The Effect of Rare Earth Cerium on Microstructure and Properties of Low Alloy Wear-Resistant Steel

Abstract

With the continuous expansion of the application field of low alloy wear-resistant steel, higher processing plasticity and toughness are prioritized on the basis of ensuring strength and hardness. In this article, a low alloy wear-resistant steel Hardox400 was studied: by adding a mass fraction of 0.0030% of rare earth cerium as microalloying treatment, the pilot scale simulation of the rare earth wear-resistant steel was carried out using vacuum induction furnace and a four-high reversible laboratory mill. The effects of the rare earth on the occurrence state of the inclusions, microstructure, mechanical properties and wear resistance of the steel were studied by means of optical microscope (OM), scanning electron microscope (SEM) and wet sand/rubber wheel wear tester. The results show that the fine spherical CeAlO₃, CeAlO₃-MnS and elliptical Ce₂S₂O-CaO are formed by adding 0.0030% Ce, which enhances the binding force between the inclusions and matrix. The addition of rare earth Ce helps to refine the as-cast structure, prevent the transformation of proeutectoid ferrite of overcooled austenite and promotes the formation of bainite ferrite, whilst simultaneously increasing the yield strength, yield ratio and surface hardness, especially the low-temperature impact toughness approximately between −40 °C~−20 °C of the tested steel. Simultaneously, the ability to resist abrasive embedment and crack propagation is enhanced, and the wear resistance is obviously improved. The research results will provide a reference for the development of high-quality rare earth wear-resistant steel utilizing national featured resources.

1. Introduction

Advanced ultra-high-strength thin gauge wear-resistant steel plate, as a lightweight and long-life material selected for the harmonious development of society, has been widely used in construction machinery, bridge construction, dump truck transportation and other fields. Generally, the wear-resistant steel dominated by martensite is obtained through heat treatment process control, and its wear resistance is improved with the increase in hardness, which leads to a loss of machinability, toughness and plasticity and the welding performance of a wear-resistant steel plate [1,2,3]. In order to solve this problem, low alloy wear-resistant steels have been micro-alloyed with rare earth elements such as cerium. This has the effect of modifying inclusions and refining grains which can improve the performance of wear-resistant steel [4,5,6], which can improve the comprehensive application performance of wear-resistant steel. Since the principle of the quenching and partitioning (Q&P) treatment process was first proposed by Professor J.G. Speer in the United States in 2003, domestic and foreign researchers have carried out in-depth research on the microstructure evolution behavior, the influence law of process parameters on properties and the carbon distribution mechanism of high-strength steel in the distribution process [7,8,9,10]. According to the characteristics of the thermo-mechanical control process (TMCP) of a hot continuous rolling mill, the author puts forward the feasibility of producing a thin wear-resistant coil by the on-line heat treatment process “Directly Quenching and Partitioning and Tempering (DQ&P&T)” and carries out industrial practice [11] through the organic combination of austenite deformation in the rolling process, sectional rate cooling after rolling and temperature control to realize the regulation of microstructure transformation and carbon distribution and the self-tempering effect in the slow cooling process after coiling. The product microstructure is composed of bainite, martensite and retained austenite, which was successfully applied to the dump truck compartment. This study focused on the systematic analysis and study of the influence of cerium microalloying on the microstructure and properties of a wear-resistant coil plate, providing basic data support for the development of high-quality wear-resistant steel with rare earth characteristics.

2. Materials and Methods

2.1. Tested Steel Composition Design

Based on the composition design system of low alloy wear-resistant steel, the addition of the alloy Mn is beneficial for expanding the austenite phase zone, reduce the critical quenching rate, stabilize austenite, refine grain and delay the transformation from austenite to pearlite. The design of a higher Si content can inhibit the precipitation of cementite in a certain temperature range and contribute to making the carbon atoms diffuse from martensite to retained austenite, while a certain content of Al helps to improve the diffusion rate of carbon atoms from martensite to retained austenite; the two elements are reasonably matched, so as to increase the thermal stability of retained austenite and obtain as much metastable retained austenite as possible at room temperature. The addition of Cr mainly improves the hardenability of the material; at the same time, it is easy to form complex carbides and produce a strong precipitation strengthening effect, which is helpful to improve the wear resistance. This paper focuses on the effect of cerium microalloying on the microstructure and properties of low alloy wear-resistant steel plate after adding a certain amount of Ce-Fe alloy (Ce content 30%). The chemical compositions of tested steels are shown in

Table 1. Chemical composition of tested steels (wt.%).

