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GB/T 224-2008 PDF in English


GB/T 224-2008 (GB/T224-2008, GBT 224-2008, GBT224-2008)
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GB/T 224-2008: PDF in English (GBT 224-2008)

GB/T 224-2008
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.040.99
H 24
Replacing GB/T 224-1987
Determination of depth of decarburization of steels
(ISO 3887.2003, MOD)
ISSUED ON. AUGUST 5, 2008
IMPLEMENTED ON. APRIL 1, 2009
Issued by. General Administration of Quality Supervision, Inspection and
Quarantine (AQSIQ);
Standardization Administration (SAC) of the People's
Republic of China.
Table of Contents
Foreword ... 3 
1 Scope ... 5 
2 Normative References ... 5 
3 Terms and Definitions ... 5 
4 Measuring Method ... 7 
4.1 General Provisions ... 7 
4.2 Metallographic Method ... 8 
4.3 Hardness Method ... 11 
4.4 Method of determining the Carbon Content ... 13 
5 Test Report ... 14 
Annex A (Informative) ... 15 
Foreword
This standard is modified in relation to ISO 3887.2003 "Steels-Determination of Depth
of Decarburization", and adds the sampling requirements and reference pictures for
metallographic method assessment according to ASTME1077-01 "Standard Test
Methods for Estimating the Depth of Decarburization of Steel Specimens".
For the convenience of application, this standard has made the following
modifications over ISO 3887.2003.
a) The phase "this international standard" is replaced by "this standard";
b) The decimal comma "," is replaced by decimal point ".";
c) The international standards in the references are replaced by relevant national
standards;
d) The definition of "complete decarburization" is modified in relation to
ASTME1077;
e) Sampling schematic diagrams of specimens of different specifications are
increased;
f) Rockwell Hardness Method is increased in the hardness methods;
g) Pictures of decarburized metallurgical structures are increased as informative
Annex A.
This standard replaces GB/T 224-1987 "Determination of Depth of Decarburization of
Steel".
The main differences between this standard and GB/T 224-1987 are as follows.
a) Add "Foreword" and "Normative References";
b) Modify the terms and definitions; add the terms and definitions of "complete
decarburization", "depth of total decarburization", and "depth of functional
decarburization" and "schematic diagram of typical decarburization";
c) Sampling schematic diagrams of specimens of different specifications are
added;
d) 4.2.2 "sample preparation" recommends to use automatic or semi-automatic
system samples;
e) 4.2.3.1 "determination of total decarburization" adds the high degree
Determination of Depth of Decarburization of Steels
1 Scope
This standard specifies the terms and definitions, measuring methods and test report
of steel decarburization.
Methods stated in this standard are applicable to determining the depth of
decarburization of steel products (billet).
2 Normative References
The following normative documents contain the provisions which, through reference in
this text, constitute the provisions of this standard. For dated reference, subsequent
amendments or revisions of these publications do not apply. For undated references,
the latest edition of the normative document referred to applies.
GB/T 230.1 Metallic Rockwell Hardness Test - Part 1. Test method (scales A, B, C,
D, E, F, G, H, K, N, T) (GB/T 230.1-2004, ISO 6508-1.1999, MOD)
GB/T 1172-1999 Conversion of hardness and strength for ferrous metal
GB/T 4340.1 Metallic materials - Vickers hardness test - Part 1. Test method (GB/T
4340.1-1999, eqv ISO 6507-1.1997)
GB/T 20126-2006 Unalloyed steel - Determination of low carbon content - Part 2.
Infrared absorption method after combustion in an induction furnace (with
preheating) (GB/T 20126-2006, ISO 15349-2.1999, IDT)
3 Terms and Definitions
For the purposes of this standard, the terms and definitions given in the following
apply.
3.1
Decarburization
It refers to carbon loss on the steel surface layer. This carbon loss shall include.
a) Partial decarburization;
b) Complete decarburization, namely the carbon content on the surface layer of the
steel specimens is lower than the maximum solubility of carbon in ferrite.
Note. the complete decarburization described in b) only exists in the ferrite structures.
3.2
Depth of functional decarburization
It refers to the distance from the product surface to the point of stated carbon content
or hardness, which shall be not subject to the service performance impacts due to
