I would be very careful of heating that. Don't know why so many people on here assume things are cast steel. foundries hate casting steel and avoid it if possible, which is why they usually go for malleable cast or SG cast iron. In this case it may be cast steel as that application requires high strength but if it isn't and you heat it you will ruin it. Turn the whole thing down to 40mm up to the flange and fit a 45mm OD sleeve.