Gray cast iron refers to cast iron with flake graphite, because the fracture is dark gray when broken, so it is called gray cast iron. The main components are iron, carbon, silicon, manganese, sulfur, and phosphorus. It is the most widely used cast iron, and its output accounts for more than 80% of the total output of cast iron.
The basic characteristics of gray iron castings are: high clay content, low moisture, and low coal powder addition.
Methods to increase the tensile strength of gray iron castings:
1. A small amount of carbon can be added to the raw materials. In the carbon content of gray iron castings, the carbon content is mostly 2.6% to 3.6%, and the silicon content is 1.2% to 33.0%. In the case of determining the wall thickness of gray iron castings, manganese should also be added in an appropriate amount, and the manganese content should be .4%~
2. Use alloying method to improve the tensile strength of gray iron castings, adding appropriate amount of trace alloys, chromium, molybdenum, tin and other elements can also significantly improve the tensile strength of gray iron castings, and do a good job of inoculation treatment of molten iron.
The mechanical properties of gray cast iron are related to the structure of the matrix and the morphology of graphite. The flake graphite in gray cast iron severely splits the matrix, and it is easy to cause stress concentration at the sharp corners of graphite, so that the tensile strength, plasticity and toughness of gray cast iron are far lower than steel, but the compressive strength is equivalent to steel, and it is also commonly used in cast iron. The cast iron with the worst mechanical properties in the parts. At the same time, the matrix structure also has a certain influence on the mechanical properties of gray cast iron. The graphite flakes of gray cast iron with ferrite matrix are thick, with the lowest strength and hardness, so they are rarely used; the graphite flakes of gray cast iron with pearlite matrix are fine and have high Strength and hardness, mainly used to make more important castings; graphite flakes of ferrite-pearlite matrix gray cast iron are slightly thicker than pearlitic gray cast iron, and the performance is not as good as pearlitic gray cast iron. Therefore, gray cast iron with a pearlite matrix is mostly used in industry.