Detail of GB/T 6394-2017

Introduction of GB/T 6394-2017

Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative. This standard is developed in accordance with the rules given in GB/T 1.1-2009. This standard replaces GB/T 6394-2002 Metal-Methods for Estimating the Average Grain Size. The following main technical changes have been made with respect to GB/T 6394-2002: ——The terms "grain boundary", "grain boundary intersection count", "grain intercept count" and "intercept length" and their definitions are added (see Chapter 3); ——The heat treatment method, sampling location, specimen orientation, polished surface area, preparation requirements, etc. of specimen forming austenite grains are added (see Chapters 6 and 7); ——Requirements for test parameters, selection of fields and rating details are added in the comparison procedure (see 8.1); ——Requirement of using the Chart IV for outlining the grains with cementite is added (see Table 2 in 8.1.1.3). ——Values of grain diameter and magnification corresponding to 400X and 500X rating charts are modified, and the converted values of 500X and 1,000X rating charts are added (See Tables 3 and 4 in 8.1.2.3); ——Calculation formulae for rectangular test grid are added in planimetric procedure, and methods for selection of fields and precision of counting are added (see 8.2.2); ——Contents of intercept procedure are modified, and calculation formulae of intercept procedure are added (see 8.3.1.8); ——Calculation methods for non-equiaxed grains are added, and the calculation process is defined (see Chapter 9); ——Phase characteristics and proportion determination reporting requirements are added for estimation of two-phase and multi-phase grains, and intercept procedure is added (see 10.4.3); ——Essential data for determination with planimetric procedure and intercept procedure and requirements for contents of reports about non-equiaxed grains and multi-phase grains are added, and report on grain size is improved (see Chapter 11); ——Requirements for precision and bias are added (see Chapter 12); ——Annex C - "Establishing and Outlining of Austenite Grain Size of Ferritic and Austenitic Steels" in the former standard is revised to Annex A - "Establishing and Outlining Methods for Grain Size", the quenching temperature in establishing of austenite grains is all changed from 900℃ to 890℃, fine pearlite outlining procedure is added, the etchants for parts of grain sizes and their application methods are added, and the method for determination of ferrite grain of ferritic steel is added (see A.2); ——Annex B is revised from "Calculation for Confidence Limit and Relative Error of Grain Size Determination Results" to "Statistical Techniques - Calculation for Confidence Interval and Relative Error of Grain Size Determination Results", and the calculation methods are corrected; ——In Annex C, the calculation formulae and derivation process used in various measurement methods for grain size are added (see C.1), the relationship between common measurements, calculation and conversion methods of relative data and the difference between routine measurement methods of grain size are added (see C.2), the relationship between grain size in this standard and ISO grain size and the relationship between micro-grain size number and macro-grain size number are added (see C.3). This standard was proposed by China Iron and Steel Association. This standard is under the jurisdiction of the National Technical Committee on Iron and Steel of Standardization Administration of China (SAC/TC 183). The previous editions of this standard are as follows: ——GB/T 6394-1986; GB/T 6394-2002.   Introduction In order to determine the average grain size of metal, comparison procedure is primarily used, and intercept procedure and planimetric procedure may also be used. These basic procedures are on the basis of the geometric figures of grains, are independent of the metal or alloy concerned, and may also be used for the estimation of average grain, crystal or cell size in nonmetallic materials. The comparison procedure may be used if the structure of the material approaches to the appearance of one of the standard rating charts. However, the rating charts in comparison procedure cannot not be used for measurement of individual grains. Test methods described in this standard are only used to measure the average grain size of specimens with a unimodal grain size distribution. For the specimens with bimodal (or more complex) size distributions, the grain size shall be measured in accordance with this standard and YB/T 4290 Test Methods for Estimating the Largest Grain Observed in a Metallographic Section (ALA Grain Size), and the grain distribution characteristics shall be characterized in accordance with GB/T 24177 Standard Test Methods for Characterizing Duplex Grain Sizes. For the specimens with individual very coarse grains in a fine grained matrix, the determination of ALA grain size may be carried out in accordance with YB/T 4290. Determination of Estimating the Average Grain Size of Metal 1 Scope 1.1 This standard specifies the representation and determination methods for average grain size of metallic structure, including comparison procedure, planimetric procedure and intercept procedure; these methods are applicable to single-phase structure, but they, with specific requirements, may also be applied to determine the average size of a particular type of grain in a multi-phase or multi-constituent specimen. These methods may also be applied to nonmetallic materials with structures having appearances similar to those of the metallic structures shown in the comparison charts. 