Doram As has been said, you’re looking at the mg/l figures for calcium and magnesium, together with the mg/l figures for alkalinity (sometimes derived from bicarbonate expressed as CaCO3 and sometimes helpfully expressed as simply alkalinity or bicarbonate alkalinity). These figures together with the temperature determine scaling potential. The spreadsheet in my signature allows you to specify either hardness an alkalinity if known, or calcium, magnesium, and bicarbonate concentration in mg/l along with the temp of your boilers to see if the water will form scale or not.
Re corrosion: it’s not a simple matter. In terms of water purity there’s not too much to worry about, especially with good alkalinity. There are other issues like chloride and sulfate presence (depending on boiler material, with an increasing corrosion risk if scale will also form).