With the development of science and technology and the continuous innovation of cast iron production technology, the ductile iron grades currently produced include QT400-18, QT500-7, QT600-3, QT700-2, etc., but the matrix structures of QT500-7 and QT600-3 contain 30% – 60% pearlite. Although the castings produced from this material have reached high tensile strength, their elongation and yield strength are relatively low. In addition, the processing performance of these castings is relatively poor compared with that of full ferrite matrix material QT400-18, Because the matrix contains a certain amount of pearlite, the wear of machining tools is relatively large. In order to make the produced castings have high tensile strength, high yield strength, elongation and good machinability, through many tests, it has been shown that the principle of increasing silicon content for solid solution strengthening is applied. The author has successfully developed the process method for producing all ferrite matrix brand QT500-14 and QT600-10 ductile iron. The mechanical properties of the two brand materials specified in en 1563:2012 are shown in the table.
| Material brand | Main wall thickness t/mm | Yield strength /MPa | Tensile strength /MPa | Elongation /% |
| EN-GJS-500-14 | t≤30 | 400 | 500 | 14 |
| EN-GJS-500-14 | 30＜t≤60 | 390 | 480 | 12 |
| EN-GJS-500-14 | 60＜t≤200 | Negotiation between the supplier and the demander | Negotiation between the supplier and the demander | Negotiation between the supplier and the demander |
| EN-GJS-600-10 | t≤30 | 450 | 600 | 10 |
| EN-GJS-600-10 | 30＜t≤60 | 430 | 580 | 8 |
| EN-GJS-600-10 | 60＜t≤200 | Negotiation between the supplier and the demander | Negotiation between the supplier and the demander | Negotiation between the supplier and the demander |
Solid solution strengthening is to strengthen the metal by forming a solid solution by adding some solute elements. The solute atoms in the solid solution cause lattice distortion, which increases the resistance of dislocation movement and makes it difficult to slip, thus increasing the strength and hardness of the alloy solid solution. When the concentration of solute atoms is appropriate, the strength and hardness of the material can be improved, but its toughness and plasticity are decreased.
The solid solution strengthening of silicon in cast iron is a well-known fact, as shown in the figure is the curve of the effect of Si on the strength of Ferritic Ductile iron. The tensile strength increases with the increase of Si content.