Mild steel wheel blanks

[Mike BrettParticipant @mikebrett89695]

Hi

I purchased some mild steel blanks of E-Bay 60 mm x 10 mm to machine some railway carriage wheels. They where listed as laser cut, and as I am having great difficulty trying to machine them I wondered if the laser cutting is the problem.

I have tried different speeds and different tools but all I have managed to do is polish the outer rim which seems to be very hard. Would the process of laser cutting leave a hard skin.

Mike

[Mike BrettParticipant @mikebrett89695]

Lath not cutting

[Alain FooteParticipant @alainfoote90915]

Yes laser cutting can leave a hard skin, suggest you tickle them with an angle grinder first.

[Mike BrettParticipant @mikebrett89695]

I was afraid that would be the answer. If I tried to grind the edges it would no longer be a perfect round and I would never get it back in the chuck.

[John HaineParticipant @johnhaine32865]

Get them red hot and hold them red for a few minutes, then allow to cool slowly.

[John BaronParticipant @johnbaron31275]

Hello Mike, Guys,

I treat laser cut edges the same, similar to machining cast iron, you have to get under the skin ! Once you do it tends to machine easily.

I agree with John Haine, annealing them will work.

[AdrianRParticipant @adrianr18614]

Couple of thoughts.

The hard skin should be very thin, so you should be able to get under it with a carbide tool.and an aggressive first cut.

Are the sides hard too? Can you get under the skin from the side?

As it is a wheel wont you need a hole in the middle for the axle?. You could make the hole in the middle on all the wheels. Then make an arbour and with out removing it from the chuck mount the wheels to finish them. You wont need them to be round then, so the angle grinder is an option.

Adrian

[Martin ConnellyParticipant @martinconnelly55370]

I thought you could not harden mild steel so is this a scale formed from the gases used in the process? If so I doubt annealing would work but getting under the skin would.

Martin C

[Mike BrettParticipant @mikebrett89695]

Many thanks for replies.

I will try and anneal them tomorrow, although I only have a small propane torch but I will give it a go. I will also try from the side , might work. The axle hole will only be 8 mm so not a lot to play with. At least they only cost me 10 pounds so not to much of a lose if it ends up in the bin.

Mike

[JasonBModerator @jasonb]

If you have enough spar on diameter you can run the edge against a linisher/belt sander or even use an angle grinder. If the flat surfaces have mill scale on them I'd also suggest an acid dip.

[Dave HalfordParticipant @davehalford22513]

Posted by Martin Connelly on 22/05/2020 18:23:22:

I thought you could not harden mild steel so is this a scale formed from the gases used in the process? If so I doubt annealing would work but getting under the skin would.

Martin C

It's a bit like case hardening

[Ady1Participant @ady1]

If your lathe is up to it, backgear and a 5% cobalt tool (M35)

[John HaineParticipant @johnhaine32865]

Thay may well not be "mild" steel but some form of structural steel with a higher carbon content.

[Neil WyattModerator @neilwyatt]

Although mild steel contains only very small amounts of carbon it is possible to achieve a degree of hardness with very rapid quenching.

It is tricky to do but can be done – I was reading about it a few weeks ago.

Laser cutting meets these difficult to achieve conditions, unfortunately! I've had to deal with laser cut blanks…

Water jet cutting is better from this perspective, especially if you want holes spotted for small drills.

Neil

[Phil H1Participant @philh196021]

Have you considered some slices of steel bar – they are only 60mm diameter and most of the suppliers will cut 'slices' for you. Put the laser cut stuff in your scrap bin – they will be useful for something else – unless you have 100 of them of course.

[Mike BrettParticipant @mikebrett89695]

Hi all

Yes next time I have to make wheels I will buy mild steel bar , but I persevered and have finally got four nice wheels. I think they could indeed have had a higher carbon content , certainly the hardest bit of mild steel I have machined. I finally got there by annealing then using a carbide tipped tool. Took a while to get under the skin though, thicker than I imagined. Tried back gear and slow speed , but while it was cutting through ok ,the finish was poor. In the end I used a medium speed and the finish was much better. Had to keep stopping though because of heat build up.

Anyway many thanks for all your help.

Stay safe Mike

[John HaineParticipant @johnhaine32865]

The kit for the Acute tool grinding system I bought contained a number of laser cut items and yes, they were hard to machine, not sure they had hard spots but the material was "sticky", definitely not free-cutting!

[IanTParticipant @iant]

Mike,

I purchased some blanks a little while ago that sound very similar (mine are 10mm x 50mm). I've not tried turning them as yet, although I have drilled mounting holes in their centres – which was not a problem. Generally when I turn wheel castings I use an insert tool to get under the surface – and the outer edge of my blanks look like they will need the same treatment.

Regards,

IanT

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 23/05/2020 14:13:47:

Although mild steel contains only very small amounts of carbon it is possible to achieve a degree of hardness with very rapid quenching.

It is tricky to do but can be done – I was reading about it a few weeks ago.

Laser cutting meets these difficult to achieve conditions, unfortunately! I've had to deal with laser cut blanks…

…

Neil

Or could it be Nitriding as well as or instead of? The welded join along rolled mild-steel pipe can be very hard too. Maybe a laser generates a plasma like an electric welder and the hardness is Nitrogen ions reacting with Iron to form a thin but tough outer skin.

