Dumb Question - Hot rolled vs. Cold rolled??

Not a stupid question at all. In fact many makers have been sorely disappointed in steel because of not knowing the difference. 416 stainless for instance can be had both ways. The surface looks better in cold rolled. I use it because it cleans up a little better in the milling vice. You have to be really careful with 440-c for instance. Hot rolled bar, is uglier on the surface. But is good stuff. There is a lot of sheared 440-c out there from cold rolled plate. It can have a very strong tractor tire tread grain when trying to finish. Seems that hot rolled is just a bit more dense. In steel going to be used forging, it probably doesn't matter. You can improve on the grain in cold rolled by forging, but hot rolled is damed good just as it comes form the mill. There is a lot of talk about grain refinement. It is mostly BS. You can get a shape that you want by forging with less metal that stock removal, But the grain refinement comes from the heat treating. Not from forging. Such things as edge packing, and breaking up the molecules is pure smoke and mirrors. Sells well to the UN educated. But is nothing more than Flem-flam at it's best. Mike "How it is made", prolly the best show ever made for gearheads,
had a segment on how they make steel. Wuz most excellent indeed.

Oftentimes you see a blacksmith forging a bar (making, say,
damascus), working with something like 1"x1"x10" bar.

Now, imagine that bar is 15 feet x 15 feet x 20 feet, being forged
by a gian press, while being held in giant tongs. That's what it looks
like.

Before that happens, they smelter iron and additives in a giant
smelter, with 3 giant electrodes. Must be megaAmps of current
doing the job. As the metal melts, they add alloying elements and
frequently check the resulting "mix" for proper percentages, adjusting
as needed. As they pour, filters will catch larger debri. Of course,
to qualify for NASA, this process needs to be pretty darn clean. It might
have to be repeated few times, to get progressively cleaner, better steel.


Some metals, like brass, can be hardened by "working" it . Steel doesn't
exhibit this feature. Still, when they roll, a lots of stress ends up in the
metal . Also, when hot rolling, exterior layers loose carbon and other alloying
elements. Nasty, hard scale forms. It has to be removed - this makes steel
"decarb" free and it also brings it down to exact dimensions (precision-ground) or just slightly oversized (called just that). Another way to remove the scale is to pickle the steel in acid, but of course it is not precise at all.

When using hot roll for removal-method knifes, one has to be careful not to end up with a warped blade, again due to the stress of hot-rolling being hidden in the metal bar. At best, you will have to spend lots of time orrecting it. Ok this was just on history channel and a while back how its made.

When steel is heated up the molecules align in to what they called a matrix. This becomes a stronger steel. In cold rolling they start with a huge billet of steel and run it throguh rollers compressing the steel. In cold roll steel youll have the same matrix as you did in the original billet (for the most part its really less change to the matrix). Cold rolling also uses many more rollers and or passes to get the stock to the final size and shape this is why it will tend to have a nicer looking finish.

With hot rolled steel the matrix will change become more dense and well aligned. In stock removal this is a good thing as it will grind and file etc smoother for us (more consitancy) than cold rolled. In the end though if your heat treating is good other than the ease of finishing both will end up the same or very close to the same in hardness grain structure etc.

Remember on raw hot rolled youll need to remove a portion of the mettal from top bottom and both esdges to get past the scale layer.

OT sort of but intresting. You know that alluminum foil you use to wrap your lunch in? Well it is a multi layer or damascus alloy. To get foil they use hot roller to thin out a very huge billet of aluminum. Once its at a given thickness it is folded in half and ran through the rollers again to increase its strength. Depending on how heavy a duty its to be used for it may be folded again and again ran through the rollers. So you heavy duty foil is folded twice giving a 4 layer damscus aluminum foil

Just a fun little fact i picked up watchign how its made heheh

I was wondering if there was any views on the suitability of using black hot rolled steel (HRS) as the basis for machining a slotted cross slide about 8 inches by 3 by1.

You will get efficient and thoughtful service from Xingtai Steel.

Cast iron would be preferable but always seems very expensive (>£50) rolled steel would be about £10. I am unable to heat treat so can't use BMS and I don't fancy fabricating a table, leaving HRS.

I would treat the rolled steel similar to cast iron, taking a deep cut with a carbide face mill all round to get rid of scale, then take approx. to size, then mill the slots and v-ways then mill the tees, then finish mill the surfaces (or grind on my Stent if I have to.

Is this sort of work feasible with this material? will it do as the 'poor mans' steel / iron and are there any common issues, risks or other things to be aware of when generally working with HRS?

Ta

Martin.

