GB/T 13299-2022Determination of free cementite, pearlite and Widmanstaten structure in steel (English PDF)

4.1 Cutting of Specimens

4.1.1 Cutting positions Under general circumstances, the specimens shall be cut from the steel (or intermediate billet) in the delivery state; the sampling method and sampling size shall comply with the stipulations of the product standards or technical conditions. If there is no special stipulation, the inspection surface of free cementite and pearlite specimens shall be parallel to the longitudinal axis of steel strips, steel plates and steel rods (billets); the inspection surface of Widmanstaten structure specimen shall be perpendicular to the longitudinal axis of steel strips, steel plates and steel rods (billets).

4.1.2 Sampling method of steel plate or steel strip The sampling of steel plate or steel strip is as follows:

4.1.3 Sampling method of steel rod or steel billet The sampling of steel rod or steel billet is as follows:

4.1.4 Method of specimen cutting The specimen shall be cut through a mechanical method in a cold state that does not affect the structure of the specimen. If gas cutting or hot cutting is adopted for the cutting, the melting zone, heat affected zone and plastic deformation zone shall be completely removed.

4.2 Preparation of Specimens The grinding and polishing of the specimens shall be carried out in accordance with the stipulations of GB/T 13298.4% nitric acid ethanol solution should be adopted for the etching of the specimens. The etching effect shall be subject to the clear display of structural characteristics.

5.2 Comparison Method with Standard Rating Pictures

5.2.1 Place the specimen under the bright field of a metallographic microscope for observation; the magnification is 500 times. The diameter of the field of view of the magnified image is 80 mm. Observe the entire inspection surface; select the most serious field of view on the inspection surface. During the determination, compare the most serious field of view of free cementite on the inspection surface with the standard rating pictures in Appendix A for rating, so as to determine the level of the free cementite.

5.2.2 In accordance with the characteristics of the cementite, such as. shape, distribution and size, determine the rating of the free cementite.

5.2.3 In accordance with the structural characteristics, the rating pictures of free cementite are divided into three series.

5.2.4 The pictures of each series are from Level 0 to Level

5.Table 1 provides a detailed description of the structural characteristics of each level.

5.2.5 The determination results are expressed in levels, and the characteristics of the levels are between two adjacent levels, and half levels can be added. If necessary, a series of letters shall be marked, such as. 1.0A and 2.5B, etc.

5.3 Quantitative Analysis Method with an Image Instrument

5.3.1 The metallographic manual measurement method (grid cut point method and microscope scale method) or metallographic image analysis software can be adopted to determine the area content of free cementite. The magnification shall adopt 500 times.

5.3.2 Calculate the standard deviation s of the results, the expanded uncertainty U95 and the relative expanded uncertainty U95rel of the probability 95%. The relative expanded uncertainty is an estimate of the relative precision of the measurement mean; the change of the number of fields of view will affect the relative precision.

6.2 Determination Method

6.2.1 Place the specimen under the bright field of a metallographic microscope for observation; the magnification is 500 times. The diameter of the field of view of the magnified image is 80 mm. Observe the entire inspection surface; select the most serious field of view on the inspection surface for determination. During the determination, compare the most serious field of view on the inspection surface with the standard rating pictures in Appendix C for rating, so as to determine the level of the pearlite.

6.2.2 In accordance with the characteristics of the pearlite, such as. structure (granular, fine- grained pearlite colony or flaky), quantity and distribution, determine the rating of the pearlite.

6.2.3 In accordance with the structural characteristics, the rating pictures of pearlite are divided into three series.

6.2.4 The pictures of each series are from Level 0 to Level

5.Table 2 provides a detailed description of the structural characteristics of each level.

6.2.5 The determination results are expressed in levels, and the characteristics of the levels are between two adjacent levels, and half levels can be added. If necessary, a series of letters shall be marked, such as. 1.0A and 2.5B, etc.

7.2 Determination Method

7.2.1 Place the specimen under the bright field of a metallographic microscope for observation; the magnification is 100 times. The diameter of the standard field of view is 80 mm. Observe the entire inspection surface; select the most serious field of view on the inspection surface. During the determination, compare the most serious field of view on the inspection surface with the standard rating pictures in Appendix D for rating, so as to determine the level of the Widmanstaten structure.

7.2.2 In accordance with the quantity and size of the precipitated acicular ferrite and the size of ferrite network, determine the level of the Widmanstaten structure.

7.2.3 In accordance with the structural characteristics, the rating pictures of Widmanstaten structure are divided into two series.

7.2.4 The pictures of each series are from Level 0 to Level

5.Table 3 provides a detailed description of the structural characteristics of each level.

7.2.5 The determination results are expressed in levels, and the characteristics of the levels are between two adjacent levels, and half levels can be added. If necessary, a series of letters shall be marked, such as. 1.0A and 2.5B, etc.