GOST R ISO 643-2015

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  ГОСТ Р ИСО 643-2015

GOST R ISO 643−2015 Steel. Metallographic determination of the observed grain size

GOST R ISO 643−2015

NATIONAL STANDARD OF THE RUSSIAN FEDERATION

STEEL

Metallographic determination of the observed grain size

Steels. Micrographic determination of the apparent grain size

OKS 77.040.99
AXTU 0709

Date of introduction 2016−08−01

Preface

1 PREPARED by the Federal state unitary enterprise «Central research Institute of ferrous metallurgy them.And.P.Bardin," on the basis of their own authentic translation into the Russian language of the international standard indicated in paragraph 4

2 SUBMITTED by the Technical Committee for standardization TC 145 «monitoring Methods of steel products"

3 APPROVED AND put INTO EFFECT by the Federal Agency for technical regulation and Metrology dated 16 October 2015 N 1568-St

4 this standard is identical with ISO 643:2012* «Steel. Metallographic determination of the observed grain size» (ISO 643:2012 «Steels — Micrographic determination of the apparent grain size»).
The name of the standard changed with respect to names specified international standard for compliance with GOST R 1.5−2012 (subsection 3.5).

In application of this standard should be used instead of reference standards, relevant national standards of the Russian Federation and interstate standards, details of which are given in Appendix YES

5 REPLACE GOST R ISO 643−2011


Application rules of this standard are established in GOST R 1.0−2012 (section 8). Information about the changes to this standard is published in the annual (as of January 1 of the current year) reference index «National standards» and the official text changes and amendments — in monthly information index «National standards» case of revision (replacement) or cancellation of this standard a notification will be published in the upcoming issue of the monthly information index «National standards». Relevant information, notification and lyrics are also posted in the information system of General use — on the official website of the Federal Agency for technical regulation and Metrology on the Internet (www.gost.ru)

1 Scope

This standard specifies the metallographic method for the determination of the observed size of the ferritic or austenitic grain in the steel. It describes the methods of revealing grain boundaries and of estimating the average grain size in specimens with a unimodal distribution of grain size. Although the grains have a three-dimensional shape, the plane of the microsection can cross the grain at any point from the angle of the grain to the maximum diameter of the grain, thus creating a wide range of grain sizes observed in the two-dimensional plane, even in the sample with perfectly matching grain size.

2 Normative references

The present standard features references to the following standards*:
________________
* The table of conformity of national standards international see the link. — Note the manufacturer’s database.


ISO 3785 Steel. Denote the axes of the test sample (ISO 3785, Steel — Designation of test piece axes)
_______________
Valid ISO 3785:2006 «the metal Materials. Marking the axes of the test specimens relative to the texture of the product."


ISO 14250 Steel. Metallographic evaluation of duplex grain size and its distribution (ISO 14250 Steel — Metallographic characterization of duplex grain size and distributions)

ASTM E112 Standard test methods for determining average grain size (ASTM E112, Standard Test Methods for Determining Average Grain Size)

3 Terms and definitions

This standard applies the following terms with the appropriate definitions:

3.1 grain (grain): a polygon is a Closed figure with more or less curved sides, which can be identified on the flat section of the sample prepared for metallographic examination.

The grain is divided into two types:

3.1.1 austenitic grain (grain austenitic): a Crystal with face-centered cubic crystal structure, which may contain or not contain annealing twins.

3.1.2 ferritic grains (ferritic grain): a Crystal with body-centered cubic crystal structure, which never contain annealing twins.
_______________
The grain size of ferrite is usually estimated for non-alloy steels with a carbon content of 0.25% or less. If the structure includes Islands of pearlite, the size of which is identical to the grain size of the ferrite, these Islands are also counted as ferritic grains.

3.2 number of grain (index): Positive, zero or negative value the number of grains Gthat is determined from the average number of grains mcalculated at the 1 mmarea of the microsection.

Note — By definition, G=1, if m=16, the rest of the rooms of the bean is determined by the formula m =8x2.

3.3 the intersection of grain N (intercept): Number of grains crossed by a straight or curved measuring line (see figure 1).

Note — Direct measurement lines usually end within the grain. Finite segments of these straight lines is calculated as ½ of the intersection. represents the mean value of several estimates of the number of grains crossed by a measuring line, and randomly applied in various places. divided by the true line length , usually measured in millimeters to determine the intersection number of grains per unit length of the measuring line .

3.4 the intersection of the grain boundary P (intersection): Number of points of intersection of the grain boundaries of straight or curved measuring line (see figure 1).

