345MPa-grade low-yield-ratio weather-proof checkered plate for rail wagon and manufacturing method thereof

Abstract

The invention belongs to the field of metallurgical manufacturing, and particularly relates to a 345MPa-grade low-yield-ratio weather-proof checkered plate for a railway wagon and a manufacturing method of the weather-proof checkered plate. The steel comprises the following chemical components in percentage by weight: 0.06%-0.1% of C, 0.25%-0.3% of Si, 0.2%-0.5% of Mn, 0.06%-0.13% of P, less than or equal to 0.008% of S, 0.5%-0.7% of Cr, 0.25%-0.40% of Cu, 0.12%-0.18% of Ni, 0.02%-0.03% of Ti, 0.19%-0.31% of carbon equivalent and the balance of Fe and inevitable impurities. The low-yield-ratio weather-proof checkered plate for the rail wagon is obtained through alloy element matching and the controlled rolling and controlled cooling process, the surface quality is excellent, grains are high, the plate shape meets the standard, the yield strength is larger than 345 MPa, and the yield ratio is not larger than 0.70.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metallurgical manufacturing, and particularly relates to a 345MPa-grade low-yield-ratio weather-resistant pattern plate for railway freight cars and a manufacturing method thereof. BACKGROUND

[0002] With the progress of science and technology, the manufacturing materials of railway freight cars are upgraded, and users have the demand for some positions of railway freight cars to bear impact force and friction, and new requirements are put forward for the manufacturing materials: corrosion resistance, low yield ratio, anti-skid, easy to clean. The strength grade of the pattern plate widely used in daily life is 235MPa, and the corrosion resistance is poor. At present, there is no weather-resistant pattern plate for railway freight cars on the market. The present application develops a weather-resistant hot-rolled pattern plate with a yield strength of 345MPa, corrosion resistance, low yield ratio, excellent surface quality and anti-skid, and the production of the hot-rolled pattern plate is stabilized by controlling rolling and cooling.

[0003] The patent document with the publication number CN110093568A discloses "a high-strength low-yield-ratio weather-resistant carriage steel and a preparation method thereof", which proposes a high-strength low-yield-ratio weather-resistant carriage steel. The steel composition is C: 0.10-0.12%; Si: 0.30-0.50%; Mn: 0.30-0.50%; P≤0.015%; S≤0.005%; Al≤0.050%; Cu: 0.26-0.36%; Cr: 0.50-0.60%; Ni: 0.15-0.25%; N≤50ppm, by controlling the heating temperature 1230±10℃, the heating time≥180min, the final rolling temperature 860-900℃, and the coiling temperature 700-730℃, the yield ratio≤0.75, a carriage steel with a yield strength not less than 345Mpa is obtained. The composition is different, and it is not a pattern plate, and the rolling process is different.

[0004] The patent document with the publication number CN105220078A discloses "a low-yield-ratio weather-resistant steel and a preparation method thereof", which proposes a low-yield-ratio weather-resistant steel with the chemical composition of C≤0.07%; Si:≤0.5%; Mn≤1.5%; P≤0.02%; S≤0.01%; Cu: 0.2-0.55%; Cr: 3-3.7%; Ni: 0.1-0.65%, Ti: 0.01%-0.03%, after controlled rolling and controlled cooling, a low-yield-ratio weather-resistant steel with a yield strength of 546MPa, a yield ratio of 0.74, and a relative corrosion rate of 26.5% is obtained. It is not a high-P corrosion-resistant steel and not a pattern plate.

[0005] The patent document with publication number CN118563222A discloses "a 450MPa grade non-coating weathering steel strip and its preparation method", the proposed weathering steel composition is C: 0.04-0.07%, Si: 0.10-0.25%, Mn: 0.75-0.95%, P: ≤0.025%, S: ≤0.004%, Cu: 0.30-0.45%, Cr: 0.85-1.25%, Ni: 0.05-0.15%, Nb: 0.010-0.020%, Ti: 0.020-0.045%, Alt: 1.20-1.60%, N: ≤0.006%, B: ≤0.0005%, Ca: 0.001-0.005%. Containing Nb, Ni cost is high, non-high P type weathering steel.

