Energy-saving mncr-series cold-forging steel and manufacturing method therefor

Abstract

Disclosed in the present invention is energy-saving MnCr-series cold-forging steel, which contains Fe and inevitable impurities, and further contains the following chemical elements in percentages by mass: C: 0.16-0.19%, Si: 0.10-0.30%, Mn: 1.0-1.3%, Cr: 0.80-1.10%, S: 0.01-0.02%, Al: 0.015-0.04% and N: 0.008-0.016%. Further disclosed in the present invention is a manufacturing method for the energy-saving MnCr-series cold-forging steel, which method comprises the steps of: smelting and casting; rolling of round steel; controlled cooling after rolling, involving: cooling the round steel to 350-450°C at a cooling speed of 8-12°C / s, and maintaining the temperature for 2-3 h; and annealing, involving: controlling the annealing temperature at 690-710°C.

Description

Energy-saving MnCr cold forging steel and manufacturing method thereof Technical Field

[0001] The present invention relates to a steel material and a manufacturing method thereof, in particular to a cold forged steel and a manufacturing method thereof. Background Art

[0002] Cold forging is a forming process performed below the recrystallization temperature of a material, a forging process performed below the recovery temperature. In production, forging performed without heating the blank is commonly referred to as cold forging. Cold forging materials are primarily aluminum and some alloys, copper and some alloys, low-carbon steel, medium-carbon steel, and low-alloy structural steel, which have low deformation resistance and good plasticity at room temperature. Cold forgings offer excellent surface quality and high dimensional accuracy, and can replace some cutting processes. Cold forging strengthens metals and increases component strength. Replacing hot forging with cold forging can reduce environmental pollution in industrial production. However, cold forging places high demands on the plasticity of the material being forged.

[0003] Conventional steel for cold forging is usually hot rolled, cooled to room temperature, and finally spheroidized annealing. Spheroidized annealing takes more than ten hours or even dozens of hours, which consumes a lot of time and energy.

[0004] Based on this, in response to the defects and shortcomings in the existing technology, the present invention hopes to obtain a cold forging steel with excellent plasticity and cold working properties, which can be effectively used in the cold forging production of gears, and can effectively save energy and reduce environmental pollution compared to conventional cold forging materials during the production process. Summary of the Invention

[0005] One of the objectives of the present invention is to provide an energy-saving MnCr-based cold-forged steel. This cold-forged steel, through rational chemical composition design and coordinated processing, not only achieves excellent plasticity and cold working properties, but also eliminates the spheroidizing annealing process during production. Furthermore, cold-forged round steel eliminates the need for heating and normalizing parts prior to hot forging, thereby significantly saving energy and reducing environmental pollution. In the present invention, cold-forged steel refers to steel suitable for cold forging.

[0006] To achieve the above object, the present invention provides an energy-saving MnCr-based cold forging steel, which contains Fe and unavoidable impurities, and further contains the following chemical elements in the following mass percentages:

[0007] C: 0.16 to 0.19%, Si: 0.10 to 0.30%, Mn: 1.0 to 1.3%, Cr: 0.80 to 1.10%, S: 0.01 to 0.02%, Al: 0.015 to 0.04%, N: 0.008 to 0.016%.

[0008] Furthermore, in the energy-saving MnCr-based cold forging steel of the present invention, the mass percentage of each chemical element is:

[0009] C: 0.16-0.19%, Si: 0.10-0.30%, Mn: 1.0-1.3%, Cr: 0.80-1.10%, S: 0.01-0.02%, Al: 0.015-0.04%, N: 0.008-0.016%; the balance is Fe and other inevitable impurities.

