dear numerous Legends surrounding powerful Japanese swords with Incredible strengths such as ishkirimaru which is said to have cut a massive Rock in half and ishidoro which cut through a stone Lantern nearby when cutting a pine branch although these stories seem exaggerated they might have provided interesting insights into how swordsmith's craftsmanship can affect his sword performance what do you think the answer is that the sword strengths can vary significantly depending on how it is made in this video I will discuss scientific possibility of creating the strongest Source by exploring the effects of grain size on Steel in this channel we share scientific knowledge of Samurai culture and exciting facts related to traditional Japanese practice if you're ready to level up your knowledge of a summer culture don't forget to smash the Subscribe button and join us on a journey [Music] have you ever wondered how slight changes in the processing of the metals can drastically alter their strengths it's fascinating to consider that even Metals with identical appearances can have widely different properties take copper for example this is 99.9 copper bar and the thickness is around 2 millimeters very thin however it's really really difficult to bend with my bare hand but once it is heated up to high temperature and cool down look at this become incredibly soft only two finger is enough to bend [Music] this is an example of how the strengths of the metal changed with a simple heat treatment of course not all metal is affected in exact the same way I'm too curious about how the heating treatment during Source making affect its strengths today I will discuss the importance of internal structure within steel for creating strong Source explaining why it occurs and how it can be achieved in the final part I will present a previous study that explores how the internal structure of Japanese Source varied across the different historical errors [Music] actually the steel which is a material of Japanese Source has a structure looks like a lump sticking together when viewed under a microscope each of the lumps is called a crystal grain this happens because the orientation of the crystals in each grain is different others have a comfortable positional relationship with each other making them easy to connect this leads to the formation of beautiful shapes like crystals when iron or steel is heated and melted and then cool it down various small crystals form and grow independently from each other these result in a large mass of iron with crystals sticking together in different orientations it is known that a smaller the grain size in the metal the higher the various strengths can be I will explain the principle behind this in two parts [Music] the first reason is that the deformation is difficult because the strains and defects within the crystal grains is not easily transmitted there will always be defects in strains within the crystal grains and it becomes impossible to have a perfect beautiful Crystal as the size of the crystal grows when their defects the crystal will easily shift and deform in a particular direction however when the crystal grains are small they can more easily act as a stopper for each other they become harder and less likely to deform under impact the second reason is that the area of the crystal grain boundaries is large allowing the absorption and dispersion of the impact at the boundaries the space between the crystal grains is relatively easy for atoms to move so when the impact occurs these atoms can absorb the energy as a whole and prevent the pores from being localized when the crystal grains are small the area of these grain boundaries becomes larger making it easier to absorb impact now I know you are curious about how much the strength actually changes there is a useful formula called whole patch equation the equation estimating the strengths of materials based on this the smaller the grain size the higher the tensile strength for example steel typically has a grain size of 25 micrometers when well made but if you have several micrometer grain size can be achieved that strength can be more than double so various research is being conducted for industrial applications in extreme cases using the same material the sword strings can change by more than double depending on how it's made I will tell you how we can make a source with smaller Crystal grains [Music] you can imagine crushing ice to make it into small pieces while preventing them from melting and sticking together you want to crush them you need to hit them with a large energy if not they just move and size never changes and you need to keep the low temperature if the temperature is high their surface smells a bit and easily stick together forming the larger pieces I'll explain the case of metals when copper is heated its Crystal grains combine together and form larger crystals making it much softer as the metal is heated the atoms being to move more vigorously and atoms at the boundaries between Crystal grains which are not tightly fixed gradually merged and form the same crystal as a result larger Crystal formed the higher the temperature the more likely the crystals are to grow larger to avoid larger Crystal formation it is necessary to create the materials at relatively low temperature in a short time this is below around 700 degrees Celsius the temperature at which iron Berry turns red if a blade is made at this temperature it is difficult for Crystal grains to grow moreover to make the crystal grains even smaller a large amount of energy must be applied in a short time enough to crush low crystals instead of using the flat Hammer I think it's more effective to use the rounded one to strike the material so that the deformation is as large as possible [Music] it is common to distinguish between sores made before and after Edo period referring to the former as Koto and the latter as Shinto people often claim that Koto possesses Superior sharpness color and the distinct sensation during sharpening but I find it interesting to speculate on how changes in heating techniques and forcing process throughout the history might have affected the grain size of the source a Japanese metallurgist named Masahiro kitada once conducted a study on crystal grain of 30 different katanas dating from Kamakura to Edo period he found that among 30 randomly corrected swords doors made from Edo period has larger Crystal grain size compared to the one made in earlier period the difference was especially noticeable in the grain size near the blade edge with Kamakura Pure Source having a great range size of around 1 to 5 micrometers wire and appearance swords have grain size of around 20 to 30 micrometers that's a big difference it means that the source from Kamakura period which are analyzed in this study are harder in high possibility and when the crystal grains are smaller which can lead to differences in the texture and the color even if the material is the same I think it is possible that a sword making techniques such as heating techniques changed over time differences in the size of the crystal grains emerged which could have contributed to spread the rumors about Superior sores from certain periods but please note that following the difference in Crystal grain size across different periods is only a possibility and the truths are unclear this is because only 30 source is examined and there may be biased the discussions about Crystal phrase I presented here is just only one way to strengthen steel there are different principles at play such as the structure of the crystal themselves and solid solution strengthening it can also make steel stronger I'd like to create a video about those topics as well [Music]