Understanding Material Classifications for Your Next Steel Spring Project
The spring industry, over the years, has divided the common spring materials into different classifications. Some of these classifications have somewhat confusing or misleading names, but are used as jargon within the industry nevertheless.
These classifications begin with raw materials, so we’ll first discuss them. Look for our upcoming blog on classification of spring materials—think of this as a primer to define some basic terms as they relate to spring steel.
Metal is a class of element such as gold, silver, or copper, which are opaque, ductile, and have a luster to them. No springs are made from the primary elements—these are the first building blocks of steel—iron being the most common element in steel.
Steel consists of artificially produced forms of iron which contain varying amounts of carbon. When looking at a certification for steel, the certification will always indicate the amount of other materials contained in the steel. But the percentages will not add up to 100% because the iron content is, by definition, the balance of the contents.
Almost all springs are made from a steel, although there are some plastic ones now a days. There’s another way to look at steel in relation to steel spring manufacturing: think about steel as a classification, such as meat. We all know what meat is, but meat could mean lamb or beef or chicken or pork. Alloys are the specifics, such as lamb or beef. Steel is just the classification they all belong to.
Alloys comprise two or more metals or metal with a non-metal content permanently mixed together. Alloys are similar to a recipe in a cookbook. At the top of the recipe are the contents, and at the bottom are the means of processing. Many of the steels have the same or similar chemical content, but are processed differently. This is much the same as if you take three eggs and fry one, hard boil another, and scramble the third. Obviously the “raw material” is identical, but the end product is vastly different because of the means of processing. When considering what material (alloy) to use conductivity, constant modulus, corrosive resistance, heat hardenability, magnetism, platability, stress and temperature all come into play.
Within the spring industry, carbon is a term applied to “ordinary” steel. It comprises mostly one of three types of steel—hard drawn, oil-tempered medium basic, or music wire. These are the least expensive and probably the most often used forms of spring steel.
They are the most common for two reasons. One is definitely price, but just as important is the fact that most springs are used in a machine of some sort and most machines have an oily environment, which means the springs are protected by the oil and there is no need for corrosive resistance.
Alloy steel is related to one of the confusing terms mentioned above. In order to make carbon steel stronger, the carbon steel is mixed with either chromium and vanadium or chromium and silicon. Consequently, the alloy names are oil-tempered chrome vanadium and oil-tempered chrome silicon. The two are a carbon steel but are usually classified as “alloy steel.”
Alloy steels are more expensive than plain carbon steel. They are typically used when there is not enough room for an “ordinary” steel and some steel must be removed—meaning the remaining steel has to do extra duty, and therefore, has to be extra strong.
Many different types of stainless steel are used in spring manufacturing. They are usually alloyed for one specific reason or another, but all of them have the typical stainless qualities of being corrosion resistant. The 300 series of stainless gets most of its hardness from being forced through reduction dies, and therefore, the molecules are “crunched together” to make them hard. The 400 series can be formed in a softer condition and then hardened later. Stainless is more expensive than carbon steel, and therefore, is only used when corrosive resistance is required in the manufacturing of stainless steel springs.
High nickel is one of the components of stainless steel, and can also be added in different quantities for different specific purposes. For example some high-nickel alloys are used for high temperature, some are used for corrosion resistance in very caustic environments, and some are used for lack of magnetism. They are usually expensive, and generally used only when absolutely necessary.
Red metal is the only class of spring steel that does not have iron content. The common red metals are hard drawn copper, beryllium copper, and phosphor bronze. They are typically used in electronic applications. They also are “weaker” than the alloys that contain iron. But in today’s world, there is a large market for springs made out of these products.
Contact Person: Ms. Florence Tang