[0010] In the energy-saving MnCr cold forging steel of the present invention, the design principles of the chemical elements are as follows:

[0011] C: In the energy-saving MnCr-based cold-forging steel described in this invention, element C ensures good hardenability and adequate strength, which helps improve the wear resistance of finished parts. However, excessive C addition to steel is not recommended. Increasing the C content in the steel increases the material's hardness and leads to excessive strength during subsequent processing, increasing mold wear during cold forging and raising downstream processing costs. Therefore, the mass percentage of C in the energy-saving MnCr-based cold-forging steel described in this invention is controlled between 0.16% and 0.19%.

[0012] Si: In the energy-saving MnCr-based cold-forged steel described in this invention, Si is a ferrite-forming element with a strong solid-solution strengthening effect, effectively increasing the steel's strength. However, it's important to note that the Si content in the steel should not be too high, as excessive Si content can reduce the steel's plasticity. Therefore, in the energy-saving MnCr-based cold-forged steel described in this invention, the mass percentage of Si is controlled between 0.10 and 0.30%.

[0013] Mn: In the energy-saving MnCr-based cold-forging steel described herein, when a certain amount of S is present, Mn readily reacts with S to form a plastic MnS, effectively enhancing chip breaking and cutting performance during subsequent gear finishing. However, the Mn content in the steel should not be too high. Excessive Mn content can lead to increased segregation in the steel, compromising its structural uniformity. Therefore, in the energy-saving MnCr-based cold-forging steel described herein, the mass percentage of Mn is controlled between 1.0 and 1.3%.

[0014] Cr: In the energy-saving MnCr cold forging steel described in the present invention, an appropriate amount of Cr element can be added to the steel. The diffusion rate of Cr element in austenite is relatively low, and it can hinder the diffusion of C. It can inhibit the diffusion-type phase transformation of steel, which is beneficial to the stability of austenite, and shifts the C curve of the steel to the right, reducing the critical cooling rate. However, it should be noted that the Cr content in the steel should not be too high. If it is too high, coarse carbides will be formed, which will deteriorate the cold deformation performance. Based on this, in the energy-saving MnCr cold forging steel described in the present invention, the mass percentage of Cr element is controlled between 0.80 and 1.10%.

[0015] S: In the energy-saving MnCr-based cold-forging steel described herein, S combines with Mn to form MnS, improving cutting performance. Adding an appropriate amount of S to the steel can prevent tool sticking during subsequent finishing. Therefore, the mass percentage of S in the energy-saving MnCr-based cold-forging steel described herein is controlled between 0.01% and 0.02%.

[0016] Al: In the energy-saving MnCr-based cold-forged steel described in the present invention, the Al element can effectively reduce the oxygen content in the steel during the steelmaking process. The Al element can also form fine AlN compounds and precipitate, refining the austenite grains and improving the plasticity of the material. However, it should be noted that the Al content in the steel should not be too high. If the Al content in the steel is too high, it will lead to the formation of larger Al oxides and larger Class B inclusions, which will deteriorate the fatigue properties of the steel. Based on this, in the energy-saving MnCr-based cold-forged steel described in the present invention, the mass percentage of the Al element is controlled between 0.015 and 0.04%.

[0017] N: In the energy-saving MnCr-based cold-forged steel described herein, N forms AlN, which refines the austenite grains. However, excessive N content in the steel can lead to increased concentrations at defects and the formation of coarse nitride precipitates, which can affect the fatigue life of the steel. Therefore, in the energy-saving MnCr-based cold-forged steel described herein, the mass percentage of N is controlled between 0.008% and 0.016%.

[0018] Furthermore, in the energy-saving MnCr-based cold forging steel of the present invention, among other inevitable impurities, the content of each impurity element satisfies at least one of the following conditions: P≤0.015%, O≤0.003%.

[0019] It should be noted that in the above technical solution of the present invention, P and O are both unavoidable impurity elements. Under the premise of technical conditions allowing, the content of impurity elements in the steel should be controlled to be as low as possible.

