Homogeneous forging process for large-specification Cr-Mo-V high alloy steel

Abstract

The invention relates to a homogeneous forging process of large-specification Cr-Mo-V high alloy steel, and belongs to the technical field of alloy steel preparation. Comprising the following steps: a, smelting to obtain steel ingots; b, the temperature of the steel ingot is gradually increased to 1250-1260 DEG C, and heat preservation is conducted; c, the steel ingot is cooled to 1170-1190 DEG C, heat preservation is conducted for 1-2 h, the steel ingot continues to be cooled to the initial forging temperature, axial compression deformation is conducted, and then the steel ingot is drawn to be 1540-2700 mm and returned to a furnace; d, the temperature is raised to 1250-1260 DEG C after remelting, and heat preservation is conducted; and e, the steel billet is cooled, and when the steel billet is cooled to the initial forging temperature, axial compression deformation is carried out, the steel billet is drawn to 1700-3700 mm, then axial compression deformation is carried out, and finish forging forming is carried out. According to the method, two-time high-temperature homogenization and two-time forging processes are alternately implemented, so that the compactness, isotropy and flaw detection quality of the material are remarkably improved. The problems that an existing technological process is complex, energy consumption is high, and efficiency is low are solved.

Description

TECHNICAL FIELD

[0001] The application relates to a homogenizing forging process of large-specification Cr-Mo-V high-alloy steel and belongs to the technical field of alloy steel preparation. BACKGROUND

[0002] A shield machine is an important way for tunnel construction, and in the construction process, the core cutter of the shield machine needs to withstand high stress impact, rock abrasive wear and underground water corrosion, and the service life of the cutter is crucial. Chromium-containing medium-high alloy hot work die steel is widely used in the cutter of the shield machine, and a conventional heat treatment process has a single temperature range, insufficient element diffusion, long high-temperature homogenization time, high energy consumption, and a forging process that is difficult to apply to large-size ingots, thereby restricting the improvement of the performance of the steel.

[0003] CN112391581A Hot work shield steel and preparation method thereof. The application provides a hot work shield steel, which comprises 0.48-0.58wt% of C, 0.80-1.20wt% of Si, 0.20-0.65wt% of Mn, 4.80-5.80wt% of Cr, 1.20-1.75wt% of Mo, 0.80-1.20wt% of V, 0.30-0.50wt% of Ni, 0.040-0.100wt% of Nb, and further limited contents of P, S, N, H and O; and the application also provides a preparation method of the hot work shield steel. The application helps to refine the grains and improve the mechanical properties of the hot work shield steel by adding the above alloy elements and adjusting the element contents. The hot work shield steel provided by the application still has high toughness under high hardness of 57HRC and is suitable for various common rock strata, including hard strata such as quartzite. The heat treatment temperature range of the method is single, which easily leads to insufficient element diffusion, especially for the high-melting-point element Mo, and the homogenization holding time is long, and the energy consumption is high.

[0004] CN108277431A A shield cutter for round steel and its manufacturing method. The chemical composition of the steel is as follows: C 0.65-0.75%, Si 0.90-1.10%, Mn 0.40-0.50%, Cr 3.00-4.00%, Mo 1.10-1.40%, V 1.20-1.50%, N 0.02-0.03%, S≤0.005%, P≤0.020%, and the rest is Fe and inevitable impurities. The manufacturing process is as follows: induction melting→casting into Φ(360-280)mm×(2200-2500)mm electrode rod→electroslag remelting into rectangular ingot with width×height×length≈(378-344)mm×(500-443)mm×(1100-900)mm→electroslag ingot annealing→three-way refining and uniformity and FM method forging into Φ(200-180)mm×(6500-5400)mm→heat treatment after forging. After quenching and tempering, the core hardness of the round steel for shield cutter reaches 60-61HRC, and the impact energy of the 10×10×55mm3 V-shaped notch specimen reaches 34-38J. The forging process is relatively complex, the production cycle is long, and multiple soaking is required, resulting in high energy consumption. SUMMARY

[0005] The technical problem to be solved by the present application is that the existing preparation process is complex, energy consumption is high, and efficiency is low.

