Post-forging heat treatment method for medium-high carbon Cr-Mo series hypoeutectoid alloy steel

Abstract

The invention discloses a post-forging heat treatment method of medium-high carbon Cr-Mo series hypoeutectoid alloy steel, and relates to the technical field of post-forging heat treatment of alloy steel, in particular to the post-forging heat treatment method of the medium-high carbon Cr-Mo series hypoeutectoid alloy steel. The method comprises the steps that 1, a steel ingot is forged and transferred into a soaking pit furnace at the temperature of 700-800 DEG C for soaking for more than or equal to 3 h; 2, the temperature of the forge piece is increased to 820-840 DEG C, and the temperature increasing speed is larger than or equal to 100 DEG C / h; 3, the temperature of the forge piece is increased to 870-890 DEG C again, and the temperature increasing speed is larger than or equal to 100 DEG C / h; 4, the forge piece is rapidly cooled to 300-360 DEG C; 5, the temperature is increased to 720-730 DEG C, and the temperature increasing speed is larger than or equal to 100 DEG C / h; 6, the temperature is reduced to 670-690 DEG C, and the cooling speed is smaller than or equal to 40 DEG C / h; and 7, the cooling speed is smaller than or equal to 40 DEG C / h, cooling is conducted till the temperature is smaller than or equal to 300 DEG C, and discharging and air cooling According to the method, components and structures of forgings are uniform, the grain size is fine and uniform, unsteady-state structures such as Widmannstatten structures and net-shaped secondary carbides distributed along the grain boundary are eliminated, meanwhile, the hydrogen content is reduced to be within the safety limit range, and spherical pearlite structures with dispersively distributed carbides are obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of post-forging heat treatment of alloy steel, and particularly to a post-forging heat treatment method for medium-high carbon Cr-Mo series hypoeutectoid alloy steel. Background Art

[0002] Forgings often need to undergo several heat treatments during production, and the heat treatment carried out after forging is called post-forging heat treatment. Heat treatment after forging of ingots can improve the structure and properties of forgings, enhance the homogenization level of chemical composition and structure, eliminate forging stress and defects, prevent the occurrence of white spots and hydrogen embrittlement, etc. At the same time, post-forging heat treatment can also enable forgings to obtain a structure close to the equilibrium state and good mechanical properties, preparing good structural conditions for the final performance heat treatment. In addition, post-forging heat treatment can also eliminate problems such as overheating and coarse grains that may exist in the structure during forging or heating. Through post-forging heat treatment, these structures can be adjusted and improved to obtain an ideal and controllable microstructure.

[0003] Due to the large size of the original ingot, slow crystallization; long forging time, small forging ratio, uneven deformation, slow heating rate and long holding time of forgings, etc., the austenite grains in some forging steels are coarse, and due to genetic reasons such as coarse liquid segregation carbides and other structures, the grains are often coarse and uneven. During ultrasonic flaw detection, there is no bottom wave reflection, and it is impossible to determine whether the forging meets the technical requirements. In addition, before forging, the ingot generally undergoes a high-temperature diffusion homogenization treatment aimed at eliminating liquid segregation carbides, network secondary carbides, composition segregation and coarse grains formed under the mechanism of fractional crystallization during the solidification of the ingot. During the high-temperature diffusion homogenization treatment, due to long-term holding at high temperature, coarse grains or mixed crystal phenomena often occur. Therefore, in post-forging heat treatment, coarse grains and mixed crystal phenomena are eliminated, so that the grains are fine and uniform and the carbides are dispersed in the matrix.

[0004] At present, the post-forging heat treatment of forgings generally adopted at home and abroad generally uses a post-forging heat treatment process of high-temperature annealing, aiming to refine grains and make the hydrogen in the steel diffuse out as much as possible, so as to obtain a structure close to the equilibrium state. However, this method cannot completely eliminate the coarse original grains, and a mixed crystal structure with coexisting coarse grains and fine grains may be formed after quenching, which will reduce the comprehensive performance of the material. At the same time, if the post-forging high-temperature annealing process is not properly formulated, such as when the heating temperature of post-forging high-temperature annealing is relatively low, due to the obvious tissue heredity of the non-steady state structure of alloy steel, the grains are not significantly refined during annealing. When the annealing holding time is short or the alloy content is high, the tissue transformation is also relatively slow and the tissue transformation is not sufficient. In addition, improper temperature control during the annealing process will also lead to an increase in tissue inhomogeneity, which will cause the phenomenon of no bottom wave in flaw detection. Summary of the Invention

[0005] The object of the present invention is to provide a post-forging heat treatment method for medium-high carbon Cr-Mo series hypoeutectoid alloy steel, so as to ensure that the composition and structure of the forgings are uniform, the grain size can be strictly controlled within the technical requirements, the grains are uniform and fine, at the same time, it can achieve the elimination of Widmanstätten structure, non-steady-state structures such as network secondary carbide distributed along the grain boundaries, reduce the hydrogen content to within the safety limit range, and obtain a globular pearlite structure with carbide dispersed distribution, etc.