[0020] Phosphorus (P) in steel can segregate at grain boundaries, reducing the binding energy and worsening the steel's plasticity. Furthermore, P combines with Fe to form the hard and brittle Fe3P phase, which can cause cold brittleness during cold working, leading to poor plasticity and, when subjected to impact loads, intergranular fracture, resulting in large cleavage planes. Therefore, to prevent increased brittleness, the P content in the energy-saving MnCr-based cold-forging steel described herein can be controlled to ≤ 0.015% by mass.

[0021] O: Impurity element O can form Al2O3 with Al in steel. Therefore, to ensure uniformity of steel structure, the mass percentage of O in the energy-saving MnCr cold forging steel of the present invention can be controlled to be O≤0.0030%.

[0022] Furthermore, in the energy-saving MnCr-based cold-forged steel according to the present invention, the microstructure matrix is ​​ferrite, and carbide precipitates are present on the ferrite matrix, wherein the carbide precipitates having an aspect ratio of no more than 4 account for no less than 85% of the total carbide precipitates. In some embodiments, in the energy-saving MnCr-based cold-forged steel according to the present invention, the carbide precipitates having an aspect ratio of no more than 4 account for 85% to 100%, for example, 85% to 95%, of the total carbide precipitates.

[0023] The present invention achieves the performance sought by this application by obtaining a structure in which carbide precipitates with an aspect ratio of no more than 4 account for no less than 85% of all carbide precipitates. This is because lamellar structures, due to their layered structure, are susceptible to dislocation accumulation and subgrain refinement during deformation, exacerbating work hardening and leading to poor plasticity. This is detrimental to cold working and can easily cause cold forging cracking and die loss. Structures with an aspect ratio of no more than 4 can more effectively reduce obstacles to dislocation movement, as the gaps between these carbides allow dislocations to continue to move, thereby dispersing and alleviating dislocation accumulation, thereby maintaining good plastic deformation capacity. Therefore, within this range, the lower the aspect ratio and the higher the proportion, the more significant the improvement in the material's plasticity.

[0024] Furthermore, the energy-saving MnCr-based cold-forged steel described in the present invention has the following properties: a yield strength of 200-250 MPa, a tensile strength of 400-450 MPa, an elongation of 37% or greater, and a reduction of area of ​​66% or greater, for example, 68% or greater. In some embodiments, the yield strength of the energy-saving MnCr-based cold-forged steel described in the present invention is 200-250 MPa, for example, 210 MPa, 220 MPa, 230 MPa, or 240 MPa. In some embodiments, the tensile strength of the energy-saving MnCr-based cold-forged steel described in the present invention is 400-450 MPa, for example, 410 MPa, 420 MPa, 430 MPa, or 440 MPa. In some embodiments, the elongation of the energy-saving MnCr-based cold-forged steel described in the present invention is 37% to 50%, for example, 38%, 39%, 40%, 41%, 42%, 45%, or 47%. In some embodiments, the energy-saving MnCr-based cold-forged steel of the present invention has a cross-sectional reduction rate of 66% to 75%, for example, 67%, 68%, 69%, 70%, 71%, 72%, 73%, or 74%.

[0025] Another object of the present invention is to provide an energy-saving method for manufacturing MnCr-based cold-forged steel, which is easy to operate and has simple steps. The cold-forged steel produced by this manufacturing method has excellent plasticity and cold working properties and consumes low energy.

[0026] In order to achieve the above object, the present invention proposes a method for manufacturing energy-saving MnCr cold forging steel, which comprises the following steps:

[0027] smelting and casting;

[0028] rolled round steel;

[0029] Controlled cooling after rolling: Cool the round steel to 350-450℃ at a cooling rate of 8-12℃ / s and keep it at this temperature for 2-3h;

[0030] Annealing: Control the annealing temperature to 690-710℃.

[0031] In conventional cold forging steel production processes, natural cooling and spheroidizing annealing steps are often required after rolling round steel, and the spheroidizing annealing time often requires at least 20 hours.