[0006] The technical solution adopted by the present application to solve the technical problem is: a homogenizing forging process for large-size Cr-Mo-V high alloy steel, comprising the following steps: a. smelting a Cr-Mo-V high alloy steel ingot, the C content in the steel ingot is 0.48-0.53wt%, the V / C content ratio is 1.9-2.1, the Cr / Mo content ratio is 3.6-3.7, and the total content of Cr, Mo and V is 7.0-7.8wt%; b. heating the steel ingot to 600-650℃, holding for 4-5h, then heating to 840-860℃, holding for 2-4h, and then heating to 1250-1260℃, holding for 5-8h; c. cooling the steel ingot to 1170-1190℃, holding for 1-2h, and then continuing to cool to the initial forging temperature, applying 10-15% axial compression deformation, forging the cross section of the steel ingot into a square, and realizing 40-45% axial compression, and then lengthening to 1540-2700mm for remelting; d. controlling the remelting temperature at 1100-1150℃, holding for 10-14h, then heating to 1250-1260℃, holding for 15-20h; e. cooling the billet, holding at 1170-1190 DEG C for 1-2 hours, applying 45-50% axial compression deformation when it is lowered to the initial forging temperature, elongating to 1700-3700 mm, and then applying 40-45% axial compression deformation to finish forging.

[0007] In the above method, the size of the ingot in step a is: diameter 600-800 mm, length 1500-2000 mm.

[0008] In the above method, the furnace temperature uniformity after the terminal temperature is raised in step b is controlled within ±10 DEG C.

[0009] In the above method, the temperature difference of the core of the ingot after cooling in step c is ≤15 DEG C.

[0010] In the above method, the cross section is changed in step e as square-octagon-circle.

[0011] The beneficial effects of the present application are: the present method enhances the compactness of the steel material through two high-temperature homogenization and multiple upsetting and drawing treatments, eliminates small granular eutectic carbides, dissolves large granular eutectic carbides, and has qualified microstructure without obvious primary carbide precipitation. The good homogenization effect realizes the improvement of the transverse impact performance, and the impact toughness Aku value of the steel material is ≥16 J at a hardness of 55-59 HRC. The application will significantly prolong the service life of the cutter head of the shield machine, and ensure the efficient and safe advancement of tunnel engineering such as high-speed rail and subway. DETAILED DESCRIPTION

[0012] The present application will be further described below in combination with examples.

[0013] The technical solution of the present application is a homogenization forging process for large-size Cr-Mo-V high-alloy steel, which comprises the following steps: a. smelting a Cr-Mo-V high-alloy steel ingot, the C content in the ingot is 0.48-0.53 wt%, the ratio of V to C content is 1.9-2.1, the ratio of Cr to Mo content is 3.6-3.7, and the total content of Cr, Mo and V is 7.0-7.8 wt%; b. heating the ingot to 600-650 DEG C, holding for 4-5 hours, then raising the temperature to 840-860 DEG C, holding for 2-4 hours, and then raising the temperature to 1250-1260 DEG C, holding for 5-8 hours; c. cooling the ingot to 1170-1190 DEG C, holding for 1-2 hours, continuously cooling to the initial forging temperature, applying 10-15% axial compression deformation, forging the cross section of the ingot into square, and realizing 40-45% axial compression, then elongating to 1540-2700 mm for re-melting; d. controlling the re-melting temperature at 1100-1150 DEG C, holding for 10-14 hours, then raising the temperature to 1250-1260 DEG C, holding for 15-20 hours; e, the billet is cooled, and held at 1170-1190 °C for 1-2 h, and when it is lowered to the initial forging temperature, 45-50% axial compression deformation is applied, elongated to 1700-3700 mm, and then 40-45% axial compression deformation is applied to finish forging. Those skilled in the art can understand that in the heat treatment process of the ingot and the billet, the corresponding gradient temperature interval is set respectively, which promotes the full diffusion of elements, and at the same time, by adding a medium temperature interval, the total time length and energy consumption of the high temperature section are significantly reduced, and the risk of overburning is reduced. At the same time, it is proposed to alternately implement two high-temperature homogenization and two forging processes, which can improve the production efficiency while ensuring the uniformity of the steel, and reduce the energy consumption caused by multiple heating. The ingot of the process is mainly used as the raw material of the cutter head of the shield tunneling machine, and is essentially a chromium-containing medium-high alloy hot work die steel. If the carbon content is too low, the matrix hardness will be insufficient, and if it is too high, the toughness will not be enough, so in step a, the C content in the ingot is limited to 0.48-0.53wt%, and vanadium can refine the grains to further improve the toughness, but too high will reduce the thermal conductivity and impact toughness, so the ratio of V and C content is limited to 1.9-2.1. And Mo and V can precipitate fine carbides during tempering, which plays a role of secondary hardening, ensuring that the steel has high hardness and wear resistance; and if the chromium content is too low, the wear resistance, hardenability, high temperature performance and toughness will be insufficient, but too high will reduce the high temperature performance, so the ratio of Cr and Mo content in the ingot is preferably 3.6-3.7, and the total content of Cr, Mo and V is 7.0-7.8wt%. In step b, the ingot is heated to 600-650 °C, and held for 4-5 h, then heated to 840-860 °C, and held for 2-4 h to prevent excessive thermal stress from causing the ingot to crack. Continue to heat to 1250-1260 °C, control the furnace temperature uniformity to ±10 °C, and hold for 5-8 h to completely dissolve coarse VC. In step c, continue to cool to the initial forging temperature, and apply 10-15% axial compression deformation to induce recrystallization and refine the grains. In step d, the temperature of the reheat furnace is controlled at 1100-1150 °C, and held for 10-14 h, then heated to 1250-1260 °C, and held for 15-20 h to homogenize the ingot and the billet, and completely eliminate the eutectic carbides caused by segregation. Compared with the traditional process, the time ratio of the medium temperature section is >40%, which significantly reduces the total time length and energy consumption of the high temperature section, and reduces the risk of overburning. In step e, the billet is cooled, and held at 1170-1190 °C for 1-2 h to obtain a temperature field with a slightly lower surface temperature than the core temperature. When it is lowered to the initial forging temperature, 45-50% axial compression deformation is applied, elongated to 1700-3700 mm, the cross section is changed to square-octagonal-circular, and then 40-45% axial compression deformation is applied to finish forging. After multiple upsetting and drawing forging, the isotropy and flaw detection quality of the steel are significantly improved, and the ultrasonic inspection is carried out according to the GB / T4162-2008 standard, and the qualified level is A level.