Figure 1 — Examples of counting border crossings and intersections P bean N

	Counting intersections of grains of N for a straight line on a single-grain structure, where arrows indicate the 6 intersections of the grains, and the numbers ½ and two linear segment ending inside the grains (2x½=1N) and N=7.
	Counting border crossings P with a straight line placed on a single-grain structure, where arrows indicate the 7 border crossings and P=7.

Figure 1 — Examples of counting border crossings P and intersections of grains N

Note — denotes the average value of the number of calculations of grain boundaries crossed by a measuring line, and randomly applied in various places. divided by the true line length , usually measured in millimeters to determine the number of grains per unit line length .

4 Denote

Designations used are given in table 1.


Table 1 — Symbols

Marking	Definition	The value
	The average area of grain in square millimeters
	The observed area of specimen in square millimeters	-
	The average grain diameter in millimeters
D	The diameter of the circle on the screen of frosted glass of the microscope or on photomicrographs limiting the reference image of the sample surface	79,8 mm (area=500 mm)
g	Linear increase (chosen as reference) microscopic image	Usually 100
G	The number of grain	-
K	The transition rate from a linear increase in gleads to a linear increase 100
	The average length of line of intersection, expressed usually in millimeters
	The actual line length divided by the magnification, in millimeters	-
m	The number of grains per square millimeter of the surface of the sample for the investigated area	(increase 100) (increase g)
M	The number of the nearest reference image of a standard scale, when g is not equal to 100	-
	Complete the equivalent number of grains counted in the image diameter, D(by increasing g)	-
	The number of grains completely inside a circle with diameter D	-
	The number of grains crossed by the circle of diameter D	-
	Complete the equivalent number of grains counted in the image with a diameter D(at magnification 100)
	The average number of grains crossed by a measuring line of length L	-
	The average number of intersections of grains per unit length of the measuring line
	The number of intersections of grains of one millimeter in the longitudinal directions	-
	The number of intersections of grains of one millimeter in transverse directions	-
	The number of intersections of grains of one millimeter in the direction perpendicular to the thickness	-
	The average number of intersections of grain boundaries measuring line, randomly applied in various places	-
	The average number of intersections of grain boundaries per unit length of the measuring line
Refer the directions correspond to the standard ISO 3785.

5 the essence of the method

The grain size detected by microscopic examination of the polished sample prepared by an appropriate method depending on the type of steel and the required information.

Note — If the order or product standard does not specify a method to identify the grain, the choice of this method is at the discretion of the manufacturer.

Determine the average grain size is characterized by:

a) a number of grain received:

— usually by comparison with standard scales to measure the grain size;

or by counting to determine the average number of grains per unit area;

b) or the average value of the length crossing the grain.

6 Selection and preparation of samples

6.1 Location selection

If the ordering or standard metal products not specified number of samples and locations in which they should be selected from metal, this issue is at the discretion of the manufacturer, although it has been shown that the accuracy of determining the grain size increases with increasing number of evaluated samples. It is therefore recommended to assess the sample of two or more. It should be borne in mind that samples should be representative for the bulk of its products (i.e. to exclude areas of highly deformed material, which, for example, at the ends of certain types of products or in places where cuttings samples were used shears, etc.).

The samples shall be polished in accordance with commonly used methods.

If the product standard or in the agreement with the purchaser not otherwise agreed, the polished plane of the sample should be longitudinal, i.e. parallel to the main axis of deformation in the deformed product. Measurement of the grain size on the transverse plane will cause errors if the shape of the grains is equiaxed.

6.2 identification of the boundaries of ferritic grains

Ferritic grain should be identified by etching in a 2−3% solution of nitric acid in ethyl alcohol or other suitable reagent.

6.3 identification of the boundaries of a valid and original grains of austenite

6.3.1 General information

In that case, if the steels have a single phase or two-phase austenitic structure (grain -ferrite in the austenitic matrix) at room temperature, the grain should be identified by etching. For single-phase austenitic corrosion-resistant steels most commonly used reagents for chemical etching are a solution of Aqua Regia in glycerol, reagent Kallinge (N 2), and Marble’s reagent. The best option electrolytic etching for single-phase and two-phase corrosion-resistant steels is the use of a 60% aqueous nitric acid solution at a voltage of 1.4 V for 60 to 120 s. Because this etching reveals the grain boundaries, but does not identify twin boundaries, typically using a 10% aqueous solution of oxalic acid at a voltage of 6 V and the etching time to 60 s, however, this appears less effective than the 60% solution of HNO.

