1 Scope
This document specifies a metallographic method for determining the level of non-metallic inclusions in metal powders using powder forging specimens. The method requires powder forged specimens to be forged with as little lateral flow as possible (<1%) and requires the central area of the powder forged specimen to be free of visible porosity when examined at a magnification of 100 x.
This document is suitable for testing the content of non-metallic inclusions in powder forged parts. In the case of parts with significant lateral material flow, the proximity separation distance needs to be adjusted or the size of the inclusions to be adjusted can be determined by agreement between the parties concerned.
This document does not apply to the determination of the level of non-metallic inclusions in internally porous forgings. Residual porosity can be difficult to distinguish from inclusions during the amplification of the test. Too much residual porosity makes the determination of the distribution of inclusions difficult.
This document can be applied to the testing of materials containing manganese sulphide (pre-blended or pre-combined), for which an adjustment of the near-neighbour separation distance from 30 u.m to 15 um is required.
2 Normative references
The following documents constitute essential provisions of this document by means of normative references in the text. Where a reference is dated, only the version corresponding to that date applies to this document; where a reference is not dated, the latest version (including all amendment sheets) applies to this document.
ASTMB796 Standard test method for nonmetallie inclusion content of powders intended for powder forging (P/F) applications]
ASTM E3 Standard guide for preparation of metallographie specimens
ASTME768 Standard guide for preparing and evaluating specimens for automatic inclusion assessment of steel
3 Terminology and definitions
There are no terms and definitions that need to be defined in this document.
4 Principles
Prior to metallographic grinding and polishing, a section is cut from the specimen (part) with a central area representative of the specimen (part) (mounting is optional, but post-mounting polishing of the cut specimen is strongly recommended).
The polished specimens are examined under a microscope at 100 x magnification to mark inclusions larger than the preset size. The maximum Ferret diameter is used to characterise the inclusions. The Ferret diameter is the caliper diameter, as shown in Figure 1.
5 Significance and function
5.1 The level of non-metallic inclusions in iron powders is an indicator of the cleanliness of the powder. In pressed and sintered iron-based powder metallurgy (PM) materials, the presence of a large number of pores masks the effect of inclusions on mechanical properties. In contrast, the properties of powder metallurgical materials machined to near non-porosity are significantly influenced by the composition, size, size distribution and location of non-metallic inclusions.
5.2 Detection of non-metallic inclusions in fully dense steel parts for:
--To classify or distinguish the characteristics of different grades of powder or batches of parts;
- to compare the quality levels of powders used in powder forging from batch to batch.
5.3 The content of non-metallic inclusions will change significantly if:
-- the powder used to form the specimen (part) does not meet the requirements of the quality standard for non-metallic inclusions;
--the specimen (part) is processed in such a way that the following reactions occur: oxidation and/or reduction.
5.4 The use of the near-neighbour concept provides a more conservative assessment of inclusions: the content is usually overestimated rather than underestimated.
6 Instrumentation
6.1 Sample preparation equipment: for the preparation of specimens for metallographic testing.
6.2 Metallographic microscope: can be magnified 100 x for observation and measurement, light wavelength of 544 nm (green filter), objective magnification of 8 x to 12.5 x, numerical aperture of 0.16-0.20.
Note: It is important to define the optics used, as they determine the object characteristics that can be resolved by the microscope to assess the size of the inclusions.
6 Instrumentation
6.1 Sample preparation equipment: for the preparation of metallographic test specimens.
6.2 Metallographic microscope; can be magnified 100 × for observation and measurement, light wavelength of 544 nm (green filter), objective lens magnification of 8 × 12.5 ×, numerical aperture of 0.16 ~ 0.20.
Note: It is important to define the optics used, as they determine the object characteristics that can be resolved by the microscope to assess the inclusions size.
7 Specimens
7.1 In order to assess the content of non-metallic inclusions in powders for powder forging, the powder should be mixed with an appropriate amount of graphite and lubricant and pressed to a specified raw density. The test method requires the smallest possible lateral flow during forging (≤1%) and therefore the diameter of the pressed billet relative to the diameter of the dolly shall accordingly meet this requirement.
7.2 Metallographic specimens should be taken from powder forging specimens (parts), austenitised and quenched. Specimen heat treatment to avoid soft inclusions caused by dragging effect and scratching, to facilitate sample preparation.
7.3 The polished surface area of the specimen (part) to be examined should be not less than 350 mm good for small parts, allowing the detection of multiple sections to obtain the area required for measurement.
7.4 The polished surface should be parallel to the direction of force, i.e. the forging direction, and should be representative of the central area of the specimen (part).
