As-cast Structure Research Articles

Effect of Co addition on solidification velocity, hardness and refined structure transformation mechanisms of undercooled Ni-Cu-Co alloys

In this work, the effect of Co addition on the solidification velocity, hardness and refined structure transformation of the undercooled Ni-Cu-Co alloys have been systematically investigated. The results show that the grain refinement of Ni-Cu-Co ternary alloys at low undercooling is caused by the intense dendrite remelting. However, the grain refinement at high undercooling is attributed to recrystallization, and the driving force of recrystallization comes from the stresses and plastic strains accumulated by the interaction between liquid flow induced by rapid solidification and primary dendrites. The Co addition can significantly increase the solidification velocity and recalescence effect of Ni-Cu-Co alloys by increasing the number of solidified crystal nucleus and solute diffusion velocity. Under the same undercooling level, the increase of solidification velocity and recalescence effect have strengthened the remelting effect and stress accumulation, which can enlarge the critical range for grain refinement gradually. Meanwhile, due to the significant improvement of solidification velocity and stress-induced deformation effect by Co addition, the low angle GBs in the refined structure of Ni-Cu-Co alloys increase and the grain size decreases significantly, which have significantly improved the average hardness of the refined structure. When Co addition reaches 6 %, the refined structures can appear in almost the whole undercooling range and the hardness are improved by more than 100 % compared with the as-cast structure.

Dynamic recrystallization in severely plastically deformed iron aluminide coatings obtained by friction surfacing

In the present work, the friction surfacing process was applied to produce iron aluminide (Fe-24.5Al-0.31C) coatings on a low carbon steel substrate under different deposition conditions and the influence of process parameters on coating geometry, microstructure and hardness was analysed. Thermographic data obtained during the tests indicated average deposition temperatures in the range of 862–951 °C, according to consumable rod rotation speed. By the proposed method, it was possible to obtain homogenous coatings with up to 0.75 mm thickness. Additionally, with increasing tool rotation a considerable reduction of grain size relative to the initial as-cast structure was observed. Keywords: Friction Surfacing, Intermetallics, Dynamic Recrystallization, Severe Plastic Deformation.

Texture Development in Aluminum Alloys with High Magnesium Content

The evolution of texture in the AlMg6Mn0.7 (1565 ch) alloy throughout the entire cycle of its thermomechanical treatment has been studied. Using this alloy as an example, a new way is shown to control the texture development, which is applicable to alloys with high magnesium content. An integrated approach is applied, including optical and electron microscopy, as well as X-ray diffraction analysis, the determination of mechanical properties and texture modeling using algorithms of the crystallographic plasticity theory. All stages of the thermomechanical treatment have been studied, namely the development of the deformation structure out of the as-cast structure in the reversing hot-rolling stand, continuous hot rolling, cold rolling and final recrystallization annealing. The study showed that second phase particles are the main source of recrystallization nuclei at all stages of high temperature thermomechanical treatment. The importance of these particles increases when the Zener-Hollomon parameter increases. To obtain the maximum possible proportion of a random texture, thermomechanical processing must be carried out at high Zener-Hollomon parameters. However, the temperature should not interfere with the complete recrystallization process at the same time. After cold rolling and recrystallization annealing at temperatures equal or greater than 350 °C, a large proportion of random texture is formed, and the properties of the metal are almost isotropic.

Experimental Evaluation of MHD Modeling of EMS During Continuous Casting

Electromagnetic stirring (EMS) has been recognized as a mature technique in steel industry to control the as-cast structure of steel continuous casting (CC), and computational magnetohydrodynamic (MHD) methods have been applied to study the EMS efficiency. Most MHD methods de-coupled the calculations of electromagnetic and flow fields or simplifications were made for the flow–electromagnetic interactions. However, the experimental validations of the MHD modeling have been rarely reported or very limited. In this study, we present a benchmark, i.e., a series of laboratory experiments, to evaluate the MHD methods, which have been typically applied for steel CC process. Specifically, a rotating magnetic field (RMF) with variable intensity and frequency is considered. First experiment is performed to measure the distribution of magnetic field without any loaded sample (casting); the second experiment is conducted to measure the RMF-induced torque on a cylindrical sample (different metals/alloys in solid state); the third experiment is (based on a special device) to measure the RMF-induced rotational velocity of the liquid metal (Ga75In25), which is enclosed in a cylindrical crucible. The MHD calculation is performed by coupling ANSYS Maxwell and ANSYS Fluent. The Lorentz force, as calculated by analytical equations, ANSYS Fluent addon MHD module, and external electromagnetic solver, is added as the source term in Navier–Stokes equation. By comparing the simulation results with the benchmark experiments, the calculation accuracy with different coupling methods and modification strategies is evaluated. Based on this, a necessary simplification strategy of the MHD method for CC is established, and application of the simplified MHD method to a CC process is demonstrated.

