Production method of railway anti-seismic steel with low yield ratio

Abstract

The invention belongs to the technical field of metallurgy, and relates to a production method of railway anti-seismic steel with a low yield ratio. Comprising the procedures of converter smelting, refining, continuous casting, hot rolling and cooling. The cooling process comprises the following steps: quickly cooling to 650 DEG C after rolling at the cooling speed of more than or equal to 20 DEG C / s and the pit entering temperature of more than or equal to 630 DEG C, and slowly cooling for more than or equal to 48 hours; the anti-seismic steel is composed of the following components in percentage by mass: 0.11-0.15% of C; si is equal to 0.10%-0.30%; mn is equal to 1.30 to 1.60 percent; p is less than or equal to 0.013%; s < = 0.008%; v is equal to 0.06 to 0.08 percent; ti is less than or equal to 0.02%; al > = 0.025%; and the balance of Fe and inevitable impurity elements. And the produced anti-seismic steel has the characteristics of high tensile strength, low yield ratio, good low-temperature impact performance and stable performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy and relates to a production method of low yield ratio railway anti-seismic steel. BACKGROUND

[0002] In earthquake-prone areas such as the southwest of China, infrastructure such as railway bridges and tracks is prone to be impacted by earthquakes, and traditional steel may fail due to brittle fracture in high-intensity earthquakes; low yield ratio steel, i.e., steel with a low ratio of yield strength to tensile strength, has higher plastic deformation capacity and can absorb seismic energy to avoid sudden fracture failure.

[0003] Generally, low yield ratio steel used for railway bridge structures requires a tensile strength of ≥450 and a yield ratio of ≤0.80.

[0004] With the development of modern industry, high-speed and heavy-load trends of high-speed rail and heavy-load rail have higher requirements for the strength and toughness of steel rails and bridge steel. Railway anti-seismic steel needs to consider both high strength and low yield ratio to achieve the characteristics of "strong and not brittle". However, traditional steel often cannot meet the requirements of high strength and low yield ratio at the same time.

[0005] Traditional strengthening mechanisms (such as fine-grain strengthening and precipitation strengthening) can improve tensile strength, but often simultaneously increase yield strength, resulting in an increase in yield ratio.

[0006] By designing a multi-phase structure, the tensile strength is selectively increased by a hard phase, the proportion of a soft phase is increased to reduce the initial yield strength, and the excessive growth of yield strength is inhibited during processing, which can meet the requirements of "strong and not brittle". SUMMARY

[0007] To achieve the above-mentioned purpose, the application provides a production method of low yield ratio railway anti-seismic steel, which develops a low yield ratio railway anti-seismic steel by adjusting the chemical composition and combining existing equipment and process technology, thereby solving the problems in the prior art.

[0008] The technical scheme adopted by the application is a production method of low yield ratio railway anti-seismic steel, which comprises the steps of converter smelting, refining, continuous casting, hot rolling and cooling.

[0009] The cooling process is as follows: after rolling, rapid cooling to 650 DEG C, cooling rate ≥ 20 DEG C / s, slow cooling at a pit temperature ≥ 630 DEG C, slow cooling time ≥ 48 hours.

[0010] The anti-seismic steel is composed of the following components in mass percentage: C=0.11-0.15%; Si=0.10-0.30%; Mn=1.30-1.60%; P≤0.013%; S≤0.008%; V=0.06-0.08%; Ti≤0.02%; Al≥0.025%; and the rest is Fe and inevitable impurity elements.

[0011] Further, the anti-seismic steel has a yield ratio of 0.62-0.65, a tensile strength of 520-600 MPa, a yield strength of 330-395 MPa, an impact energy AKV2 at -40℃ of more than 60 J, and a metallographic structure of pearlite + ferrite.

[0012] Further, the converter smelting process is as follows: mass ratio of molten iron to scrap steel=4:1, total slag amount 18 kg / t of steel, mass ratio of lime to dolomite=5:4; tapping temperature≥1560℃, alloy is added during tapping, 2 kg / t of steel of aluminum iron is used for deoxidation, 1.2-1.5 kg / t of steel of silicon iron, 16-20 kg / t of steel of manganese iron, and 1.2-2.0 kg / t of steel of vanadium-nitrogen alloy.

