Cold drawing involves pulling a hot-rolled, descaled bar through a die at room temperature to reduce its diameter and improve its surface finish and dimensional accuracy.
Effects, Characteristics, and Comparison:
| Aspect | Hot-Rolled AISI 4140 | Cold-Drawn AISI 4140 |
|---|---|---|
| Process | Shaped at high temperature (>1100°C). | Drawn through a die at room temperature. |
| Surface Finish | Rough, with mill scale. | Very smooth, bright, or shiny finish. |
| Dimensional Accuracy | Commercial tolerances (e.g., ±0.8mm on 50mm). | Tight tolerances (e.g., ±0.1mm on 50mm). |
| Mechanical Properties | As-rolled (annealed/normalized) state. | Work Hardened: Higher yield and tensile strength, lower ductility in the as-drawn state. |
| Grain Structure | Equiaxed, recrystallized grains. | Elongated, directional grains. |
| Residual Stress | Possible from uneven cooling. | Higher surface compressive stresses introduced. |
| Primary Use | Forging, machining where stock is removed, final heat treatment. | Precision components, shafts, pins where minimal machining is needed; often used as-is without further heat treatment. |
Cold-drawn bars offer "ready-to-use" precision but have less uniform properties across their cross-section and may require stress relieving if severe machining is planned.