Double-hardness alloy hammerhead and preparation method thereof

Abstract

The invention relates to a double-hardness alloy hammer head and a preparation method thereof. The double-hardness alloy hammer head comprises the following components in percentage by mass: 0.38 to 0.45 percent of C, 1.8 to 2.0 percent of Si, 2.5 to 3.0 percent of Mn, 1.5 to 2.0 percent of Cr, 0.4 to 0.7 percent of Mo, 0.5 to 0.7 percent of Ni, 0.08 to 0.15 percent of V, 0.02 to 0.05 percent of Nb, 0.02 to 0.03 percent of Ti, 0.005 to 0.008 percent of B, 0.03 to 0.06 percent of rare earth La + Ce, less than or equal to 0.011 percent of P, less than or equal to 0.01 percent of S and the balance of Fe and inevitable impurities. Compared with the working end of the hammer head at the position of 20mm and the working end of the hammer head at the position of 35mm, the hardness and the tensile strength of the position of 35mm are reduced, but the impact toughness and the ductility are improved. The hammerhead has hardness and toughness matching at different thicknesses of the working end, and also has good toughness and strength at the hammerhead mounting end.

Description

Technical Field

[0001] The invention belongs to the technical field of wear-resistant parts of mining machinery, and particularly relates to a double-hardness alloy hammer head and a preparation method thereof. Background Art

[0002] Hammer crushers are widely used in crushing operations in industries such as cement, mining, coal, and metallurgy. The hammerhead is the core working component of a hammer crusher, subject to the combined effects of impact and abrasion during operation. The operating conditions are complex and harsh, requiring the hammerhead to possess high strength, toughness, and wear resistance. The hammerhead consists of a working end and a mounting end, with the mounting end provided with a shaft hole. The hammerhead is arranged on the hammer shaft of the crusher's rotor. During high-speed operation, the crusher directly strikes the material, ultimately crushing it to the desired particle size.

[0003] Existing hammer heads are primarily made of high-manganese steel or alloy steels with a medium-to-low carbon martensite matrix. High-manganese steel hammer heads often fail prematurely due to wear and tear during service. Medium-to-low carbon martensite alloy steel hammer heads typically have a thickness of 100-200 mm and are generally not sufficiently hard. While hammer head hardness is proportional to wear resistance, excessive hardness reduces impact toughness, thus limiting the hammer's service life. Existing medium-to-low carbon martensite alloy steels struggle to strike a balance between wear resistance and impact resistance. Large-scale crusher hammer heads, measuring over 300 mm, are subject to significant impact loads and intense wear in actual operation. Existing alloy steels for large-scale crusher hammers suffer from insufficient hardenability, resulting in an insufficiently deep hardened layer. Increasing hardenability through the addition of alloying elements increases product cost, making it difficult to achieve a good balance between hardness and toughness. On the one hand, insufficient hardness at the hammer's working end leads to rapid wear and shortened service life; on the other hand, insufficient toughness at the core makes it prone to fracture.

[0004] With the increasing scale of mining equipment, there is an urgent need for larger crusher hammers with excellent hardness and toughness to extend their service life. Reducing product costs is also a pressing issue. Therefore, traditional crusher hammers struggle to meet these low-cost and high-performance requirements. There is an urgent need to develop a crusher hammer with high toughness and hardness at a low cost to meet market demands and drive industry development. Summary of the Invention

[0005] The present invention provides a double-hardness alloy hammer head and its preparation method, which are used to solve the problems of the current crusher hammer head with a thickness of more than 300mm, which has insufficient hardenability, resulting in insufficient hardened layer depth, poor matching between hardness and toughness, and high product cost. The obtained double-hardness alloy hammer head has a lower hardness and tensile strength at the working end at 20mm than at 35mm, but the impact toughness and elongation are improved. The tensile strength at 20mm on the working end surface of the hammer head is 1800-1900MPa, the hardness is 57-61HRC, and the impact toughness is 8-13J / cm 2 , elongation 4.6~6.1%; tensile strength 1675~1740MPa at 35mm from the working end surface of the hammer head, hardness 43~48HRC, impact toughness 21~28J / cm 2 , elongation 10.2~15.5%.

