Page 260 - CITS - Welder - Trade Theory

WELDER - CITS

seconds in the case of iron and steel and for at least 30 seconds in the case of other metals. The diameter of the
indentation left in the test material is measured with a low powered microscope. The Brinell harness number is
calculated by dividing the load applied by the surface area of the indentation. When the indentor is retracted two
diameters of the impression, d1 and d2, are measured using a microscope with a calibrated graticule and then
averaged as shown in Fig 11.

Fig 11

The diameter of the impression is the average of two readings at right angles and the use of a Brinell hardness
number table can simplify the determination of the Brinell hardness. A well structured Brinell hardness number
reveals the test conditions, and looks like this, “75 HB 10/500/30” which means that a Brinell Hardness of 75 was
obtained using a 10mm diameter hardened steel with a 500 kilogram load applied for a period of 30 seconds.
On tests of extremely hard metals a tungsten carbide ball is substituted for the steel ball. Compared to the
other hardness test methods, the Brinell ball makes the deepest and widest indentation, so the test averages
the hardness over a wider amount of material, which will more accurately account for multiple grain structures
and any irregularities in the uniformity of the material. This method is the best for achieving the bulk or macro-
hardness of a material, particularly those materials with heterogeneous structures.
Guided bend test: A guided bend test is one in which the specimen as in Fig 12.
There are two types of specimens prepared for this - one for face bend and the other for root bend. (Fig 13)
This test measures the ductility of the weld metal in a butt joint in a plate. This test shows most weld faults quite
accurately and it is very fast. A sample specimen can be tested on destruction to determine (a) the physical
condition of the weld and thus check on the weld procedure and (b) the welder’s capability.

Fig 12 Fig 13

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CITS : C G & M - Welder - Lesson 83 - 97