Production method of weather-resistant non-quenched and tempered steel for cutting

Abstract

A production method of weather-resistant non-quenched and tempered steel for cutting adopts a process route of a converter, an LF furnace, an RH furnace, continuous casting and hot rolling, and is characterized in that the steel comprises the following chemical components: 0.41%-0.48% of C, 0.20%-0.35% of Si, 0.60%-0.80% of Mn, 0.20%-0.35% of P, less than or equal to 0.035% of S, 0.03%-0.05% of Cr, less than or equal to 0.05% of V, less than or equal to 0.03% of Ni, less than or equal to 0.025% of Cu, 0.15%-0.25% of Al, 0.0070%-0.0120% of N, less than or equal to 0.0002% of H, less than or equal to 0.0020% of O and the balance of Fe and essential impurities; the steel produced by the method is used for manufacturing weather-proof rod parts, the performance requirements that Rm is equal to 630-700 MPa, Rel is larger than or equal to 350 MPa, A is larger than or equal to 15%, Z is larger than or equal to 40%, AKU2 is larger than or equal to 49 J, the hardness is 180-220 HBW and the like can be met without quenching and tempering the whole sections of the parts, and energy conservation and environmental protection are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to a production method of non-quenched and tempered steel for energy-saving, environmentally friendly, weather-resistant cutting. Background Art

[0002] At present, the pin shaft parts for engineering machinery are generally used after tempering and heat treatment of medium carbon structural steel, such as 45 steel, 40Cr, 42CrMo, which are tempered and heat treated. The tempering cost is high and the production efficiency is low. In addition, the tempering process will increase energy consumption and pollute the environment, and there will be some waste loss, which does not meet the current energy-saving and environmental protection requirements. Therefore, in recent years, various companies have developed some non-tempered steels for motor shafts and hydraulic piston rods, that is, adding vanadium, titanium, and niobium microalloying elements on the basis of medium carbon manganese steel, and using the fine carbides and nitrides precipitated by the microalloying elements vanadium, titanium, and niobium to strengthen the steel, so that the steel can reach the strength of tempered steel without tempering treatment.

[0003] Currently, motor shafts, hydraulic piston rods, or pin rod parts in a quenched and tempered state need to be plated with Ni, Cr and other elements or the steel surface needs to be coated with anti-rust materials to achieve corrosion resistance before final use. The complex process increases the production cycle and process costs.

[0004] Therefore, it is of practical research significance to develop a non-quenched and tempered steel for weather-resistant engineering pins with a suitable cost and process control and a tensile strength of 630~700Mpa for round steel with a diameter of less than 100mm. Summary of the invention

[0005] The purpose of the present invention is to provide a production method of non-quenched and tempered steel for energy-saving, environmentally friendly and weather-resistant cutting. The method adopts medium carbon steel microalloying design and combines steelmaking and rolling processes to control the organization and performance of hot-rolled round steel to produce a non-quenched and tempered steel with a round steel diameter of less than 100 mm, a tensile strength of 630 to 700 MPa, a yield strength of ≥350 MPa, an elongation of ≥17%, Z ≥40%, room temperature AKU2 ≥49J, a grain size of ≥7.0, and a hardness of 180-220 HBW.

