S35c annealing process dynamic matching manufacturing method based on hot rolling coiling temperature

Abstract

The application discloses a kind of S35C annealing process dynamic matching manufacturing methods based on hot rolling coiling temperature, including hot rolling process and annealing process;Coiling temperature T1 is divided into three grades: first grade 580℃≤T1<620℃, second grade 620℃≤T1<670℃, third grade 670℃≤T1≤690℃;According to the coiling temperature T1 of different gears, set different annealing process.The finished product Rockwell hardness HRB is stably in 60~71 interval, hardness fluctuation is ≤5 in the same roll, and fluctuation is ≤11 between different rolls, far superior to the fluctuation level of prior art, greatly improve downstream processing qualification rate.

Description

Technical Field

[0001] This invention belongs to the field of steel materials technology, specifically relating to a dynamic matching manufacturing method for the S35C annealing process based on hot rolling coiling temperature. Background Technology

[0002] S35C, a typical medium-carbon high-quality structural steel, achieves a balanced match of strength, toughness, and processing performance with a carbon content of 0.32-0.38%, manganese content of 0.60-0.90%, and silicon content of 0.15-0.35%. Its hot-rolled tensile strength can reach over 530 MPa, making it widely used in automotive powertrain components, engineering machinery transmission components, lightweight aerospace structural parts, and high-end mold substrates. With the increasing demands for precision and consistency in components from the new energy vehicle and aerospace industries, the limitations of traditional production processes are becoming increasingly apparent. The conventional "continuous casting billet heating-hot rolling-laminar cooling-coiling" process results in a hot-rolled microstructure of ferrite + lamellar pearlite, with high and uneven hardness and large residual internal stress. This directly leads to problems such as subsequent cold stamping cracking, accelerated wear of cutting dies, and dimensional deviations in parts. Therefore, the industry commonly uses annealing processes for softening and microstructure homogenization.

[0003] Existing annealing technologies generally suffer from process fragmentation: for example, CN101307378A discloses a bell-type furnace spheroidizing annealing method for medium carbon steel plates, which involves single-sheet rolling and annealing, but is not adapted to the microstructure inheritance characteristics of the hot-rolled coiling process; CN121518762A discloses a high spheroidization rate medium carbon steel and its production method based on medium-low annealing temperature, including hot rolling process, cold rolling process, and bell-type annealing process, with a cold rolling reduction rate ≥35% + bell-type annealing temperature of 700~710℃, emphasizing the promoting effect of cold rolling deformation on spheroidization, adopting a large cold rolling reduction + low-temperature annealing path, relying on cold deformation to promote spheroidization, which is not suitable for hot-rolled direct-supply annealing; CN111809029A discloses a high formability medium carbon steel material and its preparation method, but does not solve the hardness dispersion problem caused by the difference in hot-rolled coiling temperature between different batches.

[0004] The existing process uses annealing for softening, but the hot rolling and annealing processes are optimized independently without considering the genetic effects of different coiling temperatures. Furthermore, the general annealing process cannot be adapted to steel coils with different coiling temperatures, resulting in large fluctuations in hardness between different batches and coils with different coiling temperatures. This affects the pass rate of customer parts and makes it difficult to meet the needs of high-end customers. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the shortcomings of independent optimization of hot rolling and annealing processes for S35C steel coils of full thickness specifications, and to provide a dynamic matching manufacturing method for S35C annealing process based on hot rolling coiling temperature. Through the collaborative design of parameters of the two processes, the interference of coiling temperature difference on the final hardness is eliminated, and the goal of achieving Rockwell hardness HRB≤71 with minimal fluctuation and stable performance of finished product is achieved.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A dynamic matching manufacturing method for the S35C annealing process based on hot rolling coiling temperature includes a hot rolling process and an annealing process; the hot rolling process includes: The roughing stage is rolled in the austenite recrystallization zone, with the descaling water fully open at the roughing mill inlet and outlet; the finishing mill opening temperature is controlled at 1010~1050℃, and the finishing mill closing temperature is controlled at 860~890℃. After rolling, laminar flow cooling is adopted in the front section, with a cooling rate of 30~40℃ / s. The coiling temperature T1 is divided into three levels: the first level is 580℃≤T1<620℃ (low temperature coiling), the second level is 620℃≤T1<670℃ (medium temperature coiling), and the third level is 670℃≤T1≤690℃ (high temperature coiling). To better spheroidize pearlite, eliminate internal stress, and suppress the formation of hard phase structures, thereby stabilizing the product hardness at a low level and reducing the impact of different winding temperatures on product hardness, different annealing processes are set according to different winding temperatures T1: When the winding temperature T1 is at the first setting, the annealing temperature T2 is 720~730℃, the holding time t is 10~12h, and the cooling rate v from the annealing temperature T2 to 600℃ after the holding time is 10~15℃ / h; when T1 is at the second setting, the annealing temperature T2 is 700~710℃, the holding time t is 8~10h, and the cooling rate v from the annealing temperature T2 to 600℃ after the holding time is 18~20℃ / h; when T1 is at the third setting, the annealing temperature T2 is 680~690℃, the holding time t is 6~8h, and the cooling rate v from the annealing temperature T2 to 600℃ after the holding time is 23~25℃ / h.