Improved hot ductility of an as-cast high Mn TWIP steel by direct implementation of an MnS-containing master alloy

Transverse cracking is the main issue during continuous casting of TWIP steels due to degraded hot ductility at 700–950 °C. In this study, we improve the hot ductility of an 18.1Mn-0.68C-1.5Al (wt.%) TWIP steel by refining the as-cast structure via inoculation. Inoculation was implemented by direct addition of MnS-containing master alloy to the melt. Since MnS did not dissolve in the melt, they acted as heterogeneous nucleation sites for austenite nucleation. Consequently, MnS-inoculated steel shows finer grain sizes than reference steel. Additionally, MnS particles are found to have a polygonal shape, randomly distribute, and share a cube-on-cube orientation relationship with austenite; both habit planes are parallel to {111}. A periodic array of b= 1/6<112> edge dislocations at every fourth {222} planes of MnS is necessary to accommodate the large lattice misfit of the cube-cube relationship. The MnS-inoculated TWIP steel shows significantly improved hot ductility compared to previously reported TWIP steels.

Microstructure and mechanical properties of wrought Al0.2CoCrFeNiMo0.5 high entropy alloy using gas tungsten arc welding process

In the present study, wrought processed Al0.2CoCrFeNiMo0.5 high entropy alloy (HEA) was welded using gas tungsten arc welding (GTAW) to determine its potential as a structural material. The microstructural changes during welding were analyzed and correlated with the mechanical properties. The welded HEA specimen has shown similar microstructural constituents, a typical FCC matrix with BCT secondary phase (sigma). The microstructure changed from irregular and heterogeneous secondary phase in base metal (BM), to eutectic broken lamellae of sigma phase in FCC matrix at heat affected zone (HAZ) and as-cast structure (dendritic and interdendritic regions) of sigma phase in FCC matrix at fusion zone (FZ). Upon tensile testing, the welded specimens fractured in the FZ with comparable tensile properties.

Modeling of the as-cast structure and macrosegregation in the continuous casting of a steel billet: Effect of M-EMS

Mold electromagnetic stirring (M-EMS) has been introduced into the continuous casting of steel billets to promote the formation of a central equiaxed zone; however, the formation mechanism of the equiaxed crystals and the effect of M-EMS on crystal transport are not fully understood. Currently, a three-phase volume average model was used to study the solidification in a billet continuous casting (195 mm × 195 mm). The modeling results showed that the main function of M-EMS in this type of billet casting is to promote superheat dissipation in the mold region, leaving the liquid core out of the mold region undercooled. Although both, heterogeneous nucleation and crystal fragmentation, are considered to be the origins of equiaxed crystals, M-EMS appeared to impact crystal fragmentation more effectively. A small portion of equiaxed crystals could be brought by the M-EMS induced swirling flow into the superheated zone (upper mold region) and remelted; most equiaxed crystals settled in the lower undercooled zone, where they continued to grow and form a central equiaxed zone. These simultaneous phenomena represent an important species/energy transport mechanism, influencing the as-cast structure and macrosegregation. Negative segregation occurred in the central equiaxed zone, positive segregation occurred at the border of the columnar zone, and a trail of negative segregation occurred in the subsurface region of the billet. Finally, parameter studies were performed, and it was found that the shielding effect of the copper mold, electrical isolation at the strand-mold interface, and relatively high electrical conductivity of the strand shell affect the M-EMS efficiency.

