The best heat treatment for achieving the hardest results in mild steel, such as 1018, is challenging due to its low carbon content, which limits its ability to be through-hardened. Quenching in water after heating to a medium red temperature can increase surface hardness, but case-hardening may be necessary for better results. The process of tempering is also important to relieve stresses and enhance toughness, which can affect hardness measurements like the Brinell test. Techniques used in traditional sword-making, such as applying clay to control cooling rates, illustrate the balance between hardness and flexibility. Ultimately, achieving the hardest result in laboratory tests requires careful consideration of the steel's chemistry and the heat treatment process.