[0032] Different from the prior art, the present invention adopts a new post-rolling controlled cooling and annealing process, eliminating the spheroidizing annealing process, thereby effectively reducing energy consumption and having the characteristics of short time consumption and energy saving.

[0033] In addition, the present invention controls the process conditions, especially the cooling and annealing process parameters, so that the cold forged steel produced by the manufacturing method of the present invention has a ferrite matrix structure and a structure of carbide precipitates with an aspect ratio of no more than 4 precipitated on the matrix structure, and the proportion of carbide precipitates with an aspect ratio of no more than 4 in the total number of carbide precipitates is no less than 85%, which effectively ensures that the cold forged steel of the present invention has good plasticity, eliminates the internal stress of the steel, and has good structural uniformity.

[0034] In the post-rolling controlled cooling step of the manufacturing method described in the present invention, the cooling rate is controlled between 8-12°C / s, which exceeds the critical cooling rate of bainite but does not reach the critical cooling rate of martensite. This allows bainite structure to be formed in the matrix, thereby ensuring that there is a large amount of distortion energy in the matrix, which can provide phase change energy for subsequent structural transformation in the subsequent annealing process, thereby facilitating the precipitation and spheroidization of carbides.

[0035] Furthermore, after extensive testing and analysis, the inventors determined that the Bs point (bainite transformation start temperature) of the energy-saving MnCr-based cold-forged steel described herein is approximately 550°C. Based on this, the cooling temperature can be controlled between 350°C and 450°C, ensuring that the matrix completes the bainite transformation while also reducing heating energy consumption during the subsequent annealing process.

[0036] Furthermore, in the annealing step of the method for manufacturing energy-saving MnCr-based cold-forged steel described in the present invention, the annealing time is 4-6 hours. It can be seen that this annealing time is much shorter than the conventional spheroidizing annealing time of more than 20 hours, thus significantly shortening the process time.

[0037] Furthermore, in the manufacturing method of the present invention, the steps of heating the cast slab and rolling the intermediate slab are further included between the smelting and casting steps and the round steel rolling step.

[0038] Furthermore, in the slab heating step, the slab heating temperature is controlled to be 1080-1120° C. In the slab heating step, the holding time can be 4-5 hours.

[0039] Furthermore, in the round steel rolling step of the manufacturing method described in the present invention, the billet (such as the intermediate billet or the continuous casting billet) is heated to 1150-1200°C and kept warm for 3-4 hours, and the finishing rolling temperature is controlled to be 980-1020°C.

[0040] Compared to conventional processes, this method utilizes a higher finishing temperature, which partially dissolves AlN in the austenite, reducing the pinning effect, coarsening the grains to a certain extent, and increasing the bainite transformation. However, during cooling, the precipitated AlN disperses at the grain boundaries, where it serves as nucleation sites for carbide precipitation. This shortens the incubation period for carbide nucleation and precipitation, thereby reducing annealing time and saving energy.

[0041] The energy-saving MnCr-based cold forged steel and its manufacturing method described in the present invention have the following advantages and beneficial effects compared to the prior art:

[0042] The presence of C, Mn, and Cr in solid solution in the matrix can cause lattice distortion, hindering the diffusion of C atoms during the spheroidization of the precipitated phase. From a macroscopic perspective, this requires extended heating time to achieve spheroidization. Cr is a carbide-forming element and can combine with C to form carbides that precipitate rapidly. Furthermore, nucleation is a critical step in the precipitation of carbides with an aspect ratio of no more than 4, and the presence of uniform nucleation sites in the matrix is ​​beneficial to this process. Therefore, the energy-saving MnCr-based cold forging steel described in the present invention fully utilizes the effects of various C, Mn, and Cr alloying elements on phase transformation and microstructure through reasonable chemical composition design. The present invention controls the Al and N contents to ensure the amount of AlN precipitation, accelerates the nucleation process, and increases the number of carbide precipitates with an aspect ratio of no more than 4. In combination with a specific controlled cooling process, the precipitation phase structure is uniformly dispersed and precipitated and grown, thereby forming a uniform ferrite matrix and a structure in which sufficient carbide precipitates with an aspect ratio of no more than 4 are precipitated on the matrix. This ensures that the obtained cold forging steel has suitable strength, excellent plasticity and elongation, while effectively saving energy consumption.

