Posted on 19 March, 2013 by Mathew
My metallurgist colleague was very disappointed in this knife because she believed that stainless steel wouldn’t corrode. Unfortunately if left in still water oxidation pitting will occur in all stainless steels. My colleague was very surprised to get corrosion in this knife because it is usually hand washed and then just left with a little water on it, similar to other utensils, but after six months it had started to rust. The corrosion may be the result of the relatively high carbon content in the knife, which means it is likely to form carbide particles which act to sensitise the steel.
X50CrMoV15 is a German standard with around 0.5 wt% carbon (percentage by weight) and total around 15 wt% chromium, molybdenum and vanadium. This is regarded as being highly stain resistant. Usually a steel is regarded as stainless it is possible to maintain a chromium level above 12 wt% at the surface, since this has been found to form a stable oxide layer.
|0.45 – 0.55
|| max 1
|| max 0.04
|| max 0.015
||14 – 15
||0.5 – 0.8
||0.1 – 0.2
Z-knives have previously found that rusting occurred on X50CrMoV15 as a result of using dishwasher on otherwise unused knife.
`Japanese’ Cooks Knife
New York Times announcement regarding the discovery of stainless steel.
Filed under: Stainless Steel, Steel | Tagged: corrosion, Harrods, Knife, pitting, stainless steel | Leave a Comment »
Posted on 9 March, 2013 by Mathew
These are some pictures of the beautiful microstructure of super-bainite. The fine structure of bainite plates and austenite thin films is formed by isothermal transformation at 200°C (or alternatively 473.15 K, or 392 F). With this fine microstructure (or more accurately nanostructure) it is possible to reach very high strength in steel (more than 2 GPa ultimate tensile strength).
Super Bainite Before Tempering (as transformed at 200°C), as seen in transmission electron microscope
Super bainite as transformed at 200°C, as seen in scanning electron microscope.
‘Super bainite’ after severe tempering.
This is what happens if you attempt to temper at the highest possible temperature. As expected the microstructure approches equilibrium and coarsens. We found that the temperature calculated using thermodynamic software is not applicable to this heat treatment. Rather than an equilibrium structure of ferrite and carbides as we expected at this temperature, austenite, ferrite and carbide phases were all stable. On cooling, the austenite transformed, usually to pearlite as seen here, but in some cases bainite and martensite were also observed.
Read more: Severe tempering of bainite generated at low transformation temperatures (mathewpeet.org) or Severe tempering of bainite generated at low transformation temperatures (phase transformations)
Filed under: Academic papers, Steel | Tagged: equilibrium structure, isothermal transformation, scanning electron microscope, Science, tempering, transmission electron microscope | Leave a Comment »
Posted on 2 July, 2012 by Mathew
“Boron Extrication dot com” is a site by a fire-fighter with automotive engineering experience (he’s from Detroit – autocity). There is a large collection of schematics and photographs of car bodies showing use of different materials.
UHSS B Pillars
Filed under: Steel | Leave a Comment »