GB 1814-79 — Steel Fracture Surface Inspection Method (English Translation)
GB 1814-79 — Steel Fracture Surface Inspection Method
Scope
This standard applies to hot-rolled, forged, and cold-drawn bars and billets of structural steels, free-cutting steels, tool steels, and spring steels. Other steel grades requiring fracture surface inspection may refer to this standard.
I. Specimen Preparation and Inspection Method
1. The quantity of specimens and sampling locations shall comply with the relevant technical specifications or the agreement between both parties.
2. Specimens shall be cut by cold cutting or cold sawing methods. When hot cutting, hot sawing, or gas cutting is used, the notch must be positioned away from the deformed zone and heat-affected zone.
3. For steel materials with diameter (or side length) not exceeding 40 mm, transverse fracture specimens shall be used. Specimen length shall be 100–140 mm, with a notch machined on one or both sides at the center of the specimen, as shown in Figure 1. When notching, the fracture cross-section shall retain no less than 50% of the original cross-section.
Figure 1 — Transverse fracture specimen (100~140 mm length)
4. The condition of the specimen before fracturing shall be such that defects are displayed truthfully. When special requirements are specified in technical specifications or agreements between parties, those requirements shall be followed. If quenching in oil is required before fracturing, the oil shall be cleaned off or burned off below 300°C prior to fracturing.
5. At room temperature, notch-down specimen is fractured. During operation, the notch should be placed downward so that the knife edge aligns with the notch center line, then fractured under impact loading. It is preferred to fracture the specimen in one strike; repeated hammering is strictly prohibited.
6. When fracturing specimens, proper measures shall be taken to avoid damage and contamination of the fracture surface.
7. The fracture surface shall be carefully examined with the naked eye. When identification is unclear, a magnifying glass of up to 10× magnification may be used.
8. Whether various fracture defects are permissible and the acceptance/rejection criteria shall be stipulated in the relevant technical specifications or agreements between both parties.
II. Classification of Fracture Types
9. Fibrous Fracture
Appears on the fracture surface as a uniform structure without luster and without crystalline grains. Significant plastic deformation is usually visible at the edges of such fractures (see Figures 3a, b, c).
10. Porcelain-like Fracture
A bright gray fracture with a silky luster, dense, resembling fine porcelain fragments (see Figure 4). This type of fracture commonly appears in hypereutectoid steels and certain alloy steels after quenching or quenching and low-temperature tempering. It is considered a normal fracture.
11. Crystalline Fracture
A silvery-gray fracture with strong metallic luster, obvious crystalline grains, and a flat cross-section (see Figure 5). This type commonly appears in hot-rolled or annealed steel materials (billets). It is considered a normal fracture.
12. Shelf-like Fracture
On longitudinal fracture surfaces, appears as flat plate-like (shelf-like) structures that are slightly lighter in color than the matrix, with slightly poorer deformability, and varying in width (see Figure 6). Shelf-like features generally develop in the head and middle sections of ingots with developed dendritic crystals. It results from fracture along coarse dendritic crystals. This defect has no effect on longitudinal mechanical properties; it slightly reduces transverse plasticity and toughness.
13. Tear-mark Fracture
On longitudinal fracture surfaces, appears as grayish-white, dense, smooth strips along the hot-working direction with poorer deformability. Distribution has no regular pattern; in severe cases, it covers the entire cross-section (see Figures 7a, b). Tear marks can develop throughout the ingot, generally more severe in the tail and lighter in the head. Minor tear marks have no obvious effect on mechanical properties; severe cases significantly reduce transverse plasticity and toughness.
14. Laminar Fracture
On longitudinal fracture surfaces, appears as strips without metallic luster, uneven and layered along the hot-working direction, accompanied by white or gray lines within the strips. This defect resembles rotten wood appearance and generally distributes within segregation zones (see Figures 8a, b). Laminar fracture is mainly caused by the presence of multiple parallel non-metallic inclusions.
15. Pipe Remaining Fracture
In the central zone of longitudinal fracture surfaces, appears as non-crystalline strips or loose zones, sometimes with non-metallic inclusions or slag entrapment. Oxidation color often appears along the strips (see Figure 9). Pipe remnants generally occur in the axial zone of the ingot head. Mainly caused by insufficient feeding of the ingot or insufficient cropping of the head.
16. Flake Fracture
On the fracture surface, mostly appears as round or oval silver-white spots, with granular structure inside the spots. Individual ones appear as duck-bill-shaped cracks. Flake size varies greatly and generally distributes within segregation zones (see Figure 10). Flakes are mainly caused by excessive hydrogen content in the steel combined with internal stress.
17. Blowhole Fracture
On longitudinal fracture surfaces, appears as smooth-walled, non-crystalline elongated strips along the hot-working direction. Mostly distributed near the surface (see Figure 11a), sometimes appearing internally (see Figure 11b). Blowholes are mainly caused by excessive gas in the molten steel, wet teeming systems, or rusty ingot molds.
18. Internal Crack Fracture
Common internal cracks are divided into “forging cracks” and “cold cracks.” Forging cracks appear as smooth planes or fissures resulting from sliding friction during hot working. Cold cracks appear as planes and fissures with clear boundaries from the matrix. Internal crack fractures mostly occur near the central axis and severely destroy the continuity of the metal.
19. Non-metallic Inclusion (Visible to Naked Eye) and Slag Entrapment Fracture
On longitudinal fracture surfaces, appears as non-crystalline fine strips or lump-like defects of different colors (white-gray, light yellow, yellow-green, etc.). This defect is caused by slag and refractory material impurities introduced during the steel teeming process.
20. Foreign Metal Inclusion Fracture
On longitudinal fracture surfaces, appears as strips with clear boundaries from the base metal, different deformability, different metallic luster and structure. This defect is caused by foreign metal dropping in or incomplete melting of alloying materials.
21. Black-brittle Fracture
On the fracture surface, appears as locally or entirely black-gray, with graphite-like particles visible in severe cases (see Figure 15). This defect commonly appears in annealed eutectoid and hypereutectoid tool steels, and silicon-containing spring steels. It is caused by graphitization of the steel.
22. Rock-candy Fracture
On the fracture surface, appears without metallic luster, light gray in color, angular, resembling magnetite block fragments. This defect is caused by severe overheating or burning. It reduces the plasticity and toughness of the steel, especially toughness.
23. Gammaroid Fracture
On the fracture surface, appears as bright spots or small facets with metallic luster. When illuminated with grazing light, these bright spots or small facets flash with gammaroid crystal-like luster. This defect is generally considered to be caused by overheating in alloy steels; for high-speed tool steels, it is caused by repeated quenching.
Note: The images attached to this standard are typical examples and not boundary/reference images.
Note: Effective from the implementation date of this standard, the original ministry standard YB/ZR 46-64 is cancelled.
Standard: GB 1814-79
Issued by: General Administration of National Standards, PRC
Proposed by: Ministry of Metallurgical Industry, PRC
Drafted by: Qiqihar Steel Plant
Implementation Date: September 1, 1980
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