Mechanism Study On Refining Solidification Microstructure Of High Speed Tool Steel By Magnesium/Rare Earth

In recent years,the high-speed steel industry has developed rapidly in our country.The output and export volume of high-speed steel rank first in the world and become the main supplier of high-speed steel in the world.However,the rapid development of manufacturing industry has put forward higher requirements for cutting and processing performance of high-speed steel,the quality of high-speed steel must be further improved.The homogeneity of solidification structure of HSS is one of the key factors affecting HSS products.It has been proved that magnesium and rare earth can refine the solidification structure of HSS and improve the size and distribution of carbides.However,there is no clear explanation about their influence mechanism.In order to solve this problem,it is of great significance to study the effect mechanism of magnesium,rare earth and rare earth-magnesium treatment on the solidification quality of M2 high speed steel.In this paper,the magnesium,rare earth and rare earth-magnesium were added to M2 high speed steel to study the action mechanism of magnesium,rare earth and rare earth-magnesium on solidification quality in steel.Under the experimental conditions,the following conclusions are obtained:?1?The solidification structure of M2 high speed steel can be refined by adding magnesium.Compared with the samples without magnesium addition,when magnesium content is 8 ppm,the secondary dendrite spacing decreases by 17%and the area of carbide decreases by 32.9%.The type of carbide in high speed steel will not change by adding magnesium,but it can promote the conversion of MC to M₂C.?2?The addition of rare earth can refine the solidification structure of M2 high speed steel.When the rare earth content was 0.0344%,the secondary dendrite spacing and carbide area decreased by 14.7%and 30.3%,respectively,compared with the samples without rare earth addition.Besides,rare earth can also promote the morphological change of M₂C carbides.The regularity of carbide morphology change is as follows:flat sheet layered?curved short rod shape?honeycomb shape?needle shape.?3?In the process of treating M2 high speed steel by adding rare earth-magnesium compound,when the content of rare earth is 0.02%,the spacing of secondary dendrites is almost unchanged with the increase of magnesium content,and the proportion of carbide area hardly changes.While the content of rare earth is0.036%,the secondary dendrite spacing increases with the increase of magnesium content,and the proportion of carbide area increases.And the content of rare earth is0.04%,the secondary dendrite spacing decreases with the increase of magnesium content,and the proportion of carbide area decreases.?4?In the process of treating M2 high speed steel by adding rare earth-magnesium compound,when the content of magnesium is 11 ppm,the secondary dendrite spacing decreases with the increase of rare earth content,and the proportion of carbide area decreases;while the content of magnesium is 16 ppm,the secondary dendrite spacing basically does not change with the increase of rare earth content,and the proportion of carbide area is basically the same;and the content of magnesium is 20 ppm,the secondary dendrite spacing increases with the increase of rare earth content,and the proportion of carbide area is approximately the same.