A high plastic toughness phosphorus-containing hot-rolled weathering steel plate and a manufacturing method thereof

Abstract

The invention provides a high plastic toughness phosphorus-containing hot-rolled weathering steel plate and a manufacturing method thereof, wherein the composition is as follows: C: 0.070%-0.100%, Si: 0.30-0.50%, Mn: 0.25%-0.55%, P: 0.080%-0.120%, S: ≤0.0050%, Cr: 0.80%-1.10%, Ni: 0.03-0.09%, Cu: 0.20%-0.30%, Als: 0.015%-0.030%, Ca: 0.0010%-0.0030%, Ti: 0.015%-0.035%, N≤0.0040%, and the rest is Fe and unavoidable impurity elements. Compared with the prior art, the steel plate of the invention has good atmospheric corrosion resistance, with a corrosion rate of <45% relative to Q345B, and the steel plate has high strength and excellent plastic toughness.

Description

Technical Field

[0001] The invention belongs to the field of steel material manufacturing, and specifically relates to a phosphorus-containing hot-rolled weathering steel plate with excellent atmospheric corrosion resistance and plastic toughness and a tensile strength of 550 MPa and a manufacturing method thereof. Background Art

[0002] Weathering steel is also called atmospheric corrosion resistant steel. By adding a small amount of alloying elements such as Cu, P, Cr, and Ni, it has good corrosion resistance in the atmospheric environment. Compared with ordinary carbon steel, weathering steel has excellent atmospheric corrosion resistance, reduces corrosion rate, and increases service life; compared with stainless steel, the manufacturing cost is greatly reduced, and it has good welding performance. It is widely used in the manufacture of railway vehicles, containers, bridges, buildings, outdoor towers, photovoltaic brackets, etc.

[0003] P is a very cheap non-metallic element that easily reacts with oxygen and water in the air to form insoluble and dense phosphates, which evenly cover the surface of the steel matrix and prevent oxygen and water from penetrating into the matrix, thereby improving the atmospheric corrosion resistance of the steel. It can also improve the strength of the steel through solid solution strengthening, greatly reducing the production cost of weathering steel. However, P is easy to segregate at the grain boundary, reduce the grain boundary bonding force, significantly reduce the impact toughness and plasticity of the steel, and increase the sensitivity of welding cracks. In particular, as the temperature decreases and the thickness of the steel plate increases, phosphorus-containing weathering steel is very likely to produce "cold brittleness". Therefore, P-containing weathering steel is usually used in the production of thin-gauge plates and strips.

[0004] The patent with publication number CN111850406A, published on October 30, 2020, discloses 380MPa grade high-phosphorus weathering steel and its preparation method, whose chemical composition and mass percentage content are: C≤0.12%, Si: 0.20-0.60%, Mn≤1.50%, P: 0.060-0.150%, S≤0.015%, Cr: 0.20-0.80%, Ni: 0.10-0.40%, Cu: 0.20-0.60%, Als≥0.010%, and the balance is Fe and unavoidable impurities. The preferred chemical composition and mass percentage content are: C: 0.06-0.08%, Si: 0.30-0.50%, Mn: 0.85-1.00%, P: 0.080-0.120%, S≤0.007%, Cr: 0.40-0.60%, Ni: 0.20-0.30%, Cu: 0.28-0.38%, Als: 0.015-0.050%, the remainder is Fe and unavoidable impurities. This patent increases the strength by increasing the Mn content, and the content of precious metal element Ni is relatively high, which greatly increases the manufacturing cost. The elongation is ≥18%, the impact energy at -40℃ is ≥27J, and the plasticity and toughness are insufficient. The use of LF→RH double refining treatment not only increases the production cost, but is also not conducive to efficient production.