[0006] The purpose of the present invention is achieved through the following technical solutions: The process route is converter + LF furnace + RH furnace + continuous casting + hot rolling. The chemical composition of the steel is C = 0.41% ~ 0.48%, Si = 0.20% ~ 0.35%, Mn = 0.60% ~ 0.80%, P = 0.20% ~ 0.35%, S ≤ 0.035%, Cr = 0.03% ~ 0.05%, V ≤ 0.05%, Ni ≤ 0.03%, Cu ≤ 0.025%, Al = 0.15% ~ 0.25%, N = 0.0070% ~ 0.0120%, H ≤ 0.0002%, O ≤ 0.0020%, and the rest are Fe and essential impurities; the key process steps include: 1) Smelting: C of steel out of converter is ≥0.08%, LF+RH furnace refining process is adopted, argon is blown throughout the LF furnace refining, slag is deoxidized, and the white slag holding time is ≥20min; after the white slag is made, Al wire or Al block is used to adjust the Al content, and the outgoing Al is 0.20-0.35%; RH furnace vacuum treatment, vacuum degree is below 0.5tor, vacuum holding time is not less than 20min, RH furnace is circulated with nitrogen throughout the process, and nitrogen content is analyzed by sampling after breaking the air, and nitrogen is fed into the nitriding core wire according to the test results to ensure that the nitrogen content is 0.0070%~0.0120%, and the outgoing molten steel H≤2ppm, O≤10ppm; 2) Continuous casting: The cooling section adopts weak cooling process, and the casting is protected throughout the whole process. The overheat of the tundish is ≤35℃ for continuous casting furnace and ≤40℃ for open casting furnace. The size of the ingot is 280mm×280mm. The ingot is densely stacked and cooled; 3) Heating: The heating time of the casting is 200-300 minutes, the temperature of the heating section is 1000-1050°C, and the temperature of the soaking section is 1010-1060°C; 4) Rolling: starting rolling temperature 920-960℃; final rolling temperature 800~850℃; 5) Cooling: The rolled round steel adopts the slow cooling process of the cooling bed; 6) Finishing: The finished round steel is subjected to ultrasonic flaw detection + magnetic particle surface flaw detection, and is straightened by a two-roll straightening machine to control the straightness of the round steel within 1.5mm / m, so as to obtain a round steel with a diameter of less than 100mm, a tensile strength of 630-700Mpa, a yield strength ≥350Mpa, an elongation ≥17%, Z ≥40%, a room temperature AKU2 ≥49J, a grain size ≥7.0, and a hardness of 180-220HBW, which is a non-quenched and tempered steel.

[0007] Principle of the invention: The present invention mainly ensures the strength, hardness and toughness of the product from the following aspects.

[0008] Chemical composition design. Non-quenched and tempered steel refers to adding a small amount of strong carbide-forming elements such as V, Nb, and Ti to medium carbon steel, cooling it to room temperature after controlled rolling and controlled cooling, and using the precipitation strengthening of carbon (nitride) to make it reach the strengthening level of medium carbon steel after quenching and tempering, thereby eliminating the quenching and tempering process. It is not only energy-saving and environmentally friendly, shortens the production cycle, but also avoids quenching deformation and cracking, improves product quality, and reduces manufacturing costs.

[0009] Determination of C content. C is the most economical and basic strengthening element in steel. It can significantly improve the strength of steel through solid solution strengthening and precipitation strengthening, but too high C content will have an adverse effect on the central segregation, plasticity and welding performance of steel; the range of C content in the present invention is determined to be 0.41% to 0.48%, and the steel material involved in the present invention belongs to the category of medium carbon steel; Determination of Si content. Si here is to strengthen ferrite, which can improve the matrix strength of the material and make a significant contribution to the yield strength and tensile strength of the material. The Si content range of the present invention is determined to be 0.20% to 0.35%; Determination of Mn content. Here, Mn can improve the tensile strength of steel through solid solution strengthening, and at the same time improve the hardenability of steel. Moreover, as a deoxidizing element in the steelmaking process, Mn can also fix the form of sulfur in the steel and form MnS and (Fe, Mn)S, which have less harm to the performance of the steel, and reduce or inhibit the formation of FeS. However, the Mn element is an element that is easy to segregate, and too high a content will cause serious central segregation of the steel. The range of the Mn content in the present invention is determined to be 0.60% to 0.80%; Determination of Al content. Al element plays a role in refining grains, improving toughness and plasticity, fixing N elements, improving corrosion resistance, hardness and wear resistance in steel. However, if Al content is high, brittle inclusions such as Al2O3 are easily formed during molten steel smelting, which is easy to form nodules at the nozzle, affecting castability and reducing the purity of molten steel. The Al content of the present invention is determined to be in the range of 0.15% to 0.25%; Determination of S element. S element can combine with Mn element to form hard and brittle MnS, improve the cutting performance of steel and promote the formation of intracrystalline ferrite. However, too much S content will make the steel hot brittle, reduce the plasticity and toughness of the steel, and increase the center segregation of the steel. The range of S content in the present invention is determined to be ≤0.035%; Determination of P content. P element plays the role of corrosion resistance, increasing cutting performance, and improving cutting surface finish in steel. At the same time, P in steel seriously causes segregation during solidification. P dissolves in ferrite to cause grain distortion and coarsening, and increases cold brittleness. The range of P content in the present invention is determined to be 0.25% to 0.30%; Determination of N content. V and Al elements in steel need to combine with N to form nitrides in order to play the role of improving strength and refining grains. Therefore, an appropriate amount of N element is required. According to the content of V and Al and the stoichiometric ratio of the corresponding nitrides, the range of N content in the present invention is determined to be 0.0070% to 0.0120%.