[0013] Further, the refining process is as follows: alkaline slag is formed in an LF furnace, basicity 2-5, diffusion deoxidation is performed after 1 kg / t of aluminum particles is added, and then calcium treatment is performed, calcium wire feeding amount 0.5 kg / t, RH vacuum extraction is performed to below 67 Pa, and the vacuum extraction is maintained for more than 10 min, and soft blowing + standing is performed for more than 20 min.

[0014] Further, the continuous casting process is as follows: the superheat of molten steel in a tundish is below 20℃, electromagnetic stirring in a crystallizer + end electromagnetic stirring + heavy reduction is used, the current of electromagnetic stirring in the crystallizer is 300 A, the frequency is 3 Hz, the current of end electromagnetic stirring is 300 A, the frequency is 16 Hz, and the reduction amount is 25-30 mm; the specific water amount of secondary cooling is 0.16-0.26 L / kg, and preferably 0.17 L / kg; after entering a slow cooling pit, slow cooling is performed for more than 24 hours, and the entering temperature is≥550℃.

[0015] Further, the hot rolling process is as follows: the billet tapping temperature is 1050-1100℃, after high-pressure water descaling, reciprocating mill large reduction is used to roll to an intermediate billet type to refine initial austenite grains, the billet temperature reaches 800-900℃ after waiting for 1-2 min, the surface temperature is lower than the core temperature, the surface deformation resistance is greater than the core, differential temperature rolling is performed to improve the internal quality; short stress rolling mill is used to roll to a size close to the final size, and finally KOCKS rolling mill is used to roll out the finished product, accumulated deformation energy is stored, and phase transformation is induced to refine the structure.

[0016] It needs to be further explained that: the molten steel composition at the end of the converter smelting in the above steps: P element will have a certain degree of "phosphorus return" phenomenon during the heating process in the refining process step (LF), so it will increase by a certain amount; S element will be mostly removed into the refining slag in the refining steps (LF) and (RH); C element is mainly derived from ferrosilicon, manganese iron and other alloys, and the element yield of C is about 90%; alloys (such as Si with ferrosilicon, Mn with manganese iron, V with vanadium-nitrogen alloy) are used to adjust the contents of Si, Mn and V, among which the element yield of Si is about 88%, the element yield of Mn is about 93%, and the element yield of V is about 98%; aluminum iron is used for deoxidization and aluminum increase, and aluminum particles are used for diffusion deoxidization, and the element yield of Al is about 50%; the added Al element will be oxidized by a certain amount in the vacuum process of the refining process step (RH) and the continuous casting process, and will enter the refining slag in the form of Al2O3.

[0017] The component design principle of the application is as follows:

[0018] According to the influence of alloy elements on the performance and microstructure of the material, and combined with the existing equipment and process conditions, the inventors have designed and developed a low yield ratio railway anti-seismic steel. Specifically, in the research and development process, the inventors found that the influence of each related chemical element on the tensile strength (TS), yield strength (YS) and other performances is as follows:

[0019] The main element C (carbon) promotes the formation of pearlite and carbide, which can significantly improve the strength of the steel: about 80-100 MPa of TS and about 60-80 MPa of YS are increased per 0.1% C; but the increase in strength will also increase the brittleness of the steel;

[0020] The main element Si (silicon) is solid solution strengthened in the steel, inhibits the precipitation of cementite, and can improve the strength of ferrite and austenite: about 30-50 MPa of TS and about 20-40 MPa of YS are increased per 0.1% Si;

[0021] The main element Mn (manganese) can improve the strength of the steel through solid solution strengthening and improving the hardenability of the steel, inhibiting the formation of ferrite and promoting the transformation of bainite / martensite: about 50-80 MPa of TS and about 40-60 MPa of YS are increased per 0.1% Mn;

[0022] The main element P (phosphorus) slightly improves the strength, but significantly reduces the toughness of the steel, which needs to be strictly controlled.

