EN32B Steel

Hi. I have not got much experience of machining EN32B steel. I am currently trying to machine a 75mm length of the stuff of what started out as 40 x 50 mm section to make a tool holder, so after cleaning up the sides to size and cutting out the slot for the tool am now machining a slot on the back, about 37mm wide initially, to make the dovetails to fit the QCTP.  However, I seem to have hit a largish hard spot which so far has trashed 3 HSS 12mm dia milling cutters in quick succession.

So, the question initially is: are hard sports common in EN32B or am I just unlucky, and how do you deal with them? I had thought of heating to red and cooling slowly but, I only have a propane torch for heating and wonder if I could get it hot enough but willing to give it a burst and see, but also if this would work anyway?

Am reluctant to machine further as I am running out of milling cutters! So the next question is how do I continue to machine, or rather, what do I do next? I don't have a shaper so that's out. I don't have a small enough flycutter but I do have an adjustable boring bar holder with carbide boring tools, but even if I cut the initial slot that way I am concerned that the dovetail milling cutter which is a HSS one will get trashed cutting the dovetails.

Or do I just bin this bit of material and get another bit and hope it's OK. I am actually making two tool holders, the other one cut from the same original length of steel has been OK so far, no worries.

I am not sure EN32B is the right steel to use but it was the only material in the size I wanted.

Chris

PS  Not quite true that EN32B was the only steel available, I could have got some EN3 square but there would have been a bit more waste and I was not sure if EN3 would be robust enough.

Edited By ChrisH on 17/12/2017 11:44:26

Edited By ChrisH on 17/12/2017 11:57:36

a PS to the OP. I do have a stove in my shed which heats the shed using one of the smokeless coal fuels. I could get that going red hot, chuck the steel on and then put more coal on top and leave it a good while.

Would this be any good to do?

Chris

Had similar a few months back with some EN32B, trashed a few HSS cutters, then snapped two carbide ones and finally turned a third carbide one into a bull nose cutter. I tried heat but it did not help much but the carbides did get there eventually. I had a lot of time in the part already so was reluctant to bin it but that may well be your best bet.

It was suggested that sometimes the very ends of the long lengths that go through the rolling mill can have hard spots so if your supplier got the first 3m or 6m length of the run and you got the bar end from that it could explain the hard spot.

You would probably be best making it from some square 50x50 EN3, can't see it needing to be much harder, maybe turning the unwanted 10mm off in the 4 jaw then milling the rest.

PS Its worth a try in the stove then grind off one of your blunted cutters at a slight angle so you have sharp edges further up the flute and take a test cut with that rather than risk another cutter

Edited By JasonB on 17/12/2017 12:14:10

Jason, so glad that I'm not the only one trashing cutters with this problem even though it was not good for you. Interesting you mention EN3 at 50mm sq. as I have just added that as a PS as an alternative. It would certainly be worth a go, no difference in price from m-Machine metals.

Chris

Strategy using the stove and grinding up a trashed cutter is a good one Jason, just have to hope that I can hand hold the cutter sufficiently well on the grinder as no tool cutter/jig made yet. Harold Hall's Tool Grinding Jig is on the to-do list, at times like this I wish I had got on with it before! Chris

There is not much between EN3B and EN32B its the case hardenable EN32 that would have the higher carbon content if you were going to treat it. M-Machine also do EN8 in squares which would be a bit more resistant to ware than 3B and 32B.

The second page of Parker's colour code chart gives a summary of uses

I'll give EN3 a go first I think, Jason, see how it goes, EN8 will be worth remembering about but it's much more expensive. See they do Black in square too, cheaper still than EN32 and EN3, that may be another option still. Chris.

It's a long while since I've machined EN32B, but I don't recall any problem turning and milling it all with HSS tooling, to make bevel gears that were then case hardened. I'd have been right in it if I had badgered the special bevel gear involute cutter that I borrowed from the RAE main workshop!

What was the provenance of the material that caused the problem?

