GB/T 231.2-2012 in English

《GB/T 231.2-2012金属材料 布氏硬度试验 第2部分：硬度计的检验与校准》由TC122（全国试验机标准化技术委员会）归口，主管部门为中国机械工业联合会。

ChinaStandards.net is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
“Metallic Materials - Brinell Hardness Test” (GB/T 231) is classified into the following four parts:
- Part 1: Test Method;
- Part 2: Verification and Calibration of Testing Machines
- Part 3: Calibration of Reference Blocks;
- Part 4: Tables of Hardness Values.
This is Part 2 of GB/T 231.
This part is drafted according to the rules given in GB/T 1.1-2009.
This part supersedes "Metallic Brinell Hardness Test - Part 2: Verification and Calibration of Hardness Testers" (GB/T 231.2-2002). Compared with GB/T 231.2-2002, the main technical changes in this standard are as follows:
- The name is modified;
- The introduction is modified (see Introduction; Introduction in 2002 edition);
- In Normative References "Chapter 2", GB/T 7997-1987 is superseded by GB/T 4340.1-2009 (see Chapter 2; Chapter 2 in 2002 edition);
- Calculation equations of the relative repeatability and relative deviation of indication value of the testing machine (see 5.6 and 5.8) are added;
- Annex A is modified and contents related to "uncertainty of measurement of the calibration results of the hardness testing machine" are added (see Annex A; Annex A in 2002 edition).
This part is modified by adopting international standard "Metallic Materials - Brinell Hardness Test - Part 2: Verification and Calibration of Testing Machines" (ISO 6506-2: 2005) (Second Edition) with redrafting method and is consistent with ISO 6506-2: 2005 in text structure and technical content.
Compared with ISO 6506-2: 2005, the technical differences in this part and their causes are as follows:
- Foreword in ISO 6506-2: 2005 is deleted and reformulated.
- Adjustment on technical differences are made in normative references of this part so as to adapt to technical conditions in China. Adjustment contents are intensively reflected in "Normative References" (Chapter 2), and the specific adjustment is as follows:
ISO 6506-1 is superseded by the standard GB/T 231.1 modified by adopting international standard (see Chapter 1, 4.2.4, 4.5, 5.4 and Annex A);
ISO 6506-3 is superseded by the standard GB/T 231.3 modified by adopting international standard (see 5.1);
·ISO 6507-1 is superseded by the standard GB/T 4340.1 modified by adopting international standard (see 4.3.4.2);
·ISO 376 is superseded by the standard GB/T 13634 modified by adopting international standard (see 4.2.3);
- The maximum permissible time control deviation in 4.5 is modified from "±1.0s" to "±0.5s" so as to correct the inharmonic error of this technical index in 4.5 and A.1.4 of ISO 6506-2005 (see 4.5 and A.1.4 in Annex A);
- Since the note in 5.3 contains requirements, it is changed to text (see 5.3);
- Some incorrect calculation results and data in Table A.1 and Table A.5 in Annex A are corrected and the corrected place are noted with underline;
- Expression methods of substituting numerical values in some calculation equations in Annex A are regulated;
- The symbol " " is superseded with "E" in Equations (A.10) and (A.13) and Table A.9;
- Bibliography was deleted.
Compared with ISO 6506-2: 2005, technical differences are made in this part. Clauses involved with these differences are indicated by perpendicular single line (|) at page margin.
The following editorial changes are made in this part:
- "This part of ISO 6506" is changed to "this part";
- The decimal point "," is changed to the decimal point ".".
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The issuance organization of this document shall not undertake the responsibility of identifying these patents.
This part is proposed by the China Machinery Industry Federation.
This part is under the jurisdiction of the National Technical Committee on Testing Machines of Standardization Administration of China (SAC/TC 122).
Drafting organizations of this part: Innovation Testing Technology Co., Ltd., Changchun Research Institute for Mechanical Science Co., Ltd., Test Instrument Co., Ltd. Laizhou Huayin, Shanghai Taiming Optical Instrument Co., Ltd., Shanghai Shangcai Tester Machines Co., Ltd. and Center Testing International (Shenzhen) Co., Ltd.
Chief drafting staff of this part: Tao Zecheng, Wang Xuezhi, Yang Fengming, Ma Guoyi, Ma Caike, Yang Qiong and Guo Bing.
The previous editions of standards superseded by this part are as follows:
- GB 6269-1986, GB/T 6269-1997;
- GB/T 231.2-2002.

Introduction

Attention is drawn to the fact that in this part of GB/T 231, only the use of the hardmetal ball indenter is specified.
The designation of the Brinell hardness is HBW and should not be confused with the former designation HB, or HBS when a steel ball indenter was used.

