Method of determining metal and alloy grain size

FIELD: investigating or analyzing of materials.

SUBSTANCE: method comprises choosing a region on the visible image of grain structure of metal, applying two mutually perpendicular sets of secants, and measuring the lengths of the chords formed by intersecting of the boundaries of the grains by the secants. The grain size is determined from the measurements performed.

EFFECT: expanded functional capabilities.

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The invention relates to the field metallographic studies and analysis of materials, in particular to methods for determination of grain size of metals and alloys.

It is known that the grain size of metallic materials is one of the main indicators of quality of manufactured products, such as sheets of transformer steel, boiler tubes, pipes and fuel element cladding of nuclear power plants, wire filaments in electrical engineering and many others. Therefore, in the regulations on the production of such products the grain size is strictly regulated.

It is known that the real structure of metals contain grains of different sizes. In practice, there are two types of structures: homogeneous and grain size.

Homogeneous structure called a structure corresponding to one of poliatlonu scale GOST 5639. Such a structure evaluate one number.

Grain structure is considered a structure in which there is a grain different from the main, predominant, the number corresponding to a specific fototale scale GOST 5639 more than one room (see GOST 5639-82. Steel and alloys. Methods for detection and determination of grain size).

There are two types of raznozernistoy:

- island raznozernistoy, when some very large grains or group full-time is large or very small grains are randomly dispersed throughout the volume of the product;

- strokecol raznozernistoy, when the area of abnormally large or abnormally small grains played in bands with grains smaller or larger sizes (Say. Recrystallization of metals and alloys. Ed. Metallurgy,1987. - 316 C.).

The known method of determining the amount of grain metals, including production of cut, obtaining visible images of the grain structure of the metal structure, the choice of image structure representative of its region, which is applied to a group of random straight lines (hooking), measure the lengths of segments obtained from the intersection of random straight lines (clipping) boundaries visible on the representative image area of the grains, and then calculate the average of the segment, characterizing the average grain size (Devices and methods of physical metallurgy. Issue 1. Edited by F. Weinberg, M.: Mir, 1973. - 301 S.).

When using this method, the accuracy of determination of grain size very low, because the number of measured lengths of typically less than 200, but the grain size is judged by its average value, which is approximately characterizes only homogeneous structure.

Since this method estimates the grain gives an indication only of its average value, it cannot be used for estimation of grain size in raznozernistaya, want to have an idea about the maximum grain size, since both these values give a more complete picture of the degree of homogeneity of the structure, and this, in turn, characterizes the degree of homogeneity common structure-sensitive properties of all finished products.

There is also known a method of determining the amount of grain, including manufacturing of cut, obtaining visible images of the grain structure of the metal structure, the choice of image structure representative of its region, which is applied to a group of parallel equally-spaced hooking subsequent measurement values of the chords formed by the intersection of a representative area group intercept and the received set of measurements judged on the size of the grain. As a representative region choose the image maximum cross-section of one of the grains (A.S. No. 1397832, G01N 33/20, 88).

Using this method gives reliable results only for homogeneous structures, however, are selected as a representative area of only one grain with a maximum cross-section does not take into account any form of grains or the ratio of other size groups of grains present in the structures of the island or strokecol raznozernistoy. Therefore, when using this method for grain structures in General there is no possibility of the ity determination of grain size by this method.

The basis of the invention is the task of improvement of the method of determining grain of metals and alloys by changing the treatment conditions of the visible images of the grain structure of the metal structure, which results in the expansion of technological capabilities.

The problem is solved by the fact that in the method of determination of grain size of metals and alloys receive the visible image of the grain structure of the metal structure, choose the image patterns of a representative area that put a group of parallel equally-spaced hooking subsequent measurement values of the chords formed by the intersection of grain boundaries of a representative area of the image group intercept and the received set of measurements judged on the size of the grain, according to the invention as a representative region choose a set from 3 to 48 adjacent to each other grains, which is applied to two mutually perpendicular groups of equally spaced parallel intercept, the number of representative areas set depending on the kind of structure while the determination of grain size in a homogeneous structure performed on one representative region, determination of grain size in the structure of the island raznozernistoy carried out on areas with maximum and minimal is th raznozernistoy in two representative areas of the image patterns, at each selected site take into account the maximum and average size of grain, and in the case of determining the amount of grain in the structure with strokecol raznozernistoy choose three representative areas, while the grain size in such a structure determined separately in coarse-grained and fine-grained areas, and then on the boundary of the coarse-grained and fine-grained areas so that in this representative area was large and fine grains in equal amounts on occupied by them in the sample space.