Sample	C	Si	Mn	Al	P	S	Nb + Ti	Cr	O	Ce (Addition)	Ce (Content)
Hardox400	≤0.32	≤0.70	≤1.60	≥0.015	≤0.025	≤0.010	/	≤2.50	/	/	/
1#	0.21	0.62	1.54	0.055	0.013	0.003	0.045	0.42	0.0030	/	/
2#	0.22	0.60	1.57	0.060	0.015	0.003	0.042	0.42	0.0025	0.0100	0.0030

.

2.2. Test Method

A 50 Kg vacuum induction furnace was used for refining, and argon gas was used to protect molten steel from oxidation during the whole process of smelting and ingot casting; the vacuum degree in the furnace is less than 40 Pa, the initial temperature of the mold is room temperature (20 °C), the cooling speed is 3–4 °C/min after casting to the demolding (demolding temperature 850–950 °C), and then cooled to room temperature by air, the cooling speed is 8–12 °C/min. The ingot with a diameter of 100 mm was heated to 1220 °C (heating rate of 10 °C/min) for 30 min, and then, the 8 mm steel plate was rolled in eight passes in two stages (recrystallized zone and non-recrystallized zone) by using four-roll reversible rolling mill in the laboratory. Through theoretical calculation (Ac3 = 955 °C − 350[C%] − 25[Mn%] + 51[Si%] + 106[Nb%] + 100[Ti%] + 68[Al%] − 11[Cr%] − 33[Ni%] − 16[Cu%] − 67[Mo%] + Degree of superheat(about 50~80 °C), by PARK, S.H. et al.), the starting temperature of recrystallization was calculated to be 945 °C and the final rolling temperature was set at 870 °C. The DQ&P&T process was adopted to directly and rapidly (cooling rate is 30 °C/s) cool the strip to 500 °C after hot rolling and isothermal treatment is approximately 8–12 s; then, the strip was cooled to 200 °C at the same cooling rate, and subsequently cooled to room temperature at the slow cooling rate (cooling rate is approximately 0.5–1.0 °C/s) to simulate the natural cooling of the strip cooling process, the test procedure is shown in Figure 1.

Samples were taken from the slab and the rolled steel plate, and ground and polished with sandpaper. The morphology and composition of inclusions in the cast billet were detected by scanning electron microscope (SEM/EDS), and the metallographic structures of polished samples were analyzed by optical microscope (OM) and scanning electron microscope (SEM) after etching by 4% nitric acid alcohol solution. At the same time, the quantitative statistical analysis of microstructure size was carried out with the help of Image Pro Plus software.

The sampling method for analyzing the mechanical properties of steel plate is shown in Figure 2, and the cutting position is 1/2 of the width direction of the steel plate. The tensile test was carried out on a Zwick testing machine at room temperature with a dumbbell plate sample (length of the middle parallel part is 80 mm, width is 25 mm and the initial gauge distance is 50 mm) at a tensile rate of 1 mm/s. The Brinell hardness machine was used to test the surface hardness of the sample (HBW5/750), the square sample size was 10 mm × 10 mm × 8 mm, the surface of which was smooth, clean and without bumps. The series of temperature impact toughness tests were carried out by impact an testing machine (750 J) that performs automatic sample delivery, which was made by the MTS company using 5.0 mm × 10 mm × 55 mm standard V notched impact samples (notches perpendicular to the rolling surface direction).

The wet sand rubber wheel abrasive wear test was used to evaluate the wear resistance of the material under engineering application conditions and the test standard was carried out according to JB/T7705-1995, as shown in Figure 3. The sample size is 25 mm × 58 mm, and the surface is ground to a roughness of 0.5–0.6 μm. The test normal load is 70 ± 3 N, the rotating speed of the rubber wheel is 245 ± 5 r/min and the abrasive particle size is 212~425 μm. After 1000 revolutions of pre-grinding and cleaning the sample with acetone, the initial mass was measured on an electronic balance at an accuracy of 10⁻⁴ kg and then the continuous wear tests for the different times were carried out to analyze the relationship between the wear weight loss of the tested steel and the test time; additionally, the wear surfaces of the samples were observed by scanning electron microscope after 20 min of wear. It is worth noting that the relevant test data are from the arithmetic mean of the three repeatability tests.

