A cast steel and a method for producing and using the same

Abstract

The application provides a cast steel. The cast steel has the following weight percentages: C 0.24-0.30%, Si 0.4-0.6%, Mn 1.2-1.3%, Cr 0.5-0.65%, Mo 0.25-0.35%, Ni 0.6-0.8%, S ≤0.04%, P ≤0.04%, and the balance of Fe. The cast steel provided by the application has the following excellent performances: yield strength ≥ 870 MPa, tensile strength ≥ 900 MPa, low-temperature impact performance at-20 ℃ ≥ 100 J, and excellent welding performance, and fully meets the use requirements of cast steel connecting pieces for hydraulic supports. The application also provides a preparation method and application of the cast steel.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology, and particularly relates to a cast steel, its preparation method and application. Background Technology

[0002] In the coal mining industry, hydraulic supports are key equipment. Their core components, such as the sockets, connectors, and guide rails, are subjected to vertical pressure from the roof and alternating impact loads from falling coal and rock over long periods. This places stringent requirements on the comprehensive mechanical properties (especially strength, toughness, and low-temperature impact resistance) and weldability of the cast steel materials used. With the development of high-extraction hydraulic supports, the demand for support strength has increased significantly. This requires that the strength and ductility of the matching cast steel sockets be upgraded simultaneously to achieve performance matching.

[0003] Currently, cast steel materials mainly include ZG27SiMn and ZG30Cr06. While ZG27SiMn has good weldability, it lacks high strength and impact toughness, and is prone to cracking during production, making it difficult to meet the alternating impact load requirements of high-extraction supports. ZG30Cr06, a commonly used steel for coal mining machinery castings, has improved performance compared to ZG27SiMn, but in practical applications, it carries the risk of sudden brittle fracture due to a sharp drop in toughness at low temperatures.

[0004] Therefore, there is an urgent need to develop a cast steel with high strength, excellent plasticity and low-temperature toughness, good weldability and moderate cost to meet the working conditions of hydraulic supports with high mining height. Attached Figure Description

[0005] Figure 1 The image shows the metallographic structure of the cast steel after heat treatment in Example 1. Summary of the Invention

[0006] The purpose of this invention is to provide a low-cost cast steel with good comprehensive mechanical and weldability properties, as well as its preparation method and application.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a cast steel, wherein the cast steel has the following weight percentages: C 0.24~0.30%, Si 0.4~0.6%, Mn 1.2~1.3%, Cr 0.5~0.65%, Mo 0.25~0.35%, Ni 0.6~0.8%, S≤0.04%, P≤0.04%, with the balance being Fe, and satisfies: Ceq≤0.72, where Ceq=C+Mn / 6+(Cr+V+Mo) / 5+(Ni+Cu) / 15.

[0008] This invention provides a method for preparing the cast steel described in the above technical solution, the method comprising the following steps:

[0009] Step (1): Add materials according to the chemical composition ratio of the cast steel and smelt to obtain a melt. The chemical composition weight percentage of the cast steel is C 0.24~0.30%, Si 0.4~0.6%, Mn 1.2~1.3%, Cr 0.5~0.65%, Mo 0.25~0.35%, Ni 0.6~0.8%, S≤0.04%, P≤0.04%, and the balance is Fe;

[0010] Step (2): Add deoxidizer to the bottom of the ladle, pour the melt into the ladle for deoxidation and refining, and obtain refined melt;

[0011] Step (3): Cast the refined melt to obtain a casting;

[0012] Step (4): The casting is heat-treated by normalizing, quenching and tempering in sequence to obtain cast steel.

[0013] Preferably, the melting temperature in step (1) is 1600-1700℃.

[0014] Preferably, the deoxidation refining in step (2) is ladle refining; the deoxidizer is aluminum bar, and the mass of the deoxidizer accounts for 0.1 to 0.13‰ of the mass of the melt; the residual aluminum content in the refined melt is ≤0.09wt%.

[0015] Preferably, the casting temperature in step (3) is 1550-1600℃.

[0016] Preferably, the normalizing process in step (4) is 880°C, held for 120 minutes, and then air-cooled.

[0017] Preferably, the quenching process in step (4) is to quench at 890°C for 30 minutes and then remove from the furnace and quench in water to room temperature.

[0018] Preferably, the tempering process in step (4) is performed at 560℃±20℃, held for 2.5 hours, and then air-cooled.