[0014] Preferably, the size of the ingot in step a of the above method is: diameter 600-800 mm, length 1500-2000 mm. Those skilled in the art can understand that, Preferably, the furnace temperature uniformity after the terminal temperature rise in step b of the above method is controlled within ±10°C. Those skilled in the art can understand that, after continuously rising to 1250-1260°C, the furnace temperature uniformity is controlled within ±10°C, and the temperature is kept for 5-8 h to completely dissolve the coarse VC.

[0015] Preferably, the temperature difference between the core and the surface of the ingot after cooling in step c of the above method is ≤15°C. Those skilled in the art can understand that, in this process, the ingot is cooled to 1170-1190°C and kept for 1-2 h, and the temperature difference between the core and the surface needs to be ≤15°C to promote the formation of a core compressive stress state.

[0016] Preferably, the cross section is changed to square-octagon-circle in step e of the above method. Those skilled in the art can understand that, in order to further refine the grains, after elongation to 1700-3700 mm, the cross section is changed to square-octagon-circle for forging, so that after multiple upsetting and drawing forging, the isotropy and flaw detection quality of the steel are significantly improved.

[0017] Example 1 An ingot is obtained after smelting, with C content of 0.48wt%, V / C content ratio of 1.98, Cr / Mo content ratio of 3.63, and total content of Cr, Mo and V of 7.2wt%. The size of the ingot is: diameter 600 mm, length 1500 mm.

[0018] The ingot is kept at 600°C for 4 h, 840°C for 2 h, and 1250°C for 5 h, and the furnace temperature uniformity in the homogenization stage is controlled within ±10°C. In the cooling stage, the temperature is kept at 1170°C for 1 h, and the temperature difference between the core and the surface is 10°C. When the initial forging temperature is reached, 10% axial compression deformation is applied, the cross section of the ingot is forged to square, and 40% axial compression is achieved, and then the ingot is elongated to 1780 mm and re-melted. The re-melting temperature is controlled at 1100°C, and the temperature is kept for 10 h, and then the temperature is kept at 1250°C for 15 h. The billet is cooled and kept at 1170°C for 1 h, and when the initial forging temperature is reached, 45% axial compression deformation is applied, the billet is elongated to 2160 mm, the cross section is changed to square-octagon-circle, and then 40% axial compression deformation is applied, and the final forging is formed.

[0019] According to GB / T4162-2008 standard, the ultrasonic inspection is qualified, and the qualified level is A level. The microstructure is qualified, and there is no obvious primary carbide precipitation. The impact toughness Aku value of the steel at a hardness of 55-59HRC is 16J.

[0020] Example 2 The steel ingot is obtained by smelting, and has a C content of 0.5 wt%, a V / C content ratio of 2, a Cr / Mo content ratio of 3.69, and a total Cr, Mo and V content of 7.1 wt%. The steel ingot has a size of 700 mm in diameter and 1800 mm in length.

