I. Differences in material structure and process
| Terms | Cast iron valves (grey cast iron) | Ductile Iron Valves |
|---|---|---|
| Material identification | Marked as HT200 (flake graphite structure) | Marked as QT450 (spheroidal graphite structure) |
| Graphite form | Flake graphite, easily induced stress concentration in the substrate | Spherical graphite, enhanced matrix mechanical properties |
| Manufacturing process | Conventional casting, cannot be strengthened by heat treatment | Heat treatable for strengthening (e.g. annealing) |
II. Comparison of Physical and Mechanical Properties
Density and weight
Ductile iron has a higher density (7.3-7.4g/cm³) and the valve is heavier;
Cast iron density is lower (6.8-7.2g/cm³), the valve is relatively lightweight.
Mechanical properties
Ductile iron tensile strength ≥ 450MPa, yield strength ≥ 310MPa, close to medium carbon steel;
Cast iron tensile strength only ≥ 200MPa, brittleness significantly higher.
Special properties
Ductile cast iron impact resistance, wear resistance and seismic performance is better, adapt to the dynamic load environment;
Cast iron vibration dissipation is better, but the impact resistance is weak, easy to crack under severe working conditions.
III. Applicable Scenarios and Economy
| Applications | Cast Iron Valves | Ductile cast iron valves |
|---|---|---|
| Typical media | Water, steam, low pressure air and oil (≤1.0 MPa) | Corrosive media, high pressure gas/liquid (≤42MPa) |
| Temperature range | -10℃~200℃ | -30℃~350℃ |
| Economics | Low cost for conventional low voltage systems | Higher cost but better value for money than cast steel |
IV. Appearance Identification Points
Surface colour
The surface of ductile iron is grey with metallic luster;
The surface of cast iron is dark grey or black, without significant luster.
Section observation
Ductile cast iron fracture is uniform silver-grey granular;
Cast iron has rough fracture and traces of flaky graphite can be seen.
