Air Quenching 4140

[Lplates]

Hey guys quick question.
I have to hold some tight tolerance on some punch pins, I can pretty much only get 01, 4140 and 1045 in a pinch. I do get some warping with both oil and water quench but do leave enough to hard turn to final D without toooooo much trouble, however wondering if there was another way, even 4140 pre-hard is pretty good left as is... I just find when it gets hard it polishes just a little better and will probably last longer. Can 4140 be air quenched by leaving it out to stop warping, 40-45C would be well hard enough.

 

[gbent]

Quenching is all about cooling rate. A quick search suggests you have about 10 seconds to get the temperature of 4340 under 800 degrees. It would have to be a very thin piece to get that fast of an air quench.

 

[stephen thomas]

For air hardening up to mid 50's, S7 is your best bet.
The 3 you posted are oil hardening, & as you posted, 1045 & 4140 won't even get very hard in oil.

You do know that for strength/durability/stability, the material needs to be hardend and then tempered?

smt

 

[Lplates]

For air hardening up to mid 50's, S7 is your best bet.
The 3 you posted are oil hardening, & as you posted, 1045 & 4140 won't even get very hard in oil.

You do know that for strength/durability/stability, the material needs to be hardend and then tempered?

smt

Hey man yeah, problem is where the diameter reduces at the square shoulder from 9.5 to 5.5mm when I quench it, the pin bends at the shoulder. Just trying to remove the step after tempering where I have to turn it down to final D. Adds time and makes truing it up a pain. Thanks -I'll chase up some S7

 

[Thunderjet]

If you're turning it after H.T. just add a fillet at the shoulder, and turn it off afterwards.

When you try to oil quench, are you going in top to bottom, or sideways?

T to B is always better, in my book.

 

[Terry Keeley]

I've made some fairly high tolerance parts from S-7 and heat treated them to 60Rc, it moves very little.

https://fordtoolsteels.com/wp-content/uploads/2017/10/LSS_S7.pdf

http://www.interlloy.com.au/our-products/tool-steel/s7-shock-resisting-tool-steel/?output=pdf

Tool Steel | S7 Shock Resisting Tool Steel | S7 Steel

Hudson Tool Steel shares technical data for S7 Shock-Resisting Tool Steel including impact toughness

www.hudsontoolsteel.com

 

[Thunderjet]

I've made some fairly high tolerance parts from S-7 and heat treated them to 60Rc, it moves very little.

+10 on that^^^^^^^^^^

It does matter HOW you Heat treat though.

We have a ceramics style Furnace that we can program a gentle ramp up to UCR, if required.
It comes in very handy for the quill punches we have Wire EDMed. We usually use D2, start cold, and ramp the furnace for half a day to UCR. If we fail to do this they come out like spaghetti.

These punches are .006 X .122 X around 7/8 long. So Heat treat is CRITICLE for a successful burn.

 

[Lplates]

If you're turning it after H.T. just add a fillet at the shoulder, and turn it off afterwards.

When you try to oil quench, are you going in top to bottom, or sideways?

T to B is always better, in my book.

Mate generally sideways but I know it's not ideal, i'm going to try one with a shoulder and try to drop it straight in.

 

[dgfoster]

Mate generally sideways but I know it's not ideal, i'm going to try one with a shoulder and try to drop it straight in.

Drop it straight in? It is a lot better to dunk it into the oil vertically as already stated. But don't just drop it. Agitate it up and down quickly once it is in the quenchant as it cools. If you just drop it, it tumbles in the oil and may hit the bottom of the container quickly where quenchant is trapped on one side and circulating on the other. Both the tumbling and trapping contribute to asymmetrical cooling and distortion as well as a poor cooling rate as a vapor layer usually develops at the interface of the part and oil or water. Vertical agitation will scrub the vapor off ensuring rapid and uniform cooling.



A good general reference that is concise, practical, and aimed at small-quantity heat treater is Bill Bryson's

Heat Treatment, Selection, and Application of Tool Steels​

In it he covers all of the advice given so far in this thread and more. It is widely available.

Denis

 

[dian]

try quenching between two pieces of aluminum (with appropriate channel).

 

[stephen thomas]

I've done S7 that way, after the Al chilled in a freezer.
Needs to be thick and "large" or it will just slow the quench too much.