[0006] In a first aspect, the present invention relates to a dual-hardness alloy hammer head, comprising the following components, by mass percentage: C 0.38-0.45%, Si 1.8-2.0%, Mn 2.5-3.0%, Cr 1.5-2.0%, Mo 0.4-0.7%, Ni 0.5-0.7%, V 0.08-0.15%, Nb 0.02-0.05%, Ti 0.02-0.03%, B 0.005-0.008%, rare earth La+Ce 0.03-0.06%, P≤0.011%, S≤0.01%, and the balance being Fe and unavoidable impurities.

[0007] The hammer head includes a working end and a mounting end. The microstructure 20 mm below the surface of the working end of the hammer head includes 75% to 80% martensite by volume, and the rest is bainite; the microstructure 35 mm below the surface of the working end of the hammer head includes 30% to 40% lath bainite, 25% to 40% martensite, and the rest is retained austenite by volume.

[0008] Preferably, the mass ratio of C, Si and Mn satisfies Mn: (C+0.3Si)=2.8-3.1; 0.5Mn+Mo=1.8-2; Cr / Mo=3.5-4.5.

[0009] Preferably, the hammer head has a thickness of 350 to 450 mm.

[0010] Preferably, the dual-hardness alloy hammer head comprises the following components by mass percentage: C 0.4%, Si 1.9%, Mn 2.8%, Cr 1.8%, Mo 0.5%, Ni: 0.5%, V 0.13%, Nb 0.05%, Ti0.02%, B 0.007%, rare earth La+Ce 0.06%, P 0.005%, S 0.006%, the balance is Fe and unavoidable impurities.

[0011] In a second aspect, the present invention relates to a method for preparing the dual-hardness alloy hammer head, comprising the following steps: (1) The alloy raw materials are smelted, deoxidized and deslagging in a vacuum induction medium frequency furnace to obtain molten steel; (2) pouring the molten steel into the sand mold and cooling it to obtain the hammer head casting; (3) Normalizing heat treatment: heat the hammer head casting to 820-880℃ at 40-45℃ / h, keep warm for 7-9h, and air cool to room temperature; (4) Double quenching heat treatment: heat the hammer casting to 550-600℃ at a rate of 41-46℃ / h and keep it warm for 6.5-9h, then heat it to 800-880℃ at a rate of 45-50℃ / h and keep it warm for 7.0-10h, then immerse it in quenching liquid and cool it to no more than 200℃; heat it to 670-700℃ at a rate of 41-46℃ / h and keep it warm for 7-10h, then immerse it in quenching liquid and cool it to below 380℃, then slowly cool it to room temperature at a cooling rate of 1-3℃ / s; during quenching, the refractory insulation layer wraps the installation end of the hammer and exposes the surface of the quenching liquid, and only the working end of the hammer is quenched; after quenching, a double hardness alloy hammer is obtained.

[0012] Preferably, the quenching liquid in step (4) is water or PAG quenching agent at a temperature not higher than 30°C.

[0013] The beneficial effects of the present invention are: The present invention optimizes the alloy element composition and fully utilizes the solid solution strengthening effect of the alloy elements and the effect of Cr and Mo on hardenability by controlling the ratios of Mn:(C+0.3Si), 0.5Mn+M, and Cr / Mo, thereby greatly reducing the content of expensive metal Mo. While achieving high hardness at the working end of the hammer head, it can also ensure that the mounting end of the hammer head has excellent toughness. Combined with the double quenching heat treatment process, an excellent match between hardness and toughness is achieved.

[0014] Compared with the traditional single quenching + tempering process, the present invention adopts a staged heating + double quenching process, and the second quenching is first fast cooling and then slow cooling. Finally, the microstructure 20 mm below the surface of the working end of the hammer head includes 75-80% martensite by volume fraction, and the rest is bainite; the microstructure 35 mm below the surface of the working end of the hammer head includes 30-40% lath bainite, 25-40% martensite, and the rest is retained austenite by volume fraction.

[0015] The slow cooling rate of the secondary quenching treatment can avoid the thermal stress and phase change stress concentration caused by the excessively fast cooling rate of the surface. Self-tempering will occur inside the hammer head, eliminating the tempering process and simplifying the production process. At the same time, a gradient hardness is formed on the working end of the hammer head, and the hardness gradually decreases from the surface to the core, while the toughness gradually increases.

