Knife alloy Banding / Steel Segregation

[Kippington]

Normalizing happens at different temps for different steels. 1084 steel, for example, has few alloying elements in it and has the right amount of carbon in it (roughly 0.8%) where it all goes into solution as the steel turns to austenite (allowing sufficient time for the carbides to dissolve). Keep in mind though that this is ignoring grain size, which is relevant but not quite on topic with this thread.

Normalizing is the first thing to happen during heat-treating. It should go in this order, with grinding/drilling happening at any stage you want, but mostly done after annealing:
1) Forge to shape (you can normalize at any stage during forging)
2) Normalize
3) Grain refinement
4) Anneal/stress relieve
5) Quench
6) Temper

At each step in the HT the temperature used goes down. The only exception to this is the quench.

 

[Nemo]

Good point, this is a little off topic... sorry.

Might start a thread on forging and HTing when I get a chance.

 

[Kippington]

Normalizing is the first thing to happen during heat-treating. It should go in this order, with grinding/drilling happening at any stage you want, but mostly done after annealing:
1) Forge to shape (you can normalize at any stage during forging)
2) Normalize
3) Grain refinement
4) Anneal/stress relieve
5) Quench
6) Temper

At each step in the HT the temperature used goes down. The only exception to this is the quench.

Actually, I should also post what I've come to understand the Japanese do:
1) Forge to rough shape, using lower temps for each consecutive heat
2) Anneal/stress relieve
3) Cut/stamp/grind to shape
4) Cold forge (at room temp)
5) Quench
6) Temper

Let me know if anyone knows otherwise.

 

[DevinT]

Alloy banding happens when there developes bands of areas that have high and low concentrations of an alloy like manganese or sulfur. This in turn causes bands that have different micro structures, like ferrite and pearlite. This originates during solidification where alloys segregate between dendrites. Hot working and sufficient reduction usually eliminate banding.

With knives we usually see carbide banding. Carbides will grow and line up if forging temperatures are low enough and time is sufficient. Carbides in simple carbon steels will all dissolve at ~1650-1700f, depending on cooling rates, pearlite, martensite, or spheroidite developes. Long soaks at low temperatures causes fine spheroidite to grow into course spheroidite. Spheroides = carbides. These carbides can grow large enough to become visible when they form bands. (Wootz)

Steels containing tungsten are prone to this because alloy carbides dissolve at higher temperatures.

Hoss