A little more information about what you are making might help.
Low carbon steel with minimal alloy elements is referred to as mild steel. It refers to the common grades used for structural and manufacturing purposes when no special properties are needed. In the US and Canada, this is sold as hot rolled structural shapes, plate, and bar, often to the A36 spec, which is loose on the alloy but specific about mechanical properties such as tensile strength. Hot roll has the black scale coating. It comes of with a wire wheel or a grinder, and machines off.
There is also cold rolled, such as 1010 and 1018, where the designation refers to a particular alloy (in these cases, iron with 0.10% and iron with 0.18% carbon by mass, respectively, and very low limits on all other elements). This is seen as rounds and square/rectangular bars. It is usually coated with an oil film left over from the rolling process, and the film helps prevent the stock from rusting. I cleans off with solvent.
These steels machine ok and, in the US, are less expensive than any other metal. Cast iron stock is not cheap and not real available.
AVOID any steel material listed as free machining or ‘easy to machine’ if you are concerned about toxic materials. These will contain either lead or high sulfur, or both, to improve machinability. Second hand materials-- old shaft stock, for example-- is often leaded. In the US, the leaded grades often, but don’t always, have an ‘L’ in the designation, such as 12L15 (a common free machining steel, with a dash of manganese for strength. Pure joy in the lathe, when it can be used)
Clean steel should not smoke. Coatings on it will.
At 300C, many aluminum grades will have degraded properties. Some ‘red’ and ‘yellow’ metals (bronzes, brasses, other copper based alloys) may have better properties in that temp range, and many machine well, but there are toxicity issues both in food contact and at elevated temperature (some contain lead and copper oxides are real bad news, which is why copper cookware MUST be coated with tin, and recoated if the coating is damaged)