[0006] The post-forging heat treatment method for medium-high carbon Cr-Mo series hypoeutectoid alloy steel provided by the present invention includes the following steps:

[0007] Step 1, after forging the ingot, it is transferred to a soaking furnace at a temperature of 700°C to 800°C for soaking, and the soaking time is ≥3h;

[0008] Step 2, after soaking heat treatment of the forging, it is heated to 820°C to 840°C for heat preservation, the heating rate is ≥100°C / h, and the heat preservation time is 8h to 12h;

[0009] Step 3, the forging is heated to 870°C to 890°C again, the heating rate is ≥100°C / h, and the re-heat preservation time is 15h to 20h;

[0010] Step 4, the forging is quickly cooled to 300°C to 360°C for heat preservation, and the heat preservation time is 5h to 8h;

[0011] Step 5, the forging is heated to 720°C to 730°C, the heating rate is ≥100°C / h, and the heat preservation time is 10h to 15h;

[0012] Step 6, the forging is cooled to 670°C to 690°C, the cooling rate is ≤40°C / h, and the heat preservation time is ≥7h;

[0013] Step 7, after the forging is cooled in the furnace to ≤300°C, it is taken out of the furnace and air-cooled.

[0014] Further, in Step 1, after forging the ingot, it is immediately transferred to a soaking furnace at the mid-line of A r3 ~A r1 with a temperature of 700°C to 800°C for soaking, and the soaking temperature is 750±10°C for heat preservation, and the heat preservation time is 4h to 6h.

[0015] Further, in Step 2, after soaking heat treatment of the forging, it is slowly heated to 20°C to 30°C above the A C3 temperature, the heating rate is ≥150°C / h, that is, it is heat-preserved at 830±10°C, and the heat preservation time is 8h to 10h.

[0016] Further, in Step 3, the forging heat-treated in Step 2 is heated to A C3Above about 80°C, the heating rate is ≥120°C / h, that is, the temperature is 880 ± 10°C, and the secondary holding time is 17 h to 18 h;

[0017] Furthermore, in step 4, the forging is rapidly cooled by high-pressure gas quenching to quickly cool the surface temperature of the forging to 320°C to 350°C for heat preservation treatment, and the heat preservation time is 7 h.

[0018] Furthermore, in step 5, the forging is heated to 20 to 30°C above the A C1 temperature, the heating rate is ≥130°C / h, that is, it is held between 720°C and 730°C, and the holding time is 13 h.

[0019] Furthermore, in step 6, the forging is further cooled to 10°C to 30°C or so below the A C1 temperature, the cooling rate is ≤30°C / h, that is, it is held at 680°C ± 10°C, and the holding time is 8 h to 10 h.

[0020] Furthermore, in step 7, after the forging is dehydrogenated, it is cooled in the furnace to ≤260°C and then taken out of the furnace for air cooling.

[0021] Furthermore, the C content of the forging is 0.42% to 0.47%; the Si content is 0.30% to 0.35%; the Mn content is 0.85% to 1.00%; the S content is 0.018% to 0.022%; the P content is ≤0.012%; the Cr content is 0.90% to 1.10%; the Mo content is 0.18% to 0.23%; the Al content is 0.015% to 0.020%.

[0022] Furthermore, the C content of the forging is 0.44% to 0.46%; the Si content is 0.32% to 0.34%; the Mn content is 0.89% to 0.92%; the S content is 0.019% to 0.021%; the P content is ≤0.011%; the Cr content is 0.96% to 1.04%; the Mo content is 0.19% to 0.21%; the Al content is 0.016% to 0.017%.

