Now everyone is familiar with the importance of pre-treatment in induction furnace melting of gray iron and ductile iron, improving the metallurgical quality of molten iron, and using a large amount of scrap steel as synthetic cast iron. The use of carburetors, silicon carbide, and high barium silicon iron pre-treatment agents is gradually becoming more widespread. For instant carburetors, based on recent information and previous practical experience, as well as previous published articles, I feel that there are several points to pay attention to during smelting:
1. The composition of instant carburizing agents should be distinguished by the amount of nitrogen content. When using them, it is important to choose the appropriate level of nitrogen content!!! We now use an induction furnace to add over 60% of scrap steel and melt it into cast iron. Due to the low content of harmful elements such as titanium, low-carbon carburetors should be used. I have introduced in previous posts that high-end customers in the United States and Japan need to test the content of harmful elements such as nitrogen, titanium, lead, arsenic, etc. in cast iron for acceptance of ordinary gray iron. In terms of mechanical properties, it is not only necessary to measure tensile strength, hardness, but also the yield strength of gray iron. For nitrogen content, it is generally recommended to be between 80-120 PPM. At this time, if you use a high nitrogen carburizing agent (usually belonging to low-end carburizing agent products), Due to the low content of titanium in molten iron, it is impossible to consume a large amount of nitrogen, making castings prone to a large number of pores, gas shrinkage, or related defects due to high nitrogen content. This phenomenon has already occurred in units where I have worked before, and many experts have also discussed in their published articles the significant losses caused by poor quality of carburetors. (Who exactly is it? I can't remember clearly, it seems that an expert surnamed Jin wrote about it in a casting magazine.). Many casting friends believe that the high sulfur content of carburetors does not affect the quality of ordinary gray iron (inoculated cast iron), but the high sulfur content of carburetors, accompanied by high nitrogen content, can cause quality problems.
2. When I worked at Taiwan's Shouwu (the factory of Taiwan Emperor House in Qingdao) in 1999, there were many carburetors in its warehouse, and the labels only labeled high nitrogen, medium nitrogen, and low nitrogen. However, I didn't know the reason for this, and now I have experienced more and gradually realized this point. Of course, many things are still gradually adapting in China, especially the high nitrogen carburetor, which is also widely used, such as petroleum coke and clean coal with poor graphitization. What kind of low-end products are used for smelting cast iron? Is it high titanium cast iron used? We still need to gradually gain experience in the future. Adding carburetors with poor graphitization to molten iron results in low and slow absorption rate; Secondly, there are many residues; Thirdly, other harmful elements affect the quality of molten iron. We hope everyone pays attention!
3. The method of adding instant carburetor has been discussed by many friends in the forum. It can be added in the early, middle, and later stages of electric furnace melting, as well as at the same time as adding scrap steel. This involves adding in the later stages of melting, which plays a role in pre-treatment and increasing graphite core. At this time, it is best not to add too much high-end carburetor. Remember at the Yangzhou Iron Casting Melting Seminar in April 2010, Ms. Song Kefei from Emperor Shougu mentioned that it should not exceed 0.2% to avoid coarse graphite.
