High-quality carbon steel, preparation method thereof and automobile part

Abstract

The invention relates to the technical field of ferrous metallurgy, in particular to high-quality carbon steel, a preparation method thereof and an automobile part. According to the high-quality carbon steel, on one hand, the design of molybdenum, micro-chromium and micro-titanium alloying is adopted, the hardenability of steel J5-J10 is remarkably improved, and meanwhile large fluctuation of the hardenability and quenching cracks caused by too high hardenability are avoided by limiting the low B content; and on the other hand, TiN inclusion is effectively inhibited by adopting a reasonable preparation method, formation of network ferrite is inhibited through a controlled cooling process, and meanwhile, the hardenability requirement of the steel is met. Tests show that the high-quality carbon steel has the advantages of being high in hardenability, small in grain size, high in cleanliness and the like, the hardenability of J3-J7 is not obviously reduced, and the high hardenability is still kept when J10 is 36-38 HRC; and meanwhile, due to the reasonable design of the controlled cooling process, the structure form of the steel is uniform, the hardness is controlled to be 180-200 HBW, and the machining requirements of customers are well met.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, in particular to high-quality carbon steel and a preparation method thereof and automobile parts. Background Art

[0002] The front axle of an automobile is a key core component of the automobile and a safety component. The annual steel consumption in China is about 600,000 tons, and the main varieties are 45 steel, 50 steel, 40Cr, 42CrMo and bainite non-quenched and tempered steel, of which high-quality carbon steel accounts for more than 30%. With the introduction of the new standard for the front axle, the organization at J10 is required to meet the level 4 requirements of GB / T 13320. At present, it is very difficult for the hardenability of high-quality carbon steel to meet the level 4 requirements at J5. The hardenability depth is usually about 4 mm, and the hardenability at J5, J7, and J9 decreases significantly, which is difficult to meet the demand for front axle steel. Although there are many element components that can improve the hardenability of steel, the impact on hardenability often fluctuates greatly, which can easily lead to problems such as poor processing performance caused by excessive hardenability or difficulty in achieving a high hardenability within a more suitable range. Summary of the invention

[0003] In view of this, the technical problem to be solved by the present invention is to provide a high-quality carbon steel and a preparation method thereof and an automotive component. The high-quality carbon steel provided by the present invention has high hardenability from J3 to J10 and can meet processing requirements, and has small fluctuation in hardenability and good stability.

[0004] The present invention provides a high-quality carbon steel, which comprises, by weight percentage:

[0005] C: 0.48%~0.53%; Si: 0.17%~0.37%; Mn: 0.70%~0.80%; Cr: 0.15%~0.25%; P: 0~0.020%; S: 0.015%~0.030%; B :0~0.0008%; Mo: 0.05%~0.10%; Ti: 0.020%~0.040%; Ni: 0~0.20%; Cu: 0~0.20%; Al: 0.020%~0.060%; O: 0~15 ppm; N: 0~40 ppm; the balance is Fe.

[0006] The mass content of Cr in the present invention is 0.15% to 0.25%, preferably 0.20% to 0.25%, and more preferably 0.21% to 0.24%; the content of Mo is 0.05% to 0.10%, preferably 0.05% to 0.08%, and more preferably 0.05% to 0.07%. The Mo in the present invention is a strong hardenability improving element, especially for the core hardness. Too high Mo will greatly increase the core hardness, resulting in insufficient core toughness of the forging. Once J10 is greater than 40HRC, brittle cracking is likely to occur, reducing the fatigue life of the steel; too low Mo, insufficient core hardness, J10 is less than 32, which is not enough to support the strength requirements of the steel, and fatigue wear is also likely to occur; the present invention significantly improves the hardenability of the high-quality carbon steel at J5-J10 by reasonably designing the added elements and their contents, wherein reasonable Mo and Cr contents improve the hardenability of the steel, and the simultaneous addition of the two elements strongly inhibits the transformation of supercooled austenite to pearlite, so that the steel has better toughness.

[0007] The mass content of Ti in the present invention is 0.020% to 0.040%, preferably 0.020% to 0.030%. The effect of Ti on hardenability in the present invention shows a trend of first increasing and then decreasing. When Ti≥0.045%, it has no significant effect on improving the hardenability of steel, but will reduce the hardenability.