[0016] The double-hardness hammer head prepared by the present invention has a lower hardness and tensile strength at 20mm than at 35mm, but an improved impact toughness and elongation. The tensile strength at 20mm on the working end of the hammer head is 1800-1900MPa, the hardness is 57-61HRC, and the impact toughness is 8-13J / cm 2 , elongation 4.6~6.1%; tensile strength 1675~1740MPa at 35mm from the working end surface of the hammer head, hardness 43~48HRC, impact toughness 21~28J / cm 2 , elongation 10.2~15.5%. The hammer head mounting end also has good mechanical properties, tensile strength 1264~1350MPa, hardness 45~48HRC, impact toughness 19~25J / cm 2 , elongation 11.2 ~ 15.6%, which can simultaneously ensure that the hammer head has a matching of hardness and toughness at different thicknesses at the working end, and also has good toughness and strength at the installation end of the hammer head. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 Schematic diagram of the structure of the hammer head in an embodiment of the present invention.

[0019] Figure 2 The present invention discloses a schematic diagram of a process flow for preparing a double-hardness alloy hammer head.

[0020] Serial numbers in the figure: 1, installation end, 2, working end. DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0022] With the development of large-scale mining equipment, large-sized crusher hammers with a diameter of more than 300mm need to withstand huge impact loads and severe wear in actual operation. The existing large-sized crusher hammers made of alloy steel have insufficient hardenability, resulting in insufficient depth of the hardened layer. Adding alloy elements to obtain high hardenability will increase product cost, and it is often difficult to achieve a good balance between hardness and toughness. On the one hand, if the hardness of the working end of the hammer is insufficient, it will cause excessive wear and shorten the service life; on the other hand, if the core is not tough enough, it is prone to fracture. There is an urgent need for larger crusher hammers with excellent hardness and toughness to increase service life. Reducing product costs is also an urgent problem to be solved. Therefore, traditional crusher hammers are difficult to meet the requirements of low cost and high performance. There is an urgent need to develop a crusher hammer with low cost, high toughness and high hardness to meet market requirements and promote industry development.

[0023] In response to the above technical problems, an embodiment of the present invention provides a dual-hardness alloy hammer head, which comprises the following components by mass percentage: C 0.38-0.45%, Si 1.8-2.0%, Mn 2.5-3.0%, Cr 1.5-2.0%, Mo 0.4-0.7%, Ni 0.5-0.7%, V 0.08-0.15%, Nb 0.02-0.05%, Ti 0.02-0.03%, B 0.005-0.008%, rare earth La+Ce 0.03-0.06%, P≤0.011%, S≤0.01%, and the balance is Fe and unavoidable impurities; In one embodiment, the mass ratio of C, Si, and Mn satisfies Mn: (C+0.3Si)=2.8-3.1; 0.5Mn+Mo=1.8-2; Cr / Mo=3.5-4.5.

[0024] In one embodiment, the hammer head has a thickness of 350-450 mm.

[0025] C: C is an interstitial solid solution strengthening element. It can play an interstitial solid solution strengthening role in the martensite structure, thereby improving the hardness and strength of the steel material. C can significantly reduce the Ms point of steel, improve the stability of supercooled austenite, increase the thermodynamic energy required for the transformation of γ phase to α phase during the cooling process, shift the CCT curve to the right, and improve the hardenability of steel. In the present invention, if the carbon content is lower than 0.38%, it will be difficult to obtain the required hardness and the ratio of martensite to bainite. If the carbon content exceeds 0.45%, the hardness of the steel will be too high, the toughness will decrease, and the risk of cracking will increase. The C content is preferably limited to the range of 0.38-0.45%.

[0026] Si: Si exists as a solid solution in ferrite or austenite, exerting a strong solid solution strengthening effect, shifting the "C" curve to the right and improving the hardenability of the steel. Si is also a ferrite-forming element, preventing carbide nucleation and growth. However, excessive Si content significantly reduces the steel's plasticity and toughness. The Si content is preferably limited to 1.8-2.2%.

