GOST 5639-82

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  ГОСТ 5639-82

GOST 5639−82 of Steel and alloys. Methods of detection and determination of grain size (with Change No. 1)

GOST 5639−82

Group B09

INTERSTATE STANDARD

STEELS AND ALLOYS

Methods of detection and determination of grain size

Steels and alloys. Methods for detection and detеrmination of grain size

ISS 77.080.20
AXTU 0909

Date of introduction 1983−01−01

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the Ministry of ferrous metallurgy of the USSR

2. APPROVED AND put INTO EFFECT by Decision of the USSR State Committee for standards from 26.08.82 N 3394

3. REPLACE GOST 5639−65

4. REFERENCE NORMATIVE AND TECHNICAL DOCUMENTS

5. Limitation of actions taken by Protocol No. 2−92 of the Interstate Council for standardization, Metrology and certification (ICS 2−93)

6. EDITION (August 2003) with amendment No. 1, approved in March 1987 (IUS 6−87)


This standard specifies the metallographic methods for detection and determination of grain size of steels and alloys.

Metallographic methods to determine:

the size of the actual grain (after hot deformation or any heat treatment);

the tendency of grain growth — definition of grain size of austenite after heating at a temperature and exposure time established by normative-technical documentation for steel and alloys;

growth kinetics of grain — definition of grain size after heating in the temperature range and exposure time established by normative-technical documentation for steel and alloys.

1. SAMPLING

1.1. Place of sampling and number of samples for the determination of grain size established by the normative-technical documentation for steel and alloys.

1.1.1. In the absence of a sampling to determine the actual grain is carried out arbitrarily; to determine the propensity of grain growth and kinetics of growth of the sampling carried out at the point of selection for mechanical testing.

1.1.2. In the absence of guidance in the normative-technical documentation the test is performed on a single sample.

1.2. The cross-sectional area of the thin section the sample shall not be less than 1 cm.

For steel products with a thickness less than 8 mm can be manufactured in thin sections with an area less than 1 cm.

To determine the propensity of grain growth and kinetics of grain growth is allowed for sampling from forged bucket samples provided comparable results test results of finished products.

2. METHODS OF DETECTING GRAIN BOUNDARIES

2.1. The grain boundaries are revealed methods:

etching

cementation,

oxidation

mesh ferrite or cementite,

mesh perlite (troostite),

vacuum thermal etching.

The method is selected depending on the chemical composition of the steel and testing purpose.

2.1.1. Method of etching

2.1.1.1. The method of etching used to identify the boundaries of the actual grain and the grain boundaries of austenite in carbon and alloy steels, the martensite zakolebalsya or beynit, and steels, which are difficult to obtain ferrite or cementite lattice.

2.1.1.2. Identification of the boundaries of the actual grain is carried out on samples without additional heat treatment.

2.1.1.3. To identify the grain boundaries of the austenite heating temperature, holding time and cooling speed set of normative-technical documentation for steel and alloys.

If the heating temperature and the holding time is not specified regulatory and technical documentation, for low carbon steels the temperature must be (930±10)°C.

For other steels the temperature must be equal to or 20°C-30°C above the quenching temperature, the established regulatory and technical documentation.

The exposure time should be not less than 1 h and not more than 3 hours.

To more clearly identify the boundaries of the valid and austenitic grain samples are subjected to release of: carbon and low alloy steel — 225°C-250°C alloy steels and alloys at 500 °C and above, depending on the chemical composition.

2.1.1.4. With the surface of the sample is removed obesplozhennym layer, produce and microsection etched in the reagents are given in Appendix 1, or other, to clearly reveal the grain boundaries.

Universal reagent for etching steel — freshly prepared, saturated at room temperature an aqueous solution of picric acid with addition of 1%-10% of surface-active substances (surfactants) type Sintanol or detergents — «Progress», «Astra», shampoo «Lada» or other alkylsulfonate connections.

To more clearly identify the grain boundaries should be perepolirovka followed by etching and heating of the reagent to 50°C-70°C.

