High-carbon rare-earth-containing wear-resistant steel ball and manufacturing method thereof

Abstract

The invention discloses a high-carbon rare-earth-containing wear-resistant steel ball and a manufacturing method thereof, and belongs to the field of metal materials. The wear-resistant steel ball comprises the following main components in percentage by weight: 0.6%-0.7% of C, 0.7%-0.9% of Si, 0.8%-1.0% of Mn, 0.6%-0.8% of Cr, 0.02%-0.04% of Al and 1t of P; 0.025%, S: lt; 0.025% of Fe, 0.01-0.05% of RE, less than or equal to 10ppm of melt O, and the balance of Fe and inevitable impurities. According to the rare-earth-containing wear-resistant steel ball, rare earth elements are introduced, one-heating forming is combined with a QP heat treatment process, a fine and uniform martensite and retained austenite structure on the surface is finally obtained, a martensite, retained austenite and pearlite mixed structure is formed in the core, the hardness of the surface of the steel ball is larger than or equal to 58 HRC, and the room-temperature unnotched ballistic energy is larger than or equal to 40 J. And high hardness, good impact toughness and wear resistance are shown.

Description

Technical Field

[0001] The invention relates to the technical field of metal wear-resistant materials, and relates to a wear-resistant steel ball whose room temperature structure at the surface is martensite and residual austenite, and whose room temperature structure at the core is martensite, residual austenite and pearlite, and a wear-resistant steel ball with high hardness, good toughness and high wear resistance, and a manufacturing method thereof. Background Art

[0002] Wear-resistant steel balls are consumables for grinding machines and are mainly used in industrial fields such as mining, cement, metallurgy, and thermal power generation. The annual consumption of steel balls in the world is 30 to 50 million tons, of which China consumes 3 to 5 million tons, making it a major consumer of steel balls. Forged grinding balls are forged into balls by air hammer free forging. The production process is simple, the production efficiency is high, and the energy consumption is low. When the grinding balls are ground to a diameter of 40 to 50 mm in the mill, the mill will discharge them. Therefore, the wear-resistant steel balls need to have high hardness and high wear resistance on the surface, and high impact toughness at the core of the steel balls to avoid poor wear resistance and easy breakage of the steel balls during service. The development of large-diameter forged grinding balls at home and abroad has a long history. In order to improve the performance of steel balls, researchers have used carbon steel, 20Mn2, 20MnVB and 18Cr2Ni4WA, and then used medium-carbon alloy steel 45Mn, 40CrNiMoA and high-carbon low-alloy steel GGr4, GGr15, GGr15SiMn to further improve the hardness of steel balls.

[0003] As microalloying elements, rare earth elements can refine grains, purify molten steel, modify inclusions, and improve the toughness and wear resistance of steel. Among rare earth elements, La and Ce are widely used in rare earth steels due to their low cost. RE exists in carbon steel in the form of (1) segregation at grain boundaries. La and Ce elements segregated at grain boundaries reduce interfacial tension and grain growth driving force, inhibiting grain growth. At the same time, they prevent harmful elements such as P and S from gathering at grain boundaries, purify grain boundaries, and strengthen grain boundaries. (2) Solid solution in iron-carbon alloys. Rare earth elements La and Ce can be solid-dissolved in α-Fe and MC, among which La can be solid-dissolved in Fe3C to increase the Fe3C lattice constant and improve the strength and stability of cementite. Ce can be solid-dissolved in γ-Fe to produce solid solution strengthening (3) Forming rare earth second phases. RE combines with P to form RE-P, reducing the P element content. However, when the amount of RE added is too much, in addition to forming RE-Fe-P and RE-Fe second phases, the toughness of the steel is reduced. (4) Inclusions. RE can combine with O and S in steel to form rare earth inclusions such as RE2O3, RES, RE2S3, and RE2O2S, thereby helping to desulfurize and deoxidize the steel. When RE0.01-0.05wt.% is added, inclusions can be effectively modified.

