Freeze-thaw-resistant frozen soil corrosion-resistant low-alloy structural steel and preparation method thereof

Abstract

The invention belongs to the technical field of steel and iron materials, and particularly relates to freeze-thaw-resistant frozen soil corrosion-resistant low-alloy structural steel and a preparation method thereof, the freeze-thaw-resistant frozen soil corrosion-resistant low-alloy structural steel adopts a component design completely different from that in the prior art to meet the freeze-thaw-resistant frozen soil corrosion-resistant requirements, meanwhile, the component design is simplified, and the cost is reduced. Zr-Ti-RE composite deoxidation and microalloying freeze-thaw-resistant steel controllable preparation is supplemented, the environmental fracture sensitivity is reduced, and the integrated design of the freeze-thaw-resistant steel component structure is achieved; through the low-carbon equivalent design, the steel plate has excellent welding performance; and Ti, Zr and RE composite microalloying is adopted, and TMCP rolling parameter regulation and control are matched, so that the steel plate is small in grain size and high in obdurability. The freeze-thaw corrosion resistant steel is particularly suitable for structural materials of plateau frozen soil roads, railways, bridges and the like used in low-temperature and freeze-thaw environments, and the material has the remarkable characteristics of high strength, easiness in welding, freeze-thaw resistance and the like besides low-temperature toughness and excellent performance.

Description

Technical Field

[0001] The invention relates to the technical field of steel materials, and in particular to a low-alloy structural steel that is resistant to freeze-thaw and frozen soil corrosion and a preparation method thereof. Background Art

[0002] There are more than 40 types of soil in my country. The properties of soil in different regions vary greatly due to differences in climate and region. Different types of soil have different porosity, water content, thermal insulation performance, etc. The pH value of the soil and the type of corrosive ions are related to the local environment. Due to the complexity of the soil environment and climate, the corrosion of metal materials in the soil is also different. The corrosive ions (anions) in the soil environment and some bacteria that can produce corrosive ions are the causes of soil corrosion. At the same time, the moisture and oxygen content in the soil will also affect the corrosion rate of metal materials in the soil. The corrosion of metals in the soil is electrochemical corrosion, and the main types of corrosion are: micro-battery corrosion, macro-battery corrosion, stray current corrosion and microbial corrosion.

[0003] Usually, the design temperature below or equal to -20℃ is called low temperature, and the steels serving in this environment are collectively called low temperature steel. Low temperature steel is an important variety of structural steel, including ferritic low temperature steel and austenitic low temperature steel; ferritic steel generally has an obvious toughness-brittle transition temperature, and when the temperature drops to a certain critical value, the toughness will suddenly drop. Therefore, ferritic steel should not be used below its transition temperature. It is usually necessary to add alloy elements such as manganese and nickel to reduce the toughness-brittle transition temperature. Austenitic steel has high low temperature toughness and generally has no toughness-brittle transition temperature. According to different alloy components, it can be divided into different series, such as Fe-Cr-Ni series, Fe-Cr-Ni-Mn series and Fe-Mn-Al series austenitic low temperature non-magnetic steel.

[0004] With the continuous advancement of economic development, national defense needs and national highway construction, the demand for highway construction in plateau frozen soil areas has increased year by year. However, under the background of global warming, the long-term freezing and thawing of plateau frozen soil has caused serious cracking of concrete used in key projects such as highway bridges and tunnels, threatening the service safety of highways. Due to the excellent strength, toughness and low-temperature performance of low-alloy steel, freeze-thaw-resistant steel structure bridges are used to replace steel-concrete structure bridges to reduce the pressure on the foundation and the risk of low-temperature cracking, increase the service life of the highway, and reduce the number of maintenance and repairs. "Bridges instead of roads" is an effective solution to alleviate this problem. However, in relatively low temperature and high ice content frozen soil areas, structural steel is subjected to external environments such as low-temperature freezing and thawing, soil corrosion, complex loads, and deformation and welding-induced organizational evolution. It is very easy to cause environmentally sensitive fracture failure under the coupling of low temperature, mechanics and electrochemical, threatening the service safety of bridges. It is urgent to develop high-service performance steel to meet the construction needs of plateau frozen soil highways. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the main purpose of the present invention is to provide a low-alloy structural steel that is resistant to freeze-thaw and frozen soil corrosion and a preparation method thereof.

[0006] To solve the above technical problems, according to one aspect of the present invention, the present invention provides the following technical solutions:

[0007] A low alloy structural steel that is resistant to freeze-thaw and frozen soil corrosion, and its composition is as follows, measured by weight percentage:

[0008] C: 0.011-0.099%, Si: 0.051-0.310%, Mn: 1.192-1.610%, Ni: 0.102-1.126%, Cr: 0.141-0.200%, Cu: 0.094-0.301%, Ti: 0.009-0.016%, Zr: 0.001-0.018%, RE: 0.001-0.015%, the rest is Fe and unavoidable impurities;

[0009] And the mass percentage of C element and Si element also satisfies the formula:

[0010] 0.19%≤C+Si≤0.25%, and Si / C=1~8;

[0011] The mass percentages of Zr and RE also satisfy the formula:

[0012] 0.001%≤RE+Zr≤0.014%, and RE / Zr=1~6.

