标准编号:	GB/T 6394-2017
中文名称:	金属平均晶粒度测定方法
英文名称:	Metal - Methods for estimating the average grain size
中标分类:	H24    金相检验方法
行业分类:	GB    国家标准
ICS分类:	77.040.99 77.040.99    金属材料的其他试验方法 77.040.99
发布机构:	中华人民共和国国家质量监督检验检疫总局 中国国家标准化管理委员会
发布日期:	2017-03-03
实施日期:	2017-11-1
标准状态:	valid
替代旧标准:	GB/T 6394-2002 金属平均晶粒度测定法
翻译语言:	英文
文件格式:	PDF
中文字符数:	33000 字
翻译价格(元):	330.0
交付时间:	付款后 1 个工作日

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.

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

金属平均晶粒度测定方法 1 范围 1.1 本标准规定了金属组织平均晶粒度的表示及测定方法，包含有比较法、面积法和截点法，适用于单相组织，但经具体规定后也适用于多相或多组元试样中特定类型的晶粒平均尺寸测定。非金属材料如组织形貌与比较评级图中金属组织相似也可参照使用。 1.2本标准利用晶粒的面积、直径或截线长度的单峰分布(近似于对数正态分布)来测定试样的平均晶粒度，不适用于双峰分布的晶粒度。双重晶粒度的评定见GB/T 24177。分布在细小晶粒基体上个别非常粗大的晶粒的测定方法见YB/T 4290。 1.3本标准仅适用平面晶粒度的测量，不适用于三维晶粒度，即立体晶粒尺寸的测量。 1.4本标准仅作为推荐性试验方法，不能确定受检材料是否接收或适合使用的范围。 2规范性引用文件 下列文件对于本标准的应用是必不可少的，凡是注日期的引用文件，仅注日期的版本适用于本文件。凡是不注日期的引用文件，其最新版本(包括所有的修改单)适用于本文件。 GB/T 4335低碳钢冷轧薄板铁素体晶粒度测定法 GB/T 13298金属显微组织检验方法 GB/T 24177双重晶粒度表征与测定方法 GB/T 30067 金相学术语 YB/T 4290金相检测面上最大晶粒尺寸级别(ALA晶粒度)测定方法 3术语和定义 GB/T 30067界定的以及下列术语和定义适用于本文件。 3.1 晶界 grain boundary 对于多晶材料，从其一个结晶方向至另一个结晶方向过渡的很窄的区域，从而将相邻的晶粒分离。 3.2 晶粒grain 晶界所包围的整个区域。即是二维面上所观察到的原始晶界范围内的面积，或是三维物体上原始晶界面内所包围的体积。对于有孪晶界面材料，孪晶界面不予考虑。 3.3 晶粒度grain size 晶粒大小的量度。通常使用长度、面积、体积或晶粒度级别数来表示不同方法评定或测定的晶粒大小，而使用晶粒度级别数表示的晶粒度与测量方法和使用单位无关。 3.4 显微晶粒度级别数micro-grain size number G 显微晶粒度级别数G定义为： N100=2G-1 …………………………(1) 3.5 宏观晶粒度级别数macro-grain size number Gm 宏观晶粒度级别数Gm定义为： …………………………(2) 3.6 晶界截点的计数grain boundry intersection count Pi 测量试验线与晶界交截点或相切点的计数。简称截点数。 3.7 晶粒截线的计数grain intercept count Ni 被测量的平面上试验线穿切过单个晶粒的次数。简称截线数。 3.8 截线长度intercept length l 测量线段通过晶粒时，与晶界相交的两个交点之间的距离。 4 符号 本标准采用的符号与说明见表1。 