8 Test procedure
8.1 Specimen preparation
When polishing the specimen, it is important to obtain a clean polished surface and that the inclusions are not pitting, trailing or obscured. Therefore, the procedures specified in ASTM E3 and ASTM E768 should be followed. An automatic grinding and polishing procedure is recommended. The specimen should be inspected in the polished condition and should not be affected by any previous corrosion (if any).
8.2 Determination of the content of non-metallic inclusions
8.2.1 The surface of the polished specimen is measured over an area of not less than 350 mm, at a magnification of 100 x, using a light wavelength of 544 nm (green filter), an objective magnification of 8 x to 12.5 x and a numerical aperture of 0.16 to 0.20.
8.2.2 Detection of inclusions size according to the nearest neighbour separation principle.
Two inclusions within 30 pm (0.03 mm) of each other (within 3 mm at 100× magnification) are considered to be the same inclusions.
8.2.3 Three inclusions with individual dimensions of less than 30 um and a distance of less than 30 um from each other are considered as one inclusions cluster according to the principle of nearest neighbour separation.
8.2.4 According to the principle of nearest neighbour separation, if two inclusions are within 30 um of each other, the individual inclusions smaller than 30 um are considered to be part of an inclusion larger than 30 um. An example is shown in Figure 2.
8.2.6 If the size of the inclusions is determined separately, the maximum Ferret diameter in 8.2.5 should also be used for dimensioning. The results of using the nearest neighbour separation concept are usually more conservative (larger inclusions are obtained).
9 Test report
The test report should include the following information:
a) the number of this document
b) Number of non-metallic inclusions per 100 mm2:
-length greater than or equal to 30 um;
-length greater than or equal to 100 um;
-length greater than or equal to 150 um;
c) whether the particle size of the inclusions is determined separately, in addition to using the principle of proximity separation; d) the total area examined.
10 Accuracy and deviation
Accuracy and deviation shall be expressed in accordance with ASTM B796. ,
1 Scope
2 Normative references
3 Terminology and definitions
4 Principles
5 Significance and function
6 Instrumentation
6 Instrumentation
7 Specimens
8 Test procedure
9 Test report
10 Accuracy and deviation
Standard
GB/T 41706-2022 Metallic powders—Test method for determination of non-metallic inclusions in metal powders for powder forging (English Version)
Standard No.
GB/T 41706-2022
Status
valid
Language
English
File Format
PDF
Word Count
5500 words
Price(USD)
165.0
Implemented on
2022-10-12
Delivery
via email in 1~3 business day
Detail of GB/T 41706-2022
Standard No.
GB/T 41706-2022
English Name
Metallic powders—Test method for determination of non-metallic inclusions in metal powders for powder forging
1 Scope
This document specifies a metallographic method for determining the level of non-metallic inclusions in metal powders using powder forging specimens. The method requires powder forged specimens to be forged with as little lateral flow as possible (<1%) and requires the central area of the powder forged specimen to be free of visible porosity when examined at a magnification of 100 x.
This document is suitable for testing the content of non-metallic inclusions in powder forged parts. In the case of parts with significant lateral material flow, the proximity separation distance needs to be adjusted or the size of the inclusions to be adjusted can be determined by agreement between the parties concerned.
This document does not apply to the determination of the level of non-metallic inclusions in internally porous forgings. Residual porosity can be difficult to distinguish from inclusions during the amplification of the test. Too much residual porosity makes the determination of the distribution of inclusions difficult.
This document can be applied to the testing of materials containing manganese sulphide (pre-blended or pre-combined), for which an adjustment of the near-neighbour separation distance from 30 u.m to 15 um is required.
2 Normative references
The following documents constitute essential provisions of this document by means of normative references in the text. Where a reference is dated, only the version corresponding to that date applies to this document; where a reference is not dated, the latest version (including all amendment sheets) applies to this document.
ASTMB796 Standard test method for nonmetallie inclusion content of powders intended for powder forging (P/F) applications]
ASTM E3 Standard guide for preparation of metallographie specimens
ASTME768 Standard guide for preparing and evaluating specimens for automatic inclusion assessment of steel
3 Terminology and definitions
There are no terms and definitions that need to be defined in this document.
4 Principles
Prior to metallographic grinding and polishing, a section is cut from the specimen (part) with a central area representative of the specimen (part) (mounting is optional, but post-mounting polishing of the cut specimen is strongly recommended).
The polished specimens are examined under a microscope at 100 x magnification to mark inclusions larger than the preset size. The maximum Ferret diameter is used to characterise the inclusions. The Ferret diameter is the caliper diameter, as shown in Figure 1.