[0005] The patent with publication number CN111926254A, published on November 13, 2020, discloses 440MPa grade high-phosphorus and high-chromium weathering steel, its preparation method and application, whose chemical composition and mass percentage content are C≤0.12%, Si: 0.20-0.60%, Mn≤1.50%, P: 0.060-0.150%, S≤0.015%, Cr: 1.20-2.00%, Ni: 0.10-0.40%, Cu: 0.20-0.60%, Als≥0.010%, and the balance is Fe and unavoidable impurities. The preferred chemical composition and mass percentage content are: C: 0.06-0.08%, Si: 0.30-0.50%, Mn: 0.85-1.00%, P: 0.080-0.120%, S≤0.007%, Cr: 1.60-1.80%, Ni: 0.20-0.30%, Cu: 0.28-0.38%, Als: 0.015-0.050%, the remainder is Fe and unavoidable impurities. This patent increases the strength by increasing the content of Mn and Cr, and the content of precious metal element Ni is relatively high, which greatly increases the manufacturing cost. The elongation is ≥18%, the impact energy at -40℃ is ≥27J, and the plasticity and toughness are insufficient. The use of LF-RH-LF three-time refining treatment not only increases the production cost, but is also not conducive to efficient production.

[0006] The patent with publication number CN106591707A published on April 26, 2017, discloses a titanium-containing low-nickel high-strength weathering steel and its production method, the chemical composition and mass percentage content of which are C: 0.07-0.12%, Si≤0.45%, Mn≤0.7%, P: 0.06-0.15%, S≤0.012%, Cu: 0.25-0.45%, Cr: 0.35-0.65%, Ni≤0.15%, Ti: 0.04-0.08%, Als: 0.010-0.050%, and the balance is Fe and unavoidable impurities. Yield strength is 415-540MPa, tensile strength is 520-750MPa, and elongation is ≥27%. This invention patent improves strength through Ti fine grain strengthening and precipitation strengthening. The Ti content is high, and the N content is not controlled, which easily generates large-sized TiN particles, reducing the plastic toughness of the material. In particular, as the thickness of the steel plate increases, the low-temperature toughness decreases significantly. This patent does not specify the applicable hot-rolled steel plate thickness range, and does not take low-temperature toughness and atmospheric corrosion resistance as control targets. Summary of the invention

[0007] The purpose of the present invention is to provide a high plasticity and toughness phosphorus-containing hot-rolled weathering steel plate and a manufacturing method thereof. The product is produced in a traditional hot continuous rolling plate and strip process, and the product thickness is 6-12mm and the tensile strength reaches 550MPa level, which solves the problem of controlling its low-temperature toughness at -40°C. It has excellent plasticity and toughness and atmospheric corrosion resistance, and can be used for the manufacture of equipment and components serving in atmospheric environments, thereby improving service life and safety.

[0008] The specific technical solutions of the present invention are as follows:

[0009] A high-plasticity and toughness phosphorus-containing hot-rolled weathering steel plate comprises the following components in mass percentage: C: 0.070%-0.100%, Si: 0.30%-0.50%, Mn: 0.25%-0.55%, P: 0.080%-0.120%, S: ≤0.0050%, Cr: 0.80%-1.10%, Ni: 0.03-0.09%, Cu: 0.20%-0.30%, Als: 0.015%-0.030%, Ca: 0.0010%-0.0030%, Ti: 0.015%-0.035%, N≤0.0040%, and the rest are Fe and unavoidable impurity elements.

[0010] The high plasticity and toughness phosphorus-containing hot-rolled weathering steel plate has a thickness of 6-12 mm;

[0011] The high plasticity and toughness phosphorus-containing hot-rolled weathering steel plate, when the steel plate is 10mm≤thickness≤12mm, adds Nb element, mass percentage: 0.008%-0.015%; as the thickness increases, the difficulty of controlling low-temperature toughness increases. If single Ti microalloying is still used to increase the strength of the steel plate by increasing the Ti content, it is difficult to simultaneously meet the -40°C low-temperature toughness requirements.

[0012] The weathering index I of the high plastic toughness phosphorus-containing hot-rolled weathering steel plate is ≥7.5, where I=26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)×(%Ni)-9.10(%Ni)×(%P)-33.39(%Cu) 2 .

[0013] The composition of the high plasticity and toughness phosphorus-containing hot-rolled weathering steel plate must also meet the following requirements: Cr+Cu≥1.1%, 3≤Cu / Ni≤7. Cr, Cu, and Ni are the main alloying elements for improving the atmospheric corrosion resistance of steel, and the effect of composite addition is more significant. Among them, Ni is the most expensive precious alloy, followed by Cu, and Cr is the lowest. Due to the low melting point of Cu, cracks are easily generated during continuous casting and hot rolling. By adding an appropriate amount of Ni, the manufacturability of weathering steel is improved, while the low-temperature toughness is also improved. In order to further improve the atmospheric corrosion resistance and low-temperature toughness of the steel plate of the present invention, Cr+Cu≥1.1%, 3≤Cu / Ni≤7 are controlled.