[0004] Chinese patent application CN 105838987A discloses a method for preparing high-strength and toughness low-alloy wear-resistant steel for bucket teeth, characterized in that the chemical composition of the wear-resistant steel is, by mass percentage, C: 0.35-0.45%, Si: 1.20-1.60%, Mn: 1.00-1.40%, Cr: 0.70-0.90%, Mo: 0.15-0.25%, Cu: 0.40-0.60%, Re: 0.05-0.10%, P: 0-0.025%, S: 0-0.025%, and the rest is Fe and unavoidable impurities, and the surface hardness of the excavator bucket teeth is 50-55HRC, and the impact value is 30-35J / cm 2 , adding alloying elements such as Mo and Cu at the same time as Re increases the cost. When the Cu content exceeds 0.5wt.%, the plasticity of the bucket tooth steel is significantly reduced. Excessive rare earth elements will form a harmful second phase, increasing the brittleness of the steel. Chinese patent application CN 201610146743.9 discloses a rare earth-doped low-chromium wear-resistant steel ball and a preparation method thereof, characterized in that the chemical composition of the wear-resistant steel ball is calculated by weight percentage, C: 0.5-1%, Cr: 0.46%, Mn: 2.1%, Si: 0.25%, V: 0.07%, Ti: 0.06-0.09%, rare earth: 0.08%, Mg: 1.3%, and the remainder is Fe. The steps of its preparation method are: smelting, pouring and oil quenching, and the impact value can reach 90-118J / cm 2 The preparation process of this patent is complicated, the cooling time of the cast ball before oil quenching is long, and the model requirements are high. Adding the alloy element Mg also increases the production cost. Chinese patent application 201110268764.5 discloses a rare earth treated high toughness wear-resistant steel plate, characterized in that the material of the steel plate contains the following chemical components in mass percentage: C: 0.10-0.30%, Si: 0.20-0.70%, Mn: 1.00-1.60%, Nb: 0.01-0.03%, Ti: 0.01-0.05%, B: 0.0005-0.006%, RE: 0.01-0.30%, Als: 0.010-0.040%, P≤0.025%, S≤0.010%, the balance is Fe, and the Brinell hardness is 410-417HB. The patent does not specify whether the rare earth addition of 0.01-0.30wt.% is suitable for the existing alloy system, whether it is excessive, and the process of determining the rare earth addition is not clear. Excessive RE is easy to form large-sized inclusions in the steel, reducing impact toughness. Summary of the invention

[0005] In view of the requirements for high hardness and good toughness of wear-resistant steel balls, the present invention adds rare earth lanthanum or cerium elements to ordinary high-carbon steel wear-resistant steel balls. The room temperature structure of the steel ball surface is martensite and residual austenite, and the core is a mixed structure of martensite, residual austenite and pearlite. It has high hardness, good plasticity and toughness and high wear resistance.

[0006] The present invention adopts the following technical scheme: a high-carbon rare earth-containing wear-resistant steel ball, whose chemical composition weight percentage is: C: 0.6-0.7%, Si: 0.7-0.9%, Mn: 0.8-1.0%, Cr: 0.6-0.8%, Al: 0.02-0.04%, P: <0.025%, S: <0.025%, RE: 0.01-0.05%, O in the melt is ≤10ppm, O in the rare earth is ≤100ppm, and the balance is Fe and unavoidable impurities.

[0007] Another object of the present invention is to provide a method for preparing a high-carbon and rare earth-containing wear-resistant steel ball, which comprises the following steps through a QP heat treatment process and a pyrolysis method:

[0008] Step 1: Weigh the raw materials according to the designed composition, smelt and cast to obtain ingots. Keep the ingots at 1130-1150℃ for 2h, forge them into round steel, and saw them into round bars at a fixed length;

[0009] Step 2: The round steel obtained in step 1 is kept at 1150°C for 2 hours;

[0010] Step 3: Place the round steel after heat preservation in step 2 into a 750Kg air hammer forging to form a spherical forging. The initial forging temperature is 1150°C and the final forging temperature is 1100°C.

[0011] Step 4: The steel ball obtained in step 3 is kept at 810°C for 2.5h;

[0012] Step 5: The steel ball obtained in step 4 is quenched in water at a temperature of 35 to 40°C, and the return temperature is 180 to 210°C;

[0013] Step 6: The steel ball obtained in step 5 is kept at 180-210° C. for 6 hours to obtain a rare earth-containing wear-resistant steel ball.

[0014] The principle of quantitative rare earth elements in the present invention:

[0015] According to the E2EM (edge-to-edge matching model), the Misfit value is used to describe the mismatch of the atomic spacing along the most densely packed crystal direction in the two phases, and the Mismatch value is used to describe the mismatch of the crystal plane spacing along the most densely packed crystal plane in the two phases. The nucleation effectiveness of the second phase particles can be predicted by the difference in lattice parameters between the particles and the solidified phase. When Misfit < 10% and the Mismatch value < 10%, one phase may become the core of the heterogeneous nucleation of the other phase. The smaller the mismatch of the atomic spacing between the two phases, the greater the possibility that one phase will become the core of the heterogeneous nucleation of the other phase.

