The quality of free forging is evaluated through several key criteria:

1. Surface Finish: The appearance of the forged part is important. A smooth surface indicates proper handling and technique, while defects like cracks or scales can signal issues.

2. Dimensional Accuracy: The forged part must meet specified dimensions and tolerances. Measurement tools like calipers and gauges are used to ensure this.

3. Material Properties: The mechanical properties, such as tensile strength, hardness, and ductility, are tested to confirm that the material has not been adversely affected during forging.

4. Microstructure: Analyzing the grain structure under a microscope can reveal whether the forging process has produced desirable properties, such as uniform grain flow and reduced porosity.

5. Defect Inspection: Techniques like ultrasonic testing, magnetic particle inspection, or dye penetrant testing are used to detect internal and surface defects.

6. Forging Ratio: The ratio of the original cross-sectional area to the final area can indicate the extent of deformation and effectiveness of the forging process.

7. Mechanical Testing: Standard tests (e.g., tensile tests, impact tests) are performed to evaluate the overall performance of the forged product under expected service conditions.

8. Heat Treatment Response: If applicable, evaluating how the forged part responds to subsequent heat treatment processes can further assess quality.

Each of these criteria contributes to a comprehensive evaluation of the quality and performance of a forged component.