[0006] The patent document with publication number CN118595160A discloses "a manufacturing method of hot-rolled thin gauge pattern plate", the proposed hot-rolled pattern plate composition is C: 0.05-0.09%; Si: ≤0.1%; Mn: 0.8-1.0%; P ≤0.02%; S ≤0.01%; Cr: 0.02-0.05%; Ti: 0.005%-0.02%, through the finishing rolling opening temperature 1020-1050℃, the latter cooling, the cooling down header and the upper header cooling flow is 1:1.2-1.3 obtained hot-rolled pattern plate, but is not weathering pattern plate, corrosion resistance is not involved.

[0007] The patent document with publication number CN118513365A discloses "a control method of thin gauge pattern plate rolling", provides a pattern plate rolling control method, the heating temperature is set to 1270±20℃, the rough rolling termination temperature is 1080±20℃, the finishing rolling final rolling temperature is 900±20℃, the coiling temperature is 650±20℃, through controlling the intermediate blank thickness, ensures the pattern plate shape and the pattern height, but does not mention the pattern plate strength, the yield ratio and the corrosion resistance.

[0008] After searching and analyzing the prior art: no same technical scheme as the present invention is found. The above-mentioned invention does not mention the development and manufacturing method of a 345MPa grade low yield ratio weathering pattern plate for railway freight cars. In order to meet the iteration and upgrading of railway freight car manufacturing materials, a low yield ratio, excellent surface quality weathering pattern plate for railway freight cars is urgently needed to meet market demand. SUMMARY

[0009] In view of the above problems that the traditional pattern plate cannot meet the market demand in strength, and has poor corrosion resistance, high maintenance cost and short service life, the application provides a hot-rolled pattern plate with corrosion resistance, low yield strength ratio, low cost and excellent surface quality. The application relates to a 345MPa-grade low yield strength ratio weather-resistant pattern plate for railway freight cars and a manufacturing method thereof. The low yield strength ratio hot-rolled pattern plate with a thickness of 4mm to 8mm is obtained through alloy element proportioning and controlled rolling and controlled cooling processes, and has excellent surface quality, satisfies the standard in pattern height and plate shape, has a yield strength greater than 345MPa, and has a yield strength ratio not higher than 0.70.

[0010] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0011] The chemical composition of the 345MPa-grade low yield strength ratio weather-resistant pattern plate for railway freight cars is as follows in terms of percentage by weight: C: 0.06% to 0.1%, Si: 0.25% to 0.3%, Mn: 0.2% to 0.5%, P: 0.06% to 0.13%, S: less than or equal to 0.008%, Cr: 0.5% to 0.7%, Cu: 0.25% to 0.40%, Ni: 0.12% to 0.18%, Ti: 0.02% to 0.03%, carbon equivalent (Ceq): 0.19% to 0.31%, and the balance of Fe and inevitable impurities.

[0012] The application requires that in the chemical composition, Cu+10*Ti is less than or equal to 0.7%. The following describes the mechanism of each alloy component of the structural steel of the application, wherein the percentage symbol % represents percentage by weight:

[0013] C: Carbon atoms are interstitially dissolved in the crystal lattice in the steel, significantly improve the strength of the steel, and can significantly improve the tensile strength of the material, thereby reducing the yield strength ratio. The steel of the application is designed with low carbon, and the carbon content is designed to be 0.06% to 0.1% to ensure the toughness and plasticity of the steel.

[0014] Si: Si improves the strength of the steel through solid solution strengthening, and Si promotes the formation of a dense protective film on the surface of the steel to improve the corrosion resistance of the steel. In the application, the Si content is not less than 0.25%. When the Si content is higher than 0.3%, olivine phase may exist in the iron oxide scale, which is not easy to remove. Therefore, in the application, the Si content is not higher than 0.3%.

[0015] Mn: Mn is one of the solid solution strengthening elements in the steel, which improves the strength of the steel, and also exists as a deoxidizing element in the steelmaking process. In the application, the Mn content is not less than 0.2%. If the Mn content is too high, the welding performance of the steel will be deteriorated. In the application, the Mn content is not higher than 0.5%.

[0016] P: P and Cu match reasonably, generate internal rust layer in the steel, significantly reduce the corrosion rate of the steel, improve the corrosion resistance of the steel. The lower limit of P content is 0.06%, and the upper limit of P content is 0.13%.