Comparative Analysis of Structure and Properties of Nb-B Inoculated Direct Chill Cast AA4032 Alloy Extruded from As-Cast and Homogenized Conditions

Al-Si wrought piston alloys can lack properties due to inefficient grain refining. A novel Al-Nb-B grain refiner was introduced some time ago, but has still not been assessed in industry for wrought alloys. This paper describes the first trial of Al-Ni-B addition and its impact on the full-scale manufacturing, structure, and properties of the AA4032 products extruded with and without billet homogenization. It is shown that Nb-B inoculation gives opportunities not only to have a refined as-cast structure but also a more homogenous distribution of the solute. In contrast, homogenization drives nucleation and coarsening of the Mg2Si phase that is retained during further extrusion and heat treatment also affecting the precipitation and properties. It was observed that non-homogenized specimens perform better during machining and tensile testing compared to homogenized specimens. The results are supported by electron microscopy investigations of microstructure formation during different steps in downstream processing.

The effect of exposure to elevated temperatures on the microstructure and hardness of Mg–Ca–Zn alloy

Abstract The die cast Mg-5 wt.% Ca-6 wt.% Zn ternary alloy was exposed to 160 °C for different times of up to 40 days. Microstructural analysis and microhardness and hardness measurements of the samples after different exposure times enabled the thermal stability of the cast alloy to be monitored. The as-cast structure is composed mainly of α-Mg solid solution, elliptical grain boundary particles of CaMg2, and an intergranular eutectics of Mg and Ca2Mg6Zn3. The grain size of α-Mg and the structure of the alloy did not change during the treatment, but the amount of the intergranular phases increased slightly. Exposure to 160 °C resulted in a decrease in micro-hardness of the α-Mg grains, but no change in the overall hardness of the samples was observed. Microstructural analyses indicated diffusion of the solute elements from the α-Mg grains to the grain boundaries, resulting in a decrease in hardness of the α-Mg which is, however, compensated by an increase in hardness related to intergranular precipitates. Using a simple diffusion model, the diffusion coefficient of Ca atoms in Mg at 160 °C was estimated to be 2.1 · 10 –17 m2 s– 1, which is greater than that of Zn by two orders of magnitude.

Microstructure and Microhardness of Directionally Solidified Al-Si Alloys Subjected to an Equal-Channel Angular Pressing Process

The directional solidification technique allows the study of growth of the solid phase, as-cast structure and, finally, its mechanical characteristics as a consequence of thermal parameters. On the other hand, in the last decade, a process called equal-channel angular pressing (ECAP) has emerged as a widely-known technique in fabrication of ultrafine-grained metals and alloys. Applicability of the ECAP technique affords an excellent potential for changing, in a controlled and beneficial manner, the resulting properties of metals and alloys. For this paper, an experimental research has been conducted to study the effects of solidification parameter (cooling rate) on resulting microhardness in hypoeutectic Al-Si alloys, upon use of an ECAP procedure. The influence of cooling on the scale of the dendritic patterns is presented and discussed with recourse to equations. The resulting microhardness variation with position throughout the as-cast materials and cooling rate were characterized by experimental power laws. Results determined after the solidification experiments have revealed microhardness as a function of both cooling rate and position (P) of the as-cast materials to be dependent on alloy composition. In the ECAP process via route C with three passes, “as-solidified” microstructures have been found to be distorted and fragmented during the severe plastic deformation. This deformation imposed on the billets during the ECAP process facilitated obtaining a fine microstructure and high levels of microhardness were observed. However, even with the ECAP process, it was shown that microhardness is strongly dependent of the cooling rates.

Effects of Zr additions on structure and tensile properties of an Al-4.5Cu-0.3Mg-0.05Ti (wt.%) alloy

The effects of different Zr additions (0.05wt.%-0.5wt.%) on the structure and tensile properties of an Al-4.5Cu-0.3Mg-0.05Ti (wt.%) alloy solidified under a high cooling rate (18 °C·s-1), in as-cast and T6 heat-treated conditions were studied. The as-cast structure of the alloy consists of equiaxed grains of α-Al with an average size of 64 μm which is unaffected by the Zr additions, indicating the ineffectiveness of Zr in the grain refinement of the alloy. Scanning electron microscopy, along with X-ray diffraction analysis revealed the presence of elongated θ-Al2Cu at the grain boundaries; in addition, coarse Al3Zr particles exist in the intergranular regions of the 0.5wt.% Zr-containing alloy. After the T6 heat treatment, the elongated θ particles were fragmented; however, the coarse Al3Zr particles remained unchanged in the microstructure. Also, the formation of fine β′-Al3Zr and θ″-Al3Cu/θ′-Al2Cu phases during T6 heat treatment was revealed by transmission electron microscopy. The results of the tensile tests showed that the Zr additions increase the strength of the alloy in both as-cast and T6 heat-treated conditions, but reduce its elongation, especially with 0.5wt.% Zr addition. The 0.3wt.% Zr-added alloy in the T6 heat-treated condition has the highest quality index value (249 MPa). Fractography of the fracture surfaces of the alloys revealed ductile fracture mode including dimples and cracked intermetallic phases in both conditions.

