GB1412637A - Method for producing ultra fine-grained microstructure in ferrous alloys - Google Patents

Abstract

1412637 Heat treating steel USS ENGINEERS & CONSULTANTS Inc 7 Sept 1972 [21 Sept 1971] 41637/72 HeadingC7A [Also in Division B3] A bainitic or martensitic structure is worked sufficiently to diminish the nucleating effect of grain boundaries, and is then annealed at a temperature between those of "austenite start" and "austenite finish" for a time sufficient to effect growth of equiaxed ultra fine austenite crystals, followed by cooling. In a preferred form the material is initially fully austenitized and then cooled to transform it to martensite or bainite prior to treatment as above. Preferably the annealing is carried out within a range of temperature extending for 150‹C from the 'As' temperature, while the deformation is such as to produce an increase of internal energy equivalent to that achieved by a 35% reduction in thickness of a ¢ inch plate. The composition may be such that the resultant structure after annealing remains austenitic, or alternatively that it transforms to pearlite bainite or martempered. In the latter case the cooling may be interrupted to produce a martensipered structure, or the martensitic structure may be tempered below As. Suitable compositions contain up to 25% Ni, up to 15% Mn, up to 1.2% C, up to 0.5% N, and balance Fe, with 15-21% Ni together with 0.009-0.053% C, and 5.7% Mn with 0.1% C, being particularly exemplified.