[0008] The mass content of B in the present invention is 0-0.0008%, preferably 0-0.0006%. The B in the present invention can significantly improve the hardenability of steel, but there is instability, mainly because the effective boron of B in steel is not easy to stably control, the higher the B content, the greater the fluctuation of its influence on hardenability, which is easy to make the hardenability fluctuation range too large, and it is difficult to ensure the performance stability of the final product, so the B content is controlled to be no more than 0.0008%, so as to avoid quenching cracks caused by the hardenability being too high and difficult to control.

[0009] The mass content of N in the present invention is 0-40 ppm. In the process of preparing the high-quality carbon steel of the present invention, the mass content of N in the steel is controlled to be ≤40 ppm, and the mass content of N in the steel obtained is also ≤40 ppm, which effectively inhibits TiN inclusions, inhibits the formation of network ferrite through the controlled cooling process, and satisfies the hardenability requirements of the steel.

[0010] In some embodiments of the present invention, the high-quality carbon steel of the present invention comprises, by weight percentage: C: 0.50%~0.52%; Si: 0.20%~0.30%; Mn: 0.74%~0.78%; Cr: 0.20%~0.25%; P: 0~0.015%; S: 0.015%~0.025%; B: 0~0.0006%; Mo: 0.05%~0.08%; Ti: 0.020%~0.030%; Ni: 0~0.20%; Cu: 0~0.20%; Al: 0.020%~0.045%; O: 0~15 ppm; N: 0~40 ppm; the balance is Fe.

[0011] In some other embodiments of the present invention, the high-quality carbon steel of the present invention comprises, by weight percentage: C: 0.50%~0.52%; Si: 0.23%~0.26%; Mn: 0.74%~0.77%; Cr: 0.21%~0.24%; P: 0.011%~0.014%; S: 0.018%~0.022%; B: 0%~0.0005%; Mo: 0.05%~0.07%; Ti: 0.023%~0.027%; Ni: 0.02%~0.03%; Cu: 0.02%~0.03%; Al: 0.025%~0.030%; O: 0~15 ppm; N: 0~40 ppm; the balance is Fe.

[0012] The present invention also provides a method for preparing the high-quality carbon steel described in any of the above technical solutions, comprising the following steps: smelting, continuously casting, rolling and cooling the raw materials in sequence to obtain the high-quality carbon steel.

[0013] The present invention first smelts the raw materials; the smelting is to carry out converter smelting, LF refining and RH vacuum treatment in sequence. The process parameters of the converter smelting of the present invention are as follows: the proportion of molten iron added to the converter smelting is more than 90%; the molten iron temperature is controlled to be ≥1300°C during the converter smelting process; the converter smelting uses C=0.12 wt%~0.16 wt% and P=0.008 wt%~0.013 wt% as the converter tapping end point, and the tapping temperature is 1620°C~1660°C. After the converter smelting, the present invention carries out LF refining; specifically, LF refining is carried out, slag making and desulfurization are strengthened in the process, so that the sulfur content is controlled below 0.005 wt%, and finally high titanium iron (titanium content ≥70 wt%) and pure sulfur wire (sulfur content ≥90 wt%) are fed before LF refining and tapping. The present invention performs RH vacuum treatment after LF refining; the RH vacuum treatment specifically comprises: maintaining the molten steel after LF refining at a high vacuum of ≤67 Pa for 16 min to 20 min, and then performing soft argon blowing, wherein the blowing flow rate of the soft argon blowing is 1200 NL / min to 1400 NL / min, and the soft argon blowing time is ≥20 min, preferably 23 min to 28 min; wherein the high vacuum is maintained to ensure the gas content in the steel, and the soft argon blowing is performed to ensure that the inclusions are fully floated and removed.

[0014] After smelting, continuous casting is performed in the present invention. The process parameters of continuous casting in the present invention are as follows: the tundish temperature is controlled to be 1500°C~1520°C; the pulling speed is 0.50 m / min~0.60 m / min, preferably 0.53 m / min~0.58 m / min; the current intensity of the electromagnetic stirring of the crystallizer is 550 A~600 A and the current frequency is 2 Hz~3 Hz, the current intensity of the end electromagnetic stirring is 330 A~360 A and the current frequency is 6 Hz~7 Hz; the specific water volume is 0.25 L / kg~0.27 L / kg to ensure the quality of the ingot.