[0027] Mn: Mn is an austenite-forming element that can infinitely expand the austenite phase, significantly lower the Ms point, enhance the stability of supercooled austenite, and increase the content of retained austenite. Mn also strengthens the ferrite phase, reduces the driving force for phase transformation, shifts the "C" curve to the right, and significantly increases hardenability. Excessive manganese content can easily cause segregation during alloy solidification, resulting in uneven alloy structure and properties. The Mn content is preferably limited to 2.5-3.0%.

[0028] Cr: Cr is a ferrite-forming element that reduces the austenite phase and increases the hardenability of steel. It forms a continuous solid solution with iron and forms various carbides with carbon, which refines grains, improves structure, and has the effect of solid solution strengthening, increasing steel strength. However, excessive Cr content increases the tendency of steel to temper brittleness. The Cr content is preferably limited to 1.5-2.0%.

[0029] Mo: Mo exists primarily in steel as carbides, dispersed throughout the matrix and strengthening it. Mo exhibits solid solution strengthening properties. Mo improves the hardenability of steel, surpassing Cr and surpassing Mn. Mo inhibits the segregation of harmful elements at grain boundaries, eliminating temper brittleness. Mo is a carbide-forming element. During tempering at high temperatures, it forms carbides that disperse throughout the matrix, enhancing the steel's thermal strength. Mo is also a scarce and valuable element, so its mass fraction should be between 0.4% and 0.7%.

[0030] Ni: Ni does not form carbides in steel, but can expand the austenite phase region, increase the amount of retained austenite in quenched steel, lower the critical transition temperature, reduce the diffusion rate of various elements in the steel, improve hardenability, and increase the strength of the steel without significantly affecting the plasticity of the steel. The Ni content is preferably limited to the range of 0.5 to 0.7%.

[0031] V: V forms fine carbides and nitrides, refining the grains and increasing the hardness and wear resistance of the steel. A small amount of vanadium can significantly improve the alloy's microstructure, making the martensite and bainite structures on the surface of the hammer's working end finer, thereby increasing hardness and wear resistance. The content is preferably limited to 0.08-0.15%.

[0032] Nb: Niobium forms stable compounds with carbon and nitrogen, contributing to precipitation strengthening and grain refinement in steel. Controlling the niobium content improves the alloy's strength and toughness, particularly optimizing the microstructure and properties of the hammer core. The content is preferably limited to 0.02-0.05%.

[0033] Titanium: Titanium combines with elements like nitrogen and oxygen to form stable compounds, purifying the molten steel and reducing the effects of harmful impurities. It also refines the grain size, improving the toughness and strength of the steel. Its content is preferably limited to 0.02-0.03%.

[0034] B: Boron is a strong hardenability element. A trace amount of boron can significantly improve the hardenability of steel, making it easier for the alloy to form martensite and bainite structures during quenching. It is especially important for ensuring the hardenability of large-sized hammer heads. The content is preferably limited to the range of 0.005-0.008%.

[0035] Rare Earth La+Ce: Rare earth elements can purify molten steel, improve the morphology and distribution of inclusions, and reduce their adverse effects on alloy properties. They also refine grain size, enhancing the alloy's toughness and wear resistance, playing a key role in improving the hammer's overall performance. Rare earth content is preferably limited to 0.03-0.06%.

[0036] Phosphorus and sulfur: Phosphorus and sulfur are harmful impurity elements. Phosphorus can cause cold brittleness in steel, while sulfur can cause hot brittleness. Therefore, the present invention strictly controls the phosphorus content to ≤ 0.011% and the sulfur content to ≤ 0.01% to reduce their adverse effects on alloy properties.

[0037] In the present invention, the contents of the core elements C, Si, Mn, Cr, and Mo are controlled to satisfy the following relationship: Mn: (C+0.3Si)=2.8-3.1, 0.5Mn+Mo=1.8-2, and Cr / Mo=3.5-4.5. This balances the strengthening effects of C, Si, and Mn on steel and the influences of Cr and Mo on hardenability and solid solution strengthening. While achieving high hardness at the working end of the hammer head, it can also ensure that the mounting end of the hammer head has excellent toughness. Combined with a double quenching heat treatment process, excellent hardness and toughness matching is achieved.

[0038] In one embodiment, the dual-hardness alloy hammer comprises the following components by mass percentage: C 0.4%, Si 1.9%, Mn 2.8%, Cr 1.8%, Mo 0.5%, Ni: 0.5%, V 0.13%, Nb 0.05%, Ti0.02%, B 0.007%, rare earth La+Ce 0.06%, P 0.005%, S 0.006%, the balance is Fe and unavoidable impurities.

