Research Of High-grade Plastic Mold Steel P80R Smelting Process

The High-grade plastic mold steel P80R (10Ni3MnCuAl) is produced by Dalian Special Steel Co., Ltd. of Dongbei Special Steel Group, which is mainly used in automobiles, household appliances, cameras, phones, computers and other plastic products mold. The outstanding feature of the steel is soft after solution treatment (i.e. quenching).The steel can be treated with cold processing and aging process after being made into mold, which can ensure keeping its performance and reducing heat deformation as well. This steel has good comprehensive mechanical properties, high hardenability, good polishing properties, nitriding properties, electrical discharge machining performance, welding performance and patterns etched performance, etc. It is suitable for manufacturing large plastic mold, precision plastic mold, high mirror plastic mold, and can also be used in the manufacture of low melting point alloy for die casting mold.In the past, the development of high-grade plastic mold steel is slow in our country, and it has a large number of imports. In last decade a number of domestic steel companies recognize the development prospects of this steel, they introduce the development of the steel energetically. However due to the limited production capacity and technology, the production scale and product quality were unable to achieve or exceed the foreign products, and the steel P80R is still conditioned by imports. Our company has designed and implemented the production process of electroslag steel and electric steel in Fushun and Dalian successively in2004, the product quality has been recognized by the market, but the disadvantages are also emerging. Electroslag smelting process can ensure the quality of products, but the production cost is high and the smelting period is long that timely delivery rate can’t be guaranteed. On the other hand, the cost of electric steel is relatively low, but it can’t form a large-scale production owing to the poor process stability and low yield, what’s more, inclusion problems occurred sometimes and made great loss for the companies and customers.It is researched the low magnification inclusion problems of P80R steel produced by our company in this paper. After a series experimental and theoretical analysis, the reasons that cause such quality problems are mainly the large Al2O3inclusions produced in the electric furnace smelting and refining process. Three important factors are identified to improve the process that soft blowing time required more than15minutes, pouring temperature up to1580℃-1590℃, with a casting speed rapidly first and then slow down, and strict personnel operating and production preparation. The Al2O3inclusions can be better controlled by improved smelting process, the inspection pass rate had improved more than10%compared to the previous process, the steel quality had been significantly improved and the improved technology got satisfactory results in the actual production.