If the material type or stainless steel grade carbon content percentage you know? hardness test is a simple way to verify that a material has been properly heat treated. Hardness testers such as Rockwell, Brinell, and Vickers can be useful to check metals for actual hardness.
Hardness tests are generally considered nondestructive, hardness testing does leave a small pit in the surface; therefore, hardness tests should not be used on sealing surfaces, fatigue critical parts, load bearing areas,etc., components which will be used in critical applications . These hardness tests provide a convenient means for determining, within reasonable limits, the tensile strength of steel. It has several limitations in that it is not suitable for very soft or very hard stainless steel pipe.
Hardness testing of aluminum alloys should be limited to distinguishing between annealed and heat-treated material of the same aluminum alloy. In hardness testing, the thickness and the edge distance of the specimen being tested are two factors that must be considered to avoid distortion of the metal. Several readings should be taken and the results averaged. In general, the higher the tensile strength, the greater its hardness.
The Shore (Scleroscope) Hardness Test
The Scleroscope test consists of dropping a diamond tipped hammer, which falls inside a glass tube under the force of its ownweight from a fixed height, onto the test specimen. The height of the rebound travel of the hammer is measured on a graduated scale.The harder the material, the higher the rebound.
The scale of the rebound is arbitrarily chosen and consists on Shore units, divided into 100 parts, which represent the average rebound from pure hardened high-carbon steel. The scale is continued higher than 100 to to allow for metals having greater hardness.
The shore scleroscope test does not normally mark the material under test. The Shore Scleroscope measures hardness in relation to the elasticity of the material.
Advantages of this method are portability and non-marking of the test surface.
The Knoop indenter has a polished rhombohedral shape with an included longitudinal angle of 172° 30’ and an included transverse angle of 130° 0’. The narrowness of the indenter makes it ideal for testing specimens with steep hardness gradients and coatings. Knoop is a better choice for hardness testing of hard brittle materials.
The Jominy test involves heating a test specimen of stainless steel 25mm diameter and 100mm long to an austenitising temperature and quenching from one end with a controlled and standardized jet of water. After quenching, the hardness is measured at intervals taken form the quenched end. The hardness gradient along the test surface provides an indication of the material’s hardenability.
The Moh's hardness scale consists of 10 minerals arranged in order from 1 to 10. Diamond is rated as the hardest and is indexed as 10; talc as the softest with index number 1.
Each mineral in the scale will scratch all those below it as follows:
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