[0023] The post-forging heat treatment method of the medium-high carbon C-Cr-Mo series hypoeutectoid alloy steel provided by the present invention has the following beneficial effects:

[0024] 1. After the steel ingot of the present invention is forged, homogenizing annealing treatment is carried out, which can eliminate the phenomenon of coarse grains and homogenize the structure at the same time. At the same time, this temperature range is the ferrite equilibrium precipitation temperature range, and the equilibrium structure eliminating Widmanstätten structure is obtained through ferrite equilibrium precipitation annealing, and the structure of ferrite equilibrium precipitation is obtained.

[0025] 2. In the present invention, at A C3During the heat preservation process at a temperature 20°C to 30°C above the specified temperature, since the temperature is relatively low, the structure has not been fully austenitized, and there are many fine and insoluble precipitate particles present at the grain boundaries or within the grains. When the grain boundaries encounter obstacles from the precipitate particles during the pushing process, they bend, resulting in an increase in the grain boundary area to hinder grain boundary migration, pinning the grain boundaries and preventing the growth of austenite grains. During the subsequent long-term isothermal transformation and slow cooling processes, carbides in the steel precipitate in a fine and dispersed manner, obtaining a uniform ferrite and fine pearlite structure; at the same time, the original coarse grains are eliminated under the action mechanism of recrystallization, obtaining fine austenite grains.

[0026] 3. The present invention raises the temperature again to A C3 Heat preservation is carried out again at a temperature of 880 ± 10°C above the above temperature. Prolonged heat preservation at this temperature can fully dissolve the network secondary carbides precipitated along the grain boundaries during the forging process, and finer and more uniform austenite grains and a large number of dispersed undissolved cementite grains can be obtained.

[0027] 4. The present invention uses a rapid cooling method of high-pressure gas quenching to quickly cool the surface temperature of the forging, which can avoid the distribution of network secondary carbides along the grain boundaries due to too slow cooling rate of the forging; at the same time, a structure of bainite + carbide + a small amount of retained austenite is obtained; then during the low-temperature heat preservation process, carbon elements will further diffuse evenly, and at the same time, the quenching stress is gradually eliminated to avoid the generation of quenching cracks.

[0028] 5. The present invention slowly raises the temperature to A C1 Between 20°C and 30°C above the temperature, that is, heat preservation at 720°C to 730°C, can fuse the lamellar or strip-shaped carbides precipitated along the grain boundaries in the forging into granular carbides, achieving a spheroidizing effect.

[0029] 6. The present invention further slowly cools the temperature to A C1 Between 10°C and 30°C below the temperature, that is, cooling to 670°C to 690°C, can further spheroidize the structure, and at the same time further achieve structure recrystallization and precipitate fine and dispersed carbide phases to homogenize the structure. At the same time, this temperature range is also a temperature range with a relatively fast diffusion dehydrogenation rate for the forging, which is beneficial to the rapid and deep dehydrogenation of the forging.

[0030] After the present invention undergoes cooling - heating - reheating - rapid cooling - heating - cooling - slow cooling, it can ensure that the composition and structure of the forging are uniform, the grain size is uniformly stable within the technical requirements range, eliminate Widmanstätten structure, liquid segregation carbides, network secondary carbides distributed along the grain boundaries and other non-steady-state structures. At the same time, the hydrogen content is reduced to within the safety limit range, obtaining a globular pearlite structure with dispersed carbides. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings partially disclose specific embodiments of the present invention, wherein,

[0032] Figure 1 is the process curve diagram of the present invention;

[0033] Figure 2 is the grain refinement effect diagram of the post-forging heat treatment of the present invention;

[0034] Figure 3 is the carbide spheroidization effect diagram of the post-forging heat treatment of the present invention;

[0035] Figure 4 is the hydrogen content diagram of the post-forging heat treatment of the present invention;

[0036] Figure 5 is the performance index diagram of the post-forging heat treatment and performance heat treatment (quenching + high-temperature tempering) of the present invention;

[0037] Figure 6 is the mechanical property index diagram of the post-forging heat treatment of the present invention; Detailed implementation manners

[0038] Example 1:

[0039] As Figure 1 shown, the post-forging heat treatment method of medium-high carbon Cr-Mo series hypoeutectoid alloy steel provided by the present invention includes the following steps:

[0040] Step 1, after the ingot is forged, it is transferred to a soaking furnace at a temperature of 700°C to 800°C for soaking, and the soaking time is ≥ 3 h;

[0041] Step 2, after the forging is soaked and heat-treated, it is heated to 820°C to 840°C for heat preservation, the heating rate is ≥ 100°C / h, and the heat preservation time is 8 h to 12 h;

