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Hardness testing of spring material

Hardness testing of spring material

Hardness testing of spring material

What are ways to test the hardness or the quality of manufacturing/heat treatment of the spring?

The problem with a normal hardness testing machine (eg a rockwell hardness testing) is that these are usually used for flat surfaces and will be difficult to make accurate on a round surface such as a wire.

Any deformation or cutting on the finished spring to make a flat surface will not work. The suppliers for the steel wire also cannot supply flat surfaces of the material.

Thanks in advance.

RE: Hardness testing of spring material

Spring wire are tested by tensile strength. The specification that the wire is supposed to meet defines the minimum and maximum tensile strength required. When you purchase a spring wire, make sure to ask for the manufacturer Certificate of Tests (C.O.T) not the C.O.C. It specifies the actual tensile test results made in the spring manufacturer facilities on the purchased wire batch, including prior and after heat treatment tests. If you do not trust the spring manufacturer you need to repeat the tests in a respected test lab.

RE: Hardness testing of spring material


Round wire/bar is routinely tested for hardness, and standards such as ASTM E18, ISO 3506, etc. account for the curvature by using a correction factor.

RE: Hardness testing of spring material

Microhardness on a mounted specimen is also employed. Keep in mind that any hardness conversions to tensile strength generally are not valid for spring wire. The main use for hardness testing on spring wire is to evaluate samples against the history of the wire you have been using, i.e. conformatory testing.

RE: Hardness testing of spring material


Is the correction factor for the curvature added onto the hardness indicated by testing machine?

How does one test the tensile strength of a 3.2mm diameter round wire? We have a tensile testing machine (with several different grips/clamps for different materials)... Most of the grips can't be used.. the one that can is just a pressing clamp and the wire slides through very easily..

RE: Hardness testing of spring material


Yes, the correction factor is added to the indicated hardness to adjust the final hardness. For example, for a 6 mm wire sample, if the indicated hardness is 55 HRC, the cylindrical correction factor is 2.0, which means that the final hardness is 55 + 2 = 57 HRC. You must purchase an appropriate hardness testing standard such as ASTM E18 or ISO 3506 in order to properly perform hardness testing. Regarding the tensile testing of wire, you need to purchase the appropriate grips for small wire samples. Instron and other providers of universal test machines also supply different grips. You need to discuss your specific application with them.

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