Heat treatment steel 4140 stress relief.

[absaul02]

Hello, everyone.

I will be performing stress relief heat treatment on 4140 steel specifically for a part as shown in the image with these measurements.

My question is, what thickness is appropriate for heating, since the standard tells me that it should be at least 1 hour per inch?

And generally, what heating ramp do you use?

Thank you for your support.

 

[mfgenggear]

Follow the procedure of AMS2759/11
Unless other wise specified
Generally the stress relieve temperature is -50 degrees F below the tempering temperature.
Again follow the spec

 

[Gr8blu]

Agree with mfgenggear.

By the way - that is a very poor representation of how the part is designed/actually looks.
The right-hand oval should be oriented vertically, not horizontally - or placed above/below the left-hand image if the orientation is not changed.
Take a look at "third angle projection".

 

[absaul02]

Follow the procedure of AMS2759/11
Unless other wise specified
Generally the stress relieve temperature is -50 degrees F below the tempering temperature.
Again follow the spec

Thank you very much for your response.

Sure, only the standard does not indicate a heating ramp. Could you help me where to start to choose a heating ramp?

Regards

 

[mfgenggear]

Thank you very much for your response.

Sure, only the standard does not indicate a heating ramp. Could you help me where to start to choose a heating ramp?

Regards

To my understanding, start up the oven with thermal probes, or thermocouples until the the correct temperature is reached. Then the time one hour per inch is used.

 

[3DDave]

The "ramp" is to allow for the rate of temperature rise via thermal conduction through the part, as in, don't expect the transformation to happen any quicker.

What matters is not exceeding the required temperature and that the entire bulk of the material reaches the required temperature and for long enough for the crystal structure to achieve equilibrium.

The measurement is for any point inside the material to the nearest exterior surface.

 

[absaul02]

Según tengo entendido, encienda el horno con sondas térmicas o termopares hasta que se alcance la temperatura correcta. Luego se usa el tiempo una hora por pulgada.

Thanks for you response.

I get that to get to the stress relief temperature or for any heat treatment, you've got to set a heating ramp on the furnace. That way you can prevent sudden temperature changes and avoid damage to the part.

 

[3DDave]

It's metal. It's not injured by the rate of temperature change in an oven. Consider the rate of temperature change from welding.

It's not a ramp - it's a timer. Like for baking cake. It can remain at the stress relief temperature forever if the oven excludes active gases.

What physical change do you imagine damages the part? I think you have seen some other problem that is unrelated to this process.

 

[absaul02]

It's metal. It's not injured by the rate of temperature change in an oven. Consider the rate of temperature change from welding.

It's not a ramp - it's a timer. Like for baking cake. It can remain at the stress relief temperature forever if the oven excludes active gases.

What physical change do you imagine damages the part? I think you have seen some other problem that is unrelated to this process.

Thanks for you response.

When I say "temperature ramp," I'm talking about the oven starting at a certain temperature, like 550 °C, and then staying at that temperature for two hours. But the process of reaching those temperatures will be with a heating ramp of, for example, 95 °C/hour.

I'm not sure if that's the right term, sorry.

 

[mfgenggear]

Thanks for you response.

I get that to get to the stress relief temperature or for any heat treatment, you've got to set a heating ramp on the furnace. That way you can prevent sudden temperature changes and avoid damage to the part.

Ramp up will not damage steel parts. However once the temperature is 1000 degrees or higher. Oxidation will occur on the surface of the steel
So it must be copper plated or in inert atmosphere. To prevent oxidation. For higher temperatures contact the manufacture of the oven.

 

[Gr8blu]

absaul02
Our processes use ovens all the time - as in 24 hours a day, 365 days a year. Generally speaking, the volume of a 4m x 4m x 3m oven (properly gas-fired) can reach operating AIR temperatures of 500 C in roughly 70 minutes. The PART temperature takes longer - but for something the size of your "donut", it wouldn't be all that much different. For reference, most of my parts weigh in at 10 to 15 tonnes each, and there is usually three to five pieces in the oven at once.

Then hold the temperature OF THE PART constant for the required anneal (1 hour per inch of material).
Then allow the PART to cool at a gradual rate (which may or may not be take longer than originally getting to temperature).

 

[3DDave]

The specification is for a cold part going into a pre-heated oven. They do this because, as Gr8blu noted, heat treaters typically have a continuous/24 hour operation so that the oven remains at the high temperature continuously rather than wasting time and energy warming the oven and then dumping the heat in cooling it. This cuts the thermal cycles on the oven and extends its life.

The part can be removed to an insulated container that slows the rate of cooling.

How fast your particular oven heats and cools is up to you.

 

[Compositepro]

Metal parts can be damaged by heating too fast. Fast heating causes temperature gradients that result in stress due to CTE. Parts that consist of thick and thin areas are particularly sensitive. For welding, preheat is often required to lessen the stress, or cracking will occur.

 

[mfgenggear]

I don't have the latest specification.
but review the AMS2759/11 para 3.5.1 and 3.5.2 , recommended stress relieve is 375 degrees f. it will prevent or mitigate stress cracking. it becomes an issue on high temperture heat treaters will do a preheat then ramp up on hight temperture heat treat.
but not required on stress relieve. which the specification specifies 375 deg f.

 

[3DDave]

That is confusing the difference between changing the temperature using a uniform heat source to reach a survivable temperature (the goal of the current thread starter) and changing the temperature of a relatively small portion of a part enough to turn the metal in to a liquid/major phase change.