[0043] The energy-saving MnCr-based cold forging steel disclosed herein has good plasticity and cross-sectional reduction at low temperatures and excellent cold forging performance. The cold forging steel has a yield strength of 200-250 MPa, a tensile strength of 400-450 MPa, an elongation of 37% or greater, and a cross-sectional reduction of 66% or greater, for example, 68% or greater, exhibiting excellent plasticity and cold working properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG1 shows a microstructure photograph of the energy-saving MnCr-based cold-forged steel according to Example 3 of the present invention under an optical microscope.

[0045] FIG2 shows a SEM image of the energy-saving MnCr-based cold-forged steel according to Example 3 of the present invention. DETAILED DESCRIPTION

[0046] The energy-saving MnCr-based cold forged steel and the manufacturing method thereof according to the present invention will be further explained and illustrated below in conjunction with the accompanying drawings and specific embodiments. However, such explanation and illustration do not constitute an undue limitation to the technical solution of the present invention.

[0047] Examples 1-6 and Comparative Example 1

[0048] The energy-saving MnCr cold-forged steels of Examples 1-6 were all prepared by the following steps:

[0049] (1) Smelting and Casting: During the smelting process, an electric furnace or a converter can be used (Examples 1-3 used an electric furnace, and Examples 4-6 used a converter). Table 1 lists the chemical composition ratios of each Example. During the casting process, mold casting or continuous casting can be used (Examples 1, 3, and 4 used continuous casting, and Examples 2 and 5 used mold casting). Examples 1-5 were cast into 320 mm * 425 mm blooms, and Example 6 was directly cast into a 215 mm * 215 mm bloom by continuous casting.

[0050] (2) Heating of ingots and rolling of intermediate billets: The ingots of Examples 1-5 were hot-charged and sent into a heating furnace. The heating temperature of the ingots was controlled to be 1080-1120°C and kept warm for 4 hours. The ingots of Examples 1-5 were rolled into 215mm*215mm intermediate square billets.

[0051] (3) Rolling round steel: The intermediate billets prepared in Examples 1-5 and the continuously cast small square billets prepared in Example 6 were heated to 1150-1200°C and kept warm for 5 hours, and then rolled with a large deformation amount, and the finishing rolling temperature was controlled to be 980-1020°C. The final size (i.e., diameter) of the round steel obtained was 20-50 mm.

[0052] (4) Controlled cooling after rolling: After rolling, the round steel is cooled by blasting, the water volume is controlled, the air volume is set according to the finishing temperature, and the round steel is cooled to 350-450℃ at a cooling rate of 8-12℃ / s and kept warm for 2-3 hours.

[0053] (5) Annealing: Place the round steel into the annealing furnace for annealing, and control the annealing temperature to 690-710℃, the holding time to 4-6 hours, and then take it out of the furnace and air cool it.

[0054] The comparative cold forged steel of Comparative Example 1 was prepared by the following steps:

[0055] Comparative Example 1 uses 16MnCr5 cold forging material subjected to conventional spheroidizing annealing in the prior art. Table 1 lists the chemical composition ratios of Comparative Example 1. The conventional continuous furnace spheroidizing annealing process employed in Comparative Example 1 is as follows: the furnace is heated to 600°C. When the furnace temperature reaches 600°C, the material is controlled to enter the furnace and heated to 740°C over approximately one hour. The material is then controlled to maintain the temperature at 740°C for one hour. After the temperature is maintained at this temperature, the material is rapidly heated to 760°C and maintained for five hours. The material is then cooled to 740°C within one hour, maintained at 740°C for two hours, cooled to 700°C within one hour, maintained for six hours, cooled to 630°C over approximately two hours, maintained at this temperature for two hours, and removed from the furnace after the temperature is maintained.

