ISO 9042:2024
Steels - Point counting method for statistically estimating the volume fraction of a constituent with a point grid
- Standard No.
- ISO 9042:2024
- Release Date
- 2024
- Published By
- International Organization for Standardization (ISO) IX / ISO
- Latest
- ISO 9042:2024
- Introduction
Analysis of the core content of the standard
ISO 9042:2024 specifies a standardized method for estimating the volume fraction of microstructure components in steel by point counting grid statistics. This method is applicable to optical microscopes or digital image analysis systems, and requires that the measured components have clear and identifiable characteristics.
Technical principles and equipment requirements
The basic principle is to calculate the volume fraction by superimposing a regularly arranged dot grid on the microscopic image and counting the proportion of points that fall into the target component. The standard provides three typical grid forms:
Grid type Point configuration Applicable scenarios Circular grid (Figure 1) 25 points Avoid periodic structure interference Square grid (Figure 2) 16/100 points General analysis Hexagonal Blaschke grid (Figure 3) Variable High-density measurement
Key operation process
- Grid selection: Determine the number of points according to the estimated area fraction according to Table 2. When it is >50%, the minority phase can be measured in reverse
- Magnification: Satisfy the grid point size < component size, and ensure the representativeness of the field of view
- Field of view number calculation: Determine according to the formula n≅40000×(100-VV)/(Erel2×VV×PT) in Table 3
- Boundary point processing: Points falling on the boundary are counted as 0.5, and the same applies to fuzzy judgment points
Main changes in the new version
- Correct the definition and value of t multiplier in Table 4 (original Table 3)
- Add grid examples and application instructions
- Clarify the digital image analysis method
- Terminology change: Error% is changed to Erel
Implementation suggestions
Case 1: When measuring pearlite with a volume fraction of 20%, a 25-point grid is used. When Erel≤10%, 85 fields of view need to be measured (Table 3)
Quality control: It is recommended to establish a three-dimensional comparison table of grid point number-relative error-number of measurements to optimize detection efficiency
Digital implementation: The computer algorithm needs to verify the accuracy of boundary recognition, and pay special attention to the processing logic of half-counting points
Statistical calculation specifications
Volume fraction calculation formula: VV = PP±CI, where:
- PP = (ΣPp(i))/n
- CI = t0.05;n-1×ŝ/√n
- Erel = (CI/PP)×100%
Note: When n≥30, t0.05;n-1 can be taken as the approximate value 2 (Note a in Table 4)
ISO 9042:2024 history
- 2024 ISO 9042:2024 Steels - Point counting method for statistically estimating the volume fraction of a constituent with a point grid
- 1988 ISO 9042:1988 Steels; manual point counting method for statistically estimating the volume fraction of a constituent with a point grid
