How to Solve The Hot and Cold Cracking Problems of Gray Cast Iron?

Gray cast iron is cast iron with flake graphite. Gray cast iron is currently the most widely used cast iron. Its output accounts for more than 80% of the total cast iron output. Because of its cheap price, gray cast iron is used in OEM Castings Supplier.

Pulley Casting

Is very extensive. The factors affecting the structure and properties of gray cast iron are generally divided into two types:

1. The influence of chemical composition is relatively large;

2. The cooling rate will also affect the casting. The faster the cooling rate, the easier it is to form white iron.

Casting Process

In the casting process, if the process is not well controlled, there will be many defects and problems. The following cast iron manufacturers will give you a detailed description of the impact of hot cracks and cold cracks on castings:

Thermal cracking

1. The characteristics and discovery methods of thermal cracking:

The places with thermal cracks have dark or almost black oxidized surfaces. Such thermal cracks can be found by visual inspection, light transmission method, and pressure test.

2. Causes of thermal cracks:

Casting hot crack

1) If the chemical composition of the molten iron does not meet the requirements, the shrinkage value of the solid will be relatively large, such as low carbon, high sulfur and so on.

2) If the casting contains low-melting slag inclusions, it will reduce the high-temperature strength, because when the thermal cracks are generated near the end of solidification, the shrinkage at the hot joints of the castings will be mechanically hindered to produce thermal cracks.

3. Prevention methods of thermal cracks

1) Cast iron manufacturers should try their best to control the chemical composition in the castings, and the sulfur content in the molten iron must be low;

2) When pouring, avoid molten slag entering the cavity;

Cold cracking

1. The characteristics and discovery methods of cold cracks:

In cold cracks, there will be a clean or slightly oxidized surface with a dark red color; the method of discovery is the same as that of hot cracks.

2. Causes of cold cracks:

1) The chemical composition of the metal liquid is unqualified, which causes the solid shrinkage value to be relatively large;

2) The phosphorus content in the molten metal is relatively high, which increases the brittleness and reduces the tensile strength of the cast iron. The cold cracks mainly occur at the stress concentration of the thick and thin castings.

3. Prevention methods of cold cracks:

1) Control the chemical composition in the castings, and the cast iron manufacturers should also try to reduce the sulfur content in the molten metal;

2) The ωp in the molten iron should be controlled below 0.15%.

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