A weather-resistant steel strip for railway vehicle doors and its CSP line production method

Abstract

The present invention provides a weather-resistant steel strip for railway vehicle doors and its CSP line production process, belonging to the technical field of weather-resistant steel manufacturing. It solves the problems that the performance effects of traditional steel strips in terms of strength and toughness, atmospheric corrosion resistance, weldability, cold stamping formability, etc. are not ideal; the traditional production process has high production difficulty, unstable production performance, and few attempts in CSP production lines. The steel strip of the present invention is composed of the following chemical components by weight percentage: C: 0.040 - 0.055, Si: 0.25 - 0.45, Mn: 0.80 - 1.00, P: ≤0.020, S: ≤0.008, Cu: 0.25 - 0.45, Cr: 0.40 - 0.55, Ni: 0.15 - 0.30, Nb: 0.015 - 0.030, V: 0.040 - 0.060, B: 0.0010 - 0.0020, N < 0.0050, Als: 0.025 - 0.045, and the balance is Fe and inevitable trace elements; the production includes the following steps: hot metal pretreatment, smelting refining, casting, heating, descaling, continuous rolling, and cooling and coiling; the steel strip prepared by the present invention has better performance, and the provided process improves the stability and quality of steel strip production.

Description

Technical Field

[0001] The present invention belongs to the technical field of weathering steel manufacturing, and particularly relates to a weathering steel strip for railway vehicle doors and its CSP line production process. Background Art

[0002] With the continuous and rapid growth of China's economy, the railway freight turnover has increased significantly. Currently, the open wagons in actual operation are mainly of C64 and C70 types, and their doors are all made of all-steel structures. To meet the economic development needs of the current society, improve the service life of key vehicle components, extend the overhaul and repair cycle, and meet the requirements of loading and unloading goods, the steel material has been continuously improved. Currently, the materials of side-opening doors and lower side doors are mainly 550Mpa grade weathering steel strips with a thickness of 5.0mm. However, the performance effects such as strength and toughness, atmospheric corrosion resistance, weldability, and cold stamping formability of this steel strip are not very ideal.

[0003] For high-strength weathering steel strips used for railway vehicle doors, since there are many alloying elements added, in addition to the five major elements and microalloying strengthening elements niobium and vanadium, corrosion-resistant elements such as chromium and copper also need to be added. In China, they are usually produced by medium-thick plates, conventional hot continuous rolling, and casting and rolling production lines. There are few attempts on CSP production lines. For CSP production lines with relatively low configurations, the production difficulty is relatively large. At the same time, in addition to certain strength and corrosion resistance indicators, this steel type also needs to have excellent plasticity indicators to reduce the stamping cracking rate and meet the welding process requirements. Summary of the Invention

[0004] The purpose of the present invention is to provide a weathering steel strip for railway vehicle doors to solve the problem that the performance effects such as strength and toughness, atmospheric corrosion resistance, weldability, and cold stamping formability of traditional steel strips are not ideal.

[0005] Another purpose of the present invention is to provide a CSP line production process for a weathering steel strip for railway vehicle doors to solve the problems of high production difficulty, unstable production performance, and few attempts on CSP production lines in traditional production processes.

[0006] The technical solution of the present invention is: a weathering steel strip for railway vehicle doors, and the steel strip is composed of the following chemical components by weight percentage: C: 0.040 - 0.055, Si: 0.25 - 0.45, Mn: 0.80 - 1.00, P: ≤0.020, S: ≤0.008, Cu: 0.25 - 0.45, Cr: 0.40 - 0.55, Ni: 0.15 - 0.30, Nb: 0.015 - 0.030, V: 0.040 - 0.060, B: 0.0010 - 0.0020, N < 0.0050, Als: 0.025 - 0.045, and the balance is Fe and inevitable trace elements such as Ca.

[0007] A CSP production process for weather-resistant steel strips used in railway vehicle doors, comprising the following steps:

[0008] Step 1: After hot metal pretreatment, it is smelted in a converter, refined in an LF furnace after smelting, and then poured into a thin slab continuous caster. The thickness of the thin slab is 70 mm, the casting speed of the continuous caster is 3.1 - 3.4 m / min, and the mold powder used in the continuous casting mold is the special APH3-C1A mold powder for weather-resistant steel, and the mold powder contains LiO2 to improve its lubrication performance.