The proposed number of grains obtained experimentally.

The proposed method differs from the method of the prototype so that the representative area includes from 3 to 48 grains, which is applied to two mutually perpendicular groups of equally spaced secants number of representative areas set depending on the kind of structure as specified.

The technical result of the proposed method in comparison with the prototype is expanding the technological capabilities of the method.

This is because as a representative region choose a set adjacent to each other of at least three grains, the number of representative areas depends on the type of structures. Furthermore, since the proposed method, for each representation of the positive areas put two groups of mutually perpendicular parallel equally-spaced hooking, it takes into account both the shape of the grains is different from the shape of a circle, while in the method-prototype drawing on one grain of only one group intercept can give reliable results only for grains having the shape of a circle, which in real structures is irrelevant, and all kinds of dimensional groups of grains.

In addition, using the proposed method does not require special training of the operator, in addition to knowledge of them standard metallographic methods of detection and determination of grain size in steels and alloys. This information about the grain size allows you to more accurately predict the structure-sensitive properties of the finished product, as well as qualified to install the heat treatment of the material to obtain regulatory documentation of grain size, which ensures the production of the finished product of the required quality.

Figure 1 shows a representative region of homogeneous structure with increasing x100.

Figure 2 shows two (a, b) representative field patterns with island raznozernistoy at magnification x100.

Figure 3 shows three (a, b, C) representative areas in the structure with strokecol raznozernistoy at magnification x100.

The proposed method is as follows.

Cut out and the products of metallographic samples polished, then polished the surface of the sample is subjected to chemical or electrolytic polishing and etching, and then using a metallographic microscope visible grain structure. After looking at all visible in the microscope image of the grain structure of the metal on the polished side of the sample is chosen on the viewed image of a representative region of the structure in a set of 3 to 48 adjacent to each other grains, which, for example, using the computer, put two mutually perpendicular groups of equally spaced parallel secants number of representative areas set depending on the type of structure, and the determination of grain size in a homogeneous structure performed on one representative region, as indicated in figure 1, and the determination of grain size in the structure of the island raznozernistoy carried out on areas with maximum and minimum raznozernistoy two representative areas of the image patterns, as indicated in figure 2, with each selected area take into account the maximum and average size of grain, and in the case of determining the amount of grain in the structure with strokecol raznozernistoy choose three representative areas, as indicated in figure 3, the grain size in such a structure is ur determined separately in coarse-grained and fine-grained areas, and then on the boundary of the coarse-grained and fine-grained areas so that in this representative area was large and fine grains in equal amounts on occupied by them in the sample space. Measurements chords carry out all representative areas and the results determine the maximum, average grain size and number of the relevant standard.

Specific examples.

Example 1.

Of pipe sizes h,5 mm (steel 08KH18N10T) made the cut, which is to reveal the microstructure protravel in nitric acid and using a metallographic microscope MIM-7 image of the uniform patterns on flat cut, presented in figure 1.

Then, selecting one representative area visible in the microscope homogeneous structure consisting of 43 grains, put this image in bold line, in the computer, and struck him two groups mutually perpendicular intercept total number of 400, and then measured the lengths of the chords, i.e. all segments, obtained from the intersection of the clipping lines and grain boundaries of the representative area, and got the following numerical characteristics grain size:

- the average diameter of 21.5 μm;

number of grain per GOST 5639-8, which corresponds to the result that was obtained by a known method ASALA - Shvartze - Saulteau The (Saulteau. Stereometric metallography. - M.: Metallurgy, 1970).

The average diameter of the grains obtained by the method prototype was 21.4 mm, which also corresponds to 8 grain number on HOST.

As can be seen from this example, determination of grain size on the prototype method for homogeneous patterns gives the same result as proposed.

Example 2.

Of pipe sizes 12×1.0 mm (steel 08KH18N10T) made the cut, which is to reveal the microstructure protravel in nitric acid and using a metallographic microscope MIM-7 image of the patterns on the flat cut, presented in figure 2.

