A 460MPa grade low temperature corrosion resistant steel for frozen soil highway and its preparation method

Abstract

The present invention relates to a 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads, which belongs to the technical field of corrosion-resistant steel and solves the problem that the corrosion-resistant steel in the prior art cannot meet the environmental requirements of highway construction in high-cold frozen soil areas. The corrosion-resistant steel comprises the following chemical components in weight percentage: C: 0.05-0.07%, Si: 0.3-0.5%, Mn: 1.5-1.8%, P: 0.015-0.02%, S: ≤0.005%, Cu: 0.02-0.03%, Ce: 0.02-0.03%, V: 0.08-0.12%, Ti: 0.015-0.02%, N: 0.02-0.03%, and the balance is Fe and inevitable inclusions; the hot-rolled structure of the 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads is a mixed structure of acicular ferrite and bainite, wherein the content of bainite is ≤3%. The corrosion-resistant steel has good low-temperature toughness, corrosion resistance and large deformation resistance.

Description

Technical Field

[0001] The invention relates to the technical field of corrosion-resistant steel, and in particular to a 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads. Background Art

[0002] The topography, geology and climate conditions of the Qinghai-Tibet Plateau are complex. The harsh climate and geographical environment, such as high altitude, high cold, permafrost and frequent earthquakes, have brought unprecedented challenges to the long-term safe and reliable service of bridges, tunnels and pavements of frozen roads. Therefore, it is imperative to develop low-temperature corrosion-resistant steel for frozen road areas, extend the service life of steel for frozen road areas, and reduce the workload of maintenance, which is of great significance to ensure the construction and safe service of frozen roads.

[0003] Corrosion-resistant steel is widely used in highway construction fields such as bridges, steel bars, and guardrails. General corrosion-resistant steel cannot meet the environmental requirements of highway construction in high-altitude frozen soil areas. The soil environment of plateau frozen soil contains a large amount of rock layers and moisture, which is more likely to form oxygen concentration difference battery corrosion than plain soil, and the corrosion resistance requirements of corrosion-resistant steel are more stringent; the winter in high-altitude frozen soil areas is accompanied by frost and snow, and the temperature difference between day and night is large, requiring corrosion-resistant steel to have excellent low-temperature toughness; the frozen soil structure undergoes periodic thawing and freezing with seasonal changes, which produces large shear stress on steel, requiring corrosion-resistant steel to also have good shear resistance. In addition, the construction of highways is long and the amount of engineering is large, which is very sensitive to construction costs, and steel materials need to have as low a manufacturing cost as possible. Therefore, there is an urgent need for a low-temperature corrosion-resistant steel that has both low-temperature toughness, corrosion resistance, and shear resistance, and has a low life cycle cost, which is suitable for frozen soil roads.

[0004] Since the plateau permafrost depth is usually 3-5m, the permafrost layer has a high strength, and many Q235 and Q345 grade rigid foundation materials have insufficient strength, deformation and failure during the piling process. There are also a lot of Cl in the plateau soil. - and SO4 2- , and the soil water content is high, and there is strong soil corrosion. Therefore, frozen soil highway construction requires 460 MPa grade low-temperature corrosion-resistant steel.

[0005] However, the existing 460MPa-grade corrosion-resistant steel cannot have low-temperature toughness, corrosion resistance and shear resistance. For example, CN116694888A discloses a method for preparing a rare earth high-strength and high-toughness steel with a yield strength of 620MPa. The rare earth alloy steel contains two very expensive alloy elements, 0.5%-0.8% Ni and 0.2%-0.45% Mo. An offline heat treatment process is added to the preparation process, which significantly increases the manufacturing cost. In terms of low-temperature performance, the impact energy at -60℃>260J is met, which is higher than the frozen soil environment that requires an environment of about -45℃, and there is a waste of performance.

