Abstract
The study was carried out to get correlation between deepdrawability and anisotropy of mild steel sheets for deep drawing.
Armco, Al-killed and rimmed steel sheets were used for samples. Deep-drawability of sheets was measured by Erichsen test and tension test, and anisotropic degree was estimated by observation of the ear-height which was formed in cupped specimen, types of magnetic torque curve and its harmonic coefficient, and directionality of strain in tension test.
The results obtained were as follows:
i) Generally, Armco sheet had the best deep-drawability and rimmed sheet had the worst, whereas anisotropic, degree of Armco sheet was the highest and that of rimmed sheet was in the least.
ii) On cupping all specimens as received state, 4 ears were formed. Two of them form in the rolling direction and others form in cross rolling direction.
Magnetic torque curves of them showed that preferred crystallographic orientation was (100)-[011].
When test specimens were strained up to maximum load in simple tension test, width train (the percentage contruction in the width dimension) was larger than thickness strain, and the ratio of width strain to thickness strain of specimen which is taken in the parallel to rolling direction was larger than that of specimen which was taken in 45° to rolling direction.
iii) The changes of anisotropies did not occur when specimens were annealed at 650°C or 820 °C for 20min, but they almost disappeared when specimens were annealed at 950°C above A3 point for 20min.
iv) Erichsen values of Armco, Al-killed and rimmed sheets as received state were 11.2, 10.2 and 9.3 respectively, and elongation percentages were 46.6, 41.4 and 34.5 respectively.
In Armco and Al-killed sheets which were annealed at 950°C for 20min, Erichsen value dropped 6-8%, elongation percentage dropped 6-7%, and tensile strength rose 8-10% comparing with them as received state.
Nevertheless these phenomena did not appear in rimmed sheets. It seemed that these were related to the experimental results that the AlN in Al-killed steels (both Armco and Al-killed sheets) was increased as they were annealed at 950°C. In Al-killed steel, such heat treatment that eliminated anisotoropy would cause precipitation of AIN and deteriorate deep-drawability
