Patent EP-0045984-B1 (EP)
IPC: C22F1/10
Filed: 1981-06-16
Granted: 1984-03-14
Abstract: 1. Process for manufacturing a workpiece from a creep-resistant, precipitation-hardenable austenitic alloy having a high nickel content and containing a metal oxide as the hardening idspersoid, this process being in accordance with the methods employed in powder metallurgy and in which a metal powder is mixed with a metal oxide powder, is mechanically alloyed, is encased in a metal container, and is densified, by hot-compaction, to 100% of the theoretical density, in a manner such that an easily deformable intermediate material is produced, which has a very fine grain size and is suitable for further processing, terminating in an annealing treatment for developing a coarse grain size, characterised in that the abovementioned intermediate material is converted to the finished workpiece by means of a purpose-designed working operation which embodies the final shaping step, the deformation rate and the degree of deformation being determined in accordance with the intermediate material, which can exhibit deformation which is insufficient, optimum, or excessive, in a manner such that the logarithm of the temperature-compensated deformation rate, expressed as log (.~epsilon DNi--1 m**2 ), where ._epsilon = d[¦In (Ao /Af )¦]/dt, and Ao and Af respectively denote the cross-sectional areas of the workpiece before and after the working operation, while DNi denotes the diffusion coefficient of nickel, which is a function of temperature, lies between the values 16.5 and 20 in case a) - insufficient deformation of the intermediate material, lies between the values 10 and 22 in case b) - optimum deformation of the intermediate material in the range of low degrees of deformation for the final-shaping step, described by 0 =< epsilon < 0.3, where epsilon denotes ¦In (Ao /Af )¦ and lies, in the range of comparatively high degrees of deformation for the final-shaping step, described by epsilon > 1.0, between the values 15.5 and 20, lies between the values 14 and 18 in case c) - excessive deformation of the intermediate material in the range of low degrees of deformation for the final-shaping step, described by 0.1 < ¦epsilon¦ < 0.2, and lies, in the range of comparatively high degrees of deformation for the final-shaping step, described by ¦epsilon¦ > 0.8, between 16 and 20, and in that the degree of deformation for the final-shaping step, described by epsilon, reaches a value of not less than 0.5 in case a) - insufficient deformation of the intermediate material, is as small as desired, and can thus also be nil, in case b) - optimum deformation of the intermediate material, increases linearly with the deformation rate, but reaches a value of not less than 0.1, in case c) - excessive deformation of the intermediate material in the range of low degrees of deformation for the final-shaping step, described by 0.1 < ¦epsilon¦ < 0.6, the above being subject to the restriction that in case a), the values must lie within the shaded region in Figure 5, in case b), the values must lie within the shaded region in Figure 6, and in case c), the values must lie within the shaded region in Figure 7.