1.2 This standard is applied to determine the average grain size of specimens with a unimodal distribution (similar to lognormal distribution) of grain areas, diameters or intercept lengths, and is not applicable to the grain size in bimodal distribution. Characterization of duplex grain size is described in GB/T 24177. Test methods for determining individual very coarse grains in a fine grained matrix are described in YB/T 4290. 1.3 This standard deals only with determination of planar grain size. Determination of spatial grain size, that is, measurement of the size of the three-dimensional grains, is beyond the scope of this standard. 1.4 This standard deals only with the recommended test methods and nothing in it should be construed as defining or establishing limits of acceptability or fitness of purpose of the materials tested. 2 Normative References The following documents for the application of this document are essential. Any dated reference, just dated edition applies to this document. For undated references, the latest edition (including any amendments) applies to this document. GB/T 4335 Determination of Ferrite Grain Size for Cold Rolled Low Carbon Steel Sheets GB/T 13298 Inspection Methods of Microstructure for Metals GB/T 24177 Standard Test Methods for Characterizing Duplex Grain Sizes GB/T 30067 Standard Terminology Relating to Metallography YB/T 4290 Test Methods for Estimating the Largest Grain Observed in a Metallographic Section (ALA Grain Size) 3 Terms and Definitions For the purposes of this document, the terms and definitions defined in GB/T 30067 and the following apply. 3.1 grain boundary a very narrow region in a polycrystalline material corresponding to the transition from one crystallographic orientation to another, thus separating one adjacent grain from another 3.2 grain a whole area enclosed by grain boundary, that is, the area within the original grain boundary observed on two-dimensional plane or the volume enclosed by the original grain boundary planes on three-dimensional body. Twin-plane boundary is not considered for materials with twin-plane boundary 3.3 grain size a magnitude of grain size. Generally, length, area, volume or grain size number are used for representing the grain size estimated or determined with different methods, while the grain size represented by grain size number is unrelated to the measurement method and unit 3.4 micro-grain size number G the micro-grain size number G is defined as: N100=2G-1 (1) 3.5 macro-grain size number Gm the macro-grain size number Gm is defined as: (2) 3.6 grain boundary intersection count Pi determination of the number of times a test line cuts across, or is tangent to grain boundaries, which is called the intersection count for short 3.7 grain intercept count Ni determination of the number of times a test line cuts through individual grains on the plane tested, which is called the intercept count for short 3.8 intercept length l the distance between two grain boundary intersection points on a test line segment that crosses the grain 4 Symbols The symbols adopted in this standard and their descriptions are given in Table 1. Table 1 Symbols and Descriptions Symbol Unit Name and description α — Matrix grains in a two-phase structure A mm2 Test area mm2 Average grain area in test grid at 1X AIl — Elongation ratio (or anisotropy coefficient for a longitudinally oriented plane) of non-equiaxed grain mm Average planar grain diameter mm Average spatial grain diameter G — Micro-grain size number Gm — Macro-grain size number G0 — ISO grain size number G′ — Grain size number estimated with a nonstandard magnification for comparison rating chart during determination of micro grain size — Grain size number estimated with a nonstandard magnification for comparison rating chart during determination of macro grain size l — Intercept length mm Average intercept length at 1X lO mm Average intercept length at the magnification Mb mm Average intercept length of the α matrix phase in a two-phase microstructure mm Average intercept length on a longitudinally oriented surface for a non-equiaxed grain structure mm Average intercept length on a transversely oriented surface for a non-equiaxed grain structure mm Average intercept length on a planarly oriented surface for a non-equiaxed grain structure mm Average intercept parallel to the deformation direction on a longitudinally oriented surface mm Average intercept perpendicular to the deformation direction on a longitudinally oriented surface mm Average intercept perpendicular to the deformation direction on a transversely oriented surface mm Average intercept perpendicular to the deformation direction on a planarly oriented surface L mm Length of a test line M — Magnification used Mb — Base magnification, that is, magnification used by a standard rating chart (100X, 75X or 1X) n — Number of fields measured N — Number of grain cross sections on a known test area A at the specified magnification M — Average value of the number N of several fields NL — Number of intercepts per unit length (mm) of test line crossing the grain at 1X Nα — Number of α matrix grains intercepted by the test line in a two-phase (constituent) microstructure NA — Number of grain cross sections per mm2 test area at 1X N1 — Number of grains per 645.16mm2 at 1X N100 — Number of grains per 645.16mm2 at 100X NAα — Number of α matrix grains per mm2 at 1X in a two-phase microstructure NAO — Number of grains per unit area (mm2) at the magnification Mb NAl — NA on a longitudinally oriented surface for a non-equiaxed grain structure NAt — NA on a transversely oriented surface for a non-equiaxed grain structure NAp — NA on a planarly oriented surface for a non-equiaxed grain structure Ni — Number of intercepts on a test line of known length L NInside — Number of grains completely within a test grid NIntercepted — Number of grains intercepted by the test grid NL — Number of grain intercepts per unit length (mm) of test line at 1X NiO — Number of grains intercepted by the test line at the magnification Mb NLl — NL on a longitudinally oriented surface for a non-equiaxed grain structure NLt — NL on a transversely oriented surface for a non-equiaxed grain structure NLP — NL on a planarly oriented surface for a non-equiaxed grain structure Pi — Number of grain boundary intersections with a test line PL — Number of grain boundary intersections per unit length (mm) of test line at 1X PLO — Number of intersections per unit length (mm) of test line at the magnification Mb PLl — PL on a longitudinally oriented surface for a non-equiaxed grain structure PLt — PL on a transversely oriented surface for a non-equiaxed grain structure PLp — PL on a planarly oriented surface for a non-equiaxed grain structure Q — Correction factor for comparison rating chart using a nonstandard magnification for microscopically determined grain size Qm — Correction factor for comparison rating chart using a nonstandard magnification for macroscopically determined grain size S — Standard deviation SV — Grain boundary surface area to volume ratio for a single-phase structure SVα — α matrix grain boundary surface area to volume ratio for a two-phase (constituent) structure t — Measurement times-related multiplier coefficient for determination of the confidence limit VVα — Volume fraction for α matrix in a two-phase structure AAα — Area fraction for α matrix in a two-phase structure 95%CI — 95% confidence interval of count 95%CL — 95% confidence interval of grain size %RA — Percent relative error Note 1: The average values are represented by aforesaid symbols with a transversal line (-). Note 2: The letter O is used as subscript to represent the number of grains (NAO), the number of intercepts (NiO), the number of intersections (PLO) or the intercept length (lO) in test at the base magnification Mb. 5 Generalities and Application 5.1 This standard specifies the basic procedures for determination of average grain size, including comparison procedure, planimetric procedure and intercept procedure. 5.2 Comparison procedure: The comparison procedure does not require counting of either grains, intersections or intercepts but involves comparison of standard rating charts, either in the form of a standard wall chart or an eyepiece reticle. There appears to be a general bias (size ±0.5) in estimating the grain size with comparison procedure. Repeatability and reproducibility of comparison chart ratings are generally ±1 grain size number. A minimum rating error can be realized if the grain appearances are completely similar to those shown in the standard rating charts. 5.3 Planimetric procedure: The planimetric procedure involves an actual count of the number of grains within a known area. The number of grains per unit area, NA, is used to determine the grain size number, G. The precision of the procedure is a function of the number of grains counted. A precision of ±0.25 grain size units can be attained with a reasonable amount of effort. Results are free of bias; repeatability and reproducibility are less than ±0.5 grain size units. An accurate count does require marking off of the grains as they are counted. 5.4 Intercept procedure: The intercept procedure involves an actual count of the number of grains intercepted by or the number of grain boundary intersections with a test line segment (or grid) of known length, used to calculate the number of intercepts, NL, or the number of intersections, PL, per unit length. NL or PL is used to determine the grain size number, G. The precision of the procedure is a function of the number of intersections or intercepts counted. An precision of better than ±0.25 grain size units can be attained with an effective amount of effort. Results are free of bias; repeatability and reproducibility are less than ±0.5 grain size units. Because an accurate count can be made without need of marking off intercepts or intersections, the intercept procedure is faster than the planimetric procedure for the same level of precision.

Contents of GB/T 6394-2017

Foreword II Introduction IV 1 Scope 2 Normative References 3 Terms and Definitions 4 Symbols 5 Generalities and Application 6 Sampling 7 Specimen Preparation 8 Determination Procedures 9 Specimens with Non-equiaxed Grain Shapes 10 Grain Size of Specimens Containing Two- or Multi-phase Structure 11 Report on Grain Size 12 Precision and Bias Annex A (Normative) Establishing and Outlining Method of Grain Size Annex B (Normative) Statistical Techniques - Calculation for Confidence Interval and Relative Error of Grain Size Determination Results Annex C (Informative) Measurement Foundation of Grain Size