Hot dip aluminizing of 9Cr-1Mo steels and their heat treatment

Abstract

Coupons of 9Cr-1Mo steels of type SA 387 Grade 9 class 2 were hot dip aluminized using Al bath at a temperature of 700 °C for 30 seconds. The samples were further heat treated at 750 °C for durations of 1, 3 and 5 hours, respectively. The samples were characterized using X-ray diffractometry, scanning electron microscopy and energy dispersive spectroscopy. The investigation showed that as coated samples contain an aluminum top coat, a reaction layer and substrate material. Within the reaction layer, two distinct regions corresponding to Fe<inf>2</inf>Al<inf>5</inf> and Fe<inf>4</inf>Al<inf>13</inf> were identified. Chromium up to 2 at% was observed. After heat treatment Al coat was not existing. Two distinct layers, corresponding to a thick Fe<inf>2</inf>Al<inf>5</inf> and a thin FeAl were observed at shorter heat treatment duration. Under longer heat treatment durations, multiple phases, namely, Fe<inf>2</inf>Al<inf>5</inf>, FeAl, Fe<inf>3</inf>Al and solid solution of Al in Fe were observed. © (2015) Trans Tech Publications, Switzerland.