[0009] Step 2: The cast continuous casting thin slab in Step 1 is heated by a tunnel type roller hearth heating furnace, the tapping temperature is 1170 - 1190 °C, and the residence time in the furnace is 18 - 25 min.

[0010] Step 3: After the slab is taken out of the furnace, descaling is carried out, followed by continuous rolling, and then dephosphorization is carried out again;

[0011] Step 4: After rolling is completed, the strip enters the 8-section laminar cooling section to be cooled to the coiling temperature. The coiling temperature is 560 - 580 °C, and the laminar cooling mode selects the "8" mode two-stage segmented cooling.

[0012] Further, in Step 3, two passes of descaling are carried out after the slab is taken out of the furnace, and three passes of dephosphorization are carried out after continuous rolling. The descaling pressure of the first pass is ≥24 Mpa, the descaling pressure of the second pass is ≥35 Mpa, and the descaling pressure of the third pass is ≥12 Mpa. The first and second passes of descaling are carried out between the heating furnace and the first stand, and the third pass of dephosphorization is carried out at the outlet of the first stand. The first stand is the F1 stand.

[0013] Further, in Step 3, the continuous rolling method is six-stand continuous rolling, and the finishing rolling temperature is 850 - 870 °C.

[0014] Further, in Step 3, the cross jets in front of the F1 - F6 stands are closed; the cooling water of the F1 - F3 stands is closed; the outlet speed of the rolling mill is intervened to carry out constant speed rolling, and the speed is 4.75 m / s.

[0015] Further, in Step 4, the laminar cooling water system is controlled according to the maximum water flow rate of the system operation, and the system pressure is ≥0.7 bar.

[0016] Further, in Step 4, the 8-section headers are numbered, and the opening sequence is defined in the secondary laminar cooling model. All the headers in the first and second groups are opened. The upper and lower cooling headers in the seventh and eighth groups are intermittently opened from the outlet to the inlet in combination with the actual detection and target control deviation of the coiling temperature; if the target coiling temperature still cannot be guaranteed after all 8 sections are opened, cooling is carried out in the way of opening one group of headers at intervals from the seventh section to the sixth section.

[0017] The beneficial effects of the present invention are as follows: By adding a certain amount of trace elements such as B, Mn, Cr, Ni, Ti, Nb, and V to plain carbon steel, the cooperation of each element with the original chemical elements ensures the strength performance of the product, improves the strength and toughness of the steel strip and its atmospheric corrosion resistance. At the same time, the obtained steel strip is easy to weld and has better cold stamping forming effect. The material properties of the obtained steel strip are as follows: yield strength: 460 - 487 MPa, tensile strength: 572 - 607 MPa, elongation: ≥ 30%, 180° cold bending test: D = a, yield ratio: 0.78 - 0.82, relative corrosion rate: ≤ 45%, meeting and even exceeding the requirements of the use standards.

[0018] This process adopts the production process of hot metal pretreatment, smelting refining, casting, heating, descaling, continuous rolling, and cooling coiling. By controlling the typical casting speed of the continuous caster and selecting the special APH3 - C1A mold powder for weathering steel, the stability of continuous casting production and the quality of the cast billet are improved; combined with the rolling process and special cooling control, the stable production of a steel strip with better process performance on the CSP line is realized, reducing the production difficulty of this steel strip. The cold stamping forming performance of the produced steel strip is excellent, and the cracking rate is lower than 3‰, which is suitable for the processing and manufacturing of the open - top car doors of C64 - type and C70 - type railway vehicles.

[0019] The design principle of the composition and proportion of the chemical components of the steel strip in the present invention is as follows:

[0020] C is the most economical and effective element to improve the strength of steel. It can dissolve into the matrix to play a role in solid solution strengthening, and can combine with V and Nb to form carbide precipitation particles, playing a role in fine grain strengthening and precipitation strengthening, improving the plasticity and toughness of the strip steel, reducing the center segregation zone of the strip steel, being beneficial to improving the cold stamping forming performance and welding performance of the steel strip. At the same time, it maximally avoids the increase in the crack sensitivity index due to the increase of C in the smelting process, reducing the risk of continuous casting breakout, improving the stability of producing this steel strip by the CSP process, improving the corrosion resistance of the product, and significantly reducing the "copper embrittlement" defect; comprehensively considering, the control range of C content is: 0.040 - 0.055%.

