crystalization result of impact with metal hammer??? 2

[daveg48]

I am aware of the saftey issues of hitting metal to metal I use a die to cut leather that was made as a punch(with a handle) rather that to be used in a press. After minimal use it crystalized and broke. Now I am told never to strike this type of tool with a metal hammer. I have chisels and punches that have seen decades of use and never crystaized and broke. I do not know the chemistry of the metal used in the die. Have I been given the right advice? The actual words were that using a metal hammer on it would make it shatter like glass.

 

[metman]

daveg48,
When I was a teenager a friend was showing us a failed pinion gear from a hypiod gear from the differential of his car. Someone said it "crystaized and broke." This was the first time that I heard this saying and it seemed to fit because the fracture face certainly had a crystaline appearnce and it was obviosly broken.

A few years later I was schooled as a metallurgical technician and then as a metallurgical engineer and learned that the saying "crystaized and broke" has very little meaning because it does not shed any light whatsoever on the failure mechanism or why it broke.

All metals and metal alloys are crystalline because when they solidify during cool-down from the melted state, they crystallize or form grains which gives a granular appearance which is usually observable when you break a piece of metal and look at the fracture face.

Some metal/alloy failures have a more pronounced granular/crystalline appearance than others. For example; There is a particular type of fracture face on some cast metal alloy failures that has such a pronounced large-grain-crystalline appearance that it is termed "rock candy failure" and this term helps to denote a specific set of conditions that leads to this type of failure.

Now about your failed punch. Maybe it needs to have enough hardness to perform its function which precludes hitting it with a hammer. Any steel over about 55 HRC(Hardness Rockwell C scale) tends to chip or shatter in a brittle mode rather than deform "plasticaly" but this does not necessarily mean that it is inappropriate to hit it with a hammer. Most punches are hard and brittle at the cutting end but less hard and more ductile on the hammering end which allows the punch to be struck with a hammer without shattering such as your other punches which have decades of use. It sounds to me like your punch is not designed to be struck with a hammer and should only be used with the wooden handle. If there is enough length to the metal part of your punch, you could draw-back (temper) the end opposite the cutting end to allow use as a hammer driven punch if you really need to use it in this fashion.

Jesus is THE life,
Leonard

 

[daveg48]

Thanks for your answer. I understand the tempering of the handle. Will it eventually "work harden" due to hitting it with a metal hammer? Will it affect the entire length(4") of the handle?

 

[NickE]

daveg48-

To contiune with metman's fine explanation-

Work hardening will only occur if you deform the metal, It is a result of the discontinuities (re: dislocations)created by tearing the atom-atom bonds of the crystal lattice.

The punches we use in our dies are commonly "triple tempered" at the heads to prevent them from popping off after hitting the steel. Do you know what steel your punch is made of? That would help me recommend a temperature to use to reduce the hardness of the head so that you can avoid it breaking. I think that w/ an oxy-acetalene torch you could get a decent temper on the head.

nick

 

[rmw]

Go look in any mechanics tool box. Find the chisel drawer, and look at the hammer blow end of the chisels and punches. I suspect you will find some fine examples of various stages of work hardening, and in the case of some I have used, pieces of the chisel head end up in your skin, or even your eye, if you are not wearing eye protection.

Since chisels and punches are by nature a "driven" tool, and the hammer is the driver of choice, this process is going to occur. As Metman has pointed out, if the chisel, or punch starts out too hard to deform, it will shatter instead of looking like some of these chisels. Be careful.

 

[metman]

daveg48,
To elaborate on rmw's comment it sounds like you have enough experience to know about grinding off the mushroomed end of a chisel so that the work hardened chunks/slivers don't become projectiles (don't go ballistic on us!).

As NickE says, "give us the alloy if you know" and a more detailed description of the geometry including steel and wood and maybe we can tell you how to modify for hammering.

Jesus is THE life,
Leonard

 

[daveg48]

OK you guys, you have helped me a bunch. I do not know the exact comp of the metal but speculate it is at least 4140 and possibly ore carbon than that. From what I gather the handle should have been tempered. The handle was split in a fork to spread the force over the die, and it was one side of the fork that appears to have given away first and then the die broke. I wish I could show you a drawing. Regardless you have helped and I thnak you.
Dave

 

[KnifeKnut]

If you use brass or copper hammer head you get two benefits.
The tools being struck do not mushroom, and the softness of the metal acts as a deadblow, transfering more energy to the struck tool.

 

[KnifeKnut]

The heat treat was definately to blame.