Brinell

Many types of hardness tests have been devised. The most common in use are the static indentation tests, eg, Brinell, Rockwell, and Vickers. Dynamic hardness tests involve the elastic response or rebound of a dropped indenter, eg, Scleroscope (Table 1). The approximate relationships among the various hardness tests are given in Table 2. 

Brinell. The first rehable indentation hardness test was developed by BrineU in 1900 and used ball bearings to make indentations in steel (1). The technique has remained rehable and essentially unchanged for nearly 100 years. The test, described by ASTM Standard ElO (2), is stiU in use. 

The principle of the Brinell hardness test is that the spherical surface area of a recovered indentation made with a standard hardened steel ball under specific load is direcdy related to the property called hardness. In the following, HBN = Brinell hardness number, P = load in kgf,... 

In practice it is stiU necessary to read the diameter of the Brinell impressions with a caUbrated microscope however, the computations to derive the Brinell hardness number are uimecessary for standard loads and indentors. Table 1 of ASTM ElO (2) contains the tabulated relation between indentation diameter and hardness number. 

Test pieces for Brinell testing must have two parallel sides and be reasonably smooth for proper support on the anvil of the test machine. Minimum sample thickness must be 10 times indentation depth. Successive indentations must not be closer than three indentation diameters to one another or to the edge of the test piece. 

Thus the Brinell test in its original manifestation is a laboratory test in which cut pieces are brought to it for testing. The lack of portabiUty spawned several modifications to achieve that property. 

The pin Brinell tester takes the form of a large C clamp with the baU indenter on the end of the screw. Load is controUed by a built-in shear pin. A modification of this device employs impact loading by a hammer to achieve similar results. 

There are also strap-on type Brinell testers in which the anvil is supplanted by a chain or other clamping device and the indenter is spring-loaded. These have the advantage of being able to test direcdy very large objects without the need for cutting samples. 

The hand-held comparative Brinell tester is the most portable device. With this device a hammer blow is substituted for the static load which is transmitted first through a standard bar of known hardness and then through the indenter into the workpiece. The indentations in both the standard bar and the workpiece are measured and from the ratio of the diameters the HBN is derived. The loss in accuracy is made up for by the exceUent portabUity. 

The latest portable Brinell testers are spring-loaded, hand-held, and digitized to read direcdy in Brinell hardness units. Their accuracy is questionable because of extreme surface sensitivity and they are not in fact Brinell testers but RockweU indenters caUbrated to read in Brinell numbers. 

The Brinell test range is limited, by the capabUity of the hardened steel baU indenters used, to HBN 444. This range can be extended upward to HBN 500 by using special cold work-hardened steel baUs and to as high as HBN 627 by using special tungsten carbide bads. 

Standard practice for Brinell testing is to measure the diameter of each indentation twice and average the measurement before entering the tables to determine HBN. The same averaging principle is appHed on nonflat (curved) surfaces which yield an ediptical, not a round, indentation. 

Brinell Tests of Steel Products Comparison Hardness Tester Practice Rockwell Test on Cemented Carbides Rockwell Test for Sintered Materials Knoop Test for Electrodeposited Coatings Webster Hardness Gauge Barcol Test of Aluminum Alloys... 

Vickers Hardness. The Vickers or diamond pyramid hardness (DPH) developed in 1924 was an improvement over the Brinell test. The Vickers test used a pyramidal diamond as the indenter. This permitted the hardness testing of much harder materials, and the constant 136° angle of the indenter eliminated the problem of variable indentation shape encountered using spherical indenters (1). 

Sodium—lead alloys that contain other metals, eg, the alkaline-earth metals, are hard even at high temperatures, and are thus suitable as beating metals. Tempered lead, for example, is a beating alloy that contains 1.3 wt % sodium, 0.12 wt % antimony, 0.08 wt % tin, and the remainder lead. The German BahnmetaH, which was used ia axle beatings on railroad engines and cars, contains 0.6 wt % sodium, 0.04 wt % lithium, 0.6 wt % calcium, and the remainder lead, and has a Brinell hardness of 34 (see Bearing MATERIALS). 

AHoy no. Nominal composition, wt % Compressive Yield Strength, MPa Ultimate Brinell hardness... 

Common name UNS designation 0.5% Yield strength, MPa " Compressive yield strength, MPa " Tensile strength, MPa " Elongation in 5 cm, % Brinell hardness, 500-kg load Electrical conductivity, % lACS Thermal conductivity at 20°C, W/(m-K) ... 

Chromium. Chromium [7440 7-3] also forms heat-treatable copper ahoys. These ahoys, in the heat-treated condition, have a Brinell hardness of about 120 and an electrical conductivity of about 80% lACS. 

Base-metal P numberf Weld-metal analysis A numberf Material group Nominal waU thickness Minimum specified tensile strength, base metal Metal temperature range h/in, nominal wall Minimum time, b Brinell hardness, maximum... 

AISI type Tensile strength, 1,000 lh /in Yield strength (0.2% offset), 1000 Ihf/in Elongation (in 2 in), % Reduction of area, % Hard- ness, Brinell Impact strength (Izod), ft-lhf... 

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