[0021] Si has a high solid solubility in steel, which is beneficial to improving the strength of steel, refining the rust layer structure at the yield point, reducing the overall corrosion rate of steel, and improving toughness. However, too high content will make descaling difficult during rolling and also lead to a decline in welding performance; comprehensively considering, the control range of Si content is: 0.25 - 0.45%.

[0022] Mn can improve the strength of steel through solid solution strengthening, significantly reduce the phase transformation temperature of steel, refine the microstructure of steel, effectively control the strip banded structure caused by composition segregation, improve the uniformity of the overall structure of the strip, and at the same time avoid the increase of N in the smelting process caused by excessive addition of alloying elements. It can minimize the generation of precipitation strengthening products such as NbCN, NbN, and VN, which cause the increase of the hardness index and brittleness of the strip steel, increase the crack sources of the material, and result in longitudinal cracks or edge cracks in the strip steel, as well as the decrease of the anti-stress and plasticity indexes. Considering comprehensively, the control range of Mn content is: 0.80 - 1.00%.

[0023] P can effectively improve the atmospheric corrosion resistance of steel. When P and Cu are added jointly, a better composite effect can be shown. However, too high P content will significantly reduce the plasticity and low-temperature toughness of steel, affecting the stamping forming performance of this steel grade. Considering the use of this steel grade, comprehensively consider that the P content ≤ 0.020%.

[0024] S will form sulfide inclusions in steel, deteriorating the properties of steel. At the same time, pitting corrosion is prone to occur and expand during the corrosion process, which has an adverse effect on the corrosion resistance. Considering comprehensively, the S content ≤ 0.008%.

[0025] Cu is beneficial to form a dense and well-adherent amorphous oxide (hydroxyl oxide) protective layer on the surface of steel, and the corrosion resistance effect is more obvious. In addition, Cu reacts with S to form insoluble sulfides, thus offsetting the harmful effect of S on the corrosion resistance of steel. Considering comprehensively, the control range of Cu content is: 0.25 - 0.45%.

[0026] Cr has a significant effect on improving the passivation ability of steel, which can promote the formation of a dense passivation film or protective rust layer on the surface of steel. Its enrichment in the rust layer can effectively improve the selective permeation characteristics of the rust layer to corrosive media. Considering comprehensively, the control range of Cr content is: 0.40 - 0.55%.

[0027] Ni can not only improve the strength and corrosion resistance of steel, but also maintain good plasticity and toughness. It is also beneficial to reduce the "copper embrittlement" phenomenon and is as close as possible to the Cu percentage content to produce a high-melting-point NiCu alloy, reducing the free low-melting-point liquid Cu in the molten steel, and thus avoiding cracking during the subsequent cold bending forming process of weathering steel. Considering comprehensively, the control range of Ni content is: 0.15 - 0.30%.

[0028] V has a high solubility in molten steel and is one of the most effective strengthening elements for microalloyed steel. It mainly precipitates in the ferrite at the austenite grain boundary, thereby refining the ferrite grains and improving the comprehensive properties of steel. Considering comprehensively, the control range of V content is: 0.040 - 0.060%.

[0029] Nb can pin the austenite grain boundaries, thus preventing grain growth, ultimately refining the microstructure and grains, improving the strength and toughness of the steel, but contributing less to the precipitation strengthening of the steel. However, if the content is too high, mixed grains are likely to appear in the structure, which is not conducive to the welding performance of the steel. Considering comprehensively, the control range of Nb content is: 0.015 - 0.030%.