2.1.2. A method of carburizing

2.1.2.1. The method of carburizing is used to identify the grains of austenite in steels intended for carburizing, and nestsementirovannyh for carbon steels with a mass fraction of carbon up to 0.25%.

The grain boundaries are revealed in a cemented layer in the form of a mesh of secondary cementite.

2.1.2.2. Samples without traces of oxidation and decarburization is heated at a temperature (930±10)°C in a tightly closed box filled with fresh carburizer one of the compounds:

60% of charcoal, 40% barium carbonate; 70% charcoal 30% of sodium carbonate;

100% ready bondarenkovo carburizing;

100% polyanskogo of carburizer according to GOST 5535.

The size of the box is chosen depending on the number of samples, the distance between them in the drawer must be at least 20 mm.

The amount of carburizer must be 30 times the volume of the samples.

The exposure time after heating box — 8 h

Samples after carburizing cooled together with drawer up to 600 °C at different speeds: carbon steel not exceeding 150 °C per hour, the alloy is not more than 50 °C per hour. The rate of cooling of the samples below 600 °C per hour is not regulated.

2.1.2.3. Samples after carburizing or cut in half with one hand and remove the surface layer to a depth of 2−3 mm and are made of the micro-sections.

To identify mesh cementite sections are encouraged to veer into one of the reagents:

3% -5% solution of nitric acid in ethyl alcohol;

5% solution of picric acid in ethyl alcohol;

a solution of sodium picrate consisting of 2 g picric acid, 25 g of sodium hydroxide (caustic soda) and 100 cmof water (the electrolytic etching, the voltage at the terminals of the bath is 6−10 In the duration of the etch — a few seconds);

a boiling solution of sodium picrate (chemical etching, the etching time of 10−20 min).

2.1.3. Oxidation method

2.1.3.1. Oxidation method is used for structural and instrumental (carbon and alloy) steels.

The grain boundaries of austenite are detected on the grid oxides.

2.1.3.2. Samples with a polished surface is subjected to heating to a certain temperature and allowed to stand over time in accordance with clause 2.1.1.3. Heating is carried out in a vacuum or in a protective atmosphere.

For the oxidation of thin sections after aging, without reducing the temperature in the oven served in air for 30−60 s.

Allowed to apply for protection from oxidation during the heating process the thin section chips of cast iron, charcoal powder, an aqueous solution of sodium tetraborate, etc. subject to obtaining the results on the grain size corresponding to the obtained by the method of etching.

2.1.3.3. After cooling in water and polishing the samples etched in one of the reagents of the composition:

15 cmof hydrochloric acid, 75 cmof ethyl alcohol; 1 g picric acid, 5 cmof hydrochloric acid, 100 CCof ethyl alcohol; 5 cmof mechanicalbiological 10 cmof ethanol.

2.1.3.2, 2.1.3.3. (Changed edition, Rev. N 1).

2.1.3.4. Before the cooling in water the cone is allowed to process in the molten aqueous solution of sodium tetraborate (heated to a temperature of austenization) for 30−40 s. the grain Boundaries after treatment in an aqueous solution of sodium tetraborate identified without additional etching.

2.1.4. The method of mesh ferrite or cementite

2.1.4.1. The method of mesh ferrite or cementite are used to detect grain boundaries in zaevtektoidnyh (with a mass fraction of carbon up to 0.6%) and hypereutectoid steels, respectively.

2.1.4.2. Samples with any surface condition is subjected to heating to a certain temperature and time in accordance with clause 2.1.1.3.

For the formation of ferrite or cementite lattice at the grain boundaries, the samples are cooled to a temperature of 650 °C at different speeds depending on the steel grade.

For carbon steels with a mass fraction of carbon, 0,5%-0,6% cooling rate of 50°C-100°C per hour, for alloy and carbon hypereutectoid — 20°C-30°C per hour, for steels with a mass fraction of carbon of 0,25%-0,5% — air cooling.

2.1.4.3. After the heat treatment the sample is cut in half or grinding removes the superficial layer (obesplozhennym), polished and etched. Grain of austenite on the ferrite grid reveal by etching in a 4% strength solution of nitric acid in ethyl alcohol, on the grid of cementite — etching the reagents specified in clause 2.1.2.3.