Metallic Materials - Brinell Hardness Test - Part 2: Verification and Calibration of Testing Machines

1 Scope

This part of GB/T 231 specifies a method of verification and calibration of testing machines used for determining Brinell hardness in accordance with GB/T 231.1.
It specifies a direct method for checking the main functions of machine operation and an indirect method suitable for the overall checking of the machine. The indirect method may be used independently for periodic routine checking of machine operation while in service.
If a testing machine is also to be used for other methods of hardness testing, it shall be verified independently for each method.
This part is also applicable to portable hardness testing machines.

2 Normative References

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 231.1 Metallic Materials - Brinell Hardness Test - Part 1: Test Method (GB/T 231.1-2009, ISO 6506-1:2005, MOD)
GB/T 231.3 Metallic Materials - Brinell Hardness Test - Part 3: Calibration of Reference Blocks (GB/T 231.3-2012, ISO 6506-3:2005, MOD)
GB/T 4340.1 Metallic Materials - Vickers Hardness Test - Part 1: Test Method (GB/T 4340.1-2009, ISO 6507-1:2005, MOD)
GE/T 13634 Calibration of Force-proving Instruments Used for the Verification of Uniaxial Testing Machines (GB/T 13634-2008, ISO 376:2004, Metallic Materials - Calibration of Force-proving Instruments Used for the Verification of Uniaxial Testing Machines, IDT)

3 General Conditions

Before a Brinell hardness testing machine is verified, the machine shall be checked to ensure that it is properly set up in accordance with the manufacturer's instructions. Especially, it shall be checked that:
a) The plunger holding the ball slides correctly in its guide;
b) The ball-holder with a ball (from a lot verified in accordance with 4.3) is firmly mounted in the plunger;
c) The test force is applied and removed without shock, vibration or overrun and in such a manner that the readings are not influenced;
d) If the measuring system is integrated into the machine:
- The change from removing the test force to measuring mode does not influence the readings;
- The illumination does not affect the readings; and
- The center of the indentation is in the center of the field of view, if necessary.

4 Direct Verification

4.1 General
4.1.1 Direct verification should be carried out at a temperature of (23±5)℃. If the verification is made outside this temperature range, this shall be reported in the verification report.
4.1.2 The instruments used for verification and calibration shall be traceable to national standards.
4.1.3 Direct verification involves:
a) The calibration of the test force;
b) The verification of the indenter ball;
c) The calibration of the indentation measuring system;
d) The verification of the testing cycle.
4.2 Calibration of the test force
4.2.1 Each test force shall be measured within the working range of the testing machine. Whenever applicable, this shall be done at no less than three positions of the plunger uniformly spaced throughout its range of movement during testing.
4.2.2 Three measurements shall be made for each force at each position of the plunger. Immediately before each measurement is taken, the plunger shall be moved in the same direction as during testing.
4.2.3 The force shall be measured by one of the following two methods:
- By means of a force-proving instrument in accordance with GB/T 13634 Class 1, or
- By balancing against a force, accurate to ±0.2%, applied by means of calibrated masses or another method with the same accuracy.
4.2.4 Each measurement of a force shall be within ±1.0% of the nominal test force, as defined in GB/T 231.1.
4.3 Verification of the indenter ball
4.3.1 The indenter consists of a ball and an indenter holder. The verification applies only to the ball.
4.3.2 For the purpose of verifying the size and the hardness of the balls, a sample selected at random from a batch shall be tested. The balls verified for hardness shall be discarded.
4.3.3 The balls shall be polished and free from surface defects.
4.3.4 The user shall either measure the balls to ensure that they meet the following requirements or shall obtain balls from a supplier certifying that the following conditions are met.
4.3.4.1 The diameter shall be determined by taking the mean value of not less than three single values of diameter measured at different positions on the ball. No single value shall differ from the nominal diameter by more than the tolerance given in Table 1.
Table 1 Tolerances for Different Ball Diameters
In mm
Ball diameter Tolerance
10
5
2.5
1 ±0.005
±0.004
±0.003
±0.003
4.3.4.2 The characteristics of the hardmetal balls shall be as follows.
a) Hardness: the hardness shall be not less than 1500HV, when determined using a test force of at least 4.903N, in accordance with GB/T 4340.1. The hardmetal ball may be tested directly on this spherical surface or by sectioning the ball and testing on the ball interior;
b) Density: ρ=(14.8±0.2)g/cm3.
The following chemical composition is recommended:
- Tungsten carbide (WC) balance;
- Total other carbides 2.0%;
- Cobalt (Co) 5.0%~7.0%.

Foreword I
Introduction III
1 Scope
2 Normative References
3 General Conditions
4 Direct Verification
5 Indirect Verification
6 Intervals between Verifications
7 Verification Report/Calibration Certificate
Annex A (Informative) Uncertainty of Measurement of the Calibration Results of the Hardness Testing Machine