For other steels, you should use one or the other of the following methods depending on the required information:

— method of etching a saturated aqueous solution of picric acid (see 6.3.2);

— method of controlled oxidation (see 6.3.3);

— the method of carburizing at 925 °C (see 6.3.4);

method of sensitization of the grain boundaries (see 6.3.7);

— other methods, specially agreed between the manufacturer and the customer when ordering.

Note — the First three methods are used to identify the boundaries of the original austenite grain, and other methods for austenitic manganese steels or austenitic corrosion-resistant steel (Annex A).


When conducting comparative tests of different methods to use the same heat treatment. Test results can vary significantly from one method to another.

6.3.2 Method of etching a saturated aqueous solution of picric acid

6.3.2.1 Scope

This method allows to reveal the grain boundaries of austenite formed during heat treatment of the sample. It is used for samples having the martensitic or bantou structure. This etching is effective, if the phosphorus content in steel is not less than 0.005%.

6.3.2.2 Preparation of samples

The reagent is usually applied to the heat treated steel samples. If the sample is in the martensitic Manitou or structure, subsequent heat treatment is usually not required. Otherwise, heat treatment is necessary.

If the mode of heat treatment of the sample is not specified in the international standard for the products and in the regulatory documents no additional requirements for structural carbon and low alloy steels subjected to heat treatment, use the following modes:

— 1.5 hours at a temperature of (850±10)°C for steels with carbon content more than 0.35%;

— 1.5 hours at a temperature of (880±10)°C for steels with a carbon content of less than or equal to 0.35 percent.

After the heating the sample is to be cooled in water or oil.

6.3.2.3 Polishing and etching

A flat surface of a sample to be polished for conducting metallographic studies. Then it is exposed to etching for an appropriate time in a saturated aqueous solution of picric acid with addition of at least 0.5% alkylsulfonate or other suitable surfactants.

Note — the duration of the etching may vary from several minutes to over one hour. Heating of the reagent to 60 °C to improve the etching effect and reduce the duration of etching.


To achieve enough contrast identification of grain boundaries in the sample is sometimes necessary to carry out several successive operations of etching and polishing of the sample. In the case of steel subjected to a through hardening, before cutting the sample can be carried out vacation products.

Warning — When heating solutions containing picric acid, it should not prevent complete evaporation of the solution, as picric acid can become explosive.

6.3.2.4 the Result

After identifying the boundaries of the original austenite grain sample should be immediately examined microscopically.

6.3.3 Method of controllable oxidation

6.3.3.1 Scope

This method allows to identify mesh boundaries of austenite grains formed by the selective oxidation boundaries during austenitization when the temperature of this heat treatment.

6.3.3.2 sample Preparation

One surface of the sample should be polished. The rest of its surface shall not show any traces of oxidation. The sample should be placed in a laboratory oven, in which either the vacuum is maintained at 1 PA or circulates an inert gas (e.g., argon purged). Heat treatment of the sample must correspond to the method of austenitization specified customer or specified in the standard for these products.

At the end of the specified period of heating in the oven should feed air to 10−15 C. Then the sample should be cooled in water. Then the sample can usually be immediately investigated under a microscope.

Notes

1 Oxidation of the sample can be carried out without using inert atmosphere.

2 Oxides observed on pre-polished surfaces should be removed by lightly polishing with fine abrasive, while preserving the oxide grid, which was formed at the grain boundaries; and then the polishing should be completed using conventional methods. After that you should carry out etching of a sample with a reagent containing:

— picric acid — 1 g;

— hydrochloric acid — 5 cm;

— ethyl alcohol — 100 cm.

6.3.3.3 Result

Selective oxidation of boundaries reveals the mesh boundaries of austenite grains. If sample preparation is performed correctly, the grain boundaries should not be observed globular oxides.

In some cases, clearer identification of boundaries may be necessary using methods oblique illumination or DICK (differential interference contrast).

6.3.4 Method of carburizing at 925°C

6.3.4.1 Scope

This method is intended for carburized steels and shows the grain boundaries of austenite, formed during carburizing these steels. The method is generally unsuitable for the detection of boundaries formed during other types of thermal treatment.

Note — Can also be used the method of «simulated ash». The sample undergoes the same thermal treatment, but in the absence of the atmosphere with high carbon content. Thereafter, it is subjected to heat treatment, which corresponds to the heat treatment of the investigated products. To identify the grain boundaries is used the reagent specified in 6.3.2.

