What is metal material testing

Metal materials are metallurgical products. The production, ordering, transportation, use, storage and inspection of metal materials must be based on unified technical standards – metallurgical product standards. Workers engaged in metal materials must understand the relevant content of the standards. The standards used for metallurgical products in my country are national standards (codenamed “GB”), ministry standards (Ministry of Metallurgical Industry standards “YB”, Ministry of Machinery Standards “JB”, etc.,) enterprise standards level three.
(1) Packaging inspection depends on the type, shape, size, accuracy and anti-corrosion of the metal material. ​

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

2. Bundle: refers to products that are small in size and have little impact on use due to corrosion, such as small and medium-sized steel, pipe steel, wire rods, thin plates, etc. ​

3. Boxed (barrel): refers to anti-corrosion, small and thin products, such as tinplate, silicon steel sheets, magnesium ingots, etc. ​

4. Shaft: finger wire, wire rope, steel strand, etc. For products packed in bundles and shafts, you should first check whether the packaging is complete.

(2) Mark Inspection The mark is a mark that distinguishes the material and specifications of the material. It mainly describes the supplier’s name, brand, inspection batch number, specification, size, grade, net weight, etc. The sign has;

5. Painting: Apply various colors of paint on the end faces of metal materials, mainly used for steel, pig iron, non-ferrous raw materials, etc. ​

6. Printing: The method of stamping or spray painting on the specified parts of the metal material (end face, end), indicating the material grade, specification, standard number, etc. Mainly used for medium and thick plates, profiles, non-ferrous materials, etc. ​

7. Tags: Bundles, boxes, shafts and other metal materials are listed outside to indicate their grade, size, weight, standard number, supplier, etc. Marks on metal materials must be carefully identified during inspection and properly protected during transportation, storage, etc.

(3) Inspection of specifications and dimensions Specifications and dimensions refer to the nominal dimensions of the main parts of the metal material (length, width, thickness, diameter, etc.). ​

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

9. Dimensional deviation: The difference between the actual size and the nominal size is called the dimensional deviation. If it is larger than the nominal size, it is called a positive deviation, and if it is smaller than the nominal size, it is called a negative deviation. Within the scope of the standard, it is called the allowable deviation, and if it exceeds the range, it is called the dimensional out-of-tolerance, and the out-of-tolerance is considered a non-conforming product. ​

10. Accuracy level: The dimensional allowable deviation of metal materials stipulates several ranges, and is divided into several levels according to the size of the allowable deviation, called accuracy levels. The accuracy levels are divided into ordinary, higher, advanced, etc. ​

11. Delivery length (width): It is the main dimension of metal material delivery, which refers to the length (width) specifications that metal materials should have when delivered. ​

12. Normal length (indeterminate length): There is no certain requirement for the length, but it must be within a specified length range (the length varies according to the variety, and is determined by the ministry and factory).

13. Short ruler (narrow ruler): The length is less than the lower limit of the specified usual length size, but not less than the specified minimum allowable length. For some metal materials, a part of the “short ruler” can be handed over according to regulations. ​

14． Fixed length: The length of the delivered metal material must be the length specified by the buyer in the order contract (generally positive deviation).

15. Multiple length: The length of the delivered metal material must be an integer multiple of the length specified by the buyer in the order contract (plus saw kerf, positive deviation). ​​

When inspecting specifications and dimensions, attention should be paid to measuring the material location and selecting appropriate measuring tools.

(4) Quantity inspection The quantity of metal materials generally refers to the weight (except for a few cases of backing plates and fishplates, which are counted in pieces). The quantity inspection methods are:

17． Measurement by actual weight: Metal materials measured by actual weight should generally be weighed and inspected. For solid packaging (such as boxes, boxes, barrels, etc.), the gross weight, net weight and tare weight should be indicated on the packaging. For example, thin steel plates, silicon steel sheets, and ferroalloys can be randomly inspected in quantities of not less than 5% of a batch. If the random inspection weight is significantly different from the marked weight, all must be unpacked and weighed. ​

18． Measurement based on theoretical conversion: The weight calculated based on the nominal size (actual size) and specific gravity of the material can be theoretically converted for those fixed-length templates and other materials, but when converting, attention should be paid to the conversion formula and the actual specific gravity of the material.