[0015] The present invention performs rolling after continuous casting. The process parameters of the rolling of the present invention are as follows: the soaking temperature is 1170℃~1220℃, preferably 1180℃~1210℃, the soaking time is 2.5h~4.0h, preferably 3.0h~3.5h; the start rolling temperature is 1000℃~1100℃, preferably 1030℃~1080℃; the final rolling temperature is 900℃~980℃, preferably 920℃~960℃.

[0016] The present invention performs cooling after rolling. The cooling described in the present invention is specifically as follows: the rolled steel is cooled at a cooling rate of 0.8°C / s ~1.5°C / s, and the cooling is six-water tank water cooling; the upper cooling bed temperature of the rolled steel is 600°C ~ 660°C and the lower cooling bed temperature is 250°C ~ 300°C, and then the steel is quickly collected into a slow cooling pit after the lower cooling bed for heat preservation and slow cooling, so that the temperature of the cooled steel is below 100°C, preferably 50°C ~ 70°C. The present invention controls the nitrogen content of the steel to ≤40 ppm during the preparation process of the high-quality carbon steel, which can not only effectively inhibit TiN inclusions, but also inhibit the formation of reticular ferrite through the controlled cooling process, while meeting the hardenability requirements of the steel.

[0017] The present invention also provides an automobile part, which is made of the high-quality carbon steel described in any of the above technical solutions or the high-quality carbon steel obtained by the preparation method described in any of the above technical solutions. The present invention has no special limitation on the automobile part, including but not limited to the automobile front axle.

[0018] The present invention provides a high-quality carbon steel and a preparation method thereof and automotive parts. The high-quality carbon steel provided by the present invention adopts a design of molybdenum, micro-chromium and micro-titanium alloying, which significantly improves the hardenability of steel J5~J10, and at the same time avoids quenching cracks caused by excessive fluctuations in hardenability and excessive hardenability by limiting the lower B content; on the other hand, by adopting a reasonable preparation method, the nitrogen content [N] in the steel is controlled to be ≤40 ppm, TiN inclusions are effectively suppressed, and the formation of network ferrite is suppressed through the controlled cooling process, while meeting the hardenability requirements of the steel. Experiments show that the high-quality carbon steel of the present invention has the advantages of high hardenability, fine grains, high cleanliness, etc. Not only does the hardenability of J3~J7 not decrease significantly, but J10 is 36 HRC~38 HRC, that is, it still maintains a high hardenability; at the same time, due to the reasonable design of the controlled cooling process, the organizational morphology of the steel is uniform, and the hardness is controlled at 180 HBW~200HBW, which well meets the processing requirements of customers. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a metallographic micrograph of the steel material of Example 1 of the present invention. DETAILED DESCRIPTION

[0020] The present invention discloses a high-quality carbon steel and a preparation method thereof and an automotive component. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve the same. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are deemed to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application of this article without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0021] The specific implementation manner of the present invention takes the preparation of Φ120 mm specification steel as an example, and the composition of the steel is as follows by mass percentage: C: 0.50%~0.52%, Si: 0.20%~0.30%, Mn: 0.74%~0.78%, Cr: 0.20%~0.25%, P: ≤0.015%, S: 0.015%~0.025%, B: ≤0.0006%, Ti: 0.022%~0.027%, Mo: 0.05%~0.08%, Ni: ≤0.20%, Cu: ≤0.20%, Al: 0.020%~0.045%, [O]≤15 ppm, [N]≤40 ppm, and the rest is Fe and unavoidable impurities.

[0022] The steps of the production process are as follows:

[0023] 1) Smelting

[0024] The converter is used for smelting, with the proportion of molten iron added ≥ 90%, the molten iron temperature of 1300~1400℃, the molten iron sulfur content controlled below 0.020%, the converter steelmaking end point [C]=0.12~0.16%, [P]=0.008~0.013%, and the steelmaking temperature of 1620~1660℃.

