| Abstrakt: |
The increase of toughness, 10 to 35 MPam1/2, with decreasing hardness,VH 950 to 500, is reported for sintered T6, T15 and T42 high-speed steels. This range of properties resulted from combinations of sintering temperatures (in N2-H2-CH4), HIPping and tempering treatments of steels processed from water-atomized powders. Toughness is related to the properties of the matrix, but more specifically to the retained austenite content, varying between 5% (HV10 ?950,Klc ? 10 MPam1/2) and 70% (HV10 ? 500,Klc ? 35 MPam1/2). Austenite retention is caused by the stabilizing affect of nitrogen (0.3 to 0.7%), picked up from the sintering atmosphere. Fractographic examination revealed that, although failure proceeded by complex modes that could be described mainly as quasi-cleavage, microplasticity was observed in the high austenite materials, as opposed to the flatter fracture surfaces, with much less plasticity apparent, for the lower retained austenite-containing materials. |
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