Typical of bright cold drawn bar. You could start with Black hot rolled bar which has less trapped stress and usually stays flat or anneal bright bar before machining.

What is the final cross section you want? Starting with Gauge plate ( ground flat stock) may be your best bet as this has a more accurate surface.

Can you post a sketch of the part and give an idea of it's use also do you know the grade of steel you have so people can give a more informed answer

J

PS if it took you hours to machine the surface then you also need to look at your machining methods!

Edited By JasonB on 17/12/2017 09:27:16

Gauge plate would be one suggestion, possibly would not need to machine it. Another idea would be to stress relieve the plate by heating to red and cooling slowly.

Brian

(Jason beat me to it)

Edited By Brian Hutchings on 17/12/2017 09:27:26

"It's possible to relieve the internal stresses in BMS by making the bar red hot and allowing it to cool very slowly. I don't have the facilities to do that."

​Where I've had this concern, I've placed the work in a garden incinerator whilst burning tree/hedge trimmings (after its been going for a short while) – and kept it stoked up for a good while longer – then left everything going overnight (with the lid on). The part (buried in the ashes) will still be very hot the next morning, so I usually leave it to cool right down. I can't say for certain that this is sufficient (and it certainly isn't controlled) but the BMS bits so treated have behaved themselves afterwards.

Something which they may have done anyway of course but it made me feel better. I've also given this treatment to some castings that had some hard spots and it also seemed to help them – but it was very subjective, so I can't be certain. Helped my confidence whilst machining though, so it worked on one level at least….

Regards,

IanT

Because it has a black, scaly surface. Generally you don't want that on the final part so you have to machine it off. The surface of bright steel is often good enough to use as-is. Depends on the application.

Murray

I may have got the wrong end of the stick about the time and temperature needed to stress relieve bright mild steel. A quick Google just showed I may have confused 'Normalising' with 'Stress Relief'. Normalising is rather complicated. It involves taking steel up to about 850C, holding it at that temperature for a couple of hours and then letting it cool down slowly in the furnace. The whole process takes several hours or more. (Normalising might be the answer to the EN32B thread, what do do about hard lumps in steel, rather than Ian's bendy problem.)

For stress relief, one site simply advises heating to 650C and allowing the steel to cool in air. Much simpler.

Can anyone confirm that Ian's idea of heating to red-heat with a torch and leaving it to cool naturally is all that's needed? If so, I'll start doing it!

Dave

Works for me.

Neil

Andrew,

Yes maybe unlucky – but it would typically go if you machine one edge of the black bar. I agree that it might not be as bad but it does seem to go. Also very noticeable when you machine quite a decent chunk then try to surface grind it. Again, not massive amounts but certainly a good couple of thou'.

Phil H

The problem of long machined strips warping occurred on almost every job I had to do on press tool stripper plates. When the clamping was released after machining the bar could be guaranteed to bend so I always had to use a fly press to straighten them after machining. This is a tricky operation too although this item doesn't usually have to be machined on the reverse side. Colin

Re Jason's comment "Better to remove the scale by pickling in acid" – what acid?

Would citric work or does it need something much stronger?

Chris