# Why Metals Turn Brittle in the Cold > In October 2026 an international team led by UC Berkeley, Berkeley Lab and the University of Oxford reported in Nature two experimental alloys that stay tough at −253 °C, although their crystal structure is the kind that usually turns brittle. This film explains the fundamentals: ductile and brittle fracture, the FCC and BCC ways of stacking atoms, how dislocations let metals bend and why they stall in the cold, the ductile-to-brittle transition, the Charpy test of 1901, the Liberty ships that cracked in the Second World War and Constance Tipper's work, the 1944 Cleveland gas-tank disaster, and the metals chosen for liquefied gas and liquid hydrogen today. Interactive film: https://www.planetpast.com/stories/why-metals-turn-brittle-in-the-cold/ Publisher: PlanetPast (https://www.planetpast.com/) · d => T('readPublished', l, { d: dateIn(d, l) }) 2026-11-02 · Chemistry, Physics, History ## Prologue ### Bend or snap *Chemistry · Physics* Why cold turns some metals brittle, and what engineers do about it. Bend a steel bar on a mild day and it sags, but holds. Cool the same bar far enough and it can snap like glass. In the Second World War, that switch broke ships in half. On the fourteenth of October 2026, an international team led by UC Berkeley, Berkeley Lab and the University of Oxford reported in Nature two experimental metals that stay tough at minus two hundred and fifty-three degrees Celsius. Why do some metals turn brittle in the cold, and how do engineers build things that must stay cold? ![The broken face of brittle steel is flat and glitters. AI-generated still.](https://assets.planetpast.com/a/cd/cdb9a46f4d6e32da.jpg) - **−253 °C**: the test temperature: 20 kelvin, just 20 degrees above absolute zero - **Nb–Ti**: niobium and titanium based, more in chapter V ![A wartime cargo ship in an icy sea, a crack across its deck. AI-generated still.](https://assets.planetpast.com/a/c7/c74bcf1bcd5146c3.jpg) Prologue #### A metal that stays tough EurekAlert! / University of Oxford (14 October 2026): in Nature, an international team led by UC Berkeley, Lawrence Berkeley National Laboratory and the University of Oxford, with partners including ISIS, reported two experimental niobium–titanium-based alloys with a body-centred cubic structure that, tested at 20 K (about −253 °C), showed no measurable ductile-to-brittle transition. ScienceDaily (29 October 2026) reported the same study. This single new study is the hook; chapter V comes back to it. The rest of the film is long-established materials science and history. The 3D scenes are simplified teaching models, not to scale. Sources: [EurekAlert! / University of Oxford (14 Oct 2026): Metal defies the deep freeze, staying tough at −253 °C (Nature)](https://www.eurekalert.org/news-releases/1147527); [ScienceDaily (29 Oct 2026): Scientists discover metals that defy the deep freeze at −424 °F](https://www.sciencedaily.com/releases/2026/10/261029072127.htm) ## Chapter I · Bend or snap ### Engineers call a material that bends and stretches before it breaks ductile. One that breaks suddenly, with almost no bending, is brittle. A ductile failure gives warning: the metal sags, stretches and soaks up energy. A brittle fracture gives none. Most steel is ductile on a mild day. Cool it far enough, and the same steel can become brittle. Try both temperatures. Sharp notches, small cuts in the surface, and sudden blows push steel the same way as cold does: towards brittle. ![A rod bent into a U without breaking. AI-generated still.](https://assets.planetpast.com/a/7f/7fbfa35dca42f186.jpg) ![Glass breaks with sharp, clean faces. AI-generated still.](https://assets.planetpast.com/a/73/73dacabc0cdce1fd.jpg) - Ductile: rough surface, stretched, energy absorbed - Brittle: flat surface, clean split, little energy ![A tough metal thins to a waist before it parts, and the break is rough rather than flat. AI-generated still.](https://assets.planetpast.com/a/d2/d2e7eef2368d4998.jpg) Chapter I · Bend or snap #### Ductile and brittle Wikipedia, Charpy impact test: ductile fracture leaves a rough surface, lateral contraction and shear lips; brittle fracture leaves a flat, smooth surface and often splits the specimen cleanly in two; brittle fracture, propagating without plastic deformation, is particularly dangerous because it gives no warning. ArcelorMittal: resistance to brittle fracture is