Wrought Metals And Alloys Question And Answers

Wrought Metals And Alloys

 

Question 1. Write a short note on 18 – 8 stainless steel.
Or
Write a short note on 18 – 8 steel.
Or
Write in brief on 18 – 8 stainless steel.
Answer:

18-8 stainless steel was introduced by Dr. W.H. Hatfield in 1924.

At temperatures between 912°C and 1394°C the stable form of iron is a face-centered cubic (FCC) structure called austenite. The austenitic stainless steel alloys are the most corrosion-resistant of the stainless steels. This alloy is also called 18-8 stainless steel based on a percentage of nickel and chromium in its composition.

Read And Learn More: Dental Materials Question And Answers

Composition Of Stainless Steel:

Uses: These are used most commonly in orthodontics and pedodontics in the form of bands and wires.

Alloy Constituents of 18-8 Stainless Steel and their Function:

Advantages Of Stainless Steel:

• It withstands the occlusal forces because of its high stiffness.
• It has high ductility and malleability, so it is easily drawn into wires or hammered into stainless steel sheets
• Cold working can be done easily with 18-8 stainless steel without the risk of fracture.
• This increases the strength of the metal.
• The formability of 18-8 stainless steel is good.
• Due to this many small stainless steel wires are twisted or braided together to form multistranded arch wires.
• Due to corrosion resistance it is stable in an oral environment.
• It resists distortion so tipping and torquing can easily be done by brackets.
• Due to the presence of a smooth surface, stainless steel brackets lead to less friction which makes orthodontic treatment faster and more comfortable.
• 18-8 stainless steel is biocompatible
• 18-8 stainless steel is economical.

Disadvantages Of Stainless Steel:

• It has a low spring back as compared to nickel–titanium alloys which makes it a poor initial alignment archwire.
• Due to its high stiffness more frequent activations are required.
• It can lead to discomfort to the patient as it delivers more force compared to the wires made of other alloys of the same diameter.
• In this soldering is needed, if the temperature becomes more than 500°C the corrosion resistance of the alloy is decreased.

Properties Of Stainless Steel:

• Sensitization: 18-8 stainless steel may lose its resistance to corrosion if it gets heated between 400 and 900°C.
• Stabilization: It is the method to minimize sensitization. In this, some element is introduced which precipitates as carbide in preference to chromium. For this titanium is used commonly.
• Annealed and partially annealed wires: Both these wires can be used as orthodontic wires. When these stainless steel wires are fully annealed they get soft and highly formable. When stainless steel wire is partially annealed its yield strength is increased and formability is decreased.
• Mechanical properties: In cases of orthodontic wires, strength, and hardness can decrease with a decrease in diameter.
  • Tensile strength is 2100 MPa
  • Yield strength is 1400 MPa
  • Hardness is 600 KHN.