Cast iron quality appraisal

iron castings are based on the core principles of iron-carbon alloy phase transformation control and casting process optimization. Through precise control of carbon equivalent, inoculation treatment and cooling rate, the synergy of strength, hardness and processing performance is achieved. They are widely used in automotive engines, machine tool bases, pipeline valves, building structural parts and other fields. In automobile manufacturing, it is used for key components such as cylinder blocks and crankshafts; in the field of heavy machinery, it meets the rigidity requirements of large gear boxes; in municipal engineering, it ensures the pressure-resistant sealing of water pipeline networks. Compared with steel castings, cast iron parts have the characteristics of low cost, good shock absorption, and excellent wear resistance. They are the core material for forming complex structural parts in the equipment manufacturing industry.

Zhongke Testing is a product quality appraisal service organization registered with the court. It can provide quality appraisal services for iron castings. It has a professional appraisal team and advanced instruments and equipment to provide fair and accurate appraisal results for the quality appraisal of iron castings.

With the widespread use of cast iron parts in key equipment, quality dispute cases have increased significantly. The judicial dispute focuses on:

1, performance index dispute: whether the tensile strength reaches the standard, Brinell hardness deviation;

2, material defects: improper control of carbon equivalent, insufficient nodularity rate of ductile iron ;

3, process problems: too low pouring temperature caused cold shut, insufficient molding sand strength led to sand inclusion;

4, contract performance dispute: material type substitution, heat treatment status did not match the technical agreement.

Iron casting quality appraisal technical methods mainly include:

1. Appearance inspection: Check whether there are cracks, pores, blisters and other defects on the surface of the casting.

2. Dimensional measurement: Use calipers, micrometers and other measuring tools to measure the size of the casting to check whether it meets the drawing requirements.

3. Material analysis: Determine the material composition of the casting through spectral analysis, chemical analysis and other methods.

4. Mechanical property testing: Conduct tensile tests, impact tests, etc. to measure the tensile strength, yield strength, elongation and other mechanical properties of the castings.

A pump and valve factory of the applicant signed a "QT600-3 Ductile Iron Valve Body Procurement Contract" with a foundry of the respondent, agreeing that the nodularization rate is ≥90%. During processing, 30% of the valve body sealing surface was found to be leaking, and the manufacturer argued that it was caused by machining errors.

Identification analysis results:

The quality analysis expert group discussed and comprehensively analyzed the relevant information of "cast iron parts", contract technical agreements, on-site inspection case materials and other data, and made the following quality analysis opinions:

The casting involved in the case has a spheroidization rate of only 75% (the graphite form is mainly flocculated), and a pearlite content of 82% (standard ≥90%); the carbon equivalent is 4.5% exceeding the standard, and the number of eutectic clusters is ≤120/cm² (standard ≥150/cm²); X-ray inspection shows that there is a Φ5mm shrinkage porosity group at the root of the flange.

The appraisal conclusion concluded that the foundry failed to control the spheroidization process and melting parameters according to the agreement, and material defects were the main cause of leakage.

Iron casting quality appraisal report mainly includes the following contents:

1. Client information

2. Appraisal equipment information

3. Appraisal basis (standards, power of attorney, etc.)

4. Identification method