International Standard for Designation of Steel
Steel is a material that is commonly used across many disciplines, from engineering and construction to home repair and industry. Its uses are varied and wide-ranging, yet all steel must meet certain standards in order for it to be suitable for these uses. This is especially true when it comes to designations of steel; different criteria must be met to assign a steel grade. In order to better standardize the designation of steel, the International Organization for Standards (ISO) has established guidelines and criteria for the designation of steel.
The ISO actually classifies steels into three categories; they are unalloyed steels, alloyed steels, and stainless steels. Unalloyed steels are characterized by a high carbon content and are normally used for non-critical applications such as pipes and tubes. Alloyed steels, on the other hand, contain various other elements in addition to carbon; common alloying elements include manganese, silicon and vanadium, and these are usually used for applications that require greater strength and resilience. Finally, stainless steels are characterized by a high chromium content, which of course makes them highly resistant to corrosion.
The ISO also specifies a number of grades for each of these categories. Unalloyed steels are divided into grades from the very lowest, Grade 1, all the way up to Grade 6. Grade 1 is usually used for light-gauge, non-critical parts and components, whereas Grade 6 is used for heavy-gauge components with high mechanical strength and/or pressure bearing capabilities. Likewise, alloyed steels also range from Grade 1 to Grade 6, although the highest grade is usually designated as Grade 8. Finally, stainless steels are divided into two categories: grades 1 to 10, and grades 11 and higher. Grades 1 to 10 are used for non-critical applications such as kitchenware, while grades 11–20 are well-suited for more advanced applications such as valves and pumps.
The ISO also specifies the designations used to describe each grade of steel. For example, the designation for unalloyed steels is simply “U-x”, where “x” is the grade from 1 to 6. Similarly, the designation for alloyed steels is “A-x”, where again “x” is the grade from 1 to 8. Lastly, the designation for stainless steels is “S-x”, where “x” is the grade from 1 to 20.
To make it easier for people to identify different grades of steel, the ISO also specifies an additional set of designations. For unalloyed steels, the additional designation is a three-digit code comprising of two letters followed by a number. The two letters stand for the application, such as “GB” for general-purpose applications, while the number denotes the grade of steel. For example, the designation “GB85” would indicate a low-carbon, unalloyed steel suitable for general purpose use.
Similarly, the additional designation for alloyed and stainless steels is also a three-digit code, comprising of a single letter followed by two numbers. The letter stands for the type of steel (i.e. A for alloyed, or S for stainless steel), while the two numbers stand for the grade. For example, the designation “A85” would indicate an alloyed steel with a grade of 8, while the designation “S120” would indicate a stainless steel of the highest grade.
In conclusion, the International Organization for Standards (ISO) has established a set of guidelines and criteria to better standardize the designation of steel. This allows us to better identify different types and grades of steel, making it easier to select the appropriate material for any given application. In order to designate a certain grade of steel, the ISO specifies a two-letter prefix followed by a single number (for unalloyed steels) and a single letter followed by two numbers (for alloyed and stainless steels). This system of steel designation is an invaluable tool for both professionals and amateurs alike.