[0014] The microstructure of the high-plasticity and toughness phosphorus-containing hot-rolled weathering steel plate is polygonal ferrite and pearlite, the average grain size of the ferrite is 7-8 μm, and the volume fraction of the pearlite is 4-6%.

[0015] The yield strength R of the high plastic toughness phosphorus hot rolled weathering steel plate eL ≥420MPa, tensile strength R m ≥550MPa, elongation A≥27%, -20℃KV2≥135J (size: 10×10×55mm), -40℃KV2≥120J (size: 10×10×55mm), with high strength and excellent plasticity and toughness.

[0016] The high-plasticity and toughness phosphorus-containing hot-rolled weathering steel plate also has excellent cold bending forming performance: no cracks appear on the outer side of the sample after 180° cold bending (d=a) and double cold bending, which is convenient for downstream users to manufacture and process.

[0017] The corrosion rate of the high plasticity and toughness phosphorus-containing hot-rolled weathering steel plate is less than 45% relative to that of Q345B.

[0018] The present invention provides a method for manufacturing a high-plasticity and toughness phosphorus-containing hot-rolled weathering steel plate, comprising the following process flow:

[0019] Hot metal pretreatment and deep desulfurization → top and bottom composite blowing in converter → LF refining → continuous casting → heating → rolling → laminar cooling → coiling → cooling to room temperature.

[0020] The molten iron pretreatment deep desulfurization: molten steel is smelted according to the above chemical composition, and the molten iron pretreatment deep desulfurization is performed to a level of ≤0.0050%.

[0021] The LF refining: the refining adopts LF furnace slag desulfurization, feeds calcium wire to carry out inclusion modification treatment, weak stirring time is greater than 10min, promotes non-metallic inclusions in molten steel to float up, improves molten steel cleanliness, and the LF outlet temperature is 1560-1580℃.

[0022] The continuous casting: electromagnetic stirring and dynamic soft pressure are used to improve the internal quality of the continuous casting billet. The temperature of the molten steel casting ladle is controlled at 1530-1560℃, and special covering agent and protective slag are used for protective casting. The continuous casting billet drawing speed is controlled at 1.0-1.5m / min. The thickness of the continuous casting slab is 230mm. After the billet is cut, it is preferred to be directly loaded into the furnace, or hot loaded, and the temperature into the heating furnace is ≥500℃.

[0023] Heating: The slab is heated in a walking beam heating furnace at a temperature of 1190°C-1250°C and a holding time of 120-170 minutes to promote full solid solution of alloy elements and homogenization of austenite. If the heating time is too long, liquid Cu will be enriched at the grain boundary and surface cracks will be generated. After the slab is removed from the furnace, high-pressure water is used to remove the primary iron oxide produced during the heating process.

[0024] The rolling process: hot rolling is divided into two stages: rough rolling and finishing rolling. In the rough rolling stage, two four-roll reversible rough rolling mills are used for three passes each, with a rolling temperature of ≥1050°C and a reduction rate of ≥75%. Reciprocating rolling is carried out in the austenite recrystallization zone, and large deformation is used in each pass to promote the recovery of austenite grains to recrystallize and refine the austenite grain size. In the finishing rolling stage, 7 four-roll rolling mills are used for continuous rolling. This stage is rolled in the austenite non-recrystallization zone, with a start rolling temperature of ≤1030°C and a reduction rate of ≥80%. By accumulating large deformations, the deformation bands and dislocation density in the austenite grains are increased, thereby increasing the phase deformation nuclei and refining the ferrite grains. The finishing rolling final rolling temperature is 850-900°C.

[0025] The laminar cooling: after rolling, the steel plate is cooled quickly by dense laminar cooling to improve the degree of supercooling, increase the phase deformation nucleation rate, reduce the critical nucleus size, and thus refine the ferrite grain size. The cooling rate is 25-40°C / s. The coiling temperature is 570-630°C. When the coiling temperature is higher than 630°C, the ferrite grain size and the two-phase precipitation particles are coarsened, and the material strength is insufficient. When the coiling temperature is lower than 570°C, a granular bainite structure is generated, which reduces the plastic toughness of the steel.

