AWS A4.2M pdf free download

AWS A4.2M pdf free download.Standard Procedures for Calibrating Magnetic Instruments to Measure the Delta Ferrite Content of Austenitic and Duplex Ferritic- Austenitic Stainless Steel Weld Metal.
The copper coating may be covered by a chromium flash. The force required to tear off a given permanent magnet from the copper coating side of such a standard increases as the thickness of the copper coating decreases.
NOTE To ensure adequate reproducibility of the calibration, the coating thickness standards defined above should be used. In particular, coating thickness standards produced by the US National Institute of Standards and Technology (NIST, formerly National Bureau of Standards or NBS) may be used.
4.2 Magnet
The standard magnet shall be a permanent magnet of cylindrical shape, 2 mm in diameter and about 50 mm in length. One end of the magnet shall be hemispherical, with a 1 mm radius and polished. As an example, such a magnet can be made of 36 % cobalt magnet steel, 48.45 mm ± 0.05 mm long, magnetically saturated and then diluted to 85 %. The magnetic strength of the magnet shall be such that the force needed to tear oft the standard magnet from the different coating thickness standards is within ± 10 % of the relationship shown in Figure 1 (the weight of the magnet excluded). This is equivalent to a relationship between tear-off force and Ferrite Number of 5.0 FN/g ± 0.5 FN/g.
4.3 Instruments
The measurement by this method shall be made by an instrument enabling an increasing tear-off force to be applied to the magnet perpendicularly to the surface of the test specimen. The tear-oft force shall be increased until the permanent magnet is detached from the test specimen. The instrument shall accurately measure the tear-off force which is required for detachment. The reading of the instrument may be directly in FN or in grams-force or in other units. If the reading of the instrument is in units other than FN, the relationship between the FN and the instrument reading shall be defined by a calibration curve2.
Finally, plot the calibration curve as the relationship between the tear-off force in the units of the instrument reading and the corresponding FN.
To calibrate the instrument for measurement of ferrite content within the range from 0 to approximately 30 FN, which is appropriate for nominally austenitic stainless steel weld metals, a set consisting of a minimum of eight standards with copper coating thicknesses between approximately 0.17 mm and approximately 2 mm is recommended3. To extend the calibration from approximately 30 FN to 100 FN, which is appropriate for duplex ferritic-austenitic stainless steel weld metals, a set consisting of a minimum of five standards with coating thicknesses between 0.03 mm and 0.17 mm is recommended.
4.5 Calibration of other instruments with primary standards
In principle, instruments with other than a standard magnet, and instruments using an approach to magnetic property measurement other than magnetic attractive force, can be calibrated with primary standards providing that sufficient statistical data is collected. This has been done only with two older “legacy” instruments — see Annex C.AWS A4.2M pdf download.