Alternative Heat Treatments for Complex-Alloyed High-Cr Cast Iron Before Machining

Autor: K. Shimizu, O. Isayev, Yu. G. Chabak, V. G. Efremenko, V. V. Kudin, Kaiming Wu
Rok vydání: 2018
Předmět:
Zdroj: Metallurgical and Materials Transactions A. 49:3430-3440
ISSN: 1543-1940
1073-5623
Popis: Four heat treatment schedules were applied to 14.6 wt pct Cr-2.2 wt pct Mn-1 wt pct Ni cast iron to improve its machinability: (a) one-step continuous annealing [holding at 1123 K (950 °C), 2 hours, cooling at 20 to 150 K/h], (b) three-step isothermal annealing [1123 K (950 °C), 2 hours + 923 K (650 °C), 6 hours + 998 K (725 °C), 15 hours], (c) two-step isothermal annealing [923 K (650 °C), 6 hours + 998 K (725 °C), up to 25 hours], (d) quenching [1123 K (950 °C), 2 hours] and tempering [998 K (725 °C), up to 15 hours]. Heat treatments (a) and (b), which include high-temperature holding at 1123 K (950 °C), result in secondary carbide precipitation, and lead to a “martensite/austenite” or “martensite/austenite/pearlite” matrix and a bulk hardness of 56 to 62 HRC with poor machinability. Heat treatments (c) and (d) provide a matrix of “ferrite + granular carbides” with a bulk hardness lower than 40 HRC. Quenching and tempering result in the elimination of retained austenite to 11.6 vol pct. The kinetics of spheroidization and coagulation of eutectoid carbides and carbides as precipitated from martensite are presented and discussed. Drill testing showed that after quenching and tempering, cast iron has a superior machinability compared with other heat treatments.
Databáze: OpenAIRE
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