Stainless Steel Essay

explanatory Essay
1272 words
1272 words

Stainless steel, especially, Austenitic stainless steel, because of their high corrosion resistance and customizable mechanical properties has become an indispensable part of the regularly evolving modern day technology. Stainless steels of various grades find applications in numerous fields starting from the household to the nuclear reactors; from food and beverage cans to construction of different automobile parts. The formation of impervious oxide layer on the surface makes it suitable for use in adverse environments such as sea water.
The high temperature application of Austenitic Stainless Steel is somewhat limited because at higher temperatures it undergoes a phenomenon called Sensitization. According to Ghosh et al. [1], it refers to the precipitation of carbides and nitrides at the grain boundaries. Precipitation of Chromium rich carbides (Cr23C6) and nitrides at the grain boundaries result when the Austenitic stainless steel is heated and held in the temperature range of 500-8500C (773K-1123K). This precipitation of carbides taking place at the grain boundary is because of their insolubility at these temperature ranges. This leads to Chromium depreciated regions around the grain boundaries. So the change in microstructure is takes place and the regions with low Chromium contents become susceptible to Intergranular Corrosion (IGC) and Intergranular Stress Corrosion Cracking (Alvarez et al.) [1, 2]. Along with carbides and nitrides there is formation of chi phase. The chi phase, which is a stable intermetallic compound, consists of Fe, Cr, and Mo of type M18C. Some studies reveal that sensitization may lead to formation of Martensite. In addition to the altered microstructure, mechanical properties of the Austenitic Stain...

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To obtain a detailed knowledge on the effect of Sensitization on the hardness of the samples, two kinds of hardness determination tests were performed.
(a) Micro Hardness
(b) Macro Hardness

(a) Micro Hardness
In order to perform the micro hardness test on the samples, they were first roughly polished using belt grinder. Then they were polished with the Emery papers as described in previous descriptions so as to obtain flat surfaces and to avoid anomalies in the results.
The micro hardness of the prepared samples were obtained by using a Vickers Micro hardness Tester (Model : Leco LV 700, USA). 5 readings were taken for each sample to calculate the average hardness. An indentation load of 5gf was used. After calculating the average hardness for each sample, mean variance and standard deviation (S.D.) was calculated to check the consistency of the data.

In this essay, the author

  • Explains that the objective of this investigation is to study the effect of sensitization on the mechanical and microstructural properties of a nonconventional stainless steel.
  • Explains that x12crmnnin17-7-5, a special grade of non-conventional austenitic stainless steel, was selected for this investigation.
  • Explains that thermo electron corporation limited, switzerland provided the chemical composition of the chosen sample determined with help of optical emission spectrometer.
  • Explains that the sample was subjected to heat treatment which included solution annealing to dissolve precipitated phases, followed by water quenching.
  • Describes how an optical microscope was used to reveal the microstructures of the prepared samples. the samples were put under the microscope lens and images were captured at various magnifications.
  • Explains that two kinds of hardness determination tests were performed to obtain a detailed knowledge on the effect of sensitization on samples.
  • Explains that austenitic stainless steel has become an indispensable part of the constantly evolving modern day technology.
  • Describes how the samples were polished with a belt grinder and etched with aqua regia. the fineness of the papers increases with their grade.
  • Explains how the liner intercept method was applied to determine the size of the grains of nonconventional stainless steel samples. the number of grains cut by a line was counted.
  • Explains how samples were polished using belt grinder, then polished with emery papers to avoid anomalies in the results. the micro hardness of the samples was calculated using a vickers micro hardness tester.
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