為什麼刀片燒過之後會出現彩虹一樣的花紋？

01-13

1. 氧化膜的厚度與溫度有關。

2. 刀片的不同位置在加熱的時候有溫差，導致氧化膜在刀片不同位置的厚度有區別。

3. 不鏽鋼能夠反射光線。

4. 由於氧化膜的作用，入射光與反射光形成干涉。

5. 由於氧化膜厚薄不均，所干涉光的波長並不相同，因此呈現了不同的顏色。

以上缺一不可。

Thin-film interference

經評論區姚瑤提示，補充參考：

Tempering

If steel has been freshly ground, sanded, or polished, it will form an oxide layer on its surface when heated. As the temperature of the steel is increased, the thickness of the iron oxide will also increase. Although iron oxide is not normally transparent, such thin layers do allow light to pass through, reflecting off both the upper and lower surfaces of the layer. This causes a phenomenon called thin-film interference, which produces colors on the surface. As the thickness of this layer increases with temperature, it causes the colors to change from a very light yellow, to brown, then purple, then blue. These colors appear at very precise temperatures, and provide the blacksmith with a very accurate gauge for measuring the temperature. The various colors, their corresponding temperatures, and some of their uses are:

Faint-yellow – 176 °C (349 °F) – engravers, razors, scrapers

Light-straw – 205 °C (401 °F) – rock drills, reamers, metal-cutting saws

Dark-straw – 226 °C (439 °F) – scribers, planer blades

Brown – 260 °C (500 °F) – taps, dies, drill bits, hammers, cold chisels

Purple – 282 °C (540 °F) – surgical tools, punches, stone carving tools

Dark blue – 310 °C (590 °F) – screwdrivers, wrenches

Light blue – 337 °C (639 °F) – springs, wood-cutting saws

Grey-blue – 371 °C (700 °F) and higher – structural steel

Beyond the grey-blue color, the iron oxide loses its transparency, and the temperature can no longer be judged in this way. The layer will also increase in thickness as time passes, which is another reason overheating and immediate cooling is used. Steel in a tempering oven, held at 205 °C (401 °F) for a long time, will begin to turn brown, purple or blue, even though the temperature did not exceed that needed to produce a light-straw color. Oxidizing or carburizingheat sources may also affect the final result. The iron oxide layer, unlike rust, also protects the steel from corrosion through passivation.

這是熱處理之後的淬藍和淬黃，具體是什麼色和溫度有關。

裝不下去了─=≡Σ((( つ??ω??)つ

我認為是被氧化了

為什麼高票答案要提到膜。。還被一個魔法師點贊了。。我看了半天以為會有神結尾。。

不同的溫度位置生成了不同的氧化物或者晶體結構，顏色不同而已