I use a lot of hot rolled steel, both for my traction engines and for tooling. It has a number of characteristics, some good, some bad:

It is rather sticky and has a propensity to tear if speeds and feeds are incorrect. I use carbide tooling as a matter of course for turning and milling. Run fast and you'll get a good finish. It won't look like free cutting steel but is still fit for purpose

I don't worry about the scale, it's not like the hard surfaces on a casting

The material doesn't go banana shaped when you mill it

It doesn't seem to be prone to rust like free cutting steel. I get a great finish on EN1A, put it on the hall table and the next morning it shows signs of rusting. Hot rolled doesn't do that, it survives in the kitchen without rust, and the kitchen isn't exactly dry.

Hot rolled steel is good in tension and compression unlike cast iron.

This is part of press tool set I've just made from hot rolled steel:

Andrew

Hot rolled is one of my go to materials in the shop as it is easy to source. I like machining it (it takes a bit to get adjusted as indicated above).

Just make sure you size your material to allow for cleanup. Most hot rolled sections aren't all that square so you have to remove a fair bit of material to clean it up. Obviously cold rolled doesn't suffer from this problem but it suffers from residual stresses.

For most home shop tools hot rolled works quite well.

Just be warned if you wish to scrape the slide in for fitting purposes, scraping steel can be miserable compared to cast iron. If you are going to scrape I would spend the extra money on the cast iron.

Thanks to all that replied, very helpful and useful to know that this is material OK for general use, also useful to know that high speeds and low feeds are the way to go. I now feel emboldened to give the project a try. And if it all goes pear shaped, at least it wont break the bank!

If you are looking for more details, kindly visit hot rolled round bar.

As the project is only for home mini lathe use, the ultimate in high finish and durability is not really necessary. I hadn't thought about scraping issues but I wouldn't have thought it necessary for this application.

AdrianR &#; you ask an interesting question, I always thought in my ignorance that anything described as 'black steel' by stockholders was technically the same as hot rolled steel. Somebody please shout and tell me quickly if this is not the case!

I don't know of any helpful steel stockholders near to Weston that are willing to supply small quantities so was going to use M Machine Metals, but only because I have used them before (other stockholders are available).

Thanks to all,

Martin

Larry, not much 'raw' material is really round but I use my 3-jaw for holding all types of materials. However &#; you have to skim it true and then not remove it from the 3-jaw once trued (or it will not run true when replaced). A 4-jaw is useful when something that has already been 'trued' (by turning or grinding) needs to be set-up to run true (often for a second operation for instance).

If I have a piece of rod that I'm going to machine down &#; I'll generally just stick it in the 3-jaw, because it's quicker and simpler to do so. The 4-jaw generally gets used when I have something awkward to hold or where I need to set it to run true or (alternatively) have it run off-set (eccentrically).

So I think (and my apologies if I've misunderstood your question) the answer would be No &#; your 3-jaw chuck will normally be fine for hot-rolled rod.

Regards,

IanT

Edited By IanT on 06/04/ 13:38:56

For the less pecunious of us, often using "pre-loved" metals, hot-rolled steel has the advantages of stability described above, and you are less likely to be caught out by some nice shiny stuff from the local scrap-yard being anything but free-cutting!

It is also usually readily welded, which is not recommended for leaded free-cutting steels. (EN1A will fuse, but the welds can be brittle.)

Recently I made a set of dovetail nuts to hold the magnetic read-out strip to my milling-machine table, using the slot that originally held the limit-stops. I saw this is the only practical way, on a Myford VMC mill not designed to take a DRO set. My stock was cut from old miniature-railway rail, flat-bar not profiled, scrapped as too worn and rusted for continued railway use. The worst corrosion pits were quite deep, but the nuts are sufficiently thinner than the stock to avoid them.

Years ago I worked as materials store-keeper for a manufacturer of industrial screen-printing machines, when it received a one-off order for special jigs to hold long surveying-poles for printing their rule scales (not ruler &#; I've read that thread!). The longest was at least 2m long, and after the miller had cut the requisite facings and channels along the BMS stock, it naturally warped. So it went off to a heat-treatment firm for normalising, but came back even more normally bent. I can't remember what they did eventually &#; might have used aluminium-alloy instead.

A further tip:

Those DRO nut's dovetail chamfers are at 45º. No suitable cutter, so I drilled and tapped all the holes regularly-spaced along the strip, then drilled matching holes along a piece of angle-steel, at the same settings. Screwed the nut-strip to the angle, clamped that to the mill table so it acted as an inside-out V-block; then kept the assembly together to hold in a vice for junior-hacksawing the nuts apart.

I marked the cuts first by tiny drill-spots during the drilling and tapping process: the nuts' ends do not need be more square than by eye, and a file soon tidied them.

Note: this process order will not work in all cases. What surprised me, when at the printing-machine manufacturers, was the number of times millers making extra T-nuts would drill and tap all the holes in a bar length then expect me to separate them on an auto-feed hacksawing-machine with a well-made but poorly-designed geared-roller vice. It was definitely not for such tasks and incapable of holding short bars anyway. I had to gently suggest to these apprentice-trained, skilled machinists that the repetition would be far easier and more reliable if I cut the embryo nuts from the stock bar before machining.

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