As a mechanical designer, in the selection of materials must understand the trend of industrial development, in accordance with national standards, combined with China's resources and production conditions, from the actual point of view of comprehensive consideration of material and its selection the most commonly used materials in mechanical manufacturing are steel and cast iron, followed by non-ferrous metal alloys.
Non-metallic materials such as plastics, rubber and so on, in mechanical manufacturing also has a unique use value. Cast iron and steel are iron carbon alloys, the difference between which is mainly the difference in carbon content. Iron carbon alloys with a carbon content of less than 2% are called steel and are called cast iron with a carbon content greater than 2%. Cast iron has proper melting and good liquid fluidity, so it can be cast into parts with complex shapes. In addition, its damping, wear resistance, cutting (refers to gray cast iron) are good and low cost, so it is widely used in mechanical manufacturing. Commonly used cast iron: gray cast iron, ductile iron, cast iron, alloy cast iron and so on. Among them, gray cast iron and ductile iron are brittle materials, can not be rolling and forging. In the above cast iron, gray cast iron is the most widely used, ductile iron is the second.
2, steel Compared with cast iron, steel has high strength, toughness and plasticity, and can improve its mechanical properties and processing properties by heat treatment method. The blanks of steel parts can be obtained by forging, stamping, welding or casting, so their application is very extensive. According to the use, steel can be divided into structural steel, tool steel and special steel. Structural steels are used to manufacture components of various mechanical parts and engineering structures; tool steels are mainly used in the manufacture of various cutting tools, molds and gauges; special steels (such as stainless steel, heat-resistant steel, acid-resistant steels, etc.) are used to manufacture parts that work in special environments. According to chemical composition, steel can be divided into carbon steel and alloy steel. The nature of carbon steel mainly depends on the carbon content, the higher the carbon content, the higher the strength of the steel, but the lower the plasticity.
In order to improve the performance of steel, some alloy elements have been specially added to the steel called alloy steel. 1) carbon structural steel such steel content of carbon is generally not more than 0.7%. Low carbon steel with a content of less than 0.25%, it has lower strength limit and yield limit, high plasticity, and good weldability, suitable for stamping, welding, commonly used to make screws, nuts, gaskets, shafts, valve guide rods and welding components.