3. Results

3.1. Effect of Cerium on the Morphology of Inclusion

The distribution of the non-metallic inclusions in the cast-tested steels are analyzed, and the typical morphologies and compositions are shown in Figure 4 and Figure 5. The non-metallic inclusions in sample 1# are mainly columnar and angular Al₂O₃ and columnar elliptic MnS, with a length of 3–5 μm. The non-metallic inclusions in the 2# sample after Ce microalloying treatment are mainly spherical CeAlO₃ and CeAlO₃-MnS with a diameter ≤2.5 μm and elliptic Ce₂S₂O-CaO with a length ≤5 μm. The addition of Ce mainly refines the size of inclusions, spheroidizes the morphology of inclusions and improves the binding force between inclusions and matrix.

The Ce-Fe alloy is added to the molten steel under the conditions of low sulfur and low oxygen at the end of smelting. Due to the strong oxidation of rare earth elements, it reacts with [O], [S], [Al₂O₃] and [(Al₂O₃)x-(CaO)y] in the molten steel to spheroidize and modify the hard and brittle Al₂O₃ inclusions with sharp corners, forming CeAlO₃ inclusions and composite inclusions CeAlO₃-CaO, and the apparent adhesion with the matrix is enhanced. At the same time, the rare earth compounds with a high melting point and low density are preferentially precipitated during liquid steel cooling; the single particles of rare earth oxide and oxysulfide inclusions constantly collided, merged and reacted together during the floating process, and then the low melting point MnS precipitates and grows around it, and the CeAlO₃-MnS composite inclusions were formed through wrapping the rare earth particle inclusions into an approximate spherical shape. However, due to its outer layer of MnS inclusion, the binding compactness between the CeAlO₃-MnS inclusion and matrix is lower than that of CeAlO₃ inclusion [12].

The test ingots are rolled into 8 mm steel plate by multiple passes: the OM and Image-Proplus image processing software are used to analyze and count the inclusions in 10 view fields of the steel plate, the results of which are shown in Figure 6 and Figure 7. The average size of the inclusions in 2# sample treated with Ce is 10% lower than that of 1# sample, and the density of inclusions in the unit area increases by 12%. From the perspective of inclusion size distribution, the proportion of inclusions ≤5 μm in sample 2# increased by 15% compared with that of sample 1#, suggests that the inclusion size was effectively refined.

The morphology of the typical inclusions of rolled steel plates are observed by SEM and EDS analysis equipment, the results of which are shown in Figure 8 and Figure 9. The 1# sample is mainly elliptical Al₂O₃-CaS composite inclusions approximately 5–7 μm in size, distributing at the grain boundary. The 2# sample is mainly round spherical CeAlO₃-Ce₂O₂S with a size of approximately 2–3 μm, which is sandwiched between the martensite blocks to refine the structure.

3.2. Effect of Cerium on Microstructure Transformation

Figure 10 and Figure 11, respectively, represent the as-cast microstructure morphology of tested steels 1# and 2# at different magnifications, both of which are composed of ferrite (F) and pearlite (P). The grain size distribution range of the 1# sample is 200~400 μm; 2# is 150~300 μm; the grain size of tested steel 2# with Ce micro-treatment is significantly reduced, the percentage of ferrite precipitated along the austenite boundaries is reduced, and the uniformity of microstructure is improved. This is mainly due to the addition of Ce in the molten steel due to its high chemical activity, and thus rare earth oxides, oxygen sulfides and aluminates with a high melting point and low mismatch with the matrix are easily formed, providing effective non-uniform nucleation initiation sites during the solidification process of molten steel and creating conditions for grain refinement. In addition, the Ce tends to segregate at grain boundaries: on the one hand, it pins the expansion of grain boundaries and inhibits the precipitation of ferrite at grain boundaries; on the other hand, this hinders the diffusion of solute atoms at the interface, which can cause the overcooling of components, which results in dendrite melting and the shortening of the length of primary dendrite, and the smaller size of melted dendrite may once again serve as the core of new grain nucleation [13].