[0016] The interatomic mismatch and interplanar mismatch are calculated by the following formula:

[0017]

[0018]

[0019] In the formula, f r is the interatomic mismatch; f d is the interatomic distance along the (nearly) close-packed atomic row of the matrix; r P is the interatomic distance along the (nearly) close-packed atomic rows of the heterogeneous primary phase; f d is the inter-surface mismatch; d M is the interplanar spacing of the matrix along the (nearly) close-packed atomic rows; d P It is the interplanar spacing along the (nearly) close-packed atomic rows of the heterogeneous primary phase.

[0020] According to the above formula, the mismatch between some modified products after La and Ce were added to the molten steel at 1500℃ and the solidified phase (γ-ferrite) of the steel for wear-resistant steel balls was calculated, and the results are shown in Table 1.

[0021] Table 1 Calculation results of mismatch between γ-Fe and related inclusions of La and Ce using E2EM model

[0022]

[0023] In order to clarify the specific effects of different La or Ce addition amounts in steel, the Factsage thermodynamic software was used to predict the results of La or Ce modified inclusions in the steel ingot for wear-resistant steel balls at 1500℃. Figure 1 shown.

[0024] Depend on Figure 1 It can be seen that after adding La, La will modify Al2O3 in steel into La-containing inclusions, such as LaAl 11 O 18 、LaAlO3、La 33 Al7O 60When the amount of La added is 0.004wt.%, the modified product containing La and Al is converted to La2O3. When it is further increased to 0.005wt.%, the modified product in the steel is stabilized as La2O3, and the La element combines with the S element to form La2S3. When the amount of La added is increased to 0.026wt.%, La2S3 is converted to LaS, and La2O3 exists stably. With the continuous addition of La, the LaS content increases and La2O3 exists stably.

[0025] When the La content in the steel is greater than 0.005wt.%, the Al-containing inclusions disappear, and when the La content is less than 0.005wt.%, the modified product contains LaAl 11 O 18 、LaAlO3、La 33 Al7O 60 , LaAl 11 O 18 、LaAlO3、La 33 Al7O 60 Al-containing inclusions are formed in different areas of the second phase surface, destroying the integrity of the surface of the nucleation base. Therefore, the La content in the molten steel should be greater than 0.005wt.%. According to the mismatch calculation, the mismatch between γ-Fe and La2O3 and LaS is less than 10%, and they can effectively nucleate. The minimum atomic distance mismatch between γ-Fe and La2O3 and LaS is 3.6145% and 9.6438%, respectively. The minimum atomic distance mismatch between γ-Fe and La2O3 is the smallest, followed by LaS. The smaller the interatomic mismatch, the easier it is to heterogeneous nucleation, and the stronger the grain refinement effect. Considering the economy and avoiding too many inclusions floating on the surface of the molten steel, affecting the hardness and impact toughness of the steel, the range of La addition is designed to be 0.03~0.05wt.%.

[0026] Depend on Figure 2 It can be seen that when a small amount of Ce is added, Ce will modify the Al2O3 in the steel into inclusions containing both Al and Ce, such as CeAl 11 O 18 , CeAlO3, when the Ce addition amount is increased to 0.0025wt.%, the Ce modified product is transformed from CeAlO3 to Ce2O3, and when it is further increased to 0.005wt.%, the modified product in the steel is stabilized as Ce2O3. When the Ce addition amount is increased to 0.007wt.%, the Ce element combines with the S element to form CeS, and Ce2O3 exists stably. Continue to add Ce, the CeS content increases, and Ce2O3 exists stably.

[0027] Combined with Table 1, the mismatch between Ce2O3 and CeS is less than 10%, which meets the requirements of being a good non-uniform nucleation core. CeAlO3 may have the effect of non-uniform nucleation. Although CeAlO3 may have the effect of non-uniform nucleation, when the Ce content is less than 0.005wt.%, the modified product is CeAlO3+Ce2O3, and CeAlO3 is formed in different areas of the second phase surface, destroying the integrity of the nucleation zone surface. Therefore, the Ce content in the molten steel should be greater than 0.005wt.%, and the mismatch between CeS and δ-Fe lattice is minimized, and the columnar crystals are refined. If too much Ce is added to the steel, too much CeS will be formed. Considering the economy and avoiding too many inclusions affecting the hardness and impact toughness of the steel ball, the range of Ce addition is designed to be 0.01~0.03wt.%.