The influence of minor additions of Y, Sc, and Zr on the microstructural evolution, superplastic behavior, and mechanical properties of AA6013 alloy

Alloy AA6013 (Al-Mg-Si-based aluminum alloy) is of particular interest to the aerospace and automotive industries because of its attractive combinations of properties, however, accelerated grain growth at elevated temperatures limits its superplastic formability. The motivation for this study was to refine grain structure and control grain growth at elevated temperature in order to eliminate the lack of superplasticity in the alloy. For this reason, minor additions of Y, Sc, Zr were considered and their influence on the microstructural evolution, superplastic deformation behavior, and room temperature mechanical properties of a novel AA6013-type alloy was studied. A noticeable refinement of as-cast grain structure was observed due to the co-effect of Sc, Zr, Y additions. It was demonstrated that the Mg2Si phase and Y-bearing phases were formed during solidification of the studied alloys. The phases of silidification origin were fragmented during thermo-mechanical treatment led to the near uniform distribution of coarse particles of 0.5–0.8 µm size in the matrix. The coarse particles caused grain refinement during the superplastic deformation due to the particle stimulated nucleation (PSN) effect. In the alloy containing yttrium, during the decomposition of the aluminum-based solid solution supersaturated by Y, Zr, Sc, the following two precipitation mechanisms were involved: continuous precipitation resulting in the formation of nanoscale L12 phase dispersoids distributed homogeneously throughout the aluminum matrix and discontinuous precipitation that caused fan-shaped aggregations of the same phase near the high-angle grain boundaries. The nanoscale continuously-formed dispersoids retarded the recrystallization and dynamic grain growth during superplastic deformation due to Zenner pinning mechanism. Both PSN and Zenner pinning effects led to the grain refinement and achievement of superplasticity. The maximum elongation of 470% was observed under the test condition of T = 520 °C and ɛ.= 1 × 10−3 − 5 × 10−2 s −1. The room temperature tensile test revealed the following maximum characteristics of the sheet of the alloy with Y additions: yield strength of 330 MPa, ultimate tensile strength of 375 MPa, and elongation at fracture of 10%.

Formation, microstructure and mechanical properties of ductile Zr-rich Zr–Cu–Al bulk metallic glass composites

We examined the microstructure, phase stability, mechanical properties and deformation behaviors of cast (Zr0.58Cu0.42)100-xAlx (x = 0, 3, 5, 7, 10) bulk metallic glass composites (BMGCs). With increasing Al content, the glass-forming ability of the new Zr-rich Zr–Cu–Al alloys gradually increases, enabling the fabrication of BMGCs for the alloys containing more than 3 at.% Al. The as-cast structure changes from Cu10Zr7 + CuZr2 for the Al-free base alloy to glass + crystal for the Al-added alloys. The new Zr-rich Zr–Cu–Al BMGCs exhibit a large fracture strain of ∼3.4–7.8% and a high fracture strength of ∼1731–1984 MPa under compression. The compressive fracture strain of Zr-rich Zr–Cu–Al alloys can be explained by the percolation theory. The (Zr0.58Cu0.42)95Al5 composite containing ∼70 vol.% crystalline phase possesses the largest plastic strain of ∼6%, and fracture strength of over 1900 MPa under compressive condition. The superior plastic deformation capability under compression is related to the following factors: (1) The formation of three types of shear bands with distinct morphological characteristics, (2) the plastic deformation of B2–CuZr phase itself, together with stress-induced martensitic transformation from B2–CuZr phase to B19’ phase, and (3) the interaction between crystals and shear bands. The present results have implications for better understanding the deformation mechanisms of the Zr-rich Zr–Cu–Al BMGCs and for designing high-performance BMGCs with enhanced plasticity.