[0039] like Figure 1 and 2 As shown, a method for preparing a dual-hardness alloy hammer head according to an embodiment of the present invention comprises the following steps: (1) The alloy raw materials are smelted, deoxidized and deslagging in a vacuum induction medium frequency furnace to obtain molten steel; (2) pouring the molten steel into the sand mold and cooling it to obtain the hammer head casting; (3) Normalizing heat treatment: heat the hammer head casting to 820-880℃ at 40-45℃ / h, keep warm for 7-9h, and air cool to room temperature; (4) Double quenching heat treatment: heat the hammer casting to 550-600℃ at a rate of 41-46℃ / h and keep it warm for 6.5-9h, then heat it to 800-880℃ at a rate of 45-50℃ / h and keep it warm for 7.0-10h, then immerse it in quenching liquid and cool it to no more than 200℃; heat it to 670-700℃ at a rate of 41-46℃ / h and keep it warm for 7-10h, then immerse it in quenching liquid and cool it to below 380℃, then slowly cool it to room temperature at a cooling rate of 1-3℃ / s; during quenching, the refractory insulation layer wraps the hammer mounting end 1 and exposes the quenching liquid surface, and only the hammer working end 2 is quenched; after quenching, a double hardness alloy hammer is obtained.

[0040] In one embodiment, the quenching liquid in step (4) is water or PAG quenching agent with a temperature not higher than 30°C.

[0041] Normalizing: Heat the hammer head casting at 40-45°C / h to 820-880°C, hold for 7-9 hours, and then air cool to room temperature. The purpose of normalizing is to homogenize the casting's microstructure, eliminate defects such as network carbides, and prepare the structure for the subsequent double quenching heat treatment. The heating rate and holding time are carefully selected to ensure uniform heating throughout the casting and sufficient microstructural transformation. Air cooling to room temperature produces a finer pearlite structure, providing a suitable starting structure for subsequent quenching.

[0042] The double quenching heat treatment begins with heating to 550-600°C at a rate of 41-46°C / h and holding for 6.5-9 hours. This heating and holding phase serves as a preheat treatment, reducing thermal stress during subsequent heating and ensuring proper dissolution and uniform distribution of carbides in the alloy. The alloy is then heated to 800-880°C at a rate of 45-50°C / h, held for 7.0-10 hours, and then immersed in a quenching liquid and cooled to no higher than 200°C. Heating in this temperature range allows the austenite in the alloy to fully dissolve carbon and alloying elements, improving its stability. The holding time is long enough to ensure compositional homogenization. Rapid cooling, using a quenching liquid of water or a PAG quenchant at no higher than 30°C, results in a martensitic structure. The hammer is then heated to 670-700°C at a rate of 41-46°C / h. After holding for 7-10 hours, it is immersed in a quenching liquid and cooled to below 380°C. It is then slowly cooled to room temperature at a cooling rate of 1-3°C / s. The hammer is then heated to 670-700°C for a second quenching process. The first stage involves rapid cooling to near the martensite transformation temperature, which results in lamellar bainite near the surface of the hammer during continuous cooling. The subsequent slow cooling allows the martensite transformation to proceed over a longer period of time, resulting in a mixed structure of bainite and martensite within the hammer. The final microstructure at 20 mm below the surface of the hammer's working end 2 consists of 75-80% martensite by volume, with the remainder being bainite. The microstructure at 35 mm below the surface of the hammer's working end 2 consists of 30-40% lath bainite, 25-40% martensite, and the remainder being retained austenite.

[0043] In addition, during the secondary quenching treatment, the steel is slowly cooled to room temperature at a cooling rate of 1 to 3°C / s. Due to the slow cooling rate, the thermal stress and phase change stress concentration caused by the excessively fast cooling rate of the surface layer can be avoided. Self-tempering will occur inside the hammer head, eliminating the tempering process and simplifying the production process. At the same time, a gradient hardness is formed at the working end 2 of the hammer head, with the hardness gradually decreasing from the surface to the core and the toughness gradually increasing.

