CN111534746A - Weathering steel for wide-width 450MPa hot-rolled container and its manufacturing method - Google Patents

Abstract

The invention discloses weather-resistant steel for a wide 450 MPa-level hot-rolled container and a manufacturing method thereof. The steel contains 0.048-0.065% of C, 0.61-0.70% of Si, 0.35-0.45% of Mn, 0.075-0.085% of P, less than or equal to 0.006% of S, less than or equal to 0.040% of Al, 0.20-0.29% of Cr, 0.11-0.19% of Cu, 0.035-0.050% of Ti, 0.010-0.025% of RE, less than or equal to 0.004% of N, and the balance of iron and inevitable impurities. The outlet temperature of the casting blank soaking section is 1278-1298 ℃, the heat preservation time of the soaking section is 23-37 min, and the total in-furnace time is less than or equal to 170 min; the outlet temperature of rough rolling is more than or equal to 1100 ℃, the initial rolling temperature of finish rolling is 1075-1093 ℃, the final rolling temperature of finish rolling is 915-938 ℃, the steel is cooled to 646-665 ℃ at the cooling speed of 31-41 ℃/s, coiling is carried out, the leveling force is 4500-5500 KN, and the roll bending force is 10-20 KN. The straightness of the steel strip is less than or equal to 3 mm/m. Has good corrosion resistance.

Description

Weathering steel for wide-width 450MPa hot-rolled container and its manufacturing method

technical field

The invention belongs to the field of steel for containers, and relates to a wide-width 450MPa-grade hot-rolled weathering steel for containers with good flatness.

Background technique

The traditional 20-foot and 40-foot ordinary containers use SPA-H with a yield strength of 345MPa, which has low material strength and large consumption. In the field of container manufacturing, my country is gradually promoting the application of 450-700MPa grade high-strength steel plates. Compared with ordinary standard container steel, the use of high-strength steel plates can reduce the weight by 15% to 40%, which can save a lot of transportation costs. Due to its special purpose, the container has high requirements on the material of steel. In addition to having good atmospheric corrosion resistance, it has high strong plasticity, and the flatness of the steel strip after being flattened is better, especially for high strength grades. If the flatness of steel plates with high height and wide width is not good, it will seriously affect the production and manufacture of containers.

Before the present invention, the invention patent of "a high-strength weathering steel plate with a yield strength of 450 MPa and its production method" with the publication number of CN101824581B is based on the CSP short-flow production process, which is not suitable for conventional production line production, and contains Nb and Ni precious metals at the same time. ,higher cost.

The publication number is CN103290331A, the invention patent of "a high-strength and high-corrosion-resistant steel sheet with a yield strength of 450 MPa and its production method", which makes the steel have excellent atmospheric corrosion resistance by adding a medium content of alloying element Cr. Compared with traditional weathering steel, the atmospheric corrosion resistance is more than doubled. However, its Cr content is 2.80% to 4.0%, which is difficult to smelt and difficult to produce, and contains precious metals such as Nb and Ni.

The publication number is CN102925798A, the invention patent of "a kind of steel with a yield strength of 450MPa for railway freight car parts and its production method", which adds Nb and V precious metal elements on the basis of C-Mn steel, although the yield strength reaches more than 450MPa , but does not have corrosion resistance.

The above-mentioned invention patents are mainly aimed at the mechanical properties and application properties of the product, and the flatness control of the wide-width high-strength steel strip after being flattened is less involved. There is the problem of warping of the ship shape after the strip is flattened, which seriously affects the use of users. Many companies have to adopt measures such as slow cooling in the pit after rolling, which greatly affects their production efficiency. Therefore, how to obtain low-cost wide-width 450MPa-grade hot-rolled container weathering steel and good flatness control is one of the technical difficulties to be solved urgently in this field.

SUMMARY OF THE INVENTION

The present invention is to overcome the deficiencies in the prior art that the weathering strip steel for 450MPa grade hot-rolled containers is high in cost and cannot be used normally by users due to warping after opening and leveling, and provides a wide-width 450MPa grade weathering steel for hot-rolled containers and a manufacturing method thereof. , in order to solve the above problems existing in the prior art. The steel plate is not only low in cost, but also has good atmospheric corrosion resistance, high strength, and excellent formability. In addition, the steel plate has good flatness and is suitable for the manufacture of lightweight containers.