6.3.4.2 the Case of samples

Samples should be no signs of surface decarburization or oxidation. Any previous treatment: cold, hot, mechanical, etc. can influence the shape of the obtained grains. In cases where it is recommended to take into account these considerations in the technical specifications for the products should indicate the processing which should be carried out before the determination of grain size.

After carburizing the specimen should be cooled with a sufficiently low speed to ensure the allocation of cementite at the grain boundaries in hypereutectoid surface area of the carbonized sample.

Carburizing should be carried out by exposure of the sample at (925±10)°C for 6 h. To do this in a carburizing furnace chamber is usually maintained at a temperature (925±10)°C for 8 h including the heating time. In most cases, the depth of the carbonized layer is approximately 1 mm., After carburizing the specimen should be cooled with a sufficiently low speed to ensure the allocation of cementite at the grain boundaries of the hypereutectoid zone of the carbonized layer.

Every time you should use fresh carburizing.

6.3.4.3 Preparation of samples

The carbonized sample is usually cut perpendicular to its carbonized surface. On one of the surfaces of the cut needs to be cooked grinding for metallographic examination, which should poison using the reagents of a) or b):

a) alkaline sodium picrate:

— picric acid 2 g;

— sodium hydroxide 25 g;

— water 100 cm.

Etching is carried out by immersing the sample into the reagent, heated to 100 °C, for at least 1 min, or by electrolytic etching at room temperature and a voltage of 6 V for 60 s;

b) alcoholic solution nitric acid:

— nitric acid is from 2 to 5 cm;

— ethyl alcohol to obtain a 100 cm.

You can use other reagents, giving the same results.

6.3.4.4 the Result

The grain boundaries of the initial austenite in hypereutectoid case-hardened surface layer will be contoured excessive cementite.

6.3.5 Method of mesh zaevtektoidnoj ferrite

Note — Recommendations for the use of this method depending on steel microstructure are given in Appendix A.

6.3.5.1 Scope

The method used for carbon steels with a carbon content of approximately 0.25% to 0.6% for low alloy steels such as manganese and molybdenum, 1% chromium, 1,5% chromium with molybdenum and 1.5% Nickel with chromium. The grain boundaries of the original austenite is detected in the form of a grid zaevtektoidnoj ferrite.

6.3.5.2 Preparation of samples

Use conditions austenitization specified in the product standard. In the case of carbon steels or other steels with low hardenability must be cooled samples in air with the oven or under a partial isothermal transformation so that the grains of austenite were outlined by ferrite.

In the case of alloy steels samples after austenitisation should be isothermal to cooling conditions of partial conversion at an appropriate temperature in the range from 650 °C to 720 °C and then cooling in water.

Notes

1 the Time required for the transformation varies depending on the chemical composition of the steel, but usually a sufficient amount of ferrite is allocated from 1 to 5 min, although in some cases may require more prolonged intervals, reaching 20 min.

2 In the case of alloy steels to obtain a uniform transformation during isothermal treatment it is advisable to use sample sizes 12х6х3 mm.

6.3.5.3 Polishing and etching

Should cut, Polish and etch the samples for metallographic investigations. For etching you must use an appropriate reagent, for example, containing hydrochloric acid or picric acid (6.3.3.2).

6.3.6 Method of tempering on the beynit or gradient hardening

Note — guidance on the use of this method, depending on the steel microstructure are given in Appendix A.

6.3.6.1 applications

This method is used for steels whose composition is close to eutectic, i.e. containing 0.7% of the masses. or more of carbon. The grain boundaries of the initial austenite are revealed in the form of a thin mesh perlite or bainite outlining grains of martensite.

6.3.6.2 Preparation of samples

The sample is heated to a temperature exceeding a point not more than 30 °C (i.e. the temperature at which completes the transformation of ferrite into austenite during heating) to provide a full austenitization.

The sample is cooled at a controlled rate to obtain a partially hardened structure of a thin layer of perlite or bainite outlining grains of martensite.

Such a structure can be obtained by one of the following ways:

a) by quenching in water or oil (as more appropriate) of the rod of such cross-sectional size, which provide complete quenching at the surface of the sample, but only a partial hardening in his mid;

b) by gradient hardening genuine rod with a diameter or a side of a square from 12 to 25 mm as the result of immersion in water only part of the length of the rod. After these operations, the sample is subjected to polishing and etching.

6.3.7 Sensitization of austenitic corrosion-resistant steels and manganese

The grain boundaries can be identified through the formation of carbides when heated in the temperature range of sensitization from 482°to 704 °C. For the detection of carbides may be any suitable reagent.