[0013] As a preferred embodiment of the freeze-thaw resistant and frozen soil corrosion resistant low alloy structural steel of the present invention, the composition thereof is as follows, in terms of weight percentage:

[0014] C: 0.03~0.09%, Si: 0.13~0.30%, Mn: 1.4~1.55%, Ni: 0.52~1.126%, Cr: 0.150~0.200%, Cu: 0.094~0.301, Ti: 0.009~0.016%, Zr: 0.001~0.018%, RE: 0.001~0.01%, and the rest are Fe and unavoidable impurities.

[0015] As a preferred embodiment of the freeze-thaw resistant and frozen soil corrosion resistant low-alloy structural steel described in the present invention, its composition, in terms of weight percentage, is: C: 0.05%, Si: 0.20%, Mn: 1.5%, Ni: 0.5%, Cr: 0.19, Cu: 0.20, Ti: 0.012%, Zr: 0.0015%, RE: 0.006%, and the rest is Fe and unavoidable impurities.

[0016] As a preferred embodiment of the freeze-thaw resistant and frozen soil corrosion resistant low-alloy structural steel described in the present invention, among the inevitable impurities, the mass percentages of P element, S element, O element, N element and H element respectively satisfy: P≤0.0049%, S≤0.0010%, O≤0.0049%, N≤0.0039%, H≤0.00019.

[0017] As a preferred embodiment of the freeze-thaw resistant and frozen soil corrosion resistant low alloy structural steel described in the present invention, the microstructure type of the low alloy structural steel is a ferrite-pearlite banded structure, and the effective grain size of the microstructure of the low alloy structural steel is ≤10 μm.

[0018] As a preferred embodiment of the freeze-thaw resistant and frozen soil corrosion resistant low-alloy structural steel described in the present invention, the V-notch impact absorption energy of the low-alloy structural steel at -40°C is greater than 300J, the tensile strength is ≥410MPa, the yield strength is ≥480MPa, and the elongation is ≥30%.

[0019] To solve the above technical problem, according to another aspect of the present invention, the present invention provides the following technical solution:

[0020] A method for preparing the above-mentioned low-alloy structural steel with freeze-thaw resistance and frozen soil corrosion resistance comprises the following steps:

[0021] S1. Before induction smelting, the steel mold is fully baked, the surface of the smelting raw materials is fully descaled, and the alloy element raw materials are added according to the calculated amount; after the molten steel is melted in the vacuum induction furnace, the alloy element raw materials are gradually added, and after all the alloy element raw materials are fully melted into the molten steel, continuous casting is performed to obtain a cast billet;

[0022] S2, heating and heat-insulating the ingot, and then continuously rough rolling and finish rolling the ingot, and controlling the final temperature of the finish rolling to be 750-850° C., water cooling to 410-550° C. after rolling, and then naturally cooling to room temperature to obtain low alloy structural steel.

[0023] As a preferred embodiment of the method for preparing freeze-thaw resistant and frozen soil corrosion resistant low-alloy structural steel described in the present invention, wherein: in the step S1, pure iron, copper, ferrochrome and nickel are added together into a vacuum induction furnace to be completely melted, and then a protective gas is filled in to maintain a vacuum state, carbon, silicon, ferrozirconium and manganese alloy are added and melted, and then ferrotitanium and rare earth are added to obtain molten steel, the furnace temperature of the molten steel is adjusted to 1450-1550°C, and the free oxygen content in the molten steel is 10-20ppm.

[0024] As a preferred embodiment of the method for preparing freeze-thaw resistant and frozen soil corrosion resistant low-alloy structural steel of the present invention, wherein: in step S1, the rare earths include lanthanum and cerium, and the weight ratio of the lanthanum element to the cerium element is (34-36): (64-66).

[0025] As a preferred embodiment of the method for preparing the freeze-thaw resistant and frozen soil corrosion resistant low alloy structural steel of the present invention, wherein: in the step S2, the heating temperature is 1200-1300°C, the insulation time is 3-4h, and the rough rolling end temperature is 950-990°C.

[0026] The beneficial effects of the present invention are as follows:

[0027] The present invention proposes a low-alloy structural steel that is resistant to freeze-thaw and frozen soil corrosion and a preparation method thereof. The steel adopts a composition design that is completely different from the prior art to achieve the requirements of freeze-thaw and frozen soil corrosion resistance. At the same time, the composition design is simplified, and the freeze-thaw steel assisted by Zr-Ti-RE composite deoxidation and micro-alloying can be prepared in a controlled manner, reduce environmental fracture sensitivity, and achieve an integrated design of the composition and structure of the freeze-thaw steel. The steel plate has excellent welding performance through low-carbon equivalent design. The steel plate has fine grains and high strength and toughness by adopting composite micro-alloying of Ti, Zr, and RE, combined with TMCP rolling parameter regulation. This type of freeze-thaw corrosion-resistant steel is particularly suitable for structural materials such as plateau frozen soil roads, railways, bridges, etc. used in low-temperature and freeze-thaw environments. In addition to its superior low-temperature toughness, this material also has significant characteristics such as high strength, easy welding, and freeze-thaw resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0029] Figure 1 This is the sample morphology after low-temperature CTOD test.

[0030] Figure 2 This is the morphology of the sample after low temperature impact test.

