Question

MTE 4595/5883/6883 practice questions. You are employed as an engineer to select a material (which at your discretion, may also be prescribed with a corrosion preventative coating or strategy). For the following applicati material would you suggest and why? ons, which (A) A pipeline for carrying natural gas across Australia. (B) A hand rail for a passenger boat that operates tours in the Great Barrier Reef (in North Queensland). I (C)The load bearing structural components of the yet to be released Boeing 797 passenger jet. (D) The filler material for welding two plates of 316 Stainless Steel together (E) A container that must be ultra corrosion resistant for the purposes of storing nuclear waste. (F) The gas turbine discs within an airline jet engine. (G) The (load bearing) structural members for a potential design to replace the Sydney. Harbour Bridge. What is stainless steel? What makes stainless steel actually be 'stainless' (i.e. what is the mechanism)? Where was stainless steel invented? hoice froma

Answer 1

Defintion of stainless steel

Stainless steel is an alloy of Iron with a minimum of 10.5% Chromium and varying amounts of Carbon, silicon, Manganese, Nickel and Molybdenum.

The corrosion resistive elements present in the stainless steel makes as stainless

Mechanism

Chromium produces a thin layer of oxide on the surface of the steel known as the passive layer'. This prevents corrosion of the surface. Increasing the amount of Chromium gives an increased resistance to corrosion.

Nickel and Molybdenum imparts other useful properties such as enhanced formability and increased corrosion resistance.

Invention

Invented in 1913 by Sheffield metallurgist Harry Brearley.

Selection of the steel for low temperature condition

• The austenitics stainless steels such as 304 (1.4301) and 316 (1.4401) are 'tough' at cryogenic temperatures and can be classed a 'cryogenic steels'.
  They are suitable for sub-zero 'ambient' temperatures sometimes mentioned in service specifications sub-arctic and arctic applications and locations
  
• This is the result of the 'fcc' (face centred cube) atomic structure of the austenite, which is the result of the nickel addition to these steels.
• The austenitics do not exhibit an impact ductile / brittle transition at low temperature.