What material to use for geared shaft

[Pete O]

I've discovered that there is a shaft missing from the drive system on my new (old) milling machine, looks like there has been a part seize on the shaft due to neglect of lubrication in a small gearbox, which has meant that the seized part of the shaft has been cut and the remainder removed. Looking at the system that the shaft is part of and the exploded diagrams, it shouldn't be difficult to make a new shaft but I'm wondering what material I should use. I'd like to provide some photos but as it is difficult to photograph something that is missing, I'll try to describe the shaft and it's function as best I can.
Over most of it's length it is around 3/4" in diameter, approx 18" long, with a few features machined into it. It is driven by a pinned drive dog at one end (this is a 5/16 brass shear pin that provides a weak link for protection of the drive train), then passes through one small gearbox (the Y and Z axis drive gearbox) where it runs in a bronze bush at either end and has one small spur gear that will be woodruff keyed onto the shaft, with an external circlip that holds that gear in position at the far end of the gearbox. Where the shaft exits that first gearbox, it will have a flange of approx 1.5", which runs in thrust against the bronze bush to prevent the shaft moving back toward the drive end. The remainder of the shaft is a constant diameter with a long keyway, this part of the shaft runs through a second gearbox with a bearing at either end, inside this second gearbox the shaft drives (via the long keyway) a worm gear for the X-axis drive. This worm gear needs to be able to slide along the shaft, with the long keyway, whilst being driven- the gearbox moves in Y with the table, sliding along the shaft whilst receiving drive for the table's X movement.
So a summary of the shaft; firstly a cross-pin hole to drive it, then running in a  bronze bush, a circlip groove, a woodruff keyway driving a gear, a second bronze bush, a flange, then a long keyed section driving a sliding worm gear.
I'm hoping for some advice on the best choice of material for this shaft, and whether it should be case hardened or some other process once it is made. The whole shaft will need to be machined from stock bar with a diameter at least equal to that of the flange (approx 1.5"), but should be a fairly straightforward machining job. I expect the woodruff keyway and the other long keyway will be the first tasks for the mill itself, will be relying on manual feed in all axes until i can get this part made and installed.