Effects of Cooling Parameter and Cryogenic Treatment on Microstructure and Fracture Toughness of AISI D2 Tool Steel
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Effects of Cooling Parameter and Cryogenic Treatment on Microstructure and Fracture Toughness of AISI D2 Tool Steel Mauro Francisco Castro Moscoso, Fabiano Dornelles Ramos , Cleber Rodrigo de Lima Lessa, Pedro Henrique Costa Pereira Cunha, Juliano Cantarelli Toniolo, and Guilherme Vieira Braga Lemos Submitted: 7 May 2020 / Revised: 14 October 2020 / Accepted: 26 October 2020 The application of cryogenic treatments is gradually increasing in tool steels. In this sense, these heat treatments can modify the mechanical properties of high chromium alloy steels. However, the influence of the cooling parameter (during quenching) is often neglected. This investigation aims at evaluating the effects of cooling parameter and cryogenic treatment on microstructure and fracture toughness of AISI D2 tool steel. The cooling parameter (k) was defined as the cooling time from 800 to 500 °C divided by 100. During quenching, different cooling parameters (k1 = 2.8 and k2 = 1.8) were employed, and the samples were tempered three times or, besides, cryogenically treated by a single tempering. Later, the samples were evaluated through phase analyses and their proportions, sizes, and distribution of carbides by optical and scanning electronic microscopy, hardness measurements, x-ray diffraction, and fracture toughness tests. For the k2 cooling parameter followed by cryogenic treatment, the results presented an increase of 51% over the initial condition of secondary carbides. However, the higher hardness values were found in the k1 cooling parameter followed by cryogenic treatment. In the fracture toughness evaluation, a reduction of 8% in KIC was observed for samples with cryogenic cycles compared to the samples without it. Keywords
carbides, cooling parameter, cryogenic treatment, fracture toughness, heat treatment, tool steel
1. Introduction The high-carbon and chromium cold work, AISI D2 tool steel, has high wear and abrasion resistance. High alloy content may provide excellent hardenability and good dimensional stability (Ref 1). Also, this grade is an air quenched steel widely used for cold working, especially for cutting tools and dies production (Ref 2). Since this tool steel has greater alloying elements content, the martensite finish temperature in a TTT diagram might be, sometimes, dislocated to values below room temperature and one consequence is the presence of retained austenite. Therefore, cryogenic treatment is recommended to reduce the amount of retained austenite in high carbon steels
Mauro Francisco Castro Moscoso, Termo Ac¸o, Caxias do Sul, Brazil; and IFRS - Instituto de Educac¸a˜o, Cieˆncia e Tecnologia do Rio Grande do Sul-Campus Caxias do Sul, Caxias do Sul, RS, Brazil; Fabiano Dornelles Ramos and Guilherme Vieira Braga Lemos, IFRS - Instituto de Educac¸a˜o, Cieˆncia e Tecnologia do Rio Grande do Sul-Campus Caxias do Sul, Caxias do Sul, RS, Brazil; and UFRGS Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil; Cleber Rodrigo de Lima Lessa and Juliano Cantarelli To
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