2.1.5. Method mesh perlite (troostite)

2.1.5.1. Method for detection of grain boundaries on the grid perlite (troostite) used for carbon and low alloy steels with a similar composition to the eutectoid. The grain boundaries are identified timetravels mesh perlite in the transition zone of the specimen.

2.1.5.2. Samples with any surface condition is subjected to heating at a certain temperature and exposure time in accordance with clause 2.1.1.3.

To form a mesh perlite samples was cooled by immersion of half of the sample; the second half is cooled in air.

2.1.5.3. After the heat treatment the sample plane, perpendicular to the transition zone at the height of the water level, sanded to remove bezoperatsionnogo layer, is polished and etched in the reagent (3% -5% solution of nitric acid in ethyl alcohol or 5% solution of picric acid in ethyl alcohol).

2.1.6. The method of thermal vacuum etching

2.1.6.1 no. The method of thermal etching in vacuum using high temperature microscope is recommended to determine the kinetics of growth of austenitic grains.

The method is based on selective evaporation of the metal at the grain boundaries at high temperatures.

2.1.6.2. Samples of specific shape and size (depending on installation type) with a polished surface is placed in a high-temperature chamber, create a vacuum 0,0133−0,00133 PA (10-10mm Hg. calendar) and heated to a certain temperature.

To suppress the evaporation of metal from the surface of the cone at high temperatures (above 900°C) chamber serves inert gas (argon, at a pressure of 0.03−0.05 MPa (0.3 to 0.5 ATM.)), previously purified from oxygen and moisture.

When determining the grain of austenite in steels with a high content legkookisljajushchihsja elements (Al, CR, etc.) it is recommended to use protective screens — getters from metals having greater affinity to oxygen (TA, Ti, Cd, Zr, etc.).

2.1.6.3. The exposure time should be not less than 20 minutes, heating temperature is not lower than 800 °C.

2.1.6.4. Evaluation of grain size is performed under a microscope or on photomicrographs.

3. METHODS FOR DETERMINATION OF GRAIN SIZE

3.1. Grain metals are individual crystals of polycrystalline conglomerate, separated from each other adjacent surfaces called grain boundaries. The grain may be equiaxed and neravnovesnye. In the presence of doppelgangers grains consider the crystals along with the twins.

3.2. Grain size — the average value of the random grain sections in the plane of metallographic section is defined by methods:

visual comparison visible under the microscope, grains with standard scales are given in mandatory Appendix 2, with the definition of the number of grains;

counting the number of grains per unit surface of the cone, with the definition of average diameter and average area of grain;

counting intersections of grain boundaries by straight line segments with the conditional determination of the average diameter in the case of equiaxed grains, number of grains per 1 mmin the case neravnovesnykh grains;

measurements of the lengths of the chords under a microscope or with the use of photomicrographs determining the relative proportion of grains of a certain size;

ultrasonic.

These methods are used to estimate the grains having the shape close to the equiaxed.

The method of counting intersections of grain boundaries used for the assessment of grain size and elongated shape.

In the case of determination of grain size in various-grained structure of average dimensions (diameter, area of the grain) are not characteristics of the evaluation structure.

3.3. Method for the determination of grain size by comparison with reference scales

3.3.1. The grain size by comparison method is determined at magnification of 100. Allowed the use of increasing 90−105.

After viewing the entire area of the cone choose some typical ground and compared with the standards given in Annex 2 scales. The comparison can be carried out, observing the image in the eyepiece of the microscope on the frosted glass or the photograph.

3.3.2. Scales 1−3 are ten references in the form of a schematized grid, limiting the grain size. The standards given in the form of a circle with a diameter of 79.8 per mm, which corresponds to the area of 5000 mmor natural area on the thin section is 0.5 mm.

Standards are designed so that an increase of 100numbers of grains G correspond to the numerical values of grain size by the equation = 8 x 2, where is the number of grains per 1 mmsquare section.