Note — This method should not be used for austenitic steels with very low carbon content.

6.3.8 Other methods of revealing grain boundaries of the original austenite

For some steel after simple heat treatment (annealing, normalizing, quenching and tempering, etc.) the grain boundaries of austenite can occur when microscopic examination in the following form: mesh zaevtektoidnoj ferrite surrounding the pearlite grains; mesh of very fine pearlite surrounding the grains of martensite, etc. of Austenitic grains can also be revealed by thermal etching in vacuum (not necessarily accompanied by oxidation). In such cases, these simplified methodsmust be specified in the technical specifications for the products.
_______________
These methods include:

— the formation of precipitates at the grain boundaries during cooling;

— gradient hardening.

7 Methods for determining grain size

7.1 evaluation of the number of grain

7.1.1 the Formula

The number of grains is determined in accordance with 3.2 according to the formula

. (1)

This formula can be represented in the form

(2A)

or

. (2b)

7.1.2 Evaluation by comparison with standard reference scales

The image obtained on the screen (or photomicrographs), compared with a number of standard imagesor transparent overlays (can also be used ocular insert, is intended to measure the grain size if they meet national or international standards). Standard image at magnification 100numbered digits from 00 to 10 in such a way that their number is equal to the number of grainG.
_______________
These reference scales are given in standard ACTM E 112 [(scale 1A and 1B) (Annex B) (the selected scale should be used throughout the study)].


Note — All standard images are given in Appendix To this if you increase 10. Numbers of grain from 00 to 2.5 and 3.0 to 10 used circles of different diameter. The standard for grain number of 1.0 corresponds to the same standard image for grain size number of 3.0, increased 2-fold, which is consistent with the formula (1).


The reference scale can be determined by standard image for the number of grains that is closest to the grain size in the studied fields of view of the sample. On each sample should be evaluated at least three randomly selected fields of view.

If the increase in g of the image on the screen or pictures is not 100, then the number of grainsG is determined by the number M closest to a standard image using the following function relationship increases

. (3)

Table 2 shows the dependence between grain for commonly used gains.


Table 2

Zoom	The number of grains of metal to the corresponding standard image
25	-3	-2	-1	0	1	2	3	4
50	-1	0	1	2	1	4	5	6
100	1	2	3	4	3	6	7	8
200	3	4	5	6	5	8	9	10
400	5	6	7	8	7	10	11	12
500	5,6	6,6	7,6	8,6	7,6	10,6	11,6	12,6
800	7	8	9	10	9	12	13	14

7.1.3 Planimetric method

This method of assessment is described in Annex C.

7.1.4 Evaluation of the accuracy of determining the number of grains

As in the evaluation by comparison method and evaluation method of calculating the accuracy of determining the number of grains rarely exceeds half of the unit. The resulting number of grains should be rounded to the nearest whole number.

7.2 Evaluation method of intersections

Count the number of grains N, or the number of grain boundaries Pcrossed the measurement line of known length on the projection screen of the microscope, the ocular insert, monitor, TV type or photomicrographs representative of the main square of the sample at a known increase in g.

The measuring line can be straight or circular. The measuring grid is shown in figure 2, shows the recommended types of measuring line.

Figure 2 — recommended measuring grid for a method of intersections

Figure 2 — recommended measuring grid for a method of intersections

The measuring grid should be imposed on the test field only once. To obtain reasonable count it is imposed arbitrarily by the corresponding number of fields.

The size of the three circles are in millimeters shall be as follows:

Diameter	The circumference
79,58	250,0
Of 53, 05	Of 166.7
Loss of 25.53	83,3
The total length of	500,0

7.2.1 Method of linear intersections

7.2.1.1 figure 2 shows the mesh lines that can be used to measure the grain size by the method of intersections. The total length of the three concentric circles is equal to 500 mm. the Use of circles allows you to average shape changes of equiaxed grains and to eliminate the problem of lines ending inside the grains. Figure 2 shows four straight lines: two lines, oriented diagonally, one vertically and one horizontally. The length of each diagonal line is equal to 150 mm, and horizontal and vertical lines have a length of 100 mm each.

Straight lines also averaged shape changes of equiaxed grains. On the other hand, if the draw ratio of the grains is of interest, the counting of grains can be performed using only vertical and horizontal lines (separately), placing them so that longitudinally oriented on a polished plane of the horizontal line is parallel to the axis of deformation (vertical and perpendicular, respectively, Kosi deformation) [see 7.2.3, enumeration)].

