GB/T 34474.1-2017 English PDF (GBT34474.1-2017)

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GB/T 34474.1-2017: Determination of banded structure of steel -- Part 1: Micrographic method using standards diagrams
GB/T 34474.1-2017
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.040.99
H 24
Determination of Banded Structure of Steel - Part 1:
Micrographic Method Using Standards Diagrams
ISSUED ON: OCTOBER 14, 2017
IMPLEMENTED ON: JULY 01, 2018
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
Introduction ... 4
1 Scope ... 5
2 Normative References ... 5
3 Terms and Definitions ... 5
4 Overview and Application ... 6
5 Sampling ... 7
6 Preparation of Sample ... 10
7 Evaluation Methods ... 10
7.1 Observation method ... 10
7.2 Comparison method ... 10
7.3 Standard grading diagram ... 10
8 Test Report ... 12
Appendix A (Normative) Standard Grading Diagram ... 13
Determination of Banded Structure of Steel – Part 1:
Micrographic Method Using Standards Diagrams
1 Scope
This Part of GB/T 34474 stipulates the method of evaluation of the hypoeutectoid steel
banded structure (including ferrite band and the Class II structure banding) by the
comparative method.
This Part is applicable to the evaluation of the banded structure of hypoeutectoid steel
after plastic deformation, but not to the evaluation of the banded structure of carbide
band in hypereutectoid steel.
2 Normative References
The following documents are essential to the application of this document. For the
dated documents, only the versions with the dates indicated are applicable to this
document; for the undated documents, only the latest version (including all the
amendments) are applicable to this document.
GB/T 13298 Inspection Methods of Microstructure for Metals
GB/T 30067 Standard Terminology Relating to Metallography
3 Terms and Definitions
For the purpose of this document, the terms and definitions given in GB/T 30067 and
the following apply.
3.1 Banded structure
Alternating zone of microstructure that is eventually formed by the deformation and
elongation of the micro-segregation zone, and parallel to the processing direction,
during the plastic processing of steel.
NOTE: This refers to ferrite and Class II structure banding.
3.2 Class II structure banding
The band that is single or mixed together among other structures rather than ferrite,
4.8 Appendix A gives the grading atlas of the five series A~E. The level of each series
of diagrams ranges from 0 to 5; and these levels raise with the increase the following
factors, such as the number of ferrite bands, the degree of penetration through the field
of view, continuity and width. See 7.3 for the specific boundaries.
NOTE: When more non-equilibrium structures appear in the structure, the segregation of alloy
elements is not fully reflected. It is recommended to control the content of non-equilibrium
structures when using standard grading diagram; generally, the content of bainite is no more
than 30%.
5 Sampling
5.1 In general, the sample shall be taken on the product in the delivery state; and the
inspection area of the sample is about 200mm2 (20mm×10mm). Sampling method and
quantity are specified according to product standards or technical conditions.
5.2 If the product standard does not specify, the sampling method is as follows:
a) For steel with diameter or side length or thickness less than 25mm, the inspection
surface shall be the entire longitudinal section passing through the steel axis or
1/4 width, see Figure 1;
b) For steel with a diameter or side length greater than 25mm and less than or equal
to 40mm, the inspection surface is the entire longitudinal section from the center
to the edge, see Figure 2;
c) For steel with a diameter or side length greater than 40mm, the inspection surface
is a longitudinal sample from the outer surface to the middle part of the center,
see Figure 3;
d) For a flat steel with a thickness less than or equal to 25 mm, the inspection
surface is located in the full thickness section at 1/4 width, see Figure 4;
e) For flat steel with a thickness greater than 25mm and less than or equal to 50mm,
the inspection surface is located in a longitudinal section at 1/4 width, and 1/2
thickness from the center to the surface, see Figure 5;
f) For flat steel with a thickness greater than 50mm, the inspection surface is located
in a longitudinal section at 1/4 width, and 1/4 thickness from the center to the
surface, see Figure 6;
g) For flat steel with a thickness greater than 80mm, the inspection surface is
located in a longitudinal section at 1/4 width, and 20mm thickness from the center
to the surface.
6 Preparation of Sample
6.1 The inspection status of the sample shall be in accordance with the provision of
product standard or agreement. When not specified, it is recommended to inspect in
delivery state.
6.2 Grinding and erosion of the sample shall be carried out in accordance with the
provisions of GB/T 13298.
7 Evaluation Methods
7.1 Observation method
The following methods may be selected for inspection under the microscope:
a) Projection method: project the image of the banded structure on the screen,
which shall be guaranteed to be magnified 100 times. The actual field of view
diameter is 0.80mm; the image size projected on the screen is 80mm; and then
compare this image with the standard grading diagram;
b) Direct observation method: direct observation through the eyepiece, magnifying
100 times. The actual field of view diameter is 0.80 mm. A ruler with a field of
view diameter of ϕ80mm or field of view light bar may be used to determine the
inspection area.
7.2 Comparison method
7.2.1 When evaluating the banded structure in the steel, the level of the banded
structure shall be determined according to the following factors, such as the number
of ferrite bands, and the degree of the ferrite band through the field of view, continuity,
and the width of the ferrite band. When grading, the most serious field of view on the
inspection surface shall be selected for comparison and grading.
7.2.2 The grading results are expressed in numbers representing levels and letters
representing series, such as 1A, 3B, etc. Between two adjacent levels, a half level is
evaluated; for example, between level 2 and level 3, a level 2.5 is evaluated.
7.3 Standard grading diagram
7.3.1 The grading diagram of banded structure is composed of white and black two
types of structures; white is ferrite, black is Class II structure, see Appendix A.
7.3.2 The grading diagram of banded structure is divided into five series from A to E
according to carbon content:
a) A series: grading of the banded structure for steel with carbon content less than