[0017] S: S is a harmful element in the steel, and the MnS inclusions formed with the Mn element seriously affect the plasticity and toughness of the steel, and the S content is controlled below 0.008%.

[0018] Cr: Cr and Cu match reasonably, form a dense Cr-Cu compound rust layer, which can improve the corrosion resistance of the steel, at the same time, the higher the Cr content, the lower the Ac3 temperature, with the increase of Cr content, the tensile strength increases, the yield strength decreases, and the yield ratio decreases, the Cr content is not less than 0.5%, considering that the higher Cr content will significantly reduce the welding performance of the steel, the Cr content is not higher than 0.7%.

[0019] Cu: Cu in the steel affects the formation and distribution of rust layer with P, the formed oxide can prevent the steel from continuing to oxidize and corrode, significantly improve the corrosion resistance of the steel, thereby prolonging the service life of the steel and reducing the maintenance cost. Considering the cost, the Cu content of the present application is controlled at 0.25% to 0.40%.

[0020] Ni: In order to ensure the atmospheric corrosion resistance of the steel, higher Cu and P are added in the present application, and high Cu content is easy to cause hydrogen embrittlement, and high P content is easy to increase the brittle transition temperature of the steel in the steel to produce cold brittleness effect, therefore, a part of Ni is added in the present application to form high melting point Cu-Ni binary alloy phase, reduce low melting point Cu phase, improve these problems and reduce crack sensitivity. In addition, Ni improves the self-corrosion potential of the steel, effectively improves the corrosion resistance; but due to the high price of Ni, the Ni content in the present application is controlled at 0.12% to 0.18%.

[0021] Ti: Because Ti is a strong oxidizing agent in the steel, it can make the structure of the steel more dense, and the effect of refining the grains is significant, and the strength and toughness are improved; during welding, it can improve the low temperature toughness of the heat affected zone, and also can reduce the aging sensitivity and cold brittleness of the steel; Ti reacts with S to form Ti4C2S2 to reduce the formation of Cu2S brittle phase; the generated TiC provides additional pinning sites to compensate for the strength loss caused by Cu, and plays a synergistic strengthening effect, but when the Ti content is higher than 0.03%, the yield strength increases sharply, and the yield ratio is significantly improved, therefore, the Ti content in the present application is controlled at 0.02 to 0.03%.

[0022] Ceq: When the carbon equivalent is not higher than 0.31%, martensite does not appear even if the cooling speed is high, the dislocation density of bainite in the weathering steel is high, the toughness is good, the deformation and crack defects are less, and the problems of deformation and cracks prone to occur in the use of martensite are avoided. When the carbon equivalent is lower than 0.19%, the strength and toughness decrease, the yield strength is high, and the like.

[0023] In addition to controlling the content of the components to meet the above requirements, the low yield ratio weathering pattern plate of the present application needs to meet Cu+10xTi≤0.7%, because Cu and Ti can improve the strength of the material through two-phase particle precipitation, but the precipitation strengthening effect will increase the yield ratio of the steel, the generated TiC provides additional pinning sites to compensate for the strength imbalance caused by Cu, and through this regulation, Ti reacts with S to form Ti4C2S2 first, reduces the formation of Cu2S brittle phase, and reduces the Cu brittleness.

[0024] The present application also provides a manufacturing process of a low yield ratio weathering hot-rolled pattern plate for railway wagons, which obtains a low yield ratio weathering hot-rolled pattern plate for railway wagons with a specification of 4mm-8mm thick through a controlled rolling and controlled cooling process, to ensure that the strength, corrosion resistance, pattern height and plate shape of the pattern plate meet the standards. The method obtains a 345MPa grade low yield ratio weathering hot-rolled pattern plate for railway wagons containing the above chemical components through molten iron pretreatment deep desulfurization, top and bottom combined blowing in a converter, LF furnace external refining, slab continuous casting, casting blank heating, hot continuous rolling, laminar cooling and coiling.

[0025] A manufacturing method of a 345MPa grade low yield ratio weathering pattern plate for railway wagons, specifically comprising the following method steps:

[0026] 1) Smelting and casting process: the molten iron of the present application is desulfurized to [S]≤0.005%, then subjected to conventional smelting in a top and bottom combined blowing converter, and then subjected to LF furnace refining. Si-Ca wire is fed for treatment, which aims to purify the molten steel and change the properties and morphology of part of the inclusions, and reduce the influence of non-metallic inclusions on the corrosion resistance of the steel.

