A method for producing a weathering cutting non-quenched and tempered steel

Abstract

The application relates to a production method of a weather-resistant cutting non-quenched and tempered steel, adopting a process route of converter+LF furnace+RH furnace+continuous casting+hot rolling, and characterized by the following chemical components of the steel: 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 is Fe and inevitable impurities; the steel produced by the method is used to produce weather-resistant rod parts, and the parts do not need to be quenched and tempered on the whole section, so that the performance requirements of Rm=630-700Mpa, Rel>=350MPa, A>=15%, Z>=40%, AKU2>=49J and hardness 180-220HBW can be achieved, and energy saving and environmental protection are achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metallurgy, and relates to a production method of an energy-saving and environment-friendly weather-resistant cutting non-quenched and tempered steel. BACKGROUND

[0002] At present, the pin shaft rod parts for engineering machinery are generally made of medium-carbon structural steel and quenched and tempered after turning, for example, 45 steel, 40Cr and 42CrMo are quenched and tempered, the quenching and tempering cost is high, the production efficiency is low, and the quenching and tempering process increases energy consumption and pollutes the environment, and meanwhile, there are some waste losses, which do not meet the current energy-saving and environment-friendly requirements. Therefore, in recent years, some non-quenched and tempered steels have been developed by various enterprises for motor shafts and hydraulic piston rods, that is, vanadium, titanium and niobium micro-alloying elements are added to the medium-carbon manganese steel, fine carbides and nitrides are precipitated from the micro-alloying elements vanadium, titanium and niobium, the steel is strengthened, and the strength of the steel reaches that of quenched and tempered steel without quenching and tempering treatment.

[0003] At present, the pin shaft rod parts in the quenched and tempered state need to be plated with Ni, Cr and other elements or coated with rust-proof materials on the surface of the steel to achieve corrosion resistance before being used finally, and the complex process increases the production cycle and process cost.

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

[0005] The purpose of the present application is to provide a production method of an energy-saving and environment-friendly weather-resistant cutting non-quenched and tempered steel, adopt medium-carbon steel micro-alloying design, combine the organization and performance of hot-rolled round steel in the process of steelmaking and rolling, produce a non-quenched and tempered steel with a diameter of less than 100 mm, a tensile strength of 630-700 Mpa, a yield strength of greater than or equal to 350 Mpa, an elongation of greater than or equal to 17%, Z of greater than or equal to 40%, room temperature AKU2 of greater than or equal to 49 J, grain size of greater than or equal to 7.0 levels, and a hardness of 180-220 HBW.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] 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 is Fe and essential impurities; the key process steps include:

[0008] 1) smelting: the C≥0.08% of converter tapping, the LF+RH furnace refining process is adopted, argon blowing is adopted in the whole process of LF furnace refining, slagging deoxidation is adopted, the white slag keeping time is ≥20 min; after the white slag making is finished, the Al content is adjusted by using Al wire or Al block, the Al content of the outlet is 0.20-0.35%; the RH furnace is treated in vacuum, the vacuum degree is below 0.5 tor, the vacuum keeping time is not less than 20 min, the whole process of the RH furnace is circulated with nitrogen, the nitrogen content is analyzed by sampling after breaking the vacuum, the nitrogen content is adjusted by feeding the nitriding cored wire according to the detection result, the nitrogen content is ensured to be 0.0070%-0.0120%, the H of the outlet molten steel is ≤2 ppm, and the O is ≤10 ppm;

[0009] 2) continuous casting: the weak cooling process is adopted in the cooling section, the whole process is protected casting, the overheat degree of the tundish is ≤35℃ for continuous furnace, the overheat degree of the starting furnace is ≤40℃, the size of the casting blank is 280mm*280mm; the casting blanks are densely stacked and cooled;

[0010] 3) heating: the heating time of the casting blank is 200-300 min, the temperature of the heating section is 1000-1050℃, and the temperature of the soaking section is 1010-1060℃;

[0011] 4) rolling: the starting rolling temperature is 920-960℃; the final rolling temperature is 800-850℃;

[0012] 5) cooling: the round steel adopts the cold bed slow cooling process after rolling;

[0013] 6) finishing: the finished round steel adopts ultrasonic flaw detection + magnetic powder surface flaw detection, adopts a two-roller straightening machine to straighten, the straightness of the round steel is controlled to be within 1.5mm / m, the non-quenched and tempered steel with the diameter of 100mm or below, the tensile strength of 630-700Mpa, the yield strength of ≥350Mpa, the elongation of ≥17%, Z of ≥40%, the room temperature AKU2 of ≥49J, the grain size of ≥7.0 levels, and the hardness of 180-220HBW is obtained.

