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Some Extremely Hard Mill Scale and Carbide Inclusions

I was machining a bushing out of 1018 HRS steel today when I ran into a few problems. While boring the hole I hit a hard spot. Initially I was using a 1/4"HSS cutter and it was cutting like butter. Then I heard that nasty squeal and stopped the lathe only to see that the whole end of my bit was gone. So I switched over to a carbide boring bar and upped the speed and it ate through it but destroyed the insert.

After I was through that I again put in the HSS and had no problems. Then I had to turn off the mill scale on the outside of the bushing. It ate every HSS bit that I tried to cut it with up to and including a

1/2"HSS bit that was razor sharp. It did not even scratch the mill scale? I guess somehow I got a piece of material that when remelted got some High Carbon Steel in it and caused carbide inclusions in the round bar.

Why is the mill scale so damn hard? It chewed up bits like they were going out of style.

Thanks, Steve

Reply to
Steve
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I don'no, but it's a fact. I hate to use the s^&t. I've had better luck using brazed carbide bits to get though this stuff. Mostly cause they are real cheap, I scored 100 lbs. of them at an auction a long time ago. I also use these bits when trueing up a weldament, or torched out steel section. Inserts won't take the interupted cut, HSS finds the welded in hard spots and dulls right up.

Karl

Reply to
Karl Townsend

some of the lower class foreign import steels can be real nasty , I have found pieces of taps and ball bearings in 4140 forgings that one of our customers has made in china and shipped here to be finished , we usually find the real nasty stuff with expensive gundrills,

Reply to
williamhenry

When digging out mill scale, I rather like using a good negative rake carbide insert at moderatly slow rpms with a bigish feed rate. You have to dig in deep and get below the scale/hardened zone. When gathering stock for a project..I always try to make sure the HR stuff is at least

1/4" bigger than finished dimensions as I immediatly plow off .100 for my first cut.

Not something you can do on a Taig however...shrug.

Gunner

"A vote for Kerry is a de facto vote for bin Laden." Strider

Reply to
Gunner

It being a dull day, I decide to respond to what Gunner fosted Fri, 21 May 2004 09:26:48 GMT on rec.crafts.metalworking , viz:

SOP when I worked at the forge. The black scale ate inserts, so the idea was to get below it. Why scale is so much harder than the steel it is made from, I do not know, but it is a fact.

tschus pyotr

Reply to
pyotr filipivich

Iron oxide, which is the main component of mill scale, is also used as an abrasive, crocus cloth is one application. So it's pretty hard stuff.

Stan

Reply to
Stan Schaefer

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