Cold forming carbide containing alloys

Question

In this post, the term "carbide containing alloys" refers to steels and other alloys that have significant carbide content that is put there intentionally, not just some small amount as result of carbon impurity. I have in mind steels like you can find in quality knives, like 440C, and alloys such as Stellite 6 which have carbon content around 1%.

Is it a bad idea to cold work sheets of these materials, e.g. cold forming on press, stamping simple shapes without sharp corners? I'm worried about those brittle and stiff carbides. For cold forming, I only saw carbide free, highly ductile materials used, and I expect there is good reason to that and that nobody cold forms these carbide containing materials for some good reason I don't know yet.

Stellite 6 for example has elongation specified as 6%. That's very low but not so low as to completely prevent cold forming. I think if there are no sharp corners, then stamping shape like a hemisphere for example should be possible, but I am not sure.

I want to know what is going to happen to the carbides as the sheet is bending. On one side I think those carbides must crack since they are stiff and brittle, on other side, they are ceramic type of material, and silicon dioxide, another ceramic material that is stiff and brittle too is actually flexible when in thin wire form. Optic cables don't break when they are bent, the carbides in Stellite 6 look like rivers, long thin shape like the optic cables,perhaps that allows them to be bent without cracking.

1. Can carbide containing materials like 440C or Stellite 6 be cold formed?

2. What happens to carbides when sheet is cold formed? Do they crack, or do they bend like optic cables?

Answer 1

the carbides of which you speak are segregated at the grain boundaries of the steel which contains them. Their purpose is to interfere with dislocation movement across the grain boundaries, thereby strengthening the steel and reducing the elongation at fracture.

The "alloys" you mention are steels which contain small amounts of other metals like vanadium and molybdenum which enhance the formation of carbides and stabilize them at elevated service temperatures which would otherwise ruin iron carbides.

What this means for formability by cold work in these alloys is: you can't. these materials are shaped by heating them red-hot and then plastically deforming them, and then cooling them at a rate which is controlled so as to allow the carbides to re-form by the time the workpiece has returned to room temperature.