The Effect of INGOT Homogenization Practice on the Properties of Wrought Alloy 718 and Structure

Abstract

A controlled laboratory experiment was conducted to explore the effects of ingot homogenization practice on the properties of forged alloy 718. Five, 101 mm diameter alloy 718 VIM ingots were static cast, homogenized at various temperatures and hot forged to 25 mm squares. These forgings were evaluated by microstructural analysis, differential thermal analysis, room temperature tensile testing and 650°C stress rupture testing. Data from this investigation are supplemented by over 200 observations collected on 25 mm to 153 mm diameter hot rolled rounds during a time period when the VIM-VAR ingot homogenization practice was altered. It was observed that the homogenization practice can have a profound effect on the macrostructure and microstructure of the as-cast and wrought products. Use of an improved step homogenization technique significantly reduces the number of rejections of wrought alloy 718 rounds due to banding, dendritic segregation or inadequate grain size control. The effect of the homogenization practice change on the room temperature tensile, 650°C temperature tensile and 650°C stress rupture results is relatively minor.