CLASSIFICATION OF STEELS OF PIPING MATERIALS

On Piping Materials there is something we have to know more, which is Classification of Steel and today Piping & Fabrication will introduce you with it and in the next post will explain more deep, so we can understand what is Classification of Steel.

There are literally hundreds of wrought grades of steel that range in composition with the variation of the many major and minor alloying elements. The simplest of these classes is known as plain carbon steel, with carbon varying between approximately 0.05 and 1.0 weight percent. Within this broad range fall three general groups according to carbon content; they are defined as follows:
1. Low carbon steels—0.05 to 0.25 percent carbon
2. Medium carbon steels—0.25 to 0.50 percent carbon
3. High carbon steels—0.50 percent and greater carbon content

Alloy steels are generally considered to be steels to which one or more alloying elements, other than carbon, have been added to give them special properties that are different than those of straight carbon steels. From the standpoint of composition, steel is considered to be an alloy steel when amounts of manganese, silicon, or copper exceed the maximum limits for the carbon steels, or when purposeful addition of minimum quantities of other alloying elements are added. These could be chromium, molybdenum, nickel, copper, cobalt, niobium, vanadium, or others.

The next higher class of alloyed steel useful to the piping industry is ferritic and martensitic stainless steels. These are steels alloyed with chromium contents above about 12 percent. Because of the chromium, these materials possess good corrosion resistance. They retain a ferritic (BCC) crystal structure, allowing the grades to be hardened by heat treatment.

When sufficient nickel is added to iron-chromium alloys, an austenitic (FCC) structure is retained at room temperature. Austenitic stainless steels possess an excellent combination of strength, ductility, and corrosion resistance. These steels cannot be hardened by quenching, since the austenite does not transform to martensite. A stronger type of stainless steel has been developed which takes advantage of
precipitation reactions within the metal matrix made possible by addition of elements such as aluminum, titanium, copper, and nitrogen. These materials are referred to as precipitation hardenable stainless steels. Both martensitic and austenitic stainless steels can be enhanced in this manner.

As annealed, these materials are soft and readily formed. When fully hardened, through aging heat treatments, they attain their full strength potential.