REASONS FOR CRACKING OF DIE-FORGED CuZn34Mn3Al2FeNi BRASS BLANKS
The structural state of annular work pieces made of brass CuZn34Mn3Al2FeNi after hot forming at temperatures of 700 and 780 °C is studied. Electron microprobe analysis of the material of rings shows the absence of any harmful impurities, low melting eutectics, silicides and non-metallic inclusions on the bʹ-grain interfaces. Irregularity of the dynamic recrystallization process in the cross section of the rings has been revealed; namely, there are two zones differing in the amount of deformation. One area with minimal deformation and excessively large grain, the second - with the maximum deformation and small grain resulting from dynamic recrystallization. Determined that heating for stamping to 780 Cresults togrowth of βʹ-grains up to 0.3 mmin the area with minimal deformation, the grains boundaries are reinforced (on the borders - 300 HV 0.2, and in the center of the grain - 170 HV 0.2), which facilitates the emergence and rapid growth of cracks under the action of internal residual stresses formed during cooling of blanks. Lowering the temperature of heating for forging to 700 C reduces the size of the maximum βʹ-grains up to 0.15 mm, thus not detected hardening of their borders that helps to preserve the integrity of the rings after cooling.