called toughness; lower temperature, faster loading and notches all promote brittle cleavage in body-centred cubic steels. Try it: room temperature or deep cold. The 3D scenes are simplified teaching models, not to scale. Sources: [Wikipedia: Charpy impact test (history, method, BCC and FCC, Liberty ships)](https://en.wikipedia.org/wiki/Charpy_impact_test); [ArcelorMittal Constructalia, SiCA Steel Academy: Toughness and resistance to brittle fracture](https://constructalia.arcelormittal.com/en/sica-steel-academy/properties-of-steel/toughness-and-resistance-to-brittle-fracture) ### To see why, look at the atoms. A metal is a crystal: its atoms sit in a regular, repeating pattern. Copper, aluminium, nickel and most stainless steel stack their atoms with one at the centre of each face of a cube. This is called face-centred cubic, or FCC. Ordinary steel puts one atom in the middle of each cube instead. This is body-centred cubic, or BCC, and it is packed less tightly. ![Under a microscope, polished steel shows many small crystals. AI-generated still.](https://assets.planetpast.com/a/d0/d0632fa75ab53624.jpg) - Copper - Aluminium - Nickel - Austenitic stainless steel ![Zinc grows grains big enough to see; in structural steel they are a few hundredths of a millimetre across. AI-generated still.](https://assets.planetpast.com/a/05/056d49b7b64d9c2b.jpg) - **ferritic steel**: the ordinary steel of beams, ships and pipes Chapter I · Bend or snap #### How atoms are stacked Wikipedia, Charpy impact test: body-centred cubic (BCC) metals such as ferritic and martensitic steels show a ductile–brittle transition; face-centred cubic (FCC) metals such as austenitic stainless steels, copper, aluminium and nickel generally do not, with exceptions. IMT Mines Albi: the BCC structure is less compact than FCC, so a higher critical shear stress is needed to start dislocation slip, and BCC metals are generally less ductile. Try it: switch between FCC and BCC. The 3D scenes are simplified teaching models, not to scale. Sources: [Wikipedia: Charpy impact test (history, method, BCC and FCC, Liberty ships)](https://en.wikipedia.org/wiki/Charpy_impact_test); [IMT Mines Albi, SciMat: Ductility, fragility and the ductile-brittle transition](https://nte.mines-albi.fr/SciMat/en/co/SM6uc1-3.html) ### A metal bends because planes of atoms slide past one another. They do not slide all at once. A flaw in the pattern, called a dislocation, glides through the crystal, shifting one row of atoms at a time. Think of moving a heavy rug by pushing a ripple along it, rather than dragging the whole thing. The more easily dislocations move, the more a metal can bend before it breaks. - An extra half-row of atoms - It moves one spacing at a time - When it leaves, the top has shifted ![Moving the flaw takes a fraction of the force it would take to slide the whole plane at once. AI-generated still.](https://assets.planetpast.com/a/de/dea1ebda9d7104ea.jpg) - **one row**: the flaw moves, so the plane never has to slide in one go > Moving a rug by pushing a ripple, not dragging the whole rug. (A common teaching picture of a dislocation) - **easy glide**: more bending before fracture Chapter I · Bend or snap #### Dislocations IMT Mines Albi: ductility, how much a metal can deform before it breaks, depends on how easily dislocations move through the crystal lattice; where dislocations are almost immobile, as in ceramics, the material is brittle. The rug picture is an analogy used in teaching, not a quoted source. The 3D scenes are simplified teaching models, not to scale. Sources: [IMT Mines Albi, SciMat: Ductility, fragility and the ductile-brittle transition](https://nte.mines-albi.fr/SciMat/en/co/SM6uc1-3.html) ## Chapter II · Why cold matters ### In BCC metals, dislocations get harder to move as the temperature falls. In deep cold, they barely move at all. So the stress is not spent on bending. It builds up, until a crack splits the crystal cleanly along a plane of atoms. This is called cleavage. FCC metals keep slipping even in deep cold, so they generally have no such switch. Compare the two. That is why a cold BCC steel can break under a load it would easily survive on a warm day. - **colder**: dislocations harder to move - Happens in BCC steels - Flat, crystalline break - Chevron marks point back to the origin ![A cleavage break follows a single plane of atoms, which is why it comes out