Effect Of Lanthanum On The Inclusion, Microstructure And Mechanical Properties Of Cr14 Steel

China is a steel superpower with the largest steel production around the world, but there still exists a considerable gap in the steel quality when compared with international advanced level, and lots of high-quality steels have to be imported. Due to its effects on the purification of molten steel, modification of inclusions, and treatment of micro-alloying during metallurgy, rare-earth elements have been widely used in iron and steel industry. The utilization of rare-earth elements as an effective additive in metallurgical process could transform the resource advantage to the advantages of steel variety and price. The improvement of the steel strength and toughness, and the refinement of steel comprehensive properties will lead to the enhancement of international competitiveness and thus improve the traditional steel industry.In this study, a new kind of steel, Crl4, which is mainly used in aviation, track in high speed railway, is studied. Rare earth element Lanthanum is added in the steel to study its influence to the steel performance and test the possibility of utilizing this rare earth element for the improvement of Cr14. This experiment discusses the influence of La on inclusions and as-cast organization by VIM. And the mechanical properties of Cr14 under different heat treatment is also been studied. We get the following conclusions.(1) When the mass fraction of La is 0.0027%, the irregular shape inclusions like Al2O3 and Al2O3-MgO nearly all (90%) change to round shape spherical rare earth compound inclusions. The average diameter is about 2 μm.(2) La can improve the as-cast organization of Cr14. Within the scope of this experiment, when the mass fraction of La is 0.0027%, it can effectively reduce the area proportion of the columnar crystal. Ingot casting is distributed as equiaxed crystal.(3) Solid solution of La can effectively reduce the harmful elements such as S and P in the grain boundary segregation.(4) With the increase of tempering temperature, the tempered martensite turn into tempered bend type and tempered sorbite. After adding La, due to its inhibition of precipitation of carbide, the shift process is slowed.(5) With the increase of tempering temperature, the hardness and strength of Crl4 don’t decline rapidly. This is due to the precipitation of carbide produced secondary hardening and second phase strengthening effect. In this tempering temperature scope no peak is found.(6) With the increase of tempering temperature, the impact energy and fracture toughness of Cr14 increased after fall first. After adding La, the toughness change better significantly. Within the scope of this study, the mass fracture of La is higher, the better the toughness is.(7) Considering the strength and toughness, the 3#-1steel, that with the mass fracture of La 0.0027% and tempering by 450 ℃ has the best comprehensive mechanical properties. Its HRC is 48.1. Tensile strength is 1860 MPa. Yield strength is 1460 MPa. Reduction of area is 51.30%. Break elongation ratio is 16%. Impact energy is 41 J. The fracture toughness is 105.4 MPa·m1/2.