Effect Of Magnesium On The Inclusion And Properties Of D2 Cold Work Die Steel

D2 cold work die steel is one of the most wide used and most representative cold working die steel.There are certain gaps in domestic die steel compared with international advanced levels,which causes more than forty percent of upscale die steel have to be imported from abroad.To develop the high-quality of D2 cold work die steel,the micro-alloying element Mg was used in D2 die steel in this work and the effects of different Mg contents on the inclusions,carbides and properties of D2 die steel were systematically studied.In this experiment,the D2 steel was treated by adding magnesium under the condition of pressure,variation of magnesium content in steel.The results show that the retention of magnesium increases with the increase of pressure when the actual amount of magnesium is added.The results showed that increasing pressure can effectively promote the dissolution of magnesium in steel.With the study of the inclusion and the carbie during the manufacturing process,the oxygen content can be decreased to the lower level by magnesium-aluminum deoxidant.Because of the large amount of the inclusions,namely MgO·Al2O3 and MgS which are in the size of 2?m,and the composite inclusion which contains magnesium,the inclusion size in the D2 die steel by magnesium processing can reach the size of 3?5?m.The percence of inclusion which equivalent diameter less than 2?m has been increased,and inclusions' area percentage,average diameter has been decreased at the same time.Magnesium alter the cast microstructure,reduce the number of coarse dendrites.On the other hand,carbides distributed uniformly and semi mesh carbides replacing reticular carbides in die steel increase the continuity of the matrix.After quenching,the carbide refined improved the proportion of small carbides,and dispersed carbides replace large abnormal carbides.By magnesium modification on cold die steel,magnesium has no effect on the high temperature strength of the tool steel,but cold die steel thermoplasticity was improved.With the increase of temperature,thermal plasticity increased.The study of the performance impact of magnesium in the D2 die steel shows that,magnesium can significantly improve the normal temperature mechanical properties of quenched and tempered D2 die steel,both strength and hardness are improved obviously.After magnesium treatment,the inclusion in the fracture is considered of MgO·Al2O3 and MgO-Al2O3-SiO2-CaO with small size.Carbide in the gracture changes into the shape of almost or approximately sphere,and it increases the tenacity of the steel.