[0023] The main element S (sulfur) has little effect on the strength, but the MnS inclusions formed by S and Mn will reduce the ductility and fatigue strength of the steel, which needs to be strictly controlled.

[0024] Micro-alloying element Nb, through grain refinement + precipitation strengthening, significantly improve the strength: about 30-50MPa per 0.01% Nb, about 25-45MPa per 0.01% Nb, the yield strength of the more obvious, will improve the yield ratio; at the same time, the surface quality has a deterioration effect.

[0025] Micro-alloying element V, through precipitation strengthening to improve the strength: about 5-8MPa per 0.01% V, about 3-5MPa per 0.01% V, the tensile strength of the more obvious, will slightly reduce the yield ratio.

[0026] Micro-alloying element Ti, through grain refinement + precipitation strengthening to improve the strength: about 15-25MPa per 0.01% Ti, about 10-20MPa per 0.01% Ti, the yield ratio is not much affected, but easy to form TiN inclusions, affect the toughness of the steel.

[0027] The beneficial effects of the present application are: according to the use requirements of railway anti-seismic steel, combined with the existing equipment capacity, the component design is carried out, at the same time, according to the designed component, the production process design is carried out, the produced material has the characteristics of high tensile strength, low yield ratio, good low temperature impact performance and stable performance, which can significantly improve the anti-seismic safety of railway bridge.

[0028] Specifically, the rolled material produced by the present application has a tensile strength of 520-600MPa, a yield strength of 330-395MPa, a yield ratio of 0.62-0.65, and a hot-rolled metallographic structure of ferrite + pearlite, which has the characteristics of high tensile strength, low yield ratio, good low temperature impact performance and stable performance. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0030] Figure 1 The metallographic structure diagram of the rolled material after slow cooling of the present application embodiment 1 is observed under 200X, and the metallographic structure is ferrite + pearlite.

[0031] Figure 2 The metallographic structure diagram of the rolled material after slow cooling of the present application embodiment 2 is observed under 200X, and the metallographic structure is ferrite + pearlite. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the protection scope of the present application.

[0033] Embodiment 1

[0034] A production method of a low yield ratio railway anti-seismic steel is produced according to a converter-LF-RH-continuous casting-heating furnace-rolling process. The chemical composition content of the final product is shown in Table 1. The process steps include:

[0035] (1) The converter smelting raw material is molten iron: scrap steel = 4:1, and the total slag amount is 18 kg / t of steel, wherein the lime: dolomite = 5:4. The tapping temperature is 1583℃. During the tapping process, the alloy is added: 2 kg / t of aluminum iron (for precipitated deoxidation and aluminum increase), 1.2 kg / t of silicon iron, 16 kg / t of manganese iron, and 1.2 kg / t of vanadium-nitrogen alloy;

[0036] (2) The LF furnace (Ladle Furnace) is used to form alkaline slag, and the basicity is 2.5. After diffusion deoxidation with 1 kg / t of aluminum particles, calcium treatment is performed, and the calcium wire feeding amount is 0.5 kg / t;

[0037] (3) The RH is vacuumized to 62 Pa (the absolute vacuum degree of the RH refining furnace), and maintained for 11 min. After breaking the vacuum, soft blowing is performed for 3 min, and standing is performed for 20 min;

[0038] (4) The continuous casting tundish steel water superheat is 18℃, and the process of the crystallizer electromagnetic stirring (stirring current is 300 A, and stirring frequency is 3 Hz) + end electromagnetic stirring (stirring current is 300 A, and stirring frequency is 16 Hz) + heavy pressing (pressing amount is 28 mm) is used. The specific water amount is 0.17 L / kg, and after the cold bed, it is cooled in the slow cooling pit for 25 hours, and the pit temperature is 562℃.

