Stainless Steel Welded pipe and Tube
Stainless steel is a metal alloy, made up of steel mixed with element such as chromium, silicon, carbon, nickel, molybdenum and aluminium. The main component of stainless steel is the iron mixed with carbon to produce steel.
There are more than 150 grades of steel, but only 15 are used regularly.
Chromium is added to make it resistant to rust. Nickel enhances corrosion resistance properties in case of aggressive usage. There are other alloying metals like titanium, copper and vanadium which are also added to improve the structure and properties.
Uses of Stainless Steel
1) It is preferred for making kitchen vessels as it does not affect the flavour of food and is easy to clean.
2) It is used in commercial kitchens and food processing plants.
3) It is used to manufacture kitchen cutlery, plates, sheets, bars, wire, surgical instruments, cookware, industrial equipment’s, building construction materials and hardware. This steel is a hard and strong substance.
Types of Stainless Steel
- Ferritic – It contains 30% chromium that is crystal structure. This steel generally have better engineering properties then austenetic grades but have reduced corrosion resistance because of lower chromium and nickel. It lacks in high temperature mechanical properties. Common grades are 18Cr-2Mo, 26Cr-1Mo, 29Cr-4Mo and 29Cr-4Mo-2Ni.
- Martensitic – It is a mixture of carbon and 18% chromium. It has less corrosion resistance as the other two classes but are extremely strong and tough and also highly machinable. It can be hardened by heat treatment.
- Precipitation Hardening – It contains a mixture of nickel and chromium. It is very strong.
- Austenetic – It is also called 200 and 300 series. It has austenetic crystalline structure. It is formed by using nitrogen, manganese and nickel. It contains 16-26% chromium and less than 35% nickel. It is tough, ductile with high temperature strength properties.
- Duplex – It is the combination of austenetic and ferritic crystal structure. Chromium and nickel are the main alloying elements in this steel. It has high chromium and less nickel content than austenetic steel. It is corrosion resistant.
Identification of Stainless Steel
It can be identified by magnet testing, spark testing, acid testing and hardness testing. Identification tests are non-destructive, inexpensive and rapid procedures. Products can be sorted when bars of grades 303 and 304 have been accidentally together or when grades 304 and 316 are mixed. These tests are very useful. There are more complex tests that have chemical reagents for grade identification. Tags, markings, stickers are not required for identification.