Test methods for hottest metal materials

2022-07-27
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Inspection methods for metal materials

the standards used for metallurgical products in China are national standards (code "GB"), ministerial standards (standards of the Ministry of metallurgical industry "Yb", standards of the Ministry of machinery and machinery "JB", etc.) and enterprise standards

I. packaging inspection

depends on the type, shape, size, accuracy and corrosion prevention of metal materials

1. Bulk: no package, ingot, block (not afraid of corrosion and not valuable), large steel (large steel, thick steel plate, rail), pig iron, etc

2. Bundling: refers to small-sized steel, pipe steel, wire rod, sheet, etc., with little impact on use due to corrosion

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

4. Shaft forming: finger wire, steel wire rope, steel strand, etc

for products packed in bales and shafts, first check whether the packaging is complete

II. Mark inspection

mark is a mark that distinguishes the material and specification of materials, mainly indicating the supplier's name, brand, inspection batch number, specification, size, grade, net weight, etc. There are signs

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

2. Printing: the method of stamping or painting on the specified parts (end face and end) of metal materials, indicating the brand, specification and standard number of materials. It is mainly used for medium and heavy plates, profiles, non-ferrous materials, etc

3. Listing: metal materials such as bundles, boxes and shafts are listed outside to indicate their brand, size, weight, standard number, supplier, etc

marks of metal materials shall be carefully identified during inspection and properly protected during transportation and storage

III. inspection of specifications and dimensions

specifications and dimensions refer to the nominal dimensions of the main parts (length, width, thickness, diameter, etc.) of metal materials

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

2. Dimension deviation: the difference between actual dimension and nominal dimension is called dimension deviation. Greater than the nominal size is called positive deviation, and less than the nominal size is called negative deviation. Within the specified range of the standard, it is called the allowable deviation, and beyond the range, it is called the dimension out of tolerance. If the out of tolerance is unqualified, is it in conformity with the alignment accuracy

3. Accuracy grade: the allowable size deviation of metal materials specifies several ranges, and is divided into several grades called accuracy grade according to the size of allowable size deviation. The accuracy grade is divided into ordinary, high and advanced

4. Delivery length (width): it is the main size of metal materials for delivery. It refers to the length (width) specification of digital display impact testing machine and microcomputer controlled screen display impact testing machine, which can be seen from the classification

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

6. Short ruler (narrow ruler): the length is less than the lower limit of the specified normal length, but not less than the specified minimum allowable length. For some metal materials, a part of "short ruler" can be handed in according to regulations

7. Fixed length: the length of delivered metal materials must be the length specified by the demander in the order contract (general positive deviation)

8. Multiple length: the length of the delivered metal material must be an integral multiple of the length specified by the demander in the order contract (plus sawing and positive deviation)

for the inspection of specifications and dimensions, attention shall be paid to the measurement of material parts and the selection of appropriate measuring tools

IV. quantity inspection

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

1. Measured by actual weight: all metal materials measured by actual weight should generally be weighed for inspection. For solid packages (such as boxes, containers, drums, etc.), the gross weight, net weight and tare weight shall be indicated on the packages. For example, the number of steel sheets, silicon steel sheets and ferroalloys that can be sampled for inspection shall not be less than 5% of a batch. If there is a big difference between the sampling weight and the marked weight, they must all be unpacked and weighed

2. Calculation by theoretical conversion: the weight calculated by the nominal size (actual size) and specific gravity of the material can be converted by theoretical conversion for those shaped plates and other materials with fixed size, but attention should be paid to the conversion formula and the actual specific gravity of the material during conversion

v. surface quality inspection

surface quality inspection mainly refers to the inspection of materials, appearance, shape and surface defects, mainly including:

1. Ovality: the phenomenon that metal materials with circular section have different diameters in all directions on the same section. Ovality is expressed by the maximum and minimum diameter difference on the same section, and the standards for different materials are different

2. Bending, bending degree: bending is rolling material. A general term used to describe a curve that is not straight in the direction of length or width. If their unevenness is expressed numerically, it is called curvature