mirror-flat. AI-generated still.](https://assets.planetpast.com/a/84/8498acc11e70ea8f.jpg) - **no cleavage**: austenitic (FCC) stainless steel does not fail by cleavage (ArcelorMittal) - **warm**: bends - **cold**: can break Chapter II · Why cold matters #### Why cold matters Oxford (EurekAlert!): body-centred cubic metals usually grow more brittle as they get colder, because dislocations become harder to move. IMT Mines Albi: low temperatures reduce dislocation mobility. ArcelorMittal: brittle (cleavage) fracture occurs in BCC metals such as ferritic steels when the maximum principal stress exceeds a critical cleavage stress; the surface is flat and crystalline, often with chevron marks pointing to the origin; austenitic (FCC) steels do not cleave under all conditions. Try it: warm and cold, BCC and FCC. The 3D scenes are simplified teaching models, not to scale. Sources: [EurekAlert! / University of Oxford (14 Oct 2026): Metal defies the deep freeze, staying tough at −253 °C (Nature)](https://www.eurekalert.org/news-releases/1147527); [IMT Mines Albi, SciMat: Ductility, fragility and the ductile-brittle transition](https://nte.mines-albi.fr/SciMat/en/co/SM6uc1-3.html); [ArcelorMittal Constructalia, SiCA Steel Academy: Toughness and resistance to brittle fracture](https://constructalia.arcelormittal.com/en/sica-steel-academy/properties-of-steel/toughness-and-resistance-to-brittle-fracture) ### Measure how much energy it takes to break a steel bar at different temperatures, and you get an S-shaped curve. Warm, the steel soaks up a lot of energy. Below a certain range, the energy drops steeply. That range is the ductile-to-brittle transition. For ordinary steels it typically lies somewhere between about minus ten and minus fifty degrees Celsius, depending on the grade. FCC metals show no such drop. Engineers use this curve to choose steel for a bridge, a pipeline or a ship: it must stay on the warm, tough side at the coldest temperature it will ever meet. - Many identical notched bars - Each broken at a different temperature - Energy plotted against temperature - **a range**: not a sharp point - **−10 to −50 °C**: typical brittle threshold, by grade ![The transition is a range, not one temperature: bars cut from the same plate can differ by tens of degrees. AI-generated still.](https://assets.planetpast.com/a/e3/e3f01c6b39e6758e.jpg) - Find the coldest temperature in service - Pick a steel still tough there Chapter II · Why cold matters #### The S-curve Wikipedia, Charpy impact test: absorbed energy usually drops as temperature falls, over a transition region rather than at a sharp point; the transition temperature can be defined in several ways that give different results. IMT Mines Albi: BCC steels that are ductile at normal temperatures become brittle at very low temperatures, typically below about −10 °C to −50 °C depending on the grade. ArcelorMittal: practical criteria include a specified impact energy (such as 27 J), half the maximum energy, or 50% ductile fracture surface. Try it: move along the curve. The curves are typical shapes, not one steel’s measurements. The 3D scenes are simplified teaching models, not to scale. Sources: [Wikipedia: Charpy impact test (history, method, BCC and FCC, Liberty ships)](https://en.wikipedia.org/wiki/Charpy_impact_test); [IMT Mines Albi, SciMat: Ductility, fragility and the ductile-brittle transition](https://nte.mines-albi.fr/SciMat/en/co/SM6uc1-3.html); [ArcelorMittal Constructalia, SiCA Steel Academy: Toughness and resistance to brittle fracture](https://constructalia.arcelormittal.com/en/sica-steel-academy/properties-of-steel/toughness-and-resistance-to-brittle-fracture) ## Chapter III · The hammer test ### How do you measure it? In 1901 Georges Charpy proposed a standard test, and its design has barely changed since. A heavy pendulum swings down and strikes a small bar with a notch cut in it. The higher the hammer swings up on the other side, the less energy the bar absorbed. A tough bar bends and slows the hammer. A brittle one snaps cleanly, with a flat, glittering break. Try a warm bar and a cold one. The test is cheap and quick, though it gives only a relative measure of toughness. - 1896: S. B. Russell: a pendulum fracture test - 1901: Charpy: a standard notched specimen - 1905: His machine, essentially today’s - **10 × 10 × 55 mm**: specimen - **2 mm**: V-notch depth ![The bar is ten millimetres