Why???

enjenjo · March 31, 2005, 11:20:58 AM

I was machining some steel this morning, cold rolled bar, and I noticed again how nice it machines. And thinking about it, hot rolled bar is much harder to machine, even thought it is pretty much the same material. Anyone with an answer?

Jbird · March 31, 2005, 12:13:23 PM

I'll bet if you took two dimensionally indentical pieces of hot and cold rolled bars and weighed them, the hot rolled would weigh a bit more than the cold rolled. I think it has to do with heating the steel close to it's eutectic point then squashing it between the rollers, kinda like forging.
Just a thought from a guy who took a one semester course in metallurgy back in college. Jbird

purplepickup · March 31, 2005, 12:38:07 PM

I always had the impression it was the opposite. I'm not a machinist but the shops I deal with at work would rather machine from hot roll because they say it machines easier. I dunno... :?

Ohio Blue Tip · March 31, 2005, 12:38:54 PM

I like to use "stress proof" when I have a choice, it machines easier than cold rolled and comes ground. Just machined a bit of 1.5" dia. for motor mount risers and it was a joy.
Best of all my friend at the steel place charged me $0.00 for a foot and a half of 1.5" dia.
Life is good!

Ohio Blue Tip · March 31, 2005, 12:54:08 PM

More info.
In addition: Hot rolled should machine better than cold rolled because cold rolled work hardness somewhat during the manufacture.
Stress Proof is 1144 steel and made by drawing the bar through a special die that stress relieves it and makes it easily machine-able. Also it is more resistant to fatigue and stress. Just greet stuff.
My $.02 worth.

enjenjo · March 31, 2005, 02:17:34 PM

Quote from: "purplepickup"I always had the impression it was the opposite. I'm not a machinist but the shops I deal with at work would rather machine from hot roll because they say it machines easier. I dunno... :?

I guess easier is a bit subjective. What I mean, cold roll is easier to get a smooth surface on, hot roll tends to tear a bit, and have a somewhat rougher surface, unless you take a smaller cut on the final pass.

I've machined some of that stress relieved bar stock, it's like butta'.

unklian · March 31, 2005, 03:19:33 PM

The scale on Hot Rolled is tough on cutters.

Dave · March 31, 2005, 05:43:23 PM

Quote from: "Ohio Blue Tip"More info.
In addition: Hot rolled should machine better than cold rolled because cold rolled work hardness somewhat during the manufacture.
Stress Proof is 1144 steel and made by drawing the bar through a special die that stress relieves it and makes it easily machine-able. Also it is more resistant to fatigue and stress. Just greet stuff.
My $.02 worth.

Also if your using stress proof and want to harden it you can just heat it red drop it in oil then sand the scale off it and heat it again to a straw color to draw it back . Its good way to harden sumpin in a pinch. I guess I never really paid any attention to maching hot rolled or cold rolled steel. I just do it.
Ive been working with various steels since about 13 yrs old. The really fun stuff is D2 air hard... ##$%%^^ It can get hard while you work with it. (no snide comments here please)

aluminum is a pain in the * to work with too. The trick there is a lot of wd 40 on the cutter. (keeps it from loading up)

Dave

Sean · March 31, 2005, 07:24:59 PM

Quote from: "Ohio Blue Tip"cold rolled work hardness somewhat during the manufacture.

Definitely. A friend of mine was needing motor mounts to put a 500 Caddy in his '69 Chevy pickup. He brought me some 1/4"x3" cold-roll and a drawing of what he wanted, and asked me to Brake them up for him at work. They Broke allright. Snapped in a clean line.

I tried it twice and both times the steel snapped. If I had rolled the bottom die over to one of the larger V's, it might have worked, but he was wanting a small radius. I ended up just cutting and Welding them together.

enjenjo · March 31, 2005, 09:00:09 PM

Quote from: "Sean"
Quote from: "Ohio Blue Tip"cold rolled work hardness somewhat during the manufacture.

Definitely. A friend of mine was needing motor mounts to put a 500 Caddy in his '69 Chevy pickup. He brought me some 1/4"x3" cold-roll and a drawing of what he wanted, and asked me to Brake them up for him at work. They Broke allright. Snapped in a clean line.

I tried it twice and both times the steel snapped. If I had rolled the bottom die over to one of the larger V's, it might have worked, but he was wanting a small radius. I ended up just cutting and Welding them together.

What kind of machine are you bending it on? I have a Pirana, and have done the same thing, but with me it's usually a piece of maganese steel I got from one of the quarry scrap piles

Spring steel bends better than that.

A few weeks ago, I was trying to straighten out some old bumper brackets for a rework to fit another bumper, I had it in the hydraulic press, and it snapped like glass, I had to weld it up, and use heat to bend the brackets the way I needed them.

Sean · March 31, 2005, 10:07:35 PM

Quote from: "enjenjo"
What kind of machine are you bending it on?

Our big hydraulic Brake at work. 12' Bed and with the dies we have for it we can brake 1/2" plate (big radius though). Bettenbender, I think is the name of it. We bought it and a 12' Shear (3/8" Capacity) a couple years ago. We had been losing out on a lot of work because all we had was an old Roto-Die that would barely brake 12g.

It turned out to be a good investment. As far as I know, we now have the largest capacity Shear and Brake in the area, and they are rarely idle.

Bruce Dorsi · April 01, 2005, 01:08:16 AM

I have drilled & tapped hot-rolled stock in the past with no problems.

Recently. I acquired some (new) hot-rolled 3/8" x 3" flats. ....I can't get clean holes or threads in this stock. ....The threads tear when tapping, and the sides of the drilled holes are very rough. ....I used cutting oil, and even tried new bits & taps.

Any suggestions for success?

Has the quality of HR steel diminished over the years?

Phil1934 · April 01, 2005, 02:02:31 AM

Cold rolled is only 1016 while hot rolled is 1032 or more. I was offered a bunch of CR plate at a good price for work and had to pass as I needed the extra strength.

enjenjo · April 01, 2005, 09:49:37 AM

QuoteHas the quality of HR steel diminished over the years?

Some time back, I bought some 4" channel from a local supplier, this was new material, and of course hot rolled. I cut all the pieces I needed to make a pair of ramps for a low boy trailer, and started welding them up. Pretty soon, I am hearing cracking and pinging as I weld, so I stop to take a look. There was a crack through each weld. I tried a few things, and was getting no where, so I went to the welding supply store, and showed him what I had. He told me that a local rolling mill was rerolling railroad rail into structural steel, and that might be the problem. I used the filler rod he reccommended at $10 a lb, and had no more problems. Just goes to show you don't always get what you think you are when buying irregular steel

Another time, the same supplier, I bought a quantity of 6" I beam, again new steel.and used it to build several cable trailers. In this case it worked very well, but as I was fabricating it, I noticed the brand name rolled into the webb of the I beam. Carnegie Steel. Considering that Carnegie was bought out in 1900 by J P Morgan, to form USS steel, that stuff must have sat in a warehouse a long time

Phil1934 · April 01, 2005, 06:27:46 PM

The problem is there are minimum standards but no maximum. HR is A36 which should be 36,000 PSI yield. But you can't find any with less than 48,000 PSI. This makes bending and welding more difficult.