View Full Version : Tempering Info Wanted

04-27-2005, 10:39 PM
I guess I should breakdown and buy me a copy of the Machnist Handbook but for now could someone help me.
I am tempering and hardening 4130 chrome moly. 1/2 inch dia pins.
I heated to 1600 deg F and quenced in oil.
Put in oven that APPEARED steading at 1050 F, then left the room and returned 45 min later, temp was at 1250 F, not sure for how long, then shut the oven off (pissed at myself cause I knew I should of checked it ever ten minutes).
Anyway by tempering to 1250 F instead of 1050 F what yeild strength and hardness (Rockwell) am I looking at for it now?

Thanks all that reply.

[This message has been edited by JimA (edited 04-27-2005).]

[This message has been edited by JimA (edited 04-27-2005).]

04-27-2005, 11:28 PM
Member posted 04-23-2005 11:34 PM
Tempering 4130
450F = 52HRC
550 = 48
650 = 45
750 = 42
850 = 39
950 = 36
1050 = 32

You can interpolate the table beyond 1050F as the HRC drops about 3.5 points/hundred degrees.
Barry Milton

04-27-2005, 11:56 PM
Thank you Berry!
If the interpolation is linear than 3.5 x 2=7 (1250-1050=200) thus 32-7=25

Rockwell 'C' @ 25.4 one chart said 126K psi
another said 124K psi
That is what i was shooting for anyway
Specs say heat treat to 125K psi They dont specify whether ultimate or yeild strength, but nether do the hardnesss charts.
Dont mean to be so anal about this, except that its for my retraction system on my airplane im building.
Maybe I screwed up and got i right anyway? Better go buy a lottery ticket then?

04-28-2005, 08:44 PM
Rockwell hardness is a measure of yield strength.

I think if I happened to be making airplane parts I'd be anal enough to do it over if I thought I didn't do it right the first time. When I fly a plane I have enough trouble not wrecking it myself without worrying about the parts failing on me.

04-29-2005, 12:18 AM
According to information i've found on net engineering sites, which isn't as consistant as i expected,by tempering to 1200 to 1250 i achieved a HRC of 24 to 25 which again depending on the chart is somewhere from 120k to 126k. If tempered at 1100 I would have a HRC of 32 which depending on yeild or ultimate or chart or maufacture is anywhere from 122k to 142k?

04-29-2005, 09:19 AM
What type of airplane do you intend to use these parts on?

If it is an RC or model, go ahead with your experimenting and have fun.

If it is a full sized, passenger carrying airplane, do not use components that have been heat treated on a kitchen stove. There is too much at risk, and too much involved in the proper heat treating of a material for a critical application such as this. Get it done by a reputable heat treater, tell them the requirements and application. I would not be surprised that some would be unwilling to undertake it knowing the application.

04-29-2005, 10:33 AM
Thank you JC for your reply and concern. It is very much appreciated. Please I mean no offense but your reaction is very normal for people outside of experimental aircraft building. This is going to be a full-size plane and my number one concern for the craftsmanship and safety is my own butt. The first thing you learn when building an airplane and you need to have something done by a third-party is not to let them know that it’s for an airplane. Like you said they either refuse to do it or they get kind of weird about it. But one thing about this forum is that I am very anonymous.
The pins are for the trailing link gear and the retraction system. Other components will fail before these do. The stresses on them are in sheer. If these did fail the only thing that would get hurt is my pride and my pocketbook. The plane and I would be fine. The tempering was done in a high temp laboratory oven. I just wanted to verify my information with some other sources. After reassessing the information I actually wanted to achieve a Rockwell hardness of 25 and according to most charts this gives a tensile strength of anywhere from 122 K to 126 K PSI, which was the original goal.

04-29-2005, 04:13 PM

I recall reading that General Dynamics had problems with the wrist pins in the F111a. Failure of the 4340 pins was occurring at stress levels below 10k psia. Article in Wings from 1973?
Here's hoping you have better QC.

04-29-2005, 04:25 PM
FAA FAR state that any part used on any aircraft registered in the US (has an N number on it) will be:

Type certfied for that specific airframe or powerplant.
Will contain an FAA Approval number.

Exception: If the airframe or powerplant is certified "Experimental" then anything can be used. "Experimental" aircraft are not allowed to carry passengers.

IIRC, it's been a while since I've had my head inside an FAR book.

04-29-2005, 05:09 PM
Thank you gentlemen. I did some metal failure analysis in my other life. I found it very interesting. I would assume that the 4340 pins were heat treated for high-strength, like above 180,000 or 200,000 psi. Parts like that, including connecting rods or piston pins in regular engines, can fail at low strength levels by either dropping the part or banging it against another metal and then putting it back into service. If you do it by the book you’re supposed to discard a part like that if you drop it. What happens is microscopic fractures are introduced into the surface of the part and under low levels of stress will fracture. There are other reasons also.
An experimental aircraft can carry passengers or anyone they want. The only restriction is in the first 20 hours of flight testing if using a certified engine and certified prop or 40 hours if not using a certified engine and prop. Flight testing is the next step after your FAA inspection. The exception even to this rule is that you are allowed to take a quote ‘flight engineer’ with you during the flight testing phase. An experimental or home built aircraft can fly at night and fly IFR if it has the proper instruments and equipment

[This message has been edited by JimA (edited 04-29-2005).]

[This message has been edited by JimA (edited 04-29-2005).]

04-29-2005, 07:52 PM
I somehow don't think you can trivialize landing gear failure, or the chance of it occurring in any part of the system.

Murphy's first law states; "Anything that can go wrong will." Further "It will happen at the worst possible time and result in the most possible damage."

You heated and quenched in oil, OK so far, but then tempered in an oven that appeared to be at 1050 deg. F. 45 minutes later it was at 1250 deg F. Did it heat up to 2000 deg F and then cool back down, or drift up to 1250? You have no way of knowing, hence no idea of tempering conditions and final condition of the part.

I am not a proponent of our current litigous society, but common sense dictates applying due caution when dealing with items of this sort. OK if the gear collapses on the way back to the hangar, not OK if it collapses under takeoff conditions and veers into a group of spectators. You can expose more than your wallet and dignity by a failure of this type. Your desire for anonymity makes me question your intent.

04-29-2005, 10:47 PM
I know for a fact JC that the oven didn’t drift up to 2000° and then come back. I just ever so very slightly bumped the dial-up hoping to attain 1100° after putting the parts in. Everything on the oven operates just fine, it’s just that the setting of the temperature by the dial is not temperature it sets on-off frequency. I am absolutely certain that the oven just drifted up to 1250 more likely in the last 20 to 15 minutes. After reflecting on this for couple days and doing some research I feel very confident that the parts are within spec and will serve their purpose just fine. I am very familiar with the unique characteristics of this particular oven.
The reason for remaining anonymous speaks to your concerns of litigation. Individuals on this forum can share their experience, ideas and knowledge without the fear of being sued by someone. I have no sinister or diabolical plan that I’m concocting. Again your care and concerned for me is also shared with my friends and family. Some in my family think I am crazy, but the fact is that the FAA speaks very highly of experimental aircraft builders. It’s pretty much unanimous among the inspectors that home built aircraft quality far exceeds production aircraft in all areas. Accidents in a homebuilder aircraft are slightly below that of production aircraft. Almost all of these accidents happen within the first few hours of flying the aircraft due mainly to being unfamiliar with the aircraft. Parts failure in experimental aircraft is almost nonexistent statistically. I am a very sane person and would like to live a long and healthy life. As the saying goes there are no old and foolish pilots just old pilots.