表1 符号及其说明 符号 单位 名称及说明 α — 两相组织中的基体晶粒 A mm2 测量面积 mm2 1倍下测试网格内平均晶粒面积 AIl — 非等轴晶粒伸长率(或纵向平面各向异性系数) mm 平面晶粒平均直径 mm 立体晶粒平均直径 G — 显微晶粒度级别数 Gm — 宏观晶粒度级别数 G0 — ISO晶粒度级别数 G′ — 测定显微晶粒度时，对比较评级图使用非标准放大倍数评定的晶粒度级别 G′m — 测定宏观晶粒度时，对比较评级图使用非标准放大倍数评定的晶粒度级别 l — 截线长度 mm 1倍下的平均截距长度 lO mm 放大倍数Mb的平均截线长度 表1(续) 符号 单位 名称及说明 mm 两相显微组织中基体α相的平均截线长度 mm 非等轴晶粒组织中纵向面上的平均截线长度 mm 非等轴晶粒组织中横向面上的平均截线长度 mm 非等轴晶粒组织中法向面上的平均截线长度 mm 纵向面上平行变形方向的平均截距 mm 纵向面上垂直于变形方向上的平均截距 mm 横向面上垂直变形方向的平均截距 mm 法向面上垂直变形方向的平均截距 L mm 试验线长度 M — 所用的放大倍数 Mb — 基准放大倍数即标准评级图所用的放大倍数(100倍、75倍或1倍) n — 测量视场数 N — 规定放大倍数M下，在已知试验面积A上的晶粒截面计数 — 几个视场计数N的平均值 NL — 1倍下单位长度(mm)试验线穿过晶粒的截线数 Nα — 在两相(组元)的显微组织中，试验线交截基体α晶粒的个数 NA — 1倍下每平方毫米试验面积内的晶粒截面个数 N1 — 1倍下645.16 mm2内晶粒个数 N100 — 100倍下645.16 mm2内晶粒个数 NAα — 在两相显微组织中，1倍下每平方毫米内的基体α晶粒个数 NAO — 放大倍数Mb下的单位面积(mm2)内晶粒数 NAl — 非等轴晶粒组织中纵向面上的NA NAt — 非等轴晶粒组织中横向面上的NA NAp — 非等轴晶粒组织中法向面上的NA Ni — 在已知长度L试验线上的截线计数 N内 — 完全落在试验网格内的晶粒个数 N交 — 被试验网格所交截的晶粒个数 NL — 1倍下单位长度(mm)试验线上晶粒截线数 NiO — 放大倍数Mb下试验线所交截的晶粒数 NLl — 非等轴晶粒组织中纵向面上的NL NLt — 非等轴晶粒组织中横向面上的NL NLP — 非等轴晶粒组织中法向面上的NL Pi — 晶界与试验线的交点数 PL — 1倍下单位长度(mm)试验线与晶界相交的截点数 表1(续) 符号 单位 名称及说明 PLO — 放大倍数Mb下单位长度(mm)试验线上的截点数 PLl — 非等轴晶粒组织中纵向面上的PL PLt — 非等轴晶粒组织中横向面上的PL PLp — 非等轴晶粒组织中法向面上的PL Q — 测定显微晶粒度时，对比较评级图使用非标准放大倍数的修正系数 Qm — 测定宏观晶粒度时，对比较评级图使用非标准放大倍数的修正系数 S — 标准偏差 SV — 单相组织中晶粒晶界表面积与体积比 SVα — 两相(组元)组织中基体α晶界表面积与体积比 t — 测定置信限用的与测量次数相关的乘积系数 VVα — 两相组织中基体α的体积分数 AAα — 两相组织中基体α的面积分数 95％CI — 计数的95％置信区间 95％CL — 晶粒度的95％置信区间 ％RA — 相对误差百分数 注1：平均值以上述符号上面的加横线表示。 注2：使用字母O作脚标，代表基准放大倍数Mb下检验的晶粒数NAO、截线数NiO、截点数PLO或者截线长度LO。 5概述与应用 5.1本标准规定了测定平均晶粒度的基本方法：比较法、面积法和截点法。 5.2 比较法：比较法不需计数晶粒、截点或截矩。与标准系列评级图进行比较，评级图有的是标准挂图、有的是目镜插片。用比较法评估晶粒度时一般存在一定的偏差(±0.5级)。评级值的重现性与再现性通常为±1级。