TPT January 2012

A rticle

3. Each element of the standard series is a monodisperse system of spheres of an equal diameter 4. To harmonise the numeric series of the new standard with the functioning standards, volumes of the monodisperse system spheres are taken equal to the volumes of the corresponding elements of the cubic model, ie the principle of geometric progression is preserved in the standard series 5. To determine the value of the structural 3D objects, structure reconstruction is made over the planar section and its initial data is distribution of chords in disperse intervals of the standard series obtained by any known quantitative method. The initial data are obtained in a planar section (microsection) by determination of chord dimensions in two mutually transverse directions 6. The structure reconstruction ismade using softwareSTRUCTURE 2001 [7] or other software used for the reconstruction of the spherical model of the equiaxial grain structure. The requirement of reconstruction is obtaining of distribution of standard sphere diameters (grain numbers) in a 3D space and numerical characteristics of this distribution the number of independent monodisperse spheres in a volume, average value of their diameters, deviations from the average value and variation coefficient determining grain anisotropy in the studied object in the space Table 3 shows data for assessment of grain size and anisotropy by the new standard in accordance with standards АSТМ Е112, DIN 50601 and GОSТ 5639. Figures 1 and 2 show examples of

assessment of a homogeneous and anisotropy structures in the specimens taken from cold-worked tubes of АSТМ316L steel type after rapid and furnace heating at 1150°C. As the above figures show, Coefficient of variation shows clearly anisotropy of the tube metal. It should be pointed out that the average value of diameters are determined in a volume, in a plane and in a chord, not only in a plane as the existing standards specify. The index of anisotropy r attitude of variation real structure (figure1, 2) can serve as toward the variation of flat cut of monodispersible spherical model (table 3). This method of assessment was used in [7] in the analysis of influence of the heating parameters on the grain size and structural anisotropy in cold-worked tubes made of corrosion-resistant steel of Kh18Н10Т, Kh17Н14МZB type and alloy Kh15N35МBТUR. Analysis of a great number of experimental data [1, 8-10] shows a high level of grain anisotropy in above Cr-Ni steels and other (16-15; 18-12; Х15Н35, Х25Н45 type) steels and alloys. It leads to the appearance of a significant unhomogeneity of physical-mechanical properties and can result in undesired consequences during service of the products from such materials. Analysis of these data makes it possible to draw the following conclusions: 1. Relative level of grain anisotropy for all studied materials subjected to isothermal heat treatment is higher (1.5 ≤ r ≤ 2.5) than during anisothermal heat treatment (1.52 ≤ r ≤ 1.8)

Table 3 : Parameters of grain structure according to the new standard

Grain number, G according to…

Parameters for the determination of grain size and grain anisotropy

In a volume

In a plane

In a line

Number of grains in 1mm 2

Diameter, D, μm

Coefficient of variation

Diameter, d, μm

Coefficient of variation

Chord, l, μm

Coefficient of variation

GОSТ 5639 ASTM E112 DIN 50601

-3 -2 -1

-3 -2 -1

1 2 4 8

1240.7

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

974.4 689.0 487.2 344.5 243.6 172.3 121.8

0.2842 0.2842 0.2842 0.2842 0.2842 0.2842 0.2842 0.2842 0.2842 0.2842 0.2842 0.2842 0.2842 0.2842 0.2842 0.2842 0.2842 0.2842

815.1 576.4 407.6 288.2

0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36

877.3 620.4 438.7 310.2 219.3 155.1 109.7

00

0 1 2 3 4 5 6 7 8 9

0 1 2 3 4 5 6 7 8 9

0 1 2 3 4 5 6 7 8 9

16 32 64

23.8

144.1 101.9

128 256 512

86.1 60.9 43.1 30.5 21.5 15.2 10.8

72.1 50.9 36.0 25.5 18.0 12.7

77.5 54.8 38.8 27.4 19.4 13.7

1024 2048 4096 8192

10 11 12 13 14

10 11 12 13 14

10 11 12 13 14

9.0 6.4 4.5 3.2 2.2

16384 32768 65536 131072

9.7 6.9 4.8 3.4

7.6 5.4 3.8 2.7

120

J anuary 2012

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