The fracture inspection method specified in this standard is applicable to carbon structural steel, low alloy structural steel plates, bars and sections. It can also be used as a reference for fracture inspection of other steels. GB/T 2971-1982 Carbon Steel and Low Alloy Steel Fracture Inspection Method GB/T2971-1982 Standard Download Decompression Password: www.bzxz.net

National Standard of the People's Republic of China
Method of fracture test for carbon and low alloy steels
UDC 669.14/.15
GB2971—82
The fracture test method specified in this standard is applicable to carbon structural steel and low alloy structural steel plates, bars and sections. It can also be used for fracture test of other steels.
1 Sample preparation
1.1 The location and quantity of the sample shall be in accordance with the relevant standards or the agreement between the two parties. If there is no provision for the sampling location, the longitudinally rolled steel plate shall be cut within the central one-tenth of the end width, perpendicular to the rolling direction, and the transversely rolled steel plate shall be cut at any location of the end width, perpendicular to the rolling direction: the bar shall be cut at the end; the section shall be cut at the same location as the tensile test specimen. 1.2 The specimen can also be cut by sawing, shearing and flame cutting, but sufficient processing allowance must be left to eliminate deformation and heat response areas.
1.3 When the thickness of the steel is less than or equal to 30mm, the width of the specimen is twice the thickness of the steel. When the thickness is greater than 30mm, the width of the specimen is 1.5 times the thickness of the steel, but not less than 60mm. The thickness of the specimen is the thickness of the pin, and the length of the specimen can be 150~300mm. In the central part of the specimen, a sharp notch is made on one side perpendicular to the surface of the material, and its depth is one-third of the width of the specimen, as shown in Figure 1.
Figure 1 Schematic diagram of steel fracture specimen
α-specimen thickness b-specimen width
1.4 The bar steel with a diameter (or side length) less than or equal to 40mm is made into a transverse fracture, and the length of the specimen can be 100~150mm. A sharp tip is made on one side of the central part of the specimen, and its depth is one-third of the diameter (or side length), as shown in Figure 2. Figure 2 Schematic diagram of transverse fracture specimen of steel bar smaller than or equal to 40mm Issued by the General Administration of Standardization on March 25, 1982
Implementation on December 1, 1982
GB297t-82
For steel bars with a diameter (or side length) greater than 40mm, longitudinal fracture is made and transverse specimens are cut. The specimen thickness can be 15-20mm. A sharp die is made on the center line of the specimen section. The depth of the notch is one-third of the specimen thickness, as shown in Figure 3. Figure 3 Schematic diagram of longitudinal fracture specimen of steel bar greater than 40mm When it is difficult to break, the notch depth can be appropriately deepened, but it should not exceed half of the diameter (or thickness). 2 Test method
2.1 The test should be carried out at room temperature (10-36℃), and the specimen should be broken by dynamic load. During operation, the notch is placed downward so that the knife edge coincides with the center line of the notch, and then it is broken sharply. www.bzxz.net
2.2 When breaking the specimen, avoid scratching and staining the fracture surface. 2.3 The fracture surface should be inspected with the naked eye. If it is unclear, a magnifying glass of 10 times or less can be used for inspection. 2.4 Whether various types of fracture defects are allowed to exist and the qualified limits should be specified in the relevant standards or the agreement between the two parties. Stone fracture structure and defect classification
3,1 Fibrous fracture
The fracture surface is dark carpet-like, dull and without crystalline particles. The fracture edge generally has obvious plastic deformation, as shown in Figure 4. It belongs to a normal fracture.
3,2 Crystalline fracture
The fracture surface is flat, bright gray, with a strong metallic luster and obvious crystalline particle structure, as shown in Figure 5, which belongs to a positive band fracture. 3.3 Hairline fracture
On the fibrous fracture, there are cracks of varying lengths, and the color is basically the same as the matrix, sometimes silvery bright color, the wall is not smooth, and it is mostly distributed in the center of the fracture, as shown in Figure 8. 3,4 Poly-seam (separation) fracture
There are irregular cracks of varying lengths distributed on the fracture, the seams are relatively smooth, and the color is different from the matrix, as shown in Figure 7, which is a defect of the continuity of the damaged metal.
3.6 Bubble fracture
On the fracture, there are smooth inner walls, non-crystalline thin strips, or smooth pits. It is mostly distributed under the skin, and sometimes appears inside, as shown in Figure 8. It is a defect that destroys the continuity of the metal. 3.6 Non-metallic inclusion fracture
On the fracture, there are non-crystalline thin strips or block defects in gray, light yellow or yellow-green colors visible to the naked eye, and the distribution is irregular, as shown in Figure 9. It is a defect that destroys the continuity of metal. 3. The fracture of heterometallic inclusions
shows different structures and different metallic luster from the base metal on the fracture, and has a clear interface with the base metal. The distribution is irregular, as shown in Figure 10. It is a defect that destroys the uniformity or continuity of metal structure. 3.8 Shrinkage residual fracture
In the axial area of ​​the fracture, there are strips or loose bands of non-crystalline structure, sometimes with visible non-metallic inclusions or slag, and the strips often have oxidation color, as shown in Figure 11, which is a defect that destroys the continuity of metal. Figure 4 Fibrous fracture
Figure 7 Crack (layered) fracture
Hairline fracture
Figure 5 Crystalline asymmetry
Bubble fracture
Attached:
GB2971—82
Figure 9 Non-metallic inclusions and central fracture
Figure 10 Fracture of metallurgical inclusions
Figure 11 Shrinkage residual fracture
This standard is proposed by the Ministry of Metallurgical Industry of the People's Republic of China. This standard is drafted by Anshan Iron and Steel Company.
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