当晶粒形貌与标准评级图的形貌完全相似时，评级误差最小。 5.3面积法：面积法是计数已知面积内晶粒个数，利用单位面积内晶粒数NA来确定晶粒度级别数G。该方法的精确度是晶粒计数的函数。通过合理计数可达到±0.25级的精确度。面积法的测定结果是无偏差的，重现性与再现性小于±0.5级。面积法精确度关键在于计数时一定要标记出已计数过的晶粒。 5.4截点法：截点法是计数已知长度的试验线段(或网格)与晶粒截线或者与晶界截点的个数，计算单位长度截线数NL或者截点数PL来确定晶粒度级别数G。截点法的精确度是截点或截线计数的函数，通过有效的计数可达到优于±0.25级的精确度。截点法的测量结果是无偏差的，重现性和再现性小于±0.5级。对同一精度水平，截点法由于不需要标记就能准确的计数，因而较面积法测量快。 5.5对于等轴晶组成的试样，使用比较法，评定晶粒度既方便又实用。对于批量生产的检验，其精度已足够了。对于要求较高精度的平均晶粒度的测定，可以使用面积法和截点法。截点法对于拉长的晶粒组成试样更为有效。 5.6在有争议时，以截点法为仲裁方法。 5.7低碳钢冷轧薄板铁素体晶粒度的测定按GB/T 4335的规定执行。 5.8不能以标准评级图为依据测定单个晶粒。因为标准评级图的构成考虑到截平面与晶粒三维排列关系，显示出晶粒从最小到最大排列分布所反映出有代表性的正态分布结果。所以不能用评级图来测定单个晶粒。 5.9测定晶粒度时，应认识到晶粒度的测定并不是一种十分精确的测量。因为金属组织是由不同尺寸和形状的三维晶粒堆积而成。即使这些晶粒的尺寸和形状相同，通过该组织的任一截面(检验面)上分布的晶粒大小，将从最大值到零之间变化。因此，在检验面上不可能有绝对尺寸均匀的晶粒分布，也不能有两个完全相同的检验面。 5.10显微组织中晶粒尺寸和位置都是随机分布。不带意向的移动视场，放置测量网格，随机测量平均晶粒度才有代表性。在试样某一部分移动视场，集中测量会产生不良的代表性。所谓“代表性”即意味着试样所有的部分对结果都有贡献，而不是带有推测地挑选平均晶粒度的视场。 注：不带有偏见的检验者进行测定时，看着挑选视场，或者排除极端值，这样做，可能不是有意伪造平均值，但对于整体结果，可能得出高精度的错觉。选取有代表性的试样，可在心里将试样划分为几个相等的互相连接的小区域，载物台预先放置在每个小区域大约中心处。连续地将载物台放置到每一个这样的位置，盲目地施加测量网格，即关掉光源、关闭视频或将眼睛移开，放置测量网格。放好位置不允许再触碰。只有按照这样方式选择视场，进行测量才是有效的，检验结果才能不带有偏见，满足精度的要求。 6取样 6.1 测定晶粒度用的试样应在交货状态材料上切取。取样部位与数量按产品标准或技术条件规定。如果产品标准或技术条件未规定，则在钢材半径或边长1/2处截取。推荐试样尺寸为10 mm×10 mm。 6.2切取试样应避开因剪切、加热影响的区域。不能使用有改变晶粒结构的方法切取试样。 7试样制备 7.1 有加工变形晶粒的试样检验平行于加工方向的检验面(纵截面)，必要时还应检验垂直于加工方向的检验面(横截面)。等轴晶粒可以随机选取检验面。 7.2检验铁素体钢的奥氏体晶粒度，需要对试样进行热处理(见附录A)，具体方法按产品标准或技术条件的规定。如果产品标准或技术条件未规定，渗碳钢采用渗碳法，其他钢可以采用直接淬硬法或者氧化法。检验铁素体晶粒度和奥氏体钢晶粒度，一般试样不需要热处理。 7.3 晶粒度试样不允许重复热处理。 7.4用于渗碳处理的试样应去除脱碳层和氧化皮。 7.5试样的磨抛和浸蚀按GB/T 13298规定执行。试样的浸蚀应使大部分晶界完全显示出来(见附录A)。 8测定方法 8.1 比较法 8.1.1 一般要求 8.1.1.1 比较法是通过与标准评级图对比来评定平均晶粒度。适用于评定具有等轴晶粒的再结晶材料。 