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A Welding Problem - Steel Type?

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Nigel Graham 223/05/2021 12:28:53
1662 forum posts
20 photos

My welding both stick and MIG, is more miss than hit at the best of times, but are some apparently mild-steel plate materials unsuitable for welding?

Steels for bar sections come in many flavours, some not recommended for welding; but plate?

This material is factory off-cut steel plate, 6mm thick, from which various shapes had been plasma-cut; probably decent quality itself for its intended uses. It may be cold-reduced, but it seems fairly tough for mild-steel.

It has a light-grey protective film (electro-plated zinc?), and I clean that from the weld area.

Yet the welds, by both methods, are so poor even by my standards, that I am replacing the fabrications with rivetted / bolted assemblies. These are the boiler-mounting brackets on my model steam-wagon, and I became afraid my welds might break in service, dropping the boiler full of steam and water at 90psi through the chassis.

Bolted or rivetted would be prototypical, but these fabrications are hidden anyway.

So is this all poor techncique, or have I also been caught by using a steel sheet/plate grade unsuitable for welding, at least by fairly basic equipment?


In similar vein, the MIG set is a fairly old Clarke machine so perhaps fusing 6mm thick material is at its maximum, but would I find it easier and better to use flex-cored wire?

Oddly, the tool retailing chains all sell MIG sets advertised as suitable for both cylinder-gas and fluxed-core welding, but not the latter wire.

J Hancock23/05/2021 12:37:23
691 forum posts

Zinc and welding , no, no , no.

I think that Zinc is 'alloyed' below the surface you believe to be clean.

Speedy Builder523/05/2021 13:02:28
2383 forum posts
181 photos

Have you run out of gas ??

Ady123/05/2021 13:08:10
4661 forum posts
709 photos


I have noticed it interferes with welding

SillyOldDuffer23/05/2021 13:45:56
7468 forum posts
1648 photos

Chances are it's not a straight mild-steel. Nigel notes 'it seems fairly tough for mild-steel'.

Long ago it was found adding Lead to mild steel greatly improves machinability but the modified steel doesn't weld. Since WW2 additives have increasingly been used to improve mild-steels for particular purposes, with the metal tweaked for machinability, toughness, malleability, hardness, anti-corrosion, or some other production purpose. Unfortunately this makes using unknown scrap in the home workshop unpredictable. Good news: most structural mild-steel is ordinary and may be welded, cut and machined without bother. Bad news, there's no guarantee scrap will be ordinary mild-steel.

Back when Sparey wrote 'The Amateur's Lathe', most scrap metal was the safe common variety. Seventy years later manufacturing is much more likely to use materials fine tuned to the product. The difference can be extreme - a resurrected Sparey would be amazed to find most cast-iron and sheet metal products are made from plastics today.

If a workshop operation doesn't work, always suspect unknown materials!


Martin Kyte23/05/2021 14:10:12
2525 forum posts
45 photos

Any leaded steel.

regards Martin

norm norton23/05/2021 14:51:16
161 forum posts
7 photos

Note, Nigel refers to plate material. Lead is added to low carbon (EN1) round bar steel to improve machinability.

Nigel, keep to MIG and CO2. Check you can hear the gas hissing when you pull the trigger, with the power still off frown. Just make lines of weld on top of some 1/8 or 1/4 thick plate and adjust the power to suit the thickness and the wire feed to get a steady 'singing' and no stop start or banging. It is all sensitive to steady wire feed. The feed rollers must grip just so, and the feed tube be clean and nice inside. Well used MIG welders benefit from new rollers and feed tube.

I haven't yet found steel that cannot be MIG welded, but yes leaded bar is not perfect and higher carbon steels might leave cracked welds. Yes, essential to remove any zinc treatment from steel. Easily done by putting it in dilute hydrochloric acid (or another acid) until bubbling stops.


Edited By norm norton on 23/05/2021 14:54:18

Dave Halford23/05/2021 15:11:55
1657 forum posts
19 photos

Are you running the mig thickness setting flat out?

What Clarke mig is it? They make several.

What gas?

What does the weld look like?

Have you vee'd the joint?

My mind reading skills are abysmal

Edited By Dave Halford on 23/05/2021 15:13:22

SillyOldDuffer23/05/2021 16:32:09
7468 forum posts
1648 photos
Posted by norm norton on 23/05/2021 14:51:16:

Note, Nigel refers to plate material. Lead is added to low carbon (EN1) round bar steel to improve machinability.



My mention of leaded mild-steel was just an example. There are others! For example Boron is added to toughen mild-steel and, like Lead, it makes the metal harder to weld.

My point is best not assume unknown scrap will be weldable, machinable or anything else. If a job using scrap goes wrong the material could be the problem rather than the equipment or the operator.


Nigel Graham 223/05/2021 18:40:15
1662 forum posts
20 photos

Thank you.

Answering the points you variously raise:


I was careful to state plate and not bar steel so know it is not leaded, but might hold other elements.


