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GB/T 34474 Determination of banded structure of steel consists of several parts as planned. This part is Part 1 of GB/T 34474.
This part is developed in accordance with the rules given in GB/T 1.1-2009.
This part was proposed by China Iron and Steel Association.
This part is under the jurisdiction of the National Technical Committee on Iron and Steel of Standardization Administration of China (SAC/TC 183).
Introduction
This part of GB/T 34474 mainly specifies the geometric distribution of the ferrite banding of hypoeutectoid steel, while does not strictly specify the composition of class II structure banding composition of class II structure banding.
This part is used for determining the banded structure of hypoeutectoid steel such as ferrite and pearlite in the nearly equilibrium state, and also for determining the banded structure of ferrite and other non-equilibrium structure.
Determination of banded structure of steel - Part 1: Micrographic method using standards diagrams
1 Scope
This part of GB/T 34474 specifies the method for determining the banded structure of hypoeutectic steel (including ferrite banding and class II structure banding) using comparison method.
This part is applicable to the determination of banded structure of plastically deformed hypoeutectoid steel, while not applicable to the determination of banded carbide of hypereutectoid steel.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 13298 Inspection methods of microstructure for metals
GB/T 30067 Standard terminology relating to metallography
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GS/T 30067 and the following apply.
3.1
banded structure
alternating microstructure banding parallel to the processing direction finally formed through deformation elongation in microsegregation area during steel plasticity processing
Note: herein it refers to ferrite and class II structure banding.
3.2
class II structure banding
banding composed of single or multiple structures (except ferrite), including pearlite, bainite and other non-equilibrium structures
Note: where determined, they participate in the rating as a structure class.
3.3
continuous banding
banding of the same class appearing in a view field, wherein, grains are separated only by grain boundaries and no structure of other class appears
4 General and application
4.1 This part describes the segregation degree of banded structure based on structure morphology.
4.2 Segregation occurring upon steel solidification forms regular arrangement during subsequent deformation; solid-state phase change is affected by microsegregation, which may generate alternately arranged banded microstructure. Such method describes the difference of banded microstructure morphology with the elongation in the deformation direction.
4.3 The microsegregation area formed due to eliquation is the root cause of the distribution of banded structure. The microsegregation area elongates in the subsequent deformation process to form a layered structure parallel to deformation direction. Other factors may also affect the formation of banded structure, such as the heating temperature and final forging temperature in hot processing, and the deformation rate in cold or hot processing. Hardenability and cooling rate determine decomposition and microstructure formation during phase change, wherein, the cooling rate of final phase change has the largest effect on the display degree of banded structure.
4.4 Banded structure will affect the uniformity of mechanical properties in each direction.
4.5 The results obtained by test may be used for inspecting product based on technical agreement between the supplier and the purchaser, comparing different manufacturing processes or process changes, or providing data for structure-property-application research.
4.6 The sample may have different banded structure levels after being subjected to different heat treatments, so the inspection state of the sample shall be indicated.
4.7 For the purpose of this part, the observed view field is compared with the diagram for rating, wherein, the magnification factor of standard diagrams is100X and the standard view field diameter is 80mm.
4.8 The rating diagrams for series A to E are given in Annex A. The levels of each series of diagrams range from 0 to 5, and increase with the increase of quantity, view field penetration, continuity and width of ferrite banding accordingly. See 7.3 for specific boundaries.
Note: where there are more non-equilibrium structures, the segregation of alloy elements is not fully reflected. It is recommended to control the content of non-equilibrium structure when using standard diagrams, generally, the bainite content is not greater than 30%.
5 Sampling
5.1 Generally, the sample shall be taken from the delivered products, of which the inspected area is about 200mm2 (20mm × 10mm). The method and quantity of sampling shall comply with the requirements of product standards or technical conditions.
5.2 If not specified in the product standards, the sampling method is as follows:
a) for steel with diameter, side length or thickness less than 25mm, the inspected surface is the entire longitudinal section through the steel axis or at 1/4 of the width, see Figure 1;
b) for steel with diameter or side length greater than 25mm but less than or equal to 40mm, the inspected surface is the entire longitudinal section from the center to edge, see Figure 2;
c) for steel with diameter or side length greater than 40mm, the inspected surface is the longitudinal sample in the middle part from the outer surface to center, see Figure 3;
d) for flat steel with a thickness of less than or equal to 25mm, the inspected surface is the through-thickness section at 1/4 of the width, see Figure 4;
e) for flat steel with a thickness greater than 25mm but less than or equal to 50mm, the inspected surface is the longitudinal section at 1/4 of the width and 1/2 of the thickness from the center to surface, see Figure 5;
f) for flat steel with a thickness greater than 50mm, the inspected surface is the longitudinal section at 1/4 of the width and 1/4 of the thickness from the center to surface, see Figure 6;
g) for flat steel with a thickness greater than 80mm, the inspected surface is the longitudinal section at 1/4 of the width and 20mm of the thickness from the center to surface.
Foreword i
Introduction ii
1 Scope
2 Normative references
3 Terms and definitions
4 General and application
5 Sampling
6 Preparation of sample
7 Determination method
7.1 Observation method
7.2 Comparison method
7.3 Standard diagrams
8 Test report
Annex A
(Normative)
Standard diagrams
