Layer Forming And Properties Of Roll 55Mn2 Steel Prepared By Selective Laser Melting

Rolls is a tool for producing continuous plastic deformation of metal.The main failure modes of rolls include exfoliation drop,large surface crack,roll body and roll neck fracture.The facing remanufacturing of failed rolls can improve the service life,reduce rolls consumption and the cost of steel milling.Inconel718?IN718?and TiC/IN718 composite coatings were prepared on roll material 55Mn2 substrate using Selective Laser Melting?SLM?.The effects of laser line energy density on the surface microstructure,relative density and microhardness of coating were studied.The relationship between laser energy density and shear strength between the IN718 coating and 55Mn2 substrate was investigated.The effects of changes of the test temperature and load on the wear properties of IN718 coating and TiC/IN718 composite coating and the mechanism of friction under different wear conditions were analyzed.The main conclusions were listed as follows:The IN718 coating was prepared on the surface of the 55Mn2 substrate using 6 different laser line energy densities.The experiment results showed that with the increase of laser line energy density,the number of spherical particles on the surface of the coating decreased due to the nodulizing phenomenon.The internal precipitated?phase refined gradually and the columnar crystal evenly distributed.The density and microhardness of the coating layer increased gradually.The density and the microhardness reached 99.6%and 428.6 HV_0.2 when the line energy density was 357.14 J/m.The IN718 coating was metallurgically bonded with the matrix.It was known that the fracture modle between coating and the matrix are ductile fracture from the shear morphology,and the shear strength was 1.9?2.15 times of the matrix.The IN718 coating was prepared on the surface of 55Mn2 substrate with laser power?P?of 90W and scanning speed???of 280mm/s.The friction and wear properties of IN718coating at different temperatures and loads were studied.The results showed that,at room temperature,the IN718 coating mainly occurred abrasive wear,and at high temperature,adhesive wear and oxidation wear mainly occurred.With the load increase,the friction coefficient decreased and the wear mass increased.The change of the two was small,when the load greater than 10N.The friction coefficient and wear mass of the coating decreased under the fixed load with the temperature increasing.When the temperature was higher than325°C,the friction coefficient was relatively stable.The higher hardness and the oxidized frictional protective layer formed at high temperatures of the Inconel718 coating lead to a good and stable wear resistance.TiC/IN718 composite coating was prepared on 55Mn2 substrate surface by adding 10%TiC micronparticles into IN718 alloy powder and using different SLM process parameters.The results showed that,when the laser line energy was low,there were a large number of powders which havd not been completely melted,and there were many holes in the coating,and the hardness was low.With the laser energy density increased,the composite powder gradually melted completely.The internal structure was refined and the microhardness increased.The wear mechanism of TiC/IN718 composite coating at room temperature was adhesive wear and abrasive wear.With the laser energy increased,there were an increasement of wear resistance of the composite coating and decreasement of the friction coefficient and the wear mass decreased.IN718 and TiC/IN718 composite strengthening coatings prepared by SLM can significantly improve the surface microhardness and friction and wear properties of 55Mn2roll steel.The coating materials and process parameters have great influence on the properties of the coating.This study can provide an experimental and theoretical basis on repairing and strengthening the roll surface by selective laser melting.