Methods to identify stainless steel

It can happen that, in the stainless steel storage points, the depositor is in great difficulty in choosing the sheet to be used because two steels could have the same surface finish and the same color but belong to two different families. Very often, they use the magnetic method to distinguish an AISI 430 from AISI 304 or AISI 316: this method is very dangerous because if the austenitic steel is subject to plastic deformation, the microstructure of the crystal lattice of the steel is transformed, acquiring magnetic properties. In these situations the probability of making mistakes is really high and can lead to mechanical problems and corrosion resistance. To avoid these problems, we rely on electrochemical devices or using sophisticated X-ray instruments.

The bending of the stainless steel causes a change of the crystal lattice, going from amagnetic to magnetic

Inox Test

Inox Test is a portable device produced by Nitty-Gritty able to recognize the different families of steels through an electrochemical system.

The electrolyte liquid flows from the tip (white) to wet an absorbent paper placed on the metal surface. The grounding tip (gold color) closes the electrical circuit generated by the internal batteries of the device. The electrical conduction helps the reaction between the electrolytic liquid (absorbed by the paper) and the surface of the stainless steel, producing a colored stain.

Depending on the color we can distinguish:

  • AISI 200: red stain;
  • AISI 300 yellow color stain. To distinguish the molybdenum-containing alloys, a chemical reagent is then used on the yellow stain. If the color changes from yellow to pink, we are in the presence of a stainless steel containing molybdenum (AISI 316). If the yellow stain disappears, we are in the presence of a stainless steel that does not contain molybdenum (AISI 304).

For more information, please visit our website. You will find a small detailed demonstration video.

Customers choose this device because it is:

  • Light and portable;
  • Use non-hazardous liquids;
  • It has a very competitive cost;
  • A non-destructive test;
  • It involves small surface areas.

Impianto realizzato con acciai inossidabili 304 e 316

X-ray fluorescence

XRF is an x-ray emission spectroscopy technique that allows the identification of the chemical elements that are present, or compose, the examined sample. This technique therefore makes it possible to establish the presence of a given element and, using an appropriate measurement and data analysis methodology, to establish the concentration of it in the sample. The chemical analysis in XRF is then obtained by recording the secondary (fluorescence) RX beam produced after the interaction of the primary RX beam with the sample. The wavelengths present in the fluorescence RX beam will be “characteristic” of the chemical elements present in the sample, and the intensity of each single wavelength will be proportional to the concentration of the relative elements. To make quantitative analysis, however, it will be necessary to simultaneously analyze the reference standards, i.e. samples with a known concentration to construct appropriate calibration lines. Obviously the transition from qualitative to quantitative analysis technique is not automatic, this can in fact only take place in particular working conditions. The use of X-rays in the analysis of materials is largely due to their high penetration in many materials; in most cases it is indeed true that, in order to obtain, with a non-destructive investigation, analytical or structural information on a sample, two facts must occur simultaneously:

  1. The radiation penetrates sufficiently in the sample in order to cross it or at least to penetrate significantly;
  2. The radiation must interact with the atoms of the material in a sufficiently frequent way to allow from the outside to observe what has happened inside the sample.

Funzionamento della pistola a raggi X

The x-ray fluorescence device:

  • Perform non-destructive tests;
  • Provides the percentage of substances contained in the material;
  • High costs;
  • Portable but cumbersome.

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