Evolution of Low-Alloy Structural Steel Standards and Levels
L-alloy structural steel is an alloy of alloys, composed of alloying elements such as carbon, chromium, manganese and vanadium, among others. Low-alloy structural steel is gaining popularity amongst the metal working industry due to its strength, workability and robustness. Low-alloy structural steel has been used in numerous applications such as bridges, buildings, power transmission lines, tanks, bridges and other constructions. It is a very important metal due to its high strength-to-weight ratio, wear resistance and corrosion resistance.
Low-alloy structural steel standards have gone through a major evolution over the years. In the early 20th century, low-alloy structural steel was mainly used for boiler and pressure vessel components and welding structural members. At this time, most of the standards were based on the chemical compositions of the materials. For example, in the United States, the American Society of Mechanical Engineers (ASME) established a set of mechanical specifications and tolerances. This defined how the steel should be formed, heated and worked with.
During the Second World War, the demand for steel increased and the American Iron and Steel Institute (AISI) started to develop a set of technical standards that were more focused on the performance of the steel materials. These standards were the basis of what is now known as the AISI designation system. This system was used to classify the various grades of low-alloy structural steels. These grades sang from low-carbon steels to Chromium-Molybdenum steels.
In the 1950s, the popularity of low-alloy structural steel increased and the American Society for Testing and Materials (ASTM) began a program to develop test methods and acceptance criteria for these materials.This program resulted in a set of standards which broke down the mechanical properties of the materials into specific categories. This system created categories such as: Cold Forming, Roll Forming, Forging, Heat Treating and Deformation. This system also set up the minimum requirements for strength, plasticity, ductility and weldability for a given grade and thickness.
In the 1970’s, along with this set of test methods, the ASTM started to develop a grade designation system to better reflect the mechanical properties of low-alloy structural steel. This system first started with three major grade numbers: A1011, A1018 and A1022. Each grade was divided into three subcategories, designated by an ‘X’, ‘C’, or ‘D’. This system has since evolved and now comprises of over 10 major grade numbers and 25 subcategories.
In the last few decades, several countries have developed national standards for low-alloy structural steel. These standards often reference the ASTM standards and provide additional requirements based on national needs. For example, Japan has its own set of standards. These standards are often stricter than those of the ASTM and often require additional testing and qualification of specific materials.
Recently, with the advancement of technology, there has been a push in the industry to develop even higher levels of quality and performance for low-alloy structural steel. This has resulted in even more stringent testing and qualification methods. Companies now have to participate in third-party qualification programs and be monitored for continuous improvement of their products. This has allowed for the production of low-alloy structural steels that are much stronger, more durable, and more performant than ever before.
In conclusion, there has been a great evolution in low-alloy structural steel standards over the years. From the early days of chemical compositional based standards, to the current levels of performance based requirements, it is clear that the industry has gone through a transformation. By developing higher levels of quality and performance for low-alloy structural steel, there has been tremendous improvements in the materials used in a number of applications. With the development of even more stringent testing and qualification methods, the industry will continue to move forward and evolve to create even better steels.
