Study on the heat treatment process of high chrome cast iron (1)
Abstract: High Chromium cast iron is a kind of excellent wear-resistant material; it not only has good wear resistance but also has a specific camber and toughness; electric Power and other industries have been widely used and achieved significant economic benefits.
While improving the morphology and distribution of Eutectic carbides in high chromium cast iron, more importantly, efforts should be made to refine the Eutectic carbides, improve the metallurgical quality of grain boundaries of high chrome cast iron, and reasonably select the matrix structure in order to achieve the high chromium cast iron high-performance requirements.
In this paper, the heat treatment process of high chromium cast iron containing titanium has been studied. A reasonable heat treatment process can improve the distribution and morphology of carbides in high chromium cast iron.
Keywords: High Chrome Cast Iron; Heat Treatment; carbide; toughness
Author: Huang Zhihui (Inner Mongolia Chifeng Pharmaceutical Co., Ltd., Inner Mongolia, Chifeng 024000)
Classification: TG164 DOCUMENT ID: A ARTICLE ID: 1006 — 17981(2014)22 — 0014 — 02
According to statistics, the world’s annual consumption of iron and steel up to 700 million tons, 509/5 due to material wear and tear consumed. According to our factory, incomplete statistics, metal material in our factory, various mechanical equipment due to wear and tear caused by the loss of one million yuan. Only in the type of transmission such as the pulley, transmission shaft, inner and outerwear parts such as the loss of up to one hundred thousand. One reason for material wear is that its strength and toughness are not enough, so the material is brittly spalling under the impact wear condition. Therefore, how to improve the strength and toughness of metal wear-resistant materials to increase the service life of various metal parts is the goal we have been pursuing.
To achieve this goal and reduce mechanical costs, we add chromium and Yttrium elements to iron castings to minimize wear.
High chrome cast iron is a kind of wear-resistant material with excellent properties. It has not only good wear resistance but also has certain bow strength and toughness. Therefore, it has been widely used in metallurgy, building materials, electric power, coal, and other industries and has achieved remarkable economic benefits. In addition to the special requirements for traditional high chromium cast iron, the hypoeutectic composition is generally used. This ensures the material has a certain toughness. Wear resistance of high chromium cast iron is the main role of alloy elements: Chromium and carbon, general, carbon content, 2.0% ~ 3.5%, chromium in 13 ~ 36%. In general, in order to ensure its full hardenability, phase silicon, copper, manganese, and other elements should be added.
The residual casting stress often causes the casting to deform or even to fracture in the course of use. The residual stresses of castings with complex shapes are often very high. The residual stress of castings can be greatly reduced, and the service performance can be improved by stress relief treatment.
Heat treatment is a necessary process in the production of high chromium cast iron. The solidification and cooling in the mold are affected by many factors, such as non-uniform wall thickness, different heat dissipation conditions, the difference of molten iron temperature in the mold after pouring, etc. . Solute segregation also occurs in the solidification process. Therefore, it is necessary to improve the situation through heat treatment.
High Chrome cast iron requires a combination of a strong matrix and a hard carbide to improve the part’s wear resistance. It is necessary to improve Matrix’s properties and the shape, size, quantity, and distribution of carbides by heat treatment to give full play to the antiwear potential of materials.
In a word, heat treatment is an essential means to change the structure and properties of high chromium cast iron. As an anti-wear material, heat treatment can make the anti-wear and mechanical properties of high chromium cast iron match reasonably, so as to improve the performance and reliability of parts.
To obtain good wear resistance of high chromium cast iron, it is necessary to undergo quenching treatment, and the choice of the heating temperature is very important. When High Chromium cast iron is heated to austenitizing temperature, it needs isothermal retention to complete austenite transformation, homogenization of composition, and secondary carbon and carbide precipitation. Both austenitizing and precipitation of Secondary Carbides require the diffusion of carbon and alloy elements. Carbon and other alloying elements then determine the time required for phase transformation, and thus the length of the holding time. The austenite temperature has an obvious effect on the microstructure and properties after heat treatment. The amount of secondary carbide precipitation and the solute concentration in austenite vary with the limiting solubility of solute at a certain temperature. When the AUSTENITIC temperature is raised, the secondary carbides that start to precipitate may re-dissolve into the solid solution due to the increase of carbon and chromium’s solubility in the austenite. Therefore, the carbon and chromium contents in austenite change with the increase of heating temperature. It is pointed out that when the quenching temperature is high in a certain temperature range, the hardness first increases and then decreases, while the impact toughness changes in the opposite direction. This is mainly because at a lower temperature, carbon and chromium’s solubility in austenite is lower, more secondary carbides are precipitated. More martensite is obtained after transformation, so the hardness increases and the impact toughness decreases. But when the quenching temperature is fixed, if the temperature continues to rise, the austenite’s carbon and chromium content will increase. The composition will become uniform, making the austenite more stable. The retained austenite and the amount of austenite will increase after quenching, so the hardness will decrease, the impact toughness increases.