square with a two-millimetre notch, and the standard has kept those sizes ever since. AI-generated still.](https://assets.planetpast.com/a/13/13994fe4a614d519.jpg) $$E = m\,g\,(h_{\text{start}} - h_{\text{end}})$$ - $m$: mass of the hammer - $h$: heights before and after the swing - **cheap, quick**: but a relative measure: good for comparing steels Chapter III · The hammer test #### The Charpy test Wikipedia, Charpy impact test: in 1896 S. B. Russell introduced a pendulum fracture test; in 1901 Georges Charpy proposed a standardised version with a precisely specified notched specimen, and his 1905 design is essentially the modern apparatus. A pendulum of known mass is released from a known height and strikes the notched specimen; the absorbed energy is inferred from the difference between the release height and the height reached afterwards. The standard specimen is 10 × 10 × 55 mm with a 2 mm deep V-notch. Try it: warm and cold bars of ordinary and stainless steel. Swing heights are schematic. The 3D scenes are simplified teaching models, not to scale. Sources: [Wikipedia: Charpy impact test (history, method, BCC and FCC, Liberty ships)](https://en.wikipedia.org/wiki/Charpy_impact_test) ## Chapter IV · Ships that broke ### The lesson was learned the hard way in the Second World War. The United States built thousands of welded steel cargo ships, among them the Liberty ships. A US Navy investigation later found that more than a fifth of the 4,694 welded-steel ships it studied suffered fractures. Some broke in half without warning. Ships in the cold North Atlantic met temperatures low enough to make their steel brittle. ![Welded hulls on the slipways of a wartime shipyard. AI-generated still.](https://assets.planetpast.com/a/38/3859b7fdbb3d3c44.jpg) - **4,694**: welded-steel ships studied - **> 20%**: suffered fractures - **in half**: how some of the ships broke - **North Atlantic**: cold enough to make the steel brittle Chapter IV · Ships that broke #### The Liberty ships Wikipedia, Charpy impact test: an investigation of the 4,694 welded-steel merchant ships built from February 1942 to March 1946, including the Liberty ships, found that over 20% suffered fractures; some broke in half without warning. University of Cambridge, Department of Engineering: during the Second World War Liberty ships were breaking in two; ships in the North Atlantic faced temperatures low enough to make them susceptible to brittle failure. The ship in the 3D scene is a generic schematic, not a model of any real vessel. The 3D scenes are simplified teaching models, not to scale. Sources: [Wikipedia: Charpy impact test (history, method, BCC and FCC, Liberty ships)](https://en.wikipedia.org/wiki/Charpy_impact_test); [University of Cambridge, Department of Engineering: Constance Tipper](https://www-g.eng.cam.ac.uk/125/1925-1950/tipper.html) ### At Cambridge, the researcher Constance Tipper showed that steel has a critical temperature, below which its fracture changes from ductile to brittle. Her test became the standard way of checking steel for brittleness, though its full importance was recognised only in the 1950s. Meanwhile, changes to ship design, to welding, and toughness requirements for the steel cut the fracture rate from more than a hundred and thirty a month in 1944 to fewer than five in 1946. - **critical temperature**: below it, steel fractures brittle - 1915: Among the first women in Cambridge’s Natural Sciences Tripos - 1940s: Studies why Liberty ships broke - 1950s: Her test becomes the standard - 1944: > 130 - 1946, after design, welding and steel changes: < 5 ![These were the first large hulls welded rather than riveted, so a running crack had no seam to stop it. AI-generated still.](https://assets.planetpast.com/a/32/322d5e9240947271.jpg) Chapter IV · Ships that broke #### Constance Tipper University of Cambridge, Department of Engineering: Constance Tipper, one of the first women to take the Natural Sciences Tripos (1915), established in the Engineering Department that steel has a critical temperature below which its fracture changes from ductile to brittle; the full implications of her work were not recognised until the 1950s, after which the “Tipper test” became the standard method for determining brittleness in steel. Wikipedia, Charpy impact test: design changes, fabrication changes and impact-energy requirements together cut the monthly fracture rate