Cold finished steel bars, as compared to Hot Rolled Black Bars of the same grade of steel, possess improved mechanical properties, greater dimensional accuracy, better surface integrity and higher machinability. These superior product qualities provide a number of significant design advantages & benefits:

1. Mechanical Properties: Cold drawing increases the hardness, yield and tensile strength, which can:

    1. Serve to reduce design mass (weight)
    2. Eliminate costly heat treating
    3. Allow the use of a less expensive grade
    4. Provide increased fatigue strength and longer service performance
    5. Provide better wear and corrosion resistance
    6. Better resist handling damage
    7. Provide faster annealing response
    8. Provide greater cross-sectional uniformity

2. Dimensional Accuracy: A cold drawn and/or turned, ground and polished bar offers more precise and consistent cross-section geometries, straightness and bar-end conditions, which can: 

    1. Reduce or eliminate machining.
    2. Reduce the whip and resulting vibration during machining
    3. Reduce strain on collets, pusher and fingers during machining
    4. Ease machine loading
    5. Reduce machine adjustments for size variability
    6. Improve work-holding and fixturing compatibility
    7. Provide nearer net shape
    8. Reduce scrap and yield loss during manufacture

3. Surface Integrity: Cold drawing or grinding and polishing greatly improves the surface texture, which can:

    1. Reduce or eliminate machining.
    2. Ease manual handling and machine loading.
    3. Significantly improve eddy current testing sensitivity and reliability

Turning and/or grinding helps a steel bar get rid  of its surface anomalies that :

    1. Eliminates decarburization
    2. Provide a defect-free surface
    3. Reduce need for all-over machining

Continued here