[0030] B can double the hardenability of the steel. Part of the dissolved B segregates at the austenite grain boundaries, inhibiting the nucleation of ferrite and reducing the nucleation rate of ferrite, thereby achieving the effect of reducing the yield ratio and improving the forming performance, and improving the hardenability of the steel strip. Part of the dissolved B segregates at the austenite grain boundaries, inhibiting the nucleation of ferrite and reducing the nucleation rate of ferrite, thereby achieving the effect of reducing the yield ratio and improving the forming performance. Considering the processing and use requirements of this steel type and relevant experimental data, the control range of B content is considered to be: 0.0010 - 0.0020%.

[0031] N is mainly an element generated during the smelting process. Since one of the characteristics of the present invention is the use of niobium-vanadium microalloying technology, if the N content is too high, the carbonitrides of Nb and V precipitated during the molten steel and (continuous casting, rolling) processes have high hardness, and at the same time increase the crack sources of the material, resulting in increased brittleness of the material and decreased anti-stress and plasticity indexes. Considering comprehensively, the N content < 0.0050%.

[0032] Als added to the steel plays a role in deoxidation. However, if the Als content is too high, its nitrogen oxides are likely to precipitate at the austenite grain boundaries, resulting in the generation of slab cracks. Considering comprehensively, the control range of Als content is: 0.025 - 0.045%.

[0033] In the production process of the present invention, selecting a higher heating temperature and controlling the slab residence time in the furnace in the hot continuous rolling process can improve the crack hazard caused by Cu, and at the same time reduce the probability of the occurrence of burrs and edge cracks at the strip edges due to the addition of Nb in the steel.

[0034] Using 3 passes of descaling can maximize the surface quality of the rolled steel strip; using a 6-stand continuous rolling mill for rolling, the reduction ratio of the front stands can all achieve a reduction ratio of more than 50%, and the degree of deformation is greater than the saturation limit of the deformation resistance, which can reduce the generation of hot cracks in the rolled steel strip within the industrial window range; closing the front transverse spray of F1 - F6 stands and the cooling water of F1 - F3 stands can minimize the cross-sectional temperature difference of the strip and the aggravation of hot cracks; controlling the finish rolling temperature at 850 - 870 °C, after laminar cooling, its microstructure is fine and uniform, the microstructure is mainly ferrite, the ferrite content can reach up to 95% at most, and the pearlite accounts for a small proportion, which makes a great contribution to reducing the yield ratio and improving the plasticity index.

[0035] Intervene in the exit speed of the rolling mill to carry out constant-speed rolling, which creates conditions for the self-learning and self-adaptation of the secondary laminar cooling model, and ensures the consistency of the overall coiling temperature in the length direction of the strip coil and the stability of the subsequent product mechanical property indicators.

[0036] Adopt the "8" mode two-stage segmented cooling. On the premise of ensuring the product strength index, through the air cooling in the middle section of laminar cooling, the cooling rate of the steel strip in the thickness direction is made as consistent as possible to obtain a uniform structure and improve the toughness and plasticity indexes.

[0037] A reasonable coiling temperature can increase the nucleation rate of ferrite and inhibit the growth of ferrite grains, effectively play the role of fine grain strengthening, with significant grain refinement effect, and the obtained structure is uniform. While improving the strength, the toughness and plasticity indexes of the steel strip are improved; Select a unidirectional or bidirectional adjustable coiling temperature compensation device and control method to ensure the temperature difference across the strip.

[0038] The laminar cooling water system is controlled according to the maximum water flow rate during system operation, and the system pressure ≥ 0.7 bar to ensure the cooling rate of the strip in the front section of laminar cooling and the cooling time of the air cooling section. Specific implementation mode

[0039] The present invention will be further described in detail below in conjunction with embodiments.

[0040] Example 1

[0041] The steel strip is composed of the following chemical components by weight percentage: C: 0.040, Si: 0.25, Mn: 0.80, P: 0.016, S: 0.006, Cu: 0.25, Cr: 0.40, Ni: 0.15, Nb: 0.015, V: 0.040, B: 0.0010, N: 0.0046, Als: 0.025, and the balance is Fe and inevitable trace elements such as Ca.

