Properties of a nanostructured bainitic steel

In some recent work, we produced a nanostructured steel was produced using a clean steel-making technique. Hoping that applying VIM-VAR processing would achieve better mechanical properties by reducing tramp elements, like sulphur and phosphorous. Resulting in less problems of embrittlement by these elements and by manganese sulphide inclusions, etc.

No doubt these steels have impressive combinations of properties. We had the chance to measure many different mechanical properties of the same batch of steel. Only complicated by the fact that we were trying to develop heat treatments to improve the properties at the same time.

These results have been published in Materials Science and Technology, here: http://dx.doi.org/10.1080/02670836.2016.1271522

The maximum strength of the material recorded was 2.2 GPa at yield, with an ultimate tensile strength of 2.5 GPa, accompanied by a Charpy impact energy of 5 J, achieved by heat treatment to refine the prior austenite grain size from 145 to 20 µm. This increased the strength by 40% and the Charpy V-notch energy more than doubled. In terms of resistance of the hardness to tempering, the behaviour observed was similar to previous alloys. Despite reducing the hardness and strength, tempering was observed to reduce the plane-strain fracture toughness.

Superbainite on stage at Apollo theatre

Dyanamic test austempered ductile iron

Drs Dawid Myszka, A. Wieczorek and Tadeusz Cybula from the Warsaw University of Technology, Poland investigated the influence of microstructure on the dynamic mechanical properties of austempered ductile iron using Taylor impact testing. Austempered dictile iron means it’s a cast iron, so has graphite particles in a matrix heat treated to become bainite!. Taylor impact testing means you fire cylinders of the material at an immovable object and see how the material gets squished.

Deforming Austempered Ductile Iron

Shattering Austempered Ductile Iron

The heavily deformed volume which faced the impact has resulted in hardening and in transformation to martensite — both hardness and magnetic measurements have been used. Hardening was due to mostly strain induced austenite-to-martensite transformation, and also due to cold-work.

References
D. Myszka, L. Cybula and A. Wievzorek
Influence of heat treatment conditions on microstructure and mechanical properties of austempered ductile iron after dynamic deformation test
Archives of Metallurgy and Materials
V59, Issue 3, 2014

DOI:10.2478/amm-2014-0204

A Bainite Blog Story

Recently ‘HKDHB.’ visited Japan and met with Teruhisa Okumara, a man who plays a vital role in the founding of this blog –that’s because he is the original author of another blog which was called bainite. It all started in one of the famous Cambridge tea breaks…

HKDHB happy at the success of his website was advising us that his quality content if what brings visitors to his website (seriously check out the phase transformations website if you are looking for information about metals). A the time blogs were quite a new phenomenon and the problem was how search engines were going to reduce the ‘blog noise’. Because blogs are heavily cross-linked and regularly updated there was a concern that it might be hard to find [other] quality content on the internet. Anyway Teruhisa mentioned this and said he would start a blog called “bainite” which would then become the topped ranked page when anyone searched for “bainite”. What happened next is a matter of some debate. He created the blog on a Japanese blogging site, and it did indeed become the top ranked page when searching for bainite when searching for Japanese language pages. Happy he had proved his point he then removed the page. Some people dispute this counts as being the number one in search engines…

Anyway the seed of having a bainite blog had been planted and later I created this blog to practice my writing and see if it was possible to claim the top result for the bainite search term.

Meanwhile, back to HKDBH and Teruhisa, Teruhisa made a song for bainite while he was in Cambridge, on a recent visit HKDBH asked him to sing the song again.

Bainite… it’s special… because it’s not Pearlite (or Martensite).

The First Bulk Nanostructured Metal Lecture

Prof Bhadeshia gives a lecture about how superbainite is the first ever bulk nanostructured metal at Darwin College, The lecture was given as part of Darwin College’s 50th anniversary celebrations.

Bainite in Steels

Harry Bhadeshia’s book Bainite in Steels has reached it’s third edition. It’s available on pre-order at a price of 80 UKP and will be available from April. The third addition has an additional 40% more content to cover the developments of the 15 years of research since the previous edition.

This book is highly recommended for those who have an interest in the physical metallurgy of steels, alloy design, and solid-solid transformations.

http://www.oxbowbooks.com/oxbow/other-subjects/materials-science-engineering/bainite-in-steels-3rd-edition.html

Cover image for Bainite in Steels, 3rd Edition.

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.