Hi Sanjay,
Great question! Untempered martensite is what you get just after quenching. It leaves a very needle-like microstructure that's very hard but also quite brittle. Tempering is then performed at much lower temperatures to make the microstructure more homogenous, shorter, and then also much more ductile. The Charpy impact toughness rises substantially and the strength decreases by quite a bit. In some cases, like knives, swords, and blades, the harder material is better so no quenching is used. Conversely, in most engineering applications you need some toughness (aka the resistance to growth of a crack), so the tradeoff of a moderate reduction in strength is worth it. Summing up:
Tempered martensite has been heat treated to make it slightly softer but much more ductile (and tougher).
Untempered martensite is fresh out of quenching, very hard but not very tough.
Best regards!
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Joshua Jackson
CEO
US Corrosion Services LLC
Houston TX
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Original Message:
Sent: 03-08-2021 11:14
From: Sanjay Kulkarni
Subject: Martensite in Steel
What is the correct way to call Martensite in steel? Is it un-tempered Martensite? Or martensite only?
I have limited years of experience in steel alloys processing, but never came across the term, "un tempered martensite" for martensite microstructure, unless there is presence of residual martensite in tempered martensite microstructure. Please advice.
Sanjay Kulkarni
Materials Engineer
MSSC
a group company of MITSUBISHI STEEL MFG. CO., LTD.
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Sanjay Kulkarni
Materials Engineer
MSSC
Troy, MI
248-840-1056
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