[0010] Reduce non-metallic inclusions in steel. The presence of non-metallic inclusions in steel destroys the continuity of the metal matrix, easily generates stress concentration, and becomes the source of metal fatigue. Most cracks occur between oxides, point-like inclusions and the matrix. When the stress is large enough, cracks occur and rapidly expand and destroy. The lower the plasticity of non-metallic inclusions and the sharper the shape, the greater the stress concentration. In order to improve the fatigue life of the product, control the vacuum degassing treatment and refining outside the furnace, reduce the content of non-metallic inclusions, and change the type and distribution of inclusions.

[0011] Optimize the rolling process and improve the grain size of the product. The metallographic structure of round steel is ferrite + pearlite, and the grain size is 7 to 9; fine grains can improve the strength and toughness of the product, and correspondingly improve the fatigue resistance.

[0012] Beneficial effects of the present invention: The medium-carbon microalloy composition of the present invention is specially designed, the LF+RH composite refining technology is used, the purity of the molten steel is strictly controlled, and the new technology of high-temperature large-pressure rolling, controlled rolling and controlled cooling is adopted. The weather-resistant turning non-quenched and tempered steel developed has reached the strength and plasticity indicators, and the production cost is lower than that of quenched and tempered steel, which has obvious economic benefits. The present invention breaks through the conventional production process, utilizes the existing equipment and process conditions of the steel plant, gives full play to the advantages of the equipment, saves energy and is environmentally friendly, and produces non-quenched and tempered steel with excellent toughness, uniform hardness and low cost, which can be widely used in the manufacture of weather-resistant engineering pins, rods and other key parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a metallographic picture of a 1 / 4 diameter round rod in Example 1.

[0014] Figure 2 This is a metallographic picture of a 1 / 4 diameter round rod in Example 2.

[0015] Figure 3 This is a metallographic picture of a round rod with a 1 / 4 diameter in Example 3. DETAILED DESCRIPTION Example 1

[0016] This embodiment is a method for producing non-quenched and tempered steel for weathering cutting, using a process route of converter + LF furnace + RH furnace + continuous casting + hot rolling, characterized in that the chemical composition of the steel is C=0.41%, Si=0.20%, Mn=0.60%, P=0.22%, S=0.008%, Cr=0.04%, V=0.02%, Ni=0.01%, Cu=0.02%, Al=0.25%, N=0.010%, H=0.00015%, O=0.0015%, and the rest is Fe and essential impurities. The key process steps include: 1) Smelting: C=0.09% for steel out of converter. No requirement for P content is made for steel out of converter. LF+RH furnace refining process is adopted. Argon is blown during LF furnace refining, slag is deoxidized, and white slag is kept for 25min. After white slag is made, Al wire or Al block is used to adjust Al content, and the outgoing Al content is 0.28%; RH furnace vacuum treatment, vacuum degree is below 0.5tor, vacuum keeping time is 22min, nitrogen is circulated throughout the RH furnace, and nitrogen content is analyzed by sampling after breaking air. According to the test results, nitrogen is fed into nitriding core wire to adjust nitrogen to ensure that the nitrogen content is 0.010%, and H=1.5ppm and O=15ppm of molten steel out of station; 2) Continuous casting: The cooling section adopts weak cooling process, and the casting is protected throughout the whole process. The superheat of the tundish continuous casting furnace = 32°C, the open casting furnace = 38°C, and the billet size is 280mm×280mm; the billet is densely stacked and cooled; 3) Heating: The heating time of the casting is 210 minutes, the temperature of the heating section is 1010°C, and the temperature of the soaking section is 1020°C; 4) Rolling: rolling specification is 28mm, starting rolling temperature is 925℃; final rolling temperature is 805℃; 5) Cooling: The rolled round steel adopts the slow cooling process of the cooling bed; 6) Finishing: The round steel is sawn, and the finished round steel is subjected to ultrasonic flaw detection + magnetic particle surface flaw detection. A two-roll straightening machine is used to straighten the round steel to control the straightness within 1.5mm / m.