Then in the resulting image selected two bold line, representative of the area visible in the microscope varying grain patterns with the minimum () and maximum (b) raznozernistoy, consisting of 46 and 36 grains, respectively, have entered this image into the computer and put each of them on two groups of mutually perpendicular intercept total number of 400, and then measured the lengths of the chords, i.e. all segments, obtained from the intersection of the clipping lines and grain boundaries of the representative area, and got the following numerical characteristics of grain size.

For the region as:

- the average diameter 43,0 mm, which corresponds to the number 6 grain according to GOST 5639;

- maximum diameter of 165 microns; which corresponds to but is ERU 2 grains according to GOST 5639.

For region b:

- average diameter to 26.7 microns; which corresponds to the number 7 grain according to GOST 5639;

- maximum diameter of 90 microns; which corresponds to the number 4 grains according to GOST 5639.

These data are consistent with the results that were obtained by a known method ASALA - Shvartze - Sailtime (Saulteau. Stereometric metallography. - M.: Metallurgy, 1970).

The average diameter of the grains obtained by the method prototype, was 163,2 μm, which corresponds to 2 the number of grains on HOST.

As you can see, the prototype method, you can determine the average diameter of the grain only for a group of maximum grain size that completely characterizes raznozernistoy real structure.

Example 3.

Of pipe sizes 12×1.5 mm (steel 08KH18N10T) made the cut, which is to reveal the microstructure protravel in nitric acid and using a metallographic microscope MIM-7 image of the patterns on the flat cut, presented in figure 3.

Then in the resulting image selected three bold line, representative of the area visible in the microscope varying grain patterns in coarse-grained (a)fine (b) and the border areas with small and large grains (b)consisting of 48, 9 and 44 grains, respectively, introduced sequentially to these representative areas in the computer and put it on to the introduced each of them two mutually perpendicular intercept total number of 1000, then I measured the lengths of the chords, i.e. all segments, obtained from the intersection of the clipping lines and grain boundaries of the representative area, and got the following numerical characteristics of grain size.

For the region as:

- the average diameter of 15.2 mm, which corresponds to the number 9 grain according to GOST 5639;

- maximum diameter of 45 μm, which corresponds to the number 6 grain according to GOST 5639.

For region b:

- the average diameter of 39.8 μm, which corresponds to the number 6 grain according to GOST 5639;

- maximum diameter of 70 μm, which corresponds to the number of 4 grains according to GOST 5639.

For the field:

- the average diameter of 23.6 mm, which corresponds to the number 7 grain according to GOST 5639;

- maximum diameter of 75 μm, which corresponds to the number of 4 grains according to GOST 5639.

These data are consistent with the results that were obtained by a known method ASALA - Shvartze - Sailtime (Saulteau. Stereometric metallography. - M.: Metallurgy, 1970).

The average diameter of the grains obtained by the method prototype, was 74.3 mm, which corresponds to 4 number of grain at HOST.

As you can see, the prototype method, you can determine the average diameter of the grain only for a group of maximum grain size that completely characterizes raznozernistoy real structure, since it does not take into account the amount of grain other size groups.

When you exit offer before the crystals, as the number of grains included in the representative region, and the number of representative areas, all considered variants were observed deterioration of the technological possibilities of determining the amount of grain.

Thus, the use of the proposed method compared with the method of the prototype allows the expansion of technological capabilities of the method.

The method of determination of grain size of metals and alloys, which receive the visible image of the grain structure of the metal structure from scratch, choose the image patterns of a representative area that put a group of parallel equally-spaced hooking subsequent measurement values of the chords formed by the intersection of grain boundaries of a representative area of the image group intercept and the received set of measurements judged on the amount of grain, characterized in that as a representative region choose a set from 3 to 48 adjacent to each other grains, which is applied to two mutually perpendicular groups of equally spaced intercept, the number of representative areas set depending on the type of structure, determination of grain size in a homogeneous structure performed on one representative region, determination of grain size in the structure of the island is anotherstate carried out on areas with maximum and minimum raznozernistoy in two representative areas of the image patterns, at each selected site take into account the maximum and the average grain size, and in the case of determining the amount of grain in the structure with strokecol raznozernistoy choose three representative areas, and the grain size in such a structure determined separately in coarse-grained and fine-grained areas, and then on the boundary of the coarse-grained and fine-grained areas so that in this representative area was large and fine grains in equal amounts on occupied by them in the sample space.