The specific technical solutions are:

Aiming at the prominent technical problem of ship warpage existing in the current production process of steel for wide-width 450MPa grade containers, the technical scheme of the present invention is specially proposed. The invention provides a weathering steel for wide-width 450MPa container and a manufacturing method thereof. The chemical composition is calculated by mass percentage, and contains C 0.048%-0.065%, Si 0.61%-0.70%, Mn 0.35%-0.45%, P 0.075% ～0.085%, S≤0.006%, Al≤0.040%, Cr 0.20%～0.29%, Cu 0.11%～0.19%, Ti 0.035%～0.050%, RE 0.010%～0.025%, N≤0.004%, the balance is Fe and inevitable impurities.

The reason why the present invention selects the above alloying element types and their contents is because:

C is the main strengthening element in steel, which can significantly improve the strength of steel. It is the main interstitial solid solution strengthening element. It can form fine carbide TiC with Ti and play a role in precipitation strengthening. But more C is detrimental to steel plate welding, toughness and plasticity. In the present invention, the content of C is limited to 0.048% to 0.065%.

Si is an essential element for deoxidation in steelmaking, and has a solid solution strengthening effect when added to a certain content. The use of Cu, Cr and other elements in combination can help refine α-FeOOH, thereby reducing the overall corrosion rate of the steel. At the same time, it can also increase the strength and wear resistance of the steel. The synergistic use of high Si and high P can significantly increase the oxidizability of heating at temperatures above 1200 °C, increase the interface area and unevenness between the iron sheet and the steel matrix, and thus accelerate the diffusion of copper. The present invention controls the range of 0.61% to 0.70%.

The main function of Mn in steel is solid solution strengthening, improving the strength of ferrite and adjusting the strength of the steel plate. It can significantly reduce the transformation temperature of austenite to ferrite and refine the microstructure of steel. It is an important strengthening and toughening element, but too much Mn content will increase the hardenability, resulting in weldability. And the toughness of the welding heat-affected zone deteriorates, and considering the cost factor, the present invention controls its content at 0.35% to 0.45%.

P is an element that is effective in increasing strength and improving weather resistance, but in the production of steel sheets with high yield strength, it may cause slab embrittlement and deteriorate weldability and formability. The invention adopts compound addition of high Si and high P to effectively suppress the problem of easy cracking of weathering steel without Ni addition, and at the same time adds RE element to effectively suppress the segregation of P element at the grain boundary, thereby improving the plastic toughness of the steel plate. The content of P in the present invention is controlled at 0.075% to 0.085%.

S is an impurity element in steel, which significantly reduces the plasticity, toughness and welding performance. Controlling a lower S is beneficial to improve the performance. In the steel of the present invention, S≤0.006% is controlled.

Al is the main deoxidizing element in steel, and adding appropriate Al can refine grains and improve the properties of steel. The present invention defines its content range as Al≤0.040%.

Cr forms a dense oxide film on the surface of the steel and improves the passivation ability of the steel. When it is added to the steel at the same time as Cu, the corrosion resistance effect is particularly obvious. In addition, Cr element can significantly improve the strength, hardness and wear resistance of steel. The present invention limits its content in the range of 0.20% to 0.29%.

Cu is the most important for improving atmospheric corrosion resistance in atmospheric corrosion resistance steel, and plays the role of active cathode. Under certain conditions, it can promote the anode passivation of steel, thereby reducing the corrosion rate of steel. The present invention limits its content in the range of 0.11% to 0.19%.

Ti is a strong carbonitride forming element, and is an important microalloy strengthening element in the present invention. It can not only effectively refine the grains, but also form fine carbides, nitrides or carbonitrides with C and N, especially It is the nano-scale TiC precipitated in the process of coiling and slow cooling, which has a high precipitation strengthening effect, which can greatly improve the strength of the steel plate. The present invention limits its range to 0.035% to 0.050%.

