this is probably a weird question but am curious if anyone has thoughts or knowledge ... i found a few pieces of the steel pictured below at a scrap yard. did a spark test and it appears to be your generic everyday mild steel. when I used a chop saw to cut it the first 1/2" or so cut just like mild steel ... easy to get through, long sparks - no problem. then as i get closer to the center it's nearly impossible to cut through and giving off short sparks that look more like spring steel ... blew my 25 amp breaker a few times trying to get through which i finally did after a while. 

my question ... is it possible or common that two types of steel were combined into a single piece? there's lot's of things i dont know about working with metals but i definately know how to use a chop saw and this is the first time i've run across something that behaved in this way. 

** the top picture is another piece as found it in the scrap yard, the bottom is a cross section of the piece i cut.

any thoughts or comments would be great. 

thanks

 

sometimes the disc in your saw gets shiney on the edge and just heats up the metal

In a word, ... Yes.

They're commonly known as "inclusions", and are often present in "recycled" steel.

19 minutes ago, SmoothBore said:

In a word, ... Yes.

They're commonly known as "inclusions", and are often present in "recycled" steel.

got it, that makes sense. thanks

Old time tools were often "steeled" on cutting edges; example axes and chisels and adzes  And of course anvils were made with a high carbon face and wrought iron body back when,  Jail cell bars were often hardened on the outside to prevent cutting and left soft inside to prevent breaking, Large bearing races were case hardened....

I assume this is a cutting disc machine you are using as opposed to a cut off saw

You may be using too much pressure on the workpiece, let the tool do the work, or as Dwarf mentions the edge will get shiny, this is due to excess friction and overloading the wheels matrix causing the "bluntness" which rubs not cuts, be patient, maybe ease off a little and if it is a hand held machine, try a little sawing type motion.

A similar phenomon also occurs in static mounted machines when discs are worn, and optimum cutting angles with disc's periphery become distorted on approach and during cutting.

I have come across inclusions too in recycled metals, the worst example seemed to be a carbide tip in an otherwise piece of mild steel. 

19 hours ago, ThomasPowers said:

Old time tools were often "steeled" on cutting edges; example axes and chisels and adzes  And of course anvils were made with a high carbon face and wrought iron body back when,  Jail cell bars were often hardened on the outside to prevent cutting and left soft inside to prevent breaking, Large bearing races were case hardened....

 

19 hours ago, John B said:

I assume this is a cutting disc machine you are using as opposed to a cut off saw

You may be using too much pressure on the workpiece, let the tool do the work, or as Dwarf mentions the edge will get shiny, this is due to excess friction and overloading the wheels matrix causing the "bluntness" which rubs not cuts, be patient, maybe ease off a little and if it is a hand held machine, try a little sawing type motion.

A similar phenomon also occurs in static mounted machines when discs are worn, and optimum cutting angles with disc's periphery become distorted on approach and during cutting.

I have come across inclusions too in recycled metals, the worst example seemed to be a carbide tip in an otherwise piece of mild steel. 

thanks for the ideas ... i suspect, based on feedback and an image search, these pieces were used as counterweights not subject to any stress so likely recycled and no one really cared what composition of the metal. 

i've made a couple of bottom fullers from them and so far so good but i guess forging a hammer from this stuff isnt a good idea.