The Research On Mechanical Properties And Microstructure Mechanisms Of Nanocrystalline Iron And Steel Materials Prepared By Aluminothermic

This paper reviewed the strengthening and toughening method, research status,mechanical peoperties and preparation method of the nanostructure steel and theresearch progress of aluminothermic reaction for preparing nanocrystalline metalmaterials. Through experimental researched the hardness, compressive properties,tensile properties, friction properties and high temperature mechanical properties ofbulk nanocrystalline materials prepared by aluminothermic reaction and summarizedthe influence of depositon substrate and the carbon content for the nanostructurematerials properties. The main conclusion are given in the following:1. The nanocrystalline iron were prepared on copper and glass substrate, and theirhardness and strength were improved significantly. The grain size of pure iron on glasssubstrate was smaller than that of pure on copper substrate and the yield strength ofpure on glass substrate was higher. Compared with the conventional pure iron, thetensile strength of pure on copper substrate was higher by43MPa and elongation waslower, the tensile strength of pure iron on copper decreased slightly and elongation waspoor. The microstructure of pure iron on glass substrate was not uniform, the tensileand elongation of pure on glass substrate were lower than that of pure iron on coppersubstrate. The fracture surface of pure iron on copper substrate was ductile facture andthat of pure iron on glass substrate was ductile and brittle mixed facture.2.20steel and45steel prepared by aluminothermic reaction were nano/microngrained dual phase steel, ferrite was nanocrystalline and pearlite was micron structure.The brinell hardness of20steel on copper and glass substrate increased slightly thanconventional20steel, the brinell hardness of45steel on copper and glass substratewas lower than conventional45steel. The yield strength of20and45steel on copperand glass substrate was improved significantly. the ferrite grain size and pearliteinterlamellar spacing of20and45steel on glass substrate were smaller relatively andtheir yield strength were higher than that of20and45on copper substrate. Themicrostructure of20steel on copper substrate was uniform, and its tensile andelongation were higher than that of20steel on glass substrate. The fracture surface of20steel on copper substrate was ductile fracture and tha of20steel on glass substratewas lamellar fracture. The facture surface of45steel on copper and glass substratewere ductile. The ferrite grain size of45steel copper substrate growed and thehardness and strength decreased obviously, the elongation increased. 3. The pearlite interlamellar spacing of T8steel prepared by aluminothermicreaction was large. Compared with conventional T8steel, the compressive yieldstrength of T8steel on copper and glass substrate had no obvious change and thetensile strength had large decline, the elongation was not very different. The T8steelon copper and glass substrate almost had the same mechanical properties. Theirfracture surface was river-like pattern cleavage fracture and it was brittle fracture.From pure iron to T8steel the strengthen effect weakened gradually along with thecarbon content increasing and the gap with the conventional materials reducedgradually.4. The hardness, compressive strength and tensile strength of white cast ironprepared by aluminothermic reaction had increasing firstly and then decreasing trend,the elongation reduced gradually. Compared with the hypoeutectic white cast ironprepared by arc furnace, the hardness, compressive strength, tensile strength andelongation of hypoeutectic white cast iron on copper and glass substrate were higherrelatively. The hardness, compressive strength and tensile strength of hypoeutectic oncopper substrate than that of hypoeutectic on glass substrate, while elongation ofhypoeutectic white cast iron on glass substrate was3%and higher relatively. Thefracture surface of white cast iron prepared by aluminothermic reaction were bittlefacture, while the plastic had been improved significantly. The friction coefficient ofhypoeutectic white cast iron reduced and wear rate increasing along with the loadincresing, when the load increased from60N to80N, the wear rate increasing trendbecame slow. The yield strength of hypoeutectic on copper substrate at600°C was273MPa, the tensile strength was344MPa and elongation was2%.