Making a welded Damascus Knife

John Neeman Tools have posted a beautiful video of manufacturing a welded Damascus patterned knife.

5 layers of 3 different steels were forge-welded, folded, and forged. With each step being repeated 8 times. This produces a patterned with 320 layers. Finally twisting and forging the steel produces a more complex pattern.

Just checking the number of layers, I get their total to be different. My calculation of the number of layers is 5 × 28 = 1280, that is 4 times more than claimed (320 layers should be the result of folding 6 times (6 folds 5 × 26).

With 1280 folds, if we assume the thickness of the knife is 2 mm, that means each layer is 1.6 μm, 320 folds would be 6 μm layers. These are both lower than what can be resolved using the naked eye. It’s very close to the wavelength of visble light — if the metal were folded one more time, or the final thickness of the knife is less than 1 mm you would be there.

MS Calculator Android App

A researcher at GIFT has produced an metallurgical application for android phones for calculation of MS, ε-MS, Ae3, Ae1, and conversion of weight percent to atomic percent.

MS Calculator Android App

MS Calculator Android App, screen shot 1

Android App

MS Calculator Android App

MS Calculator App webpage

Tempering of Martensite

Stage 1
upto – 250 C – precipitation of eta-carbide, partial loss of tetragonality of martensite.
Steels above 0.25 wt% carbon precipitate hexagonal close-packed eta-carbide within the supersaturated martensite until 0.25 wt% carbon level is reached, martensite preserves some tetragonality. The orientation relationship between the laths or rodlets and the cube planes of the matrix was first described by Jack [1].

Stage 2
200-300 C – decomposition of retained austenite.

Stage 3
200-350 C – replacement of eta-iron carbide by cemeneite,; martensite loses tetragonality

Stage 4
350 C – cementite coarsens and speroidizes, recrystallisation of ferrite.

[1] Steels 2nd Ed, Honeycombe and Bhadeshia, Edward Arnold, 1981, p172.

Making Podcasts

More podcasts this weekend…

Crystallographic texture and intervening transformations

Stress of Strain affected martensitic transformation

Quantitative Metallography of Deformed grains

Steels for Fusion

New Podcasts

I made three new podcasts with Prof. Harry Bhadeshia on his latest papers on transformation texture, the new delta-Trip steels and on prediction of Hot Strength of ferritic steels.

The work on transformation texture is from Saurabh Kundu’s thesis were Patel and Cohen’s model has been shown to correctly predict the orientation relationship between ferrite and austenite after martensitic transformation. It’s shown that variants are selected by free energy differences that can be calculated depending on the orientation.

The delta-Trip steels were developed as a result of the prediction of neural networks, were after the neural network was made computer optimisation was used to try and maximise the mechanical properties. This work was done with Saurabh Chatterjee in collaboration with Murugananth Marimuthu. Both Saurabh Kundu and Saurabh Chatterjee completed their PhD’s at Cambridge while visiting from Tata Steel, Murugananth Marimuthu is a previous member of the phase transformations group, and has now also joined Tata Steel’s research and development section.

The work on Hot Strength of ferritic steels is the part of Radu Dmitriu’s topic of research. A neural network model of the hot-strength of ferritic steels. It was observed from the neural network that the strength is expected to suddenly start to decrease at 800 Kelvin, which can has been explained to be due to changes in the mobility of dislocations.


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Podcast: Hot Strength

Podcast: Delta Ferrite

Podcast: Transformation Texture

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