[0044] When immersed in the quenching liquid, the hammer head mounting end 1 is wrapped with a refractory insulation layer and exposed to the quenching liquid surface. Only the hammer head working end 2 is quenched. This ensures that the working end 2 obtains high-hardness martensite and bainite structures, while the mounting end 1 maintains good toughness due to not quenching.

[0045] The embodiments of the present invention are described in detail below. The hammer components of Examples 1 to 3 of the present invention and Comparative Examples 1 to 2 are shown in Table 1.

[0046] Table 1: Hammer components (mass percentage) of Examples 1 to 5 and Comparative Examples 1 to 2

[0047] The preparation method adopted in the embodiment is as follows: A method for preparing a double-hardness alloy hammer head comprises the following steps: (1) The alloy raw materials are smelted, deoxidized and deslagging in a vacuum induction medium frequency furnace to obtain molten steel; (2) pouring the molten steel into the sand mold and cooling it to obtain the hammer head casting; (3) Normalizing heat treatment: heat the hammer head casting to 820-880℃ at 40-45℃ / h, keep warm for 7-9h, and air cool to room temperature; (4) Double quenching heat treatment: heat the hammer casting to 550-600℃ at a rate of 41-46℃ / h and keep it warm for 6.5-9h, then heat it to 800-880℃ at a rate of 45-50℃ / h and keep it warm for 7.0-10h, then immerse it in quenching liquid and cool it to no more than 200℃; heat it to 670-700℃ at a rate of 41-46℃ / h and keep it warm for 7-10h, then immerse it in quenching liquid and cool it to below 380℃, then slowly cool it to room temperature at a cooling rate of 1-3℃ / s; during quenching, the refractory insulation layer wraps the hammer mounting end 1 and exposes the quenching liquid surface, and only the hammer working end 2 is quenched; after quenching, a double hardness alloy hammer is obtained.

[0048] The quenching liquid in step (4) is water or PAG quenching agent at a temperature not higher than 30°C.

[0049] The process parameters used in the preparation methods of Examples 1 to 5 of the present invention and Comparative Examples 3 to 4 are shown in Table 2.

[0050] Table 2: Process parameters used in the preparation methods of Examples 1 to 5 and Comparative Examples 3 to 4

[0051] Comparative Example 1 and Comparative Example 2 are prepared in the same manner as in Example 4 except that the components are different from those in Example 4.

[0052] The components of Comparative Example 3 are the same as those of Example 4. The difference between the preparation method and Example 4 is that the double quenching heat treatment parameters are slightly different, as shown in Table 2.

[0053] The components of Comparative Example 4 are the same as those of Example 4. The difference in the preparation method from Example 4 is that the double quenching heat treatment is different, and only one quenching is performed before air cooling to room temperature. See Table 2 for details.

[0054] The mechanical properties of the examples and comparative examples were tested, and the results are shown in Table 3. Table 3: Mechanical properties data of examples and comparative examples

[0055] From Table 3, it can be found that the hardness and tensile strength of the working end of the double hardness hammer prepared by the present invention are reduced at 20mm compared with 35mm, but the impact toughness and elongation are improved. At 20mm from the working end of the hammer, the tensile strength is 1800-1900MPa, the hardness is 57-61HRC, and the impact toughness is 8-13J / cm 2 , elongation 4.6~6.1%; tensile strength 1675~1740MPa at 35mm from the working end surface of the hammer head, hardness 43~48HRC, impact toughness 21~28J / cm 2 , elongation 10.2~15.6%.

[0056] The hammer head mounting end also has good mechanical properties, with a tensile strength of 1264-1350 MPa, a hardness of 45-48 HRC, and an impact toughness of 19-25 J / cm 2 , elongation 11.2~15.4%.

[0057] It can be seen that the present application can simultaneously ensure that the hammer head has matching hardness and toughness at different thicknesses at the working end by adjusting the components and optimizing the proportion relationship between the components, and also has good toughness and strength at the installation end of the hammer head.

[0058] Compared with Examples 1 to 3, Examples 4 and 5 further optimize Mn: (C+0.3Si)=2.8~3.1; 0.5Mn+Mo=1.8~2; Cr / Mo=3.5~4.5, which can better play the coordination role of alloying elements, and have better hardness and strength as well as impact toughness and elongation performance.