I had bevelled the plate edges.

That didn't help. I find it very hard to aim the electrode accurately anyway, even if I weld in sufficiently bright sunlight to see the metal before striking the arc. Then almost everything goes black because my auto-darkening mask is if anything too powerful on the MIG setting and won't turn down enough. It might be intended for trade-grade welding with heftier arcs.


I'd also cleaned the coating back.

I know that zinc will poison the weld... while its fumes try to poison the operator.

What I do not know is what is coating this steel. It is certainly not hot-dip galvanising. It is light grey colour, very thin, easy to scratch off. Some of the metal still in my front porch is beginning to rust. It might even be a lacquer.


Gas - I thought of that and fitted a new CO2 bottle, after weighing suggested I need do that. No difference.


Welder settings - they just control the mess I make of it.


Welder models - SIP 'Weldmate T141P-ARC', I bought new and have hardly used. Clarke 'MIG150TE'. Second-hand. It had a new tube liner a few years ago and little use since. I have fitted a new nozzle and shroud and it feeds properly - whether my settings are correct is another matter.


Weld appearance -

I have always had such unsteady hands that I could never make anything in the Cherry Hill / Ron Jarvis league! So I cannot guarantee to aim the electrode properly and keep its height and speed steady.


Here though, I query the result as it differs from normal, whether using open arc or MIG:

- Normal and assuming the steel is of good weldable quality: Shiny, convex splodges of steel, most melting into one side only. Cavities full of slag. Splatter and blobs on surrounding metal. Under quarter of weld length joining both parts. On thicker materials, penetration very unlikely beyond half depth of prepared groove. Full penetration, full length impossible; any thickness. Holes very likely through <3mm thick. Faulty areas left or over-welded where inaccessible for grinding out.

- This Case: Same except - the splodges are very rough and irregular, with very little smooth area, using both welding methods. The MIG set leaves a brown "soot" on the steel.

It is that difference which is the key to my question:

Same conditions, same equipment and electrodes, same proper preparation, same poor welding skill... but noticeably different metallurgical results?

Dave Halford23/05/2021 19:46:31
1657 forum posts
19 photos

If your mask has a grinder setting turn it down till half way between grinder (9) and your existing mig setting.

It sounds like low gas, bad regulator or gas valve not operating . Take all the pressure off the wire feed wheel then switch the set on and listen for the gas, you should fell a draught on your cheek and hear an audible hiss.

Disposables should last around 20 mins. Check out this first section.

Nicholas Farr23/05/2021 20:01:43
2945 forum posts
1333 photos

Hi Nigel, according to the specs, your Weldmate will weld up to 5mm thick mild steel and your Clarke up to 6mm thick, however what isn't stated is the size of the pieces, i. e. a piece of 5mm thick by 25mm wide will conduct the heat of the arc away slower than a piece of 5mm thick by 100mm wide, so the statements can be misleading. Although the amps output seem to be impressive, the voltage is lower than industrial grade machines, so it's really the output power that's really needed to be known. Inverter welders work better as there are a lot less losses, but of course the price normally reflects this. Welding needs power and the more mass you have, the more power is needed, but of course its not really linear. In the case of stick welding, the electrodes you use will have a minimum open circuit voltage requirement for transformer type welders, which has to be taken into consideration, so if your welder is below that, then the drooping characteristics may well fall below the voltage to sustain a stable and powerful enough arc for the electrodes you are using.

Regards Nick.

fizzy23/05/2021 20:12:56
1809 forum posts
120 photos

As an ex coded welder .....150 amps will struggle with 6mm plate even if its set up well and you are a very competent welder . Needs to be about 300 amps, spray not drip and 1.2 wire. What you are describing is what I would expect given equipment, material and experience

Mark Rand23/05/2021 21:28:24
1050 forum posts
11 photos

^^^^ What Fizzy says.

The arc welder would cope with 6mm using 2.5mm rods and three passes. A 7018AC rod would give a better result than 6013, but not as good as on a DC welder. The MIG welder should be reserved for sheet.

If you want to be able to make welds you can trust, take a City & Guilds course on the process (MIG/MMA) that you want and expect to pay £500 or so for the basic level one course. The level two course tends to cost a bit more and needs level one as a prerequisite. level three is for extreme enthusiasts and earning a (good) income. To be honest, your shouldn't do any welding that you expect to hold together without some training. I speak from embarrassing experience.

Nigel Graham 223/05/2021 22:46:59
1662 forum posts
20 photos

Thank you.

It would seem then I was expecting rather too much from the equipment as much as from me - though I have managed to stick together moderately hefty stuff in the past, including old 25 X 10mm hot-rolled bar that needed a lot of cleaning to reach the steel under the rust.

The components were all small. The largest fabrications, a pair of them, were two pieces of 6mm plate about 60 X 50 mm welded to form an unsymmetrical T, with triangular 3mm thick end-plates.

So perhaps nothing massive likely to chill the weld too quickly.