[0017] The performance test results of the steel are shown in Tables 1 to 3. The metallographic diagram of the round steel is shown in the attached Figure 1 . Example 2

[0018] This embodiment is a method for producing non-quenched and tempered steel for weathering cutting, using a process route of converter + LF furnace + RH furnace + continuous casting + hot rolling, characterized in that the chemical composition of the steel is C=0.45%, Si=0.28%, Mn=0.70%, P=0.30%, S=0.010%, Cr=0.04%, V=0.02%, Ni=0.01%, Cu=0.02%, Al=0.20%, N=0.0095%, H=0.00018%, O=0.0014%, and the rest is Fe and essential impurities. The key process steps include: 1) Smelting: C=0.095% of steel tapped from the converter. No requirement for P content is made for steel tapped from the converter. LF+RH furnace refining process is adopted. Argon is blown throughout the LF furnace refining process. Slag making and deoxidation are carried out. The white slag holding time is 27 minutes. After the white slag making is completed, Al wire or Al block is used to adjust the Al content. The outgoing Al content is 0.28%. RH furnace vacuum treatment, vacuum degree is below 0.5tor, vacuum holding time is 26 minutes, nitrogen is circulated throughout the RH furnace, and nitrogen content is analyzed by sampling after breaking the air. According to the test results, nitrogen is fed into the nitriding core wire to adjust nitrogen to ensure that the nitrogen content is 0.0095%. The outgoing molten steel H=1.8ppm, O=14ppm; 2) Continuous casting: The cooling section adopts weak cooling process, and the casting is protected throughout the whole process. The superheat of the tundish continuous casting furnace = 31°C, the open casting furnace = 35°C, and the billet size is 280mm×280mm; the billet is densely stacked and cooled; 3) Heating: The heating time of the ingot is 260 minutes, the temperature of the heating section is 1030°C, and the temperature of the soaking section is 1042°C; 4) Rolling: rolling specification is 57mm, starting rolling temperature is 935℃; final rolling temperature is 826℃; 5) Cooling: The rolled round steel adopts the slow cooling process of the cooling bed; 6) Finishing: The round steel is sawn, and the finished round steel is subjected to ultrasonic flaw detection + magnetic particle surface flaw detection. A two-roll straightening machine is used to straighten the round steel to control the straightness within 1.5mm / m.

[0019] The performance test results of the steel are shown in Tables 1 to 3. The metallographic diagram of the round steel is shown in the attached Figure 2 . Example 3

[0020] This embodiment is a method for producing non-quenched and tempered steel for weathering cutting, using a process route of converter + LF furnace + RH furnace + continuous casting + hot rolling, characterized in that the chemical composition of the steel is C=0.475%, Si=0.325%, Mn=0.80%, P=0.34%, S=0.009%, Cr=0.04%, V=0.02%, Ni=0.01%, Cu=0.021%, Al=0.22%, N=0.011%, H=0.0001%, O=0.0014%, and the rest is Fe and essential impurities. The key process steps include: 1) Smelting: C=0.1% for steel out of converter. No requirement for P content is made for steel out of converter. LF+RH furnace refining process is adopted. Argon is blown during LF furnace refining, slag is deoxidized, and white slag is kept for 29 minutes. After white slag is made, Al wire or Al block is used to adjust Al content, and the outgoing Al content is 0.25%; RH furnace vacuum treatment, vacuum degree is below 0.5tor, vacuum keeping time is 30 minutes, nitrogen is circulated throughout the RH furnace, and nitrogen content is analyzed by sampling after breaking air. According to the test results, nitrogen is fed into nitriding core wire to adjust nitrogen to ensure that the nitrogen content is 0.011%, and H=1ppm and O=14ppm of the outgoing molten steel; 2) Continuous casting: The cooling section adopts weak cooling process, and the casting is protected throughout the whole process. The superheat of the tundish continuous casting furnace = 35℃, the open casting furnace = 40℃, and the billet size is 280mm×280mm; the billet is densely stacked and cooled; 3) Heating: The heating time of the casting is 300 minutes, the temperature of the heating section is 1050°C, and the temperature of the soaking section is 1060°C; 4) Rolling: rolling specification is 83mm, starting rolling temperature is 955℃; final rolling temperature is 845℃; 5) Cooling: The rolled round steel adopts the slow cooling process of the cooling bed; 6) Finishing: The round steel is sawn, and the finished round steel is subjected to ultrasonic flaw detection + magnetic particle surface flaw detection. A two-roll straightening machine is used to straighten the round steel to control the straightness within 1.5mm / m.

