Heat tint (temper) colours on stainless steel surfaces

The colour formed when stainless steel is heated, either in a furnace application or in the heat affected zone of welds, is dependent on several factors that are related to the oxidation resistance of the steel.

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The heat tint or temper colour formed is caused by the progressive thickening of the surface oxide layer and so, as temperature is increased, the colours change.

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  • SS have a thin passive layer on their surface:
  • With exposure to O2 at high temperature (400–1300F) a thin “straw tinted” Cr2O3 layer forms
  • As a result a Cr depleted layer forms beneath the heat tint
  • With additional exposure and additional O2 pickup the Cr2O3 layer becomes unstable
  • A more volatile CrO3 “dark blue/black” layer is formed
  • There is an increase in Fe content at the surface

 

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Document for refer:

+ https://docplayer.net/22629277-To-pickle-or-not-to-pickle-john-grocki-corrosion-solutions-sept-2009.html

+ https://www.bpe-technology.com/system/download/Weld%20Discoloration%20-%20Pharmaceutical%20Engineering%202011.pdf.1bc06d9aad3fc7705ca2f79bdf81ec8d

+ https://materials-welding.blogspot.com/2017/05/heat-tint-temper-colours-on-stainless.html