[0039] (5) The medium-low temperature heating is used, the billet discharge temperature is 1062℃, after high-pressure water descaling, the reciprocating mill is used for large reduction rolling to the intermediate billet type, waiting for 1 min, the billet temperature (surface temperature) reaches 886℃, the flat-stand alternating short stress rolling mill is used for rolling to the near final size, and finally the KOCKS rolling mill is used for rolling out the finished product.

[0040] (6) After rolling, it is quickly water-cooled to 650℃ at a cooling speed of 20℃ / s; high-temperature pit cooling is used, the pit temperature is 633℃, and the slow cooling time is 48 hours.

[0041] The mechanical property detection of the rolled material produced according to the above method is shown in Table 2, and the metallographic structure is as follows: Figure 1as shown.

[0042] Example 2

[0043] A production method of a low yield ratio railway anti-seismic steel is produced according to a converter-LF-RH-continuous casting-heating furnace-rolling process. The chemical composition content of the final product is shown in Table 1. The process steps include:

[0044] (1) The converter smelting raw material is molten iron: scrap steel = 4:1, and the total slag amount is 18 kg / t of steel, wherein lime: dolomite = 5:4. The tapping temperature is 1567℃. During tapping, the alloy is added: total 2 kg / t of aluminum iron (for precipitated deoxidation and aluminum increase), total 1.5 kg / t of silicon iron, total 20 kg / t of manganese iron, and total 2.0 kg / t of vanadium-nitrogen alloy;

[0045] (2) The LF furnace (Ladle Furnace) is used to form alkaline slag with a basicity of 2.2, and after diffusion deoxidation with 1 kg / t of aluminum particles, calcium treatment is performed with a calcium wire feeding amount of 0.5 kg / t;

[0046] (3) The RH is vacuumed to 62 Pa (absolute vacuum degree of the "RH refining furnace") and maintained for 13 min; after breaking the vacuum, soft blowing is performed for 10 min, and standing is performed for 15 min;

[0047] (4) The continuous casting tundish steel water superheat is 15℃, and the process of crystallizer electromagnetic stirring (stirring current is 300 A, stirring frequency is 3 Hz) + end electromagnetic stirring (stirring current is 300 A, stirring frequency is 16 Hz) + heavy pressing (pressing amount is 28 mm) is used, and the specific water amount is 0.17 L / kg, and after entering the cooling bed, it enters the slow cooling pit for slow cooling for 26 hours, and the entering pit temperature is 553℃.

[0048] (5) Medium-low temperature heating, the billet discharge temperature is 1078℃, after high-pressure water descaling, reciprocating mill large reduction rolling is adopted to roll to the intermediate billet type, waiting for 1.5 min, the billet temperature (surface temperature) reaches 848℃, and the flat-stand alternating short stress rolling mill is adopted to roll to the near final size, and finally the KOCKS rolling mill is used to roll out the finished product.

[0049] (6) After rolling, rapid water cooling is performed to 650℃, and the cooling speed is 21℃ / s; high-temperature slow cooling into the pit, the entering pit temperature is 637℃, and the slow cooling time is 48 hours.

[0050] The mechanical property detection of the rolled material produced according to the above method is shown in Table 2, and the metallographic structure is shown in Figure 2 .

[0051] Table 1 Chemical composition of the final product of the example (% by weight)

[0052] Serial number C％ Si % Mn % P％ S％ V％ Ti % Al％ Example 1 0.11 0.12 1.33 0.011 0.004 0.06 0.02 0.025 Example 2 0.14 0.26 1.57 0.008 0.005 0.10 0.01 0.035

[0053] In Table 1 above, the balance is Fe and inevitable impurity elements; the components in Table 1 above refer to the element content of the final product. The detection method of the chemical components in Table 1 above is to sample according to the GB / T 20066 standard requirement, and to detect according to the GB / T 4336 standard requirement.

[0054] Comparative Example 1:

[0055] The difference between Example 1 and Comparative Example 1 is that the cooling process is carried out at an entry pit temperature of 620℃ for slow cooling, and the other conditions are the same as those in Example 1.

