Residual stress caused by yielding - bending

[Plasticix]

A rectangular bar 1/8" thick x 2.5" wide x 30" long made of Hardox 450 steel (Fy = 170 ksi) is bent 180 degrees at the center of the bar (out of plane bending) with an outside radius of 1.25". What is the residual stress at the bent section ? Is this a simple calculation or requires FEA ?

 

[rowe]

Unless the bar is heated, the stress should be somewhere close to Fy=170ksi (the yield stress).

 

[Plasticix]

What kind of heat treatment should be used to minimise the residual stress taking into account that the mechanical properties of steel shall not be affected by the treatment ?

Thanks for your help.

 

[rowe]

Well, it didn't take long for your questions to go beyond my help.

Off hand, I would think that you could apply heat from some kind of torch, but you must be careful to not overheat (probably not more than about 1100-1200F). I would feel better if you were to call a local steel mill where the expertise is greater. They may bend it for you. Alot depends on the type of steel, carbon content, etc.

If you have the resourses, you could experiment a little.

Good Luck.

 

[Plasticix]

I've contacted the Application Engineering of SSAB Oxelösund AB (Sweden based producer of Hardox steel)and there helping me with PWHT.

We are trying to design a spring clip for replacement of leaf springs of a bridge modular expansion joint. Good ductility and high yield is required.

Regards

http://www.oxelosund.ssab.se/

http://www.hardox.com/

 

[Ron]

As rowe indicated, the residual stress in near yield, but above it. You can approximate by using the measurements and computing the strain, though you are past the proportional limit of the material, so stress-strain relationship is no longer linear. It is; however, a consistent curve with a shape similar in all steels.

The PWHT has to accommodate taking the residual to below yield and putting the new desired properties in. Tempering has to take into account the desired ductility and elastic recovery (springy-ness), without making the part brittle and fatigue prone.