[0059] In comparative examples 1 and 2, the components of the hammer head are adjusted, and the functions of the components cannot be fully exerted and coordinated, and the hardness and strength of the working end and the mounting end of the hammer head as well as the impact toughness and elongation performance are significantly reduced.

[0060] Comparative Examples 3 and 4 changed the heat treatment process parameters and could not obtain the desired ratio of martensite and bainite structures, resulting in a significant decrease in the hardness and strength, impact toughness and elongation properties of the hammer working end.

[0061] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A double hardness alloy hammer head, characterized in that: Contains the following components by mass percentage: C 0.38~0.45%, Si 1.8~2.0%, Mn 2.5~3.0%, Cr 1.5~2.0%, Mo 0.4~0.7%, Ni 0.5~0.7%, V 0.08~0.15%, Nb 0.02~0.05%, Ti 0.02~0.03%, B 0.005~0.008%, rare earth La+Ce0.03~0.06%, P≤0.011%, S≤0.01%, the balance is Fe and unavoidable impurities; The hammer head includes a working end and a mounting end. The microstructure 20 mm below the surface of the working end of the hammer head includes 75% to 80% martensite by volume, and the rest is bainite; the microstructure 35 mm below the surface of the working end of the hammer head includes 30% to 40% lath bainite, 25% to 40% martensite, and the rest is retained austenite by volume.

2. A double-hardness alloy hammer head according to claim 1, characterized in that: The mass ratio of C, Si and Mn satisfies Mn: (C+0.3Si)=2.8~3.1; 0.5Mn+Mo=1.8~2; Cr / Mo=3.5~4.

5.

3. The double-hardness alloy hammer head according to claim 1, characterized in that: The thickness of the hammer head is 350-450 mm.

4. A double-hardness alloy hammer head according to claim 3, characterized in that: The tensile strength at 20 mm from the working end surface of the hammer head is 1800-1900 MPa, the hardness is 57-61 HRC, and the impact toughness is 8-13 J / cm 2 , elongation is 4.6~6.1%; the tensile strength at 35mm from the working end of the hammer head is 1675~1740MPa, the hardness is 43~48HRC, and the impact toughness is 21~28J / cm 2 , elongation is 10.2~15.5%; the tensile strength at the hammer head installation end is 1264~1350MPa, the hardness is 45~48HRC, and the impact toughness is 19~25J / cm 2 , the elongation is 11.2~15.6%.

5. The double-hardness alloy hammer head according to claim 1, characterized in that: It contains the following components by mass percentage: C 0.4%, Si 1.9%, Mn 2.8%, Cr 1.8%, Mo 0.5%, Ni: 0.5%, V 0.13%, Nb 0.05%, Ti0.02%, B 0.007%, rare earth La+Ce 0.06%, P 0.005%, S 0.006%, and the balance is Fe and unavoidable impurities.

6. The method for preparing a double-hardness alloy hammer according to any one of claims 1 to 5, characterized in that: The steps include: (1) The alloy raw materials are smelted, deoxidized and deslagging in a vacuum induction medium frequency furnace to obtain molten steel; (2) pouring the molten steel into the sand mold and cooling it to obtain the hammer head casting; (3) Normalizing heat treatment: heat the hammer head casting to 820-880℃ at 40-45℃ / h, keep warm for 7-9h, and air cool to room temperature; (4) Double quenching heat treatment: heat the hammer casting to 550-600℃ at a rate of 41-46℃ / h and keep it warm for 6.5-9h, then heat it to 800-880℃ at a rate of 45-50℃ / h and keep it warm for 7.0-10h, then immerse it in quenching liquid and cool it to no more than 200℃; heat it to 670-700℃ at a rate of 41-46℃ / h and keep it warm for 7-10h, then immerse it in quenching liquid and cool it to below 380℃, then slowly cool it to room temperature at a cooling rate of 1-3℃ / s; during quenching, the refractory insulation layer wraps the installation end of the hammer and exposes the surface of the quenching liquid, and only the working end of the hammer is quenched; after quenching, a double hardness alloy hammer is obtained.

7. The method for preparing a double-hardness alloy hammer according to claim 6, characterized in that: In the step (4), the quenching liquid is water or PAG quenching agent not higher than 30°C.

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