[0042] Step 1: After hot metal pretreatment, converter smelting, and then LF furnace refining after smelting, enter the thin slab caster for casting. The thickness of the thin slab is 70 mm, the casting speed of the caster is 3.1 m / min, and the mold powder for the continuous casting mold adopts the special APH3-C1A mold powder for weathering steel, and the mold powder contains LiO2 to improve its lubrication performance;

[0043] Step 2: Heat the continuously cast thin slab cast in Step 1 through a tunnel type roller hearth heating furnace, with the tapping temperature of 1170 °C and the residence time in the furnace of 18 min;

[0044] Step 3: After the slab is discharged from the furnace, carry out descaling in two passes. After descaling in two passes, carry out continuous rolling, and then carry out third-pass dephosphorization;

[0045] The descaling pressure for the first pass is 24 Mpa, the descaling pressure for the second pass is 35 Mpa, and the descaling pressure for the third pass is 12 Mpa. The descaling for the first and second passes is carried out between the heating furnace and the roughing stand, and the descaling for the third pass is carried out at the outlet of the roughing stand (F1 stand);

[0046] The continuous rolling method is six-stand continuous rolling, and the final rolling temperature is 850 °C;

[0047] Close the cross jets in front of stands F1-F6; close the cooling water for stands F1-F3; intervene in the mill outlet speed and carry out constant-speed rolling at a speed of 4.75 m / s;

[0048] Step 4: After rolling, the strip enters the 8-section laminar cooling section and is cooled to the coiling temperature. The coiling temperature is 560 °C, and the laminar cooling mode is selected as the "8" mode two-stage segmented cooling;

[0049] By numbering the 8-section headers and defining the opening sequence in the secondary laminar cooling model, all the headers in the first and second groups are fully opened. For the upper and lower cooling headers in the seventh and eighth groups, in combination with the actual detection and target control deviation of the coiling temperature, they are intermittently opened from the outlet to the inlet; if the target coiling temperature still cannot be guaranteed after all 8 sections are opened, cooling is carried out in the way of opening one group of headers at intervals from the seventh section to the sixth section;

[0050] The laminar cooling water system is controlled according to the maximum water flow rate during system operation, and the system pressure is 0.7 bar.

[0051] The properties of the steel strip obtained are as follows: yield strength: 460 MPa, tensile strength: 572 MPa, elongation: 30%, 180° cold bending test: D = a, yield ratio: 0.78, relative corrosion rate: 42%; the thickness of the steel strip obtained is 5.0 mm.

[0052] Example 2

[0053] The steel strip is composed of the following chemical components by weight percentage: C: 0.050, Si: 0.30, Mn: 0.90, P: 0.018, S: 0.007, Cu: 0.35, Cr: 0.50, Ni: 0.20, Nb: 0.020, V: 0.050, B: 0.0015, N: 0.0048, Als: 0.040, and the balance is Fe and inevitable trace elements such as Ca.

[0054] Step 1: After hot metal pretreatment, it is smelted in a converter, refined in an LF furnace after smelting, and then poured into a thin slab caster after refining. The thickness of the thin slab is 70 mm, the casting speed of the caster is 3.3 m / min, and the mold powder for the continuous casting mold is the special APH3-C1A mold powder for weathering steel, and the mold powder contains LiO2 to improve its lubrication performance;

[0055] Step 2: Heat the continuously cast thin slab cast in Step 1 in a tunnel type roller hearth reheating furnace. The tapping temperature is 1180 °C and the residence time in the furnace is 22 min.

[0056] Step 3: After the slab is taken out of the furnace, carry out descaling in two passes. After two passes of descaling, carry out tandem rolling, and carry out third-pass dephosphorization after tandem rolling.

[0057] The descaling pressure for the first pass is 26 Mpa, the descaling pressure for the second pass is 37 Mpa, and the descaling pressure for the third pass is 14 Mpa. The first-pass and second-pass descaling are carried out between the reheating furnace and the roughing mill stand. The third-pass dephosphorization is carried out at the outlet of the roughing mill stand (F1 stand).

[0058] The tandem rolling method is six-stand tandem rolling, and the finishing rolling temperature is 860 °C.

[0059] Close the cross jets in front of stands F1-F6; close the cooling water for stands F1-F3; intervene in the outlet speed of the rolling mill to carry out constant-speed rolling, and the speed is 4.75 m / s.