[0042] Step 3, the forging is heated to 870°C to 890°C again, the heating rate is ≥ 100°C / h, and the heat preservation time is 15 h to 20 h;

[0043] Step 4, the forging is cooled to 300°C to 360°C for heat preservation, and the heat preservation time is 5 h to 8 h;

[0044] Step 5, the forging is heated to 720°C to 730°C, the heating rate is ≥ 100°C / h, and the heat preservation time is 10 h to 15 h;

[0045] Step 6, the forging is cooled to 670°C to 690°C, the cooling rate is ≤ 40°C / h, and the heat preservation time is ≥ 7 h;

[0046] Step 7, after the forging is cooled to ≤ 300°C, it is taken out of the furnace and air-cooled.

[0047] Example 2:

[0048] The post-forging heat treatment method for medium-high carbon Cr-Mo series hypoeutectoid alloy steel provided by the present invention comprises the following steps:

[0049] Step 1: Immediately transfer the steel ingot to a soaking furnace at the midpoint of 700°C to 800°C of A r3 ~A r1 soak at a soaking temperature of 750 ± 10°C for 4h to 6h;

[0050] Step 2: Slowly heat the forgings after soaking treatment to 20°C to 30°C above the A C3 temperature at a heating rate of ≥150°C / h, i.e., soak at 830 ± 10°C for 8h to 10h;

[0051] Step 3: Heat the forgings heat-treated in Step 2 to about 80°C above A C3 at a heating rate of ≥120°C / h, i.e., at a temperature of 880 ± 10°C, and soak again for 17h to 18h;

[0052] Step 4: Rapidly cool the surface temperature of the forgings to 320°C to 350°C for heat preservation treatment at a rate of high-pressure gas quenching, and keep warm for 7h;

[0053] Step 5: Heat the forgings to 20 to 30°C above the A C1 temperature at a heating rate of ≥130°C / h, i.e., soak between 720°C and 730°C for 13h;

[0054] Step 6: Further cool the forgings to 10°C to 30°C below the A C1 temperature at a cooling rate of ≤30°C / h, i.e., soak at 680 ± 10°C for 8h to 10h;

[0055] Step 7: After dehydrogenating the forgings, cool them in the furnace to ≤260°C and then take them out of the furnace for air cooling.

[0056] Example 3:

[0057] This example starts from the microstructure transformation law of medium-high carbon Cr-Mo series hypoeutectoid high-strength and tough steel, takes the self-developed medium-high carbon Cr-Mo alloy steel S44SY as the research object, and deeply studies the post-forging heat treatment process of this steel type to obtain a microstructure with uniform organization, fine and uniform grains, and uniform carbide distribution.

[0058] The C content of the S44SY forging is 0.42% - 0.47%; the Si content is 0.30% - 0.35%; the Mn content is 0.85% - 1.00%; the S content is 0.018% - 0.022%; the P content is ≤0.012%; the Cr content is 0.90% - 1.10%; the Mo content is 0.18% - 0.23%; the Al content is 0.015% - 0.020%.

[0059] Step 1: Immediately transfer the ingot to a soaking furnace with a temperature in the middle line of A r3 ~A r1 (800°C - 700°C) for soaking. The soaking temperature is 750 ± 10°C for heat preservation, and the soaking time is at least 3 hours. Soaking annealing treatment in this temperature range can eliminate the phenomenon of coarse grains and homogenize the structure at the same time. Through the equilibrium precipitation annealing of ferrite, the equilibrium structure with Widmanstätten structure eliminated is obtained, and the structure of ferrite equilibrium precipitation is obtained.

[0060] Step 2: Slowly heat the forging after soaking treatment to a temperature 20°C - 30°C above A C3 for heat preservation. The heating rate is ≥110°C / h, that is, heat preservation at (830 ± 10°C), and the heat preservation time is 8 - 10 hours. During the heat preservation process at a temperature 20°C - 30°C above A C3 , the structure has not been fully austenitized, and there are many fine and insoluble precipitate particles at the grain boundaries or within the grains. When the grain boundaries encounter obstacles of precipitate particles during the pushing process, they bend, resulting in an increase in the grain boundary area to hinder grain boundary migration, playing a role in pinning the grain boundaries and hindering the growth of austenite grains. During the subsequent long-time isothermal transformation and slow cooling process, carbides in the steel precipitate in a fine and dispersed manner, obtaining a uniform ferrite and fine pearlite structure; at the same time, long-time heat preservation at this temperature can fully dissolve the network secondary carbides precipitated along the grain boundaries during forging, and at the same time, eliminate the original coarse grains under the action mechanism of recrystallization, obtaining a fine austenite structure.

