S275 steel machinability

I've only recently discovered that S275 steel is much cheaper than BMS - I normally use EN1A or EN3B. So far as I can gather that's largely because S275 is normally supplied hot rolled, so not so dimensionally consistent as cold finished, but quicker and therefore cheaper to churn out. I expect there's much more to it, but that's what a quick search revealed!

Further searching told me that this alloy has 'good' machinability -but what does that mean? My only experience so far of machining black steel wasn't pleasant - horribly stringy and impossible to get a good finish. So I turned my back on the stuff. But that was a rod bought from from B&Q - so of unknown provenance.

If there's anyone out there who uses this alloy and could give more info about machining I'd be grateful.

Robin.

Hi Robin,

S275 is a weldable, non alloyed structural steel, I often use hot rolled S355 steel and have no problems machining it. It is not as machinable as EN1a or EN1a Pb so I use a carbide tipped tool for the roughing cut and switches to HSS for the finishing cut. S275 should be similar, might tear a bit more easily so use sharp tools.
The scale on the hot rolled steel can be quite abrasive but the carbide tools can cope with that. You can of course, dip the work in acid to get rid of the scale, and then sodium bicarbonate solution to neutralize the acid before rinsing and machining.

Thor

I've not knowingly machined S275, though I might have been given it after asking for EN1A or EN3, neither of which is a current steel specification. (You get a similar mild-steel.)

Looking at the spec, S275 is Mild-steel with a dash of Manganese, which improves the alloy in several ways.

Mild-steels are classified as Structural Steels, that is their main purpose is buildings, ships, bridges, girders etc. Most of them can be drilled, sawn, and welded, and although they machine reasonably well, unless you go for EN1A-Pb or similar, good machineability isn't their top priority. The problem is compounded by how the steel is made because rolling hot or cold makes a difference. Bright Mild Steel is rolled cold with good dimensional accuracy and finish, which saves time during construction work, but it tends to warp when machined when built-in strains are released by machining. Hot rolled generally machines better and doesn't warp, but it's more work,

The metals sold by DIY stores are for decorative purposes and my experience is they all machine badly. The Aluminium is too soft, the steel is gritty, and the Brass is unusually tough. Avoid!

Starting out I wasted months because my collection of scrap and DIY store metals all turned out to be horrible. Manufacturer's rarely consider mini-lathe owners when choosing metal, and many manufactured goods use alloys that are positively unfriendly in a home-workshop. It can be used, but far better for beginners to buy known metal where the description mentions the alloy is Free-cutting or has Good Machinability. There's a great deal of luck in scrap. If it came from a machine-shop, it'll be fine. If you live in an area without much industry, chances are it won't machine well.

Experiment by all means, but always bear in mind the machine, the operator and the material all matter!

Dave

Can be a bit gummy and grabby when machining but not too bad, not the nicest to brill or tap. As Thor says the scale can be abrasive so worth pickling f you have a lot of drilling to do.

I'd class it as more suitable for fabrication work than turning/milling.

S275 is a hot rolled low carbon steel similar to EN3B. Like EN3B it is a bit gummy and has a propensity to tear at low feeds and speeds. Drilling, tapping and reaming are fine and it grinds ok as long as one avoids loading the grinding wheel.

I use a lot of it. Most of my traction engine motion work and many other engine items are made from hot rolled steel. Like these slidebar clamps:

I don't worry about the mill scale. I just remove it in the course of normal machining. Anecdotally it seems less prone to rust than EN1A.

Andrew

In SW France, without mail-order and associated postal costs, I can only find S235JR at the local metal distributers.
Identical to S355 used by Thor except with 0.22% carbon instead of 0.23% for S355, it bandsaws/drills/taps/mills OK.
Haven't yet turned any. All usage so far has been able to cut under the surface. Finish reasonable.
DaveD

Ta. Sounds like it is workable-with at least - as Andrew's sidebar clamps show! Replies have given me the confidence to buy a bar and see how I get on.

I mostly use carbide insert tools, and the lathe I have now is hefty enough to push them quite hard and fast - my early experiences with hot rolled steel were with a mini-lathe sized machine and it's likely that a combination of inexperience and the limitations of the machine put me off the stuff.

Dave - I recognise your starting-out experience - the first thing I tried to turn was a piece of steel found in the street, which I later identified as an SDS drill extension bar. I'd spent good money on this lathe and the damned thing didn't work! We live and learn. On the steel designation thing - when first I plucked up courage to venture into Reception at industrial steel stockholder I went armed with codes so I could talk the talk, and asked the price for a bar of 2" 230M07. The guy at the desk rolled his eyes in a sort of 'Gawd help us' way, riffled through a file and said 'so that's EN1A you're after'. But perhaps he'd been sitting at that desk for decades. Now I just say EN1A.

Thanks to all for replies, Robin.

Edited By Robin Graham on 02/03/2021 01:59:03

Edited By Robin Graham on 02/03/2021 02:02:50