TPT January 2012

A rticle

Standard number

Structure parameter

ASTME112

GОSТ 5639

DIN 50601

G

G m = 8 . 2 G

G

N = 2 G-1 G = 10 – 2 log 2 l _ G = 10 + 2 log 2 N– L AE

log m log 2

Grain number

G =

– 3

m = 2 n

m = 2 n

100

100

N a

Number of grains in area of 1mm 2 1 inch 2

2

n

g 2

g

m = 2

,

n g

,

g

m =

100

A *) g - magnification; n - number of grains

g - magnification; n - number of grains

N ae

l m

l m

a =

a =

A–

Average grain section area, mm 2

l m

l m

d

d

=

=

d–

Average grain diameter, mm

m

m

Total length of line segments (chords), mm

L

L

L

= ∑ L

0

Total number of grains cut by line segment of length L ( L 0 ), pcs

N

N

N

= ∑ N

i

0

Average length of chords (segments, intersections) in the total length of the test line, mm

_

L

L

– L

0

d

=

=

l

L

S

N

N

0

) 1 – 3

N– A

= ( N

N

N

-

-

Average number of nonequiaxed grains: in 1 mm 2 in 1 mm 3

Al

At

Ap

N

= 0.7 N x

N

N

-

-

V

y

z

х) area of the circle confining the field of view

Таble 1 : Grain structure parameters determined by three standards

However they are not used in practice because of their laboriousness. They are used exceptionally for scientific needs or in reclamation of finished metal products. Development of computerised analysis methods makes it possible to reduce laboriousness of quantitative methods of assessment of grain structures and obtain the most comprehensive information. However the impossibility of making a reliable judgment on metal anisotropy in finished products using the standard functioning at present limits their use for a number of products made from new heat-resistant and corrosion-resistant alloys prone to grain anisotropy.

To make an objective assessment of the products made of materials prone to grain anisotropy, a new method was developed for quantitative assessment of parameters of spatial grain structures by their two-dimensional image in metallographic sections. Based on this method, an image analysis system [7] has been developed. It includes a structural analysis package which ensures obtaining of the following basic characteristics of the spatial grain structures by their two-dimensional images visible in a microscope or microphotography: • number of grains in a unit of area or volume • average and maximum diameters (in μm) of grains in a volume • numeric and graphic distribution of grain chords and diameters in

a plain section and grain diameters in a volume • areas and perimeters of all examined grains

118

J anuary 2012

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