GB/T 37598-2019Inspection of non-metallic inclusions in steel - Blue fracture test method (English PDF)

5.1 Sampling method

Cut a transverse steel sample. It may use hot-sawing, cold-sawing, flame sawing and cutting to cut. Sample thickness is 15mm~20mm. See Figure 1 for fracture sampling diagram. It shall ensure that deformation and heat-affected zone caused by sampling outside the fracture. On centerline of cross section of sample, inscribe V-groove through shaft. Groove depth shall make remaining sample thickness not less than 10mm.

Keys:

1 - Slotting;

2 - Rolling direction;

3 - Slice.

Figure 1 -- Fracture sampling diagram

5.2 Sampling quantity

Sampling quantity and sampling site shall be specified in product standard or agreed by supplier and purchaser. If not specified, it shall extract two samples on steel.

5.3 Sample preparation

5.3.1 When preparing fracture, place sample face down on fracturing machine

(or pressure testing machine) support table. Ensure that impact knife edge matches centerline of fracture sample groove. Then, under impact load (or pressure), break fracture sample once. Repeated stamping is prohibited. In order to ensure that the fracture is flush, it shall preheat sample.

5.3.2 In order to display non-metallic inclusion, perform bluing to sample

according to one of the following methods:

a) Heat sample in furnace to blue brittle temperature (300°C ~ 350°C). Take it out and quickly break it off to make sample at break at blue brittle temperature.

b) Heat broken sample to blue brittle temperature (300°C ~ 350°C), so as to make the fracture blue.

NOTE: For high-alloy steel, it may appropriately increase blue brittle temperature. But it shall not exceed 530°C.

6.1 On a fracture surface of dual fracture (usually selecting severe surface of

defect), visually inspect or use a magnification device not more than 10 times to observe the seize, quantity or distribution of non-metallic inclusion.

6.2 Equally divide fracture surface into three zones

surface zone, middle zone, central zone. Respectively use S, M, C to represent. See Figure 2 for fracture surface division.

Keys:

1 - Notch;

2 - Fracture;

3 - Rolling direction;

S - Surface zone;

M - Middle zone;

C - Central zone.

Figure 2 -- Fracture surface division

6.3 Determine fracture area. Measure length of each inclusion and inclusion

quantity of each zone. Ferritic strips, carbide strips, segregation lines or loose lines are easily confused with non-metallic inclusions. Pay attention to distinguish.

7.1 Record length of each inclusion of each sample in different zone. Calculate

the sum of lengths of inclusions on inspection area, that is, total length.

Calculate ratio of total length to inspection area, i.e., average length. For inclusions of which length is less than 1.0mm, width is less than 0.1mm, record quantity in original record. Do not participate in calculating ratio of total length to inspection area. Refer to Annex A for record of original inspection results.

7.2 According to requirements of product’s standard, record lengths, quantity of

non-metallic inclusions or maximum length of non-metallic inclusion of each sample.

7.3

Testing and inspection results shall comply with provisions of GB/T 8170.

Round values off to 0.1mm.