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GB/T 13299-2022 English PDF (GBT13299-2022)

GB/T 13299-2022 English PDF (GBT13299-2022)

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GB/T 13299-2022: Determination of free cementite, pearlite and Widmanstatten structure in steel

This document specifies the methods of the cutting, preparation and determination of free cementite, pearlite and Widmanstaten structure specimens in steel. This document is applicable to the determination of free cementite, pearlite and Widmanstaten structure in low-carbon and medium-carbon steel plates, steel strips and steel rods (billets). For other steel types, this document may be taken as a reference.
GB/T 13299-2022
GB
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 77.040.99
CCS H 24
Replacing GB/T 13299-1991
Determination of Free Cementite, Pearlite and
Widmanstaten Structure in Steel
ISSUED ON: JULY 11, 2022
IMPLEMENTED ON: FEBRUARY 1, 2023
Issued by: State Administration for Market Regulation;
Standardization Administration of the PEOPLE Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative References ... 5
3 Terms and Definitions ... 5
4 Cutting and Preparation of Specimens ... 6
4.1 Cutting of Specimens ... 6
4.2 Preparation of Specimens ... 10
5 Determination Method of Free Cementite ... 10
5.1 General Principle ... 10
5.2 Comparison Method with Standard Rating Pictures ... 11
5.3 Quantitative Analysis Method with an Image Instrument ... 12
6 Determination Method of Pearlite ... 13
6.1 General Principle ... 13
6.2 Determination Method ... 13
7 Determination Method of Widmanstaten Structure ... 14
7.1 General Principle ... 14
7.2 Determination Method ... 14
8 Test Report ... 15
Appendix A (normative) Standard Rating Pictures of Free Cementite ... 17 Appendix B (informative) An Example of Quantitative Analysis of Cementite in SPCC Steel ... 26
Appendix C (normative) Standard Rating Pictures of Pearlite ... 31
Appendix D (normative) Standard Rating Pictures of Widmanstaten Structure ... 40 Bibliography ... 46
Foreword
This document was drafted in accordance with the rules provided in GB/T 1.1-2020 Directives for Standardization - Part 1: Rules for the Structure and Drafting of Standardizing Documents. This document serves as a replacement for GB/T 13299-1991 Steel - Determination of Microstructure. In comparison with GB/T 13299-1991, apart from structural adjustments and editorial modifications, the main technical changes are as follows:
---Terms and definitions are added (see Chapter 3);
---The cutting and preparation of specimens are added (see Chapter 4);
---The magnification ?€?400 times (360 ~ 450 times allowed)?€? for the determination of free cementite and pearlite is modified into ?€?500 times?€?; the magnification ?€?100 times (95 ~ 110 times allowed)?€? for the determination of Widmanstaten structure is modified into ?€?100 times?€? (see 5.2, 6.2 and 7.2; 4.1 of Version 1991);
---The principle of dividing different series of free cementite is modified (see 5.2.3; 5.1 of Version 1991);
---The dimensional requirements of free cementite and pearlite rating series are modified (see Table 1 and Table 2; Table 1 and Table 2 of Version 1991);
---The relevant content of the determination method of banded structure is deleted (see 5.3 and A3 in Appendix A of Version 1991);
---The relevant content of the quantitative analysis method of the image instrument for the determination of free cementite is added (see 5.3);
---The requirements for the recording of the contents ?€?serial No. of this document, specimen status, test date and tester?€?s name?€? are added (see Chapter 8); ---The standard rating pictures of free cementite and pearlite are modified: the pictures with a magnification of 400 times are modified into pictures with a magnification of 500 times (see Appendix A and Appendix C; A1 and A2 in Appendix A of Version 1991). Please be noted that certain content of this document may involve patents. The institution issuing this document does not undertake the responsibility of identifying these patents. This document was proposed by China Iron and Steel Association.
This document shall be under the jurisdiction of National Technical Committee 183 on Steel of Standardization Administration of China (SAC/TC 183).
The drafting organizations of this document: Shanxi TAIGANG Stainless Steel Co., Ltd.; SHOUGANG Group Co., Ltd.; China Metallurgical Information and Standardization Institute; Determination of Free Cementite, Pearlite and
Widmanstaten Structure in Steel
1 Scope
This document specifies the methods of the cutting, preparation and determination of free cementite, pearlite and Widmanstaten structure specimens in steel.
This document is applicable to the determination of free cementite, pearlite and Widmanstaten structure in low-carbon and medium-carbon steel plates, steel strips and steel rods (billets). For other steel types, this document may be taken as a reference.
2 Normative References
The contents of the following documents constitute indispensable clauses of this document through the normative references in this text. In terms of references with a specified date, only versions with a specified date are applicable to this document. In terms of references without a specified date, the latest version (including all the modifications) is applicable to this document. GB/T 13298 Inspection Methods of Microstructure for Metals
3 Terms and Definitions
The following terms and definitions are applicable to this document.
3.1 Ferrite
Ferrite refers to ???-Fe solid solution containing alloying elements.
[source: GB/T 30067-2013, 2.2.247]
3.2 Pearlite