RE can not only improve the corrosion resistance of the steel plate, but also purify the molten steel and refine the solidification structure of the steel, change the nature, shape and distribution of the inclusions, thereby improving the properties of the steel. When RE reaches a certain amount of addition, it has a certain amount of solid solution in the steel, and its aggregation at the grain boundary can inhibit the segregation of phosphorus, sulfur and low-melting impurities at the grain boundary or form compounds with higher melting points with these impurities. Eliminates harmful effects of low melting point impurities. In addition, RE can strengthen grain boundaries, hinder the formation and expansion of intergranular cracks, improve plasticity, refine grains and inhibit high-temperature grain growth, and at the same time refine the size of the precipitated phase and promote the growth of TiC in ferrite. Precipitate. The present invention limits its range to 0.010% to 0.025%.

N is an element existing in the smelting process, because one of the characteristics of the present invention is the use of Ti micro-alloying technology, and Ti is a very active element, which will react with O, N, S and other elements in the steel. If the N content is too high If it is too high, TiN with large size will precipitate in molten steel, which can neither prevent the growth of austenite grains nor achieve precipitation strengthening, but will reduce the grain refinement and precipitation strengthening of Ti. Therefore, in the present invention, N≤0.004% is controlled.

The invention also provides a manufacturing method of weathering steel for wide-width 450MPa-grade hot-rolled containers. The manufacturing method includes smelting and continuous casting, slab reheating, rolling, coiling, and leveling, and is characterized in that:

1. Smelting and continuous casting process

Smelting according to the above components, pre-desulfurization of molten iron, combined blowing of the top and bottom of the converter, refining outside the LF furnace, using the wire feeding method, the rare earth wire is uniformly added into the molten steel through the mold slag at the nozzle of the mold.

2. Billet heating

The casting billet is reheated after hot charging, the outlet temperature of the soaking section of the casting billet is controlled to be 1278-1298°C, the atmosphere of the heating furnace is controlled to be a reducing atmosphere, and a high temperature fast burning process is adopted. The holding time of the soaking section is 23 to 37 minutes, and the total time in the furnace is not more than 170 minutes.

3. Rolling

In the controlled rolling step, two-stage controlled rolling is adopted. The rough rolling is descaled in each pass, and the rough rolling outlet temperature is above 1100°C. The starting temperature of the finishing rolling is 1075-1093°C, and the finishing rolling temperature is 915-938°C. During the rolling process, the micro-wave control is adopted.

4. Coil

After finishing rolling, laminar cooling is performed, cooled to 646-665°C at a cooling rate of 31-41°C/s, and coiled at a distance of 20m from the head and 20m from the tail to 666-685°C, and then air-cooled to room temperature. The laminar cooling adopts the centralized cooling in the front section, and the ratio of the upper and lower water is 1:3 to 1:2.

5. Flatten

For wide-width high-strength steel plates, due to the intensive cooling technology, it is easy to cause uneven cooling rate on the surface of the strip steel, which in turn generates residual stress and causes the problem of ship-shaped warping after the steel coil is flattened. In order to ensure that the flatness of the steel plate meets the requirements , In addition to the use of micro-medium wave control and reasonable proportioning of the upper and lower water volume ratios in the rolling process, the present invention also adopts a large rolling force scheme for leveling, the leveling force is 4500-5500KN, and the bending force is 10-20KN.

The reasons for controlling the individual manufacturing steps are as follows:

The soaking temperature of the casting billet is controlled at 1278-1298 °C, on the one hand, to ensure that the billet is fully austenitized and the composition of the billet is uniform; , to suppress the Cu embrittlement generated during the heating of the billet.

The finishing rolling temperature is limited to 1075-1093 °C, which is easy to roll, reduces the load of the rolling mill, and prevents the temperature difference between the head and tail of the intermediate billet from being too large, which leads to the normal progress of the next process.

In the finishing rolling stage, high temperature rolling is adopted, in order to control the precipitation induced by the deformation of the second phase particles, so as to retain more effective Ti to precipitate after coiling. Therefore, the finishing rolling temperature is controlled at 915-938°C.

Since the precipitation kinetics of TiC determines its optimal precipitation temperature range, in order to ensure that the precipitates are fully precipitated, so as to obtain the second-phase particles with smaller size, and the coiling temperature is too low, which is not conducive to the shape control. Therefore, the coiling temperature was controlled to 646 to 665°C. In order to maintain the uniformity of the performance of the whole roll, a U-shaped cooling method is adopted, the head 20m and the tail 20m are cooled to 666-685°C, and then air-cooled to room temperature. The laminar flow cooling adopts the centralized cooling in the front section, and the ratio of the upper and lower water is 1:3 to 1:2. During the rolling process, micro-medium wave control is adopted.

