The heading materials were prepared by Denis BOROVITSKY, Alexey VOROBYEV-OBUKHOV
STEEL STRONGER STEEL
“Strong as steel”, “harder than steel” - until now, such definitions serve as a reference point when comparing different materials.
Look at a section of a sample of alloy steel under a microscope and you will see that the idea of this material as a homogeneous amorphous substance is misleading. In fact, its structure is polycrystalline, formed by tightly packed grains. But what are these oblong inclusions on their borders? It turns out that carbon inclusions - they are the ones that weaken the bond between the "particles", making the grain boundaries broken lines under excessive loads.
Now, if we could distribute carbon evenly throughout the metal and make its particles round … As scientists have found out, this is quite real. It is only necessary to place a crucible with six tons of a melt heated by an electric arc in a pressure chamber filled with a mixture of argon and nitrogen at a pressure of about 40 atm, and add silicon nitride powder. Then carbon will go into the form of carbonitrides, leave the grain boundaries and this will give the alloy unprecedented strength.
“In secret” we inform the composition of the new alloy: carbon - 0.31%, nitrogen - 0.38%, silicon - 0.55%, chromium - 15.2%, molybdenum - 1.02%. As for chromium, it is needed to increase the corrosion resistance of Kronidur, which is almost 100 times superior to ordinary steel. The tensile strength is 3-15 times higher than that of traditional bearing steel (depending on the direction of the tensile force), resistance to alternating bending loads is doubled.
Where will this, still very expensive steel, created by scientists from Bochum University, find application? The Kugelfisher company from Schweinfurt succeeded in manufacturing precision ball bearings from it, which can withstand speeds of up to … 550, 000 rpm. There are no such speeds in the automobile engine yet, but, for example, the Smart’s turbocharging turbine is already spinning up to 240, 000 rpm, so a new bearing with coronal rings and ceramic balls will come in handy here.