Ironically I made each of the wagon's wheel discs approaching 20 years ago now, by welding. I rolled a 1/2" X 1/8" strip into a ring to form the flange, and welded that to the disc itself. I think the discs are only 14swg (2mm) thick. I used no more than a decidely hobbyist arc-welder capable at most of about 80A for a short time before it cut out and needed resting to cool down. It had no cooling-fan. Admittedly the flanges are given so much support by the discs and the wheel rims that they really only act as stiffeners, but they have not shown any signs of distress.


Dave -

I did think about the gas. I am fairly sure it was flowing though it might have been insufficient.


Mark -

It is having "embarrassing experiences" I was afraid of!

I could not really justify a very expensive course since its true value comes only if you are welding regularly, not on odd occasions. I'd end up with expensive hand-outs and knowledge, but gain no experience. I once took an evening-class course in basic welding at my local college when adult-education classes were wider than just holiday-Elbonian and how to send e-mails, but it was a long time ago.


There are some welded parts on the travelling hoist I built, but none in critical places. All the other joints are bolted. Similarly I will not weld anything except perhaps belt guards, on the overhead drive frame for a horizontal mill in restoration.

The question is now how to make the steam-wagon's engine-case. I've to represent the prototype's casting, but if I can't weld sheets of 3mm steel together I'd have to use screws or rivets hidden under paint.

I summarise the advice so far as I should abandon trying to weld anything worthwhile. There is nothing wrong with the equipment, but I don't have the expertise to use it for more than cobbling together the odd rough-and-ready garden-task bracketry.

noel shelley23/05/2021 22:54:52
707 forum posts
19 photos

Fizzy and Mark are both right ! I would NEVER use a small MIG For anything but very thin steel. The mention of welding in constructional articles in this day and age with £50 welders fills me with horror ! The DIY gear that's about still doesn't turn you into a welder. I have been welding for over 50 years and still have a lot to learn ! Get someone who knows how to weld to do it for you - or bring it to me and I'll do it for you ! Noel.

Nigel Graham 224/05/2021 22:37:36
1662 forum posts
20 photos

Thank you Noel.

I do not blame the welding sets. That would be right daft.

I never claimed using even the SIP arc-welder I have, and bought new only a couple of years ago, would make me a skilled welder, though it should allow someone with reasonable skill to produce decent quality work within the machine's range. That last phrase is the main point here. There is nothing wrong with a £50 DIY welder, only with trying to use it, or indeed any tool, beyond its designed limit through not knowing that limit.

I was not trying to weld submarine hulls, but had not appreciated that even small pieces of plate only 6mm thick would need a more powerful welder than I have.

I will try to find the SIP's paperwork and read its specifications again. I have them somewhere. The Clarke machine's instructions might still be available, but it's quite old so possibly not.

Why should those articles others write "fill you with horror" ? I am sure their writers are far better at welding than me and presumably obtain satisfactory results; but I appreciate that not all their readers can.


The upshot I gain from the thread is that I : -

- May have been using a steel not good for welding, but more likely remants of its unidentified coating was contaminating the welds. Possibly the wrong grade of rods, too.

- Was using reasonably good tools but outside their working range, very likely incorrectly set - my faults, not the welders' . I've yet to establish the MIG gas situation - again mine, not its, fault.

- Cannot hope for good-quality joints even with all material and machine conditions correct - should weld only occasional rough work whose strength and appearance do not matter.

norm norton25/05/2021 09:08:30
161 forum posts
7 photos

Thank you Nigel, you have done something that only the very best posters of questions do - summarise what you have learnt from the various replies and what you might do next. We all learn from that and appreciate the discussion!

Nicholas Farr25/05/2021 10:35:55
2945 forum posts
1333 photos

Hi Nigel, don't get too dishearten with your achievements, we all have to learn and when I started welding in my first job, I was utterly rubbish, but I was able to have day release to college on a City & Guilds fabrication and welding which lasted six years in all with the advanced courses. These DIY welders can produce quality welds within their scope, but it does take a bit of practice and trial and error. The biggest problem they have is the available power from a domestic supply and if you can get it plugged into a 16A or higher, you will have more chance of getting better welds with them. In effect, when you strike an arc, you are short circuiting the output of your welder in the instant before the arc is established which needs a very high inrush of current for a fraction of a second, so a larger availability of amperage will give you a better chance of the arc to be produced. Don't always think you have to use the biggest welding electrode for a given thickness of steel, just try different sizes on various thicknesses and sizes of metal, just remember more mass means more overall power needed.

As far as gas goes for your MIG, a Argon / CO2 mix will be better than CO2 by itself.

Regards Nick.

Edited By Nicholas Farr on 25/05/2021 10:37:55

Hopper25/05/2021 10:48:13
5505 forum posts
137 photos

Try welding on the same settings but using some other steel, preferably a bit of something you have welded before with success. Soon tell if its the steel or the welder/operator that is the cause.

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