[0031] Figure 3 It is the room temperature tensile curve diagram of the structural steel of Example 1 and Comparative Example 1.

[0032] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0033] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The present invention proposes a low-alloy structural steel that is resistant to freeze-thaw and frozen soil corrosion and a preparation method thereof. The requirements for the performance of freeze-thaw corrosion-resistant steel are, first of all, to ensure that the material has sufficient resistance to brittle cracking at the use temperature. In a special freeze-thaw environment, in order to prevent accidents, the material must also have good corrosion resistance. In addition, from a safety perspective, the yield strength ratio of freeze-thaw resistant steel should not be high. The larger the yield strength ratio, the smaller the reserve of plastic deformation capacity, and the lower the stress redistribution capacity at the stress concentration site, which is easy to promote brittle fracture. The technical requirements for freeze-thaw resistant steel are generally: sufficient strength and sufficient toughness at low temperatures, good process performance, processing performance and corrosion resistance, etc. Among them, corrosion resistance refers to the ability of the material to resist corrosion failure in a plateau frozen soil environment. The present invention has the following advantages:

[0035] (1) The low alloy structural steel of the present invention adopts a composition design that is completely different from the prior art to achieve the requirements of freeze-thaw resistance and frozen soil corrosion resistance. At the same time, the composition design is simplified. The freeze-thaw resistant steel supplemented by Zr-Ti-RE composite deoxidation and micro-alloying can be prepared in a controlled manner, reduce environmental fracture sensitivity, and achieve an integrated design of the composition and structure of the freeze-thaw resistant steel.

[0036] (2) The low alloy structural plate of the present invention is designed with low carbon, low silicon and medium manganese inexpensive chemical composition, which can reduce production costs.

[0037] (3) The present invention does not adopt the traditional Al deoxidation technology, but instead adopts Si-Mn deoxidation, and uses Zr-Ti-RE to add in an orderly manner to deeply deoxidize the molten steel, thereby achieving ultra-low O, P, and S control, improving the cleanliness of the molten steel, the rare earth recovery rate, and the rare earth micro-alloying effect, achieving efficient modification and dispersed distribution of inclusions (ZrO2 and Ti2O3), reducing mechanical property fluctuations and HAZ brittleness, and significantly improving plasticity and toughness; at the same time, through controlled rolling and controlled cooling, the grains are further refined, the component segregation is reduced, the grain boundaries are strengthened, and the organization homogenization is promoted, thus achieving a breakthrough in the coordinated control technology of the component structure of freeze-thaw resistant steel.

[0038] (4) The present invention adopts low carbon equivalent design, and the low alloy structural steel plate has excellent welding performance (CEV≤0.39, Pcm≤0.20, wherein CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15, Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B); adopts composite microalloying of Zr, Ti, and RE, and cooperates with TMCP rolling parameter regulation to achieve fine grains and high strength and toughness of the steel plate. This kind of freeze-thaw corrosion resistant steel is particularly suitable for structural materials such as plateau frozen soil roads, railways, bridges, etc. used in low temperature and freeze-thaw environments. In addition to its superior low temperature toughness, this material also has the remarkable characteristics of high strength, easy welding, and freeze-thaw corrosion resistance.

[0039] According to one aspect of the present invention, the present invention provides the following technical solution:

[0040] A low alloy structural steel that is resistant to freeze-thaw and frozen soil corrosion, and its composition is as follows, measured by weight percentage:

[0041] C: 0.011-0.099%, Si: 0.051-0.310%, Mn: 1.192-1.610%, Ni: 0.102-1.126%, Cr: 0.141-0.200%, Cu: 0.094-0.301%, Ti: 0.009-0.016%, Zr: 0.001-0.018%, RE: 0.001-0.015%, the rest is Fe and unavoidable impurities;

[0042] And the mass percentage of C element and Si element also satisfies the formula:

[0043] 0.19%≤C+Si≤0.25%, and Si / C=1~8;

[0044] The mass percentages of Zr and RE also satisfy the formula:

[0045] 0.001%≤RE+Zr≤0.014%, and RE / Zr=1~6.

[0046] The roles of various elements in low-alloy structural steel that resists freeze-thaw and frozen soil corrosion are as follows:

[0047] Carbon: The C content has a great influence on the mechanical properties, welding properties, and corrosion properties of steel materials. Under the same temperature, as the C content increases, the C atoms required to migrate for diffusion-controlled interface movement increase, and diffusion-type phase transformations such as ferrite and pearlite phase transformations are inhibited. If the C content is too high, bainite and martensite phases are easily formed during the cooling process. Bainite and martensite phases are hard and brittle, and their low-temperature impact properties are poor. In the present invention, appropriate C is added to obtain polygonal ferrite and fine and dispersed pearlite through appropriate diffusion-type phase transformation, without forming bainite and martensite during the cooling process. Therefore, the mass percentage of carbon element in the low-alloy structural steel of the present invention is C: 0.011~0.099%.

[0048] Silicon: Si is a ferrite-forming element with a strong solid solution strengthening effect. It interacts with the stress field of movable dislocations to hinder dislocation movement and improve the strength of steel materials. When the Si content is high, the machinability of steel is poor, which is not conducive to the welding performance of steel materials. In addition, when the Si content is too high, the plasticity and toughness of steel will be reduced. Therefore, the mass percentage of silicon element in the low-alloy structural steel of the present invention is Si: 0.051-0.310%.

