Machining EN3b mild steel

Hi all

I have a small project using EN3b mild steel flat bar. I purchased the closest size to the finished dimension the original size is 1/4" x 5/8" the 5/8" requires reducing to 7/16". The finished length is about 7" After milling the bar there is a noticeable bend in the bar. How do cure this problem ?

Take a little off one side, turn over and then a little off that side and repeat until down to your 7/16. Alternative it to heat to about 850deg bright red and hold there for 20mins then allow to cool as slowly as possible before machining but again I would still take some off each side

Basically either :-

machine equal amounts off each side

or

anneal it by heating to red and allowing to cool slowly.

Bright steel bar is finished to size by rolling which locks up stresses in the outer layers of the material.

Machining on only one side takes out the stressed layer on that side leaving the other side still stressed. So the bar bends.Machining both sides equalises any remaining stress so it stays straight. Holding it so you can machine both sides without it moving mid job due to inadequate grip or taking out the bend when remounting to do the second side can require creativity.

Heating to red (all the way through) and cooling slowly lets the stresses work themselves out as the material cools. Rather easier during open fire / soil fuel boiler days as you could dump it in the fire of an evening to get hot and retrieve it from the ashes the next morning when it had cooled down. These days you need to pay for gas to heat it and have something to bury it in for slow cooling.

Clive

PS Jason types faster! That said I'd want it red for longer and very slow cooling. These days some of the bright bar seems to have had a lot of rolling and lots of stress. Several itty bitty cuts are a good way to shorten the life of milling cutter too. So glad I have a shaper! I've been known to weld such pieces to a larger parent bar to keep them straight. Costs you the ends where the weld was but can make life very easy.

Edited By Clive Foster on 17/03/2023 19:03:36

I thought bright bar was formed by cold drawing through a tungsten carbide die? The drawing process stresses the outer layers; hence the distortion when the outer layer is removed asymmetrically.

Andrew

BDMS = bright drawn mild steel, clues in the name, black bar is rolled hence the scale rolled into the surface.

So what is cold rolled steel

Edited By JasonB on 17/03/2023 19:57:45

Normally sheet form.

Cold drawn steel

Andrew

I have seen a few suppliers listing flat section as drawn/cold rolled. Thought maybe the larger sections were rolled? And final straightening after drawing is usually by sets of rolls though they don't apply a lot of force

What the Americans call BDMS?

I machine gib head keys (full size not model,0 from key steel which is bright but a bit tougher then en3b, the material is heated to red head with propane torch ,cooled slowly, to remove internal stress ,and I find it stays flat when machining one side,

As a general rule, any cold rolled material will turn into a banana if you machine only one side.

Which is why Reeves used to sell pickled hot rolled plate for making loco frames. Does anybody sell it now?

Rod

Loads of places, BS EN 10025-2 specifies hot rolled structural and engineering steels, so if you ask any stockholder for steel plate (or section) in grades S235JR through S500J0, or E295 through E390, you'll get hot-rolled material.

The standard also specifies that +N is post-fixed (e.g. S335JR+N) for steel which has been normalised which you could go for if you need to absolutely guarantee it to be free of stresses.

It usually comes black so you'd need to specify if you required it in a Pickled & Oiled or (my preference) Blanchard Ground state and pay for the additional processing if it's required.