Structure and heat resistance of high strength Al–3.3%Cu–2.5%Mn–0.5%Zr (wt%) conductive wire alloy manufactured by electromagnetic casting

The Al-3.3Cu-2.5Mn-0.5Zr (wt%) alloy was manufactured by electromagnetic casting and further subjected to processing including cold rolling, drawing and annealing. Excellent processability of the alloy at cold rolling and drawing was observed due to the ultrafine as-cast structure. Annealing of the cold-rolled strip at 350 °C for 48 h insignificantly reduces the hardness, but the electrical resistivity (ER) decreases by almost 3 times (from 115 to 40 nΩm). The large deformation during rolling (reduction 98.4%) and high fraction of the Zr- and Mn-bearing nano dispersoids (Al20Cu2Mn3 and Al3Zr-L12) stipulated the high set of mechanical properties and electrical conductivity after annealing at 400 °C (UTS~330 MPa, YS~250 MPa, EL~7%, 42.5 IACS). A model of ER dependence on the phase composition was proposed. While at above 400 °C there is a good agreement between the calculated and experimental values, the scatter at lower temperatures is attributed to exposure times insufficient for achieving the equilibrium (Al) composition. Atom probe tomography was employed for observation of Cu, Mn and Zr concentrations in (Al) after annealing at 350–450 °C. According to the experimental results and root-mean-square calculations, annealing at between 350 and 400 °C allows achieving (Al) compositions close to the equilibrium in reasonable time while with decreasing temperature the diffusion of Zr in (Al) decreases and thus it requires extremely long exposures, e.g. at 300 °C it is about 23,000 h. From this viewpoint annealing at below 350 °C is unreasonable for achieving lower ER.

Producing CrFeCoNiSi-Based High Entropy Alloy by Spark Plasma Sintering

A high-entropy alloy (HEA) is a multi-component alloy obtained by blending at least five metal elements at compositions of 5–35%. Contrary to expectations, HEAs have a simple microstructure and exhibit unique properties such as excellent high-temperature strength, high tensile strength, and extremely slow diffusion rate. They are mainly produced by casting method, and heterogeneous microstructures have been found in the as-cast structure. Powder metallurgy has many advantages over ingot-metallurgical methods such as casting, including excellent material efficiency and ease of conversion to complex shapes. In this study, we produced a CrFeCoNiSi HEA and evaluated its properties. The Si content was changed within the range of 5–15 at% to investigate the characteristics of the corresponding HEAs. A Vickers hardness test and a corrosion test were performed. The Vickers hardness test revealed that the hardness of the samples of (CrFeCoNi)95Si5 and (CrFeCoNi)90Si10 was approximately 550 HV, whereas that of (CrFeCoNi)85Si15 was approximately 700 HV. (CrFeCoNi)95Si5 and (CrFeCoNi)90Si10 showed significant improvement in corrosion resistance. In constant, deterioration was observed for the (CrFeCoNi)85Si15 sample due to the presence of excess Si, which formed a stable silicide with metal elements.

Specific of the Recrystallization Driving Force Calculation on the early Stages of Thermomechanical Treatment of Aluminum Alloys

The article investigates the effect of the strain rate on the driving force of recrystallization during hot working of the as-cast structure. For the study, we applied previously obtained experimental data of recrystallization kinetics during this stage of thermomechanical treatment. In addition, hot laboratory rolling, followed by saltpeter bath soaking, were performed in order to obtain supplemental data on grain structure size and orientations. Grain structure size was examined by optical microscopy, and its orientation was examined by X-ray texture analysis. The studies demonstrated, that overestimated recrystallization driving force not only results in erroneous kinetics estimation, but also gives excessive number of recrystallization centers and undersized grain structure. Besides, unaccounted effect of recrystallization driving force on grain size leads to distorted predictions of texture composition. In order to avoid this, it was recommended to apply an special exponential accumulated strain dependent coefficient.

Microstructure Evolution of Al-Zn-Mg-Cu Alloy with Erbium during Homogenization

The microstructure evolution of Al-Zn-Mg-Cu alloy with erbium was studied by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) during homogenization process. The results showed that there were serious component segregation in the as-cast structure of the alloy, mainly composed of T(AlZnMgCu) , S(Al2CuMg) and a small amount of Al8Cu4Er and Al7Cu2Fe. The overheating temperature of the alloy was 482.5 °C. After homogenized at 470 °C for 24 h, the dissolution of T(AlZnMgCu) phase and S(Al2CuMg) phase reached to a balance, but the residual Al8Cu4Er phase could not be dissolved completely. Compared with single-stage homogenization, Al3(Er,Zr) dispersion phase with smaller grain size and more uniform distribution can be obtained after two stage homogenization process of 400 °C for 8 h followed by 470 °C for 24 h. By comparing the residue of non-equilibrium eutectic phase, two-stage homogenization is the best.