Figure 12 and Figure 13, respectively, represent the microstructure of the wear-resistant steel plates at different positions along the thickness direction of the 1# and 2# tested steels. The microstructure of the 1# tested steel is mainly bainite ferrite(B), supplemented by ferrite(F) and martensite(M), while the microstructure of 2# tested steel is mainly bainite ferrite(B), supplemented by martensite(M) at room temperature, the ferrite basically disappears, the proportion of bainite ferrite increases and the proportion of martensite decreases. According to SEM morphology analysis, the grain size of 2# is smaller than that of 1#, the spacing of bainite ferrite lath is reduced and the Ce can hinder the transformation of proeutectoid ferrite. The microstructure size has a certain heredity, the finer as-cast structure creates a good basic condition for the refinement of high-temperature austenite grain and room temperature grain. Mr. Liang Yilong et al. [14] pointed out that rare earth causes the CCT curve of Mn-Re bainite steel to shift to the lower right direction, which improves the hardenability of steel and reduces the starting temperature of bainitic and martensitic transformation, thus increasing the overcooling of bainite transformation to refine the bainite structure, so it increases the proportion of bainite ferrite.

3.3. Effect of Cerium on the Mechanical Properties

The tensile properties of the tested steels are shown in

Table 2. Mechanical properties of tested steels.

Sample	Yield Strength/MPa			Tensile Strength/MPa			Elongation A50/%			Ratio
	Min	Max	Avg	Min	Max	Avg	Min	Max	Avg	Min	Max	Avg
1#	850	1020	935	1340	1400	1370	9	13	11	0.65	0.71	0.68
2#	980	1100	1040	1380	1450	1415	11	14	12.5	0.70	0.76	0.73

, all property values of the rare earth tested steel sample 2# are higher than that of sample 1#, and the yield strength and yield ratio increase greatly. The increase in the yield ratio within a certain range is conducive to the improvement of elongation and flexural capacity [15]; at the same time, the surface Brinell hardness (HBW 5/750) of tested steel 2# is approximately 8% higher than that of 1#, and the impact energy at low temperature (temperature < 0 °C) is increased by 20%~50%; in particular, the impact toughness of the tested steel 2# is more obviously improved at −40 °C~−20 °C, as shown in Figure 14 and Figure 15.

The content of bainite ferrite in the 2# sample with Ce increased, the dispersed massive ferrite disappeared and the original austenite grains are effectively interspersed and divided to refine the grains by bainite ferrite. At the same time, the grain orientation in the bainite ferrite package is complex, and the proportion of a large angle grain boundary is higher compared with martensite or ferrites [16], which can effectively cut the path of crack propagation or increase the energy barrier of crack initiation, which plays a key role in improving the plastic toughness of steel.

3.4. Effect of Cerium on the Wear Resistance Property

Figure 16 shows that the slope of a wear amount of the tested steel first increases and then decreases with the extension of wear time. the time of inflection point of 2# sample is earlier than that of 1#, and the wear amount of 2# sample is less than 1# under the same wear time, which indicates that the wear resistance of sample 2# with Ce is better than that of sample 1#.

The surface morphology of the tested steels after wet sand abrasion for 20 min were analyzed by scanning electron microscope, as shown in Figure 17. The wear surfaces are mainly micro-cut, accompanied by a small amount of plastic fatigue wear and abrasive embedding. Compared with 1# sample, 2# sample of wear surface is relatively smooth, the number of furrows is less, the depth is shallow, the width is narrow and the spalling degree of plastic fatigue wear is less. It can be seen from the previous analysis that the bainite ferrite of 2# tested steel added with rare earth replaces the polygonal ferrite of 1# tested steel, the Brinell hardness of surface was increased by 8% and the impact toughness at temperature of 0 °C was improved by 20%, making its hardness and impact toughness better than 1#. At the beginning of wear, the surface hardness of the material plays a key role: the higher the hardness is, the stronger the wear resistance is, and the degree of deformation hardening of the surface also increases. Then, the good toughness of the matching material can effectively hinder the propagation and initiation of friction microcracks and improve the wear resistance [16].

4. Discussion

Rare earth Ce is added into liquid steel at the end of refining and has strong chemical activity in molten steel and plays a positive role in deoxidation, desulfurization and inclusion denaturation. Z. Adabavazeh et al. [17,18,19] calculated and studied the Gibbs free energy of rare earth compounds, and the generation priority sequence is rare earth aluminate > rare earth oxygen sulfide > rare earth oxide > rare earth sulfide.

