Low Alloy Steel New and Old Standard Designations Comparison
Low alloy steel is used in a wide variety of applications, from bridges to medical stays. Since the introduction of alloy steel grades, the choice of materials and their designations have changed over time. In this article, we will compare the new and old standards for designating low alloy steel grades.
In the early days of alloy steel production, the designation was based mostly on the chemical composition of the alloy. This system was often referred to as the ASTM designation, referencing the American Society for Testing and Materials organization. In this ASTM system of designation, the first letter would designate the grade (e.g. A, B, C, etc.) while the numbers immediately afterwards would designate the chemical composition of the alloy based on the percentage of each element. For example, AISI 4140 steel is broken down into the letter A for alloy, the number 4 representing the fourth version of the alloying components, then the letter S for stainless and finally the figure 40 for the percentage of its chromium content.
In more recent times, in order to standardize the designation of low alloy steel grades, the European Union has developed the Unified Numbering System (UNS). This system was created to create a unified approach in the designations of alloys and removes the confusion between different grades. With this system, each material has a unique combination of letters and numbers that represent the various chemical elements that comprise the alloy as well as their concentrations. For example, the UNS designation for AISI 4140 is SAE J404, where the letter S stands for steel, AE signifies the American Society for Testing and Materials, J represents the European Union and 4 stands for 4140. The numbers are then followed by the chemical composition of the alloy, which is the percentages of carbon, manganese, phosphorous, sulfur, silicon, chromium, molybdenum and other elements.
Overall, the only difference between the two systems is the way the materials are designated. However, it is important to note that the designation is not the same as the composition or grade of steel. It is only used to classify the alloy materials according to their respective chemical compositions. For example, AISI 4140 and UNS SAE J404 are both the same grade of steel, but the UNS designation describes the chemical makeup of the steel, not the physical characteristics.
In conclusion, although the ASTM and UNS designation systems for low alloy steel grades are different, the key difference is only in their designation and not in their grade or composition. The UNS system is more informative than the ASTM system due to the information it contains on the chemical compositions of alloys. As a result, being familiar with the two systems will make it easier for engineers and buyers to choose the correct alloy material for their application.
