GB 2971-82 – Method of Fracture Test for Carbon and Low Alloy Steels

UDC: 669.14/.15 : 620.18

National Standard of the People’s Republic of China

Promulgated: 1982-05-25 | Implemented: 1982-12-01

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Scope

This standard specifies the fracture test method applicable to carbon structural steels, low-alloy structural steel plates, bars, and sections. It may also be used as a reference for fracture testing of other steels.

1 Sample Preparation

1.1

The location and quantity of samples shall be specified by relevant standards or mutual agreement. When no sampling location is specified, for longitudinally rolled plates, samples shall be taken from the central third of the width at the end, perpendicular to the rolling direction. For transversely rolled plates, samples shall be taken from any location at the end, perpendicular to the rolling direction. For bars, samples shall be taken from the end. For sections, samples shall be taken from the end at the same location as the tensile test specimen.

1.2

Sample blanks may be cut by sawing, shearing, or flame cutting, but sufficient machining allowance must be left to eliminate the deformed zone and heat-affected zone.

1.3

When the steel thickness is ≤ 30 mm, the specimen width shall be twice the steel thickness. When the thickness is > 30 mm, the specimen width shall be 1.5 times the steel thickness, but not less than 60 mm. The specimen thickness shall equal the steel thickness. The specimen length may be 150-300 mm.

A sharp notch shall be made on one side perpendicular to the steel surface at the center of the specimen, with a depth equal to one-third of the specimen width, as shown in Figure 1.

1.4

For bars with diameter (or side length) ≤ 40 mm for transverse fracture testing, the specimen length may be 100-150 mm. A sharp notch shall be made on one side at the center of the specimen, with a notch depth equal to one-third of the diameter (or side length).

1.5

For bars with diameter (or side length) > 40 mm for longitudinal fracture testing, transverse specimens shall be cut with a thickness of 30-20 mm. A sharp notch shall be made on the centerline of the specimen cross-section, with a notch depth equal to one-third of the specimen thickness.

When difficulty is encountered in breaking, the notch depth may be appropriately increased, but shall not exceed half of the diameter (or thickness).

2 Test Method

2.1

Testing shall be conducted at room temperature (10-35°C). The specimen shall be broken by dynamic loading. During operation, the notch shall be placed facing downward so that the blade aligns with the notch centerline, then the specimen is broken.

2.2

When breaking the specimen, damage and contamination of the fracture surface shall be avoided.

2.3

The fracture shall be examined with the naked eye. If identification is unclear, a magnifying glass of up to 10× may be used for observation.

2.4

Whether various types of fracture defects are permissible and the acceptance limits shall be specified in relevant standards or mutual agreements.

3 Fracture Structure and Defect Classification

3.1 Fibrous Fracture

The fracture surface appears as dark gray fibrous texture, without luster and crystalline grain structure. The fracture edges generally show obvious plastic deformation. This is considered a normal fracture.

3.2 Crystalline Fracture

The fracture surface is flat, bright white, with strong metallic luster and obvious crystalline grain structure. This is considered a normal fracture.

3.3 Hairline Crack Fracture

Cracks of varying lengths appear on the fibrous fracture surface. The color is essentially the same as the matrix, sometimes appearing silver-bright with uneven fracture walls, mostly distributed in the center of the fracture.

3.4 Crack (Lamination) Fracture

Cracks of varying lengths are distributed irregularly on the fracture surface. The crack walls are relatively smooth and the color differs from the matrix. This is a defect that destroys the continuity of the metal.

3.5 Blowhole Fracture

Smooth-walled, non-crystalline elongated strips or oval smooth cavities appear on the fracture surface. Mostly distributed just below the surface, sometimes also appearing internally. This is a defect that destroys the continuity of the metal.

3.6 Non-metallic Inclusion and Slag Fracture

Non-crystalline fine strips or block defects in gray-white, light yellow, or yellow-green colors, visible to the naked eye, appear on the fracture surface without regular distribution. This is a defect that destroys the continuity of the metal.

3.7 Foreign Metal Inclusion Fracture

The fracture surface shows different structure and metallic luster from the matrix metal, with a clear interface between the inclusion and matrix metal, distributed without definite regularity. This is a defect that destroys the uniformity or continuity of the metal structure.

3.8 Pipe Remaining Fracture

In the axial center region of the fracture, non-crystalline structure strips or porous zones appear, sometimes with visible non-metallic inclusions or slag. Oxidation colors often appear along the strips. This is a defect that destroys the continuity of the metal.

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Original PDF Document

Below is the original PDF document (GB 2971-1982):

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This standard was proposed by the Ministry of Metallurgical Industry of the People’s Republic of China.

This standard was drafted by Baoshan Iron and Steel Company.

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