Optimization of annealing modes of cast tool made of R6M5L steel

Abstract

A simple configuration cast tool made by the technology of chill casting with intensive cooling during crystallization from R6M5L steel is characterized by a fine-grained structure, increased alloying of the solid solution and a hardness of 62-63 HRC; it does not require final machining. A tool of complex configuration due to the need for its mechanical processing by cutting is subjected to extended softening annealing. Recommendations for reducing the annealing time relate mainly to the rolling of tool steels. The efficiency of annealing of rapidly chilled R6M6L steel during crystallization by three technological modes is investigated: annealing at 880 ºС with continuous cooling; with isothermal exposure in the temperature range of pearlite transformation and the least stability of austenite; annealing after austenization with triple heating to 750 ºС and cooling to room temperature. Based on the research results, regression equations were obtained that describe changes in the hardness of cast rapidly cooled steel within 55–20 HRC depending on the technological annealing scheme, temperature and duration of heating, cooling rate of castings and allow choosing the optimal annealing mode of the cast tool in accordance with the requirements for its hardness and technological conditions of production.

Keywords

• thermal treatment
• annealing
• cast tool
• high-speed steel.