Eight testing methods for metal materials

Eight testing methods for metal materials

1、 Packaging inspection

It depends on the type, shape, size, precision and anti-corrosion of metal materials.

1. Bulk: that is, no packaging, ingots, blocks (not afraid of corrosion, not expensive), large steel (large steel, thick steel plate, rail), pig iron, etc.

2. Bundles: Refers to small size, corrosion has little effect on use, such as small and medium steel, pipe steel, wire, thin plate, etc.

3. Box (barrel): refers to anti-corrosion, small and thin products, such as tinplate, silicon steel sheet, magnesium ingot, etc.

4. Shafting: refers to wire, steel wire rope, steel strand, etc.

For bundled boxes and shaft-packed products, first check whether the packaging is complete.

2、mark inspection

The mark is a mark that distinguishes the material and specifications of the material, and mainly describes the supplier's name, brand number, inspection lot number, specification, size, grade, net weight, etc. Signs have

1. Coloring: paint the end surface and end of metal materials with various colors, mainly used for steel, pig iron, non-ferrous materials, etc.

2. Printing: The method of stamping or spraying paint on the specified parts of the metal material (end surface, end), indicating the brand, specification, standard number, etc. of the material. Mainly used for medium and heavy plates, profiles, non-ferrous materials, etc.

3. Listing: Bundles, boxes, shafts and other metal materials are listed on the outside to indicate their brand, size, weight, standard number, supplier, etc.

The signs of metal materials must be carefully identified during inspection and properly protected during transportation and storage.

3、 Inspection of specifications

Specification size refers to the nominal size of the main parts of the metal material (length, width, thickness, diameter, etc.).

1. Nominal size (nominal size): It is the ideal size that people want in production, but there is a certain gap between it and the actual size.

2. Size deviation: The difference between the actual size and the nominal size is called size deviation. Greater than the nominal size is called positive deviation, and less than the nominal size is called negative deviation. It is called the allowable deviation within the specified range of the standard, and the size exceeding the range is called the over-tolerance, and the over-tolerance belongs to the unqualified product.

3. Accuracy grade: Several ranges are specified for the allowable deviation of metal materials, and are divided into several grades called accuracy grades according to the size of the allowable deviation. The accuracy grades are divided into ordinary, higher, advanced, etc.

4. Delivery length (width): It is the main delivery size of metal materials, and refers to the length (width) specifications that metal materials should have when they are delivered.

5. Normal length (indefinite length): The length is not specified, but it must be within a specified length (different varieties, different lengths, according to the department and factory).

6. Short ruler (narrow ruler): The length is less than the lower limit of the prescribed normal length dimension, but not less than the prescribed minimum allowable length. For some metal materials, a part of the "short ruler" can be handed in as required.

7. Cut-to-length length: The length of the metal material to be delivered must have the length specified by the purchaser in the order contract (generally positive deviation).

8. Length of multiple rulers: The length of the metal material to be delivered must be an integer multiple of the length specified by the purchaser in the order contract (plus saw cut, positive deviation). In the inspection of specifications and dimensions, attention should be paid to the measurement of material parts and the selection of appropriate measuring tools.

4、 quantity inspection

The quantity of metal materials generally refers to the weight. The quantity inspection methods are as follows:

1. Measured by actual weight: Generally, all metal materials measured by actual weight should be weighed and inspected. For sturdy packaging, the gross weight, net weight and tare weight shall be indicated on the package. Such as thin steel plates, silicon steel sheets, and ferroalloys can be sampled at least 5% of the batch. If the sampled weight is very different from the marked weight, all must be weighed out of the box.

2. Conversion and measurement according to theory: The weight calculated by the nominal size and specific gravity of the material can be converted theoretically for those fixed-length profiles and other materials, but the conversion formula and the actual specific gravity of the material should be paid attention to when converting.

5、Surface quality inspection

Surface quality inspection is mainly to inspect materials, appearance, shape, and surface defects, mainly including:

1. Ovality: Metal materials with circular cross-sections have different diameters in all directions on the same cross-section. Ovality is expressed by the difference between the largest and smallest diameters on the same section, and the standards for different materials are different.

2. Bending and bending: bending is the rolled material. A general term that is not straight or curved in the length or width direction. If the degree of their unevenness is expressed by numbers, it is called curvature.