When the carbon content in iron-carbon alloy is greater than 0.025% and less than 6.67%, a metastable microstructure formed when local regions in austenite tend to be eutectoid. This structure is formed by slow cooling in the process of eutectoid transformation, which is an alternating lamellar structure formed by ferrite and cementite.
[source: GB/T 30067-2013, 2.2.348]
3.3 Free Cementite
Free cementite refers to granular cementite that exists independently on the ferrite matrix or grain boundaries.
NOTE: the free cementite in low-carbon annealed steel with a carbon content of no more than 0.15% is mainly a product of pearlite transformation, and a small amount of tertiary cementite may also exist; the free cementite in ultra-low carbon steel (with a carbon content of less than 0.02%) is tertiary cementite.
3.4 Pearlite Colony
Pearlite colony refers to a bounded aggregate of sheets of the same phase with the same orientation.
[source: GB/T 30067-2013, 2.2.349]
3.5 Widmanstaten Structure
Widmanstaten structure refers to a structure, in which, pearlite exists, in hypoeutectoid steel, when proeutectoid ferrite grows from the austenite grain boundary or within the grain along a certain grain plane of the austenite, and precipitates in the form of needles. [source: GB/T 30067-2013, 2.2.268, modified]
4 Cutting and Preparation of Specimens
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). See the suggested specific sampling positions and methods in Figure 1 ~ Figure 6 (in which, Position A is applicable to the sampling of Widmanstaten structure specimen; Position B is applicable to the sampling of free cementite and pearlite specimens). 4.1.2 Sampling method of steel plate or steel strip
The sampling of steel plate or steel strip is as follows:
a) Steel plate or steel strip with a thickness less than or equal to 25 mm: the specimen is cut from the middle part from the center of the steel plate (strip) to the outer surface; the inspection surface shall be a full-thickness section (see Figure 1); the length of the specimen is recommended not to be less than 20 mm;
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:
a) Series A: the cementite is distributed along the grain boundaries in the form of a network; it is determined in accordance with the ratio of the portion surrounded by the cementite network on the periphery of individual ferrite grains and the completeness of the cementite network;
b) Series B: the cementite is distributed in single-layer, double-layer or multi-layer chain; it is determined in accordance with the particle size of free cementite, the distribution degree of chain layer and the length of chain;
c) Series C: the cementite is point-shaped; it is determined in accordance with the particle size of the point-shaped cementite and the degree of banded distribution of cementite.
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. Conduct random measurement of not less than 5 fields of view. The positions of the 5 fields of view can be at the edge, quarter or center of the specimen; the specific positions can be agreed upon by the supply-side and the demand-side. If there is no clear stipulation, randomly measure 5 fields of view at a quarter of the thickness of the specimen; take the average value of the 5 fields of view as the final measurement result of the percentage composition of free cementite; 2 decimal places shall be retained. The specific determination method can refer to GB/T 15749 or GB/T 18876.1.
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. Generally, when U95rel is not greater than 30%, the measurement result is valid. If U95rel is greater than 30%, the number of fields of view shall be increased, until U95rel is not greater than 30%. Appendix B provides an example of quantitative analysis of cementite in SPCC steel.
6 Determination Method of Pearlite
6.1 General Principle
This method is applicable to the determination of pearlite in steel plates, steel strips and steel rods (billets) with a carbon content of 0.1% ~ 0.30%.
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:
a) Series A: applicable to the rating of granular pearlite in cold-rolled steel with a carbon content of 0.10% ~ 0.20%. The larger the level, then, the cementite particles aggregate and tend to form bands;
b) Series B: applicable to the rating of fine-grained pearlite colony in hot-rolled steel with a carbon content of 0.10% ~ 0.20%. The larger the level, then, the granular pearlite transitions to lamellar pearlite forming deformation bands (and forms split bands);
c) Series C: applicable to the rating of pearlite in hot-rolled steel with a carbon content of 0.21% ~ 0.30%. The larger the level, then, the fine flaky pearlite transitions from a colony structure with less uniform size and uniform distribution to an uneven band structure. At this moment, it shall be determined in accordance with the width of the continuous band constituted by pearlite aggregation.
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 Determination Method of Widmanstaten Structure
7.1 General Principle
This method is applicable to the determination of Widmanstaten structure in steel plates, steel strips and steel rods (billets) with a carbon content between 0.15% ~ 0.50%. 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:
a) Series A: applicable to the Widmanstaten structure rating of steel with a carbon content of 0.15% ~ 0.30%.
b) Series B: applicable to the Widmanstaten structure rating of steel with a carbon content of 0.31% ~ 0.50%.
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.
8 Test Report
The test report should include the following contents:
a) Designation, batch No. and specification of steel;
b) Serial No. of specimen;
c) Serial No. of this document;

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