[0006] CN112011736B discloses a method for preparing a 460MPa grade seismic, corrosion and fire resistant steel for construction containing rare earth. The rare earth alloy steel contains Cr, Ni and Mo elements, which increases the manufacturing cost. The performance meets the requirements of -40℃ impact energy ≥80J, which does not meet the low temperature requirements of frozen soil environment. The structure is mainly granular bainite, and the low temperature performance is poor.

[0007] CN117721373A discloses a Q460qENH rare earth weathering bridge steel and its production method. The steel contains Cr, Ni, Cu and Nb, which increases the manufacturing cost. The steel has an offline tempering heat treatment process, which significantly increases the manufacturing cost. The steel meets the low temperature requirement of -40℃ impact energy ≥190J, but does not meet the low temperature requirement of frozen soil environment. The steel has a yield strength of >528MPa, which is wasteful. The steel consists of fine-grained ferrite + bainite + precipitation phase, and the structure is complex and difficult to control.

[0008] CN118086762A discloses a method for producing rare earth treated 460MPa grade hot rolled structural steel. Although low-cost alloy elements are used in composition, the microalloy strengthening method is Nb and Ti strengthening. In terms of process, only low-temperature finishing rolling is used without low-temperature curling process, which has an adverse effect on the low-temperature impact performance of steel. In terms of organizational performance, ferrite and pearlite are the main components, and the low-temperature performance of this organization is significantly lower than that of acicular ferrite. Therefore, this rare earth steel has no low-temperature performance indicators and cannot meet the requirements of frozen soil environment.

[0009] In addition, the corrosion resistance of the above rare earth alloy steels is mainly based on the weathering index test, which is mainly based on the atmospheric corrosion environment, without considering the presence of Cl in the plateau frozen soil. - and SO4 2- significant differences. Summary of the invention

[0010] In view of the above analysis, an embodiment of the present invention aims to provide a 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads, so as to solve the problem that existing corrosion-resistant steels cannot meet the environmental requirements of highway construction in high-cold frozen soil areas.

[0011] On the one hand, an embodiment of the present invention provides a 460MPa-level low-temperature corrosion-resistant steel for frozen soil roads, wherein the 460MPa-level low-temperature corrosion-resistant steel for frozen soil roads comprises the following chemical components in weight percentage: C: 0.05-0.07%, Si: 0.3-0.5%, Mn: 1.5-1.8%, P: 0.015-0.02%, S: ≤0.005%, Cu: 0.02-0.03%, Ce: 0.02-0.03%, V: 0.08-0.12%, Ti: 0.015-0.02%, N: 0.02-0.03%, and the balance is Fe and unavoidable inclusions;

[0012] The hot-rolled microstructure of the 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads is a mixed microstructure of acicular ferrite and bainite, wherein the content of bainite is ≤3%.

[0013] Preferably, the 460MPa grade low temperature corrosion resistant steel for frozen soil roads has a low temperature impact energy A of -45°C. KV2 ≥120J, relative corrosion rate to Q420B steel is <50%.

[0014] Preferably, the grain size of the 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads is 10 to 11 levels.

[0015] On the other hand, the present invention also provides a method for preparing the above-mentioned 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads, the preparation method comprising molten iron pretreatment, dephosphorization converter smelting, decarbonization converter smelting, LF furnace refining, slab casting, slow cooling of the ingot, heating of the ingot, rolling, laminar cooling, and slab coiling;

[0016] Among them, rare earth Ce is added in the form of wire feeding in the later stage of LF furnace refining.

[0017] The finishing inlet temperature in the rolling process is 850-880°C;

[0018] The coiling temperature is 400-450°C.

[0019] Preferably, the temperature of the soaking section for heating the ingot is 1130-1150°C.

[0020] Preferably, the rough rolling in the rolling adopts a high temperature and large reduction process, and the finishing rolling adopts low temperature rolling in the non-recrystallization zone.