5 Significance and function
5.1 The level of non-metallic inclusions in iron powders is an indicator of the cleanliness of the powder. In pressed and sintered iron-based powder metallurgy (PM) materials, the presence of a large number of pores masks the effect of inclusions on mechanical properties. In contrast, the properties of powder metallurgical materials machined to near non-porosity are significantly influenced by the composition, size, size distribution and location of non-metallic inclusions.
5.2 Detection of non-metallic inclusions in fully dense steel parts for:
--To classify or distinguish the characteristics of different grades of powder or batches of parts;
- to compare the quality levels of powders used in powder forging from batch to batch.
5.3 The content of non-metallic inclusions will change significantly if:
-- the powder used to form the specimen (part) does not meet the requirements of the quality standard for non-metallic inclusions;
--the specimen (part) is processed in such a way that the following reactions occur: oxidation and/or reduction.
5.4 The use of the near-neighbour concept provides a more conservative assessment of inclusions: the content is usually overestimated rather than underestimated.
6 Instrumentation
6.1 Sample preparation equipment: for the preparation of specimens for metallographic testing.
6.2 Metallographic microscope: can be magnified 100 x for observation and measurement, light wavelength of 544 nm (green filter), objective magnification of 8 x to 12.5 x, numerical aperture of 0.16-0.20.
Note: It is important to define the optics used, as they determine the object characteristics that can be resolved by the microscope to assess the size of the inclusions.
6 Instrumentation
6.1 Sample preparation equipment: for the preparation of metallographic test specimens.
6.2 Metallographic microscope; can be magnified 100 × for observation and measurement, light wavelength of 544 nm (green filter), objective lens magnification of 8 × 12.5 ×, numerical aperture of 0.16 ~ 0.20.
Note: It is important to define the optics used, as they determine the object characteristics that can be resolved by the microscope to assess the inclusions size.
7 Specimens
7.1 In order to assess the content of non-metallic inclusions in powders for powder forging, the powder should be mixed with an appropriate amount of graphite and lubricant and pressed to a specified raw density. The test method requires the smallest possible lateral flow during forging (≤1%) and therefore the diameter of the pressed billet relative to the diameter of the dolly shall accordingly meet this requirement.
7.2 Metallographic specimens should be taken from powder forging specimens (parts), austenitised and quenched. Specimen heat treatment to avoid soft inclusions caused by dragging effect and scratching, to facilitate sample preparation.
7.3 The polished surface area of the specimen (part) to be examined should be not less than 350 mm good for small parts, allowing the detection of multiple sections to obtain the area required for measurement.
7.4 The polished surface should be parallel to the direction of force, i.e. the forging direction, and should be representative of the central area of the specimen (part).
8 Test procedure
8.1 Specimen preparation
When polishing the specimen, it is important to obtain a clean polished surface and that the inclusions are not pitting, trailing or obscured. Therefore, the procedures specified in ASTM E3 and ASTM E768 should be followed. An automatic grinding and polishing procedure is recommended. The specimen should be inspected in the polished condition and should not be affected by any previous corrosion (if any).
8.2 Determination of the content of non-metallic inclusions
8.2.1 The surface of the polished specimen is measured over an area of not less than 350 mm, at a magnification of 100 x, using a light wavelength of 544 nm (green filter), an objective magnification of 8 x to 12.5 x and a numerical aperture of 0.16 to 0.20.
8.2.2 Detection of inclusions size according to the nearest neighbour separation principle.
Two inclusions within 30 pm (0.03 mm) of each other (within 3 mm at 100× magnification) are considered to be the same inclusions.
8.2.3 Three inclusions with individual dimensions of less than 30 um and a distance of less than 30 um from each other are considered as one inclusions cluster according to the principle of nearest neighbour separation.
8.2.4 According to the principle of nearest neighbour separation, if two inclusions are within 30 um of each other, the individual inclusions smaller than 30 um are considered to be part of an inclusion larger than 30 um. An example is shown in Figure 2.
8.2.6 If the size of the inclusions is determined separately, the maximum Ferret diameter in 8.2.5 should also be used for dimensioning. The results of using the nearest neighbour separation concept are usually more conservative (larger inclusions are obtained).
9 Test report
The test report should include the following information:
a) the number of this document
b) Number of non-metallic inclusions per 100 mm2:
-length greater than or equal to 30 um;
-length greater than or equal to 100 um;
-length greater than or equal to 150 um;
c) whether the particle size of the inclusions is determined separately, in addition to using the principle of proximity separation; d) the total area examined.
10 Accuracy and deviation
Accuracy and deviation shall be expressed in accordance with ASTM B796. ,
Contents of GB/T 41706-2022
1 Scope
2 Normative references
3 Terminology and definitions
4 Principles
5 Significance and function
6 Instrumentation
6 Instrumentation
7 Specimens
8 Test procedure
9 Test report
10 Accuracy and deviation