The cooling rate is controlled at 31-41°C/s. One is to control the grain size; the other is to inhibit the precipitation of TiC during the cooling process, and retain more effective Ti to form during the coiling process, so that the particle size formed is smaller, up to about 6-10 nm, with Very good precipitation strengthening effect. At the same time, the cooling speed is too fast, which is not conducive to the shape control.

The purpose of leveling is to ensure the shape of the strip and reduce the bad defects of the edge wave and the middle wave. However, the present invention discloses a method for manufacturing a weathering steel plate based on a wide-width high-strength hot-rolled container, and the required flatness requirement cannot be obtained by a conventional flattening process. Through reasonable selection of key rolling temperature parameters, comprehensive optimization and combination of parameters such as water quantity and cooling rate, and the rolling force of 4500-5500 KN, the present invention obtains a good effect that the flatness is less than 3 mm/m.

Beneficial effects:

Compared with the prior art, the present invention has the following beneficial effects:

(1) The present invention adopts high Si and high P supplemented with corrosion-resistant elements Cr, Cu, RE and micro-alloying element Ti, and does not add precious metals such as Ni, Mo, and Nb. Copper, silicon, phosphorus and rare earth elements can be enriched in the inner rust layer during the corrosion process of steel, and produce a colloidal complex of copper, silicon and phosphorus, which makes the inner rust layer denser and makes the steel plate with excellent corrosion resistance .

(2) The weathering steel for wide-width 450MPa container is 2.0-4.5mm in thickness and 1350-1500mm in width. The yield strength can reach more than 450MPa, the tensile strength is not less than 550MPa, the elongation is not less than 22%, the yield strength difference of the through coil is within 50MPa, the flatness of the steel strip after flattening is not more than 3mm/m, and it has good corrosion resistance. and cold forming properties.

(3) The microstructure of the invented steel is ultrafine-grained ferrite+carbide, and the grain size is above 11. At the same time, a large number of TiC second-phase particles with a size of 6-10 nm are obtained after coiling.

(4) The corrosion rate of the steel of the present invention is obviously lower than that of the comparative steel, the cost of the steel plate is low, the slow cooling in a slow cooling hood is not required, the production is easy to organize, and the downstream users do not need to carry out leveling or straightening when using it, reducing the final The production cost of the user is improved, and the production efficiency is improved.

Detailed ways

The above-mentioned embodiments are only for illustrating the technical concept and characteristics of the present invention, rather than limiting the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. All equivalent changes or modifications made according to the spirit of the present invention should be included within the protection scope of the present invention.

Table 1 lists the chemical composition of the example steel, Table 2 lists the heating parameters of the steel slab of the example, Table 3 lists the rolling process parameters of the example steel, and Table 4 lists the Mechanical properties, Table 5 gives the atmospheric corrosion resistance of the steels of the examples.

Example steels with chemical compositions in Table 1 were manufactured by the following process: smelting in a converter, then refining outside the furnace, and casting to obtain a continuous casting slab. The continuous casting billet is hot sent to the hot rolling production line, the soaking outlet temperature of the casting billet is 1278～1298℃, the outlet temperature of rough rolling is above 1100℃, the opening temperature of finishing rolling is 1075～1093℃, and the final rolling temperature of finishing rolling is 915～938℃. After rolling, laminar cooling is adopted, the cooling rate is 31-41°C/s, the coiling temperature is 646-665°C, air-cooled to room temperature after coiling, and then flattened.

The chemical composition of the steel of the embodiment of table 1, wt%

Example C Si Mn P S Al Cr Cu Ti RE N A1 0.059 0.65 0.43 0.079 0.004 0.033 0.28 0.18 0.049 0.024 0.0036 A2 0.049 0.63 0.36 0.076 0.003 0.031 0.21 0.12 0.036 0.011 0.0033 A3 0.063 0.62 0.44 0.081 0.003 0.036 0.26 0.17 0.047 0.021 0.0034 A4 0.055 0.64 0.38 0.078 0.005 0.034 0.24 0.14 0.041 0.016 0.0035 A5 0.058 0.61 0.39 0.075 0.004 0.033 0.25 0.15 0.043 0.017 0.0036 A6 0.048 0.69 0.41 0.080 0.005 0.032 0.22 0.16 0.045 0.019 0.0039 A7 0.061 0.68 0.35 0.077 0.004 0.031 0.27 0.13 0.038 0.014 0.0032 A8 0.052 0.67 0.37 0.083 0.003 0.029 0.20 0.11 0.035 0.010 0.0036 A9 0.065 0.70 0.45 0.085 0.004 0.032 0.29 0.19 0.050 0.025 0.0033

