Crystal Orientation and Element Distribution of Spangle on Hot-dip Galvanizing Steel

Abstract

Spangles formed at hot-dip galvanized steel were classified and the distribution of Pb and Al, which were impurity and additional element respectively in molten zinc bath, on the spangle surface was investigated. The hot-dip galvanized Al-killed steel was produced with gas reduction type hot dipping testing aparatus in which steel sheet was cleaned by heating in reducing atmosphere and dipped into molten zinc bath which contained 0.25 wt%Pb and 0.17 wt%Al. X-ray Laue method was used for determination of crystal orientation and EPMA was used for the measurement of distribution of Pb and Al at the spangles.
The main results of the study are follows:
(1) The spangles are classified from the point of view of the crystal orientation and the appearance into the seven types as follows,
Fern I, Fern II, Mirror, Frost, Half fern, Feather, Triangle.
(2) The direction of the straight boundary of the spangles coincide with the projected direction of preferred crystal growth orientation (<1010>) on the spangle surface.
(3) Spangles are classified into α type and β type from the point of view of the inclination of c-axis (<0001>). The c-axis of α type spangle is inclined to the straight boundary of the spangles and the c-axis of β type spangle is inclined to the reverse direction.
(4) The amounts of Pb and Al at the spangle surface vary with the types of the spangle.
(5) The spangle with the larger amounts of Pb and Al has less brilliance.