Hi, went to b+q to get ripped off for some steel the other day, and they were selling hot rolled (the black stuff, cheapest) and cold rolled steel box sections, just wondered what the difference was, ie properties, good or bad points. Ps, i chose the cold rolled (shiny) 1"x2" 1.5mm wall to weld in for my seat runners to mount on. This should be fine shouldnt it??

B&Q steel, great choice...

The oily almost shiny stuff is a rather brittle grade that will tare if folded too much. It's not nice really to work with and is best bent at red heat. The tubes will also come apart at the seams

The black stuff, hmm only work that at red heat also as that really tares. It is really best used to make gates.

As you may have guessed I have used both of their grades before and still have most if not practically all off it left. Do yourself a favour and take a visit to your nearest scrap steel merchant. There you will find all the steal pipe and plate you could ever want at a fraction that B&Q would have you pay.

just don't get me started about their bolts...

[Edited on 12/1/07 by macnab]

Cold-rolled steel, always. It doesn't have the nasty-to-remove scale on it.

This has been asked before, don't forget to use the search function.

yep, cold rolled.

To be honest, on box section etc it makes little difference.

They are both made the same way, but one uses cold rolled sheet and the other hot rolled. To begin with both are hot rolled anyway, but the "cold rolled" is then cold rolled further to give a better structure to the steel and a better toleranced finer finish.

If you plan to bend the steel cold, you may find the hot-rolled 'black' steel more forgiving - the cold-rolled 'bright drawn mild steel' (BDMS) is very prone to cracking when bent cold. If you're prepared to bend it hot, either grade will do.

Note: this is for decent steel - not the rubbish that B&Q sell!

David

[Edited on 12/1/07 by mcerd1]

Hot is normalized - i.e. most of the stresses involved in bending and welding it have been releaved by heat treatment so its a little stronger

cold suffers from work hardening and residual stresses at the corners (which are also a larger raduis making it less stiff too) and you don't really want to weld anything to the corners of cold formed and so on

I'd go for hot (or seamless) but a much more important question is what grade is it - please don't say 'mild steel' - there are hundreds of kind of mild steel

in european structural grades (probibly what this is) there are 2 mild steels - brittish S275 and european S235 (the number is the strength)
high yield is S355 (or S460)
also diferent subgrades relating to its toughness (JR, J0, J2, K2 from worst to best - if it says nothing it means its total crap)
and then there is hot or cold

then you've got to get the right welding wire for your grade(s)

sorry, that sound a bit like a rant, but I spen half my time at work tring to get people to use the right grades

[Edited on 12/1/07 by mcerd1]

Seems like ERW 1010 hot- rolled is what is readily available here in 1x1x16ga. Seems like it should weld/work just fine?? I'm new at fabricating so learning as I go. I can get pretty much anything other steel available, so long as I know what I need. I'm not sure seamless or DOM is available here though. Never seen it in square tube.
Still trying to figure out the aluminum specs too .
Cheers.
Cory

so am i right in saying i want bs s275 k2 hot rolled ??

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Originally posted by quick n stuff
so am i right in saying i want bs s275 k2 hot rolled ??

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thanks m8

thanks for the replys, and the advice on bending it. Shouldnt be too crucial this time, but ill know next time i need some and take your advice