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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 4236-1984 Steel - Examination by sulphur print (Baumann method).
The following main technical changes have been made with respect to GB/T 4236-1984:
——The “application scope” is expanded (see Clause 1);
——The “principle and purpose” is modified (see Clause 3);
——The requirements of roughness on the specimen surface are modified (see 4.5);
——The cleaning requirements for the examination surface of the specimen are specified (see 4.6);
——The types of reagents are added, and the recommended concentration is given according to the sulphur content in the steel (see Table 1);
——“Test safety” is added (see Clause 7);
——“Examination results” is added (see Clause 8);
——The schematic diagrams for sulphur print image are added (see Annex A).
This standard was proposed by China Iron and Steel Association.
This standard is under the jurisdiction of the National Technical Committee on Iron and Steel of Standardization Administration of China (SAC/TC 183).
The previous edition of the standard replaced by this standard is as follows:
——GB/T 4236-1984.
Steel examination by sulphur print (Baumann method)
1 Scope
This standard specifies the principle and purpose, specimen preparation, materials and reagents, test procedures, test safety, examination results and test report of steel examination by sulphur print (Baumann method).
This standard is applicable to steel with sulphur content greater than 0.0050%, and may also be used for cast iron.
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 8978-1996 Integrated wastewater discharge standard
3 Principle and purpose
3.1 The sulphur print test is a qualitative test, thus it is not appropriate to estimate the sulphur content of steel only with the results of the sulphur print test.
3.2 The purpose of the sulphur print examination is to determine the distribution location of sulfide inclusions in steel by prints on printing paper pre-soaked in an acid solution.
3.3 Sulphur-enriched regions appear as a result of the blackening of the emulsion's silver halide to silver sulfide due to the precipitation of hydrogen sulfide.
3.4 Through the analysis of the distribution and amount of sulfide determined by this method, the purity degree of the steel in the examined part may be estimated. For example, sulphur prints may show inhomogeneities in chemical composition (such as segregation in free-cutting steels) and defects in certain features (such as cracks and pores). In addition, the sulphur print may be used to distinguish between rimming steel and killed steel, and may also be used to identify the parts that need to be tested (such as mechanical property tests) or sampled for analysis.
3.5 According to the test, the degree of blackening of the emulsion is not always proportional to the sulphur content of the steel. Certain factors also affect the results of corrosion.
Notes:
1 Some steels contain complex sulfides, such as titanium sulfide or chromium sulfide, which are difficult to react with acid solution, resulting in a lighter color of the sulphur print.
2 The surface condition of the specimen: The surface subjected to cold processing may affect the resulting image.
4 Sampling and preparation
4.1 The test may be performed on the product or on specimens cut from the product. For products such as bar, billet and round steel, the specimens are generally cut from the section perpendicular to the rolling direction or the appropriate surface is negotiated by both parties.
4.2 If not specified in the product standard, the number and location of the specimens shall be negotiated by both parties. However, when cut by the following methods, the examined surface of the specimen shall be kept away from the cutting surface:
a) hot shear that will deform metal fibers and inclusions and displace the segregation zone;
b) flame cutting that will cause local hardening, shrinkage cracking or local tempering to hard steels.
4.3 The processing of the specimen surface is extremely important to obtain the correct sulphur print. The following methods are generally used:
a) planing, turning or milling;
b) grinding.
4.4 The followings shall be noted when machining:
a) there is no cutting mark caused by improper adjustment and excessively deep feed of the lathe or planer; generally, the effect is better when the feed depth is 0.1mm;
b) the cold-processed surface is as small as possible in case the cutting tool is not suitable for this metal, the tool is poorly machined, and the grinding wheel is improper;
c) the inherent holes and cracks of the specimen cannot be repaired by surface processing.
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4.5 In order to obtain a good sulphur print image, the roughness of the examination surface shall be small, but too small roughness (mirror surface) will make the printing paper slip easily on the test surface and cause blurred images. The roughness Ra of the machined test surface is less than or equal to 3.2μm.
4.6 Before the sulphur print test, the examination surface shall be cleaned using acetone, ethanol and other reagents and dried to prevent dark spots from the sulphur print image.
5 Materials and reagents
5.1 Materials
Silk and glossy papers are used. Sulphur prints are produced on the photosensitive surface of printing paper cut to the appropriate dimensions.
5.2 Reagents
5.2.1 Usually sulphuric acid, citric acid or acetic acid reagents are used. The types and concentrations of recommended reagents are shown in Table 1. Other reagents may also be adopted in order to obtain clear sulphur prints.
Table 1 Types and concentrations of recommended reagents
Sulphur content in steel (mass fraction)/% Reagent concentration (volume fraction)/%
0.005~0.015 5~10 sulphuric acid aqueous solution
0.015~0.035 2 sulphuric acid
0.10~0.40 0.2~0.5 sulphuric acid, 10~15 citric acid or acetic acid
5.2.2 Commercial fixer or 15%~20% sodium thiosulfate aqueous solution is usually used.
6 Test procedures
6.1 The printing paper is immersed in a sufficient volume of acid solution (see Table 1) at room temperature for as long as the printing paper fully soaks. The printing paper shall be shaken gently when soaked to ensure even soaking of the acid on the printing paper. During the process of cutting, soaking and subsequent tests, the printing paper shall be protected from exposing to strong light.
6.2 When taking out the printing paper, absorbent cotton or absorbent paper shall be used to remove the excess dilute acid on the printing paper, and the friction between the printing paper and the examination surface may be increased to avoid blurring of the image caused by sliding. After removing the excess acid solution, the photosensitive surface of the printing paper is applied to the examined surface. If the specimen is small, it may also be placed on the soaked printing paper in advance. This method shall be used to ensure close contact between the printing paper and the specimen without any slippage, and if necessary, a heavy object may be used to press the specimen to facilitate contact.
Foreword i
1 Scope
2 Normative references
3 Principle and purpose
4 Sampling and preparation
5 Materials and reagents
6 Test procedures
7 Test safety
8 Examination results
9 Test report
Annex A (Informative) Schematic diagram for sulphur print images of steel