[0049] Manganese: Mn strengthens ferrite, especially in low-alloy ordinary structural steel, where solid solution strengthening has a good effect; Mn shifts the austenite isothermal transformation curve to the right, improving the hardenability of steel; Mn is an austenite-forming element, which expands the austenite phase region. During the cooling process, Mn dissipates free energy through solute drag and inhibits diffusion-type phase transformation. By adding an appropriate amount of Mn, the microstructure of the steel plate can be controlled under appropriate process conditions to form a fine bainite lath structure with high strength and high toughness. If the Mn content is too high, cracks may appear in the steel billet during continuous casting and subsequent cooling. Mn can also deoxidize and eliminate the influence of S during the smelting process. Mn in the steel combines with S to form MnS, which can prevent hot brittleness caused by S. Generally speaking, in low-alloy high-strength steel, an appropriate amount of Mn is added to improve the strength of the steel. Therefore, the mass percentage of manganese element in the low-alloy structural steel of the present invention is Mn: 1.192-1.610%.

[0050] Phosphorus: Phosphorus has a strong solid solution strengthening effect in steel. When added to low alloy structural steel as an alloying element, it can improve its strength and atmospheric corrosion resistance. However, the biggest harm of phosphorus is that it segregates severely, increases temper brittleness, and significantly damages the plasticity and toughness of steel. Phosphorus also has an adverse effect on weldability. It can be seen that phosphorus is a harmful element and should be strictly controlled. Therefore, the mass percentage of carbon element in the low alloy structural steel of the present invention is P≤0.0049%.

[0051] Sulfur: S segregation in steel will seriously deteriorate the internal and surface quality of the steel; S also reduces the plasticity of the steel and is a harmful element. It exists in the form of FeS with a lower melting point. The melting point of FeS alone is only 1190°C, and the eutectic temperature of FeS in steel is even lower, only 988°C. When the steel solidifies, iron sulfide precipitates at the primary grain boundaries. When the steel is rolled at 1100-1200°C, the FeS on the grain boundaries will melt, greatly weakening the bonding force between the grains and causing the hot brittleness of the steel. Therefore, sulfur should be strictly controlled. The mass percentage of sulfur in the low-alloy structural steel of the present invention is S≤0.0010%.

[0052] Nickel: Ni is an austenite-forming element. When the Ni content is high, the steel can be austenite at room temperature; Ni reduces the resistance to dislocation movement in the steel and relaxes the stress, so it can improve the toughness of the steel matrix. At the same time, Ni can also promote the segregation of harmful elements in the steel and increase the temper brittleness of the steel. Therefore, the mass percentage of nickel element in the low-alloy structural steel of the present invention is Ni: 0.102-1.126%.

[0053] Chromium: Cr can increase the hardenability of steel and make it easier for the steel to form a hardened structure during the quenching process, which helps to improve the hardness and wear resistance of the steel without making the steel brittle; the addition of Cr can make the steel have good high-temperature oxidation resistance and corrosion resistance to oxidizing media. At the same time, the Cr element forms a passivation film on the steel surface, thereby significantly improving the corrosion resistance of the steel. However, Cr will affect the melting point of the steel and the fluidity of the molten pool. Therefore, the mass percentage of the chromium element in the low-alloy structural steel of the present invention is Cr: 0.141-0.200%.

[0054] Copper: Cu can slightly improve the high temperature oxidation resistance and help improve the high temperature oxidation resistance of steel. At the same time, Cu can improve the fluidity of molten steel and have a certain improvement effect on casting performance; adding a small amount of Cu to low alloy structural steel can effectively improve its atmospheric corrosion resistance, but it should be noted that steel with a high copper content is prone to cracking during hot working, so the copper content needs to be carefully controlled. Therefore, the mass percentage of copper element in the present invention is Cu: 0.094-0.301%.

[0055] Titanium: Titanium has a strong affinity with oxygen, nitrogen and carbon, and is a good deoxidizer and an effective element for fixing nitrogen and carbon. During the welding thermal cycle, TiN particles effectively hinder the coarsening of austenite grains, which is beneficial to the improvement of toughness. TiN particles can effectively promote the formation of acicular ferrite and effectively improve the welding performance of steel. However, excessive Ti is not conducive to improving the performance of steel, and is prone to form coarse titanium carbonitrides, which become crack sources and lead to reduced toughness. Therefore, the mass percentage of titanium element in the present invention is 0.009-0.016%.

[0056] Zirconium: Zr is a strong carbide forming element, a strong deoxidizing element and a composite oxysulfide forming element. Adding a small amount of Zr has the functions of degassing, purifying and refining grains, which is beneficial to improving the low temperature performance of low alloy structural steel, improving the stamping performance, and significantly improving the hardenability of steel when dissolved in austenite. Therefore, the mass percentage of zirconium element in the low alloy structural steel of the present invention is Zr: 0.001-0.018%.

