Impact Properties of Vacuum Heat Treated AISI D2 and 8 % Cr Cold Work Tool Steels

    Volume 8, Issue 9 (October 2011)

    ISSN: 1546-962X

    CODEN: JAIOAD

    Published Online: 1 August 2011

    Page Count: 12


    Arieta, Francisco
    Schmolz-Bickenbach do Brasil Ltda,

    Netto, Eliana B. M.

    Reguly, Afonso
    Universidade Federal do Rio Grande do Sul,

    Pannes, W. K.

    Beutler, Uwe

    van Soest, Frank

    Ernst, Claudia

    (Received 21 September 2010; accepted 30 June 2011)

    Abstract

    The impact properties of the traditional 12 % Cr AISI D2 steel and a family of new generation 8 % Cr cold work tool steels (average chemical composition fulfilling the following ranges: C = 1.00 ± 0.20; Cr = 8.00 ± 0.50; Mo = 1.75 ± 0.75; V = 1.10 ± 0.70; Nb = 0.50 ± 0.45; Si = 0.95 ± 0.10; Mn ≤ 0.50; P≤0.03; S ≤ 0.015) have been investigated. All steels have been vacuum heat treated simultaneously after austenitization at 1030°C, 1060°C, and 1120°C, followed by a cryogenic treatment and triple tempers at 520°C of 2 h each. The results showed for all steels that the higher the austenitizing temperature the higher the hardness and the lower the impact properties. For the same impact value, the 8 % Cr steels presented a 3–4 Hardness Rockwell C (HRC) points higher than the AISI D2 steel. The average impact values of the 8 % Cr steels were 33 %–45 % superior to the 12 % Cr steels, but only after austenitizing at 1030°C and 1060°C. At 1120°C, the impact values dropped dramatically for both 12 % Cr and 8 % Cr steels due to the higher hardness and grain growth differences between the investigated steels. The surfaces of the fractured impact tested samples were investigated via scanning electron microscopy + energy dispersive spectroscopy techniques. The fractographic analysis showed that at 1030°C the much coarser and higher volume fraction of primary chromium carbides found in the AISI D2 than in the 8 % Cr have contributed to its lower toughness. However, as the austenitizing temperature increased to 1060°C, and in particular at 1120°C, significant grain growth, higher hardness, and consequently, high strength of the matrix, took place and played the more important roles in dropping the toughness as shown by quasi-cleavage brittle fracture appearance. Austenitizing at 1060°C and tempering at 520°C showed the best compromise for toughness and hardness. Increasing the tempering temperature to 570°C and, in particular, to 620°C, remarkably increased the toughness of the 8 % Cr steels, when the % C is kept below 1 %. For the D2 and % C > 1.15 % the increase is negligible.


    Paper ID: JAI103395

    DOI: 10.1520/JAI103395

    ASTM International is a member of CrossRef.

    Author
    Title Impact Properties of Vacuum Heat Treated AISI D2 and 8 % Cr Cold Work Tool Steels
    Symposium 18th IFHTSE Congress, 2010-07-26
    Committee A01