[0056] It should be noted that compared to the comparative cold-forged steel of Comparative Example 1, produced using a conventional spheroidizing annealing process, the energy-saving MnCr-based cold-forged steels of Examples 1-6 of the present invention eliminate the spheroidizing annealing process during production. Furthermore, in subsequent applications, the cold-forged round steel can eliminate the need for pre-hot forging heating and normalizing when manufacturing parts. Therefore, compared to conventional processes, the present invention significantly shortens process time and effectively reduces energy consumption.

[0057] Table 1 lists the mass percentages of various chemical elements in the energy-saving MnCr-based cold forged steels of Examples 1-6 and the comparative cold forged steel of Comparative Example 1.

[0058] Table 1. (wt%, the balance is Fe and other inevitable impurities except P and O)

[0059] Accordingly, Table 2-1 and Table 2-2 list the specific process parameters of the energy-saving MnCr-based cold forging steel of Examples 1-6 in the above process steps.

[0060] Table 2-1.

[0061] Note: “ / ” in the above Table 2-1 indicates that the embodiment is directly cast into 215mm*215mm square billets without performing step (2).

[0062] Table 2-2.

[0063] The energy-saving MnCr-based cold-forged steels of Examples 1-6 and the comparative cold-forged steel of Comparative Example 1 were sampled respectively, and the microstructure of each example and comparative example was observed using a Zeiss metallographic microscope to determine the type of microstructure; the number and aspect ratio of carbide precipitates were observed using a scanning electron microscope (SEM).

[0064] Through microstructural observation, the inventors found that the energy-saving MnCr-based cold-forged steels of Examples 1-6, produced using the manufacturing method described herein, all exhibited ferrite microstructures with carbide precipitates within the ferrite matrix (including at grain boundaries and within grains). Among these carbide precipitates, those with an aspect ratio of no more than 4 accounted for no less than 85% of the total number of carbide precipitates. Among these carbide precipitates:

[0065] FIG1 shows a microstructure photograph of the energy-saving MnCr-based cold-forged steel according to Example 3 of the present invention under an optical microscope.

[0066] As can be seen from FIG1 , the microstructure of the energy-saving MnCr-based cold-forged steel of Example 3 of the present invention has a matrix of ferrite, and carbide precipitates are present both within the grains and at the grain boundaries of the ferrite.

[0067] FIG2 shows a SEM image of the energy-saving MnCr-based cold-forged steel according to Example 3 of the present invention.

[0068] As shown in FIG2 , most of the carbide precipitates have an aspect ratio of no more than 4, rather than long strip-shaped carbide precipitates.

[0069] In addition, the energy-saving MnCr cold-forged steels of Examples 1-6 and the comparative cold-forged steel of Comparative Example 1 were sampled again and subjected to relevant mechanical property tests. The obtained mechanical property test results are listed in Table 3. The relevant mechanical property test methods are as follows:

[0070] Tensile test: Under room temperature conditions, M16*128 threaded specimens were processed and tensile tests were performed on the sample steels of each embodiment and comparative example in accordance with the national standard GB / T228 to obtain data on the yield strength, tensile strength, elongation, and cross-sectional reduction rate of the energy-saving MnCr-based cold-forged steels of Examples 1-6 and the comparative cold-forged steel of Comparative Example 1.

[0071] Table 3 lists the mechanical property test results of the energy-saving MnCr-based cold-forged steels of Examples 1-6 and the comparative cold-forged steel of Comparative Example 1.

[0072] Table 3.