Magnification should be selected so that each field of view were at least 50 of the intersections of grains. You should evaluate at least five randomly selected fields for total number of intersections is not less than 250.

When counting the intersections of grains and grain boundaries in single-phase grain structures with straight measuring lines observe the following rules:

7.2.1.2 When counting the number of intersections of grain N:

— if the measuring line passes through the grain, N is 1;

— if the measuring line ends within the grain, N is equal to 0.5;

— if the measuring line touches the boundaries of the grains, N is equal to 0.5.

7.2.1.3 When counting the number of intersections of grain boundaries R:

— if the measuring line passes through the boundary, R is 1;

— if the measuring line touches the boundaries of the grain, R is 1;

— if the measuring line passes through the point of junction of three grains, R equal to 1.5.

Note — the Method of «Snyder-Graff», as described in Annex C is a method of linear intersections for tool steel (high speed steel).

7.2.2 Method of intersection of segments of a circle

It is recommended to use the circumference, as shown in figure 2.

The measuring line consists of three concentric circles, shown in figure 2, or from the same circle. The total length of the three circumferences recommended measuring grid shown in figure 2 is 500 mm or Increasing diameter of a circle should be chosen in such a way that when you overlay a measurement grid in the study the number of intersections of the grains ranged from 40 to 50.

In the case of a circle using the circumference of the largest diameter length of 250 mm. In this case, you should use increase, providing the count is not less than 25 intersections beans.

When using the method of intersections of segments of a circle obtained slightly higher values of lengths of segments that intersect the grain, and thus slightly lower the number of intersections of grain boundaries. To compensate for these inaccuracies, border crossing, occurring at the junction of three grains, is 1.5 intersection should consider them as two intersections, as is common when using the method of intersection of the line segments.

7.2.3 evaluation of the results

Count the number of intersections of grain N or grain boundaries R outfit randomly selected fields.

Determine the average value of the number of intersections of grain or cross grain boundaries .

If the actual length of the measuring line, and .

In the case neravnovesnykh grain structures can be conducted by counting the number of intersections of grain N or grain boundaries of Pusing straight lines, oriented parallel to the three principal directions. These three directions can be found on any two or three main planes of the sample (longitudinal, transverse and perpendicular to the specimen thickness).

The average number of intersections of grain per millimeter , or the average number of border crossings per millimeter is defined as the cubic root of the product of the measurements in three directions are

and ,

where the dash over the variables indicate that they are average values of several measurements, and x, u and z indicate the main directions (longitudinal, transverse and parallel to the thickness).

a) Grain, corresponding to different numbers of grain

In some cases the sample may contain a grain relating to two or more rooms grain. This can be identified by the presence of several grains that differ in size from other beans (see ISO 14250).

b) Grains with twins

Unless otherwise specified, these grains count as one grain, i.e., twin boundaries are not taken into account (figure 3).

Figure 3 — estimated number of grains (grains with twins)

Figure 3 — estimated number of grains (grains with twins)

c) Neravnovesnye grain

The shape of the grain can be estimated by the value of the ratio average length of line intersection in the warp direction and the average length of the line of intersection perpendicular to the warp direction, using a longitudinally oriented sample. This ratio is called the coefficient of traction of grains or coefficient anisotropy.

d) Modern methods of measuring grain size

To determine the grain size in the corresponding materials can be used ultrasonic methods, automatic image analysis, etc., provided that the accuracy of these methods was previously confirmed by the results of careful correlation tests.

8 test report

The test report shall contain:

a) the brand of the investigated steel;

b) the type of a certain grain;

c) the method used, test conditions, evaluation method (i.e. manual method or automatic analysis);

d) number of grains or the average grain diameter.

Annex a (informative). Review of the methods of revealing grain boundaries of ferrite, austenite and the original austenite in steels

Appendix A
(reference)

Method	Scope
Method of etching a saturated aqueous solution of picric acid (6.3.2)	Steel with structure of martensite, tempered martensite or bainite containing 0.005% phosphorus
Method of controllable oxidation of (6.3.3)	Carbon and low alloy steel
A method of carburizing at 925 °C (6.3.4)	Carburized steel
The method of simulating the carburizing (6.3.4)
The method of outlining the grain boundaries zaevtektoidnyh ferrite (6.3.5)	Coarse-grained carbon steel with a carbon content of between 0.26 percent and 0.6 percent, and low-alloy steel type Mn-Mo, 1% Cr, 1% Cr-Mo, 1.5% Cr-Ni
Method of tempering on the beynit or gradient hardening (6.3.6)	Coarse-grained carbon steel of approximately eutectoid carbon content, i.e. 0,7% 0,8%
Method of sensitization of the grain boundaries (6.3.7)	Unstabilized austenitic or two-phase corrosion-resistant steel with a carbon content > 0.025% of
The method of quenching and tempering (6.3.8)	Carbon steel
Direct etching using the appropriate reagent (6.2)	All single-phase steel
In austenitic manganese steels is a selection of fine carbides at the grain boundaries during aging at temperatures between 550 °C and 600 °C.