[0057] Rare earth: The main functions of RE elements in steel are as follows: (1) Improve the purity of molten steel and remove harmful elements in steel, that is, strong deoxidation and desulfurization. By adding rare earth elements, the oxygen and sulfur contents in molten steel can be reduced to extremely low levels. Therefore, rare earth elements must undergo other deoxidation treatments before entering the molten steel as a deoxidizer to improve their utilization rate. (2) Modifier of inclusions. Compared with traditional Al deoxidizing inclusions, rare earth addition can react with Al elements in molten steel to generate REAlO3. Adding rare earth can refine and spheroidize inclusions. (3) Microalloying effect. The addition of rare earth elements is believed to reduce the temper embrittlement of steel. Elements such as phosphorus and sulfur in steel are very easy to segregate to the original austenite grain boundaries, resulting in an increase in the temperature at which the steel material changes from toughness to brittleness. The addition of rare earth elements can be used to combine with oxygen, sulfur, phosphorus and other elements distributed on the grain boundaries to form inclusions to eliminate or slow down the effects of such elements on the temper embrittlement of steel materials. However, when the rare earth addition exceeds the critical content, the rare earth will be concentrated at the grain boundary, destroying the pearlite orientation relationship, resulting in an increase in the pearlite interlamellar spacing and a decrease in impact toughness. Therefore, the mass percentage of rare earth elements in the low alloy structural steel of the present invention is RE: 0.001-0.015%.

[0058] Preferably, in terms of weight percentage, it is composed of:

[0059] C: 0.03-0.09%, Si: 0.13-0.30%, Mn: 1.4-1.55%, Ni: 0.52-1.126%, Cr: 0.150-0.200%, Cu: 0.094-0.301%, Ti: 0.009-0.016%, Zr: 0.001-0.018%, RE: 0.001-0.01%, the rest is Fe and unavoidable impurities

[0060] Further preferably, its composition, in terms of weight percentage, is: C: 0.05%, Si: 0.20%, Mn: 1.5%, Ni: 0.5%, Cr: 0.19, Cu: 0.20, Ti: 0.012%, Zr: 0.0015%, RE: 0.006%, and the rest is Fe and unavoidable impurities.

[0061] Further preferably, among the inevitable impurities, the mass percentages of the P element, the S element, the O element, the N element and the H element respectively satisfy: P≤0.0049%, S≤0.0010%, O≤0.0049%, N≤0.0039%, and H≤0.00019.

[0062] Preferably, the microstructure type of the low alloy structural steel is a ferrite-pearlite banded structure, and the effective grain size of the microstructure of the low alloy structural steel is ≤10 μm.

[0063] Preferably, the V-notch impact absorption energy of the low-alloy structural steel at a temperature of -40°C is greater than 300 J, the tensile strength is ≥410 MPa, the yield strength is ≥480 MPa, and the elongation is ≥30%.

[0064] According to another aspect of the present invention, the present invention provides the following technical solution:

[0065] A method for preparing the above-mentioned low-alloy structural steel with freeze-thaw resistance and frozen soil corrosion resistance comprises the following steps:

[0066] S1. Before induction smelting, the steel mold is fully baked, the surface of the smelting raw materials is fully descaled, and the alloy element raw materials are added according to the calculated amount; after the molten steel is melted in the vacuum induction furnace, the alloy element raw materials are gradually added, and after all the alloy element raw materials are fully melted into the molten steel, continuous casting is performed to obtain a cast billet;

[0067] S2, heating and heat-insulating the ingot, and then continuously rough rolling and finish rolling the ingot, and controlling the final temperature of the finish rolling to be 750-850° C., water cooling to 410-550° C. after rolling, and then naturally cooling to room temperature to obtain low alloy structural steel.

[0068] Preferably, in step S1, pure iron, copper, ferrochrome and nickel are added together into a vacuum induction furnace to be completely melted, and then a protective gas is filled in to maintain a vacuum state, carbon, silicon, ferrozirconium and manganese alloy are added and melted, and then ferrotitanium and rare earth are added to obtain molten steel, and the furnace temperature of the molten steel is adjusted to 1450-1550°C, and the free oxygen content in the molten steel is 10-20ppm. The free oxygen exists in the molten steel and is caused by the unavoidable oxygen element. The oxygen content should be reduced as much as possible during the smelting process to improve the quality of the steel and reduce defects.

[0069] Preferably, in step S1, the rare earth includes lanthanum and cerium, and the weight ratio of the lanthanum element to the cerium element is (34-36): (64-66).

[0070] Preferably, in step S2, the heating temperature is 1200-1300°C, the holding time is 3-4h, and the rough rolling end temperature is 950-990°C.

[0071] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0072] Example 1

[0073] A low alloy structural steel that is resistant to freeze-thaw and frozen soil corrosion, and its composition is as follows, measured by weight percentage:

[0074] C: 0.05%, Si: 0.19%, Mn: 1.5%, Ni: 0.5%, Cr: 0.20%, Cu: 0.1%, Ti: 0.012%, Zr: 0.0015%, RE: 0.0016%, the rest is Fe and unavoidable impurities;

[0075] The mass percentages of the C element and the Si element also satisfy the formula: 0.19%≤C+Si≤0.25% and Si / C=1~8;

[0076] The mass percentage contents of the Zr element and the RE element also satisfy the formulas: 0.001%≤RE+Zr≤0.014% and RE / Zr=1-6.

