Cu, Nb, And Pre-deformation The Impact On The The Ulcb Steel ¦Å-cu Precipitates

The aging hardening response of a series of ultra-low bainitic steels containing copper have been investigated. The effect of various copper content, addition some alloy elements and pre-deformation(adding pre-deformation process between solution and aging treatment) on aging-kinetics behavior of precipitation hardening, the precipitates distribution and microstructure evolution during aging was discussed by means of hardness measurement, light microscope and TEM .The results indicate: 1. Three kinds of precipitatesε-Cu, Nb,Ti(C,N), Fe,Mo carbide during aging response have been observed, they lead to the aging hardening. The second hardness peak appearing after a long periods aging was attributed to the precipitation of Fe,Mo carbide. At the early stage of aging there are two hardness peaks caused byε-Cu, Nb,Ti(C,N) respectively in steel with 1.52% copper but there is only one hardness peak in steels with 0.98% copper. 2. The aging kinetics of Cu-added steels is strongly dependent on the aging temperature and the copper content. Increasing the aging temperature increases the aging kinetics and decreases the maximum hardness. When the copper content of steels increases the hardening effect increases and the nucleation and growing ofε-Cu precipitate was accelerated. 3. With the increase of copper content of steel the Nb carbonitride precipitation in bainite accelerated. When the content of copper is 1.52% the Nb carbonitride precipitation was promoted obviously but when the content of copper is 0.98% there is little influence on the Nb carbonitride precipitation. 4. ε-Cu nucleated at the boundary of bainite lath retards the recovery of bainite structure during aging and suppresses the softening of the matrix. 5. The steels which have pre-deformation process, the time of appearing hardness peak can be shorten, and the height of hardness peak is also heighten. When the temperature is low, such as 450℃, the effect of pre-deformation is more evidence. After aging, theε-Cu precipitation is increased and is more equality.