[0026] The design principle of alloy elements and their mass percentages of the hot-rolled high corrosion-resistant steel plate provided by the present invention is as follows:

[0027] C (carbon): C is the most economical element for improving the strength of steel and can improve the strength through interstitial solid solution strengthening. However, too high a C content will increase the pearlite content, reduce the ferrite content, and reduce the plasticity and low-temperature toughness of the steel. In order to improve the plasticity and toughness of the weathering steel plate, the present invention designs the C content to be 0.070-0.100%.

[0028] Si (silicon): Si is beneficial to refine corrosion products, promote the formation of a dense protective rust layer on the surface of steel, and thus improve atmospheric corrosion resistance; Si can also reduce the austenite phase area, promote the formation of ferrite, and dissolve in ferrite to improve strength; however, too high Si content will reduce the welding performance of steel. Therefore, the present invention designs the Si content to be 0.30-0.50%.

[0029] Mn (Manganese): Mn is one of the important solid solution strengthening elements in steel, improving the strength of steel, and is also an important deoxidizing element in steel. However, too high a Mn content will not only increase the manufacturing cost of weathering steel, but also expand the austenite phase region, increase the stability of supercooled austenite, and reduce the content of proeutectoid ferrite. Therefore, its content is designed to be 0.25-0.55%.

[0030] P (Phosphorus): P is the most economical element for improving the atmospheric corrosion resistance of steel. It easily reacts with oxygen and water in the air to form insoluble dense phosphates, which evenly cover the surface of the steel matrix, preventing oxygen and water from penetrating into the matrix, thereby improving the atmospheric corrosion resistance of the steel. It also has a strong solid solution strengthening effect, but P is easy to segregate at the grain boundary to reduce the low-temperature toughness of the steel and increase the sensitivity of welding cracks. The present invention adds P to improve the atmospheric corrosion resistance, so the P content is designed to be 0.080-0.120%;

[0031] S (sulfur): S is a harmful residual element in steel. It is easy to react with Mn to form MnS non-metallic inclusions, which become a crack initiation source and a fast channel for expansion, reducing the toughness of the material; non-metallic inclusions are easy to cause pitting corrosion, reducing atmospheric corrosion resistance; S is also easy to react with Ti to form Ti4C2S2, reducing the content of effective Ti. Therefore, the present invention controls the S content to ≤0.0050%.

[0032] Als (aluminum): Al is the main deoxidizing element added to steel. It can also react with nitrogen to form aluminum nitride, reducing the consumption of oxygen and nitrogen on the microalloying element titanium. However, too high Al content will increase the inclusion of Al oxides in the steel, reducing the low-temperature toughness and atmospheric corrosion resistance of the steel. Therefore, its content is designed to be 0.015-0.030%.

[0033] Cr (chromium): Cr is enriched in the rust layer to promote the formation of a dense protective rust layer that is closely bonded to the substrate, promote anode passivation, and improve the atmospheric corrosion resistance of steel. Too high Cr content will deteriorate the welding performance of steel, so the Cr content is designed to be 0.80-1.10%.

[0034] Cu (copper): Cu can significantly improve the atmospheric corrosion resistance of steel, and the effect is better when added in combination with Cr; Cu can also precipitate fine second-phase particles during the cooling process to improve the strength of steel. However, the melting point of Cu is only 1083°C, and too high a content can easily cause cracks in the steel billet during continuous casting and hot rolling, so the Cu content is designed to be 0.20-0.30%.

[0035] Ni (nickel): Ni can increase the self-corrosion potential of the material, reduce the corrosion tendency, and improve the atmospheric corrosion resistance of steel; it can also react with Cu to form a high melting point Cu-Ni binary alloy phase, effectively preventing cracks caused by Cu; it can also improve the low-temperature toughness of the material. However, Ni is a precious metal element, and excessive content significantly increases the manufacturing cost, so the Ni content is designed to be 0.03-0.09%.

[0036] Nb (Niobium): Nb is a strong carbonitride-forming element, which inhibits the recrystallization of deformed austenite, expands the unrecrystallized zone, and improves the unrecrystallized zone's function of controlling rolling and refining grains; during the cooling process, nano-scale second-phase particles are precipitated, which has significant grain refinement and precipitation strengthening effects, and improves strength and toughness. However, too high a Nb content will significantly increase the cost of steel manufacturing, so its content is controlled at 0.008-0.015%.