[0027] 2) Continuous casting process: the molten steel is cast by using dynamic soft reduction technology, and the whole process is protected by using special protective slag for weathering steel, and the casting temperature of the tundish is controlled at 1546-1566℃, to obtain a 200-230mm thick casting blank.

[0028] 3) Rolling process: the pattern plate of the present application is rolled, the heating temperature is controlled at 1200-1230℃, the furnace time is not higher than 120 min, rough rolling is carried out in 5 passes, in order to ensure that the secondary oxide scale is removed, the phosphorus removal is started before rough rolling, the rough rolling temperature is 1050-1080℃; the reduction rate of finish rolling is controlled in 7 passes, in order to avoid the slip of F1 rolling mill, the reduction rate is not higher than 56%, the reduction rate of F2 rolling mill is controlled at 51%-55%, the reduction rate of F3 rolling mill is controlled at 40%-44%, the reduction rate of F4 rolling mill is controlled at 31%-35%, the reduction rate of F5 rolling mill is controlled at 18%-22%, the reduction rate of F6 rolling mill is controlled at 16%-20%, the reduction rate of F7 rolling mill is controlled at 15%-17%, the upper roller of F7 rolling mill is a pattern roller, the lower work roller adopts a flat roller without convexity, the lower work roller adopts a sinusoidal roller type with -20μm, the F7 roller shifting is disabled, the convexity feedback and flatness feedback are disabled, and the plate shape is manually adjusted. The present application shifts the rolling load, and the purpose is to ensure the high pattern bean and the reduction rate is not lower than 15%. The finish rolling termination temperature is at 860-920℃.

[0029] 4) Cooling process: in order to reduce the influence of water on the surface of the pattern plate on the determination of coiling temperature, the laminar flow cooling adopts the water spraying mode with interval 2 groups of Changcheng, and the tail end header is closed, the flow rate of each group is 400-500m 3 / h, at the same time, the feedback control is disabled, and the cooling is carried out to the coiling temperature; the cooling mode can reduce the yield ratio, and the innovative cooling mode and cooling intensity can realize the control of the plate shape and yield ratio. This is because the pattern plate is cooled to room temperature after isothermal holding for a certain time in the bainite formation temperature range, so as to increase the strain accumulation degree, supercooling degree and phase transformation driving force of the non-recrystallization zone of austenite, so as to promote the formation of acicular ferrite structure.

[0030] 5) Coiling process: the pattern plate is coiled after cooling, and the coiling temperature is controlled at 580-660℃, compared with the traditional high-strength corrosion-resistant steel, the coiling temperature is slightly lower, the ε-Cu precipitation size is reduced, the Cu brittleness is reduced, and the pattern plate bean height is ensured.

[0031] The low yield ratio weather-resistant pattern plate for railway freight cars obtained by using the above chemical composition and hot rolling process has a yield strength of 375-410MPa, a tensile strength of 548-585MPa, an elongation of 25%-28%, a yield ratio not higher than 0.70, a corrosion rate relative to Q345B of 35%-40%, a pattern height up to standard, and excellent pickling-free plate shape.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] The application provides a hot-rolled patterned plate with corrosion resistance, low yield ratio, low cost and excellent surface quality. The low yield ratio hot-rolled patterned plate with a thickness of 4mm-8mm, excellent surface quality, standard pattern height and plate shape, yield strength of 375-410MPa, tensile strength of 548-585MPa, elongation of 25%-28%, yield ratio of not more than 0.70, corrosion rate of 35%-40% relative to Q345B and standard pattern height is obtained by alloy element proportioning and controlled rolling and controlled cooling process. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a steel plate surface picture of the hot-rolled patterned plate of the application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the application more clear, the specific embodiments of the application are further described below, and the following embodiments are used to specifically describe the application content, which are only general description of the application content and do not limit the application content.

[0036] The chemical composition of the embodiments of the application is shown in Table 1; the process system parameters of the embodiments are shown in Table 2; the finishing mill reduction rate distribution of the embodiments is shown in Table 3; the properties of the finished steel plate of the embodiments are shown in Table 4; Table 5 is the pattern height data of Example 1; and the rapid corrosion test comparison results of the steel of the embodiments and the comparison steel are shown in Table 6.