3.3.3. Average numerical value of square of grain, number of grains in 1 mm, diameter and conventional diameter and also the number of grains on square 1 mm, corresponding to standard scale G (-3) — 14 given in table.1.

Table 1

3.3.4. Scale 1 and 2 are used for estimation of grain size in all steels and alloys, scale 3 for austenitic, in which after etching revealed the twins.

3.3.5. If the grain size in the sample is beyond the standards of the scales with numbers 1−10, use other magnifications. To translate the numbers of the benchmark while increasing 100use table.2 or more scales 1, 2.

Table 2

If the amount of grain used for the increase, other than those specified in table.2 and supplementary scales 1, 2, you should use the schedule given on the drawing to determine the value of the correction factor for the conversion magnification of the microscope at a magnification of 100

.

The number of grains are according to the formula

,

where is the number of the grain under magnification .

3.3.6. For a homogeneous structure adopts a structure corresponding to one of the standards of the scale. This structure is estimated by one number.

Various-grained structure consider the structure in which there are grains that differ from the main (dominant) numbers, which corresponds to one standard scale of more than 1 room and covering the socket area more than 10%. Such a structure is assessed by two or more numbers that are written in descending order of area occupied by them, for example: , .

If necessary, indicate the relative area percentage occupied by the grains each of these numbers, for example: (65%), (35%).

3.3.7. The discrepancy between the estimates of grain size by comparison method should be no more than one number.

3.4. A method of counting beans

3.4.1. The method consists in determining the number of grains per unit surface of the thin section (1 mm) and calculating the average area of grains and the average diameter of the grains.

3.4.2. Counting beans is carried out on the frosted glass of the camera of the microscope or on photomicrographs, which restrict the field of view of one of the flat shapes: circle with a diameter of 79,8 mm or square with sides of 70.7 mm, or a rectangle with dimensions of the sides 65х77, 60х83, 55х91 or 50x100 mm, which corresponds to 0.5 mmof the surface of the cone with increasing 100.

3.4.2.1. Count the number of grains that fall inside the selected shape (), and the number of grains crossed her boundaries (a) (see Annex 3).

The total number of grains () in the square 0.5 mmsections at magnification 100calculated by the formula

 — for the circle;

 — for a rectangle or square.

The number of grains per 1 mmsquare sections, determined by the formula .

3.4.2.2. If you use a different zoom different from 100, the number of grains per 1 mmof the surface of the cone, is determined by the formula

,

where is the total number of beans inside the shape bounding box of the cone or photos if you increase .

Increase pick up from calculation that on the surface was not less than 50 grains.

3.4.2.3. Counting beans is carried out in at least three characteristic points of the cone and the results calculated arithmetic mean value.

3.4.2.4. The average cross-sectional area of grains () in mmis determined by the formula

.

3.4.2.5. The average diameter of grain () in mm is determined by the formula

.

3.4.2.6. Comparison of the obtained values , and with values of the corresponding parameters in table.1 determine the number of grain size G.

An example of counting the number of grains per unit surface area of the cone is given in Appendix 3.

3.4.2.7. Permissible discrepancies in the results of the three definitions when counting the number of grains shall not exceed 50%.

3.5. Methods of calculation of intersections of grain boundaries

3.5.1. The method consists in counting the grains intersected by a line segment, and determining the average conditional diameter — in the case of equiaxed grains or the number of grains in 1 mm — in case neravnovesnykh beans.

3.5.2. Counting intersections of kernels in both cases is carried out on the frosted glass of the microscope or photomicrographs, which are several segments of arbitrary length (e.g., 80 or 100 mm at a magnification of 100, which corresponds to the length of 0,8 or 1 mm on the socket). The length of the segments chosen in such a way that each of them was crossed by not less than 10 grains, the increase is selected so that on the surface was not less than 50 grains. Calculate the points of intersection of straight lines with the grain boundaries. Grain on the ends of the line, not crossed it entirely, taking one grain.

Determine the total length of segments , expressed in millimeters actual size on the cone, and the total number of the intersected grains .

The measurements were carried out in at least five characteristic points of the cone.

Permissible discrepancies in the results of the five definitions when counting intersections should be no more than 50%.

