The standard for metallographic inspection of ductile iron is the fundamental basis for ductile iron production, product quality inspection, and quality control. Metallographic analysis and hardness testing can be conducted in accordance with the international standard ISO 945-4:2019 Metallographic Inspection of Ductile Iron, and the process is as follows:
I.Cutting and Sampling:
A metallographic cutting machine is used for sample cutting. Water cooling is adopted throughout the cutting process to prevent changes in the metallographic structure of the sample caused by improper sampling methods. Specifically, different models of metallographic cutting machines can be selected for cutting and sampling based on the size of the sample and the required automatic procedures.
II.Sample Grinding and Polishing:
After cutting, the sample (for irregular workpieces, the mounting press is also needed to make the sample) is ground on a metallographic sample grinding and polishing machine using sandpapers of different grit sizes from coarse to fine. Three or four types of sandpapers can be selected for grinding according to different workpieces, and the rotation speed of the grinding and polishing machine also needs to be chosen based on the product.
The sample after sandpaper grinding is polished using a polishing felt cloth with diamond polishing compound. The rotation speed of the grinding and polishing machine can be adjusted according to the workpiece.
III.Metallographic Testing:
In accordance with the requirements of GB/T 9441-2021 Metallographic Testing Standard for Ductile Iron, a metallographic microscope with an appropriate magnification is selected to take photos of the metallographic structure before and after corrosion.
IV.Hardness Testing of Ductile Iron:
Hardness testing of ductile iron is based on the international standard ISO 1083:2018. Brinell Hardness (HBW) is the preferred and most stable hardness testing method.
- Applicable Conditions
Sample Thickness: ≥ 10mm (indentation diameter d ≤ 1/5 of the sample thickness)
Surface Condition: The surface roughness Ra after processing is ≤ 0.8μm (no scale, sand holes, or blowholes)
- Equipment and Parameters
| Parameter Item | Standard Requirement (for Ductile Iron Specifically) | Basis |
| Indenter Diameter (D) | 10mm (preferred) or 5mm (for thin samples) | Use 10mm when HBW ≤ 350;use 5mm when HBW > 350 |
| ApplyForce (F) | For 10mm indenter: 3000kgf (29420N);For 5mm indenter: 750kgf (7355N) | F = 30×D² (Brinell hardness formula, ensuring the indentation matches the graphite size) |
| Dwell Time | 10-15 seconds (15s for ferritic matrix, 10s for pearlitic matrix) | Preventing graphite deformation from affecting indentation measurement |
Post time: Nov-26-2025
