COMPARATIVE ANALYSIS AND EFFICIENCY ASSESSMENT OF COMPLEX IMPACT ON QUALITY OF HEAVY CASE CASTINGS OF MEDIUM-ALLOYED HIGH-STRENGTH STEEL

Methods of increase in firmness and uniformity of the structure of cast blanks of responsible appointment from high-strength alloyed steels are briefly considered. It is shown that only alloying not always provides necessary mechanical and office properties of the responsible products received by casting. It is noted that the most widespread mode of casting in sandy forms doesn't allow to effect on hardening and consequently on the structure and properties of cast metal and characteristic hardly removable defects, arising at the same time. The critical technological parameters of casting are specified to thin-walled forms: thickness of a facing layer and the metal equipment, metal supply mode, technological parameters of the filled-in metal, mode of creation of the directed casting hardening, and also quantity and material of microrefrigerators. The researched results of influence of ladle impact on the hardening metal of heavy case castings of special steel are given. Quality of metal of the castings received by the following options is analyzed: suspension priming of liquid metal in a metalshell form with compulsory cooling (complex influence), in a metalshell form with compulsory cooling (external influence), in a volume sandy form. Probe of a macro structure showed that the largest grain turns out in a volume sandy form; in the central area of casting the shrinkable porosity is observed. Increase in speed of crystallization and hardening of casting leads to structure crushing and increase in firmness of metal along the height and section of casting. Conditions of hardening influence also on morphology of nonmetallic inclusions and on the nature of dendrite structure. Noted advantages are especially noticeable at complex impact on the hardening casting. At the same time there is sharper drop of overheat temperature at the input of microrefrigerators and compulsory cooling of a thin-walled form and increase in the centers of crystallization and in effect of suspension supply at closing stage of hardening. Mechanical properties of the steel castings, received with complex influence, especially impact strength and plasticity, are much higher than at the casting received in a volume sandy form. Increase in mechanical properties is explained by the accelerated heat sink, structure crushing and increase in firmness of casting metal and more favorable distribution of nonmetallic inclusions. Not less important advantages of the developed technology are increase in metal yield through the metal consumption, increase in surface smoothness of casting and a possibility of reference of this mode in the low-waste and resource-saving category.

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