[0061] Step 3: Heat the forging after the above heat treatment to about 880°C (880°C ± 10°C) above A C3 again. The heating rate is ≥110°C / h, and heat preservation is carried out for 15 - 20 hours again, and finer and more uniform austenite grains and a large number of dispersed undissolved cementite grains can be obtained.

[0062] Step 4: After the forging is treated as above, use the rapid cooling method of high-pressure gas quenching to quickly cool the surface temperature of the forging to 300°C - 350°C for heat preservation treatment. The high cooling rate of high-pressure gas quenching can avoid the distribution of network secondary carbides along the grain boundaries due to too slow cooling rate of the forging; at the same time, a structure of bainite + carbide + a small amount of retained austenite is obtained; then, keep it at 300°C - 350°C for 7 hours at low temperature. During the heat preservation process, carbon elements will diffuse more uniformly, and at the same time, the quenching stress will be gradually eliminated to avoid the generation of quenching cracks.

[0063] Step 5, slowly raise the temperature to A C1 Above the temperature of 20 °C to 30 °C, the heating rate ≥ 105 °C / h, that is, keep warm for 13 hours in the temperature range of 725 ± 5 °C. Keeping warm for a long time in this temperature range can melt the lamellar or strip carbides precipitated along the grain boundaries in the forging into granular carbides, achieving a spheroidizing effect.

[0064] Step 6, further slowly cool the temperature to A C1 To the following temperature of 10 °C to 30 °C, the cooling rate is controlled to be ≤ 35 °C / h, that is, keep warm at 680 °C ± 10 °C for at least 7 hours. Further spheroidize the structure, and at the same time further achieve recrystallization of the structure and precipitate fine and dispersed carbide phases to homogenize the structure. At the same time, this temperature range is also the temperature range where the diffusion dehydrogenation rate of the forging is the fastest, which is beneficial to the deep dehydrogenation of the forging.

[0065] Step 7, after dehydrogenation treatment, slowly cool at a cooling rate ≤ 30 °C / h until ≤ 300 °C, then take out of the furnace and air-cool.

[0066] As Figure 2 shown, the grain size of the S44SY forging is fine and uniform, and stably controlled at 6 - 9 grades. As Figure 3 shown, the S44SY forging achieves a good spheroidizing effect. As Figure 4 shown, the hydrogen content of the S44SY forging is stably controlled at 1 ppm and below. As Figure 5 shown, the Rm and Rp0.2 of the S44SY forging after quenching and tempering are much higher than the requirements of Rm ≥ 827 Mpa and Rp0.2 ≥ 517 Mpa in the delivery technical conditions. As Figure 6 shown, the mechanical property indexes such as elongation, reduction of area, V-notch impact energy, Brinell hardness, etc. of the S44SY forging all meet the technical requirements. Therefore, after cooling - heating - heating again - rapid cooling - heating - cooling - slow cooling in the present invention, it can ensure that the composition and structure of the forging are uniform, the grain size is uniformly stable within the technical requirements, eliminate non - steady - state structures such as Widmanstätten structure, liquid - phase carbide, and network secondary carbide distributed along the grain boundaries. At the same time, reduce the hydrogen content to within the safety limit range, and obtain a globular pearlite structure with dispersed carbides.

[0067] Example 4:

[0068] On the basis of Example 3, the C content of the S44SY forging is 0.44% - 0.46%; the Si content is 0.32% - 0.34%; the Mn content is 0.89% - 0.92%; the S content is 0.019% - 0.021%; the P content ≤ 0.011%; the Cr content is 0.96% - 1.04%; the Mo content is 0.19% - 0.21%; the Al content is 0.016% - 0.017%.

[0069] The above embodiments include, but are not limited to, any of the foregoing technical details, and should be broadly construed within the scope defined by the appended claims. Therefore, all changes and modifications falling within the scope of the claims or their equivalents shall be covered by the appended claims.