[0014] Invention principle: the strength, hardness and toughness of the product are mainly guaranteed from the following aspects.

[0015] Chemical composition design. The non-quenched and tempered steel refers to adding trace amounts of strong carbide forming elements V, Nb, Ti and the like in medium carbon steel, controlling rolling and cooling, and cooling to room temperature after controlling rolling and cooling, so that the strength level of the medium carbon steel after quenching and tempering is reached by using the precipitation strengthening of carbon (nitrogen) carbide, thereby the quenching and tempering process is saved. It not only saves energy and protects the environment, shortens the production cycle, but also avoids quenching deformation and cracking, improves product quality, and reduces manufacturing cost.

[0016] C content determination. As the most economical and basic strengthening element in steel, C can significantly improve the strength of steel through solid solution strengthening and precipitation strengthening, but too high C will adversely affect the center segregation, plasticity and toughness and welding performance of the steel; the C content range of the present application is determined to be 0.41% to 0.48%, and the steel material involved in the present application belongs to the category of medium carbon steel;

[0017] Si content determination. The Si here can strengthen ferrite and improve the base strength of the material, and has a significant contribution to the yield strength and tensile strength of the material. The Si content range of the present application is determined to be 0.20% to 0.35%;

[0018] Mn content determination. Mn can improve the tensile strength of steel through solid solution strengthening, and improve the hardenability of steel material, and as a deoxidizing element in the steelmaking process, Mn can also fix the form of sulfur in steel and form MnS and (Fe, Mn) S which are less harmful to the performance of steel, and reduce or inhibit the generation of FeS; however, Mn element is an easy segregation element, and too high content will cause serious center segregation of steel; the Mn content range of the present application is determined to be 0.60% to 0.80%;

[0019] Al content determination. Al element can refine grains, improve toughness, plasticity, fix N element, improve corrosion resistance, and improve hardness and wear resistance in steel, but too much Al content can form brittle inclusions such as Al2O3 during molten steel smelting, which can easily cause nozzle clogging and reduce the purity of molten steel; the Al content range of the present application is determined to be 0.15% to 0.25%;

[0020] S element determination. S element can combine with Mn element to form hard and brittle MnS, improve the cutting performance of steel material, and promote the formation of intracrystalline ferrite; however, too much S content will cause hot brittleness of steel, reduce the plasticity and toughness of steel, and increase the center segregation of steel material; the S content range of the present application is determined to be ≤0.035%;

[0021] P content determination. P element in steel plays a role in corrosion resistance, increasing cutting performance, and improving cutting surface finish. At the same time, P can cause serious segregation during solidification, P dissolves in ferrite to make the grains twisted and coarse, and increase the cold brittleness. The P content range of the present application is determined to be 0.25% to 0.30%;

[0022] Determination of N content. The V and Al elements in steel need to combine with N to form nitrides to enhance strength and refine grains. Therefore, an appropriate amount of N is required. Based on the V and Al contents and the stoichiometric ratios of the corresponding nitrides, the N content of the present invention is determined to be within the range of 0.0070% to 0.0120%.

[0023] Reduce non-metallic inclusions in steel. The presence of non-metallic inclusions in steel disrupts the continuity of the metal matrix, easily causing stress concentration and becoming a source of metal fatigue. Most cracks occur between oxides, point-like inclusions, and the matrix. When the stress is high enough, cracks form and rapidly expand, leading to damage. The lower the plasticity of the non-metallic inclusions and the sharper their shape, the greater the stress concentration. To improve product fatigue life, control vacuum degassing and refining outside the furnace, reduce the content of non-metallic inclusions, and change the type and distribution of inclusions.

[0024] Optimize the rolling process and improve the product grain size. The metallographic structure of round steel is ferrite + pearlite, with a grain size of 7 to 9. Fine grains can improve the strength and toughness of the product, and correspondingly improve fatigue resistance.

