A method for producing a low carbon steel forging material

Abstract

This invention discloses a method for producing low-carbon steel forgings, comprising the following steps: (1) Smelting process, controlling the C content of low-carbon steel to be 0.17%-0.22%, S content to be 0.015%-0.025%, and Mn content to be at the upper limit; (2) Casting, controlling the casting temperature and casting speed, when the outdoor temperature is -8℃ to 20℃, controlling the superheat to be 55℃-60℃, casting in two batches; when the room temperature is 20℃ to 42℃, controlling the superheat to be 50℃-55℃, casting in a single batch; (3) After the steel ingot is cast and demolded, placing it in a container with a temperature ≥20℃. Slow cooling is performed in a slow cooling pit at 0℃ until the surface temperature is below 100℃ and then the steel ingot is removed from the pit; (4) The steel ingot is heated to 1220-1260℃ and the holding time of the steel ingot is determined according to the weight m of the steel ingot; (5) The forging deformation adopts the WHF wide anvil compaction method to directly draw and form the steel ingot; when the steel ingot is taken out of the heating furnace, the surface of the steel ingot is first lightly pressed 10mm, and then the main deformation is carried out by full anvil large reduction, with each deformation amount ≥20% and the forging ratio ≥3.5 until the steel ingot is formed; the method of the present invention improves the qualification rate and utilization rate of low carbon steel forgings and reduces production costs.

Description

Technical Field

[0001] This invention relates to the field of steel forging technology, and in particular to a method for producing low-carbon steel forgings. Background Technology

[0002] The low-carbon steels involved in this invention mainly include 070M20, C15, 16Mn, S355J2G3, 1018, 17CrNiMo6, and 16MnCrS5. These low-carbon steels are generally forged using red-hot ingots. While no defects are initially detected during the forging process, numerous cracks and longitudinal fissures develop as the deformation progresses. These cracks, with a depth of 20-40 mm and significant tearing, render the forged material unusable, causing substantial losses to the factory.

[0003] Low-magnification analysis of samples taken from the cracked forging revealed well-developed dendrites and general porosity at the crack site. Because the carbon content of this type of low-carbon steel falls within the peritectic reaction zone, a large amount of high-temperature ferrite is generated in the ingot during the early solidification stage. Therefore, a significant amount of high-temperature ferrite participates in the peritectic reaction (L + δ → γ, liquid phase + high-temperature ferrite → austenite), resulting in substantial linear shrinkage. This generates significant tensile stress on the surface of the ingot. If the ingot is immediately sent to the forging plant for heating before this surface tensile stress is fully released, the surface tensile stress is exacerbated, leading to cracks in the columnar region of the ingot.

[0004] Therefore, solving the problem of numerous cracks and longitudinal cracks that easily occur during the forging process of low-carbon steel, which have obvious tearing effects and lead to the direct scrapping of forging materials and cause great losses to the factory, is an urgent problem to be solved in the industry. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that a large number of cracks and longitudinal cracks easily occur in the current low-carbon steel forging production process, and the cracks have obvious tearing, which leads to the direct scrapping of forgings and causes great losses to the factory. The invention provides a method for producing low-carbon steel forgings.

