Inspection of metal materials

34. Additional guarantee conditions: refer to items that are inspected only when the purchaser specifies the requirements in the order contract and that the inspection results meet the requirements.
35. Agreement guarantee conditions: items negotiated between the supplier and the buyer and guaranteed in the order contract.

36. Participation conditions: The two parties negotiate the inspection items, but they are only for reference and not for evaluation.

The internal quality inspection of metal materials mainly includes mechanical properties, physical properties, chemical properties, process properties, chemical composition and internal organization inspections. The first part of mechanical properties and process properties has been introduced, here only the principle and simple process of the chemical composition and internal organization inspection methods are introduced.

(7) Chemical composition inspection

Chemical composition is the main factor that determines the performance and quality of metal materials. Therefore, the standard stipulates the chemical composition that must be guaranteed for most metal materials, and some even serve as the main quality and variety indicators. The chemical composition can be analyzed and identified through a variety of chemical and physical methods. At present, chemical analysis and spectroscopy are the most widely used. In addition, the spark identification method with simple equipment and fast identification is also one of the methods for identifying steel composition. A practical and easy way.

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37. Chemical analysis: Determine the composition of metals based on chemical reactions. This method is collectively referred to as chemical analysis. Chemical analysis methods are divided into qualitative analysis and quantitative analysis. Through qualitative analysis, we can identify which elements the material contains, but cannot determine their content; quantitative analysis is used to accurately determine the content of various elements. Quantitative analysis is mainly used in actual production. The methods of quantitative analysis are gravimetric analysis and volumetric analysis.

Gravimetric method: Use appropriate separation means to separate the measured element from other components in the metal, and then use the weighing method to measure the element content.

Volumetric analysis method: Use a standard solution (a solution of known concentration) to completely react with the measured element in the metal, and then calculate the content of the measured element based on the volume of the consumed standard solution.

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38. Spectral analysis method: Various elements can produce their own unique spectra under high temperature and high energy excitation. The method to determine the chemical composition and approximate content of metals according to the characteristic spectra generated after the elements are excited is called spectral analysis law. Usually, the sample is excited by external energy sources such as electric arc, electric spark, laser, etc., so that the measured element emits a characteristic spectrum. After spectroscopy, compare it with the chemical element spectrum table for analysis.

39. Spark identification method: It is mainly used for steel. Under grinding wheel grinding, due to friction and high temperature, the number, shape, bifurcation and color of sparks generated when various elements and particles are oxidized are different to identify the chemical composition (composition Element) and approximate content.

(8) Internal quality inspection

Common internal organizational defects are:

40. Porosity: During the solidification process of cast iron or castings, the melt in the area between the crystal branches finally solidifies and shrinks and emits gas, resulting in the generation of many small pores and gas, resulting in incompactness.

41. Slag inclusion: impurity phase or foreign particles surrounded by a solid metal matrix.

42. Segregation: The uneven distribution of chemical composition in various regions within the alloy metal.

43. Decarburization: The phenomenon that all or part of the carbon in the surface of steel and iron-based alloy materials or parts is lost. In addition, bubbles, cracks, delamination, white spots, etc. are also common internal structural defects. Commonly used inspection methods for internal structure (grain, structure) and internal structural defects are: 44. Macro inspection: use the naked eye or less than 10 times Low-power magnifying glass to observe the internal structure and defect inspection of metal materials. Commonly used methods include fracture inspection, low magnification inspection, tower turning hairline inspection and sulphur mark test.

Mainly check bubbles, slag inclusions, delamination, cracks, coarse grains, white spots, segregation, porosity, etc.

45. Microscopic inspection: Microscopic inspection is also called high-magnification inspection. It is an inspection method in which the prepared sample is observed and measured under a phase microscope at a prescribed magnification to inspect the organization and defects of metal materials. Generally check inclusions, grain size, depth of decarburization layer, intergranular corrosion, etc.

46. ​​Non-destructive testing: Non-destructive testing includes magnetic testing, fluorescent testing and color testing. Magnetic inspection is used to inspect the surface cracks, inclusions, white spots, folds, shrinkage holes, scars, etc. of ferromagnetic materials such as steel. Fluorescent flaw detection and colored flaw detection are used for the inspection of small cracks and loose holes on the surface of non-magnetic materials such as non-ferrous metals, stainless steel, and heat-resistant alloys.

47. Ultrasonic inspection: also called ultrasonic inspection. Utilize the ultrasonic wave to make linear propagation in the same homogeneous medium. But at the interface of two different substances, some or all reflections will appear. Therefore, when ultrasonic waves detour into the material with pores, cracks, shrinkage holes, and inclusions, they will reflect on the metal interface. The larger the heterogeneous interface, the stronger the reflection ability, and vice versa. In this way, the location and size of the internal defect can be reflected by the waveform of the fluorescent screen of the flaw detector. Commonly used ultrasonic flaw detection includes X-ray and radiographic flaw detection.