Correct method for preparing ductile iron samples - Master's thesis - Dissertation

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When the spheroidal graphite cast iron is measured by the general method of drilling, the measurement error is large and often fails to meet the production requirements. The main reason is that the carbon content of the ductile iron itself is unevenly distributed in the structure, and a large part of the carbon exists in the structure in the form of spherical or spheroidal graphite. When the drill is obtained, a mixture of iron filings and free graphite is obtained, so that the carbon content error is large. In the past, there have been some reports on the sampling and sample preparation methods of ductile iron. Although the overall improvement is improved, it is not perfect. At present, the following methods are generally used in practical work:

(1)

As a control between production processes, the carbon content can be sampled before spheroidization; and the carbon content of ductile iron is estimated based on the carbon content of the spheroidizing agent. Used for inter-process control.

(2)

When smelting, the film is sampled by a thin film method, and the small piece is taken as an analysis sample.

(3)

For the test bar or the finished product, the planing method is adopted, and the small sample is used as the analysis sample.

(4)

Drill the fines with a small drill bit, then crush as much as possible in a closed environment, sift through all, and mix to form an analytical sample.

When the surface is processed or the unknown sample is analyzed, it should be noted that the chemical composition of the surface chemical composition and the internal material of the sample may be different, such as: carburizing, nitriding, boronizing or decarburization during thermal processing to make the surface of the sample Chemical composition changes.

When analyzing these sample components, the surface should be removed.

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The depth is left and right, and then the sample for analysis is prepared.

For large castings or steel castings (especially high alloy castings), component segregation is prone to occur. Generally, the method of sampling inspection should be agreed upon by the supplier and the buyer at the time of ordering. It should be determined whether it is a test strip sampling analysis or a physical sampling analysis. If it is a physical sampling analysis, the sampling site should be specified to avoid controversy due to segregation of product components.

Alloy steel pipes (especially high-alloy steel pipes) have large segregation of chemical components, and the carbon and titanium contents are different from the surface layer and the inner layer, and the segregation is large. Samples should be taken and prepared at the specified location and depth for verification analysis.