yes Marty , that was most helpful,,,,,,,"key-to-steel" helped me most..........
i'm still having problems trying to understand how it becomes "work hardened".........
i can understand how some steels can become work hardened thru some sort of "impact",,,,,,,,,,but not the opposite,,,,,,,,,,by ripping something apart,,,,,,,,,i just cant understand that once you start destroying it , in that sense , it just can't be anything but weaker than original form from that point on..........?????????
i understand they say that it becomes stronger and harder (these dislocations) before it finally begins to fail.............like i said , i just can't comprehend that........
Any time you distort the atomic lattice structure, you strengthen the material. Stretch it, roll it, bend it, or add alloying elements, the results is the same, you distort the crystalline structure, i.e., lattice structure of the grain and it is hardened and strengthened.
Best regards - Al
Work hardening: An example You can see for Yourself - Take a welding rod, coat hanger or even a paper clip and bend a tight 180 deg bend in it. Now try to make it straight again. The material has work hardened from bending, and now is easier to bend on each side of the first bend as You try to straighten it out. Seeing is believing.
803056 really captures it. Distortion of the lattice through work hardening prevents easy slip along lattice planes. Like the difference between sliding two faying pieces of glass or two pieces of sand paper.
Wikipedia does a fairly decent job of capturing this in their "Work Hardening" article:
"Work hardening, or strain hardening, is an increase in mechanical strength due to plastic deformation. In metallic solids, permanent change of shape is usually carried out on a microscopic scale by defects called dislocations which are created by stress and rearrange the material by moving through it. At low temperature, these defects do not anneal out of the material, but build up as the material is worked, interfering with one another's motion; strength is increased thereby, and ductility decreased by considerable amount."
In other words, the more you distort the material, the closer it gets to where it can't distort any more. Since strength is resistance to distortion, the material gets stronger. But it also gets less ductile--it's closer and closer to where it'll break without distorting much further.
Think of it not so much as "ripping something apart" but as pulling the slack out of the crystalline structure.
Hg
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