[0021] The performance test results of the steel are shown in Tables 1 to 3. The metallographic diagram of the round steel is shown in the attached Figure 3 .

[0022] Table 1 Mechanical properties of example steel.

[0023] .

[0024] Table 2 Test results of impact energy, hot rolling hardness, grain size and banded structure of the steel in the example .

[0025] Table 3 Inspection results of non-metallic inclusions in example steel.

[0026] .

[0027] It can be seen from the test results in Tables 1 to 3 that the weather-resistant engineering pin rod non-quenched and tempered steel produced by the method of the present invention has excellent inspection indicators, low steel gas content and non-metallic inclusions, and can well meet the use requirements of engineering machinery products.

Claims

1. A method for producing non-quenched and tempered steel for weathering cutting, using a process route of converter + LF furnace + RH furnace + continuous casting + hot rolling, characterized in that: The chemical composition of steel is C=0.41%~0.48%, Si=0.20%~0.35%, Mn=0.60%~0.80%, P=0.20%~0.35%, S≤0.035%, Cr=0.03%~0.05%, V≤0.05%, Ni≤0.03%, Cu≤0.025%, Al=0.15%~0.25%, N=0.0070%~0.0120%, H≤0.0002%, O≤0.0020%, the rest is Fe and essential impurities; The key process steps include: 1) Smelting: C of steel out of converter is ≥0.08%, LF+RH furnace refining process is adopted, argon is blown throughout the LF furnace refining, slag is deoxidized, and the white slag holding time is ≥20min; after the white slag is made, Al wire or Al block is used to adjust the Al content, and the outgoing Al is 0.20-0.35%; RH furnace vacuum treatment, vacuum degree is below 0.5tor, vacuum holding time is not less than 20min, RH furnace is circulated with nitrogen throughout the process, and nitrogen content is analyzed by sampling after breaking the air, and nitrogen is fed into the nitriding core wire according to the test results to ensure that the nitrogen content is 0.0070%~0.0120%, and the outgoing molten steel H≤2ppm, O≤10ppm; 2) Continuous casting: The cooling section adopts weak cooling process, and the casting is protected throughout the whole process. The overheat of the tundish is ≤35℃ for continuous casting furnace and ≤40℃ for open casting furnace. The size of the ingot is 280mm×280mm. The ingot is densely stacked and cooled; 3) Heating: The heating time of the casting is 200-300 minutes, the temperature of the heating section is 1000-1050°C, and the temperature of the soaking section is 1010-1060°C; 4) Rolling: starting rolling temperature 920-960℃; final rolling temperature 800~850℃; 5) Cooling: The rolled round steel adopts the slow cooling process of the cooling bed; 6) Finishing: The finished round steel is subjected to ultrasonic flaw detection + magnetic particle surface flaw detection, and is straightened by a two-roll straightening machine to control the straightness of the round steel within 1.5mm / m, so as to obtain a round steel with a diameter of less than 100mm, a tensile strength of 630-700Mpa, a yield strength ≥350Mpa, an elongation ≥17%, Z ≥40%, a room temperature AKU2 ≥49J, a grain size ≥7.0, and a hardness of 180-220HBW, which is a non-quenched and tempered steel.

Images