Annex B (mandatory). Determination of grain size. Scale reference

Appendix B
(required)

_______________
The scales are reproduced from ACTM E 112.


Scale 1A. Grains without twins (uniform etching) 100

Figure B. 1 — 1A Scale. Grains without twins (uniform etching) by increasing 100

Figure V. 1, sheet 2

Figure B. 1, sheet 3

Figure V. 1, sheet 4

Figure B. 1 sheet 5

Figure B. 1, sheet 6

Figure B. 1, sheet 7

1 V. scale of Grains without twins (uniform etching) 100

Figure B. 2 — Grains without twins (uniform etching)

Figure B. 2, sheet 2

Figure B. 2, sheet 3

Figure B. 2, sheet 4

Figure B. 2, sheet 5

Figure B. 2, sheet 6

Figure B. 2, sheet 7

Figure B. 2, sheet 8

Application (required). Evaluation method

Application
(required)

C. 1 Principle the planimetric method

Traditionally, measuring the diameter of 79,8 mm charted or put on a micrograph or image is projected on the screen of frosted glass. The increase was chosen so that the area of the circle containing not less than 50 grains. This recommendation was intended to minimize the counting error associated with the estimate of the round square.

Figure C. 1 — Evaluation of number of grains on the area bounded by a circle

Figure C. 1 — Evaluation of number of grains on the area bounded by a circle

Hold two counts:  — the number of grains completely inside the circumference, and the number of grains intersected by the circumference.

The total number of equivalent grains is

. (C. 1)

The number of grains per 1 mmof the sample surface m is determined from the formula

(C. 2)

or in the case of any increase in g

, (C. 3)

where 5000 is the area of a circle bounded measuring circumference, mm.

This approach assumes that on average half of the grains crossed by the measuring circle is the circle and the other half outside the circle. This assumption is true for a straight line passing through the grain structure, but not for the curve. The error resulting from this assumption increases with a decrease in the number of grains inside the measurement circle. If the inside measurement of the circle is not less than 50 grains, the error is about 2%.

A simple way to eliminate this error, regardless of the number of grains in the measuring circumference is to use a square or rectangle. However, in this case the method of calculation must be altered. First, assume that the grain crossing each of the four corners, there is an average of one quarter inside the shape and three-quarters out of it. Thus, the four corner grain together counted as one grain within the measuring figure.

Conceding four corner grain, tabulating the number of grains completely inside the rectangle , and the number of grains crossed by the four sides of the rectangle(figure C. 1). The expression C. 1 in this case takes the form:

. (P. 4)

Figure C. 2 — estimation of the number of intersections of grains and grain boundaries

Figure C. 2 — estimation of the number of intersections of grains and grain boundaries

The number of grains per 1 mmof the surface of the sample m is:

(S. 5)

where is the observed area of the figure used to estimate the number of grains, mm.

Average grain area, mm, is determined by the formula

. (P. 6)

A common method of calculating the mean diameter of grains was the use of the expression below. However, this approach is not recommended because it assumes that the grains are square in cross section, which is not true.

. (P. 7)

Each value G corresponds to the nominal value m. Table C. 1 shows the limit values m calculated from the formula (C. 2) (C. 3), for values of Gcorresponding to the whole numbers.

C. 2 Method Snyder-Graff

P.2.1 Scope

This method is used to determine the grain size of original austenite in quenched and tempered high speed steels, using the method of intersections beans straight lines.

P.2.2 Preparation of samples

The sample is typically taken from the product after quenching and tempering, is not subjected to any further heat treatment.

After polishing the specimen should etch in 10% nitric acid solution in ethyl alcohol. The etching has to be long enough for a clear detection of grain boundaries of the original austenite. Can take a few consecutive cycles of polishing/etching. The surface of the sample becomes more or less colored, depending on the type of heat treatment applied to the product.

P.2.3 Dimension

If you increase 1000must be counted the number of grains crossed by a measuring line length of 125 mm. you Must perform five calculations with different orientations of the measuring line in randomly selected fields.