[0021] Preferably, the starting rolling temperature of the rough rolling is 1100-1150° C., and the deformation amount of the first pass is greater than 20%.

[0022] Preferably, the cumulative deformation of the finish rolling passes is greater than 30%.

[0023] Preferably, the temperature is kept for 2 to 4 minutes before entering the finishing rolling entrance.

[0024] Preferably, the cooling rate of the laminar cooling is 35-45°C / s.

[0025] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0026] 1. The 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads of the present invention is based on low-carbon medium manganese steel and uses V and Ti composite microalloying to ensure the basic strength and toughness of the steel; controls the S content at a lower level (further preferably the low oxygen content) through LF refining, and strictly controls the size and content of inclusions in the steel to ensure that the steel has relatively good low-temperature impact performance; appropriately relaxes the P content, and adds rare earth Ce in a suitable manner to improve the soil and atmospheric corrosion resistance of the steel in a plateau frozen soil environment, thereby giving play to the role of rare earth in purifying steel quality and improving corrosion resistance.

[0027] 2. The final structure of the 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads of the present invention is uniform acicular ferrite and a small amount of bainite (content ≤3%). The acicular ferrite enables it to have a higher elongation after fracture and a lower yield strength ratio, which meets the performance requirements of steel for high-cold frozen soil roads to resist large deformation and is suitable for use in frozen soil roads in high-cold areas.

[0028] 3. The steel environment for plateau frozen soil roads involves -45℃~-50℃, while the existing standard E-grade plate (-40℃) only stipulates -40℃Akv≥47J, which cannot meet the actual needs. The cost of using the existing standard F-grade plate (-60℃) is too high and the manufacturing process is complicated. The production of good low-temperature toughness steel is difficult. The 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads of the present invention can ensure -45℃ low-temperature impact. Under the corrosion conditions of the soil ion concentration environment in the simulated plateau frozen soil, the average corrosion rate is <1.4g / m 2 h. Compared with steel of the same strength level (Q420B steel), the relative corrosion rate of this low-temperature corrosion-resistant steel is less than 50%. It has good corrosion resistance, not only against atmospheric corrosion, but also against soil sulfate and chloride ion corrosion, and is suitable for plateau permafrost environments.

[0029] 4. The preparation method of the present invention improves the basic strength and toughness of steel through low-temperature finishing rolling, low-temperature curling, controlled rolling and controlled cooling process, and adds rare earth Ce in a suitable manner to improve the steel's resistance to soil and atmospheric corrosion in plateau permafrost environments, thereby playing the role of rare earth in purifying steel and improving corrosion resistance.

[0030] 5. Since rare earth Ce is very easy to be oxidized, the present invention adds rare earth Ce in the form of wire feeding in the later stage of LF refining, which can reduce the oxidation of Ce and make the final corrosion-resistant steel have the target content of solid solution Ce.

[0031] 6. The present invention adopts TMCP (controlled rolling and controlled cooling technology) rolling and low-temperature coiling process, so that the final product structure is mainly uniform acicular ferrite, and the content of bainite is reduced as much as possible, and the content of bainite can be controlled below 3%.

[0032] 7. Because the frozen soil steel of the invention uses C, Si, and Mn as the basic elements, and adds a small amount of V and Ti for microalloy strengthening, combined with production process control, the cost is greatly reduced from the composition design. Secondly, the controlled rolling and controlled cooling process does not exceed the equipment limit, there is no offline heat treatment process, and continuous industrial production is possible. In addition, rare earth Ce is a relatively cheap light rare earth, which can also improve the corrosion resistance of steel. Therefore, the low-temperature corrosion-resistant steel of the present invention has a lower cost.