[0077] The method for preparing the above-mentioned low-alloy structural steel with freeze-thaw resistance and frozen soil corrosion resistance comprises the following steps:

[0078] S1. Before induction smelting, the steel mold is fully baked, the surface of the smelting raw materials is fully descaled, and the alloy element raw materials are added according to the calculated amount; after the molten steel is melted in a vacuum induction furnace, the alloy element raw materials are gradually added, and after all the alloy element raw materials are fully integrated into the molten steel, continuous casting is carried out to obtain a cast billet with a thickness of 95 mm; pure iron, copper, ferrochrome, and nickel are added together into a vacuum induction furnace to be completely melted, and then a protective gas is filled in to maintain a vacuum state, carbon, silicon, ferrozirconium, and manganese alloy are added, and after melting, ferrotitanium and rare earth are added to obtain molten steel, and the furnace temperature of the molten steel is adjusted to 1510°C, and the free oxygen content in the molten steel is 16.75ppm; the rare earth includes lanthanum and cerium, and the weight ratio of the lanthanum element to the cerium element is 35:65.

[0079] S2. The ingot is heated and kept warm at a heating temperature of 1250° C. for a holding time of 3.5 h. The ingot is then subjected to continuous rough rolling and finish rolling, and the rough rolling end temperature is controlled to be 990° C. and the finish rolling end temperature is controlled to be 825° C. After rolling, the ingot is water-cooled to 480° C. and then naturally cooled to room temperature to obtain a low-alloy structural steel with a thickness of 13 mm.

[0080] Example 2

[0081] A low alloy structural steel that is resistant to freeze-thaw and frozen soil corrosion, and its composition is as follows, measured by weight percentage:

[0082] C: 0.05%, Si: 0.19%, Mn: 1.52%, Ni: 1.00%, Cr: 0.15%, Cu: 0.30%, Ti: 0.012%, Zr: 0.0015%, RE: 0.0016%, the rest is Fe and unavoidable impurities;

[0083] The mass percentages of the C element and the Si element also satisfy the formula: 0.19%≤C+Si≤0.25% and Si / C=1~8;

[0084] The mass percentage contents of the Zr element and the RE element also satisfy the formulas: 0.001%≤RE+Zr≤0.014% and RE / Zr=1-6.

[0085] The method for preparing the above-mentioned low-alloy structural steel with freeze-thaw resistance and frozen soil corrosion resistance comprises the following steps:

[0086] S1. Before induction smelting, the steel mold is fully baked, the surface of the smelting raw materials is fully descaled, and the alloy element raw materials are added according to the calculated amount; after the molten steel is melted in a vacuum induction furnace, the alloy element raw materials are gradually added, and after all the alloy element raw materials are fully integrated into the molten steel, continuous casting is carried out to obtain a cast billet with a thickness of 110 mm; pure iron, copper, ferrochrome, and nickel are added together into a vacuum induction furnace to be completely melted, and then a protective gas is filled in to maintain a vacuum state, carbon, silicon, ferrozirconium, and manganese alloys are added, and after they are melted, ferrotitanium and rare earths are added to obtain molten steel, and the outlet temperature of the molten steel is adjusted to 1489°C, and the free oxygen content in the molten steel is 15.54pm; the rare earths include lanthanum and cerium, and the weight ratio of the lanthanum element to the cerium element is 35:65.

[0087] S2. The ingot is heated and kept warm at a heating temperature of 1250° C. for a holding time of 3.5 h. The ingot is then subjected to continuous rough rolling and finish rolling, and the rough rolling end temperature is controlled to be 986° C. and the finish rolling end temperature is controlled to be 833° C. After rolling, the ingot is water-cooled to 480° C. and then naturally cooled to room temperature to obtain a low-alloy structural steel with a thickness of 14 mm.

[0088] Example 3

[0089] A low alloy structural steel that is resistant to freeze-thaw and frozen soil corrosion, and its composition is as follows, measured by weight percentage:

[0090] C: 0.05%, Si: 0.19%, Mn: 1.52%, Ni: 0.5%, Cr: 0.2%, Cu: 0.2%, Ti: 0.012%, Zr: 0.0015%, RE: 0.0065%, the rest is Fe and unavoidable impurities;

[0091] The mass percentages of the C element and the Si element also satisfy the formula: 0.19%≤C+Si≤0.25% and Si / C=1~8;

[0092] The mass percentage contents of the Zr element and the RE element also satisfy the formulas: 0.001%≤RE+Zr≤0.014% and RE / Zr=1-6.

[0093] The method for preparing the above-mentioned low-alloy structural steel with freeze-thaw resistance and frozen soil corrosion resistance comprises the following steps:

[0094] S1. Before induction smelting, the steel mold is fully baked, the surface of the smelting raw materials is fully descaled, and the alloy element raw materials are added according to the calculated amount; after the molten steel is melted in a vacuum induction furnace, the alloy element raw materials are gradually added, and after all the alloy element raw materials are fully integrated into the molten steel, continuous casting is carried out to obtain a casting billet with a thickness of 100 mm; pure iron, copper, ferrochrome, and nickel are added together into a vacuum induction furnace to be completely melted, and then a protective gas is filled in to maintain a vacuum state, carbon, silicon, ferrozirconium, and manganese alloys are added, and after they are melted, ferrotitanium and rare earths are added to obtain molten steel, and the outlet temperature of the molten steel is adjusted to 1500°C, and the free oxygen content in the molten steel is 15.75ppm; the rare earths include lanthanum and cerium, and the weight ratio of the lanthanum element to the cerium element is 35:65.

