Low alloy steels are a family of steels that have been developed to provide better mechanical properties and greater resistance to environmental corrosion than conventional carbon steels. These low alloy steels can range from a simple alloying element such as silicon or manganese to very complex combinations. It should be noted that most of these steels are the result of careful metallurgical research and are specifically designed for certain applications.
Low alloy steels are usually identified by number or letter designation. AISI (American Iron and Steel Institute) designates these as series numbered 1009 through 1045. The first three digits of the series define the carbon content, while the remaining two indicate the specific alloying elements. AISI low alloy steels normally contain 1 to 2 percent of alloying elements such as molybdenum, nickel, chromium, titanium and vanadium.
The purpose of alloying elements in the low alloy steels is to improve certain properties of the base steel. For example, the presence of chromium and molybdenum in the alloy helps increase the resistance to corrosive environments, particularly in chloride based atmospheres. The addition of nickel can also help improve the toughness of the alloy by decreasing the hardenability. The addition of other elements such as titanium can improve the weldability of the alloy.
In the automotive industry, these low alloy steels have become an important material for many components such as crankshafts and pistons. Many cylinder heads are made from these steels and it is increasingly more common to find valve components such as valve springs and their retainers made from such low alloy steels. Recently, several tool steels have also been developed which contain very small amounts of alloying elements. These steels are used in applications such as cutting tools and dies.
The major disadvantage of low alloy steels is their higher cost compared to plain carbon steels. This increased cost is due to the extra production and processing techniques required to form the alloy. However, in the right application, the superior properties of these alloys can provide substantial cost savings by extending component life and reducing maintenance costs.
In terms of grade, there are a variety of low alloy steels that are used in different applications. Generally speaking, low alloy steels are divided into two categories – ferrite-pearlite and martensite. Ferrite-pearlite is a type of steel that is formed by a combination of ferrite and pearlite. It is used for structural and pressure vessels applications. On the other hand, martensite is a type of steel that is formed by quenching and then tempering with cold water. This type of steel is suitable for use on components that require high strength and hardness such as cutting tools and automotive components.
Low alloy steels are widely used in various industries, ranging from automotive to aerospace. In addition to providing excellent mechanical properties, these steels are more resistant to corrosion than other carbon steels. They are available in both ferrite-pearlite and martensite grades, allowing for a wide range of applications.
