High speed steel is a sub category of tool steel that is hugely used as cutting tool material. These have replaced the conventional high carbon steel that was also used as the cutting tool. High speed steel contains tool steel alloys that provide high resistance against abrasion and wears. It also exhibits excellent robustness and strong resistance against softening at exceptionally high temperatures because of the heat treatment and alloys used in its composition. Mild steel, on the other hand, can be categorized as ferrous metal and is high in iron and carbon. Mild steel comes in a quite affordable pricing and can be used for regular engineering applications. Mild steel that is low in carbon has outstanding magnetic properties due to the high carbon in its composition. Therefore, it is alternatively also known as ferromagnetic.
Composition: High speed steel has multiple alloys in it. In high alloy content, the percentage of tungsten and molybdenum is specifically high. Chromium, cobalt, and vanadium are present in a lower percentage. High speed steel has a general carbon content of 0.65%. However, the carbon content might actually vary between 0.8% and 1.5%. The amount of any alloy present in high speed steel determines the field where it will be perfect for use. Mild steel has a carbon content between 0.16% and 0.29%.
Properties: High speed steel exhibits Rockwell hardness of 64 HRC at normal temperatures. This steel is popular and has high market demand due to its outstanding robustness, endurance against wears, abrasions, etc. even after regularly using it to cut metals. The heat treatment procedure used for high speed steel generates a large quantity of complex metallic carbides such as molybdenum, vanadium or tungsten which are all suspended within a steel substrate. This renders the hardness and wear resistance properties in the steel. Mild steel does not exhibit high resistance against corrosion in its regular untreated form. However, mild steel can also be made corrosion resistant by applying surface protection. Red oxides, primers, metal paints, etc. which are easily available in the market give impressive protection against both corrosion and dust. Mild steel has quite a high melting point between 1450 degrees Celsius and 1520 degrees Celsius. It shows excellent ductility. However, mild steel is not suitable for hardening. Even if the steel is hardened, through chemical reactions, the surface layer is hardened making it impossible to work with.
Application: High speed steel is ideal for uses in places where the hardness of the steel is appreciated. Through multiple treatments, the brittleness of the steel can also be reduced. Each grade of the steel shows different levels of hot hardness and robustness, with the original properties being intact. Saw blades, drills, taps, broaches, milling cutters, tool bits etc. are common areas where high speed steel is needed. High speed steel also retains the sharpness for a longer period compared to other carbon steel. This makes it more reliable for long term use. Dies, punches, and products in progressive stamping can also be made from high speed steel. Blades used in hand planes, chisels, pocket and kitchen knives, files, etc. also use high speed steel due to hardness and wear resistance properties. Mild steel has many applications – items, decoration, furniture, automobile, structural steel, signs, fencing, nails etc.
These reflects that high speed steel and mild steel vary in a lot of spheres but both have wide range of usage in several industries.