3.5.3. Counting the number of intersections of equiaxed grains is carried out in two mutually perpendicular straight segments spent in each of five locations of the cone (see Annex 4).

The average nominal diameter of grain () in mm is calculated by the formula

,

where is the total length of the segments, mm;

the total number of grains crossed by long segments .

3.5.4. Neravnovesnykh the number of grains in 1 mmof the cone is determined on the thin sections made along and across the main axis of symmetry. In this case, straight line segments is carried out parallel to the axes of symmetry (see Annex 4).

The average number neravnovesnykh bean () 1 mmvolume of a cone is calculated by the formula

,

where 0,7 is a coefficient taking into account neravnomernosti grains;

 — the number of intersections of grain boundaries per 1 mm length in the longitudinal direction (along the axis of the elongated grains);

 — the number of intersections of grain boundaries per 1 mm length in the transverse direction;

 — the number of intersections of grain boundaries per 1 mm of length in the perpendicular direction.

3.5.5. The method of counting intersections of grain boundaries in high-speed steel (method Sneijder-Count) is to count intersections of grains and determining the average of their numbers in the interval 63.5 mm with the increase of 500and on a piece of 127 mm at magnification 1000.

Determination of the granules is usually carried out on hardened samples not less than 5 areas of the cone.

The result of the determination is the average number of the intersected grains.

The relationship between the average number of grains intersected on a segment 63.5 mm at magnification 500or on a piece of 127 mm at magnification of 1000, the corresponding number of grain on a scale and conditional classification of grain size given in table.3.

Table 3

3.6. A method of measuring a chord length of

3.6.1. The method is based on measuring of linear sizes of intervals, chords, intercept beans straight lines, and is used for the determination of grain size in various-grained structure.

3.6.2. Measurements of the lengths of the chords are:

directly under the microscope using the eyepiece with the line method (movable cone) for one or more lines in any direction on the cone;

for photomicrographs, in this case comply with the provisions of clause 3.5.2.

The measurements were carried out in at least five of the most typical fields of view, wherein each field of view carry out not less than three lines in any direction.

The total number of measurements depends on the uniformity of grain size, the required accuracy and reliability of the results.

For example, when the accepted reliability of 90% and error of 10% of the total number of intersections of the grains must be at least 250, at the reliability of 90% and error of 5% — not less than 1000.

3.6.3. The values of the lengths of the chords belong to a particular dimension group. It is recommended that the magnitude of the linear dimensions in groups to present a geometric series with a factor of 1.45. In this case, the dimension groups associated with grain size numbers (G) by the average conditional diameter.

Count the number of chord length of each size on all lines.

Determine the relative proportion of grains in percent with certain length of a chord formula

%,

where is chord length, mm;

 — number of grains with a chord length ;

 — the total length of the chords, mm.

.

In accordance with the laws of mathematical statistics can be calculated the following parameters: average nominal diameter (the average size of the chord ), the standard deviation (), coefficient of variation (), etc. the average nominal diameter is not a feature of various-grained structures (see p.3.3.6).

Example of determination of grain size in various-grained structure is given in Appendix 5.

3.7. To determine the grain size of the finished products is used the ultrasonic method. The essence of the method, the method of preparing reference samples, equipment and methods of control are given in Appendix 6.

3.8. Results detection and determination of grain size are recorded in the Protocol, the form of which is given in Annex 7.

ANNEX 1 (recommended). REAGENTS FOR THE DETECTION OF GRAIN BOUNDARIES IN STEELS AND ALLOYS BY ETCHING

ANNEX 1
Recommended

ANNEX 2 (mandatory). SCALE FOR THE DETERMINATION OF GRAIN SIZE

ANNEX 2
Mandatory

An increase of 100

Scale 1 (number of grains 1−6)

Scale 1 (7−10 grains)

Scale 2 (number of grains 1−6)

Scale 2 (number of grains 7−10)

Scale 3 (number of grains 1−6)

Scale 3 (7−10 grains)

ADDITIONAL SCALE 1 TO DETERMINE THE AMOUNT OF FINE GRAINS

An increase of 100, 200, 400, 800

2 ADDITIONAL SCALE TO DETERMINE THE AMOUNT OF LARGE GRAINS

An increase of 100, 50, 25

APPENDIX 3 (reference). AN EXAMPLE OF COUNTING THE NUMBER OF GRAINS PER UNIT SURFACE OF THE CONE AND CALCULATE THE AVERAGE AREA AND AVERAGE DIAMETER OF GRAIN

APPENDIX 3
Reference

The drawing shows one of the three most characteristic sections of the cone by increasing 100.

