GB/T 30834-2022Rating and classifying of inclusions in steel - Scanning electron microscope method (English PDF)

Foreword

This document was issued on 12 October 2022 by the State Administration for Market Regulation; Standardization Administration of the PRC and takes effect on 1 February 2023.

It is a GB/T standard: recommended rather than compulsory, but it is the text a Chinese reviewer applies when assessing a submission.

1 Scope

GB/T 30834-2022 covers the rating and classification of non-metallic inclusions in steel with a scanning electron microscope — the microscope and the accessories it needs, including image acquisition software and the spectrometer, the calibration and verification of that equipment, the sampling, the specimen preparation, the test steps, the classification, rating and statistics of what is found, the inspection report, and the precision and bias of the result. Three methods sit alongside each other. Method 1 keeps the inclusion classes of GB/T 10561 and uses the characteristic spectrum to confirm and separate them; Method 2 shares its sampling; Method 3 is sampled by agreement between supplier and purchaser. Informative annexes give typical acquisition conditions, worked examples of results from Method 1 and Method 3, results on rare-earth-treated steel, and X-ray counting with chemical classification statistics. Under an optical microscope, two inclusions of the same shape and shade are the same inclusion. Under the electron microscope one may be an oxide and the other a sulphide, and only that difference points back to the process step — deoxidation practice, refractory wear, casting — that produced it. Since inclusions are where fatigue cracks begin, the chemistry is what turns a rating into something a steelmaker can act on. Written for steelworks metallurgists, materials laboratories and purchasers writing cleanliness requirements into a steel specification.

This document specifies the equipment for evaluating and classifying non-metallic

inclusions in steel by scanning electron microscope (SEM), calibration and verification

of equipment, sampling, specimen preparation, test procedures, inclusion classification,

rating and statistics, test reports, precision and bias.

This document recommends three inspection methods. Method 1 mainly classifies

inclusions according to their morphology. Method 2 mainly classifies inclusions

according to their chemical composition. Method 1 and Method 2 are suitable for

microscopic evaluation of non-metallic inclusions larger than 2um in rolled or forged

steel with a compression ratio greater than or equal to 3. Method 3 is used to determine

the specific details of a certain type of inclusion such as volume fraction, number

fraction and other stereological parameters. It is suitable for the statistical classification

of inclusions of all sizes (including below 2um) in various slabs or steel products.

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 10561, Steel - Determination of content of nonmetallic inclusions -

Micrographic method using standards diagrams

GB/T 13298, Inspection methods of microstructure for metals

GB/T 17359, Microbeam analysis - Quantitative analysis using energy dispersive

spectrometry

GB/T 18876.1, Standard practice for determining the metallographic constituent

and inclusion content of steels and other metals by automatic image analysis - Part

1: Determining the inclusion or second-phase constituent content of steels and other

metals by automatic

GB/T 18876.2, Standard practice for determining the metallographic constituent

and inclusion content of steels and other metals by automatic image analysis - Part

2: Determining the inclusion ratings of steels by automatic image analysis and

stereology

GB/T 27788, Microbeam analysis - Scanning electron microscopy - Guidelines for

calibrating image magnification

GB/T 30067, Standard terminology relating to metallography

3 Terms and definitions

For the purposes of this document, the terms and definitions defined in GB/T 30067 as

well as the followings apply.

3.1 acquisition analysis rules

The conditions for terminating X-ray acquisition (count, time or both), the list of

elements to be analyzed, the number of fields or particles to be analyzed, the shape of

particles to be analyzed, and so on.

NOTE: Typical acquisition conditions for SEM (see Annex A).

3.2 post-acquisition analysis rules

The elemental composition that identifies the chemical classification of the inclusions.

NOTE: For Method 1 and Method 2, in addition to setting the elemental composition of the

chemical classification of inclusions, it is also necessary to set the type of inclusion (class A, class

B or class C) to which each chemical classification belongs.

3.3 chemical classification

Set the category to which inclusions belong based on elemental composition.

NOTE: It can be broadly classified, such as sulfide, alumina, and silicates. It can also be finely

classified, such as calcium sulfide, calcium silicate, and anorthite.

3.4 aspect ratio; AR

The ratio of the longitudinal and transverse directions of the extension of the inclusions.

3.5 stringer

A single inclusion that is highly extended in the direction of deformation. Two or more

type A or type C inclusions, three or more type B inclusions, and these two or more

inclusions must be arranged in a row, parallel to the direction of the thermal processing

axis. The center line of offset stringer inclusions is less than or equal to 15um. The

distance between any two adjacent inclusions is less than or equal to 40um.

3.6 Feret's diameter

chemical classification should be indicated in the inspection report.

4.4 Method 1 and Method 2 provide a quantitative evaluation method for each type of

inclusion and each width series of inclusion levels (level 0~5) in half-level increments.

4.5 Method 3 specifies procedures for analyzing and counting inclusions by size and

chemical classification. Method 3 is used to determine and record some basic

stereological parameters of inclusions, such as the area fraction of sulfides and oxides,

the number of sulfides or oxides per square millimeter. Method 3 is not used for rating.