3. Torsion: The strip rolled material is twisted into a spiral along the longitudinal axis.

4. Sickle curve (side curve): refers to the bending of metal plates, belts and shapes close to the rectangular section along the length (narrow side), one side is concave and the other side is convex, called "sickle" "Bend". Expressed by recessed height.

5. Curvature: It refers to the phenomenon of undulating waves in the length and width direction of the plate or belt at the same time, forming a curvy shape, which is called the camber. The value indicating the degree of buckling is called buckling.

6. Surface cracks: refers to the cracks on the surface of metal objects.

7. Ears: due to improper roll fit and other reasons, the protrusions that extend along the rolling direction are called ears.

8. Injuries: refers to the straight or curved grooves on the surface of the material, and the bottom of the groove can usually be seen.

9. Scarring: refers to the tongue-like, nail-like or fish-scale flakes that are unevenly distributed on the surface of the metal material.

10. Adhesion: The mutual adhesion of points, lines, and surfaces between layers and layers of metal plates, foils, and strips during rolling and annealing. After being opened, there are traces of bonding on the surface, which is called bonding.

11. Iron oxide scale: Iron oxide scale refers to the metal oxide formed on the surface of the material in the process of heating, rolling and cooling.

12. Folding: It is a kind of surface defect formed in the process of hot rolling (or forging) of metal. The bimetallic layer folded on each other on the surface overlaps in a straight line or a curve.

13. Pockmark: Refers to the rough surface of the metal material with uneven surface.

14. Subcutaneous bubbles: The surface of metal materials presents irregular distributions of different sizes, different shapes, small round bulges around them, and ruptured bumps that are chicken-foot-shaped cracks or tongue-shaped scars, which are called bubbles.

Surface defects are mainly due to improper operations such as production, transportation, loading and unloading, and storage. Depending on the impact on the use, some defects are not allowed to exceed the limit at all. Although some defects do not exist, they are not allowed to exceed the limit; whether various surface defects are allowed to exist, or the extent to which they are allowed, are clearly stipulated in the relevant standards.

6、Guarantee conditions for internal quality inspection

The basis for the inspection of the internal quality of metal materials is to adapt to different requirements according to the material, and the guarantee conditions are also different. The inspection must be carried out according to the guarantee conditions at the time of delivery and acceptance, and meet the requirements and guarantee conditions;

1. Basic guarantee conditions: The minimum requirements for material quality, whether proposed or not, must be guaranteed, such as chemical composition, basic mechanical properties, etc.

2. Additional guarantee conditions: refer to items that are inspected according to the requirements specified in the order contract by the purchaser, and the inspection results are guaranteed to meet the requirements.

3. Agreement guarantee conditions: items negotiated between the supplier and the buyer and guaranteed in the order contract.

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

The 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 the identification of steel components. A practical and easy way.

1. 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 gravimetric 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.

2. 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.

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

8、 Common internal organizational defects in internal quality inspection include:

1. 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.

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

3. Segregation: the uneven distribution of chemical composition in each area of the alloy metal.

4. Decarburization: The phenomenon that all or part of the carbon in the surface layer of steel and iron-based alloy materials or parts is lost. In addition, bubbles, cracks, delamination, white spots, etc. are also common internal organizational defects. Commonly used inspection methods for internal organization and internal organizational defects include:

a. Macro inspection: Use the naked eye or a low-power magnifying glass below 10 times to observe the internal structure and defects of metal materials. Commonly used methods include fracture inspection, low magnification inspection, tower turning hairline inspection and sulfur mark test. Mainly check bubbles, slag inclusions, delamination, cracks, coarse grains, white spots, segregation, porosity, etc.

b. 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 structure and defects of metal materials. Generally inspect inclusions, grain size, depth of decarburization layer, intergranular corrosion, etc.

c. Non-destructive inspection: Non-destructive inspection includes magnetic flaw detection, fluorescent flaw detection and color flaw detection. Magnetic inspection is used to check the surface cracks, inclusions, white spots, folds, shrinkage holes, scars, etc. of ferromagnetic materials such as iron and 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.

d. 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 the ultrasonic wave reaches the inside of the material with pores, cracks, shrinkage holes, and inclusions, it will be reflected at the metal interface. The larger the heterogeneous interface, the stronger the reflection ability, and vice versa. In this way, the location and size of internal defects can be reflected by the waveform of the fluorescent screen of the flaw detector. Commonly used ultrasonic inspections are X-ray and radiographic inspections.