Today we will discuss some difficult problems in the pr […]
Today we will discuss some difficult problems in the production of heat resistant steel castings.
China has been producing heat resistant steel since 1952. Later, some new low-alloy hot-strength steels were developed, thus increasing the working temperature of pearlite hot-strength steels to 600 ~ 620℃, and some new low-chromium nickel oxidation resistant steels were also developed.
Heat-resistant steel and stainless acid-resistant steel intersect each other in the application range. Some stainless steels have the characteristics of heat-resistant steel and can be used as both stainless acid-resistant steel and heat-resistant steel. Elements formed by ferrite such as chromium, aluminum and silicon can promote the formation of dense oxide film on the metal surface at high temperature to prevent further oxidation, and are the main elements for improving the oxidation resistance of steel and resisting high-temperature gas corrosion. However, the high content of aluminum and silicon will seriously deteriorate the room temperature plasticity and thermoplasticity.
Smelting heat-resistant steel is usually done in electric arc furnace or induction furnace. Vacuum refining and out-of-furnace refining are often used for those with high quality requirements. It is difficult to process and deform some high alloy heat resistant steel castings. It is not only more economical to produce castings than rolled materials, but also the castings have higher lasting strength. Therefore, heat-resistant cast steel accounts for a considerable proportion in heat-resistant steel. Besides sand casting, precision casting can be used to obtain products with smooth surface and accurate size. Centrifugal casting is often used for high temperature furnace tubes for ammonia synthesis and ethylene cracking.
Heat-treated pearlite hot-strength steel is usually used after normalizing or quenching and tempering. Martensitic heat resistant steel is quenched and tempered to stabilize the structure and obtain good comprehensive mechanical properties and high temperature strength. Ferritic steel in refractory steel cupping line cannot be strengthened by heat treatment.
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