from over 130 in March 1944 to fewer than 5 by March 1946. The 3D scenes are simplified teaching models, not to scale. Sources: [University of Cambridge, Department of Engineering: Constance Tipper](https://www-g.eng.cam.ac.uk/125/1925-1950/tipper.html); [Wikipedia: Charpy impact test (history, method, BCC and FCC, Liberty ships)](https://en.wikipedia.org/wiki/Charpy_impact_test) ## Chapter V · Built for the cold ### Very cold liquids raise the stakes. In 1944, in Cleveland, Ohio, a tank of liquefied natural gas built of steel with about three and a half percent nickel leaked. The outer steel shell then failed, the gas spread into streets and sewers, and the vapour cloud ignited in a massive explosion. Steel with nine percent nickel, researched from the early 1940s, came into use in the 1950s. Today, tanks for liquefied natural gas must stay ductile below minus a hundred and sixty-five degrees. - **~3.5%**: nickel in the tank steel, chosen because of wartime stainless shortages - Inner tank leaks - Outer carbon-steel shell fails - Vapour cloud ignites ![A frosted storage sphere at a gas terminal. AI-generated still.](https://assets.planetpast.com/a/3e/3ee0b491d37054ee.jpg) Chapter V · Built for the cold #### Cleveland, 1944 PetroSkills: in Cleveland in 1944 a tank built with about 3.5% nickel steel, because of wartime stainless-steel shortages, leaked; the outer carbon-steel shell then failed, releasing liquefied natural gas into the streets and sewers, and the resulting vapour cloud ignited in a massive explosion. PetroSkills dates 9% nickel steel to the early 1940s; the Nickel Institute says International Nickel researched it from the early 1940s, presented results in 1947, and it entered service in 1952. The base material of LNG tanks must stay ductile below −165 °C. The film does not give a casualty figure, because the source used does not. The 3D scenes are simplified teaching models, not to scale. Sources: [PetroSkills: LNG containment tanks, why the inner liner is 9% Ni](https://petroskills.com/en/blog/entry/may21-lng-containment-tanks); [Nickel Institute: Nine percent nickel steel, 28 years of reliable service in LNG containment](https://www.nickelinstitute.org/media/8daa618cfd28feb/10030_ninepercentnickel_28yearsofreliableserviceinlngcontainment.pdf) ### Nine percent nickel steel, stainless steel and aluminium have no ductile-to-brittle transition at these working temperatures, so they are the metals chosen for this work. Aluminium makes the big round tanks on many gas carrier ships, because it is light. Stainless steel holds liquid hydrogen, at about minus two hundred and fifty-three degrees. - 9% nickel steel: large land tanks - Stainless steel: liquid hydrogen vessels - Aluminium: spherical tanks on gas carriers - **−104 to −196 °C**: its main working range ![A gas carrier with round tanks on deck. AI-generated still.](https://assets.planetpast.com/a/6f/6f81e8af636eae19.jpg) - LNG tank material must stay ductile below: −165 - 9% nickel steel, used down to: −196 - Liquid hydrogen: −252.8 Chapter V · Built for the cold #### Metals for the deep cold PetroSkills: 9% nickel steel, stainless steel and aluminium do not have a ductile/brittle transition temperature; 9% nickel steels are mainly used from −104 °C down to −196 °C and offer an attractive combination of properties at a moderate price; aluminium is used for large spherical tanks on gas tankers because of its lower weight; stainless steel is used for liquid hydrogen (−252.8 °C) vessels. The bars show temperatures below zero, so a longer bar means colder. The 3D scenes are simplified teaching models, not to scale. Sources: [PetroSkills: LNG containment tanks, why the inner liner is 9% Ni](https://petroskills.com/en/blog/entry/may21-lng-containment-tanks) ### That is why the new result caught attention. The two experimental alloys, based on niobium and titanium, are BCC, the kind expected to turn brittle. Yet stretched at minus two hundred and fifty-three degrees, they showed no measurable ductile-to-brittle transition. Tiny regions of the crystal flipped into mirror-image copies, called twins, and changed their structure locally. That created new defects, which let the metal keep deforming instead of cracking. The team watched this with beams of neutrons at a laboratory in Oxfordshire, which reveal how the crystal changes while the metal is being stretched. The researchers say it