[0060] Step 4: After rolling is completed, the strip enters the 8-section laminar cooling section to be cooled to the coiling temperature. The coiling temperature is 570 °C, and the laminar cooling mode is selected as the "8" mode two-stage segmented cooling.

[0061] By numbering the 8-section headers and defining the opening sequence in the secondary laminar cooling model, all the headers in the first and second groups are opened. For the upper and lower cooling headers in the seventh and eighth groups, in combination with the actual detection and target control deviation of the coiling temperature, they are intermittently opened from the outlet to the inlet; if the target coiling temperature still cannot be guaranteed after all 8 sections are opened, cooling is carried out in the way of opening one header group at intervals from the seventh section to the sixth section.

[0062] The laminar cooling water system is controlled according to the maximum water flow rate during system operation, and the system pressure is 0.8 bar.

[0063] The properties of the produced steel strip are as follows: yield strength: 477 MPa, tensile strength: 595 MPa, elongation: 33%, 180° cold bending test: D = a, yield ratio: 0.80, relative corrosion rate: 44%; the thickness of the produced steel strip is 5.0 mm.

[0064] Example 3

[0065] The steel strip is composed of the following chemical components by weight percentage: C: 0.055, Si: 0.45, Mn: 1.00, P: 0.020, S: 0.008, Cu: 0.45, Cr: 0.55, Ni: 0.30, Nb: 0.030, V: 0.060, B: 0.0020, N: 0.0050, Als: 0.045, and the balance is Fe and inevitable trace elements such as Ca.

[0066] Step 1: After the hot metal pretreatment, it is transferred to the converter for smelting. After smelting, it enters the LF furnace for refining. After refining, it enters the thin slab continuous caster for casting. The thickness of the thin slab is 70 mm, the casting speed of the continuous caster is 3.4 m / min, and the mold powder used in the continuous casting mold is the APH3-C1A mold powder special for weathering steel. The mold powder contains LiO2 to improve its lubrication performance;

[0067] Step 2: The continuously cast thin slab cast in Step 1 is heated by a tunnel type roller hearth heating furnace. The tapping temperature is 1190 °C and the residence time in the furnace is 25 min;

[0068] Step 3: After the slab is taken out of the furnace, descaling is carried out in two passes. After two passes of descaling, continuous rolling is carried out, and dephosphorization is carried out in the third pass;

[0069] The descaling pressure in the first pass is 28 Mpa, the descaling pressure in the second pass is 39 Mpa, and the descaling pressure in the third pass is 16 Mpa. The first pass and the second pass of descaling are carried out between the heating furnace and the roughing mill stand. The third pass of dephosphorization is carried out at the outlet of the roughing mill stand (F1 stand);

[0070] The continuous rolling method is six-stand continuous rolling, and the finishing rolling temperature is 870 °C;

[0071] The cross jets in front of the F1-F6 stands are closed; the cooling water of the F1-F3 stands is closed; the outlet speed of the rolling mill is intervened to carry out constant speed rolling, and the speed is 4.75 m / s;

[0072] Step 4: After rolling, the strip enters the 8-section laminar cooling section to be cooled to the coiling temperature. The coiling temperature is 580 °C, and the laminar cooling mode is selected as the "8" mode two-stage segmented cooling;

[0073] By numbering the 8-section headers and defining the opening sequence in the secondary laminar cooling model, all the headers in the first and second groups are opened. The upper and lower cooling headers in the seventh and eighth groups are intermittently opened from the outlet to the inlet in combination with the actual detection and target control deviation of the coiling temperature; if the target coiling temperature still cannot be guaranteed after all 8 sections are opened, cooling is carried out in the way of opening one header at intervals from the seventh section to the sixth section;

[0074] The laminar cooling water system is controlled according to the maximum water flow rate during system operation, and the system pressure is 0.9 bar.

[0075] The properties of the steel strip obtained are as follows: yield strength: 487 MPa, tensile strength: 607 MPa, elongation: 35%, 180° cold bending test: D = a, yield ratio: 0.82, relative corrosion rate: 45%; the thickness of the obtained steel strip is 5.0 mm.

