There are many alloying elements added to steel to achieve various enhanced properties. We previously looked at 5 common alloying elements, and in this blog we take a look at 5 more elements and how they affect steel.
Silicon is perhaps the most common alloying element in steel, as almost all steel requires silicon during the manufacturing process. Silicon helps to purify the iron ore during the smelting process by deoxidizing it and removing other impurities from it. Aside from its cleansing properties, silicon can also have an effect on the mechanical properties of steel. It can be used to increase the strength and hardenability of certain steels, as well as magnetic properties.
Copper is frequently added to steel in small amounts. Copper can enhance the chemical properties of steel by increasing its corrosion resistance. A large amount of copper can help prevent the formation of rust. Many of the different types of weathering steel have relatively high amounts of copper when compared to standard carbon steel, as they are typically used in applications that expose them to corrosive environments. Copper can also be used to increase the mechanical properties of steel by allowing it to be precipitation hardened. Precipitation hardening is a process that is used to block dislocations in the crystal structure of a metal, thus increasing its strength.
Copper is found in trace amounts in many different steels. In low carbon steel, it is usually found in amounts under 0.40% by weight. ASTM A36, for instance, has a maximum allowable copper content of 0.20%. Higher amounts of copper can be found in weathering steels and other types of high strength low alloy (HSLA) steels. Examples of these include ASTM A588 and ASTM A440.
Steels also have varying amounts of tungsten in their composition. Some of this is residual and unintended, such as in AISI 1018 steel. However, some steels have added amounts of tungsten to improve the mechanical and chemical properties of the steel for different applications. Because of its high melting temperature, tungsten can be used to increase the melting temperature of steel. The high hardness of tungsten can also increase the wear resistance of steel. Lastly, tungsten can also improve the corrosion resistance of steel.
The amount of tungsten in an alloy steel can range widely. In high strength low alloy steel, it can be under 1%. High speed tool steels, where tungsten is frequently used as an alloying element, can have amounts of tungsten greater than 15% by weight. Examples of high speed tool steels with tungsten include T1, M1, and M7, to name a few.
Some alloying elements are more efficient at altering the properties of steel than others. For example, a boron addition of as little as 0.001% by weight can have a huge effect on the mechanical properties of steel. The mechanical property most affected by added boron is hardenability. Heat-treatable steels frequently have boron alloyed into their chemical composition for this reason. Excessive amounts of boron in steel can actually cause a reduction in hardenability. High amounts of boron can cause a steel to become brittle and lose toughness.
Steels with additions of boron can be found across many different grades, many of which are proprietary. Common applications of steels alloyed with boron include components subject to wear such as earthmoving equipment and crankshafts.
While lead is often added to steel alloys, it is actually not an alloying element itself. When added to steel, lead does not join with the carbon, iron, and other elements. Lead is actually not soluble in steel. Rather, lead remains in the steel in the form of inclusions. Lead also has almost no impact on the mechanical properties of the steel, but improves the machinability of the steel because it acts as a lubricant between the cutting tool and the steel. Welding steel with lead additions almost always results in cracks and is not recommended.
Lead is added to steels that will undergo machining but not welding. AISI grades of steel that contain lead typically have an “L” designation. Common alloys include 11L18 and 12L14.
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