[0095] S2. The ingot is heated and kept warm at a heating temperature of 1250° C. for a holding time of 3.5 h. The ingot is then subjected to continuous rough rolling and finish rolling, and the rough rolling end temperature is controlled to be 989° C. and the finish rolling end temperature is controlled to be 793° C. After rolling, the ingot is water-cooled to 466° C. and then naturally cooled to room temperature to obtain a low-alloy structural steel with a thickness of 14 mm.

[0096] Comparative Example 1

[0097] The difference from Example 1 is that the structural steel is Q355.

[0098] The microstructure type of the freeze-thaw resistant and frozen soil corrosion resistant low-alloy structural steel prepared in Examples 1-3 is a ferrite-pearlite banded structure, and the effective grain sizes of the microstructure are 9.5 μm, 9.4 μm, and 9.5 μm, respectively.

[0099] The low-temperature impact properties of the freeze-thaw resistant and frozen soil corrosion resistant low-alloy structural steel prepared in Example 1 were tested and analyzed, and the results are as follows:

[0100] The low-temperature impact test refers to the national standard GB / T229-2020 "Metallic Materials Charpy Pendulum Impact Test Method". The specimen size is a standard specimen of 55×10×10mm, with a V-notch, a notch depth of 2mm, and a root radius of 0.25mm. The edge curvature radius of the pendulum hammer blade is 2mm. The test temperature is -40℃. During the pendulum impact process, the resistance strain gauge on the hammer blade and the optical method are used to record the force and displacement values ​​respectively, thereby obtaining the force-displacement curve of the impact process, and then the impact absorption work is calculated by integration.

[0101] The low-temperature CTOD (CTOD stands for Crack Tip Opening Displacement) test is carried out in accordance with the national standard GB / T21143-2014 "Uniform test method for quasi-static fracture toughness of metallic materials". The three-point bending specimen with a specimen specification of 10×20×100mm is pre-cracked at the front end of the processed specimen notch using a fatigue testing machine. The CTOD test is carried out on an NSTRON8802-100kN electro-hydraulic servo fatigue testing machine at a loading rate of 2mm / min. The testing machine automatically records the load F and the crack opening displacement V at the notch, and draws the FV curve. The specimen after crushing is observed under a microscope, and the crack extension length a and the initial crack length a0 are measured. After judging that the specimen is valid, the CTOD value is calculated.

[0102] Table 1 shows the -40°C impact energy and CTOD results of the freeze-thaw and frozen soil corrosion resistant low alloy structural steel prepared in Example 1 of the present invention. From Table 1, it can be seen that the freeze-thaw and frozen soil corrosion resistant low alloy structural steel prepared in Example 1 has good fracture toughness and crack propagation resistance; Figure 1-2 The surface morphology of three groups of parallel samples from the same batch prepared in Example 1 after CTOD and impact tests; Figure 1 From the CTOD fracture morphology, it can be seen that the fracture surface produced when the sample is overloaded is an obvious ductile fracture surface. Figure 2 The morphology after the low-temperature impact test shows that the sample did not break and also exhibited obvious toughness behavior.

[0103] Table 1 -40℃ CTOD and low temperature impact results of low alloy structural steel in Example 1

[0104]

[0105] The tensile properties of the structural steel prepared in Example 1 and Comparative Example 1 were tested and analyzed, and the results are as follows:

[0106] The tensile test refers to the national standard GB / T 228.1-2021, "Tensile test of metallic materials Part 1: Test method at room temperature". The sample surface is mechanically polished on both sides with 400 mesh, 600 mesh, 800 mesh, and 1200 mesh sandpaper in turn. To ensure that the tensile test is not affected by the surface state of the sample and the burrs generated by wire cutting, the tensile test is carried out on a universal material tensile testing machine. The force sensor used has a load range of 30kN and a strain rate of 5×10 -3 .

[0107] Figure 3 The room temperature tensile curves of the low alloy structural steel of Example 1 of the present invention and the structural steel (Q355) of Comparative Example 1 are compared. There is a relatively obvious yield platform in the stress-strain curves of the two groups of tensile specimens. As the stress gradually increases, the specimens begin to neck after the stress gradually reaches the ultimate tensile strength in the strengthening stage, and finally break. Figure 3 It can be clearly seen that the yield strength and tensile strength of the low alloy structural steel in Example 1 of the present invention are improved compared with the Q355 in Comparative Example 1. At the same time, it can be seen from Table 2 that the elongation of the low alloy structural steel in Example 1 of the present invention is also greatly improved compared with the Q355 in Comparative Example 1.