Edited By SillyOldDuffer on 23/05/2020 17:51:20

[JasonBModerator @jasonb]

A lot of the laser cut stuff is S275 which is not the nicest stuff to machine, better suited to teh welding and fabrication guys than machinists, it also has a slightly higher carbon content (0.25% ) which may be what the heat is affecting. The other downsid eis it is a hot rolled steel and does have a thin smooth coating of mill scale, not so much black but a dark silvery grey which can be hard and abrasive to tools.

If getting stuff laser cut then ask for HR4 which is hot rolled so no scale and about 1/3rd the carbon content. Still not a snice as a slice of 230M07 though

Edited By JasonB on 23/05/2020 19:01:09

[Neil WyattModerator @neilwyatt]

Took some tracking down to find details!

This paper found water quenching actually caused a low carbon steel to be harder (and more brittle) than case hardening it.

International Journal of Advance Research, IJOAR .org
ISSN 2320-9135 1
IJOAR@ 2015
http://www.ijoar.org
International Journal of Advance Research, IJOAR .org
Volume 3, Issue 6, June 2015, Online: ISSN 2320-9135
COMPARATIVE STUDY OF CASE-HARDENING AND
WATER-QUENCHING OF MILD STEEL ROD ON ITS
MECHANICAL PROPERTIES
O.R Adetunji*, A.O Adegbola, S.A Afolalu.

ABSTRACT
Mild steel is easily available and affordable having all material properties that are acceptable for many applications. It
has carbon content up to 0.15%. While case-hardening and water-quenching are carried out on mild steel to improve
toughness, strength and hardness, ductility declines as a result of internal stress developed in the material. This
research work evaluated the effect of case-hardening and water-quenching on the mechanical properties of mild
steel rod. Fifteen samples of mild steel rod of diameter 50 mm were prepared and heat treated in all, 12 of which
were tensile samples. The other materials used for the project work were; powdered charcoal (4.44 g), barium
carbonate (250 g), venier caliper, optical microscope, heating furnace and the material testing equipment. The waterquenched
specimens were heated to 950 oC and soaked for 40 minutes, after which the specimens were quenched
in water. The case-hardened specimens were heated to 950 oC and for a period of 40 minutes and then quenched in
salt solution. Various tests were carried out on the heated samples such as; tensile strength test, hardness test,
microstructural analysis and chemical analysis were all carried out. The results showed that the case-hardened
specimens had more ductility than the water-quenched. The hardness test revealed that the water-quenched
samples were the hardest, followed by the case-hardened samples. The case-hardened specimens had higher value
than water-quenched specimens for strain at break. Various microstructures which were product of austenite were
got such as, martensite (BCT, fine grains), Bainites and Pearlites.

[IanTParticipant @iant]

Posted by JasonB on 23/05/2020 18:46:40:

A lot of the laser cut stuff is S275 which is not the nicest stuff to machine, better suited to teh welding and fabrication guys than machinists, it also has a slightly higher carbon content (0.25% ) which may be what the heat is affecting. The other downsid eis it is a hot rolled steel and does have a thin smooth coating of mill scale, not so much black but a dark silvery grey which can be hard and abrasive to tools.

If getting stuff laser cut then ask for HR4 which is hot rolled so no scale and about 1/3rd the carbon content. Still not a snice as a slice of 230M07 though

Certainly fits the description Jason – mine are dark silvery grey as described above. They were purchased on eBay and I've always assumed that they were a by-product of some other commercial manufacturing process – and that either the company itself has found an additional revenue source, or some enterprising soul has discovered extra income by raiding the company's scrap bin…

Regards,

IanT

[HopperParticipant @hopper]

Posted by Mike Brett on 22/05/2020 17:35:50:

I was afraid that would be the answer. If I tried to grind the edges it would no longer be a perfect round and I would never get it back in the chuck.

Sure you would. Or you could even use a four jaw if needed. But it sounds like you are proposing to hold the blanks by the OD while you machine the OD, so could be kind of flimsy holding power.

You might be far better off to either mount the wheel on an arbor/mandrel or bolt it to a faceplate. You can drill and tap threaded holes part way through the wheel if you don't want the holes visible on the finished wheel outer. Or make a stub mandrel out of a piece of say 1.5" or 1" bar with a bolt hole in the centre. Bolt the wheel on and hold in position with Loctite or superglue while machining to stop rotation. A blast with the propane torch afterwards will break it loose. Or even a rap from a hammer often does it.

What RPM did you try machining at? For 2" diameter you would need to be down around 100rpm for HSS and maybe 200 or 300 for carbide inserts. Hard if you have one of those small lathes with variable speed motor with no torque at low rpm so your best shot then would be grind off the scale and carry on as above. Use backgear if you have an old banger from that primitive era.

i machine laser cut discs all the time without problem. Our local steel merchant sells the "holes" he cuts out of structural steel work. Very handy and usually machines quite nicely. The hard layer is only a few thou thick so takes not much at all to grind or machine it off.

[vintage engineerParticipant @vintageengineer]

Depending on whether it was made from new mild steel or it was recycled mild steel will affect it's composition. Recycled mild steel can contain all sorts of unwanted crap including boron.

The only mild steel that I know that is made from raw iron ore is structural steel as this has to have a certificate of conformity. Where as run of the mill mild steel doesn't.

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