The activity coefficients of each element in the steel and the corresponding activity were calculated by the Wagner model (Formulas (1) and (2)) and the interaction coefficients [20,21] of each element in liquid steel at 1873 K in

Table 3. Interaction coefficient $e_i^j$ of various elements in tested steel at 1873 K.

${\mathit{e}}_{\mathit{i}}^{\mathit{j}}$	C	Si	Mn	Al	P	S	Cr	O	Ce
Ce	−0.077	-	0.13	−2.25	1.746	−39.8	-	−5.03	−0.003
O	−0.45	−0.131	−0.012	−3.9	−0.07	−0.133	−0.04	−0.2	−0.57
S	0.11	0.063	−0.026	0.035	0.029	−0.028	−0.011	−0.27	−0.231
Al	0.091	0.0051	0.012	0.045	0.05	0.03	0.025	−6.6	−0.043

; accordingly, the Gibbs free energy of the formation of rare earth compounds was obtained through using the Gibbs free energy equation (Formula (3)) under the tested steel composition at a 1873 K temperature of liquid steel, as shown in

Table 4. Gibbs free energy of formation of rare earth inclusions in tested steel at 1873 K.

Reaction Equation	ΔGθ/(J⋅mol−1)	ΔG/(KJ⋅mol−1)
$[Ce]+A{l}_2{O}_3{}_{(s)}^{}=CeAl{O}_{3(s)}+[Al]$	$\Delta G^{\theta }=-423900-247.3T$	−930.9
$[Ce]+3[O]+[Al]=CeAl{O}_3{}_{(s)}$	$\Delta G^{\theta }=-1366460+364.3T$	−532.6
$2A{l}_2{O}_3{}_{\left(s\right)}+6[Ce]+3[S]=4[Al]+{3Ce}_2{O}_2{S}_{(s)}$	$\Delta G^{\theta }=-348359+221.6T$	−572.5
$[Ce]+[O]+\frac{1}{2}[S]=\frac{1}{2}C{e}_2{O}_2{S}_{(s)}$	$\Delta G^{\theta }=-675700+165.5T$	−202.7
$[Ce]+\frac{3}{2}[O]=\frac{1}{2}C{e}_2{O}_3{}_{(s)}$	$\Delta G^{\theta }=-714380+179.74T$	−189
$C{e}_2{O}_{3(s)}+A{l}_2{O}_3{}_{(s)}^{}=2CeAl{O}_{3(s)}$	$\Delta G^{\theta }=-55635-25.37T$	−67.3
$[Ce]+[S]=Ce{S}_{\left(s\right)}$	$\Delta G^{\theta }=-422100+120.38T$	9.7

.

$$\lg f_{\mathrm{i}}={\displaystyle \sum _j^n{e}_i^j}w[j]$$

(1)

$$a_{\mathrm{i}}=f_{i}w[i]$$

(2)

$$\Delta G=\Delta G^{\theta }+RT\ln K$$

(3)

The f is the activity coefficient, ${\mathrm{e}}_i^j$ is the interaction coefficient of element j and element i, w[j] is the mass fraction of j element, w[i] is the mass fraction of element i and α_i is the activity of element i. K is the ratio of product activity to reactant activity, ΔG is Gibbs free energy of formation of products, R is the molar gas constant and T is the thermodynamic temperature.

In the generation of the Gibbs free energy of Ce compounds, as shown in Table 4, the CeAlO₃ is generated first, followed by Ce₂O₂S and Ce₂O₃, and CeS is not generated to a significant extent. The calculated results are consistent with the actual detected inclusions.

By summary and analysis of the physical properties of the second phase particles studied by many scholars [22,23,24,25], as shown in

Table 5. Physical properties of the second-phase particles during the solidification of molten steel.

Heterogeneous Nucleation Particle	Melting Points/°C	Degree of Nucleation Overcooling/°C	Equilibrium Constant Angle/°	Mismatch Degree/%
				δ	$\mathit{\gamma }$
Al2O3	2054	13.9	20.5	8.0	15.5
CeAlO3	2050	*	*	3.1	4.7
Ce2O2S	1949	4.5	*	1.2	8.5
Ce2O3	1692	3.0	9.4	5.0	6.8

Note: * indicates that related parameters are not reported.