[0073] As shown in Table 3, the energy-saving MnCr-based cold-forged steels of Examples 1-6 of the present invention exhibit excellent comprehensive mechanical properties. The yield strength of each example ranges from 207 to 248 MPa, the tensile strength ranges from 408 to 448 MPa, the elongation is greater than or equal to 37%, and the reduction of area is greater than or equal to 66%.

[0074] Although the performance of comparative example 1 is similar to that of the embodiments of the present invention, it should be noted that comparative example 1 adopts a high-energy consumption and long-process manufacturing process, which cannot achieve the technical effect of mechanical properties that can be achieved by the present invention by using low energy consumption.

[0075] In summary, it can be seen that the present invention, through reasonable chemical composition design, fully utilizes the effects of various alloying elements on phase transformation and microstructure, and combines with a specific heat treatment process to obtain an energy-saving MnCr-based cold forging steel having a uniform ferrite matrix structure and a large number of carbide precipitates with an aspect ratio of no more than 4. It also has good plasticity and cross-sectional reduction rate at low temperatures and excellent cold forging performance.

[0076] In addition, the manufacturing method of the energy-saving MnCr-based cold forged steel described in the present invention has a short process, low energy consumption, and a wide process window, and can achieve batch commercial production on a bar production line.

[0077] In addition, the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0078] It should also be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples, and many similar variations are possible. Any variations that can be directly derived or conceived by those skilled in the art from the present disclosure are intended to fall within the scope of protection of the present invention.

Claims

1. An energy-saving MnCr-based cold forging steel containing Fe and unavoidable impurities, characterized in that: It also contains the following chemical elements in the following mass percentages: C: 0.16 to 0.19%, Si: 0.10 to 0.30%, Mn: 1.0 to 1.3%, Cr: 0.80 to 1.10%, S: 0.01 to 0.02%, Al: 0.015 to 0.04%, N: 0.008 to 0.016%.

2. The energy-saving MnCr cold-forged steel according to claim 1, characterized in that: The mass percentage of each chemical element is: C: 0.16-0.19%, Si: 0.10-0.30%, Mn: 1.0-1.3%, Cr: 0.80-1.10%, S: 0.01-0.02%, Al: 0.015-0.04%, N: 0.008-0.016%; the balance is Fe and other inevitable impurities.

3. The energy-saving MnCr cold forging steel according to claim 1 or 2, characterized in that: Among other inevitable impurities, the content of each impurity element satisfies at least one of the following conditions: P≤0.015%, O≤0.003%.

4. The energy-saving MnCr cold forging steel according to claim 1 or 2, characterized in that: The matrix of its microstructure is ferrite, and carbide precipitates are present on the ferrite matrix, wherein the carbide precipitates with an aspect ratio not exceeding 4 account for no less than 85% of the total carbide precipitates.

5. The energy-saving MnCr cold forging steel according to claim 1 or 2, characterized in that: Its performance meets the following requirements: yield strength of 200-250MPa, tensile strength of 400-450MPa, elongation ≥37%, and section shrinkage ≥66%.

6. The method for producing energy-saving MnCr cold forging steel according to any one of claims 1 to 5, characterized in that: It includes the steps of: smelting and casting; rolled round steel; Controlled cooling after rolling: Cool the round steel to 350-450℃ at a cooling rate of 8-12℃ / s and keep it at this temperature for 2-3h; Annealing: Control the annealing temperature to 690-710℃.

7. The manufacturing method according to claim 6, wherein: In the annealing step, the annealing time is 4-6 hours.

8. The manufacturing method according to claim 6 or 7, characterized in that: Between the smelting and casting steps and the round steel rolling step there are also steps: heating the cast strand and rolling the intermediate strand.

9. The manufacturing method according to claim 8, wherein: In the slab heating step, the slab heating temperature is controlled to be 1080-1120°C.

10. The manufacturing method according to claim 6, wherein: In the round steel rolling step, the billet is heated to 1150-1200°C and kept warm, and the finishing rolling temperature is controlled at 980-1020°C.

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