[0007] When the annealing process cools to below 600°C, the cooling rate is increased to 30~40°C / h, and the temperature is cooled to room temperature.

[0008] The S35C steel coil has a yield strength of 230~270MPa, a tensile strength of 400~440MPa, and a Rockwell hardness (HRB) of 60~71. The HRB fluctuation of the same coil product is ≤5, and the HRB fluctuation of different coil products is ≤11.

[0009] The Rockwell hardness (HRB) of the finished product manufactured by the above method satisfies the following empirical relationship: HRB = 475 - 0.2T1 - 0.4T2 - 0.5t + 0.4v Among them, 580℃≤T1≤690℃.

[0010] Furthermore, the chemical composition of the S35C steel plate, by mass percentage, is: C 0.32%~0.38%, Si 0.15%~0.35%, Mn 0.60%~0.90%, P≤0.030%, S≤0.035%, Cu≤0.30%, Ni≤0.20%, Cr≤0.20%, with the balance being Fe and unavoidable impurities, and Ni+Cr≤0.35%.

[0011] This invention relates to a dynamic matching manufacturing method for the S35C annealing process based on hot rolling coiling temperature. The key focus is the coordinated design of hot rolling coiling temperature and annealing parameters: In the hot rolling stage, the coiling temperature is precisely divided into three ranges by controlling the initial rolling temperature (1010~1050℃) and the final rolling temperature (860~890℃) in conjunction with pre-stage laminar flow cooling. In the annealing stage, a fixed process is no longer used; instead, differentiated annealing temperatures, holding times, and slow cooling rates are matched to each coiling temperature range. At low temperatures, the coiled state has smaller lamellar spacing and higher internal stress, thus requiring higher annealing temperatures and longer holding times to promote spheroidization. At high temperatures, the pearlite in the coiled state has partially recovered, so the annealing temperature is appropriately lowered, the holding time is shortened, and the cooling rate is adjusted to suppress the precipitation of hard phases. The lower the coiling temperature, the higher the energy input required for annealing, the longer the atomic diffusion time, and the slower the corresponding slow cooling rate. These three factors work together to affect the degree of pearlite spheroidization and the effect of internal stress relief, ultimately achieving stable hardness control.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) The Rockwell hardness HRB of the finished product of this invention is stable in the range of 60~71, the hardness fluctuation within the same roll is ≤5, and the fluctuation between different rolls is ≤11, which is far better than the fluctuation level of the existing technology, and greatly improves the downstream processing qualification rate. 2) The finished product of this invention has a yield strength of 230~270MPa and a tensile strength of 400~440MPa, which takes into account both softening and sufficient load-bearing strength, and is suitable for processing needs in multiple scenarios such as stamping and cutting. 3) This invention does not require an additional cold rolling process and can be achieved based on existing hot rolling-annealing production lines. It is applicable to S35C steel coils of different thicknesses and specifications, with low production costs and strong scalability. Detailed Implementation

[0013] The present invention will be further described below with reference to specific embodiments and comparative examples. The chemical composition of the steel plates in the embodiments meets the requirements of the S35C standard: C 0.32%~0.38%, Si 0.15%~0.35%, Mn 0.60%~0.90%, P≤0.030%, S≤0.035%, Cu≤0.30%, Ni≤0.20%, Cr≤0.20%, with the balance being Fe and unavoidable impurities, and Ni+Cr≤0.35%.