[0037] Ti (titanium): The main function of Ti is to inhibit the growth of austenite grains during heating, refine the original austenite grain size, and precipitate fine TiC particles during cooling to improve material strength; it can also inhibit the growth of coarse grains in the welding process and improve the toughness affected by heat. However, if the Ti content is too high, large-sized TiN particles are easily generated, which reduces the low-temperature toughness of the material. Therefore, its content is controlled at 0.015%-0.035%.

[0038] Ca (Calcium): Ca can promote the spheroidization of non-metallic inclusions, avoid stress concentration at the sharp corners of non-metallic inclusions, lead to crack initiation, become a fast channel for crack expansion, and improve low-temperature toughness. Its content is controlled at 0.0010%-0.0030%.

[0039] N (nitrogen): N is a harmful gas element in steel. It is easy to react with Ti to form large particles of TiN, which is difficult to dissolve in the heating process. TiN is large in size and is not conducive to low-temperature toughness control. Therefore, the N content is strictly controlled to be ≤ 0.0040%.

[0040] The present invention adopts the following method to improve the low temperature toughness of phosphorus-containing hot-rolled weathering steel sheet and obtain high strength, excellent plastic toughness and good atmospheric corrosion resistance:

[0041] 1) Low C-low Mn components are used to obtain a microstructure dominated by polygonal ferrite. Ti microalloying or Nb+Ti composite microalloying is used according to the thickness range of the steel plate. The fine-grained polygonal ferrite + pearlite structure is obtained by combining the rolling and cooling process matching design, in which the polygonal ferrite with good plasticity and toughness accounts for about 94-96%;

[0042] 2) Adopt P-Si-Cr-Cu-Ni collaborative design, with weathering index I value ≥7.5, Cr+Cu ≥1.1%, 3≤Cu / Ni≤7, adopt high P and high Cr content, reduce the content of precious alloy Ni, and reduce the cost of weathering steel;

[0043] 3) High-cleanliness molten steel smelting. Non-metallic inclusions are pitting induction sources and crack initiation sources, which reduce the low-temperature toughness and atmospheric corrosion resistance of weathering steel. The present invention adopts LF refining to improve the crystallinity of molten steel and control the S content below 0.005%. During the refining process, calcium wire is fed to promote the spheroidization of non-metallic inclusions. During the continuous casting process, special covering agents and protective slag are used for protective casting to avoid non-metallic inclusions from being involved in the molten steel, thereby reducing the adverse effects of non-metallic inclusions on corrosion resistance and low-temperature toughness.

[0044] Compared with the prior art, the present invention adopts P-Si-Cr-Cu-Ni collaborative design, with a weathering index I value of ≥7.5, reduces the content of precious alloy Ni, reduces alloy cost, has good atmospheric corrosion resistance, and has a corrosion rate of <45% relative to Q345B. In addition, the mechanical properties of the steel plate: yield strength R eL ≥420MPa, tensile strength R m ≥550MPa, elongation A≥27%, -20℃ KV2≥135J (size: 10×10×55mm), -40℃ KV2≥120J (size: 10×10×55mm), with high strength and excellent plastic toughness. The corrosion rate relative to Q345B is <45%, and it has excellent atmospheric corrosion resistance. The steel plate of the present invention also has excellent cold bending forming performance: no cracks appear on the outer side of the sample after 180° cold bending (d=a) and double cold bending, which is convenient for downstream users to manufacture and process. The present invention can be hot-rolled, saves energy consumption of the heating furnace, eliminates the need to clean the corners of the ingot, and further reduces manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The microstructures of the steel plate produced in Example 3 of the present invention at different thickness positions are polygonal ferrite and pearlite. The average grain size of the ferrite in this example is about 8 μm, and the volume fraction of pearlite is 5%. DETAILED DESCRIPTION

[0046] Example 1-Example 4

[0047] A high plasticity and toughness phosphorus-containing hot-rolled weathering steel plate comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and unavoidable impurities.

[0048] Comparative Example 1-Comparative Example 3

[0049] A high plasticity and toughness phosphorus-containing hot-rolled weathering steel plate comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and unavoidable impurities.

