1. The composition of the carburizer should be distinguished by the nitrogen content. What level of nitrogen content you choose is very important!!! We now add more than 50-60% scrap steel into the induction furnace to melt synthetic cast iron. The greater the amount of scrap steel, the greater the nitrogen content of molten iron. Because the harmful elements such as titanium, lead and antimony in the molten iron of synthetic cast iron are very low, low nitrogen carburizers should be used. If the nitrogen content of the carburizer is high, the nitrogen porosity will appear in the casting due to the synthetic nitrogen content.
In my casting work in 2004-09, I found that high-end customers in the United States and Japan need to test the content of nitrogen, titanium, lead, arsenic and other harmful elements in cast iron for the acceptance of ordinary gray iron. The content of nitrogen is generally expected to be 80-120ppm. If you use high nitrogen carburizing agent (generally belonging to low-end carburizing agent products), since the content of titanium in molten iron is very low, it is impossible to use TI to consume a large amount of nitrogen, which makes the casting easy to have nitrogen pores, crack nitrogen pores or related defects due to the high nitrogen content. This phenomenon has occurred in the unit where I worked before.
Many experts have also talked about the great losses brought to them by the poor quality of carburizing agent in their published articles. They especially emphasize that the key to smelting synthetic cast iron is to use calcined petroleum coke with good quality and low nitrogen content. Many foundry friends think that the high sulfur content of the carburizer will not affect the quality of ordinary gray iron (inoculated cast iron), but the high sulfur content of the carburizer will be accompanied by high nitrogen, which will bring quality problems.