| Nowadays, about 98 percent engineering magnesium-alloy components demand in the world are from die casting industry, rigorous requirements for sevice life and security of the equipment components in the high temperature and high pressure environment are brought forward due to the continuity of die casting for magnesium alloys, for example, the chamber is always employed in the magnesium alloys melting at 630-700℃, which is also subject to 30-50 MPa pressure impact, high abrasion and corruption from magnesium alloys melting. So far,high quality chambers are almost dependent on importation at expensive price,which has severely restricted the progress of the domestic complete magnesium-alloy die casting set of equipment and increases the cost of the magnesium-alloy castings. Therefore, it is very significant to work out eligible material and its foundry technology in the engineering field.Besides higher hardness, the heat conductivity of body-centered cubic ferritic heat resisting steels is higher than that of face-centered cubic austenitic heat resisting steels, while the former thermal expansion coefficient is lower than that of the latter,so better heat fatigue and wear-resistant properties are showed in ferritic refractory steels, for which the rigorous requirements for the material of chambers are better satisfied. The high cobalt and high tungsten (9%-12%)Cr ferritic heat resisting and corrosion resisting steel without nickel introduced in this paper is such kind of novel material used as hot worked components in the die casting industry, the martensite after quench and temper at high temperature showes high obdurability and creep strength,favourable high temperature oxidation resistant property, abradability and corrosion resistance from magnesium alloys melting. The supercriterion of Fe impurity and Ni impurity dissolution in magnesium ingot are both prevented due to application of this steel without Ni,so it is the best choice for chambers of magnesium-alloy hot die-casting machines both at home and abroad.The research in this paper is to exploit high cobalt and high tungsten (9%-12%)Cr ferritic heat resisting and corrosion resisting cast steels without nickel on the basis of (9%-12%)Cr ferritic heat resisting and corrosion resisting alloy steel. The modified 9-12%Cr cast steels in this paper is designed to apply between 630 and 700℃in a long time. The service performance arrives at equivalent level compared with the inward material. Namely, the out-of-service time is more than 2 years and the knockout times exceed100,000.Therefore, the general situation in the ferritic heat resisting steels is retrospected first, then the chemical component are designed according to the calculation of crystal properties based on molecule orbit using discrete Variational Xa,final heat treatment regime is established through experiments, which could be used for reference in the similar material exploitation, its heat treatment and its market.The vacuum melting technology is adopted for the refractory steel through component optimization,first the steel is molten in vacuum induction furnace and then remelted in the electroslag remelting furnace, by which the impurity qutient is improved and the component segregation is avoided effectively. After that the chamber is quenched between 1060 and 1120℃in the air and tempered between 650 and 720℃. The quenching cracks are prevented because of the technology according the cracks prevention mechanism. The research results show that the steel with martensite structure has excellent comprehensive mechanical properties. |
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