(5) Surface quality inspection Surface quality inspection is mainly the inspection of materials, appearance, shape and surface defects, mainly including:

19． Ovality: The phenomenon that 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 maximum and minimum diameters on the same cross-section, and the standards for materials for different uses are different. ​

20. Bend, curvature: Bend is rolling material. A general term for a shape that is not straight or curved in the length or width direction. If their unevenness is expressed numerically, it is called curvature. ​

twenty one. Twisting: A strip of rolled material is twisted along the longitudinal axis into a spiral shape. ​

twenty two. Sickle bend (side bend): refers to the bending of metal plates, strips and shapes with nearly rectangular cross-sections along the length (narrow side), with one side showing a concave curve and the other facing a convex curve, which is called “sickle bend” . Expressed as concave height. ​​

twenty three. Scoop curvature: refers to the phenomenon of high and low waves appearing simultaneously in the length and width directions of the plate or strip, forming a scoop shape, which is called scoop curvature. The numerical value indicating the degree of curvature is called curvature. ​

twenty four. Surface cracks: refers to cracks on the surface of metal objects. 25. Ears: The protrusions extending along the rolling direction due to improper roller coordination and other reasons are called ears. ​

26. Wounds: Refers to straight or arc-shaped groove marks on the surface of the material, and the bottom of the groove can usually be seen. 27． Scarring: refers to tongue-shaped, nail-shaped or fish scale-shaped flakes unevenly distributed on the surface of metal materials. ​

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

29. Iron oxide scale: Iron oxide scale refers to the metal oxide generated on the surface of the material during the heating, rolling and cooling processes. ​

30. Folding: It is a surface defect formed in metal during the hot rolling process (or forging). The double metal layers on the surface are folded into each other and overlap in a straight line or curve. ​

31. Pit: Refers to the uneven and rough surface of a metal material. ​​

32. Subcutaneous bubbles: The surface of metal materials presents irregular distribution of small bumps of different sizes and shapes with smooth surroundings. The ruptured bumps appear as chicken claw-shaped cracks or tongue-shaped scars, which are called bubbles. Surface defects are mainly caused by improper operations such as production, transportation, loading and unloading, and storage. Depending on the impact on 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 to exist, are clearly stipulated in the relevant standards. ​​

(6) Guarantee conditions for internal quality inspection The basis for the inspection of internal quality of metal materials is to adapt to different requirements according to the material, and the guarantee conditions are also different. When leaving the factory and acceptance, inspection must be carried out according to the guarantee conditions, and the requirements are met, and the guarantee conditions are divided into points;

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

34. Additional guarantee conditions: refers to items that will only be inspected based on the requirements specified by the purchaser in the order contract, and ensure that the inspection results comply with the regulations. ​

35. Agreement guarantee conditions: Items negotiated by the supplier and the buyer and guaranteed in the order contract. ​

36. Conditions for participating in the modification: The inspection items will be negotiated by both parties, but it is only used as a reference condition and will not be used for assessment. The internal quality inspection of metal materials mainly includes mechanical properties, physical properties, chemical properties, process performance, chemical composition and internal organizational inspection. The first part of the mechanical properties and process properties has been introduced. Here, only the principles and simple processes of the inspection methods for chemical composition and internal organization are briefly introduced.

(7) Chemical composition inspection Chemical composition is the main factor that determines the performance and quality of metal materials. Therefore, the standards stipulate chemical compositions that must be guaranteed for most metal materials, and some even serve as the main quality and variety indicators. Chemical composition can be analyzed and identified through a variety of chemical and physical methods. The most widely used methods at present are chemical analysis and spectral analysis. In addition, the spark identification method with simple equipment and fast identification is also an important method for identifying steel composition. A practical and simple method. ​​

37. Chemical analysis: Determine the composition of metals based on chemical reactions. This method is collectively called chemical analysis. Chemical analysis methods are divided into two types: qualitative analysis and quantitative analysis. Qualitative analysis can identify which elements a material contains, but not 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 analysis method: Use appropriate separation means to separate the element to be measured from other components in the sheet metal copper, 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. ​

38. Spectral analysis method: Various elements can produce their own unique spectra when excited by high temperature and high energy. The method of determining the chemical composition and approximate content of metals based on the characteristic spectra produced after the elements are excited is called spectroscopic analysis. Usually, the sample is excited by external energy sources such as arc, electric spark, laser, etc., so that the measured element emits a characteristic spectrum. After spectroscopy, compare it with the chemical element spectrum table to make an analysis. ​

39. Spark identification method: Mainly used for steel. Due to friction, high temperature, and the oxidation of various elements and particles under grinding wheel, the number, shape, bifurcation, color, etc. of sparks are different to identify the chemical composition (component elements) of the material. and a method of approximate content. ​​

(8) Internal quality inspection