[0019] Preferably, the cast steel has a tensile strength ≥900MPa, a yield strength ≥870MPa, and an impact toughness ≥100J at -20℃.

[0020] This invention provides the application of the cast steel as described above in the casting connectors of hydraulic supports.

[0021] The beneficial effects of this invention are:

[0022] This invention optimizes the composition of cast steel by adding Cr and Mo to improve hardenability, Ni to improve low-temperature toughness, and rationally controlling the content of elements such as Si and Mn. Combined with a specific preparation process, the material exhibits excellent performance in terms of strength, plasticity, and low-temperature impact toughness. By deoxidizing and refining aluminum bars and controlling the residual aluminum content, the purity of the melt is effectively improved. Combined with normalizing treatment, the grains are refined and the microstructure is homogenized, laying a good foundation for subsequent heat treatment. Quenching treatment enables the material to form strong microstructures such as martensite, significantly improving its strength and hardness. Tempering heat treatment can eliminate the internal stress generated by quenching and improve the toughness of the material. This not only ensures the stability of the cast steel microstructure but also ensures the stability of the machining dimensions of the hydraulic support casting connectors.

[0023] The application of the cast steel prepared by this invention in the field of casting connectors for hydraulic supports effectively solves the problems of insufficient strength and impact toughness, high cracking tendency of existing ZG27SiMn, and the problem of easy brittle fracture caused by the sudden drop in low-temperature toughness of ZG30Cr06. Compared with existing cast steel materials for hydraulic supports, the cast steel of this invention has the advantages of high strength, excellent plasticity and low-temperature toughness, good weldability, stable manufacturing process and moderate cost. It can better meet the working conditions of large mining height hydraulic supports bearing alternating impact loads and extend the service life of core components of hydraulic supports. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] This invention provides a cast steel with the following weight percentages: C 0.24-0.30%, Si 0.4-0.6%, Mn 1.2-1.3%, Cr 0.5-0.65%, Mo 0.25-0.35%, Ni 0.6-0.8%, S≤0.04%, P≤0.04%, with the balance being Fe, and satisfying: Ceq≤0.72, where Ceq=C+Mn / 6+(Cr+V+Mo) / 5+(Ni+Cu) / 15.

[0026] In this invention, the mass content of C is preferably 0.28%; the mass content of Si is preferably 0.5%; the mass content of Mn is preferably 1.2%; the mass content of Cr is preferably 0.6%; the mass content of Mo is preferably 0.28%; the mass content of Ni is preferably 0.7%; the mass content of S is preferably 0.025%; and the mass content of P is preferably 0.025%.

[0027] This invention provides a method for preparing the cast steel described in the above technical solution, comprising:

[0028] Step (1): Add materials according to the chemical composition ratio of the cast steel and smelt to obtain a melt. The chemical composition weight percentage of the cast steel is C 0.24~0.30%, Si 0.4~0.6%, Mn 1.2~1.3%, Cr 0.5~0.65%, Mo 0.25~0.35%, Ni 0.6~0.8%, S≤0.04%, P≤0.04%, and the balance is Fe;

[0029] Step (2): Add deoxidizer to the bottom of the ladle, pour the melt into the ladle for deoxidation and refining, and obtain refined melt;

[0030] Step (3): Cast the refined melt to obtain a casting;

[0031] Step (4): The casting is heat-treated by normalizing, quenching and tempering in sequence to obtain cast steel.

[0032] The present invention does not impose any special restrictions on the alloy raw materials. Those skilled in the art can select commonly used metal raw materials for batching according to the pre-obtained composition of the cast steel.

[0033] In this invention, the smelting is preferably carried out using a medium-frequency induction furnace.

[0034] In this invention, the deoxidation refining is ladle refining, and the deoxidizer is preferably pure aluminum bar; the mass of the aluminum bar is preferably 0.1 to 0.13% of the mass of the alloy liquid, more preferably 0.12%, and the residual aluminum content in the refined melt is ≤0.09wt%.

[0035] In this invention, the melting temperature during the melting process is preferably 1600-1700℃, more preferably 1620-1680℃, even more preferably 1640-1660℃, and most preferably 1650℃.

[0036] In this invention, the casting temperature during the casting process is preferably ≥1550℃, more preferably 1550~1600℃.