[0028] The key points of the present invention are:

[0029] 1. The present invention adds rare earth lanthanum or cerium elements to ordinary high-carbon steel wear-resistant steel balls. Through reasonable alloy system design and innovative introduction of lanthanum or cerium elements into high-carbon wear-resistant steel, the hardness is increased while the impact performance is greatly improved in combination with the QP heat treatment process, and the wear resistance is greatly improved, ultimately achieving the goal of high service life of low-cost wear-resistant steel balls. The present invention adds a small number of alloy elements, and after introducing a small amount of rare earth La or cerium elements, the needle-shaped martensite structure in the steel ball can be refined, so that the material can withstand large loads and deformations, and has good plasticity and impact resistance. The room temperature structure of the steel ball surface is martensite and residual austenite, and the core is a mixed structure of martensite, residual austenite, and pearlite, with high hardness, good plasticity and toughness, and high wear resistance.

[0030] 2. The surface Rockwell hardness of the wear-resistant steel ball containing lanthanum is ≥58, and the impact work without notch is ≥40J. The surface Rockwell hardness of the wear-resistant steel ball containing cerium is ≥58, and the impact work without notch is ≥45J. The wear resistance of the steel ball is greatly improved, and the service life of the steel ball is greatly extended. Therefore, this kind of wear-resistant steel ball containing rare earth has excellent comprehensive performance, greatly improves production efficiency, and is an ideal material for wear-resistant steel ball steel.

[0031] 3. The appropriate amount of rare earth elements added in the high-carbon low-alloy system was scientifically determined by combining Thermo-calc software and mismatch theory. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The prediction of La modification results of the steel inclusions for wear-resistant steel balls at 1500℃ is given in Table 1.

[0033] Figure 2 The prediction of the modification results of Ce inclusions in the wear-resistant steel ball at 1500℃ is given in Table 1.

[0034] Figure 3is a light microscope image of the surface of the wear-resistant steel ball in Example 1 of the present invention;

[0035] Figure 4 is a light microscope image of the surface of the wear-resistant steel ball in Example 2 of the present invention;

[0036] Figure 5 This is a light microscope image of the surface of the wear-resistant steel ball in Example 3 of the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0038] Embodiment 1:

[0039] First, smelting and casting are carried out according to the above composition range, and then the composition of the ingot is tested, see Table 3.

[0040] Table 3 Composition of ingot

[0041]

[0042] The ingot was heated to 1150℃ and homogenized for 2h, and forged into Φ80mm round bars at 1100℃ with a forging ratio of 1.72. The round bars with a length of 180mm were cut and free forged within the temperature range of 1150℃ to obtain Φ120mm steel balls. The final forging temperature was 1100℃.

[0043] The specific heat treatment process parameters of the steel ball are shown in Table 4.

[0044] Table 4 Heat treatment process parameters

[0045]

[0046] The mechanical properties of the surface and core of the lanthanum-containing wear-resistant steel ball prepared according to Table 3 and Table 4 are shown in Table 5.

[0047] Table 5 Mechanical properties of the surface and core of lanthanum-containing wear-resistant steel balls

[0048]

[0049] From Table 5, we can see that all mechanical properties have reached very high mechanical performance indicators. The hardness of the wear-resistant steel ball surface is 58HRC, the impact energy of the unnotched part at room temperature is 41.84J, the hardness of the core is 36HRC, and the impact energy of the unnotched part at room temperature is 111.87J. The 500× optical microscope photo of the surface is as follows: Figure 3 As shown, the structure is acicular martensite and a small amount of retained austenite.

[0050] Embodiment 2:

[0051] First, smelting and casting are carried out according to the above composition range, and then the composition of the ingot is tested, see Table 6.

[0052] Table 6 Composition of ingot (wt.%)

[0053]

[0054] The ingot was heated to 1150℃ and homogenized for 2h, and forged into Φ80mm round bars at 1100℃ with a forging ratio of 1.72. The round bars with a length of 180mm were cut and free forged at 1150℃ to forge Φ120mm steel balls with a final forging temperature of 1100℃.

[0055] The specific heat treatment process parameters of the steel ball are shown in Table 7.