[0033] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components;

[0035] Figure 1 This is a metallographic structure photograph of the low temperature corrosion resistant steel of Example 1;

[0036] Figure 2a This is a scanning electron microscope photograph of the rare earth modified inclusions of the 460MPa grade low temperature corrosion resistant steel of Example 1;

[0037] Figure 2b The energy spectrum test results of the rare earth modified inclusions of the 460MPa grade low temperature corrosion resistant steel of Example 1;

[0038] Figure 3a The circumferential immersion corrosion test specimen of Q420B corrosion resistant steel of Comparative Example 1;

[0039] Figure 3b The 460MPa grade low temperature corrosion resistant steel of Example 1 was subjected to immersion corrosion test. The main ion components of the corrosive solution in the immersion corrosion test included: 0.14 g / kg Cl - , 0.1g / kg SO4 2- , 0.06 g / kg Ca 2+ The pH value is weakly alkaline (8.0-9.0), which mainly simulates the soil ion concentration environment in plateau permafrost. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0041] On the one hand, the present invention provides a 460MPa-level low-temperature corrosion-resistant steel for frozen soil roads, wherein the 460MPa-level low-temperature corrosion-resistant steel for frozen soil roads comprises the following chemical components in weight percentage: C: 0.05-0.07% (e.g., 0.055%, 0.06%, 0.065%), Si: 0.3-0.5% (e.g., 0.35%, 0.4%, 0.45%), Mn: 1.5-1.8% (e.g., 1.6%, 1.7%), P: 0.015-0.02% (e.g., 0.016%, 0.017%, 0.018%, 0.019%), S: ≤0.005%, Cu: 0.02 ~0.03% (e.g. 0.022%, 0.024%, 0.026%, 0.028%), Ce: 0.02~0.03% (e.g. 0.022%, 0.024%, 0.026%, 0.028%), V: 0.08~0.12% (e.g. 0.09%, 0.1%, 0.11%), Ti: 0.015~0.02% (e.g. 0.016%, 0.017%, 0.018%, 0.019%), N: 0.02~0.03% (e.g. 0.022%, 0.024%, 0.026%, 0.028%), the balance is Fe and inevitable inclusions.

[0042] The hot-rolled microstructure of the 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads is a mixed microstructure of acicular ferrite and bainite, wherein the content of bainite is ≤3%.

[0043] It should be noted that the structure of the 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads is mainly acicular ferrite, because the acicular ferrite can make it have a higher elongation after fracture and a lower yield strength ratio, which meets the performance requirements of steel for high-cold frozen soil roads to resist large deformation; however, it will inevitably contain a small amount of bainite during the preparation process. If there is too much bainite, although the strength will increase, the low-temperature toughness will decrease. Therefore, the content of bainite in the 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads is ≤3%.

[0044] Compared with the prior art, the 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads of the present invention, on the basis of low-carbon medium manganese steel, utilizes V and Ti composite microalloying to ensure the basic strength and toughness of the steel; controls the lower S content through LF refining, and strictly controls the size and content of inclusions in the steel to ensure that the steel has relatively good low-temperature impact performance; appropriately relaxes the P content, and adds rare earth Ce in a suitable manner to improve the soil and atmospheric corrosion resistance of the steel in a plateau frozen soil environment, and play the role of rare earth in purifying steel and improving corrosion resistance; the final organization is uniform acicular ferrite and a small amount of bainite, and the acicular ferrite enables it to have a higher elongation after fracture and a lower yield strength ratio, which meets the performance requirements of steel for high-cold frozen soil roads to resist large deformation, and is suitable for use in frozen soil roads in high-cold areas.

[0045] The main chemical composition of the 460MPa grade low temperature corrosion resistant steel for frozen soil highway of the present invention is limited for the following reasons:

[0046] Carbon (C): The steel of the present invention takes acicular ferrite as the final main structure, and the range of C content needs to be strictly controlled; the addition of an appropriate amount of C can play a role in solid solution strengthening in the steel and improve the strength of the matrix; strictly controlling the C content can effectively reduce the sensitivity of the Mn / S ratio of the continuous casting billet and reduce the probability of continuous casting longitudinal cracking. A relatively low C content can improve the uniform elongation of the steel, so the carbon content of the steel of the present invention is controlled to be 0.05-0.07%.

