The grades in this group are the only important alloy group containing between 11 percent and 17 percent chromium. These products show some similarities with ferritic groups. However, the 0.10 – 0.65% carbon it contains is known to radically change the reaction of the group. Fairly high carbon can become harder with heat treatment. Like many high carbon steels, 420 quality stainless steel can be further hardened with certain heat treatments. This stainless steel, which can be increased to 50 Rockwell hardness by heat treatment, has a good softness when annealed. The best corrosion resistance is achieved by cleaning and hardening or polishing the surface. Martensitic stainless steels, which are the most suitable group for high hardness, have very poor weldability and require hardening by some annealing process after welding.