[0056] Effect Example:

[0057] The rolled material (without additional heat treatment) after slow cooling in step (6) in each example and comparative example is directly sampled according to the GB / T 2975 standard requirement, and then a standard test sample is processed according to the GB / T 2975 standard requirement, the mechanical properties are detected according to the GB / T 228.1 standard requirement, and the impact energy at -40℃ is detected according to the GB / T 229 standard requirement. The results are shown in Table 2.

[0058] Table 2 Product properties of each example and comparative example

[0059]

[0060] In summary, the technical scheme of the present application can produce an anti-seismic steel with the following comprehensive properties: tensile strength of 520-600MPa, yield strength of 330-395MPa, and yield strength ratio of 0.62-0.65.

[0061] The above only describes the preferred embodiments of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for producing low yield strength ratio railway seismic-resistant steel, characterized in that, This includes converter smelting, refining, continuous casting, hot rolling, and cooling processes; The cooling process is as follows: after rolling, the temperature is rapidly cooled to 650°C with a cooling rate of ≥20°C / s, and then slowly cooled at a pit temperature of ≥630°C for a slow cooling time of ≥48 hours. The earthquake-resistant steel is composed of the following components by mass percentage: C = 0.11-0.15%; Si = 0.10-0.30%; Mn = 1.30-1.60%; P ≤ 0.013%; S ≤ 0.008%; V = 0.06-0.08%; Ti ≤ 0.02%; Al ≥ 0.025%; the remainder being Fe and unavoidable impurity elements.

2. The method for producing low yield strength ratio railway seismic-resistant steel as described in claim 1, characterized in that, The earthquake-resistant steel has a yield strength ratio of 0.62-0.65, a tensile strength of 520-600MPa, a yield strength of 330-395MPa, an impact energy (AKV2) of over 60J at -40℃, and a metallographic structure of pearlite + ferrite.

3. The method for producing low yield strength ratio railway seismic-resistant steel as described in claim 2, characterized in that, The converter smelting process is as follows: the ratio of molten iron to scrap steel is 4:1, the total slag is 18 kg / t steel, and the ratio of lime to dolomite is 5:4; the tapping temperature is ≥1560℃, and alloys are added during the tapping process: 2 kg / t steel of ferroaluminum, 1.2-1.5 kg / t steel of ferrosilicon, 16-20 kg / t steel of ferromanganese, and 1.2-2.0 kg / t steel of vanadium-nitrogen alloy.

4. The method for producing low yield strength ratio railway seismic-resistant steel as described in claim 3, characterized in that, The refining process is as follows: alkaline slag is produced in the LF furnace with an alkalinity of 2-5. After diffusion deoxidation with 1 kg / t of aluminum particles, calcification treatment is carried out. The calcium wire feed rate is 0.5 kg / t. The RH vacuum is drawn to below 67 Pa and maintained for more than 10 minutes. Soft blowing + standing is carried out for ≥20 minutes.

5. The method for producing low yield strength ratio railway seismic-resistant steel as described in claim 4, characterized in that, The continuous casting process is as follows: the superheat of the molten steel in the ladle is below 20°C, and electromagnetic stirring in the crystallizer + electromagnetic stirring at the end + heavy pressure is used. The electromagnetic stirring current in the crystallizer is 300A and the frequency is 3Hz. The electromagnetic stirring current at the end is 300A and the frequency is 16Hz. The reduction is 25-30mm. The secondary cooling water volume is 0.16-0.26L / kg. After leaving the cooling bed, the steel is quickly placed into a slow cooling pit for slow cooling for ≥24 hours. The temperature in the pit is ≥550°C.

6. The method for producing low yield strength ratio railway seismic-resistant steel as described in claim 5, characterized in that, The hot rolling process is as follows: the billet exits the furnace at a temperature of 1050-1100℃, and after descaling with high pressure water, it is rolled into an intermediate billet shape using a reciprocating rolling mill with high reduction. After waiting for 1-2 minutes, the billet temperature reaches 800-900℃ and is rolled into near-final size using a horizontal and vertical alternating short stress rolling mill. Finally, the finished product is rolled out by a KOCKS rolling mill.

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