[0076]

[0077] It can be seen from the data comparison in Table 1 that when the steel strip produced by this production process is compared with the original steel strip, both the yield strength and the tensile strength are greatly improved, the elongation and the grain size are significantly increased, and the relative corrosion rate is significantly reduced. It can be seen that the properties such as the strength and toughness, atmospheric corrosion resistance, weldability, and cold stamping formability of the steel strip produced by this production process have all been improved; when the steel strip produced by this production process is compared with the steel strip standard, all properties meet the requirements of standards TB / T1979-2014 and GB / T4171-2008.

[0078] At the same time, this production process has the following advantages: simple technical equipment requirements, low energy consumption and alloy cost, continuous casting with other steel grades can be realized, short order delivery cycle, stable mechanical properties of products, excellent elongation index, etc. The cracking rate of the cold-stamped products made is less than 3‰, and the corrosion resistance index I is greater than 6.0, fully meeting the processing and use requirement standards for the side doors and middle doors of open wagons of railway vehicles; this production process can be realized on most CSP continuous casting and rolling production lines, with strong industrial production operability, low continuous casting breakout rate, easy to produce, and stable product performance indicators.

Claims

1. CSP production process of weather-resistant steel strip for railway vehicle doors, Characterized in that: It includes the following steps: Step 1: After hot metal pretreatment, converter smelting is carried out, and after smelting, LF furnace refining is carried out. After refining, it enters the thin slab continuous caster for casting. The casting speed of the continuous caster is 3.1 - 3.4 m / min, and the mold powder for the continuous casting mold adopts the special APH3-C1A mold powder for weather-resistant steel; Step 2: The cast continuous casting thin slab in Step 1 is heated by a tunnel type roller hearth heating furnace, with the tapping temperature of 1170 - 1190 °C and the residence time in the furnace of 18 - 25 min; Step 3: After the slab is taken out of the furnace, descaling is carried out, and after descaling, continuous rolling is carried out, and then dephosphorization is carried out again; Step 4: After rolling is completed, the strip enters the 8-section laminar cooling section to be cooled to the coiling temperature. The coiling temperature is 560 - 580 °C, and the laminar cooling mode selects the "8" mode two-stage segmented cooling; The weather-resistant steel strip for railway vehicle doors consists of the following chemical components by weight percentage: C: 0.040 - 0.055, Si: 0.25 - 0.45, Mn: 0.80 - 1.00, P: ≤0.020, S: ≤0.008, Cu: 0.25 - 0.45, Cr: 0.40 - 0.55, Ni: 0.15 - 0.30, Nb: 0.015 - 0.030, V: 0.040 - 0.060, B: 0.0010 - 0.0020, N < 0.0050, Als: 0.025 - 0.045, and the balance is Fe and inevitable trace elements.

2. The CSP production process of the weather-resistant steel strip for railway vehicle doors according to claim 1, Characterized in that: In the said Step 3, two passes of descaling are carried out after the slab is taken out of the furnace, and three passes of dephosphorization are carried out after continuous rolling. The descaling pressure of the first pass ≥ 24 Mpa, the descaling pressure of the second pass ≥ 35 Mpa, the descaling pressure of the third pass ≥ 12 Mpa. The first pass and the second pass of descaling are carried out between the heating furnace and the roughing mill stand, and the third pass of dephosphorization is carried out at the outlet of the roughing mill stand.

3. The CSP production process of the weather-resistant steel strip for railway vehicle doors according to claim 1, Characterized in that: In the said Step 3, the continuous rolling method is six-stand continuous rolling, and the finishing rolling temperature is 850 - 870 °C.

4. The CSP production process of the weather-resistant steel strip for railway vehicle doors according to claim 1, Characterized in that: In the said Step 3, the front cross jets in front of F1 - F6 stands are closed; The cooling water of F1 - F3 stands is closed; the outlet speed of the rolling mill is intervened to carry out constant speed rolling, and the speed is 4.75 m / s.

5. The CSP production process of the weather-resistant steel strip for railway vehicle doors according to claim 1, Characterized in that: In the said Step 4, the laminar cooling water system is controlled according to the maximum water flow rate of the system operation, and the system pressure ≥ 0.7 bar.

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