Calculating section thickness for heat treat. 3

[defogman]

Could someone direct me to resource to determine effective thickness of various geometric shapes?Currently we have alloy steel tubing 8" OD 2"ID x 20" long to quench&temper.Does it matter if the parts are processed laying down or stood up?Parts are rough machined so distortion not an issue.I recall seeing something in an ASM (I think)publication years ago,but lost track of where it was.

 

[metengr]

What is specific alloy for Q&T?

 

[defogman]

Alloy is 4330.The furnaces used for heat treat are equipped with recirc fans for even heating.Our rule of thumb is to temper 1hr per inch of thickness.My thinking is that this tube is 6" thick(subtracting the ID from the OD).Others say it"s 3"thick based on wall thickness.

 

[metengr]

The tube is 3" thick, not 6". Typically, 1 hour per inch of thickness up to 2", over 2", 15 minutes for every additional inch of section thickness.

 

[tbuelna]

metengr is correct, the section is 3" thick and that's what matters. MIL-H-6875 recommends a heat up time of 120 minutes for a 3" section with class A steel alloys, and a min. hold time of 55 minutes.

Hope that helps.
Terry

 

[defogman]

Yes,many thanks to you both.

 

[MOB1]

Suggest you look at MIL-HDBK-5H for equivalent diameters of various shapes.

 

[redpicker]

Yes, you should base the time on 3" thickness.

You should also have them standing up for quenching. You are wrong is assuming that distortion will not be a problem since they are rough machined. When quenching, if they are laying down, the parts will become oval in cross-section and "bannana-shaped" along the length. While you might be able to "machine" the distorion away, there may be residual stresses that can cause the material to move after machining.

In addition, circulation of the quenchant on the ID will be restricted, leading to lesser hardening and increasing the chances of quench cracking. Yes, stand them up during heat treatment, at least for the quenching. If you want to lay them down for tempering it won't hurt.

rp

 

[stanislasdz]

Great answer redpickler !

Respects