GB/T 224-2008 Determination of depth of decarburization of steels (Text of Document is in English) - Beijing translation compay

1 Scope

This national 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 provision which, through reference in this text, constitute provisions of this national standard. For dated reference, subsequent amendments to, or revisions of, any 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.l-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.