[0006] The present invention provides a method for producing low-carbon steel forgings, comprising the following steps: (1) During the smelting process, control the C content of low carbon steel to be 0.16%-0.22%, S content to be 0.015%-0.025%, and Mn content to be taken as the upper limit of the range. Other components are smelted according to the component range required by the steel grade. (2) When pouring, control the pouring temperature and pouring speed. When the outdoor temperature is -8℃ to 20℃, control the superheat at 55℃ to 60℃ and pour in two batches. When the outdoor temperature is 20℃ to 42℃, control the superheat at 50℃ to 55℃ and pour in one batch. (3) After the steel ingot is cast and demolded, it is placed in a slow cooling pit with a temperature ≥200℃ for slow cooling. The cooling rate is controlled to be ≤30℃ / h. The steel ingot is slowly cooled until the surface temperature is below 100℃ before being removed from the pit. (4) Heat the steel ingot to 1220-1260℃ to ensure that the steel ingot is thoroughly heated and there are no uneven surfaces; the holding time of the steel ingot is determined according to the weight m of the steel ingot. If m < 4t, the holding time of the steel ingot at high temperature is 2.5-3.5h; if 4 ≤ m ≤ 6.5t, the holding time of the steel ingot at high temperature is 3.5-4h; if 7 ≤ m ≤ 9.5t, the holding time of the steel ingot at high temperature is 4-5h; if 10 ≤ m ≤ 13.5t, the holding time of the steel ingot at high temperature is 5-6h; if 14t ≤ m ≤ 19t, the holding time of the steel ingot at high temperature is 6-8h. (5) The forging deformation adopts the WHF wide anvil compaction method, without upsetting, and directly elongates the shape; when the steel ingot is taken out of the heating furnace, the surface of the steel ingot is lightly pressed 10mm, and then the main deformation is carried out by full anvil large pressing amount. Each deformation amount is ≥20%, the forging ratio is ≥3.5, until the shape is formed.

[0007] The low-carbon steel mentioned in this invention refers to carbon structural steel and alloy structural steel with a carbon content of 0.08%-0.22%, specifically including steel grades such as 070M20, C15, 16Mn, S355J2G3, 1018, 17CrNiMo6, and 16MnCrS5.

[0008] The method of this invention was derived by the inventors through long-term practical work, repeated research, reasoning, and verification. The reasons for the process and process parameters used in the method of this invention are as follows: (1) The C content in low carbon steel is 0.08%-0.16% in the peritectic reaction region. During the solidification process of steel ingots within this range, a large amount of high-temperature ferrite will participate in the peritectic reaction. Therefore, C should be avoided as much as possible in the range of 0.08%-0.16%. Mn and S elements shift the peritectic point to the left. Increasing Mn can avoid the peritectic region, and appropriately increasing S can also avoid the peritectic region. Excessive increase of S will cause hot brittleness. Therefore, S should be controlled at 0.015%-0.030%.

[0009] (2) Controlling the superheat during casting can reduce the tensile stress on the surface of the steel ingot caused by the static pressure of the molten steel during casting. Through long-term production practice and repeated research, this invention has determined that when the outdoor temperature is -8℃ to 20℃, the superheat should be controlled at 55℃ to 60℃, and two batches should be cast; when the outdoor temperature is 20℃ to 42℃, the superheat should be controlled at 50℃ to 55℃, and a single batch should be cast.

[0010] (3) The steel ingot is cooled slowly instead of hot-pressed, which can fully release the stress during the solidification process of the steel ingot, especially the tensile stress generated by the peritectic reaction.

[0011] (4) Heat the steel ingot to 100-150°C below the solidus temperature and hold it for a sufficient time to fully austenitize it, improve the surface of the steel ingot, reduce the tensile stress caused by uneven deformation during forging, and thus avoid cracking.

[0012] (5) The direct drawing process without upsetting is adopted to prevent large tensile stress on the surface of the steel ingot during the upsetting process, thereby avoiding cracks.

[0013] The beneficial effects of this invention are: (1) By optimizing the alloy composition, the low-carbon steel grade is deviated from the peritectic reaction zone, reducing the crack sensitivity of the forging material; (2) Reduce the crack sensitivity of steel grades by optimizing the casting and forging processes; (3) By applying the method of the present invention, the qualification rate and utilization rate of low carbon steel forgings are improved, and the production cost is reduced. Detailed Implementation

[0014] To better explain the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to specific embodiments. The following embodiments are merely illustrative of the technical solution of the present invention and do not limit the present invention in any way.