The diameter of the circle 79,8 mm.

The area of the cone is 0.5 mm.

Recording the results of counting the number of grains in three characteristic sections of the cone by increasing 100.

ANNEX 4 (reference). EXAMPLES OF COUNTING THE INTERSECTIONS OF THE GRAINS

ANNEX 4
Reference

Calculation of average nominal size (equiaxed grains) is represented as a table.1.

Table 1

Calculate the number of grains in 1 mmsections (neravnovesnye grain)

The drawing shows the scheme of the straight lines in three directions in two sections.

Recording the results of counting the number of intersections of kernels in five characteristic sections of the cone with increasing 100(line length of 50 mm, which corresponds to the length in thin section 0.5 mm) are shown in table.2.

Table 2

Note. If the count is conducted by increasing different from 100, the length of the segments used to divide the increase, the rest of the calculation is as under magnification of 100.

ANNEX 5 (reference). AN EXAMPLE OF ESTIMATING THE MAGNITUDE OF VARIOUS-GRAINED GRAINS IN THE STRUCTURE BY MEASURING THE LENGTHS OF THE CHORDS

ANNEX 5
Reference

In the drawing at magnification 400represents one of the five photomicrographs from randomly held it three straight line segments, each of length approximately 60 mm, so that the ends of the lines ended at the grain boundaries. All five photos were 15 segments with a total length of approximately 900 mm.

The length and number of lines in five fields of view selected according to the intersections of ~250 grains.

The results of the measurements are presented in the table.

From these data it follows that the structure of the investigated metal are present with a grain size of from chords of 0.0036 to 0,0232 mm. the highest number of grains (taking into account neighboring groups) are in two size group: 0,0110−0,0160 mm (9) and 0,0052−0,0076 mm (11).

The results are used to determine the standard deviation () from the average of the chord and the coefficient of variation (), which is calculated by the formula

,

where is the total number of measured chords equal ;

 — the average chord length calculated by the formula

.

The coefficient of variation is calculated by the formula

.

APPENDIX 6 (recommended). ULTRASONIC DETERMINATION OF GRAIN SIZE

APPENDIX 6
Recommended

1. The ultrasonic method used for determining average grain size, based on the attenuation of ultrasonic waves in polycrystalline material grain size.

2. Determination of grain size is in Rayleigh region scattering of ultrasound.

3. The frequency of ultrasonic vibrations is selected in accordance with the condition

,

where is the wavelength of the ultrasonic vibrations in the material, mm;

 — average diameter of grain, mm.

4. For determining grain size using ultrasonic structural analyzers, and ultrasonic flaw detectors.

5. The grain size is determined by the damping factor acompulsory method according to GOST 21120 or relative method.

6. For the determination of grain size by ultrasonic method pre-set dependence of attenuation of ultrasonic vibrations from the grain size on the test samples.

7. Test specimens shall be the maximum permissible number of grains in accordance with Annex 2 and table.1 of this standard.

Test specimens shall be made for each grade of steel or alloy, which is subjected to testing by ultrasonic technique. They should have the same thickness (or diameter) and the same surface finish, and controlled the metal.

8. The roughness of the contact surface should be not more than 2.5 µm according to GOST 2789.

APPENDIX 7 (recommended). TEST REPORT

ANNEX 7
Recommended

In the test report indicate:

grade of steel or alloy;

method for detection and determination of grain size;

the number of grain size;

average diameter, mm;

the average nominal diameter, mm;

the average cross-sectional area of the grain, mm;

the number of grains in 1 mm.