[0021] The steel ingot is kept at 620 ℃ for 4.5 h, at 850 ℃ for 3 h, and at 1255 ℃ for 6 h, and the furnace temperature uniformity in the homogenization stage is controlled to be ±10 ℃. In the cooling stage, the steel ingot is kept at 1180 ℃ for 1.5 h, and the core-surface temperature difference is 12 ℃. When the initial forging temperature is reached, 13% axial compression deformation is applied to forge the cross section of the steel ingot into a square shape and achieve 43% axial compression, and then the length of the steel ingot is elongated to 2050 mm for remelting. The remelting temperature is controlled to be 1120 ℃, and the steel blank is kept at 1120 ℃ for 11 h, and then kept at 1255 ℃ for 18 h. The steel blank is cooled, kept at 1180 ℃ for 1.5 h, and then elongated to 2500 mm when the initial forging temperature is reached, and the cross section is changed into a square shape, an octagonal shape and a circular shape in sequence, and then 43% axial compression deformation is applied to finish the forging.

[0022] The ultrasonic inspection is performed according to the GB / T4162-2008 standard, and the qualified level is A grade. The microstructure is qualified, and no obvious primary carbide is precipitated. The impact toughness Aku value of the steel at a hardness of 55-59 HRC is 17 J.

[0023] Example 3 The steel ingot is obtained by smelting, and has a C content of 0.52 wt%, a V / C content ratio of 2.02, a Cr / Mo content ratio of 3.64, and a total Cr, Mo and V content of 7.55 wt%. The steel ingot has a size of 800 mm in diameter and 2000 mm in length.

[0024] The steel ingot is kept at 650 ℃ for 5 h, at 860 ℃ for 4 h, and at 1260 ℃ for 8 h, and the furnace temperature uniformity in the homogenization stage is controlled to be ±10 ℃. In the cooling stage, the steel ingot is kept at 1190 ℃ for 2 h, and the core-surface temperature difference is 15 ℃. When the initial forging temperature is reached, 15% axial compression deformation is applied to forge the cross section of the steel ingot into a square shape and achieve 45% axial compression, and then the length of the steel ingot is elongated to 2340 mm for remelting. The remelting temperature is controlled to be 1150 ℃, and the steel blank is kept at 1150 ℃ for 14 h, and then kept at 1260 ℃ for 20 h. The steel blank is cooled, kept at 1190 ℃ for 2 h, and then elongated to 2920 mm when the initial forging temperature is reached, and the cross section is changed into a square shape, an octagonal shape and a circular shape in sequence, and then 50% axial compression deformation is applied to finish the forging.

[0025] The ultrasonic inspection is performed according to the GB / T4162-2008 standard, and the qualified level is A grade. The microstructure is qualified, and no obvious primary carbide is precipitated. The impact toughness Aku value of the steel at a hardness of 55-59 HRC is 17 J.

Claims

1. A homogeneous forging process for large-size Cr-Mo-V high-alloy steel, characterized in that... Includes the following steps: a. A Cr-Mo-V high-alloy steel ingot is obtained by smelting. The C content in the ingot is 0.48-0.53 wt%, the V to C ratio is 1.9-2.1, the Cr to Mo ratio is 3.6-3.7, and the total content of Cr, Mo, and V is 7.0-7.8 wt%. b. Heat the steel ingot to 600-650℃, hold for 4-5 hours, then raise the temperature to 840-860℃, hold for 2-4 hours, and continue to raise the temperature to 1250-1260℃, hold for 5-8 hours; c. Cool the steel ingot to 1170-1190℃, hold for 1-2 hours, continue cooling to reach the initial forging temperature, apply 10-15% axial compression deformation, forge the cross section of the steel ingot from round to square, and achieve axial compression of 40-45%, then draw it to 1540-2700mm and return it to the furnace. d. The temperature of the furnace is controlled at 1100-1150℃ and held for 10-14 hours. Then the temperature is raised to 1250-1260℃ and held for 15-20 hours. e. Cool the steel billet to 1170-1190℃ and hold it for 1-2 hours. When it drops to the initial forging temperature, apply 45-50% axial compression deformation and draw it to 1700-3700mm. Then apply 40-45% axial compression deformation to finally forge it.

2. The homogeneous forging process for large-size Cr-Mo-V high-alloy steel according to claim 1, characterized in that: The dimensions of the steel ingot in step a are: diameter 600-800mm and length 1500-2000mm.

3. The homogeneous forging process for large-size Cr-Mo-V high-alloy steel according to claim 1, characterized in that: In step b, the furnace temperature uniformity after terminal heating is controlled within ±10℃.

4. The homogeneous forging process for large-size Cr-Mo-V high-alloy steel according to claim 1, characterized in that: The temperature difference between the steel ingot core and the surface after cooling in step c is ≤15℃.

5. The homogeneous forging process for large-size Cr-Mo-V high-alloy steel according to claim 1, characterized in that: In step e, the cross-section is transformed from square to octagon to circle.