[0025] LF refining strengthens the slag making and desulfurization process to control the sulfur content below 0.005%. High titanium iron (titanium content ≥ 70%) and pure sulfur wire (sulfur content ≥ 90%) are fed before steelmaking.

[0026] For RH vacuum treatment, the steel is kept at a vacuum of 50~67 Pa for 16~20 min to ensure the gas content in the steel. After vacuum treatment, the soft argon blowing time is 23~28 min, and the argon blowing flow rate is 1200~1400 NL / min to ensure that the inclusions are fully floated and removed.

[0027] 2) Pouring

[0028] Continuous casting was adopted to cast the ingot, the tundish temperature was controlled at 1500~1520℃, the pulling speed of 320 mm×420 mm ingot was 0.53~0.58 m / min, the electromagnetic stirring of the crystallizer was 550~600 A, 2~3 Hz, the electromagnetic stirring of the end was 330~360 A, 6~7 Hz, and the specific water content was controlled at 0.25~0.27 L / kg to ensure the quality of the ingot.

[0029] 3) Rolling

[0030] The heating furnace is controlled to have a uniform heating temperature of 1180-1210°C, a heating time of 3.0-3.5 hours, a starting rolling temperature of 1030-1080°C, a final rolling temperature of 920-960°C, and six water tanks for water cooling after rolling. The cooling rate is controlled at 1.0-1.3°C / s, an upper cooling bed temperature of 610-640°C, and a lower cooling bed temperature of 260-320°C. After the lower cooling bed, the steel is promptly collected and put into a pit for slow cooling. The temperature out of the slow cooling pit is ≤80°C to obtain hot-rolled round steel.

[0031] The present invention will be further described below in conjunction with embodiments:

[0032] Examples 1 to 3 and Comparative Examples 1 to 2

[0033] The steel materials of Examples 1 to 3 and Comparative Examples 1 to 2 were prepared according to the chemical compositions shown in Table 1:

[0034] Table 1

[0035]

[0036] The steel materials of Examples 1 to 3 and Comparative Examples 1 to 2 were prepared according to the key process parameters of the smelting and continuous casting processes shown in Table 2:

[0037] Table 2

[0038]

[0039] The steel materials of Examples 1 to 3 and Comparative Examples 1 to 2 were prepared according to the key process parameters of the rolling process shown in Table 3:

[0040] Table 3

[0041]

[0042] The steels prepared in the above-mentioned Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests, and the results are shown in Tables 4-6, wherein Table 4 is the high-magnification structure test results, Table 5 is the hardenability test results, and Table 6 is the hardness test results; in addition, the steel in Example 1 was subjected to metallographic microscopy, and the results are shown in Tables 4-6. Figure 1 As shown, Figure 1 This is a metallographic micrograph of the steel material of Example 1 of the present invention.

[0043] Table 4

[0044]

[0045] Table 5

[0046]

[0047] Table 6

[0048]

[0049] From Tables 4 to 6 and Figure 1 It can be seen that the high-quality carbon steel of the present invention has the advantages of high hardenability, fine grains, high cleanliness, etc. J3=60~62 HRC, J5=58~60 HRC, J7=56~58 HRC, the hardenability has not decreased significantly, and J10=36~38 HRC still maintains a high hardenability, and the J10 hardenability is improved by about 10 HRC compared with conventional high-quality carbon steel products; the grain size is not coarser than grade 7.5; the indicators such as gas inclusions are well controlled, and the cleanliness of the steel is high; at the same time, due to the reasonable design of the controlled cooling process, the steel has a uniform organizational morphology, and the hardness is controlled at 180~200 HBW, which well meets the processing requirements of customers.

[0050] From Comparative Example 1, it can be seen that when the content of Mo and B is high, the hardenability is extremely high, the J10 is greater than 40 HRC, the hardness of the core is high, the toughness of the steel is poor, and the steel is easy to break. The hardness is above 260 HBW, which causes certain difficulties in processing.

[0051] It can be seen from Comparative Example 2 that under the condition of extremely low Mo content, J7 and J10 drop significantly. After quenching heat treatment, J10 is difficult to meet the product's requirements for organization. The core hardness is low and the supporting effect is not strong, which is not conducive to the strength and wear resistance requirements of steel.