Effect of Heterogeneous Composite Structure on the Microstructure and Properties for Nanostructured 2205 Duplex Stainless Steel

2205 duplex stainless steel (DSS) is a kind of complex structure stainless steel, which has advantages of both austenitic and ferritic stainless steel. Compared with 300 series stainless steel, it has better performance and can be used in more severe environment. Bulk 2205 DSS with heterogeneous composite structure is prepared via aluminothermic reaction. The volume percentage of ferrite phase is 32.3%, that of austenite phase is 59.7%, and σ phase is 8.1%. Average grain size of nanocrystalline and ultrafine austenite is 20.9 nm, accounting for 74.2%. The relatively mechanical properties deteriorate, which belongs to brittle fracture. The joint action mechanism of dual-phase structure and micro/nanostructure is analyzed by fracture observation. At present, the tensile strength and fracture elongation of as-cast heterogeneous composite structure 2205 DSS are poor. Therefore, different rolling and annealing systems are needed to coarsen grains and adjust mechanical properties through structure design.

Structure formation and processability of the Al—Zn—Mg—Ca—Fe—Zr—Sc alloy at hot rolling and TIG welding

Process conditions are suggested for manufacturing wrought semi-finished products (2 and 1 mm sheets) from the Al-4.5%Zn-2.5%Mg-2.5%Ca-0.5%Fe-0.2%Zr-0.1%Sc experimental alloy including thermomechanical processing at t = 400450 °С and reduction ratios up to 98 %, as well as softening annealing of the sheet metal at t = 350400 °C for 1—2 hours. It was found that the as-cast structure consists of eutectic phases (Al, Zn)4Ca, Al10CaFe2 5 to 25 gm in size, and a Al2Mg5Zn5 nonequilibrium T-phase located along the boundaries of dendritic cells (Al). Zirconium and scandium form a solid solution with aluminum as a result of solidification. After hot rolling, the structure of 2 mm sheets consists of lineage-oriented discrete intermetallic particles and their conglomerates up to 40 gm in size in the (Al) matrix. The structure of 1 mm sheets features by greater fineness and structure uniformity. The fine structure of deformed semi-finished products was analyzed using transmission electron microscopy (TEM), and this analysis showed that nanoparticles in the Al3(Zr, Sc) phase of the L12 structural type are maximum 20 nm in cross-section. The following level of mechanical properties was achieved in wrought semi-finished products: ultimate strength σв ~ 310330 MPa, yield strength σ0,2 ~ 250280 MPa with relative elongation δ ~ 4.57.0 %. The possibility of TIG welding using standard AMg5 wire as a filler material was studied. It was shown that the new alloy demonstrated no tendency to form hot cracks. According to the results of X-ray tomography, the percentage of porosity in the weld was 1.27 vol.%. The prevalent pore diameter did not exceed 0.2 mm. In general, the resulting structural and qualitative parameters of weld joints contribute to obtaining a strength of 75 % of the strength index of the initial wrought semi-finished products (sheets) achieved by stabilizing annealing at t = 350 °С for 3 hours.

Effect of La-Ce on Microstructure and Properties of 30MnCrNiMo Alloy Steel

The 30MnCrNiMo alloy steel was modified by La-Ce mixed rare earth. The experiment used metallographic microscope, scanning electron microscope and energy spectrum to analyze the improvement behavior of rare earth on the as-cast structure of the alloy steel, the structure after heat treatment, and the morphology of inclusions; a thermal dilatometer was used to analyze the phase transition point, and a reasonable heat treatment process was developed; the effect of rare earth on the mechanical properties of alloy steel at room temperature, low temperature impact and tensile was analyzed. The results show that the 30MnCrNiMo alloy steel modified by rare earth has better refinement of the as-cast grains and the grains after heat treatment, and the size, morphology and distribution of inclusions have been improved. The addition of rare earths improves the impact toughness, especially the low-temperature impact. Compared with alloy steel without rare earth, the toughness can be increased by up to 38%, and the alloy strength has been improved to a certain extent.