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What is the difference between piano wire and hard steel wire? 

These two materials are very similar and visually indistinguishable like stainless steel wire for springs. What exactly is the difference?

In a nutshell, piano wire is a high-grade material and hard steel wire is a general material. Of course, piano wire is more expensive. Although it cannot be generalized, piano wire is often used for springs of precision machinery, and hard steel wire is often used for springs of everyday items such as sundries and shutters.

Although they are the same high-carbon steel wire and have almost the same chemical composition, the reason why piano wire is of higher quality is that piano wire is manufactured with more care than hard steel wire.

First, regarding the chemical composition, stricter standards are used for impurities and inclusions than for hard steel wire. Hard steel wire has no standard for the depth of scratches on the surface and the depth of the decarburized layer, but piano wire is standardized and checked.

It's a subtle difference that you can't see, but it has a big impact on spring quality.

 Japanese Page ↓

＞Comparison of chemical composition of piano wire and hard steel wire

> JIS standards for spring materials

> Spring design "Five points for material selection"

> Prototype springs, even one piece...

How to distinguish between piano wire and hard steel wire

 It's almost impossible to tell them apart visually. Even if you order expensive piano wire, if the manufacturer uses cheap hard steel wire, it is almost impossible to tell the difference from the outside. We won't know unless something goes wrong with the springs. In order to identify it, it is necessary to ask an inspection agency to analyze the ingredients of the material.

Hard steel wire material inspection report