[0052] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A high-quality carbon steel, characterized in that: In terms of weight percentage, it includes: C: 0.48%~0.53%; Si: 0.17%~0.37%; Mn: 0.70%~0.80%; Cr: 0.15%~0.25%; P: 0~0.020%; S: 0.015%~0.030%; B :0~0.0008%; Mo: 0.05%~0.10%; Ti: 0.020%~0.040%; Ni: 0~0.20%; Cu: 0~0.20%; Al: 0.020%~0.060%; O: 0~15 ppm; N: 0~40 ppm; the balance is Fe.

2. The high-quality carbon steel according to claim 1, characterized in that: The Cr content is 0.20% to 0.25%; The content of Mo is 0.05% to 0.08%.

3. The high-quality carbon steel according to claim 1, characterized in that: The Ti content is 0.020%~0.030%.

4. The high-quality carbon steel according to claim 1, characterized in that: In terms of weight percentage, it includes: C: 0.50%~0.52%; Si: 0.20%~0.30%; Mn: 0.74%~0.78%; Cr: 0.20%~0.25%; P: 0~0.015%; S: 0.015%~0.025%; B :0~0.0006%; Mo: 0.05%~0.08%; Ti: 0.020%~0.030%; Ni: 0~0.20%; Cu: 0~0.20%; Al: 0.020%~0.045%; O: 0~15 ppm; N: 0~40 ppm; the balance is Fe.

5. The high-quality carbon steel according to claim 1, characterized in that: In terms of weight percentage, it includes: C: 0.50%~0.52%; Si: 0.23%~0.26%; Mn: 0.74%~0.77%; Cr: 0.21%~0.24%; P: 0.011%~0.014%; S: 0.018%~0.022%; B: 0 ~0.0005%; Mo: 0.05%~0.07%; Ti: 0.023%~0.027%; Ni: 0.02%~0.03%; Cu: 0.02%~0.03%; Al: 0.025%~0.030%; O: 0~15 ppm; N: 0~40 ppm; the balance is Fe.

6. The method for preparing high-quality carbon steel according to any one of claims 1 to 5, characterized in that: The following steps are involved: The raw materials are sequentially smelted, continuously cast, rolled and cooled to obtain the high-quality carbon steel; The cooling is specifically as follows: cooling the rolled steel at a cooling rate of 0.8°C / s to 1.5°C / s, controlling the upper cooling bed temperature of the rolled steel to be 600°C to 660°C and the lower cooling bed temperature to be 250°C to 300°C, and then performing insulation and slow cooling to make the temperature of the cooled steel below 100°C.

7. The preparation method according to claim 6, characterized in that: The smelting includes sequentially performing converter smelting, LF refining and RH vacuum treatment; The process parameters of the converter smelting are as follows: the proportion of molten iron added in the converter smelting is more than 90%; the converter smelting uses C=0.12 wt%~0.16 wt% and P=0.008 wt%~0.013 wt% as the converter tapping end point, and the tapping temperature is 1620°C~1660°C; The RH vacuum treatment is specifically as follows: the molten steel after LF refining is kept at a high vacuum of ≤67 Pa for 16 min to 20 min, and then soft argon blowing is performed, and the time of soft argon blowing is ≥20 min.

8. The preparation method according to claim 6, characterized in that: The process parameters of the continuous casting are as follows: The temperature of the tundish is controlled at 1500℃~1520℃; the pulling speed is 0.50 m / min~0.60 m / min; the current intensity of the electromagnetic stirring of the crystallizer is 550 A~600 A and the current frequency is 2 Hz~3 Hz, the current intensity of the end electromagnetic stirring is 330 A~360 A and the current frequency is 6 Hz~7 Hz; the specific water volume is 0.25 L / kg~0.27 L / kg.

9. The preparation method according to claim 6, characterized in that: The rolling process parameters are as follows: The soaking temperature is 1170℃~1220℃, and the soaking time is 2.5 h~4.0 h; the starting rolling temperature is 1000℃~1100℃, and the finishing rolling temperature is 900℃~980℃.

10. Automobile parts, characterized in that The steel is made of the high-quality carbon steel described in any one of claims 1 to 5 or the high-quality carbon steel obtained by the preparation method described in any one of claims 6 to 9.

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