Andrew

Mine was some 2" x 1" flat bar from M-Machine most of their flat bar is listed as this grade. The pocket was very small maybe less than a 10mm cube and the rest of the bar was fine. I blunted a couple of 5.0mm FC-3 cutters as I started to hit it, then tried some 3/16" carbide ones I had which promptly snapped, Finally went oversize with a 1/4" carbide which got ground away into a ball nosed shape so just ground it off at a slight angel and kept at it which eventually did the job.

Hard spot was in the bottom right of one of the flared pockets. No visible difference in colour though I don't think it was this on of the pair that had the hard bit.

I've never had an issue with material from M-Machine, so far. Although I rarely buy steel from them, preferring to use a local stockholder.

I had a problem with some cold drawn low carbon steel rectangular section when machining the rear spokes for my traction engines. One particular spoke took the teeth off a carbide milling cutter; didn't break it, just converted it to a rather poor ballnose cutter. The replacement cutter machined a further 40+ spokes, and then broke in the same way on the spoke that caused the original problem. I suspect there was something in the metal that shouldn't have been there, a small bit of HSS or carbide tooling may be? Who knows what goes into the mix with the scrap these days.

Andrew

Read all about it in this report.

The good news is that inclusions aren't caused by random scrap bunged in by incompetent steel makers. The bad news is that there are plenty of other ways in which 'steel cleanliness' might fall during production. For instance refractory material flaking off the furnace wall, turbulence causing top slag to mix with metal, or similar when molten metal is moved from vessel to vessel during production. Some unwanted chemical reactions with the molten metal result in hard crystals growing inside the matrix as the steel freezes.

Apart from inclusions it's also possible for heat related hardness to occur when steel cools and for mechanical hardening to happen during rolling and other processing.

Dave

EN32 is nominally 0.15% carbon, 0.8% manganese, EN3 is 0.2% carbon, 0.7% manganese, so in its non case hardened condition I'd expect EN32 to be slightly softer than EN3, but not by very much. You can't make it hard by heat treatment unless you add carbon to the skin, which is where the name case hardening comes from. I think you must have an inclusion. You can case harden EN3.

I machined EN32 for many years using HSS tools and never had any problems. Is it anything to do with imported steel? I wonder. Colin

Hello Chris H.

I sympathise with you, I have the same problem, it may be rose tinted specs but do not recall this problem in years gone by.,

I suspect that it is not actually imports as such that are the problem, that Colin H mentions, but the fact that a lot of steel is now recycled. Some while ago I asked the question of how the composition of steel was assured during recycling, and was given the textbook answer that in effect the impurities were burned off. I must admit this didn't quite convince me as some of the more exotic materials such Chrome Nickel etc. I imagine will remain. I also get the impression that even if there are no extreme hard spots in the material there is a general inconsistency in a given piece of material. To my mind it is simply poor process control. Lessons and knowledge from the past , ignored and forgotten.

A related issue, material stresses. This has certainly become more of a problem, I now normalise material that has to make a component more than a couple of inches long. Even supplied gauge steel seems to have inbuilt stresses in recent times.

Kind regards

Anna

Years ago as an apprentice at BAC Weybridge (Think VC10, 1-11 TSR2 etc), I was sent to the bar stores to do a little machining job as I had finished a production job in 1 day instead of 2.5 days ! That was to machine the ends off 15' long bars of 5/8" hex steel. The bars then went through NDT (non destructive testing) before any machining was done. About 10% of bars failed, then having the bad sections cut out before sending down to the auto lathes section and making further components.
BobH

When You can hear of People finding half melted ball bearings, bolts etc. in a bar of steel, the quality of that steel is assured. . All the makers care about is "head them up, move Them on out."

But is it true? Anyone have personal experience of finding a recognisable object in steel, or even seen a photograph of one on the web?

What I know about steel making suggests its very unlikely that a bolt or ball bearing would fail to melt in a furnace. Thousands of tons of molten steel sloshing about in the melt and a ball bearing stays intact in it? I think not. I suppose odd bolts might fall into a rolling mill and get crushed into the output, but again not very likely.

I suspect it's an urban myth. People hit something nasty whilst machining and guess what caused it. After a few repetitions the guess becomes fact - we've all heard it, so it must be true.

