| Austenitic heat resistant steel ZG40Cr25Ni20Si2 has the characteristics of good high-temperature mechanical properties,oxidation resistance,corrosion resistance and microstructure stability,it has been widely applied in parts such as automobile exhaust manifold,turbocharger housing etc.However,the coarse dendrite in the as-cast alloy generally produces serious segregation,which could not be eliminated by heat treatment,resultsing in the decreases of the alloy performance and the service life.The purpose of this paper is to explore the rule of single element alloying and double elements alloying on the microstructure and mechanical properties of ZG40Cr25Ni20Si2 steel.The research shows that:The amount of carbide in ZG40Cr25Ni20Si2 steel is 8.49%.After alloying with single element,the amount of carbides increases with the increase of alloying elements.Meanwhile,the addition of Ti,V and Nb can improve the morphology of carbides in the alloys and its distribution condition in grain boundary,which transformes from the continuous network distribution to the small discontinuous distribution.The secondary arm spacing and primary dendrite diameter of ZG40Cr25Ni20Si2 steel is 13.99?m and 174.73?m,the hardness of steel is 174 HB.Added Ti,V and Nb to steel,the secondary arm spacing and primary dendrite diameter are reduced and the hardness are improved in different degrees due to single element alloying treatment for ZG40Cr25Ni20Si2 steel.The secondary arm spacing and primary dendrite diameter decreases first and then increases,while the hardness increases first and then decreases with the addition of alloying elements Ti,V and Nb.When the content of Ti is 0.15%,the secondary arm spacing and primary dendrite diameter of the alloy decreases to minimum of 11.15?m and 93.05?m,the hardness of the alloy reaches to the maximum of 184HB;when the content of V is 0.05%,the secondary arm spacing and primary dendrite diameter of the alloy reduces to the minimum of 10.63?m and 75.11?m,the hardness of the alloy reaches to the maximum of 186HB;when the content of Nb is 0.05%,the secondary arm spacing and primary dendrite diameter of the alloy diminishes to the minimum of 10.21?m and 73.43?m,the hardness of the alloy reaches to the maximum of 198 HB.The dendrite refinement ability of Nb and V elements are stronger than Ti element in ZG40Cr25Ni20Si2 steel,and the strengthening effect of Nb element is higher than that of Ti and V.The microstructure of the alloy was obviously refined,meanwhile,the amount of carbide precipitation increases and the hardness of the alloy increases after double elements alloying treatment.When 0.05%Ti and 0.05%V are compositely added to ZG40Cr25Ni20Si2 steel,the secondary arm spacing and primary dendrite diameter of alloy decreases to the minimum of 12.07?m and 99.36?m,the amount of carbide increases to the maximum of 14.56% and the hardness of the alloy reaches to the maximum of 195 HB.When 0.10%Nb and 0.05%V are compositely added to ZG40Cr25Ni20Si2 steel,the secondary arm spacing and primary dendrite diameter of alloy reduces to the minimum of 10.59?m and 86.93?m,the amount of carbide increases to the maximum of 15.09% and the hardness of the alloy reaches to the maximum of 202 HB.In addition,the morphology and distribution of grain boundary carbides in the alloys are also improved.Although the refining effect of double elements composite alloying with different kinds of elements on microstructure of the alloy is similar,the strengthening effect of Nb and V composite alloying on ZG40Cr25Ni20Si2 steel is higher than that of Ti and V.In addition,the second phase particles are dispersed in the matrix by alloying with single element Ti and two elements Ti and V,which has the strengthening action of the second phase. |
PDF Full Text Request