[0037] Table 1 Chemical composition of the embodiments, %

[0038]

[0039]

[0040] Table 2 Process system of the embodiments

[0041]

[0042] Table 3 Reduction rate distribution of the finishing mill

[0043] Serial number F1 reduction ratio F2 reduction ratio F3 reduction ratio F4 reduction ratio F5 reduction ratio F6 reduction ratio F7 reduction ratio Example 1 54 52 41 32 19 17 16 Example 2 55 53 42 33 20 18 17 Example 3 56 53 43 34 21 18 17 Example 4 54 51 41 32 18 17 16 Example 5 55 53 41 33 20 18 16 Example 6 56 54 43 34 21 18 17 Example 7 54 52 41 33 19 17 16 Example 8 55 52 42 34 20 18 17 Example 9 54 52 41 33 19 17 16 Example 10 54 53 42 34 20 18 17

[0044] Table 4 Properties of the finished steel plate of the embodiments

[0045]

[0046]

[0047] Table 5 Pattern height of Example 1, mm

[0048]

[0049] Table 6 Comparison results of rapid corrosion test of the inventive steel and the comparative steel

[0050]

[0051] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable the person skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A 345MPa grade low yield ratio weather-resistant checkered plate for railway freight cars, characterized in that: Its chemical composition by weight percentage is: C: 0.06%~0.1%, Si: 0.25%~0.3%, Mn: 0.2%~0.5%, P: 0.06%~0.13%, S≤0.008%, Cr: 0.5%~0.7%, Cu: 0.25%~0.40%, Ni: 0.12%~0.18%, Ti: 0.02%~0.03%, carbon equivalent 0.19%~0.31%, and the balance is Fe and unavoidable impurities.

2. The 345MPa grade low yield ratio weather-resistant patterned plate for railway freight cars according to claim 1, characterized in that: Chemical composition: Cu+10×Ti≤0.7%.

3. The 345MPa grade low yield ratio weather-resistant patterned plate for railway freight cars according to claim 1, characterized in that: The patterned plate has a thickness of 4 mm to 8 mm.

4. The 345MPa grade low yield ratio weather-resistant patterned plate for railway freight cars according to claim 1, characterized in that: The patterned plate has a yield strength of 375-410 MPa, a tensile strength of 548-585 MPa, an elongation of 25%-28%, a yield strength ratio not higher than 0.70, and a corrosion rate relative to Q345B of 35%-40%.

5. A method for manufacturing a 345 MPa grade low yield ratio weather-resistant checkered plate for railway freight cars according to any one of claims 1 to 4, characterized in that: The specific method steps include: 1) Continuous casting process: the tundish casting temperature is controlled at 1546~1566℃; 2) Rolling: The heating temperature is controlled at 1200-1230°C, the furnace time is not higher than 120 minutes, the rough rolling temperature is 1050-1080°C; the finishing rolling end temperature is 860-920°C; 3) Cooling: Laminar cooling adopts the watering method of two groups of Great Walls at intervals, and the end header is closed, with a flow rate of 400-500m 3 / h, while feedback control is disabled and cooled to coiling temperature; 4) Coiling: After the patterned plate is cooled, it is coiled and the coiling temperature is controlled at 580-660℃.

6. The method for manufacturing a 345MPa grade low yield ratio weather-resistant patterned plate for railway freight cars according to claim 5, characterized in that: In the step 2), the reduction rate of the finishing mill F1 is not higher than 56%, the reduction rate of the F2 mill is controlled at 51% to 55%, the reduction rate of the F3 mill is controlled at 40% to 44%, the reduction rate of the F4 mill is controlled at 31% to 35%, the reduction rate of the F5 mill is controlled at 18% to 22%, the reduction rate of the F6 mill is controlled at 16% to 20%, and the reduction rate of the F7 mill is controlled at 15% to 17%, wherein the upper roll of the F7 mill is a patterned roll, the lower working roll adopts a flat roll without crown, the lower working roll adopts a -20μm sinusoidal roll profile, the F7 roll shifting is disabled, the crown feedback and flatness feedback are disabled, and the plate shape is manually adjusted.

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