Table 2 Heating parameters of steel slabs of the embodiment

Example The outlet temperature of the soaking section of the slab/℃ Soaking section holding time/min Total time in furnace/min A1 1278 twenty three 163 A2 1280 34 162 A3 1283 31 165 A4 1287 33 161 A5 1289 29 164 A6 1291 28 159 A7 1293 25 168 A8 1296 36 169 A9 1298 37 170

The rolling process parameters of the steel of the embodiment of table 3

The mechanical properties of the steel of the embodiment of table 4

Table 5 Atmospheric corrosion resistance of the steel of the embodiment of the present invention (g/m ² ·h)

Example 72h cycle infiltration corrosion test A7 1.0728 A8 1.0824 A9 1.0969 Comparative Steel 1 (SPA-H) 1.6421 Comparative Steel 2 (Q345B) 3.7270

Note: A1-A6 cannot carry out the 72h cycle infiltration corrosion test because the thickness of the steel plate is less than 4.0mm.

It can be seen from Table 4 that the yield strength of the steels of the embodiments of the present invention are all greater than 450 MPa, the tensile strength is greater than 550 MPa, the elongation is greater than 22%, and the cold bending properties are all qualified.

According to TB/T 2375-1993, a 72-hour cycle infiltration corrosion test was performed. The comparative steels in Table 5 are SPA-H and Q345B. It can be seen from Table 5 that the weather resistance of steels A7, A8 and A9 of the present invention is obviously better than that of Q345B and SPA-H, which can effectively ensure the service life when the thickness of the steel plate is reduced.

Claims (3)

1. A weathering steel for wide-width 450MPa-grade hot-rolled containers, characterized in that the chemical components in the steel are: C 0.048%-0.065%, Si 0.61%-0.70%, Mn 0.35%-0.45%, P 0.075%～0.085%, S≤0.006%, Al≤0.040%, Cr 0.20%～0.29%, Cu 0.11%～0.19%, Ti 0.035%～0.050%, RE 0.010%～0.025%, N≤0.004%, more The amount is iron and inevitable impurities. 2. The weathering steel for wide-width 450MPa-grade hot-rolled containers according to claim 1, characterized in that the width specification of the finished steel plate is 1350-1500mm, the yield strength is greater than or equal to 450MPa, the elongation is greater than or equal to 22%, and the through-roll yield strength is The difference is within 50MPa, and the flatness of the steel strip after flattening is ≤3mm/m. 3. A manufacturing method of wide-width 450MPa grade hot-rolled container weathering steel as claimed in claim 1 or 2, wherein the production process of the steel plate is: continuous casting by smelting, reheating of slab, rolling, coiling, leveling, It is characterized by: (1) Smelting and continuous casting The molten iron is pre-desulfurized, the top and bottom of the converter are combined for blowing, and the LF furnace is refined. (2) Reheating of the slab The billet shall be reheated after hot feeding and hot charging, and the outlet temperature of the soaking section of the billet shall be controlled to be 1278-1298 °C, and the atmosphere of the heating furnace shall be controlled to be a reducing atmosphere. ; (3) Rolling Two-stage controlled rolling is adopted, and descaling is carried out in each pass of rough rolling. The outlet temperature of rough rolling is above 1100 °C, the opening temperature of finishing rolling is 1075-1093 °C, and the final rolling temperature of finishing rolling is 915-938 °C. In the process, micro-medium wave control is adopted; (4) Coiling After finishing rolling, laminar cooling is performed, cooled to 646-665°C at a cooling rate of 31-41°C/s, and coiled at a distance of 20m from the head and 20m from the tail to 666-685°C, then air-cooled to room temperature, laminar cooling Centralized cooling in the front section is adopted, and the ratio of upper and lower water is 1:3 to 1:2; (5) Flattening Use a large rolling force for leveling, the leveling force is 4500-5500KN, and the bending force is 10-20KN.