, it can be seen that the Ce compounds with a high melting point are preferentially precipitated in the solidification process of steel liquid, the heterogeneous second phase particles have a smaller nucleation overcooling degree and equilibrium contact angle with the crystal nucleus, which is beneficial for increasing the nucleation rate. In addition, the rare earth compounds as heterogenous nucleators have a low mismatch degree with steel liquid, which meets the grain refinement condition($\delta$ ≤ 6%) proposed by Bramfitt [25]. Therefore, the CeAlO₃, Ce₂O₂S and Ce₂O₃ in 2# tested steel which was treated with Ce effectively refine the grain size and improve the strength and toughness of the material.

The relative atomic radius of Ce is 0.1877 nm, while the radius of iron atoms is 0.1210 nm. The maximum lattice gap of an austenite facing cubic structure is 0.0352 nm. Thus, by the analysis of atomic size and crystal structure, the solid solubility of Ce in the steel is very weak; therefore, the free Ce atoms are mainly concentrated at the grain boundary or phase interface, occupying the diffuse channel of solute atoms using a defect, hindering the diffusion of carbon atoms and other solutes, weakening the carbon emission ability of austenite and inhibiting the formation of local carbon poor conditions of austenite that is needed of ferrite transformation; hence, the ferrite in the microstructure of the 2# tested steel disappears. In addition, on the one hand, the rare earth Ce increases the stability of overcooled austenite by hindering the diffusion of other atoms and reducing the activity of carbon atoms in austenite [26,27], which weakens the ability of carbon emission from austenite during bainite transformation and contributes to the occurrence of bainite ferrite transformation [28,29]; on the other hand, the Ce impedes the diffusion of carbon atoms, enlarges the gap between the rich and poor sides of the carbon concentration fluctuation in austenite grains and the carbon poor area provides favorable conditions for bainite nucleation [30], and both of these jointly promote the formation and refinement of bainite ferrite and improve the strength, toughness and wear resistance of materials.

In the process of wear service, the hardness of the material can reflect its ability to resist the external abrasiveness and damage the substrate surface to a certain extent, but it is not the only indicator to determine the wear resistance of the material, because the hardness index cannot represent its ability to prevent crack initiation and propagation. At the beginning of wear, the higher the surface hardness of the material, the less the wear. In the middle and late stage of wear, the better the toughness of the material, the stronger the wear resistance. Only when the hardness and toughness of the material are well matched can its wear resistance be improved. The bainite ferrite takes into account both the toughness of ferrite and the strength and hardness of martensite, and it has good strength and toughness [31]. The proportion of bainite ferrite increased in 2#, which tested steel treated with rare earth, replacing polygonal proeutectoid ferrite, and the strength, hardness and impact energy were improved. Rare earth Ce was pinning grain boundaries to refine austenite grains, facilitated the nucleation of intragranular bainite ferrite and further divided and refined the original microstructure [32]. The fine bainite ferrite bundles have different grain orientations and a high proportion of large angle grain boundaries; in the process of crack tip propagation, the interlaced bainite ferrite bundles will change their direction and propagate in a “Z” shape, which increases the driving force of propagation and improves the wear resistance. Therefore, the action process of the rare earth element Ce in low alloy wear-resistant steel is briefly shown in Figure 18, which is mainly reflected in the inclusion metamorphism, the refinement of microstructure grains and the promotion of bainite ferrite precipitation in the addition of rare earth element to steel, thus comprehensively improving the strength, toughness and wear resistance of low alloy wear-resistant steel.

5. Conclusions

In this study, the effects of Ce on the inclusion denaturation, microstructure transformation and mechanical properties of low alloy wear-resistant steel were investigated in detail. Based on the experimental results and analyses, the following conclusions can be drawn:

• Adding Ce with a mass fraction of 0.0030% to the low alloy wear-resistant tested steel formed spheroidal CeAlO₃ and CeAlO₃-MnS with a diameter ≤2.5 μm and elliptic Ce₂S₂O-CaO with length ≤5 μm, refined the inclusion size, globalized the inclusion morphology and enhanced the binding force of the inclusion to the matrix.
• The addition of Ce in steel significantly refined the size of the as-cast structure, prevented the transformation of proeutectoid ferrite of overcooled austenite and contributed to the formation of bainite ferrite.
• The addition of Ce can improve the yield strength, yield ratio and surface hardness of the tested steel, especially the impact toughness at −40 °C~−20 °C.
• With the prolongation of the test time, the inclined wear amount of the tested steel first increases and then decreases; after adding Ce, the inflection point of the wear loss rate decreases in advance and the wear amount reduces under the same wear time.