Reasons for the formation of cold cracking phenomenon on cast iron marking platform

The unreasonable structure of cast iron lined flat castings, large alloy shrinkage, poor sand retreat, and unreasonable casting processes can all cause hot cracking. The sulfur and phosphorus in steel and iron reduce their toughness and increase their tendency towards hot cracking. To prevent hot cracking, it is necessary to adjust the alloy composition reasonably, strictly control the sulfur and phosphorus content in steel and iron, design the casting structure reasonably, adopt the principle of simultaneous solidification and the concessive of the core sand, all of which are measures to prevent hot cracking.

Cold cracking is the sum of thermal stress and shrinkage stress generated when a cast iron marking platform casting is cooled to a low temperature and in an elastic state. If it is greater than the strength of the alloy at that temperature, cold cracking occurs. Cold cracking is formed at lower temperatures, with small, continuous, and straight cracks that are clean and sometimes slightly oxidized. Castings with large differences in wall thickness and complex shapes, especially large and thin castings, are prone to cold cracking.

Cold cracking can be prevented by measures that reduce the internal stress of casting or decrease the brittleness of alloys. Phosphorus in steel and cast iron can significantly reduce the impact toughness of alloys, increase brittleness, and easily lead to cold cracking tendency. Therefore, it is strictly restricted in metal melting. The thin-walled part of the large area of the iron plate is placed under the casting, so that this part can fill the mold under high metal liquid pressure to prevent insufficient pouring. The surfaces or main machined surfaces with high quality requirements on the cast iron platform should be placed under the mold. If this is not possible, the surface can be placed on the side of the mold or tilted for pouring.

For some cast iron marking platforms that require shrinkage, the thicker section should be placed on the upper or side of the mold. This facilitates the placement of risers at the thick walls of the cast iron marking platform, resulting in a good sequential solidification, which is beneficial for supplementing the shrinkage of the marked cast iron plate. The main purpose is to reduce the hardness of metal materials, improve plasticity, facilitate cutting or pressure processing, reduce residual stress, improve the uniformity of structure and composition, or prepare the structure for subsequent heat treatment.

Metal heat treatment of cast iron marking platform is one of the important processes in mechanical manufacturing. Compared with other processing techniques, heat treatment generally does not change the shape and overall chemical composition of the workpiece. Instead, it imparts performance to the workpiece by changing its internal microstructure or surface chemical composition. Its characteristic is the inherent quality of the workpiece, which is generally not visible to the naked eye.

In order to provide metal workpieces with the required mechanical, physical, and chemical properties, in addition to selecting materials and various forming processes reasonably, heat treatment processes are often used. Steel is a widely used material in the mechanical industry, with a complex microstructure that can be controlled through heat treatment. Therefore, heat treatment of steel is the main content of metal heat treatment.