[0050] Table 1 Composition of steel sheets in various embodiments and comparative examples (wt%)

[0051]

[0052] The method for manufacturing the high plasticity and toughness phosphorus-containing hot-rolled weathering steel plate of the above embodiments and comparative examples includes the following process flow:

[0053] Hot metal pretreatment and deep desulfurization → top and bottom composite blowing in converter → LF refining → continuous casting → heating → rolling → laminar cooling → coiling → cooling to room temperature.

[0054] Specifically:

[0055] Molten steel is smelted according to the above chemical composition, and the molten iron is pretreated for deep desulfurization to ≤0.0050%. LF furnace slag desulfurization is used for refining, and calcium wire is fed for inclusion modification. The weak stirring time is greater than 10 minutes to promote the floating of non-metallic inclusions and improve the cleanliness of molten steel. The LF outlet temperature is 1560-1580℃. Continuous casting adopts electromagnetic stirring and dynamic light pressure to improve the internal quality of continuous casting billets. The temperature of the molten steel casting ladle is controlled at 1530-1560℃, and special covering agents and protective slag are used for protective casting; the continuous casting billet drawing speed is controlled at 1.0-1.5m / min. The thickness of the continuous casting slab is 230mm. After the billet is cut, it is preferred to be directly loaded into the furnace, or hot loaded, and the temperature entering the heating furnace is ≥500℃.

[0056] The slab is heated by a walking beam heating furnace at a temperature of 1190°C-1250°C and a holding time of 120-170min to promote full solid solution of alloy elements and homogenization of austenite. Hot rolling is carried out in two stages: rough rolling and finishing rolling. In the rough rolling stage, two four-roll reversible rough rolling mills are used for rolling 3 passes each, the rolling temperature is ≥1050°C, and the cumulative reduction rate of rough rolling is ≥75%. In the finishing rolling stage, 7 four-roll rolling mills are used for continuous rolling. This stage is rolled in the austenite non-recrystallization zone, the start rolling temperature is ≤1030°C, the finishing rolling temperature is 850-900°C, and the cumulative reduction rate of finishing rolling is ≥80%. After rolling, dense laminar cooling is used to quickly cool the steel plate, the cooling rate is 25-40°C / s, and the coiling temperature is 570-630°C. The main process parameters of the embodiment and comparative example rolling are shown in Table 2.

[0057] Table 2 Main process parameters of each embodiment and comparative example

[0058]

[0059] The steel plates produced in the above embodiments and comparative examples were subjected to performance tests. The tensile performance test was conducted according to GB / T228.1 "Metallic material tensile test Part 1: Room temperature test method", and the cold bending performance test was conducted according to GB / T 232 "Metallic material bending test method". The impact performance test was conducted according to GB / T 229 "Metallic material Charpy pendulum impact test method". The main mechanical properties of the embodiments and comparative examples of the present invention are shown in Table 3.

[0060] Table 3 Main process parameters and performance of each embodiment and comparative example

[0061]

[0062] According to TB / T 2375 "Cyclic Immersion Corrosion Test Method for Weathering Steel for Railways", a 72h periodic immersion corrosion test was conducted to evaluate the atmospheric corrosion resistance of each embodiment, the corrosion sample size was 40mm×60mm×4mm, and Q345B low alloy steel was used as a comparative corrosion sample. The test results are shown in Table 4. The corrosion rate of each embodiment is <45% relative to Q345B low alloy steel, and has excellent atmospheric corrosion resistance.

[0063] Table 4 Atmospheric corrosion resistance of various embodiments and comparative examples

[0064] <![CDATA[Average corrosion weight loss rate, (g / (m 2 ·h))]]> Relative corrosion rate, % Example 1 1.83 41％ Example 2 1.85 41％ Example 3 1.75 39％ Example 4 1.77 40％ Comparative Example 1 1.84 41％ Comparative Example 2 2.37 53％ Comparative Example 3 1.79 40％ Q345B 4.48 100

[0065] The underlined data above are data that do not meet the requirements of the present invention.