[0047] Silicon (Si): The Si element can not only play a role in solid solution strengthening, but also improve the corrosion resistance of steel. Too high silicon content will have an adverse effect on the plasticity and toughness of steel, so the Si content is controlled within the range of 0.3-0.5%.

[0048] Manganese (Mn): Mn is the most effective element for expanding the austenite phase, refining grains and ensuring the comprehensive performance of steel. 0.1% Mn can increase the tensile strength of the matrix by 10 MPa. Taking all factors into consideration, the Mn content in steel should be controlled in the range of 1.5-1.8%.

[0049] Phosphorus (P) and sulfur (S): Phosphorus and sulfur elements have a great influence on the low-temperature toughness of steel. The enrichment or segregation of phosphorus and sulfur elements will seriously reduce the low-temperature toughness of steel. Therefore, the phosphorus and sulfur content in steel needs to be strictly controlled. The control range of P element is 0.015-0.02%, and the control range of S element is ≤0.005%.

[0050] Copper (Cu): Cu is a solid solution strengthening element that can improve the strength of the steel matrix. The addition of Cu can enhance the corrosion resistance of steel and make it more durable in corrosive environments such as acid, alkali, and salt. Therefore, the Cu content in steel is controlled within a range of 0.02 to 0.03%.

[0051] Cerium (Ce): Ce can effectively improve the inclusion characteristics in steel, purify molten steel, refine grains, improve the corrosion resistance and oxidation resistance of steel, and effectively resist plateau soil corrosion. Therefore, the Ce content range is controlled at 0.02-0.03%.

[0052] Vanadium (V) Titanium (Ti): V and Ti are strong carbonitride production elements, which can improve the strength of steel through fine grain strengthening, precipitation strengthening and solid solution strengthening. Adding V elements can reduce the toughness-brittle transition temperature of steel; the addition of Ti elements, its precipitates can effectively pin the austenite grain boundaries, play a role in refining grains, and improve the low-temperature toughness of the heat-affected zone of steel welding.

[0053] Nitrogen (N): N forms nitrides with V and Ti, which can play a role in precipitation strengthening, better play the role of microalloy strengthening in steel, and increase the strength and corrosion resistance of the steel matrix. Therefore, the nitrogen content in steel is controlled in the range of 0.02-0.03%.

[0054] For example, in the 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads, the weight percentage content of O is ≤30ppm. O in the steel mainly exists in the form of oxide inclusions, which seriously affects the low-temperature toughness of the steel. In order to better play the role of rare earth elements in purifying molten steel and the corrosion resistance of solid-solution rare earths, it is necessary to strictly control the oxygen content in low-carbon steel. Therefore, the control range of oxygen content in steel is ≤30ppm.

[0055] Exemplarily, the grain size of the 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads is 10 to 11 levels.

[0056] Exemplarily, the thickness of 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads ranges from 1.2 to 20 mm.

[0057] The yield strength R of the 460MPa grade low temperature corrosion resistant steel for frozen soil highway of the present invention is el ≥460MPa, tensile strength R m ≥580MPa, yield strength ratio <0.8, elongation A≥20%, -45℃A KV2 ≥120J, relative corrosion rate to Q420B steel is <50%.

[0058] In a second aspect, the present invention further provides a method for preparing the above-mentioned 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads, the preparation method comprising molten iron pretreatment, dephosphorization converter smelting, decarbonization converter smelting, LF furnace refining, slab casting, slow cooling of the ingot, heating of the ingot, rolling, laminar cooling, and slab coiling;

[0059] Among them, rare earth Ce is added in the form of wire feeding in the later stage of LF furnace refining.

[0060] The finishing rolling inlet temperature in the rolling is 850-880°C.