Claims

1. A post-forging heat treatment method for medium-high carbon Cr-Mo series hypoeutectoid alloy steel, characterized in that, It includes the following steps: Step 1: After forging the ingot, transfer it to a soaking furnace at a temperature of 700°C to 800°C for soaking, and the soaking time is ≥ 3 h; Step 2: After the soaking heat treatment of the forging, heat it up to 820°C to 840°C for heat preservation, the heating rate is ≥ 100°C / h, and the heat preservation time is 8 h to 12 h; Step 3: Heat the forging to 870°C to 890°C again, the heating rate is ≥ 100°C / h, and the heat preservation time is 15 h to 20 h; Step 4: Cool the forging to 300°C to 360°C for heat preservation, and the heat preservation time is 5 h to 8 h; Step 5: Heat the forging to 720°C to 730°C, the heating rate is ≥ 100°C / h, and the heat preservation time is 10 h to 15 h; Step 6: Cool the forging to 670°C to 690°C, the cooling rate is ≤ 40°C / h, and the heat preservation time is ≥ 7 h; Step 7: After the forging is cooled in the furnace to ≤ 300°C, take it out of the furnace and air-cool it.

2. The post-forging heat treatment method of the medium-high carbon Cr-Mo series hypoeutectoid alloy steel according to claim 1, characterized in that the steps In 1, the ingot is immediately transferred to A after forging r3 ~A r1 Soak in a soaking furnace on the midline with a temperature of 700°C to 800°C, soak at a temperature of 750 ± 10°C for heat preservation, and the heat preservation time is 4h to 6h.

3. The post-forging heat treatment method of the medium-high carbon Cr-Mo series hypoeutectoid alloy steel according to claim 1, characterized in that, In Step 2, after the forgings are all heat-treated, they are slowly heated to 20°C to 30°C above the A C3 temperature at a heating rate ≥150°C / h, i.e., they are held at 830 ± 10°C for a holding time of 8 h to 10 h.

4. The post-forging heat treatment method of medium-high carbon Cr-Mo series hypoeutectoid alloy steel according to claim 1, characterized in that, In step 3, the forging heat-treated in step 2 is heated up again to A C3 above about 80 °C, with a heating rate ≥ 120 °C / h, i.e., the temperature is 880 ± 10 °C, and the re-holding time is 17 h to 18 h.

5. The post-forging heat treatment method for medium-high carbon Cr-Mo series hypoeutectoid alloy steel according to claim 1, characterized in that, In Step 4, the surface temperature of the forging is quickly cooled to 320°C to 350°C by high-pressure gas quenching for heat preservation treatment, and the heat preservation is for 7 h.

6. The post-forging heat treatment method of the medium-high carbon Cr-Mo series hypoeutectoid alloy steel according to claim 1, characterized in that, Step 5: Heat the forging to 20 - 30 °C above the A C1 temperature at a heating rate of ≥ 130 °C / h, i.e., hold at a temperature between 720 °C and 730 °C for 13 h.

7. The post-forging heat treatment method for medium-high carbon Cr-Mo series hypoeutectoid alloy steel according to claim 1, characterized in that, Step 6, further cool the forging to temperature A C1 to the following temperature of about 10°C to 30°C, with a cooling rate ≤ 30°C / h, i.e., hold at 680°C ± 10°C for 8 h to 10 h.

8. The post-forging heat treatment method of the medium-high carbon Cr-Mo series hypoeutectoid alloy steel according to claim 1, characterized in that, Step 7: After dehydrogenating the forging, cool it in the furnace to ≤ 260°C, then take it out of the furnace and air-cool it.

9. The post-forging heat treatment method of the medium-high carbon Cr-Mo series hypoeutectoid alloy steel according to claim 1, characterized in that, The C content of the forging is 0.42% to 0.47%; the Si content is 0.30% to 0.35%; the Mn content is 0.85% to 1.00%; the S content is 0.018% to 0.022%; the P content is ≤ 0.012%; the Cr content is 0.90% to 1.10%; the Mo content is 0.18% to 0.23%; the Al content is 0.015% to 0.020%.

10. The post-forging heat treatment method for medium-high carbon C-Cr-Mo series hypoeutectoid alloy steel according to claim 9, characterized in that, The C content of the forging is 0.44% to 0.46%; the Si content is 0.32% to 0.34%; the Mn content is 0.89% to 0.92%; the S content is 0.019% to 0.021%; the P content is ≤ 0.011%; the Cr content is 0.96% to 1.04%; the Mo content is 0.19% to 0.21%; the Al content is 0.016% to 0.017%.

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