Machinist

[Lawrence London <lfljvenaura@gmail.com>]

I decided to Google a number of metalworking terms: critical temperature, austenite, normalizing, tempering, hardening, ductility, toughness, cold working for example. One site defined normalizing with this: "For normalization to occur, steel is warmed to a temperature just above its upper critical point. This is generally more than 50 C of that temperature. The steel is then held long enough for smaller metal grains to form and high energy grain shapes to come together. This transformation is called grain refinement and leads to the formation of a more uniform piece of metal. After steel is heated to a temperature above its critical point, it is air-cooled until it drops to room temperature." I was curious why you would quench as part of the normalizing process. Critical temperature is defined as "As the steel is heated above the critical temperature, about 1335°F (724°C), it undergoes a phase change, recrystallizing as austenite. Continued heating to the hardening temperature, 1450-1500°F (788-843°C) ensures complete conversion to austenite." And then: "On some steels, this normalize process is followed by a temper or stress relief anneal below the Ac1 to remove residual stresses resulting from the air cooling and to reduce hardness.
Normalizing Steel gives you reduced hardness and removes residual stress, improves machinability, develops desired mechanical properties (especially in larger sections), Improved austenitizing for subsequent quench and tempering". This is info from 3 websites found in my Google searches.
I wonder what all this has to do with typical hardening and tempering where you heat steel to where it loses its magnetic properties, do a quick quench, wait until the steel turns the color you want, i.e. straw or blue (maybe that is called "drawing out") then do a complete quench leaving the steel or portion of a workpiece in the desired condition of hardness and toughness, i.e. tempered.

Info from:

https://www.google.com/search?q=normalizing+steel&ie=utf-8&oe=utf-8

https://www.google.com/search?q=critical+temperature+of+steel&ie=utf-8&oe=utf-8

https://en.wikipedia.org/wiki/Annealing_(metallurgy)

https://pmpaspeakingofprecision.com/2013/10/24/4-reasons-to-consider-normalizing-steel/

https://www.thebalance.com/how-does-steel-undergo-the-normalizing-process-2340017

http://www.instructables.com/id/Normalizing-Carbon-Steels/

https://www.quora.com/What-is-the-critical-temperature-of-steel

Critical temperature means the highest temperature at which it is possible to separate substances into two different phases (vapour and liquid).

For steel the critical temperature is slightly higher which is around 1600–2300 degree Fahrenheit. If it is heated till this temperature then it is called austenite or it is in austenitic stage.

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Lawrence F. London, Jr.
lfljvenaura@gmail.com

https://sites.google.com/site/avantgeared