3. Torsion: the strip rolling material is twisted into a spiral shape along the longitudinal axis

4. Sickle bend (side bend): refers to the bending of metal plates, strips and shapes close to the rectangular section along the length (narrow side). One side presents a concave curve and the other side presents a convex curve, which is called "sickle bend" Expressed in concave height

5. Scoop curvature: refers to the wave phenomenon of high and low fluctuations in the length and width of the plate or belt, forming a scoop shape, which is called scoop curvature. The value indicating the degree of curvature is called the degree of curvature

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

7. Ears: protrusions extending along the rolling direction due to improper roll matching and other reasons are called ears

8. Inclusion: it refers to that the material surface is in a straight line or arc groove, and the groove bottom can usually be seen

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

10. Bonding: mutual adhesion between layers, points, lines and surfaces of metal plates, foils and strips during overlapping rolling and annealing. After being lifted, there is a bonding trace on the surface, which is called bonding

11. Iron oxide scale: iron oxide scale refers to the metal oxide formed on the surface of materials during heating, rolling and cooling

12. Folding: it is a kind of surface defect formed by metal during hot rolling (or forging). The surface of the bimetallic layer is folded and overlapped in a straight line or curve

13. Pitting: refers to the uneven rough surface of metal materials

14. Subcutaneous bubbles: irregular distribution of small bumps with different sizes and shapes on the surface of metal materials. The broken bumps are chicken claw shaped cracks or tongue like 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 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 or not various surface defects are allowed to exist, or to what extent, are clearly specified in the relevant standards

VI. assurance conditions for internal quality inspection

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

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 the items that are inspected according to the requirements specified by the demander in the order contract, and the inspection results meet the requirements

3. Agreement guarantee conditions: items negotiated by the supplier and the demander and guaranteed in the order contract

4. Conditions for modification: both parties negotiate to carry out inspection items, but only for reference conditions, not for assessment

the internal quality inspection of metal materials mainly includes mechanical property, physical property, chemical property, process property, chemical composition and internal structure inspection. The first part of mechanical properties and process properties has been introduced. Here, only the principle and simple process of inspection methods for chemical composition and internal structure are briefly introduced

VII. Chemical composition test

chemical composition is the main factor determining the performance and quality of metal materials. Therefore, the standard specifies the chemical composition 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 by various chemical and physical methods. At present, the most widely used methods are chemical analysis and spectral analysis. In addition, spark identification method with simple equipment and fast identification speed is also a practical and simple method for identification of steel composition

1. Chemical analysis method: determine the composition of metals according to chemical reactions. This method is collectively referred to as chemical analysis method. Chemical analysis methods are divided into qualitative analysis and quantitative analysis. Through qualitative analysis, the elements contained in the material can be identified, but their content cannot be determined; 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 elements from other components in the metal, and then measure the element content by weighing method

the coupling of volumetric analysis is to completely react the standard solution (solution with known concentration) with the measured elements in the metal, and then calculate the final content of the measured elements according to 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. It is called spectral analysis method to determine the chemical composition and approximate content of metals according to the characteristic spectra generated after the elements are excited. Usually, the sample is excited by external energy such as arc, electric spark and laser to make the measured elements emit characteristic spectra. After spectroscopic analysis, it was compared with the spectral table of chemical elements and analyzed

3. Spark identification method: it is mainly used to identify the chemical composition (constituent elements) and approximate content of materials due to the difference in the number, shape, bifurcation, color, etc. of sparks generated by the oxidation of various elements and particles due to friction and high temperature under the grinding wheel

VIII. Common internal structure defects in internal quality inspection are:

1. Porosity: during solidification of cast iron or casting, the melt in the area between the crystal branches shrinks and emits gas due to final solidification, resulting in many small pores and gases, resulting in non compactness

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

3. Segregation: uneven distribution of chemical composition in various areas of 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 products is lost

in addition, bubbles, cracks, delaminations, white spots, etc. are also common internal structural defects. The common inspection methods for internal structures (grains, structures) and internal structural defects are:

a. macro inspection: the inspection of internal structures and defects of metal materials by using the naked eye or a low magnification less than 10 times. The commonly used methods are fracture inspection, low magnification inspection, tower turning hairline inspection and sulfur printing

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