ASTM grain size number

There are two commonly used ways of characterizing the grain size of a crystalline solid. One is the ASTM grain size number, N, defined by... 

EXAMPLE 1.1. Figure 1.1 is a micrograph taken at 200X. What is the ASTM grain size number ... 

What is the linear intercept grain size (in millimeters) corresponding to an ASTM grain size number of 8 ... 

If the ASTM grain size number is increased by one, by what factor is the number of grains per volume changed ... 

Little difference was observed in the hardness values between the two cold-worked plus solution-treated and double-aged (STDA) Inconel 718 materials, although a significant difference in ASTM grain size numbers was apparent. 

Table II. Heat Treatment, Hardness, and ASTM Grain Size Number Relative to VIM-VAR Inconel 718 and Udimet 718...

Relationships have been developed that relate mean intercept length to ASTM grain-size number these are as follows ... 

Determine the ASTM grain-size number if O 30 grains per square inch are measured at a magnification of 250 X. 

Count the number of triple points in Figure 1.10 and deduce the ASTM grain size from this count. Compare with your answer to Problem 2A. 

Chemical compositions plus processing and heat treatment schedules relative to Inconel 718 and Udimet 718 are presented in Tables I and II. Hardness and ASTM grain size (average numbers) are included in Table II. Both the Inconel 718 and Udimet 718 superalloys were obtained as large-diameter (29 cm and 26 cm, respectively) hot-finished forging billets, vacuum-induction-melted and vacuum-arc-remelted (VIM-VAR). The two alloys have comparable chemical compositions, but the Inconel 718 has a significantly higher silicon content. 

Comparison of a photomicrograph (taken at a magnification of 100 X) with ASTM standard comparison charts may be used to specify grain size in terms of a grain-size number. 

In addition to chemical analysis a number of physical and mechanical properties are employed to determine cemented carbide quaUty. Standard test methods employed by the iadustry for abrasive wear resistance, apparent grain size, apparent porosity, coercive force, compressive strength, density, fracture toughness, hardness, linear thermal expansion, magnetic permeabiUty, microstmcture, Poisson s ratio, transverse mpture strength, and Young s modulus are set forth by ASTM/ANSI and the ISO. 

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