As I posted earlier there are plenty of mundane reasons why steel might have hard spots and other flaws. It's not a new phenomenon. Nor is it because steel is imported or carelessly made or because the secret of making it properly has been forgotten!

Possibly small scale-users are more likely to encounter problems with steel than the big boys. I buy it in tiny quantities and almost always get bar ends...

Dave

To answer Andrew, the provenance was the same as Jason's, was off a length of 40 x 50 mm I purchased from M-Machine Metals, as detailed in he invoice. Never had any worries with stuff from M-Machine Metals, always buy from them and have good results and service too, this is the only bit. I guess there might be something in it from somewhere, like SOD and others have suggested, I will give the stove heat treat method a go and if no good bin it and order some more, when I can get another shed day. Not a good time now in the run in to Christmas, SWMBO seems have have more priorities than I have time slots. Nothing new there then for most of us I guess. Be glad when it's over and can get back to normality!

Chris

One point that folk using the EN steel designations tend to overlook is that its been a goodly number of years since steels were actually made to EN specifications so you can't actually get EN steels. What you get are the suppliers (hopefully) best estimate as to an equivalent steel of effectively similar properties. Which covers a multitude of sins especially with the relatively simple, uncomplicated, EN specifications advised for Model Engineer and Home Shop Workers.

Fact is the broad performance specifications covering any given EN number can be hit in whole or in part by a fair number of steels. Given that for our purposes the actual limiting strength, toughness, hardness and all the other properties important to an engineer actually properly exploiting the steel characteristics are of little or no import . The main thing we need to worry about is machining characteristics. Especially give that most folk have lighter machinery. Unfortunately most of the variations in steels of broadly similar performance are about machining, forming and manufacturing characteristics. Specifically, as far as large scale industrial users are concerned, doing the job as fast and economically as possible. Its the large users who define what steels are going tube available in a decent range of sizes so we need to work with what is supplied for them.

In my experience most of the poor finish and unexpected machining behaviour from supposedly EN steels can be dealt with by cutting faster and, often, harder. Even folk like me running industrial type machines can hit problems. The last length of so called EN19T inch / 25 mm bar needed approaching 2,000 rpm and a fairly exotic insert to get a sensible finish. Awesome finish actually. Grinding level. Pure luck as those inserts I got in error by misreading the spec (m/min as ft/m). Even with coolant HSS wasn't going to behave. Ordinary guy with Myford, Boxford or lighter machine is going to be stuck. Then there was the bit of so-called BMS that took the tip straight off a HSS tool!

Looking at the EN32 offerings on Jasons link to the Parker Colour Code chart illustrates the problem as the there are 4 steels that could be supplied against EN32. I prefer to use BS 970:1991 numbering as at least you have a reasonable chance of getting something consistent so long as you order one with M in the middle. Decoding first three numbers are a type code, last two are 100 times mean carbon content and letter defines how the specification was arrived at. A is chemical composition, H combination of harden ability and composition, M combination of mechanical properties and composition and S for stainless. H steels are exotic for us. A is very risky as you don't know how its going to behave when you go to cut it. M is fairly safe but still room for variation.

Many steels specified by chemical composition are dual or even triple rated depending on where the actual analysis falls in the permitted range and whether a mechanical test certificate can be supplied. 080A15 can be supplied as 080M20 i.e. EN 3B but EN 3B is often considered equivalent to 080M15 which is EN 32B, more or less. Big firms can test what they get and demand consistency. Small suppliers largely have to take what they can get and hope its all small machine friendly and pretty much the same. With the best will in the world thats difficult. When it comes to E-Bay bargain all bets are off. Trouble is there is no way to actually know how what you have will behave until you put a tool on it.

Clive.

Edited By Clive Foster on 18/12/2017 23:01:18

Black mild steel will contain all sorts of "crap" as it is normally made from recycled frag steel, that contains high carbon steel, tool steel and boron steel.

If you need new mild steel you need to cut it from rsj's, universal beams and columns.

I don't know if BMS is made from new steel or recyled crap!