Causes And Preventive Measures Of Pores in Grey Cast Iron

cause

When the molten iron contains a lot of gas, and the pouring temperature is too low, the precipitated gas is too late to float and escape from the casting.

1) Increasing nitrogen content in molten iron can inhibit the formation of ferrite, increase the volume fraction of pearlite, reduce the spacing between pearlite lamellae, increase the number of eutectic groups, and promote the formation of A-type graphite, thereby improving the mechanical properties of gray cast iron. Comprehensive properties of gray cast iron. However, nitrogen needs to be in a suitable range to play its role. If the nitrogen content is too high, nitrogen holes will be formed, causing the casting to be scrapped. Generally, the nitrogen content should be controlled at 100-450ppm.

2) The gas content of the charge itself is high, or the rust is serious, and the surface has a lot of grease.

3) Subcutaneous pinholes are mainly caused by hydrogen. Silicon can reduce the content of oxygen in cast iron, but it can increase the content of hydrogen, so high-silicon cast iron is prone to hydrogen pores. When the charge contains aluminum or aluminum oxide, pinholes are also prone to occur.

4) The molten iron ladle is not dry.

5) The inoculant does not work.

Prevention method

1) The charge should be properly managed. For the charge with severe rust or a lot of grease on the surface, it can only be used after cleaning or treatment.

2) For the charge with high gas content, it should be remelted and regenerated before it can be used.

3) An appropriate amount of rare earth can be added before the furnace for degassing.

4) Control the appropriate molten iron release temperature and pouring temperature.

5) The hearth, forehearth and molten iron ladle need to be dried.

6) When pouring, avoid flow interruption.

7) The inoculant should be fully preheated.

8) When pouring, it is necessary to ignite and bleed air.