[0014] The main hot rolling process parameters of each embodiment and comparative example of the present invention are shown in Table 1, and are executed according to the conventional austenite recrystallization zone rough rolling process, with the inlet and outlet descaling water fully open.

[0015] Table 1 Hot rolling process parameters of various embodiments and comparative examples of the present invention The main annealing process parameters of the various embodiments and comparative examples of the present invention are shown in Table 2.

[0016] Table 2 Annealing process parameters for various embodiments and comparative examples of the present invention The properties of each embodiment and comparative example of the present invention after spheroidizing annealing are shown in Table 3.

[0017] Table 3. Performance of each embodiment and comparative example of the present invention after spheroidizing annealing As shown in Table 3 above, the dynamic matching manufacturing method of S35C annealing process based on hot rolling coiling temperature according to the present invention, through reasonable dynamic collaborative design of hot rolling coiling temperature and annealing process parameters, produces hot-rolled coils of full thickness specifications with good Rockwell hardness (HRB) stability. The HRB fluctuation of the same coil product is controlled within the range of ≤5, and the HRB fluctuation of different coil products is controlled within the range of ≤11.

[0018] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dynamic matching manufacturing method for S35C annealing process based on hot rolling coiling temperature, characterized in that, It includes a hot rolling process and an annealing process; the hot rolling process includes: The initial rolling temperature of the finishing mill is controlled at 1010~1050℃, and the final rolling temperature is controlled at 860~890℃. After rolling, laminar flow cooling is adopted in the front section cooling method, with a cooling rate of 30~40℃ / s. The coiling temperature T1 is divided into three levels: the first level is 580℃≤T1<620℃, the second level is 620℃≤T1<670℃, and the third level is 670℃≤T1≤690℃. Different annealing processes are set according to the different winding temperatures T1: When the winding temperature T1 is at the first level, the annealing temperature T2 is 720~730℃, the holding time t is 10~12h, and the cooling rate v when the annealing temperature T2 reaches 600℃ is 10~15℃ / h; when T1 is at the second level, the annealing temperature T2 is 700~710℃, the holding time t is 8~10h, and the cooling rate v when the annealing temperature T2 reaches 600℃ is 18~20℃ / h; when T1 is at the third level, the annealing temperature T2 is 680~690℃, the holding time t is 6~8h, and the cooling rate v when the annealing temperature T2 reaches 600℃ is 23~25℃ / h.

2. The method according to claim 1, characterized in that, In the annealing process, when the temperature cools to below 600°C, the cooling rate is increased to 30~40°C / h, and the temperature is cooled to room temperature.

3. The method according to claim 1, characterized in that, The chemical composition of the S35C steel plate, by mass percentage, is as follows: C 0.32%~0.38%, Si 0.15%~0.35%, Mn 0.60%~0.90%, P≤0.030%, S≤0.035%, Cu≤0.30%, Ni≤0.20%, Cr≤0.20%, with the balance being Fe and unavoidable impurities, and Ni+Cr≤0.35%.

4. The method according to claim 1, characterized in that, The S35C steel coil has a yield strength of 230~270MPa, a tensile strength of 400~440MPa, and a Rockwell hardness (HRB) of 60~71. The HRB fluctuation of the same coil product is ≤5, and the HRB fluctuation of different coil products is ≤11.

5. The method according to claim 1, characterized in that, The Rockwell hardness (HRB) of the finished product manufactured by the aforementioned method satisfies the following empirical relationship: HRB = 475 - 0.2T1 - 0.4T2 - 0.5t + 0.4v Among them, 580℃≤T1≤690℃.

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