In order to improve the performance of Gray Iron Castings, often take the following measures: select a reasonable chemical composition; change the charge composition, overheating treatment of iron liquid; breeding treatment; trace or low alloying. What measures are taken depends on the required performance and production conditions, often taking two or more measures at the same time.
Gray alloy iron alloy elements can be divided into four categories, namely, graphitized elements, cementite stabilizing elements, pearlite stabilizing elements and refined pearlite elements.
Cast iron solidification process, carbon, silicon, aluminum, sulfur, copper and nickel and other elements have to promote the role of graphite formation, can be considered a graphitizing element. However, the effectiveness of each element is very different, for example, the role of copper is about 20% of silicon. Nickel and copper have a dual role: eutectic transition to promote the graphitization; eutectoid transformation but inhibit the graphitization, help to form more fine pearlite, it can also be regarded as pearlite stabilizing elements.
Titanium is also very complex. In general, titanium is a very strong carbide forming element, but when its content is very small (such as <0.08%), its fine compounds can be used as the core of graphite, to promote the role of graphitization.
Tin, antimony, manganese, molybdenum, chromium, vanadium and niobium can hinder the precipitation and growth of graphite, and enhance the tendency to form cementite, are cementitious elements. Among them, the role of molybdenum and its added amount. Molybdenum molybdenum content, <0.8%, the role of mild molybdenum, the performance of the pearlite refinement, the content is to improve the cementite stability element. It is generally believed that the role of manganese is to increase the amount of pearlite cast iron to improve the strength of cast iron. In fact, the manganese is also a multi-faceted, high content, will make the graphite coarse, thereby reducing the strength of cast iron.
Gray iron castings in the production of industrial machinery manufacturing widely used, there are many kinds of production processes, today, Xiaobian to take you to understand the Gray Iron Castings heat treatment process applications.
1, high temperature graphite annealing for the matrix structure contains more eutectic cementite castings to reduce the hardness and improve the machinability.
2, low temperature graphite annealing for gray iron casting hardness is too high, the matrix structure is not eutectic cementite, requires a high plasticity and high toughness of the gray iron castings.
3, to stress annealing for casting, casting welding, machining and other residual stress, to ensure that gray iron castings and dimensional stability.
4, fully austenitized normalizing for the excessive amount of ferrite, the hardness of Gray Iron Castings, to improve the strength of gray iron cast, hardness and wear resistance.
5, part of the austenitizing normalizing for the matrix is relatively uniform, and requires a certain strength and toughness of the gray iron castings.
6, complete austenitic quenching, tempering for the use of different tempering temperature of the matrix structure, to improve the gray iron cast strength, hardness and wear resistance.
7, fully austenitic isothermal quenching for obtaining bainite matrix, improve the overall performance of gray iron castings.
8, surface hardening used to improve the strength of gray iron casting, surface strength and wear resistance.
9, chemical heat treatment for the gray iron castings surface special physical, chemical and mechanical properties.