[0015] Example 1 This embodiment uses the production process of 070M20 steel forging as an example to explain the present invention. 070M20 steel mainly contains the following chemical composition by weight percentage: C: 0.16-0.20%, Si: 0.10-0.40%, Mn: 0.70-0.90%, S: 0.020-0.035%, Cr: 0.30-0.40%. Forged round bars are Φ400mm in diameter, using 7t octagonal ingots with a diameter of 878mm, a forging ratio of 4.8, and an outdoor temperature of 32℃ during production. The specific implementation process is as follows: (1) During the smelting process, the composition of 070M20 steel was optimized according to the following weight percentages: C: 0.17-0.20%, Si: 0.20-0.40%, Mn: 0.80-0.90%, S: 0.020-0.030%, Cr: 0.30-0.40%; After smelting, 29.5 tons of molten steel with qualified composition were obtained. (2) Single-pan casting is adopted, the casting temperature is 1559℃, and 4 pieces of 7t octagonal steel are cast; (3) After the steel ingot is demolded, it is placed in a pit at ≥200℃ for slow cooling, and the cooling rate is controlled at ≤30℃ / h. It is then slowly cooled until the surface temperature is below 100℃ before being removed from the pit. (4) Heat the steel ingot to 1240℃ and hold for 4 hours to ensure that the steel ingot is thoroughly heated and has no uneven surfaces; (5) After the steel ingot is kept warm, forging begins. Forging is carried out by direct drawing and forming using a wide anvil with a width of 650mm. When the steel ingot is taken out of the heating furnace, the surface of the steel ingot is first lightly pressed by 10mm, and then the main deformation is carried out by full anvil with large pressing amount. Each pressing amount is ≥20%, and the pressing passes are ≥4 times until the ingot is formed.

[0016] After forging, the composition of the forging produced by the method of this embodiment was tested and found to be C: 0.18%, Si: 0.32%, Mn: 0.83%, S: 0.023%, Cr: 0.32%; all of which meet the requirements of the steel grade composition.

[0017] The 070M20 steel forgings produced using the production method of this embodiment, after flaw detection, showed no cracks or longitudinal cracks, with a 100% first-pass yield and a 13.2% increase in yield.

[0018] Example 2 This embodiment uses the production process of C15E steel forging as an example to explain the present invention. C15E steel mainly contains the following chemical composition by weight percentage: C: 0.12-0.18%, Si: 0.15-0.40%, Mn: 0.30-0.60%, S: 0.020-0.035%. Forged round bars are Φ350mm in diameter, using 5t octagonal ingots with a diameter of 750mm, a forging ratio of 4.6, and an outdoor temperature of 28℃ during production. The specific implementation process is as follows: (1) During the smelting process, the composition of C15E steel was optimized according to the following weight percentages: C: 0.16-0.18%, Si: 0.20-0.40%, Mn: 0.50-0.60%, S: 0.020-0.030%; After smelting, 31.5 tons of molten steel with qualified composition were obtained. (2) Single-pan casting is adopted, the casting temperature is 1566℃, and 6 pieces of 5t octagonal steel are cast; (3) After the steel ingot is demolded, it is placed in a pit at ≥200℃ for slow cooling, and the cooling rate is controlled at ≤30℃ / h. It is then slowly cooled until the surface temperature is below 100℃ before being removed from the pit. (4) Heat the steel ingot to 1240℃ and hold for 3.5 hours to ensure that the steel ingot is thoroughly heated and has no uneven surfaces; (5) After the steel ingot is kept warm, forging begins. Forging is carried out by direct drawing and forming using a wide anvil with a width of 650mm. When the steel ingot is taken out of the heating furnace, the surface of the steel ingot is first lightly pressed by 10mm, and then the main deformation is carried out by full anvil with large pressing amount. Each pressing amount is ≥20%, and the pressing passes are ≥4 times until the ingot is formed.

[0019] After forging, the composition of the forging produced by the method of this embodiment was tested and found to be C: 0.17%, Si: 0.26%, Mn: 0.53%, S: 0.021%, all of which meet the requirements of the steel grade composition.