[0037] In this invention, the normalizing process temperature is 880℃, which effectively refines the grain structure of the material, eliminates compositional segregation formed during casting, and provides a uniform microstructure for subsequent quenching. If the normalizing temperature is too low, insufficient microstructure homogenization may occur; if the temperature is too high, coarse grains may be caused, affecting material properties. The holding time (min) of the normalizing process is equal to the effective thickness (mm) of the cast steel × the temperature coefficient, where the temperature coefficient is 1.5~3.5min / mm. In a specific embodiment of this invention, the holding time of the normalizing process is 120min, and the preferred cooling method after normalizing is air cooling.

[0038] In this invention, the quenching process temperature is 890℃. Choosing 890℃ for quenching ensures complete austenitization of the material, allowing carbon and alloying elements to fully dissolve in the austenite, thereby obtaining a high-strength martensitic structure after rapid cooling. This temperature guarantees hardenability while avoiding grain coarsening and deformation tendencies caused by excessively high temperatures. In a specific embodiment of this invention, the holding time for the quenching process is 30 minutes, after which the material is removed from the furnace and quenched in water to room temperature.

[0039] In this invention, the tempering process temperature is 560℃±20℃. Choosing 560℃±20℃ for tempering eliminates quenching stress while promoting the precipitation of alloy carbides, achieving an optimal balance between strength and toughness. This temperature range effectively avoids temper brittleness and prevents insufficient toughness due to excessively low tempering temperatures or strength reduction due to excessively high temperatures. In a specific embodiment of this invention, the holding time for tempering is 2.5 hours, and the preferred cooling method after tempering is air cooling.

[0040] In this invention, the tensile strength is ≥900MPa, the yield strength is ≥870MPa, and the impact toughness at -20℃ is ≥100J.

[0041] This invention provides the application of the cast steel described in the above technical solution in the casting connectors of hydraulic supports, specifically the application of the cast steel in the casting connectors of hydraulic supports operating at low temperatures below -20℃.

[0042] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments.

[0043] Example 1

[0044] Step (1): Add materials according to the chemical composition ratio of cast steel, and use medium frequency induction to melt to obtain melt. The melting temperature is 1650℃.

[0045] Step (2): The obtained melt is refined outside the ladle. 0.12wt% pure aluminum strips are added to the bottom of the ladle, and the melt is placed in the ladle for deoxidation and refining.

[0046] Step (3): Cast the refined melt to obtain a casting. The casting temperature during the casting process is 1600℃.

[0047] Step (4): The above castings are subjected to heat treatment by normalizing + quenching + tempering. The normalizing temperature is 880℃, and the castings are held for 120 minutes and then air-cooled. The quenching temperature is 890℃, and the castings are held for 30 minutes and then quenched in water to room temperature. The tempering temperature is 560℃, and the castings are held for 2.5 hours and then air-cooled. The samples taken with the furnace are used for mechanical property testing.

[0048] The cast steel prepared in Example 1 of this invention has the following composition: C: 0.28%, Si: 0.5%, Mn: 1.2%, Cr: 0.6%, Mo: 0.28%, Ni: 0.7%, P: 0.025%, S: 0.025%, with the balance being iron. Its metallographic structure is shown in [image missing]. Figure 1 .

[0049] After the heat treatment of the cast steel in this invention, strict control of the welding process parameters is still required in actual production to avoid cold and hot cracks that could affect product quality and reliability. The welding process for the cast steel includes three steps: preheating, welding the weld seam, and post-weld treatment. The cast steel dimensions are 360mm × 400mm × 25mm. Preheating refers to preheating in a heat treatment furnace at 138℃ for 30 minutes. The welding process parameters are as follows: 80% Ar + 20% CO2 argon-rich gas shielded welding is used, with a gas flow rate of 15 L / min, DCEP / + power supply electrode, and ER70-G welding wire. The chemical composition of the welding wire is: C: 0.077%, Si: 0.65%, Mn: 1.59%, Cr: 0.39%, Cu: 0.087%, V: 0.032%, Ti: 0.12%, P: 0.025%, S: 0.025%. The interpass temperature is controlled at 140-180℃, the welding current is 300-330A, the welding voltage is 28-30V, the welding speed is 30-35cm / min, and the weld structure consists of five layers and nine passes. The first layer is pass 1; the second layer is pass 2; the third layer includes passes 3 and 4; the fourth layer includes passes 5 and 6; and the fifth layer includes passes 7, 8, and 9. The welding process parameters for each pass are shown in Table 1. After welding, the weld is kept at 500℃ for 4 hours and then air-cooled.