 

[Willbird64]

I've made some fairly high tolerance parts from S-7 and heat treated them to 60Rc, it moves very little.

https://fordtoolsteels.com/wp-content/uploads/2017/10/LSS_S7.pdf

http://www.interlloy.com.au/our-products/tool-steel/s7-shock-resisting-tool-steel/?output=pdf

Tool Steel | S7 Shock Resisting Tool Steel | S7 Steel

Hudson Tool Steel shares technical data for S7 Shock-Resisting Tool Steel including impact toughness

www.hudsontoolsteel.com

My apologies if this is a newbie question. But when you heat treat those parts do you stand them up vertically like that ?? Is that general good practice rather than laying them on their side ?? Might be obvious to an RKI but I am not one :-). Just bought a small heat treat furnace off Ebay. I have done a lot of "stuff" with an oxy acetylene torch over the years but I never had a furnace :-).

Planning to start with A2. I have some O1 around too. Have a basic understanding of the process but how to place the parts in the oven just has me curious.

Bill

 

[eKretz]

My apologies if this is a newbie question. But when you heat treat those parts do you stand them up vertically like that ?? Is that general good practice rather than laying them on their side ?? Might be obvious to an RKI but I am not one :-). Just bought a small heat treat furnace off Ebay. I have done a lot of "stuff" with an oxy acetylene torch over the years but I never had a furnace :-).

Planning to start with A2. I have some O1 around too. Have a basic understanding of the process but how to place the parts in the oven just has me curious.

Bill

Ideally one would like to set up the parts so that the hot air from the oven can hit every surface freely. Since that isn't really possible in an environment with the law of gravity in effect, we have to settle for raising the part off the floor of the oven with some form of spacers while minimizing the area in contact with the bottom and if larger parts, preferably setting the parts so they are symmetrically pulled by gravity and such that its effects re: distortion are minimized. One can get away with a lot more on more substantial (thicker cross section) smaller parts.

 

[stephen thomas]

Get the Bill Bryson book DGFoster mentions. The information is cheap at the price, especially when starting. And it has actual cookbook recipes for common tool steels

When using an oxy acetylene torch and presumably a slightly carburizing flame, perhaps in shelter of fire bricks, the surface of small parts can actually be somewhat protected from oxygen, depending on flame-to-part size and the way it is played.
(CO & CO2 provides a varying cover, but inert atmosphere).

When the parts are placed in an electric furnace (that does not have provision for inert atmosphere) for an extended heat cycle, it will be necessary to wrap them snug and sealed against the air/oxygen with the typical stainless foil for the purpose. Perhaps with a little square of brown untreated paper bag to scavenge any remaining oxygen as it chars. This is especially true as the heat treating temperatures become higher for higher alloyed steels, like air hardening steels, or for HSS.

So my parts are usually in a foil bag, and hang from the top of my pot furnace.
Sometimes they stand on the bottom.
But usually vertical because that is the longest dimension in mine.

Overall, as has been mentioned, it is best if the part is positioned so it is symmetrically heated, and not a bad thing if the position is one that gravity least affects.

smt

 

[Willbird64]

Get the Bill Bryson book DGFoster mentions. The information is cheap at the price, especially when starting. And it has actual cookbook recipes for common tool steels

When using an oxy acetylene torch and presumably a slightly carburizing flame, perhaps in shelter of fire bricks, the surface of small parts can actually be somewhat protected from oxygen, depending on flame-to-part size and the way it is played.
(CO & CO2 provides a varying cover, but inert atmosphere).

When the parts are placed in an electric furnace (that does not have provision for inert atmosphere) for an extended heat cycle, it will be necessary to wrap them snug and sealed against the air/oxygen with the typical stainless foil for the purpose. Perhaps with a little square of brown untreated paper bag to scavenge any remaining oxygen as it chars. This is especially true as the heat treating temperatures become higher for higher alloyed steels, like air hardening steels, or for HSS.

So my parts are usually in a foil bag, and hang from the top of my pot furnace.
Sometimes they stand on the bottom.
But usually vertical because that is the longest dimension in mine.

Overall, as has been mentioned, it is best if the part is positioned so it is symmetrically heated, and not a bad thing if the position is one that gravity least affects.

smt

One past employer the foreman had a couple books published by tool steel mfg. They had a TON of information. I wish I at least had the titles of them. One mfg had a matrix of tool steels they they described as "water hard" or "water tough" and the same for oil hardening steels. And they described how to move within the matrix if a test part of one type of steel failed.

To come back square on topic quenching was covered too, and one process was to use a fixture that pumped cold water through the ID of something like a draw die so that the inner surface was glass hard, they even spelled out how high the water jet should ride up before the hot part is set into the fixture for quenching.

I did just order the book from Amazon.