Manganese is an alloying element that improves the strength of ferrite and the hardenability of steels. It could be a valid substitute for expensive and toxic elements (as Mo and Ni) in sintered steels, increasing mechanical properties. The hardenability of four low alloy Mn steels was studied to establish the influence of manganese on the heat treatments. The effect of Mn on steel hardenability is well established. The multiplying hardenability factors in the range 0.05-1% Mn are known, and so the hardenability of the alloy to be investigated can be predicted. The Grossmann approach was adopted, which uses cylinders with different diameters to induce different gradients of cooling rate in the cross section. Quenching experiments were carried out in the vacuum furnace, recording the actual cooling rate (on the external surface and in the central axis). The maximum cooling rate attainable is 10 K/s. Hardness, microhardness and microstructure profiles were determined, and correlated to cooling rate for the different alloying elements and C contents. The correlation of microstructure and microhardness to the actual cooling rate makes the results independent on the process parameters and applicable to each industrial condition, once the actual cooling rate in the parts is known.