Steel structure: macroscopic analysis

Macroscopy of steel

Macroscopic analysis (macroanalysis) consists in determining the structure of the metal by viewing its surface with the naked eye or under a magnifying glass at low magnifications - up to 30 once.

Macroanalysis does not determine the details of the structure and is often a preliminary view of the study.. At the same time, it allows you to select those areas, which require further microscopic examination.

What determines the macroanalysis of the structure of steel

Macroanalysis is used to determine
1) metal discontinuity:
– shrinkage looseness;
– gas bubbles and shells;
– cracks;
– emptiness, formed in cast metal;
– cracks, arising from hot mechanical or heat treatment;
– since hydrogen in general adversely affects most of the properties and performance of steel;
– welding defects (in the form of lack of penetration, gas bubbles, voids);
2) dendritic structure and transcrystallization zone in cast metal;
3) chemical heterogeneity of the alloy (segregation):
– sulfur distribution;
liquidation carbon and phosphorus;
4) alloy structure inhomogeneity, caused by pressure treatment:
– banding;
– slip lines (shifts) in riveted metal;
5) heterogeneity, created by thermal or chemothermal treatment:
– hardened layer thickness;
– cemented layer depth.

Macroslice

Surface, subject to macroanalysis , study directly (by type of fracture) or ground and etched with special reagents. The sanded surface must be free of contaminants., traces of oil and the like. Therefore, it is wiped with cotton wool before etching., soaked in alcohol. The prepared sample is called macrosection.

Of great importance for the successful implementation of macroanalysis is the correct choice of the most characteristic section or fracture for the part under study..

Methods of macroanalysis are different depending on the composition of the alloy and the task..

The sequence of macroanalysis of the steel structure

If necessary, a full macroscopic examination, as well as determining metal discontinuities and structural defects, it is advisable to adhere to the following sequence of work:

1) first etch the sample with a reagent, containing 85 g copper chloride CuCl2 and 53 g ammonium chloride NH4Cl on 1000 ml of water;
2) photograph the results;
3) grind the sample again and determine the distribution of sulfur on the print on photographic paper;
4) perform deep etching to determine discontinuities and flocs.

GUEST 10243

Methods for testing and evaluating the macrostructure of steel are regulated by GOST 10243-75. This standard applies to forged and rolled, doped and high alloy steels. It establishes test methods and reference scales for assessing macrostructure, as well as the classification of defects in the macrostructure and fractures of bars and blanks with a diameter or thickness from 40 to 250 mm cross section.

Source: Metallurgy and heat treatment of steel