# Which one is more work-hardened than the other?

• StudentForming
In summary, the conversation discusses the question of which cold drawing process results in more work hardening. The final diameter is the same, but the number of cold drawing steps is different. The participants suggest that the more complex strain path in a cold drawing process may lead to more work hardening, but they cannot provide a definitive answer without further research.

#### StudentForming

TL;DR Summary
The effect on number of cold drawing to work-hardening.
Hi.

I wonder which one is more work-hardened in cold drawing process.

① φ7 -> φ6.5
② φ7 -> φ6.8 -> φ6.5

Final diameter is same, but the number of cold drawing is different.
In my guess, ② is more work-hardened even thought I can't explain the reason exactly.

If you know the answer and the mechanism, I hope you tell me about that.

When a strain hardening material is loaded beyond yield, the stress reduced to zero, then again loaded beyond yield, the result is as shown below. The first loading takes it to Point A, then unloading takes to Point B. The material has yielded. On further loading, the material follows the dashed line back to Point A, after which it yields some more.

That is for simple tensile loading. A cold drawing process involves a more complex stress-strain path that complicates matters. Answering your question requires finding the exact strain path as the part goes through the cold drawing process. The image below shows a part that was cold drawn in two halves. Each half had lines scribed before drawing. After drawing, the two halves were separated. The lines are no longer straight. I believe this means that the actual strain path is more complex than that of a simple tensile test, which would imply (but does not prove) that drawing in two stages might cause more work hardening than drawing in one stage.

I cannot explain it exactly either, but I think you are right. Proving it would require studying the strain path through the cold drawing process.

Jodo

## 1. What is work hardening?

Work hardening is the process by which a material, such as metal, becomes stronger and more resistant to deformation through plastic deformation. This occurs when the material is subjected to repeated stress or strain, causing the individual grains of the material to become more compact and aligned.

## 2. How does work hardening affect the properties of a material?

Work hardening can increase the strength and hardness of a material, making it less malleable and more difficult to deform. It can also improve the material's resistance to wear, corrosion, and fatigue.

## 3. Which materials are most susceptible to work hardening?

Metallic materials, such as steel and aluminum, are most susceptible to work hardening due to their crystalline structure. However, other materials, such as plastics, can also undergo work hardening under certain conditions.

## 4. How can work hardening be measured?

Work hardening can be measured using various methods, such as tensile testing, hardness testing, and metallography. These tests can determine the material's strength, ductility, and microstructure, which can indicate the degree of work hardening.

## 5. Which is more work-hardened, a cold-rolled or hot-rolled material?

Cold-rolled materials are typically more work-hardened than hot-rolled materials. This is because the cold-rolling process involves repeatedly passing the material through rollers at room temperature, causing more plastic deformation and work hardening. Hot-rolled materials, on the other hand, are heated and rolled at high temperatures, which can reduce the amount of work hardening.