

[Geof]

Me? Argumentative? I did say should not are.

However, as I have been accused of ignorance and have been told that it behooves (sic) me to learn the language before playing in the industry..... I consulted a book!!

The term ALLOY applies generally to any combination of metals. Steel is a mixture of iron and carbon but carbon is not a metal so this mixture cannot be called an alloy; it is STEEL. Steels with less than 0.15% carbon are technically classed as IRONs, although the name steel is used especially when other alloying elements are present

As soon as other elements are added; specified minimum amounts for copper, manganese, nickel or silicon or any amounts of titanium, tungsten, or molybdenum the mixture is called an ALLOY STEEL. However, when very large percentages of other elements are added the result is a High-alloy steel but these can have very low carbon so they are often not steel in the true sense, but are IRON ALLOYS.

STAINLESS STEEL is the name for iron alloys which have a high chromium content (and low carbon).

So TECHNICALLY it is the carbon content that distinguishes steel from iron, the presence of other alloying elements that distinguish alloy steels and the amount and purpose of other alloying elements that define stainless steels.

When the carbon content in an iron carbon mixture is between 2 and 6% the material is called cast iron.

[NC Cams]

First I must appologize to Geoff - I did not mean to imply or say he was ignorant. After rereading the post I can see where it LOOKS that way but I did NOT MEAN it that way. I appologize profusely.

The point I was trying to make simply was with regard to oversimplifiaction. Many folks get into CNC and or machining as a hobby. Not everyone is an engineer or machinist thus they are not as well versed or educated with regard to metallurgy. Yet, when a novice starts asking questions, it is easy to try to simplify things so as to faciltate the understanding of the technology. Been there done that.

The iron versus steel comment took me back to my college days. It also took me back to the degrading diatriabe that was leveled against me by this retired metallurgist (long dead) who formerly worked at the local steel mill (now long closed). I vowed never to make that mistake again (calling steel iron) and have this "thing" about correcting (in a nicer way I hope/try) the folks who make a similar mistake when they interchange the iron/steel terms.

SOrt of like the motor versus engine controversy but that is for a different thread..

When we have a novice asking the question as to whether or not 4140 is an alloy (which it surely is), we have a question being posed by someone who apparently does NOT have the training to know what constitues a steel alloy, free machining or otherwise. Ignorance of a subject is due to a lack of proper training/education therein. Using inappropriate terms suggests that the person has not been propely trained. We are all here to learn and train.

I would say the the original question re: free machining 4140 alloy has had numerous responses that raised the knowlede level of Cowbell.

My concern was that what I percied as an oversimplified response ran the risk of further confusing the person. The person could thus and inadvertently end up becoming misinformed due to a misunderstading of the oversimplified reply. MILJNOR's illustration said it better perhaps (re 4130 "iron") but that's what I was shooting for as to prevent - no more no less.

As proof of the risk one takes when trying to oversimplify, my reply didn't provide sufficient detail and led to an impression that I didn't mean to convey. Guilty of doing what I was trying to caution against. Again, I appologize for that.

By the way, you can have martensitic stainless that rusts and is magnetic and austenitic stainless that neither rusts nor is magnetic (both sink in water), however. Stainless is another term that one runs the risk of oversiiimplifying but I"ve caused enough grief already.