[0050] Table 1. List of welding process parameters for cast steel in Example 1

[0051]

[0052] Example 2

[0053] Step (1): Add materials according to the chemical composition ratio of cast steel, and use medium frequency induction to melt to obtain melt. The melting temperature is 1600℃.

[0054] Step (2): The obtained melt is refined outside the ladle. 0.1wt% pure aluminum strips are added to the bottom of the ladle, and the melt is placed in the ladle for deoxidation and refining.

[0055] Step (3): Cast the refined melt to obtain a casting. The casting temperature during the casting process is 1550℃.

[0056] Step (4): The above castings are subjected to heat treatment by normalizing + quenching + tempering. The normalizing temperature is 880℃, and the castings are held for 120 minutes and then air-cooled. The quenching temperature is 890℃, and the castings are held for 30 minutes and then quenched in water to room temperature. The tempering temperature is 540℃, and the castings are held for 2.5 hours and then air-cooled. The samples taken with the furnace are used for mechanical property testing.

[0057] The cast steel prepared in Example 2 of this invention has the following composition: C: 0.30%, Si: 0.4%, Mn: 1.3%, Cr: 0.5%, Mo: 0.25%, Ni: 0.6%, P: 0.04%, S: 0.04%, with the balance being iron.

[0058] After the heat treatment of the cast steel in this invention, strict control of the welding process parameters is still required in actual production to avoid cold and hot cracks that could affect product quality and reliability. The welding process for cast steel includes three steps: preheating, welding the weld seam, and post-weld treatment. The cast steel dimensions are 360mm × 400mm × 25mm. Preheating refers to preheating in a heat treatment furnace at 138℃ for 30 minutes. The welding process parameters are: 80% Ar + 20% CO2 argon-rich gas shielded welding, gas flow rate of 15L / min, DCEP / + power supply electrode, ER70-G welding wire, and the chemical composition of the welding wire is: C: 0.077%, Si: 0.65%, Mn: 1.59%. The composition of the weld is as follows: Cr: 0.39%, Cu: 0.087%, V: 0.032%, Ti: 0.12%, P: 0.025%, S: 0.025%. The interpass temperature is controlled at 140-180℃, the welding current is 300-330A, the welding voltage is 28-30V, and the welding speed is 30-35cm / min. The weld structure consists of five layers and nine passes. The first layer is pass 1; the second layer is pass 2; the third layer includes passes 3 and 4; the fourth layer includes passes 5 and 6; and the fifth layer includes passes 7, 8, and 9. The welding process parameters for each pass are shown in Table 2. After welding, the weld is held at 500℃ for 4 hours and then air-cooled.

[0059] Table 2. List of welding process parameters for cast steel in Example 2

[0060] Example 3

[0061] Step (1): Add materials according to the chemical composition ratio of cast steel, and use medium frequency induction to melt to obtain melt. The melting temperature is 1700℃.

[0062] Step (2): The obtained melt is refined outside the ladle. 0.13wt% pure aluminum strips are added to the bottom of the ladle and the melt is placed in the ladle for deoxidation and refining.

[0063] Step (3): Cast the refined melt to obtain a casting. The casting temperature during the casting process is 1600℃.

[0064] Step (4): The above castings are subjected to heat treatment by normalizing + quenching + tempering. The normalizing temperature is 880℃, and the castings are held for 120 minutes and then air-cooled. The quenching temperature is 890℃, and the castings are held for 30 minutes and then quenched in water to room temperature. The tempering temperature is 580℃, and the castings are held for 2.5 hours and then air-cooled. The samples taken with the furnace are used for mechanical property testing.

[0065] The cast steel prepared in Example 3 of this invention has the following composition: C: 0.24%, Si: 0.6%, Mn: 1.25%, Cr: 0.65%, Mo: 0.35%, Ni: 0.8%, P: 0.03%, S: 0.03%, with the balance being iron.

