Observation on metallographic structure of cast impeller

a) Metallographic observation of casting state

Etchant: aqua regia solution

Magnification: 100X

The as cast structure of zg1crl8ni9ti is shown in Figure 1.

Structure description: there are ferrite distributed in dendrite on the austenitic matrix, forming austenite + ferrite + granular carbide.

After 18-8 stainless steel is cooled slowly from high temperature, a certain amount of ferrite will appear in the structure, especially after adding titanium to the steel, which will further increase the content of ferrite in the steel. The composition segregation of as cast 1Crl8Ni9Ti steel is relatively large, so the existence of ferrite in steel is inevitable. Therefore, the microstructure obtained at room temperature is austenite + ferrite + granular carbide.

b) Metallographic observation of solution treated state

Etchant: aqua regia solution.

Magnification: 100X

The solution treated microstructure of zg1cr18ni9ti steel is shown in Figure 2.

Microstructure Description: the microstructure of zg1crl8ni9ti after solid solution treatment is austenitic structure + a small amount of ferrite. During solution treatment, heating the steel to high temperature can fully dissolve the carbides into the austenite, and then quickly cool it to room temperature, so that the carbides can not precipitate in time, so as to avoid chromium deficiency at the grain boundary, so as to improve the corrosion resistance of austenitic stainless steel. However, in the actual process, a small amount of carbides often appear in the microstructure due to incomplete treatment.

c) Metallographic structure of solution treatment + stabilization treatment

Etchant: aqua regia solution

Magnification: 100X

The solution treated microstructure of zg1cr18ni9ti steel is shown in Figure 3.

The microstructure of zg1crl8ni9ti steel after solution treatment + stabilization treatment is austenite + a small amount of ferrite, which is basically the same as that after solution treatment.

The cast impeller is tested to be non-magnetic after heat treatment.

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