GB/T 14979-1994Steel - Micrographic method for assessing the inhomogeneity of eutectic carbides using standard diagrams (English PDF)

GB/T 14979-1994 is the English-translated version of 钢的共晶碳化物不均匀度评定法.

China's national method for rating how unevenly the eutectic carbides are distributed in a steel, by comparison against standard reference diagrams. It specifies the micrographic method for assessing eutectic carbide inhomogeneity, the specimen preparation, the examination and the rating series.

Eutectic carbides are what make a high speed steel or a high-carbon high-chromium tool steel able to cut and to resist wear: they are hard, they are formed during solidification, and they are far harder than any matrix.

But they are formed in the last liquid to freeze, which is between the dendrites, so they arrive segregated into a network or into bands, and hot working stretches that network into stringers running along the rolling direction rather than dispersing it.

A tool made from steel with a coarse, banded carbide distribution behaves differently in every direction, distorts unpredictably during heat treatment because the carbide bands transform at different rates, and chips at the edge where a carbide stringer intersects it.

Two bars of identical composition and hardness can differ by a large factor in tool life for this reason alone, which is why the property is rated and why the rating appears on a certificate.

Rating it numerically is not practical, so the method is comparison: a polished and etched longitudinal section is examined at a fixed magnification and matched against a series of standard diagrams graded from fine and dispersed to coarse and banded.

The standard therefore has to fix the section, the preparation, the etchant, the magnification, the field selection and the reporting - everything that would otherwise make two ratings incomparable. Issued on 13 June 1994 and in force since 1 January 1995.

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This preview omits tables, figures, formulas and parts of the technical clauses. The complete document — 21 pages — is available in the English PDF.

GB/T 13298-2015|GB/T 6394-2017|GB/T 18254-2016|GB/T 1299-2014|GB/T 9943-2008|GB/T 10561-2005

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