[0066] After the heat treatment of the cast steel in this invention, strict control of the welding process parameters is still required in actual production to avoid cold and hot cracks that could affect product quality and reliability. The welding process for cast steel includes three steps: preheating, welding the weld seam, and post-weld treatment. The cast steel dimensions are 360mm × 400mm × 25mm. Preheating refers to preheating in a heat treatment furnace at 138℃ for 30 minutes. The welding process parameters are: 80% Ar + 20% CO2 argon-rich gas shielded welding, gas flow rate of 15L / min, DCEP / + power supply electrode, ER70-G welding wire, and the chemical composition of the welding wire is: C: 0.077%, Si: 0.65%, Mn: 1.59%. The composition of the weld is as follows: Cr: 0.39%, Cu: 0.087%, V: 0.032%, Ti: 0.12%, P: 0.025%, S: 0.025%. The interpass temperature is controlled at 140-180℃, the welding current is 300-330A, the welding voltage is 28-30V, and the welding speed is 30-35cm / min. The weld structure consists of five layers and nine passes. The first layer is pass 1; the second layer is pass 2; the third layer includes passes 3 and 4; the fourth layer includes passes 5 and 6; and the fifth layer includes passes 7, 8, and 9. The welding process parameters for each pass are shown in Table 3. After welding, the weld is held at 500℃ for 4 hours and then air-cooled.

[0067] Table 3. List of welding process parameters for cast steel in Example 3.

[0068]

[0069]

[0070] Comparative Example 1

[0071] The preparation method is basically the same as that in Example 1, except that the cast steel composition is: C: 0.28%, Si: 0.5%, Mn: 1.2%, Cr: 0.3%, Mo: 0.15%, Ni: 0.5%, P: 0.03%, S: 0.03%, with the balance being iron.

[0072] Test case

[0073] The mechanical properties of the cast steels prepared in Examples 1-3 and Comparative Example 1 were tested, and the results are shown in Table 4.

[0074] Mechanical properties and metallurgical effects were tested on the welded joints of cast steel in Examples 1-3. The results are shown in Table 5.

[0075] Table 4 shows the test results of the mechanical properties of the cast steel in the various embodiments and comparative examples of the present invention.

[0076]

[0077] Table 5 shows the results of mechanical property testing and metallurgical effect testing of welded joints in various embodiments of the present invention.

[0078]

[0079] As shown in Table 4, the cast steel in Examples 1-3 of this invention has a tensile strength ≥900MPa and a yield strength ≥870MPa, significantly higher than that of Comparative Example 1. This indicates that by optimizing the alloy composition and heat treatment process, the material strength is greatly improved, enabling it to withstand the high load requirements of hydraulic supports with large mining heights. As shown in Table 5, the cast steel welded joint meets the tensile strength standard, exhibits good low-temperature toughness, and in particular, the heat-affected zone is close to the surface level of the main body. There are no cracks on the surface or cross-section, the hardness distribution is uniform, and the welding process is reliable, fully meeting the usage requirements of hydraulic support connectors.

[0080] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A type of cast steel, characterized in that, The cast steel has the following weight percentages: C 0.24~0.30%, Si 0.4~0.6%, Mn 1.2~1.3%, Cr 0.5~0.65%, Mo 0.25~0.35%, Ni 0.6~0.8%, S≤0.04%, P≤0.04%, with the balance being Fe, and satisfies: Ceq≤0.72, where Ceq=C+Mn / 6+(Cr+V+Mo) / 5+(Ni+Cu) / 15; The cast steel has a tensile strength ≥900MPa, a yield strength ≥870MPa, and an impact toughness ≥100J at -20℃. The cast steel is prepared by a method comprising the following steps: Step (1): Add materials according to the chemical composition ratio of cast steel and smelt to obtain melt; Step (2): Add deoxidizer to the bottom of the ladle, pour the melt into the ladle for deoxidation and refining to obtain a refined melt; wherein the deoxidation and refining is ladle refining; the deoxidizer is aluminum bar, and the mass of the deoxidizer accounts for 0.1 to 0.13‰ of the mass of the melt; the residual aluminum content in the refined melt is ≤0.09wt%; Step (3): Cast the refined melt to obtain a casting; Step (4): The casting is heat-treated sequentially by normalizing, quenching, and tempering to obtain cast steel; wherein, the normalizing process temperature is 880℃, the holding time of normalizing process min = effective thickness of cast steel mm × temperature coefficient, wherein the temperature coefficient is 1.5~3.5min / mm, and air cooling is performed after holding; the quenching process is 890℃, and after holding for 30min, the casting is removed from the furnace and quenched in water to room temperature; the tempering process is 560℃±20℃, and after holding for 2.5 hours, the casting is air-cooled.

2. The cast steel according to claim 1, characterized in that, The melting temperature in step (1) is 1600-1700℃.

3. The cast steel according to claim 1, characterized in that, The casting temperature in step (3) is 1550-1600℃.

4. An application of the cast steel according to claim 1 in a casting connector in a hydraulic support.

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