[0061] The coiling temperature is 400-450°C.

[0062] Since rare earth Ce is very easy to oxidize, the present invention adds rare earth Ce in the form of wire feeding in the later stage of LF refining, which can reduce the oxidation of Ce and make the final corrosion-resistant steel have a target content of solid solution Ce. The present invention adopts a low-temperature finishing rolling and low-temperature coiling process, and the finishing rolling inlet temperature is 850-880°C. If the finishing rolling temperature is too high, it will affect the basic strength and toughness of the steel. If the finishing rolling temperature is too low, the bainite content will increase; the coiling temperature is 400-450°C. If the coiling temperature is too high, it will affect the basic strength and toughness of the steel. If the coiling temperature is too low, the bainite content will increase.

[0063] In the present invention, rare earth Ce is added in the form of wire feeding in the later stage of LF furnace refining, and the yield of Ce is 48%.

[0064] Exemplarily, the temperature of the dephosphorization converter smelting is 1250-1330°C, and the dephosphorization slag does not enter the decarburization furnace, thereby reducing the rephosphorization in the decarburization converter smelting process.

[0065] For example, in decarburization converter smelting, the end-point composition of smelting is controlled as follows: C≤0.05%, P≤0.005%. Here, the C and P contents are the process contents of converter smelting. In order to ensure the process quality of molten steel, they are not the final contents. The C and P contents can be adjusted in the refining process. After slag blocking and steel tapping, the steel is sent to the argon station for bottom blowing of argon after deoxidation and alloying, and alloying components such as Mn, V, and Ti are added.

[0066] Exemplarily, the slow cooling of the continuous casting slab adopts a cold charging furnace.

[0067] Exemplarily, the temperature of the soaking section for heating the ingot is 1130-1150° C., which is conducive to the diffusion of alloy elements.

[0068] Exemplarily, the rolling includes rough rolling and finish rolling. The rough rolling adopts a high-temperature and large-reduction process, which is beneficial to the deformation of the core of the plate, improves the uniformity of the structure, and improves the mechanical properties of the steel; the finish rolling adopts low-temperature rolling in the non-recrystallization zone, which is beneficial to improve the mechanical properties of the steel.

[0069] Exemplarily, the starting rolling temperature of the rough rolling is 1100-1150° C., and the deformation amount of the first pass is greater than 20%.

[0070] Exemplarily, the cumulative deformation of the finish rolling passes is greater than 30%, which can effectively refine the grain structure and improve the low-temperature toughness of the steel.

[0071] Exemplarily, the steel is kept at temperature for 2 to 4 minutes before entering the finishing rolling entrance.

[0072] Exemplarily, the cooling rate of the laminar cooling is 35-45°C / s. This laminar cooling rate can better control the low-temperature curling process, achieve the curling temperature target of 400-450°C, and improve the strength of the sheet.

[0073] The following is a further explanation of the 460MPa grade low temperature corrosion resistant steel for frozen soil roads of the present invention through specific examples.

[0074] Example 1

[0075] This embodiment provides a 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads and a preparation method thereof.

[0076] The chemical composition of the 460MPa grade low temperature corrosion resistant steel for frozen soil roads in this embodiment is shown in Table 1.

[0077] The preparation method of the 460MPa grade low temperature corrosion resistant steel for frozen soil roads includes: molten iron pretreatment → dephosphorization converter smelting → decarburization converter smelting → LF furnace refining → slab casting → slow cooling of the ingot → heating of the ingot → rolling → laminar cooling → slab coiling → finished product. Among them:

[0078] (1) The temperature of the dephosphorization converter smelting process is controlled at 1280℃, and the dephosphorization slag does not enter the decarburization furnace, reducing the rephosphorization in the decarburization converter smelting process.

[0079] (2) Decarburization converter smelting, control the end-point composition of smelting: C ≤ 0.05%, P ≤ 0.005%, slag blocking steel tapping, deoxidation and alloying, enter the argon station for bottom blowing of argon, and add alloy components such as Mn, V, and Ti.