[0020] The C15E steel forgings produced using the production method of this embodiment, after flaw detection, showed no cracks or longitudinal cracks in the steel, with a 100% first-time pass rate and a yield rate 17.3% higher than before.

[0021] Example 3 This embodiment uses the production process of 18CrNiMo7-6 steel forging as an example to explain the present invention. 18CrNiMo7-6 steel mainly contains the following chemical composition by weight percentage: C: 0.15-0.21%, Si: 0.15-0.40%, Mn: 0.50-0.90%, S: ≤0.025%, Cr: 1.50-1.80%, Ni: 1.40-1.70%, Mo: 0.25-0.35%. The forged round bar is Φ290mm, using a 3.2t square ingot with a diameter of 550mm, a forging ratio of 4.6, and the outdoor temperature during production is 7℃. The specific implementation process is as follows: (1) During the smelting process, the composition of 18CrNiMo7-6 steel was optimized according to the following weight percentages: C: 0.17-0.21%, Si: 0.20-0.35%, Mn: 0.80-0.90%, S: 0.015-0.025%, Cr: 1.50-1.60%, Ni: 1.40-1.50%, Mo: 0.25-0.30%; After smelting, 33.5 tons of molten steel with qualified composition were obtained. (2) Double-pan casting is adopted, the casting temperature is 1567℃, and 10 pieces of 3.2t square ingot steel are cast; (3) After the steel ingot is demolded, it is placed in a pit at ≥200℃ for slow cooling, and the cooling rate is controlled at ≤30℃ / h. It is then slowly cooled until the surface temperature is below 100℃ before being removed from the pit. (4) Heat the steel ingot to 1230℃ and hold for 3 hours to ensure that the steel ingot is thoroughly heated and has no uneven surfaces; (5) After the steel ingot is kept warm, forging begins. Forging is carried out by direct drawing and forming using a wide anvil with a width of 500mm. When the steel ingot is taken out of the heating furnace, the surface of the steel ingot is first lightly pressed by 10mm, and then the main deformation is carried out by full anvil with large pressing amount. Each pressing amount is ≥20%, and the pressing passes are ≥4 times until the ingot is formed.

[0022] After forging, the composition of the forging produced by the method of this embodiment was tested and found to be C: 0.20%, Si: 0.26%, Mn: 0.81%, S: 0.016%, Cr: 1.53%, Ni: 1.41%, Mo: 0.26%, all of which meet the steel composition requirements.

[0023] The production method of this embodiment produces 18CrNiMo7-6 steel forgings. After flaw detection, the forgings are free of cracks and longitudinal cracks. The first-pass yield is 100%, and the yield is 8.5% higher than before.

[0024] Example 4 This embodiment uses the production process of 16MnCrS5 steel forging as an example to explain the present invention. 16MnCrS5 steel mainly contains the following chemical composition by weight percentage: C: 0.14-0.19%, Si: 0.15-0.40%, Mn 1.00-1.30%, S: ≤0.035%, Cr: 0.80-1.10%. Forged round bars are Φ500mm in diameter, using 10t octagonal forging equipment. The octagonal ingot diameter is 942mm, the forging ratio is 3.5, and the outdoor temperature during production is 1℃. The specific implementation process is as follows: (1) During the smelting process, the composition of 16MnCrS5 steel was optimized according to the following weight percentages: C: 0.17-0.19%, Si: 0.15-0.35%, Mn: 1.15-1.30%, S: 0.015-0.025%, Cr: 0.80-0.90%; After smelting, 31.5 tons of molten steel with qualified composition were obtained. (2) Single-pan casting is adopted, the casting temperature is 1570℃, and 3 pieces of 10t octagonal steel are cast; (3) After the steel ingot is demolded, it is placed in a pit at ≥200℃ for slow cooling, and the cooling rate is controlled at ≤30℃ / h. It is then slowly cooled until the surface temperature is below 100℃ before being removed from the pit. (4) Heat the steel ingot to 1240℃ and hold for 5 hours to ensure that the steel ingot is thoroughly heated and has no uneven surfaces; (5) After the steel ingot is kept warm, forging begins. Forging is carried out by direct drawing and forming using a wide anvil with a width of 650mm. When the steel ingot is taken out of the heating furnace, the surface of the steel ingot is first lightly pressed by 10mm, and then the main deformation is carried out by full anvil with large pressing amount. Each pressing amount is ≥20%, and the pressing passes are ≥4 times until the ingot is formed.