P.2.4 results

If in technical conditions there are no other indications, the grain size is characterized by the mean value of the number of grains crossed with five counts. This value can be determined the average value of the crossing grain.


Table C. 1 — Determination of number of grains depending on various parameters

The number of grainG	The number of grains per 1 mm,M			The average grain diameter d, mm	Average grain area A, mm	The average length of the Peres- tion of grain , mm	The average number of pérez- values grains per 1 mm measure- tional line
Nomi- vocational value	The limit value
from (excl.)	up to (incl.)
-7	0,0625	0,046	0,092	4	16	3,577	0,279
-6	0,125	0,092	0,185	2,828	8	2,529	0,395
-5	0,25	0,185	0,37	2	4	1,788	0,559
-4	0,50	0,37	0,75	1,414	2	1,265	0,790
-3	1	0,75	1,5	1	1	0,894	1,118
-2	2	1,5	3	0,707	0,5	0,632	1,582
-1 (00)	4	3	6	0,500	0,25	0,447	2,237
0	8	6	12	0,354	0,125	0,320	3,125
1	16	12	24	0,250	0,0625	0,226	4,42
2	32	24	48	0,177	0,0312	0,160	6,25
3	64	48	96	0,125	0,0156	0,113	8,84
4	128	96	192	0,0884	0,00781	0,080	12,5
5	256	192	384	0,0625	0,00390	0,0566	17,7
6	512	384	768	0,0442	0,00195	0,0400	25,0
7	1024	768	1536	0,0312	0,00098	0,0283	35,4
8	2048	1536	3072	0,0221	0,00049	0,0200	50,0
9	4096	3072	6144	0,0156	0,000244	0,0141	70,7
10	8192	6144	12288	0,0110	0,000122	0,0100	100
11	16384	12288	24576	0,0078	0,000061	0,00707	141
12	32768	24576	49152	0,0055	0,000030	0,00500	200
13	65536	49152	98304	0,0039	0,000015	0,00354	283
14	131072	98304	196608	0,0028	0,0000075	0,00250	400
15	262144	196608	393216	0,0020	0,0000037	0,00170	588
16	524288	393216	786432	0,0014	0,0000019	0,00120	833
17	1048576	786432	1572864	0,0010	0,00000095	0,00087	1149
Note — this table lists the values of various parameters for equiaxed grains.

C. 3 an Alternative system for the determination of grain size

P.3.1. General characteristics

In addition to determining the grain size described in this standard, there is a different system used in the United States.

In this system (ACTM E-112) grain size is determined by the index G, called the grain room of the ACTM, as shown in p.3.2 and p.3.3

P.3.2 Method the average length of line intersection of grain

The number of grains G (ACTM)=0 corresponds to the average length of a line intersection of grain 32.0 mm, measured at the magnification of 100.

Expressions for the other numbers of grains, depending on:

— the average length of line intersection of grain

; (P. 8)

— the average number of intersections of grains per unit length (mm)

. (P. 9)

C. 3.3 Method of calculation

By definition, the number of grains G (ACTM)=1 and corresponds to 15.5 grains per unit area (mm).

The dependence of the other rooms from the number of grains per unit area (square millimeter) has the form

. (P. 10)

P.3.4 Numerical correlations between the various indicators of grain size in the case of regular structures

The number of grain ACTM corresponds to a slightly larger grain size than the same number of grains defined by the present standard, however, this difference does not exceed one-twentieth of unit numbers. This difference is negligible because the accuracy of the estimation of the grain size generally may not exceed half of the unit even under the most favorable conditions.

Expressions (2A) and (2b) given in 7.1 of this standard, may be represented in the form

. (P. 11)

Comparison of this expression with the expression (C. 10) shows that

.

App YES (reference). Compliance information reference standards to the national standards of the Russian Federation (and acting in this capacity inter-state standards)

App YES
(reference)

Table YES.1

Marking reference standard	The degree of compliance	Designation and name of the relevant national standard
ISO 3785:2006	-	*
ISO 14250:2000	IDT	GOST R ISO 14250−2013 «Steel. Metallographic evaluation of duplex grain size and distribution"
ASTM E 112−13	-	*
* The corresponding national standard is missing. Prior to its adoption, it is recommended to use the translation into Russian language of this international standard. The translation of this standard is the Federal information Fund of technical regulations and standards. Note — In this table used the symbol of compliance of the standards: — IDT — identical standards.

UDC 669.14:620.2:006.354	OKS 77.040.99	AXTU 0709
Keywords: steel, metallographic method determination of grain size