[0080] (3) Rare earth Ce is added in the form of wire feed in the later stage of LF refining, and the yield is controlled at 48%. The O content in the later stage of refining is controlled at ≤30ppm.

[0081] (4) The slow-cooling continuous casting billet is cold-charged into the furnace, and the temperature of the soaking section of the heating furnace is controlled at 1140°C.

[0082] (5) The rough rolling adopts high temperature and large reduction process, the starting rolling temperature of the rough rolling is 1120℃, and the deformation of the first pass is 25%; the finishing rolling stage adopts low temperature rolling in the non-recrystallization zone, the cumulative deformation of each pass is 32%, and the temperature is kept for 4 minutes before entering the finishing rolling entrance. The finishing rolling entrance temperature is 860℃.

[0083] (6) A low-temperature coiling process is adopted, the cooling rate of the laminar cooling section is controlled at 40°C / s, and the coiling temperature is controlled at 420°C.

[0084] The 460MPa grade low temperature corrosion resistant steel for frozen soil highway has a thickness of 1.5mm, and the hot rolled structure is acicular ferrite (content 98%) and a small amount of bainite (content 2%), and the grain size is 10-11. Figure 2aand Figure 2b It can be seen that rare earth can modify inclusions and play a role in purifying the purity of molten steel. The mechanical properties and low temperature toughness of the low temperature corrosion resistant steel are shown in Table 2, and the corrosion resistance is shown in Table 3.

[0085] Example 2

[0086] This embodiment provides a 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads and a preparation method thereof.

[0087] The chemical composition of the 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads in this embodiment is shown in Table 1, and the preparation method is the same as that in Example 1.

[0088] The thickness of the 460MPa grade low temperature corrosion resistant steel for frozen soil roads is 5mm. Figure 1 The metallographic structure of the low-temperature corrosion-resistant steel is shown in Table 2. The hot-rolled structure is acicular ferrite (97%) and a small amount of bainite (3%), and the grain size is 10 to 11. The mechanical properties and low-temperature toughness of the low-temperature corrosion-resistant steel are shown in Table 2, and the corrosion resistance is shown in Table 3.

[0089] Example 3

[0090] This embodiment provides a 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads and a preparation method thereof.

[0091] The chemical composition of the 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads in this embodiment is shown in Table 1, and the preparation method is the same as that in Example 1.

[0092] The 460MPa grade low temperature corrosion resistant steel for frozen soil highway has a thickness of 8mm, and the hot rolled structure is acicular ferrite (content 97%) and a small amount of bainite (content 3%), and the grain size is 10 to 11. The mechanical properties and low temperature toughness of the low temperature corrosion resistant steel are shown in Table 2, and the corrosion resistance is shown in Table 3.

[0093] Comparative Example 1

[0094] Comparative Example 1 provides an existing corrosion-resistant steel Q420B with a strength level of 460 MPa, and its chemical composition is shown in Table 1.

[0095] Comparative Example 2

[0096] This embodiment provides a 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads and a preparation method thereof similar to Embodiment 1, except that the finishing rolling inlet temperature is 800°C.

[0097] The hot-rolled microstructure of the 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads is acicular ferrite (94%) and a small amount of bainite (6%), with a grain size of 10 to 11. The mechanical properties and low-temperature toughness of the low-temperature corrosion-resistant steel are shown in Table 2, and the corrosion resistance is shown in Table 3.

[0098] Comparative Example 3

[0099] This comparative example provides a 460MPa grade low temperature corrosion resistant steel for frozen soil roads and a preparation method thereof similar to Example 1, except that the finishing rolling inlet temperature is 930° C. The mechanical properties and low temperature toughness of the low temperature corrosion resistant steel are shown in Table 2, and the corrosion resistance is shown in Table 3.