[0056] Table 7 Heat treatment process parameters

[0057]

[0058] The mechanical properties of the cerium-containing wear-resistant steel balls prepared according to Tables 6 and 7 are shown in Table 8.

[0059] Table 8 Mechanical properties of cerium-containing wear-resistant steel balls

[0060]

[0061] From Table 8, we can see that all mechanical properties have reached very high mechanical performance indicators. The hardness of the wear-resistant steel ball surface is 58HRC, the impact energy of the unnotched part at room temperature is 46.14J, the hardness of the core is 40HRC, and the impact energy of the unnotched part at room temperature is 138.26J. The 500× optical microscope photo of the surface is as follows: Figure 2 As shown, the structure is acicular martensite and a small amount of retained austenite.

[0062] Embodiment 3:

[0063] Smelting and casting are carried out according to the above composition range, and then the composition of the ingot is tested, see Table 9.

[0064] Table 9 Composition of ingot (wt.%)

[0065]

[0066] The ingot was heated to 1150℃ and homogenized for 2h, and forged into Φ80mm round bars at 1100℃ with a forging ratio of 1.72. The round bars with a length of 180mm were cut and free forged at 1150℃ to forge Φ120mm steel balls. The final forging temperature was 1100℃.

[0067] The specific heat treatment process parameters of the steel ball are shown in Table 10.

[0068] Table 10 Heat treatment process parameters

[0069]

[0070] The mechanical properties of the surface of the cerium-containing wear-resistant steel ball prepared according to Table 9 and Table 10 are shown in Table 11.

[0071] Table 11 Mechanical properties of cerium-containing wear-resistant steel balls

[0072]

[0073] From Table 11, it can be seen that all mechanical properties have reached very high mechanical performance indicators. The hardness of the wear-resistant steel ball surface is 58HRC, the impact energy of the unnotched part at room temperature is 69.03J, the hardness of the core is 40HRC, and the impact energy of the unnotched part at room temperature is 138.79J. The 500× optical microscope photo of the steel ball surface is as follows Figure 3 As shown, the structure is acicular martensite and a small amount of retained austenite.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention, and should be included in the scope of the claims of the present invention.

Claims

1. A high carbon rare earth-containing wear-resistant steel ball, characterized in that: The chemical composition of the wear-resistant steel ball includes, by mass percentage, C: 0.6-0.7%, Si: 0.7-0.9%, Mn: 0.8-1.0%, Cr: 0.6-0.8%, Al: 0.02-0.04%, P: <0.025%, S: <0.025%, RE: 0.01-0.05%, melt O≤10ppm, and the remainder is Fe and unavoidable impurities.

2. The high carbon rare earth-containing wear-resistant steel ball according to claim 1, characterized in that: The rare earth element in the high-carbon rare earth-containing wear-resistant steel ball is lanthanum or cerium, wherein the surface Rockwell hardness of the lanthanum-containing wear-resistant steel ball is ≥58HRC, the core Rockwell hardness is ≥36HRC, the room temperature impact toughness at the surface is ≥40J, and the room temperature impact toughness at the core is ≥100J.

3. The high carbon rare earth-containing wear-resistant steel ball according to claim 1 or 2, characterized in that: The rare earth element in the medium-carbon rare-earth wear-resistant steel ball is cerium, wherein the surface Rockwell hardness of the cerium wear-resistant steel ball is ≥58HRC, the core Rockwell hardness is ≥36HRC, the room-temperature impact toughness at the surface is ≥45J, and the room-temperature impact toughness at the core is ≥138J.

4. A method for preparing a high-carbon rare earth-containing wear-resistant steel ball as claimed in claim 1 or 2, characterized in that: The following steps are involved: Step 1: weigh the raw materials according to the designed composition, smelt and cast them to obtain ingots, keep the ingots at 1130-1150°C for 2h, forge them into round steel after keeping them warm, and cut them into round steel bars at a fixed length; Step 2: heating the round steel billet prepared in step 1 to 1150° C. and keeping the temperature for 2 hours; Step 3: Place the round steel after heat preservation in step 2 into a 750Kg air hammer forging to form a spherical forging. The initial forging temperature is 1150°C and the final forging temperature is 1100°C. Step 4: The steel ball prepared in step 3 is kept at 810°C for 2.5 hours; Step 5: quenching the steel ball obtained in step 4 in water; Step 6: The steel ball obtained in step 5 is kept at 180°C to 210°C for 6 hours to obtain a lanthanum- or cerium-containing wear-resistant steel ball.

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