Different types of Steels are used in Valve manufacturing. Due to wide variety of steels available in market, overwhelmed by the variety of material available and different name by which they are called. Here I have tabulated 20 different types steels that are most widely used depending on their usage.
Steel is of various categories: a) Carbon Steel b) High Temperature Steel c) Low Temperature Steel d) Stainless Steel. Each Category of Steel is produced from two different manufacturing technique known as Casting and Forging.
ASME B 16.34 defines the material to be selected for a valve body construction depending on its pressure, temperature Class. ASME B 16.34 is basically a Valve Design Standard, whereas ASTM is material standard. ASTM defines the chemical components and manufacturing process of a material.
1) Carbon Steel: It is most widely used material for valve manufacturing. Within this category, there is two sub categories namely casting and forging. Casting and forging are two different manufacturing process. Grades of Carbon Steel under Casting are WCB and WCC. WCB and WCC follow ASTM A216 material standard. Grades of Carbon Steel under Forging is ASTM A105. There is a single grade under Forging Carbon Steel category. So, name of the standard and material are the same. Carbon Steel should not used beyond 425 Degree Centigrade as per ASME B16.34.
2) High Temperature Steel: This category of material is normally used where process temperature is more than 400 degrees centigrade. Commonly used grades of High Temp Steel under casting category are WC6 and WC9. They follow ASTM A217. Commonly used grades of High Temp Steel under forging category are F11, F12, F21, F22, F91. They follow ASTM A182.
3) Low Temperature Steel: In this category only casting is used. Commonly used materials are LCB and LCC and ASTM A352 is followed.
4) Stainless Steel: For Casting subcategory most popular materials are CF3, CF8, CF3M and CF8M. Related ASTM standard is A351. For Forging subcategory most popular materials are 304,304L,316 and 316L. Related ASTM standard is A182.
Iron is soft element. When carbon (0.2 to 2%) is mixed with Iron, steel is formed. Steel has higher mechanical strength required for making mechanical items. There are different grades of steels are produced combining different chemical components in proper percentages. These chemicals components are Iron, Carbon, Nickel, Chromium, Molybdenum, Manganese.
a) Iron: Iron is one of the most commonly found chemical element on earth. Atomic No. 26 Denoted with symbol Fe Iron is basically soft material, when mixed with carbon( 0.02 to 2 %), steel is produced which is harder material. There is another item called Cast Iron which is Iron- Carbon Alloy. In Cast Iron Carbon > 2%. Cast Iron is very brittle in nature
b) Carbon: Carbon is fourth most abundant material on earth. Carbon when mixed with Iron in proper quantity produces Steel. When Carbon % is between 0.02% to 2 %: Addition of more carbon makes the material stronger When Carbon % is more than 2 %: Material becomes brittle.
c) Nickel: Nickel is a chemical element with the symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile. More than two thirds of global nickel production is used to produce stainless steel. As an alloying element, nickel enhances its important properties such as formability, weldability and ductility, while increasing corrosion resistance in certain applications. The alloying element that makes steel ‘stainless’ is chromium; however it is the addition of nickel that enables stainless steel to become such a versatile alloy.
d) Chromium: Chromium is a chemical element with the symbol Cr and atomic number 24. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium is the main additive in stainless steel, to which it adds anti-corrosive properties. Chromium metal is of high value for its high corrosion resistance and hardness. A major development in steel production was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel.
e) Manganese: Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard brittle silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy uses, particularly in stainless steels. It improves strength, workability, and resistance to wear.
f) Molybdenum: Molybdenum is a chemical element with the symbol Mo and atomic number 42. Molybdenum is also valued in steel alloys for its high corrosion resistance and weldability. Molybdenum contributes corrosion resistance to type-300 stainless steels (specifically type-316) The addition of 1 % to 2 % of Mo to ferritic stainless steels also significantly increases the corrosion resistance and the elevated temperature strength.
Material Grouping Using ASME B16.34
In ASME B16.34, Valve body materials are categorised into different groups. The Groups start with 1.1 and goes up to 3.19. These groups are really important as they are directly linked with Pressure, Temperature Rating. Here is snapshot for the material group.
In each Row there are different material group numbers. In the second column, there is material composition (Main Chemical Elements, the material is made up of). There are several columns there after denoting different method of manufacturing like casting, forging etc. Within these different manufacturing techniques, there are different Specification Number and Grades. Now, the grades are basically trade names of different materials and specification numbers are basically ASTM standard of respective materials.
For example, take the material WCB. Main component of these material is Carbon and Silica apart from Iron. The related ASTM standard is ASTM A216. ASTM A216 basically deals with chemical composition of WCA, WCB, WCC and their manufacturing process. As a Valve design or maintenance engineer, we are mainly concerned with chemical requirement of the WCB or WCC.