4140 differences

[Hertz]

I've heard many different designations of 4140, I'm wondering the differences. Even when I search on the net, it seems to bring up different types than what I'm actually looking for. Are some of these not actual standards and just "slang" per se?
4140 pre hard
4140 HT
4140 QT
4140 HTSR
4140 Annealed
4140 with just a hardness attached to it. (Dwg says 4140 steel 40rc)
I understand what they stand for, for the most part but I guess what I'm mostly wondering, is what is the difference between Pre Hard, QT, and HT?
How do they relate to HTSR?
I've also read that HT, QT, HTSR and Pre hard and generally the same.

 

[hvnlymachining]

Different companies use different designations, but can mean the same thing. You have to get a spec sheet to get exact data as even by the same manufacturer lot to lot differences of hardness and even element content will vary.

PH = Pre Hard
QT = Quenched &Tempered
HT = Heat Treated
SR = Stress Relieved
AN = annealed

PH, Qt, HT all mean the same thing.... Usually.

CDHT ( Cold Drawn, Heat Treated) is the term used frequently from the supplier I use to describe the shiny, half hard (usually 30-32 Rockwell C) 4140 I use frequently. But a second supplier refers to it as CFQT ( Cold Finished, Quenched & Tempered) but still the same material and condition.

HTSR is not only heat treated, ( to harden ) but also stress relieved which can be critical in steels like 4140, which is often used where tight tolerances are required of the finished part, but is a steel that likes to store internal stresses especially in the cold finished form.

Also remember heat treating can mean different things from different people, annealing, stress relieving, hardening, and normalizing are all performed by heat treating.

 

[Cole2534]

I don't know off hand, but the definitive place to look, IMO, is on the MTRs for each type. Compare hardness, elongation, UTS/YTS, and maybe the Charpy numbers to see where each falls on the strength/toughness/price matrix.

 

[DanASM]

Different companies use different designations, but can mean the same thing. You have to get a spec sheet to get exact data as even by the same manufacturer lot to lot differences of hardness and even element content will vary.

PH = Pre Hard
QT = Quenched &Tempered
HT = Heat Treated
SR = Stress Relieved
AN = annealed

PH, Qt, HT all mean the same thing.... Usually.

CDHT ( Cold Drawn, Heat Treated) is the term used frequently from the supplier I use to describe the shiny, half hard (usually 30-32 Rockwell C) 4140 I use frequently. But a second supplier refers to it as CFQT ( Cold Finished, Quenched & Tempered) but still the same material and condition.

HTSR is not only heat treated, ( to harden ) but also stress relieved which can be critical in steels like 4140, which is often used where tight tolerances are required of the finished part, but is a steel that likes to store internal stresses especially in the cold finished form.

Also remember heat treating can mean different things from different people, annealing, stress relieving, hardening, and normalizing are all performed by heat treating.

Hit it right on the money with this explanation.

Look for Rc Hardness, if its 28-34 or so, it will be pre-hard. Anything with a lower hardness will most likely be cold drawn annealed. Anything above 34 Rc will be heat treated after machining to attain a higher hardness.

The "Pre-Hard" 28-34 RC stuff can be machined as is, and is mostly used when a harder material is needed without the heat treatment afterwards.

 

[Nerdlinger]

ANN (annealed) is usually about 10 HRC in my experience, just FYI.

 

[Mtndew]

what is the difference between Pre Hard, QT, and HT?

Nothing.

We cut this stuff all day every day. Some people use different terminology that's all.

 

[jackal]

Most of the accurate stuff I make '(electric motor shafts, gear shafts, etc) is Heat Treat Stress Relieved .
Simple parts like bulldozer pins, are just 4140 raw form.
If I can get a print on some stuff, it will specify grade.
Also, some of the better material sales people will have an engineer that can recommend a grade for you.

 

[4GSR]

Me, down in oilfield country, we specify 41xx materials by yield strength. Most prehard materials are within our specifications as having a yield of 110-140K psi. We don't care much about hardness in this case. Hardness's generally run anywhere from 26 to 36 HRC.
If the material must meet a NACE requirement like MR0175, then for 41xx materials, it cannot have a hardness greater than 22 HRC. We specify a yield strength of 80-105K psi. and a hardness no greater than 22 HRC. The yield strength will dictate what the minimum hardness can be.
Virtually every industry out there has its own methods and standards to this madness of materials!

 

[Hertz]

Very good info guys. Thank you, appreciate it.

 

[Rickyb]

I agree with stated definitions but would like to clarify HTSR. This is a process where you are willing to trade high strength for low machining distortion. The HTSR process is a standard quench and temper but you “essentially“ leave the part to cool from 1100-1300°F in the tempering furnace. This maintains the material‘s martensitic structure but softens it dramatically. Softer can be translated to lower tensile and yield strength.
Tempering is by its very natural a stress relieving process. It’s just a matter of how far you take it.