decarburization (for example. minimum carbon content stated in product standard).
3.3
Depth of total decarburization
It refers to the distance from the product surface to the point with carbon content
equaling to matrix carbon content, equaling to the sum of partial decarburization and
complete decarburization.
3.4
Depth of ferrite decarburization
It refers to the depth of the complete decarburization on the surface.
Note. the depth of ferrite decarburization shall be determined by micro-structural examination.
Different decarburization zones are shown in Figure 1.
used for observation to determine the boundary. It shall carry out preliminary
observation in low magnification to guarantee that the peripheral decarburization
change may find the deepest uniform decarburization zone.
The deepest point of the decarburized layer shall be determined by preliminary
detection on the sample surface, and is not affected by surface defects and angle
effects. For each sample, within the field of view of microscope of the deepest uniform
decarburization zone, several measures at least five shall be carried out at random.
The average value of these measured values is regarded as the depth of total
decarburization. For bearing steel, tool steel and spring steel, the deepest depth of
total decarburization shall be measured. If there are no special regulations in product
standards or technical agreements, in measure, the deepest points of decarburization
of the sample shall be excluded (but the deficiencies shall be indicated in the test
record).
4.2.3.2 The determination of complete decarburization
The measuring method of complete decarburization is same as 4.2.3.1.
4.2.3.3 The determination of functional decarburization
The measuring method of functional decarburization is same as 4.2.3.1. The
functional decarburization shall be judged by the product standards or determined by
the mutual agreement.
4.2.3.4 The typical structure picture of the depth of decarburization determined
through metallographic method
The typical structures pictures of depth of decarburization determined by
metallographic method are illustrated in Annex A.
4.3 Hardness Method
4.3.1 Micro (Vickers) Hardness Measurement
This method is measuring the distribution gradient of the micro-hardness value be
normal to surface direction on the sample's cross section.
This method is only applicable to hypo-steel, eutectoid steel and hypereutectoid steel
with rather deep decarburized layer and relative thin quenching zone. This kind of
decarburized layer is completely in the hard zone. It is inaccurate for low carbon
steels.
4.3.1.1 Selection and Preparation of Samples
The selection and preparation of samples are same as metallographic method (4.2.2),
but whether the sample is eroded or not shall be determined by the accurate
determined impress dimension. The over - heating of samples shall be prevented with
caution.
4.3.1.2 Determination
The testing method shall be carried out according to provisions stated in GB/T 4340.1.
In order to reduce the dispensability of measured data, load as large as possible shall
be applied. In principle, this load shall be with in the range of 0.49 N ~ 4.9 N (50 gf ~
500 gf). The distance between impresses shall at least be 2.5 times of the length of
impress diagonal.
The depth of decarburization is stated as distance from the surface to the point
reaching the required hardness value (dispensability shall be considered in measure).
In principle, two-sets of determination shall be carried out at two locations with
distance as far as possible, and the average value shall be regarded as the depth of
decarburization.
Measuring boundary of the depth of decarburization may be.
a) From the sample fringe to the section with hardness value stated in product
standard or technical agreement;
b) From the fringe to the section with stable hardness value;
c) From the sample fringe to the percentage of the section with stable hardness
value.
Which measuring boundary shall be adopted is determined by product standard or
mutual agreement.
4.3.2 Rockwell Hardness Measurement
While the Rockwell hardness tester is used, for products not allowing decarburized
layer, it shall directly detect on the surface of the sample's originating product; for
specimen allowing decarburization, it shall detect on the surface removing the
decarburized layer.
Rockwell Hardness Method is to determine the Rockwell hardness value HRC
according to GB/T 230.1, and is only used to verdict whether the product is qualif...
......
 
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.