[0025] The present invention has the following beneficial effects: Through the unique design of the medium-carbon microalloying composition, the LF+RH composite refining technology, strict control of the molten steel purity, and the use of high-temperature, high-reduction rolling, controlled rolling, and controlled cooling technologies, the developed weather-resistant turning non-quenched and tempered steel achieves both strength and plasticity specifications, while maintaining a production cost lower than that of quenched and tempered steel, resulting in significant economic benefits. This invention breaks through conventional production processes, utilizing existing steel mill equipment and process conditions, fully leveraging the advantages of these equipment, and achieving energy conservation and environmental protection. The resulting non-quenched and tempered steel has excellent toughness, uniform hardness, and low cost, and is widely applicable to the manufacture of key components such as weather-resistant engineering pins and rods. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a metallographic picture of a quarter diameter round rod in Example 1.

[0027] Figure 2 This is a metallographic picture of a quarter diameter round rod in Example 2.

[0028] Figure 3 This is a metallographic picture of a 1 / 4 diameter round rod in Example 3. DETAILED DESCRIPTION Example 1

[0029] The embodiment is a production method of weathering cutting non-quenched and tempered steel, adopting a process route of converter+LF furnace+RH furnace+continuous casting+hot rolling, and 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 inevitable impurities. Key process steps include:

[0030] 1) Smelting: the converter tapping C=0.09%, the converter tapping does not require P content, the LF+RH furnace refining process is adopted, the LF furnace refining is blown with argon throughout, slagging deoxidation is performed, the white slag maintaining time is 25 min, after the white slag is finished, the Al content is adjusted by using Al wire or Al block, the outgoing Al content is 0.28%; the RH furnace is vacuum treated, the vacuum degree is below 0.5 tor, the vacuum maintaining time is 22 min, the RH furnace is circulated with nitrogen gas throughout, after the vacuum is broken, the nitrogen content is analyzed by sampling, the nitrogen content is adjusted to 0.010% by feeding the nitriding cored wire according to the detection result, the outgoing molten steel H=1.5 ppm, O=15 ppm;

[0031] 2) Continuous casting: the weak cooling process is adopted in the cooling section, the whole process is protected casting, the tundish superheat is 32 DEG C for continuous furnace, the starting furnace superheat is 38 DEG C, the size of the casting blank is 280 mm*280 mm; the casting blanks are densely stacked and cooled;

[0032] 3) Heating: the casting blank heating time is 210 min, the heating section temperature is 1010 DEG C, the soaking section temperature is 1020 DEG C;

[0033] 4) Rolling: the rolling specification is 28 mm, the starting rolling temperature is 925 DEG C; the finish rolling temperature is 805 DEG C;

[0034] 5) Cooling: the round steel adopts the cold bed slow cooling process after rolling;

[0035] 6) Finishing: the round steel adopts sawing, the finished round steel adopts ultrasonic flaw detection+magnetic powder surface flaw detection. The two-roller straightening machine is adopted for straightening to control the round steel straightness within 1.5 mm / m.

[0036] The steel performance detection results are shown in Tables 1-3. The round steel metallographic chart is shown in the attached Figure 1 . Example 2

[0037] The embodiment is a production method of weathering cutting non-quenched and tempered steel, adopting a process route of converter+LF furnace+RH furnace+continuous casting+hot rolling, and 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. Key process steps include:

[0038] 1) Smelting: the converter tapping C=0.095%, the converter tapping does not require P content, the LF+RH furnace refining process is adopted, the LF furnace refining is blown with argon throughout, slagging deoxidation is performed, the white slag maintaining time is 27 min, after the white slag is finished, the Al content is adjusted by using Al wire or Al block, the outgoing Al content is 0.28%; the RH furnace is vacuum treated, the vacuum degree is below 0.5 tor, the vacuum maintaining time is 26 min, the RH furnace is circulated with nitrogen gas throughout, after the vacuum is broken, the nitrogen content is analyzed by sampling, the nitrogen content is adjusted to 0.0095% by feeding the nitriding cored wire according to the detection result, the outgoing molten steel H=1.8 ppm, O=14 ppm;

[0039] 2) Continuous casting: the weak cooling process is adopted in the cooling section, the whole process is protected casting, the tundish superheat continuous furnace=31 ℃, the tundish superheat starting furnace=35 ℃, the size of the casting blank is 280 mm*280 mm; the casting blanks are densely stacked and cooled;

[0040] 3) Heating: the casting blank heating time is 260 min, the heating section temperature is 1030 ℃, the soaking section temperature is 1042 ℃;

[0041] 4) Rolling: the rolling specification is 57 mm, the opening rolling temperature is 935 ℃; the finish rolling temperature is 826 ℃;

[0042] 5) Cooling: the round steel adopts the cold bed slow cooling process after rolling;

[0043] 6) Finishing: the round steel adopts sawing, the finished round steel adopts ultrasonic flaw detection+magnetic powder surface flaw detection. The two-roller straightening machine is adopted for straightening to control the round steel straightness within 1.5 mm / m.