[0108] Table 2 Tensile properties of structural steel of Example 1 and Comparative Example 1

[0109]

[0110] It can be seen from the embodiments and comparative examples of the present invention that the present invention adopts a completely different composition design from the prior art to achieve the requirements of freeze-thaw resistance and frozen soil corrosion resistance, and at the same time simplifies the composition design, and the freeze-thaw steel assisted by Zr-Ti-RE composite deoxidation and micro-alloying can be controlled to prepare, reduce environmental fracture sensitivity, and achieve an integrated design of the composition structure of the freeze-thaw steel; the present invention has excellent welding performance through low-carbon equivalent design; the composite micro-alloying of Ti, Zr, and RE is adopted, and the TMCP rolling parameter regulation is coordinated to achieve fine grains and high toughness of the steel plate. This kind of freeze-thaw corrosion-resistant steel is particularly suitable for structural materials such as plateau frozen soil roads, railways, bridges, etc. used in low temperature and freeze-thaw environments. In addition to its superior low-temperature toughness, this material also has significant characteristics such as high strength, easy welding, and freeze-thaw resistance.

[0111] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A low alloy structural steel with freeze-thaw resistance and frozen soil corrosion resistance, characterized in that: In terms of weight percentage, its composition is: C: 0.011-0.099%, Si: 0.051-0.310%, Mn: 1.192-1.610%, Ni: 0.102-1.126%, Cr: 0.141-0.200%, Cu: 0.094-0.301%, Ti: 0.009-0.016%, Zr: 0.001-0.018%, RE: 0.001-0.015%, the rest is Fe and unavoidable impurities; And the mass percentage of C element and Si element also satisfies the formula: 0.19%≤C+Si≤0.25%, and Si / C=1~8; The mass percentages of Zr and RE also satisfy the formula: 0.001%≤RE+Zr≤0.014%, and RE / Zr=1~6.

2. The freeze-thaw resistant and frozen soil corrosion resistant low alloy structural steel according to claim 1, characterized in that: In terms of weight percentage, its composition is: C: 0.03~0.09%, Si: 0.13~0.30%, Mn: 1.4~1.55%, Ni: 0.52~1.126%, Cr: 0.150~0.200%, Cu: 0.094~0.301%, Ti: 0.009~0.016%, Zr: 0.001~0.018%, RE: 0.001~0.01%, and the rest are Fe and unavoidable impurities.

3. The freeze-thaw resistant and frozen soil corrosion resistant low alloy structural steel according to claim 1, characterized in that: Calculated by weight percentage, its composition is: C: 0.05%, Si: 0.20%, Mn: 1.5%, Ni: 0.5%, Cr: 0.19, Cu: 0.20, Ti: 0.012%, Zr: 0.0015%, RE: 0.006%, and the rest is Fe and inevitable impurities.

4. The freeze-thaw resistant and frozen soil corrosion resistant low alloy structural steel according to claim 1, characterized in that: Among the inevitable impurities, the mass percentages of P element, S element, O element, N element and H element respectively satisfy: P≤0.0049%, S≤0.0010%, O≤0.0049%, N≤0.0039%, H≤0.00019.

5. The freeze-thaw resistant and frozen soil corrosion resistant low alloy structural steel according to claim 1, characterized in that: The microstructure type of the low alloy structural steel is a ferrite-pearlite banded structure, and the effective grain size of the microstructure of the low alloy structural steel is ≤10 μm.

6. The freeze-thaw resistant and frozen soil corrosion resistant low alloy structural steel according to claim 1, characterized in that: The V-notch impact absorption energy of the low-alloy structural steel at a temperature of -40°C is greater than 300J, the tensile strength is ≥410MPa, the yield strength is ≥480MPa, and the elongation is ≥30%.

7. A method for preparing the freeze-thaw resistant and frozen soil corrosion resistant low alloy structural steel according to any one of claims 1 to 6, characterized in that: The steps include: S1. Before induction smelting, the steel mold is fully baked, the surface of the smelting raw materials is fully descaled, and the alloy element raw materials are added according to the calculated amount; after the molten steel is melted in the vacuum induction furnace, the alloy element raw materials are gradually added, and after all the alloy element raw materials are fully melted into the molten steel, continuous casting is performed to obtain a cast billet; S2, heating and heat-insulating the ingot, and then continuously rough rolling and finish rolling the ingot, and controlling the final temperature of the finish rolling to be 750-850° C., water cooling to 410-550° C. after rolling, and then naturally cooling to room temperature to obtain low alloy structural steel.

8. The method for preparing freeze-thaw resistant and frozen soil corrosion resistant low alloy structural steel according to claim 7, characterized in that: In the step S1, pure iron, copper, ferrochrome and nickel are added together into a vacuum induction furnace to be completely melted, and then a protective gas is filled in to maintain a vacuum state. Carbon, silicon, ferrozirconium and manganese alloy are added and melted, and then ferrotitanium and rare earth are added to obtain molten steel. The furnace temperature of the molten steel is adjusted to 1450-1550° C., and the free oxygen content in the molten steel is 10-20 ppm.

9. The method for preparing freeze-thaw resistant and frozen soil corrosion resistant low alloy structural steel according to claim 7, characterized in that: In the step S1, the rare earth includes lanthanum and cerium, and the weight ratio of the lanthanum element to the cerium element is (34-36): (64-66).

10. The method for preparing freeze-thaw resistant and frozen soil corrosion resistant low alloy structural steel according to claim 7, characterized in that: In the step S2, the heating temperature is 1200-1300°C, the holding time is 3-4h, and the rough rolling end temperature is 950-990°C.

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