| The control of inclusions in hot work die steel during ESR process is the most important factor in the production of high-end hot work die steel.The composition,shape,size and distribution of inclusions in H13 steel directly affect the performance.Therefore,the characteristic of inclusions in remelted ingot is one of the main factors affecting the quality performance of H13 steel.In this article,the control and modification of inclusions in H13 steel as well as the evolution behavior during ESR process were studied.It is found that the inclusion control in Austrian BOHLER H13 steel is optimal after the comparison study of H13 steel inclusions domestic and abroad after electroslag remelting.90%of the inclusions in Austrian BOHLER H13 steel are close to the spherical shape,and the inclusions are relatively uniform in shape,and the composition and size are not greatly fluctuated.Domestic H13 steel has a large gap in the control of inclusions.It was found that the circularity of the inclusions was significantly improved and the distribution of inclusions was more uniform after Ca treatment in H13 steel.The original(Mn,Cr)S is completely removed in the steel after electroslag remelting.The inclusions in the remelted ingot are modified into A12O3,CaO-Al2O3(-CaS)and CaO-Al2O3-MgO(-CaS).More than 70%of the inclusions are below 3 ?m in the remelted ingot,and the amount of Al2O3 accounts for about 70%of the total amount of inclusions,most of which are below 2 ?m,and the average size of complex inclusions are larger than Al2O3.The Al2O3 inclusions in the remelted ingot are newly formed in the liquid metal pool,which is different from the traditional A1 deoxidation to form cluster-like A12O3.The greater cooling rate led to the smaller size of Al2O3 inclusions.Mg was added in H13 steel and then refined through ESR process,it is found that the inclusions become finer and more dispersed,and the Mg content in the inclusions increased with the increase of Mg content in the steel after Mg treatment.There is no inclusion larger than 5 ?m after ESR process,and the removal rate of inclusions in the Mg-contained electrode during ESR process was higher.Since the MgO-Al2O3 inclusions are smaller than Al2O3,the contact time at the slag steel interface is longer,so it is easier to remove.Rare earth Ce was added in steel,it is found that the rare earth inclusions in the Ce-containing electrode and the remelted ingot are all oxysulfides of Ce.Since the solidification rate of the molten metal pool is fast,the reaction of S-substituted Ce2O3 cannot be completely performed,so the S content of rare earth inclusions in the remelted ingot is lower than the electrode.The yield of Ce during ESR process is about 20%?30%ESR deoxidation experiments were carried out on electrodes with two oxygen levels.It is found that Al-Mg deoxidation during ESR process could not further reduce the oxygen content in steel,but oxygen pick-up was avoided.In the trial of electrode with oxygen content of 0.0015%,the inclusions were changed from CaO-MgO-Al2O3-CaS(-SiO2)to CaO-MgO-Al2O3-CaS.The amount of inclusions in the remelted ingot was reduced with the increasing of amount of deoxidizer addition,and the type of inclusions did not change.In the trial of electrode with high oxygen content of 0.0075%,the inclusions in the electrode were SiO2-Al2O3-MnO,and the inclusions in the free trial were mainly spherical A12O3,and the amount of deoxidizer added is 4.5g/kg and 6.5 g/kg,the proportion of CaO-Al12O3-MgO and CaO-Al2O3 inclusions in the remelted ingot increased.The oxygen content of remelted ingot is related to the oxygen content of the comsumable electrode.The content of inclusions and impurity elements in the consumable electrode should be controlled as low as possible,and the remelted ingot with high cleanliness can be obtained by the deoxidation during the ESR process. |
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