How can you determine whether steel shot has uniform hardness?

Determining the hardness uniformity of steel shot requires the use of standardized test methods to measure and analyze data from multiple points on the sample. The key criteria and procedures are as follows:

**Multi-point measurement:** According to testing standards, the hardness of an individual steel shot cannot be measured in isolation. Measurements are typically performed across multiple cross-sections of the steel shot, and multiple readings may be required for each cross-section to obtain a statistically significant dataset.

**Use of specialized equipment:** Rockwell (HRC) or Vickers microhardness testers are commonly used to measure hardness. These instruments enable precise indentation testing on steel shot cross-sections, ensuring data accuracy.

**Data analysis:** Statistical analysis is performed on the hardness values from all measured points to calculate the mean, standard deviation, or hardness distribution range. If the hardness values at all measured points fall within the established standard range (for example, the hardness range for cast steel shot is typically HRC 40–50, potentially reaching HRC 57–62 after hardening) and the standard deviation is low, this indicates good hardness uniformity. Standards: The testing process must comply with relevant international or industry standards, such as SAE J444 and ISO 11124. These standards specify requirements regarding permissible deviations in hardness uniformity.

Additional verification: In addition to direct hardness measurement, metallographic analysis (e.g., observing the morphology and distribution of martensite and retained austenite) can indirectly reflect the uniformity of the heat treatment process, thereby confirming the degree of hardness uniformity.