[0025] After forging, the composition of the forging produced by the method of this embodiment was tested and found to be C: 0.19%, Si: 0.26%, Mn: 1.15%, S: 0.017%, Cr: 0.81%; all of which meet the requirements of steel composition.

[0026] The production method of this embodiment produces 16MnCrS5 steel forgings. After flaw detection, the forgings are free of cracks and longitudinal cracks, with a 100% pass rate on the first inspection and a yield rate that is 9.2% higher than before.

[0027] As can be seen from the above embodiments, the low-carbon steel forgings produced by the production method of the present invention are free from cracks and longitudinal cracks. The first-pass yield of the low-carbon steel forgings is 100%, which is 10.3% higher than that of conventional production methods. The yield is increased by about 8.5%, and the production cost per ton of steel is reduced by about 420 yuan. Taking a company with an annual production of 5,000 tons of low-carbon steel as an example, the annual production cost is saved by 2.1 million yuan.

[0028] The above embodiments are merely specific examples exemplified to explain the present invention and do not limit the present invention in any way. Any non-substantial changes made by any person based on the above content and form that do not depart from the scope of protection of the claims of the present invention should be considered to fall within the scope of protection of the claims of the present invention.

Claims

1. A method for producing low-carbon steel forgings, characterized in that... Includes the following steps: (1) During the smelting process, control the C content of low carbon steel to be 0.16%-0.22%, S content to be 0.015%-0.025%, and Mn content to be taken as the upper limit of the range. Other components are smelted according to the component range required by the steel grade. (2) When pouring, control the pouring temperature and pouring speed. When the outdoor temperature is -8℃ to 20℃, control the superheat at 55℃ to 60℃ and pour in two batches. When the room temperature is 20℃ to 42℃, control the superheat at 50℃ to 55℃ and pour in one batch. (3) After the steel ingot is cast and demolded, it is placed in a slow cooling pit with a temperature ≥200℃ for slow cooling. The cooling rate is controlled to be ≤30℃ / h. The steel ingot is slowly cooled until the surface temperature is below 100℃ before being removed from the pit. (4) Heat the steel ingot to 1220-1260℃ to ensure that the steel ingot is thoroughly heated and there are no uneven surfaces; the holding time of the steel ingot is determined according to the weight m of the steel ingot. If m < 4t, the holding time of the steel ingot at high temperature is 2.5-3.5h; if 4 ≤ m ≤ 6.5t, the holding time of the steel ingot at high temperature is 3.5-4h; if 7 ≤ m ≤ 9.5t, the holding time of the steel ingot at high temperature is 4-5h; if 10 ≤ m ≤ 13.5t, the holding time of the steel ingot at high temperature is 5-6h; if 14t ≤ m ≤ 19t, the holding time of the steel ingot at high temperature is 6-8h. (5) The forging deformation adopts the WHF wide anvil compaction method, without upsetting, and is directly drawn into shape; When the steel ingot is taken out of the heating furnace, the surface of the steel ingot is first lightly pressed 10mm, and then the main deformation is carried out by full anvil large reduction, with each deformation amount ≥20% and forging ratio ≥3.5, until it is formed; The low-carbon steel is any one of 070M20, C15E, 18CrNiMo7-6, and 16MnCrS5.