[0066] In Comparative Example 1, the composition is improperly controlled, the Ti and P contents are relatively high, and it does not contain Nb and Ni. Although it is produced according to the process of the present invention, it is easy to generate large-sized TiN particles, and the P content is too high, and the low-temperature toughness is poor; in Comparative Example 2, the composition is improperly controlled, the C, Mn, and S contents are relatively high, and the low-temperature impact toughness at -40°C is very poor, the product elongation is low, and the Cr content is low. The Cr+Cu content does not meet the requirements of the present invention, resulting in a small weathering index I and corrosion resistance that cannot meet the requirements; in Comparative Example 3, the composition is properly controlled according to the present invention, but the reduction rate during rolling is low, the cooling rate is slow, and the coiling temperature is high, which makes the ferrite grain size and the two-phase precipitation particles coarsened, the material strength is insufficient, and the low-temperature toughness is also poor. Example The yield strength R of the weathering steel plate obtained according to the chemical composition, smelting, continuous casting and controlled rolling and controlled cooling process control technology of the present invention eL ≥420MPa, tensile strength R m≥550MPa, elongation A≥27%, -40℃ KV2≥120J, with high strength and excellent plasticity and toughness matching, relative corrosion rate of Q345B <45%, with excellent atmospheric corrosion resistance. It can be used in the manufacturing and operation of outdoor components and equipment such as railway vehicles, buildings, towers, etc. in extremely cold areas.

Claims

1. A high plastic toughness phosphorus-containing hot-rolled weathering steel plate, characterized in that: The high plasticity and toughness phosphorus-containing hot-rolled weathering steel plate includes the following mass percentage components: C: 0.070%-0.100%, Si: 0.30-0.50%, Mn: 0.25%-0.55%, P: 0.080%-0.120%, S: ≤0.0050%, Cr: 0.80%-1.10%, Ni: 0.03-0.09%, Cu: 0.20%-0.30%, Als: 0.015%-0.030%, Ca: 0.0010%-0.0030%, Ti: 0.015%-0.035%, N≤0.0040%, and the rest are Fe and unavoidable impurity elements; The high plasticity and toughness phosphorus-containing hot-rolled weathering steel plate, when the steel plate is 10 mm ≤ thickness ≤ 12 mm, is added with Nb element, with a mass percentage of 0.008%-0.015%; The weathering index I of the high plasticity and toughness phosphorus-containing hot-rolled weathering steel plate is ≥7.5; The composition of the high plasticity and toughness phosphorus-containing hot-rolled weathering steel plate meets the following requirements: Cr+Cu≥1.1%, 3≤Cu / Ni≤7; The microstructure of the high-plasticity phosphorus-containing hot-rolled weathering steel plate is polygonal ferrite and pearlite, the average grain size of ferrite is 7-8 μm, and the volume fraction of pearlite is 4-6%; The yield strength R of the high plastic toughness phosphorus-containing hot rolled weathering steel plate eL ≥420MPa, tensile strength R m ≥550MPa, elongation A≥27%, -20℃KV2≥135J, -40℃KV2≥120J.

2. The high plasticity and toughness phosphorus-containing hot-rolled weathering steel sheet according to claim 1, characterized in that: The high plasticity and toughness phosphorus-containing hot-rolled weathering steel plate has a thickness of 6-12 mm.

3. A method for manufacturing the high plasticity and toughness phosphorus-containing hot-rolled weathering steel sheet according to claim 1 or 2, characterized in that: The manufacturing method comprises continuous casting: the temperature of the molten steel casting ladle is controlled at 1530-1560°C, protective casting is adopted, and the continuous casting billet drawing speed is controlled at 1.0-1.5 m / min.

4. The manufacturing method according to claim 3, characterized in that: The manufacturing method comprises heating: heating the slab by a walking beam heating furnace, the temperature of the slab entering the heating furnace is ≥500°C, the heating temperature is 1190°C-1250°C, and the insulation time is 120-170 minutes.

5. The manufacturing method according to claim 3, characterized in that: The manufacturing method comprises rolling: hot continuous rolling is divided into two stages: rough rolling and finishing rolling; the rolling temperature in the rough rolling stage is ≥1050°C, and the cumulative reduction rate is ≥75%; the starting rolling temperature in the finishing rolling stage is ≤1030°C; the finishing rolling final rolling temperature is 850-900°C, and the cumulative reduction rate is ≥80%.

6. The manufacturing method according to claim 3, characterized in that: The manufacturing method comprises laminar cooling: after rolling, the steel plate is rapidly cooled by dense laminar cooling, the cooling rate is 25-40°C / s, and the coiling temperature is 570-630°C.

Images