GB/T 13320-2007Metallographic grading atlas and assessing method for steel die forgings (English PDF)

Foreword

This Standard replaces GB/T 13320-1991, Metallographic grading atlas and assessing

method for steel die forgings.

Compared with GB/T 13320-1991, the main changes of this Standard are as follows.

-- Add terms and definitions, i.e., "isothermal normalization", "control cooling

after forging" process and "effective thickness";

-- Remove the words "automobiles, tractors, general machinery" in the scope of

application;

-- Cancel the various steel grades listed in Chapter 2 of the original standard;

-- Combine the third and fourth groups of grading atlases of the original standard

into the third group of grading atlases of this standard, i.e., grading atlas of

forgings made of quenched and tempered steel;

-- Cancel Subclause 3.2 of the original standard;

-- Cancel the words "two representative places may be taken" in 4.1 of the

original standard, and replace the preparation of samples by 5.2 of this

standard;

-- Cancel the method of "can be expressed in half-grade" in 5.1 of the original

standard;

-- Cancel the descriptions of words such as "part" and "a small amount" in the

figures, and use shapes and uniformity to describe the situation instead.

Appendix A of this Standard is an informative appendix.

This Standard was proposed by China Machinery Industry Federation.

This Standard shall be under the jurisdiction of National Technical Committee 74 on

Forging of Standardization Administration of China.

Drafting organization of this standard. Faw Bharat Forge Co., Ltd.

Main drafters of this Standard. Yang Jianjun, Lu Dongyuan, Wang Dewei.

The previous versions of the standards which are replaced by this Standard are.

-- GB/T 13320-1991.

Metallographic grading atlas and assessing method for steel

die forgings

1 Scope

This Standard specifies the metallographic grading atlas (hereinafter referred to as

grading atlas) and assessing method for steel die forgings.

This Standard applies to structural steel die forgings that have been subjected to

quenching and tempering, normalizing, isothermal normalization, and control cooling

after forging.

This Standard is not applicable to the assessment of decarburization, overheating, over-

burning and other microstructures of forgings.

2 Terms and definitions

The following terms and definitions are applicable to this Standard.

2.1

isothermal normalization

A heat treatment process in which the forging is heated to a temperature higher than Ac3

(or Ac1), kept at that temperature for a period of time, then cooled to a temperature in

the pearlite transformation zone and kept isothermally for a period of time to transform

the austenite into a pearlite structure, and then cooled in air.

2.2

control cooling after forging

A process of controlling the cooling rate of the forging by residual heat so that the

forging, after forming, obtains pearlite plus ferrite or bainite structure.

2.3

effective thickness

When the wall thickness of different parts of the forging is different, if determining the

heating time according to the wall thickness at a certain place can ensure the quality of

heat treatment, then the wall thickness at that place is called the effective thickness of

the forging.

3 Grouping and grading of grading atlas

The grading atlases are divided into the following three groups, each with 8 grades.

The first group of grading atlases is shown in Figure 1, which is applicable to forgings

of medium carbon structural steel that have been subjected to normalizing and forgings

of medium carbon low alloy non-quenched-and-tempered steel that have been subjected

to control cooling after forging.

The second group of grading atlases is shown in Figure 2, which is applicable to

forgings that have been subjected to carburizing steel normalizing, isothermal

normalization and control cooling after forging.

The third group of grading atlases is shown in Figure 3, which is applicable to forgings

made of quenched and tempered steel.

4 Application of grading atlas

5 Sample selection and preparation