[0044] The steel performance detection results are shown in Tables 1-3. The round steel metallographic chart is shown in the attached Figure 2 . Example 3

[0045] The embodiment is a production method of a weathering cutting non-quenched and tempered steel, adopting a process route of converter+LF furnace+RH furnace+continuous casting+hot rolling, and 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 inevitable impurities. Key process steps include:

[0046] 1) Smelting: the converter tapping C=0.1%, the converter tapping does not require P content, the LF+RH furnace refining process is adopted, argon is blown in the whole LF furnace refining process, slagging deoxidation is performed, the white slag maintaining time is 29 min, after the white slag making is completed, the Al content is adjusted by using Al wire or Al block, the outgoing Al content is 0.25%; the RH furnace is vacuum treated, the vacuum degree is below 0.5 tor, the vacuum maintaining time is 30 min, the whole RH furnace circulating nitrogen is used, after the vacuum is broken, the nitrogen content is analyzed by sampling, the nitrogen content is adjusted to 0.011% by feeding the nitriding cored wire according to the detection result, the outgoing molten steel H=1 ppm, O=14 ppm;

[0047] 2) Continuous casting: the weak cooling process is adopted in the cooling section, the whole process is protected casting, the tundish superheat is 35℃ for continuous furnace, the starting furnace superheat is 40℃, the size of the casting blank is 280mm*280mm; the casting blanks are densely stacked and cooled;

[0048] 3) Heating: the casting blank heating time is 300 min, the heating section temperature is 1050℃, the soaking section temperature is 1060℃;

[0049] 4) Rolling: the rolling specification is 83mm, the starting rolling temperature is 955℃; the finish rolling temperature is 845℃;

[0050] 5) Cooling: the round steel adopts the cold bed slow cooling process after rolling;

[0051] 6) Finishing: the round steel adopts sawing, the finished round steel adopts ultrasonic flaw detection+magnetic powder surface flaw detection. The two-roller straightening machine is used for straightening to control the round steel straightness within 1.5mm / m.

[0052] The performance detection results of the steel are shown in Tables 1-3. The round steel metallographic chart is shown in the attached Figure 3 .

[0053] Table 1 Mechanical properties of the steel of the embodiment

[0054] .

[0055] Table 2 Impact energy, hot rolling hardness, grain size, banded structure test results of the steel of the embodiment

[0056] .

[0057] Table 3 Inspection situation of non-metallic inclusions of example steel

[0058] .

[0059] From the test results of Table 1 to Table 3, it can be seen that the weather-resistant engineering pin shaft rod non-quenched and tempered steel produced by the method has excellent test indexes, low 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%, and the rest is Fe and essential impurities; The key process steps include: 1) Smelting: The C of steel tapped from the converter is ≥0.08%. The LF+RH furnace refining process is adopted. Argon is blown throughout the LF furnace refining process, slag is made and deoxidized, and the white slag holding time is ≥20 minutes. After the white slag is made, the Al content is adjusted using Al wire or Al block, and the outlet Al is 0.20-0.35%. The RH furnace is vacuum treated, with a vacuum degree below 0.5 tor and a vacuum holding time of not less than 20 minutes. Nitrogen is circulated throughout the RH furnace. After breaking the air, samples are taken for nitrogen content analysis. According to the test results, nitrogen is fed into the nitriding cored wire to adjust the nitrogen content to ensure that the nitrogen content is 0.0070%-0.0120%. The outlet molten steel H ≤ 2ppm, O ≤ 10ppm. 2) Continuous casting: The cooling section adopts a weak cooling process, with full protection during casting. The tundish superheat of the continuous casting furnace is ≤35℃, and the open casting furnace is ≤40℃. The billet size is 280mm×280mm. The billets are densely packed 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℃; finishing rolling temperature 800~850℃; 5) Cooling: The rolled round steel adopts the slow cooling process on 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. The resulting round steel has a diameter of less than 100mm, a tensile strength of 630-700Mpa, a yield strength ≥350Mpa, an elongation ≥17%, Z ≥40%, room temperature AKU2 ≥49J, a grain size ≥7.0, and a hardness of 180-220HBW, which is non-quenched and tempered steel.

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