High-Speed Tool Steel Large Section Forging Steel (GB/T9942-1988)
Introduction
High-speed tool steel is one of the most important materials used in the manufacture of molds and tools. As a kind of carbon tool steel, high-speed tool steel needs to be heat treated for proper performance, and requires special processing methods to achieve the required performance due to its high hardness, abrasion resistance, thermal shock resistance, and higher machinability. High-speed tool steel is mainly used in the manufacture of cutting tools, such as milling cutters, sliding blocks, reamers, etc., as well as in the manufacture of molds such as forming tools, cold heading tools and hot pressing tools. In such applications, it is necessary to use high-speed tool steel with large cross-sectional areas.
GB/T9942-1988 ‘High-Speed Tool Steel Large Section Forging Steel’ stipulates the requirements, test methods, and inspection rules for hot rolled steel used for the production of tool steel with large cross-sections. The standard is applicable to carbon tool steel with a nominal chemical composition of C 0.58~1.02%, Si 0.17~0.41%, Mn 0.4~1.2%, Cr 0.4~1.5%, W 0.4~1.0%, and V 0.15~ 0.4%. The test methods specified in this standard include chemical composition analysis, hot-rolled strip thickness measurement, hydrostatic pressure test, tensile test, hardness test, macrostructure inspection, and fatigue test.
Chemical composition analysis
Chemical composition analysis is an important part of the inspection of high-speed tool steel. GB/T 9942-1988 stipulates that chemical components of molten steel should be checked by use of a spectrometer. First, the molten steel sample is prepared. It is then placed in an open vessel and the required amount of flux is added if necessary for spectroscopic analysis. The flux is melted and the steel is melted in the induction melting furnace. The molten steel is poured into the sample holder.
The sample is then placed in the spectrometer and the measurement is performed following the manufacturer’s instructions. The results of the spectrometry must comply with the requirements of GB/T9942-1988.
Hot-rolled strip thickness measurement
The thickness of the hot-rolled strip should be measured with a micrometer in accordance with GB/T9942-1988. The thickness should be measured at the both roll gap sides, at the center of the roll gap and the two sides of the roll gap 1200mm away from the center in the longitudinal direction, while in the transverse direction 200mm away from the center in each side. The average value of the results should be measured.
Hydrostatic pressure test
After hot-rolled strip thickness measurement, the hydrostatic pressure test should be conducted in accordance with the requirements of GB/T9942-1988. First, the sample should be inspected for surface quality. Then, the sample should be clamped on the hydrostatic pressure testing apparatus, and the oil pressure should be fully loaded in a few minutes. The test results should meet the requirements.
Tensile test
The tensile test should be performed in accordance with the requirements of GB/T9942-1988. First, the sample should be subjected to tension test, with a given tensile rate, until polarization occurs. The maximum force at the time of fracture, the elongation and the yield point should be recorded. The results should meet the requirements of the standard.
Hardness test
The hardness of the steel should be tested in accordance with the requirements of GB/T9942-1988. A Vickers hardness tester with a load of 10kg should be used, and the test should be performed at the position of the roll gap. The test results should meet the requirements of the standard.
Macrostructure inspection
The macrostructure inspection of high-speed tool steel should be performed in accordance with the requirements of GB/T9942-1988. First, the samples should be polished by grinding to a No. 5 or a No. 6 finish. The samples should then be etched with a 5% nital solution or a 5% picric acid solution. The macrostructure should meet the requirements of the standard.
Fatigue test
The fatigue test should be performed in accordance with the requirements of GB/T9942-1988. A fatigue tester should be used for the fatigue test, and the test should be performed for cycles between 5000 and 10000 cycles. The test results should meet the requirements of the standard.
Conclusion
High-speed tool steel is an important engineering material used in the manufacture of molds and tools. To meet the strict requirements of such applications, special processing methods and GB/T9942-1988 ‘High-Speed Tool Steel Large Section Forging Steel’ are necessary. This includes chemical composition analysis, hot-rolled strip thickness measurement, hydrostatic pressure test, tensile test, hardness test, macrostructure inspection, and fatigue test. All of these tests should conform to the requirements of the standard and the results should meet the requirements of the standard.
