The Effect Of Heat Treatments On The Microstructures And Properties Of The High Speed Steel Rolls

In this thesis, many measures such as color and grey metallography,XRD, SEM and EDS were utilized to systematically analyze the, heat treatment technology and properties of high speed steel (HSS) composite rolls of Fe-1.8%C-4%Cr-6%Mo-6%V without tungsten. Investigate the effect of microstructure and hardness with different heat treatment.The following method was applied: F 236 mm metallic mold centrifugal casting.Study was carried out for the Fe-1.8%C-4%Cr-6%Mo-6%V high speed steel without tungsten containing. The achieved conclusions were as follows:After modified with using 1.0% ferrovanadium, the as-cast structure of sand mold specimens was remarkably improved and the reticular carbides were gradually broken. Having being quenched at a high temperature of 1180℃, greater parts of as-cast reticular carbides dissolved in the matrix, the net form vanished, and the carbides were distributed in the matrix in shape of particles. For the high speed steel roll collars centrifugally cast, after 1180℃×4hquenching in air plus double tempering of 550℃×3h cooling in stove, the structuralmorphology was martensite matrix on which were distributed dispersed carbides. The carbides in the outer collar were finer, dispersing and uniformly distributed, the grains were smaller than in the inner collar, and the carbides became thin strip in shape from granular and clustered as balls and chrysanthemums. Under the condition of 1080℃×3h quenching in air plus three times of tempering treatment of 540℃×1h cooling in air, the size, shape and distribution of carbides were obviously changed, reticular carbides were essentially diminished, carbides grains became iner and their distribution tended to homogenization.The hardness of high speed steels after annealing were lower and met the requirements of machining. The hardness of high speed steels after heat treatment reached roughly HRC 63 and was able to meet the demands for roll properties. After modified with ferrovanadium, the structure and properties of the centrifugally cast roll collars were improved, and the particles of carbides became finer and finer. When the amount of ferrovanadium was increased to 1.0%, the carbides were fine and round, uniformly distributed,60.6.The impact toughness strength and other mechanical was the hardness reached its peak of HRC58.4 while the elastic modulus, tensile properties also reached their ideal values.It was obtained from an orthogonal test that the hardness would be the highest as the heat treatment condition was 1100℃×3h quenching plus double tempering of 600℃×1h.And it could be seen from the calculated level means, an even better combination was 1100℃×3h quenching plus single tempering of 600℃×1h. The order of the main hardness influencing factors was as follows: tempering temperature, quenching temperature, the number of time for tempering, and the time for quenching-temperature keeping. For the high speed steel roll collars that were modified using 1.0% ferrovanadium, after the heat treatment technology of 1180℃×3h quenching in air plus double tempering of 550℃×4h cooling in stove. their hardness HRC 58.2,combined properties being better.