[0100] Comparative Example 4

[0101] This comparative example provides a 460MPa grade low temperature corrosion resistant steel for frozen soil roads and a preparation method thereof similar to Example 1, except that the coiling temperature is 500° C. The mechanical properties and low temperature toughness of the low temperature corrosion resistant steel are shown in Table 2, and the corrosion resistance is shown in Table 3.

[0102] Comparative Example 5

[0103] This comparative example provides a 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads and a preparation method thereof similar to Example 1, except that rare earth Ce is added together with the ferroalloy when the steel is tapped from the converter.

[0104] The mechanical properties and low temperature toughness of the low temperature corrosion resistant steel are shown in Table 2, and the corrosion resistance is shown in Table 3.

[0105] Table 1 Chemical composition of examples and comparative examples (wt%)

[0106]

[0107] Table 2 Mechanical properties of examples and comparative examples

[0108]

[0109] Table 3 Corrosion resistance of examples and comparative examples

[0110]

[0111] It can be seen from the performance data in Table 2 and Table 3 that the 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads of the present invention can have good low-temperature toughness, corrosion resistance and mechanical properties.

[0112] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A 460MPa grade low temperature corrosion resistant steel for frozen soil roads, characterized in that: The 460MPa grade low temperature corrosion resistant steel for frozen soil highway comprises the following chemical components in weight percentage: C: 0.05-0.07%, Si: 0.3-0.5%, Mn: 1.5-1.8%, P: 0.015-0.02%, S: ≤0.005%, Cu: 0.02-0.03%, Ce: 0.02-0.03%, V: 0.08-0.12%, Ti: 0.015-0.02%, N: 0.02-0.03%, and the balance is Fe and unavoidable inclusions; The hot-rolled microstructure of the 460MPa grade low-temperature corrosion-resistant steel for frozen soil roads is a mixed microstructure of acicular ferrite and bainite, wherein the content of bainite is ≤3%; The 460MPa grade low temperature corrosion resistant steel for frozen soil highway has a yield strength Rel≥460MPa, a tensile strength Rm≥580MPa, a yield strength ratio <0.8, an elongation A≥20%, and a low temperature impact energy A of -45°C. KV2 ≥120J, relative corrosion rate to Q420B steel is <50%.

2. The 460MPa grade low temperature corrosion resistant steel for frozen soil roads according to claim 1, characterized in that: The grain size of the 460MPa-grade low-temperature corrosion-resistant steel for frozen soil roads is 10 to 11 grades.

3. A method for preparing 460MPa grade low temperature corrosion resistant steel for frozen soil roads as claimed in claim 1 or 2, characterized in that: The preparation method comprises molten iron pretreatment, dephosphorization converter smelting, decarbonization converter smelting, LF furnace refining, slab casting, slow cooling of the ingot, heating of the ingot, rolling, laminar cooling, and slab coiling; Among them, rare earth Ce is added in the form of wire feeding in the late stage of LF furnace refining; The finishing inlet temperature in the rolling process is 850-880°C; The coiling temperature is 400-450°C.

4. The preparation method according to claim 3, characterized in that: The temperature of the soaking section for heating the ingot is 1130-1150°C.

5. The preparation method according to claim 3, characterized in that: The rough rolling in the rolling adopts a high temperature and large reduction process, and the finishing rolling adopts low temperature rolling in the non-recrystallization zone.

6. The preparation method according to claim 5, characterized in that: The starting rolling temperature of the rough rolling is 1100-1150° C., and the deformation amount of the first pass is greater than 20%.

7. The preparation method according to claim 5, characterized in that: The cumulative deformation of the finish rolling passes is greater than 30%.

8. The preparation method according to claim 3, characterized in that: Wait for 2 to 4 minutes before entering the finishing rolling entrance.

9. The preparation method according to claim 3, characterized in that: The cooling rate of the laminar cooling is 35-45°C / s.

Images