should change how we think about what makes these metals brittle. It is a single study, and others will now test it. - **Nb–Ti**: niobium–titanium based - **BCC**: the structure that usually turns brittle - **no transition**: measurable at the lowest temperature tested - Nanoscale twinning: mirror-image regions - A local change in crystal structure - New defects at grain boundaries keep it deforming - **neutrons**: pass through metal and reveal its crystal while it is pulled > Our results suggest we should change how we think about what governs the transition to brittleness for these metals. (David Cook, lead author (Oxford release)) Chapter V · Built for the cold #### A BCC metal that does not snap EurekAlert! / University of Oxford: the two experimental niobium–titanium-based BCC alloys, cooled with gaseous helium and pulled in tension at 20 K (Engin-X, ISIS Neutron and Muon Source), showed no measurable ductile-to-brittle transition at the lowest temperature tested; nanoscale twinning, in which small regions of the crystal reorient into mirror-image arrangements, is paired with a local change in crystal structure, creating stress concentrations at grain boundaries that trigger new defects and let the metal keep deforming. Prof. Dong Liu: “For decades, the ductile-to-brittle transition has been viewed as a fundamental limitation of body-centred cubic metals.” This is one new study, reported as published; it has not yet been reproduced by other groups. The 3D scenes are simplified teaching models, not to scale. Sources: [EurekAlert! / University of Oxford (14 Oct 2026): Metal defies the deep freeze, staying tough at −253 °C (Nature)](https://www.eurekalert.org/news-releases/1147527); [ScienceDaily (29 Oct 2026): Scientists discover metals that defy the deep freeze at −424 °F](https://www.sciencedaily.com/releases/2026/10/261029072127.htm) ## Epilogue ### So the next time you see a frosted gas tank or a ship in icy water, remember that choosing the metal means choosing its crystal. Atoms that can keep slipping in the cold bend. Atoms that cannot, snap. And whether a BCC metal can be made to stay tough in the deepest cold, outside a single study, is an open question again. - 1901: Charpy’s standard test - 1940s: Liberty ships crack - 1944: Cleveland gas-tank disaster - 1950s: Tipper’s test becomes standard - 2026: BCC alloys tough at −253 °C ![The weld is the hardest part to get right: the metal beside it is reheated, and its grains come out a different size. AI-generated still.](https://assets.planetpast.com/a/47/47a4873f26a6a5ba.jpg) - FCC: keeps bending in the cold - BCC: can snap below its transition - **1**: study so far: others now need to repeat it Epilogue · Sources #### Sources Every fact in this film comes from the sources below. The chapter stills and pictures are AI-generated and show no real people, ships or brands. The bars, crystals, dislocation, curves, pendulum, ship and tank in the 3D scenes are simplified teaching models; the curves are typical shapes, not measurements of one steel. The 2026 alloy study is a single new result, presented as reported. Sources: [EurekAlert! / University of Oxford (14 Oct 2026): Metal defies the deep freeze, staying tough at −253 °C (Nature)](https://www.eurekalert.org/news-releases/1147527); [ScienceDaily (29 Oct 2026): Scientists discover metals that defy the deep freeze at −424 °F](https://www.sciencedaily.com/releases/2026/10/261029072127.htm); [Wikipedia: Charpy impact test (history, method, BCC and FCC, Liberty ships)](https://en.wikipedia.org/wiki/Charpy_impact_test); [ArcelorMittal Constructalia, SiCA Steel Academy: Toughness and resistance to brittle fracture](https://constructalia.arcelormittal.com/en/sica-steel-academy/properties-of-steel/toughness-and-resistance-to-brittle-fracture); [IMT Mines Albi, SciMat: Ductility, fragility and the ductile-brittle transition](https://nte.mines-albi.fr/SciMat/en/co/SM6uc1-3.html); [University of Cambridge, Department of Engineering: Constance Tipper](https://www-g.eng.cam.ac.uk/125/1925-1950/tipper.html); [PetroSkills: LNG containment tanks, why the inner liner is 9% Ni](https://petroskills.com/en/blog/entry/may21-lng-containment-tanks); [Nickel Institute: Nine percent nickel steel, 28 years of reliable service in LNG containment](https://www.nickelinstitute.org/media/8daa618cfd28feb/10030_ninepercentnickel_28yearsofreliableserviceinlngcontainment.pdf)