8.1.1.2本标准有下列四个系列标准评级图： a)评级图I：无孪晶晶粒(浅腐蚀)100倍； b)评级图Ⅱ：有孪晶晶粒(浅腐蚀)100倍； c)评级图Ⅲ：有孪晶晶粒(深腐蚀)75倍； d)评级图Ⅳ：钢中奥氏体晶粒(渗碳法)100倍。 8.1.1.3表2给出常用材料推荐使用的标准评级图片。 表2 常用材料推荐使用的标准评级图片 标准评级图 适用范围 图I 1)铁素体钢的奥氏体晶粒即采用氧化法、直接淬硬法、铁素体网法及其他方法显示的奥氏体晶粒； 2)铁素体钢的铁素体晶粒； 3)铝、镁和镁合金、锌和锌合金、高强合金 图Ⅱ 1)奥氏体钢的奥氏体晶粒(带孪晶的)； 2)不锈钢的奥氏体晶粒(带孪晶的)； 3)镁和镁合金、镍和镍合金、锌和锌合金、高强合金 图Ⅲ 铜和铜合金 图Ⅳ 1)渗碳钢的奥氏体晶粒； 2)渗碳体网显示的晶粒； 3)奥氏体钢的奥氏体晶粒(无孪晶的) 8.1.1.4观测者需要正确的判断需要选择所使用的放大倍数、合适的检验面的尺寸(晶粒数)、试样代表性截面的数量与位置和测定特征或平均晶粒度用的视场。不能凭视觉选择出似乎是平均晶粒度的区域评定。推荐按5.10选取视场。 8.1.1.5晶粒度的评定应在试样截面上随机选取三个或三个以上的代表性视场测量平均晶粒度，以最能代表试样晶粒大小分布的级数报出。 8.1.1.6若试样中发现晶粒不均匀现象，经全面观察后，如属偶然或个别现象，可不予计算。如较为普遍，则应计算出不同级别晶粒在视场中各占面积百分比。若占优势晶粒所占的面积不少于视场面积的90％，则只记录此一种晶粒的级别数。否则，应用不同级别数来表示该试样的晶粒度，其中第一个级别数代表占优势的晶粒的级别。出现双重晶粒度，按GB/T 24177评定，出现个别粗大晶粒可以按照YB/T 4290评定。 8.1.1.7使用比较法时，如需复验，可改变放大倍数，以克服初验结果可能带有的主观偏见。 8.1.2显微晶粒度的评定 8.1.2.1 通常使用与相应标准系列评级图相同的放大倍数，直接进行对比。通过有代表性视场的晶粒组织图像或显微照片与相应表2的系列评级图或标准评级图复制透明软片比较，选取与检测图像最接近的标准评级图级别数或晶粒直径，记录评定结果。介于两个整数级别标准图片之间，以两个图片级别的平均值记录。 8.1.2.2如将检测的晶粒图像与标准系列评级图投影到同一荧屏上，可提高评级精确度。 8。1.2.3 当待测晶粒度超过标准系列评级图片所包括的范围，或基准放大倍数(75倍或100倍)不能满足需要时，可采用其他的放大倍数，通过表3、表4或按8.1.2.4给出的式(3)进行换算处理。通常，所选用的放大倍数是基准放大倍数的简单整数倍。 8.1.2.4若采用其他放大倍数M进行比较评定，将放大倍数M的待测晶粒图像与基准放大倍数Mb(75倍或100倍)的系列评级图片比较，评出的晶粒度级别数G′，其显微晶粒度级别数G为： G=G′+Q …………………………(3) 式中： Q=6.643 9 lg(M/Mb)，保留0.5单位。 8.1.2.5在晶粒度图谱中，最粗的一端即00级一个视场中只有几个晶粒，在最细的一端晶粒的尺寸非常小，准确评定级别很困难。当试样的晶粒尺寸落在图谱的两端时，可以变换放大倍数使晶粒尺寸落在靠近图谱中间的位置。 表3 评级图Ⅲ在不同放大倍数下测定的显微晶粒度的关系 放大 倍数 评级图Ⅲ图片编号 (75倍) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 25 0.015 (9.2) 0.030 (7.2) 0.045 (6.0) 0.060 (5.2) 0.075 (4.5) 0.105 (3.6) 0.135 (2.8) 0.150 (2.5) 0.180 (2.0) 0.210 (1.6) 0.270 (0.8) 0.360 (0) 0.451 (0/00) 0.600 (00+) 50 0.007 5 (11.2) 0.015 (9.2) 0.022 5 (8.0) 0.030 (7.2) 0.037 5 (6.5) 0.053 (5.6) 0.067 5 (4.8) 0.075 (4.5) 0.090 (4.0) 0.105 (3.6) 0.135 (2.8) 0.180 (2.0) 0.225 (1.4) 0.300 (0.5) 75 0.005 (12.3) 0.010 (10.3) 0.015 (9.2) 0.020 (8.3) 0.025 (7.7) 0.035 (6.7) 0.045 (6.0) 0.050 (5.7) 0.060 (5.2) 0.070 (4.7) 0.090 (4.0) 0.120 (3.2) 0.150 (2.5) 0.200 (1.7) 100 0.003 7 (13.2) 0.007 5 (11.2) 0.011 2 (10.0) 0.015 (9.2) 0.019 (8.5) 0.026 (7.6) 0.034 (6.8) 0.037 5 (6.5) 0.045 (6.0) 0.053 (5.6) 0.067 (4.8) 0.090 (4.0) 0.113 (3.4) 0.150 (2.5) 200 0.001 9 (15.2) 0.003 7 (13.2) 0.005 6 (12.0) 0.007 5 (11.2) 0.009 (10.5) 0.013 (9.6) 0.017 (8.8) 0.019 (8.5) 0.022 5 (8.0) 0.026 (7.6) 0.034 (6.8) 0.045 (6.0) 0.056 (5.4) 0.075 (4.5) 400 — 0.001 9 (15.1) 0.002 8 (14.0) 0.003 8 (13.1) 0.004 7 (12.5) 0.006 7 (11.5) 0.008 4 (10.8) 0.009 (10.5) 0.012 (10.0) 0.013 3 (9.5) 0.016 8 (8.8) 0.022 5 (8.0) 0.028 (7.3) 0.037 5 (6.5) 500 — — 0.002 2 (14.6) 0.003 (13.7) 0.003 75 (13.1) 0.005 25 (12.1) 0.006 7 (11.5) 0.007 5 (11.1) 0.009 (10.6) 0.010 (10.3) 0.013 3 (9.5) 0.018 (8.7) 0.022 5 (8.0) 0.03 (7.1) 注：括号外为晶粒平均直径d (mm)；括号内为相应的显微晶粒度级别数。 表4与标准评级图I、Ⅱ、Ⅳ等同图像的晶粒度级别数 图像的 标准评级图编号(100倍) 放大倍数 No.1 No.2 No.3 No.4 No.5 No.6 No.7 No.8 No.9 No.10 25 -3 -2 -1 0 1 2 3 4 5 6 50 -1 0 1 2 3 4 5 6 7 8 100 1 2 3 4 5 6 7 8 9 10 200 3 4 5 6 7 8 9 10 11 12 400 5 6 7 8 9 10 11 12 13 14 500 5.5 6.5 7.5 8.5 9.5 10.5 11.5 12.5 13.5 14.5 800 7 8 9 10 11 12 13 14 15 16 1 000 7.5 8.5 9.5 10.5 11.5 12.5 13.5 14.5 15.5 16.5 8.1.3宏观晶粒度的评定 8.1.3.1 对于特别粗大的晶粒使用宏观晶粒度进行的测定，放大倍数为1倍。直接将准备好的有代表性的晶粒图像与评级图I(非孪晶)和图Ⅱ及图Ⅲ(孪晶)进行比较评级。由于标准评级图是在75倍和100倍下制备的，待测宏观晶粒不可能完全与系列评级图的级别一致。为此，宏观晶粒度可用平均晶粒直径或表5所列的宏观晶粒度级别数Gm来表示。 8.1.3.2 当晶粒较小时，最好选用稍高的放大倍数M进行宏观晶粒度的评定。若评出的晶粒度级别数为G′m，其宏观晶粒度级别数Gm按式(4)计算：