Steel, its preparation method and application in the preparation of crash boxes

Abstract

The present invention belongs to the technical field of steel smelting, and specifically relates to a steel, a preparation method thereof, and an application in the preparation of a crash box. The steel provided by the present invention is used to prepare a crash box and comprises, by weight percentage, the following: C: 0.16% to 0.20%, Si: 0.20% to 0.40%, Mn: 1.30% to 1.50%, P ≤ 0.015%, S: ≤ 0.010%, Cr: 0.10% to 0.20%, V: 0.03% to 0.05%, and the remainder being Fe and unavoidable impurities. The present invention optimizes the composition design of the steel billet to ensure that it has high strength and sufficient toughness, meeting the goal of direct use by users.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to steel and a preparation method thereof and application in the preparation of a crash box. Background Art

[0002] With the continuous advancement and development of rail transit technology, rolling stock collision safety has become a crucial component of locomotive design. To improve collision safety, a key approach is to install anti-collision elements within the vehicle's buffer system. The function of a rolling stock crash box is to absorb energy by deforming during a collision, thereby reducing the impact and protecting the vehicle during abnormal operation. Crash performance is primarily determined by the crash box's material and structure.

[0003] Based on the specific uses of railway locomotive crash boxes, rolling stock manufacturers have established performance requirements for the raw steel billets: The steel must have a narrow strength range, with a yield strength of 360-420 MPa, a tensile strength of 500 MPa or higher, an elongation of 25% or higher, and a -40°C impact toughness of 40 J or higher. This ensures that the steel does not generate fragments during a vehicle collision and maintains good impact toughness at -40°C. The billets are directly machined, requiring excellent core and surface quality. Summary of the Invention

[0004] The purpose of the present invention is to address the defects of the prior art and provide a steel and a preparation method thereof and an application in the preparation of a crash box.

[0005] Specifically, the steel provided by the present invention comprises, by weight percentage, the following: C: 0.16% to 0.20%, Si: 0.20% to 0.40%, Mn: 1.30% to 1.50%, P≤0.015%, S: ≤0.010%, Cr: 0.10% to 0.20%, V: 0.03% to 0.05%, and the remainder being Fe and unavoidable impurities.

[0006] The above-mentioned steel comprises, by weight percentage: C: 0.16% to 0.19%, Si: 0.25% to 0.35%, Mn: 1.35% to 1.45%, P: ≤0.010%, S: ≤0.005%, Cr: 0.18% to 0.28%, V: 0.035% to 0.045%, and the rest is Fe and unavoidable impurities.

[0007] On the other hand, the present invention also provides a method for preparing the above steel, comprising:

[0008] (1) Adding molten iron and scrap steel into an electric furnace to smelt crude molten steel;

[0009] (2) Pour the crude molten steel into a ladle for LF+VD refining;

[0010] (3) After the molten steel composition is qualified, the steel billet is obtained through mold casting, ingot heating and rolling.

[0011] In the above preparation method, the crude molten steel comprises, by weight percentage: C 0.05-0.10%, Si≤0.10%, Mn≤0.10%, P≤0.020%, and S≤0.035%.

[0012] In the above preparation method, when the crude steel is tapped, 3.5-4.0 kg of aluminum shot per ton of steel, 7.5-8.0 kg of silicon-manganese alloy per ton of steel, 6.2-6.7 kg of low-manganese alloy per ton of steel, 7-7.5 kg of lime per ton of steel, and 2.5-3.0 kg of synthetic slag per ton of steel are added along with the steel flow, calculated by weight percentage.

[0013] In the above preparation method, during LF furnace refining, the basicity control target R (CaO / SiO2) is 1.4-1.8, the bottom blowing argon flow rate is 800-1600 liters / minute, stirring reduction is carried out, the composition is fine-tuned, and 0.75-0.85 kg / ton of steel of ferrovanadium is added.

[0014] In the above preparation method, when the LF furnace is refined and steel is tapped, the molten steel includes: C≤0.16~0.19%, Si: 0.20~0.40%, Mn: 1.30~1.50%, P≤0.015%, S: ≤0.010%, Cr: 0.20%~0.30%, V: 0.03%~0.05%, and the rest is Fe and unavoidable impurities.

[0015] In the above preparation method, during VD refining, the high vacuum degree is maintained for 15 to 20 minutes, [H] is set online to ≤ 1.5 ppm, 2.0 to 2.5 kg of calcium wire is fed per ton of steel, and the soft stirring time is 15 to 20 minutes.

[0016] In the above preparation method, the temperature of the steel ingot is heated to 1270-1290°C, and the holding time is 210-270 minutes; the rolling is performed by two passes with a maximum reduction of 90-100 mm on the vertical surface of the steel ingot.

[0017] In another aspect, the present invention further provides use of the above steel in preparing a crash box.

[0018] The technical solution of the present invention has the following beneficial effects:

[0019] (1) The steel billet for the crash box of the present invention can be used by users to produce railway locomotive crash boxes after heat treatment and machining. The various performances meet the use requirements and can be used on high-power railway locomotives such as the "Fuxing" and "Harmony" locomotives, which is of great significance.

[0020] (2) The present invention optimizes the composition of the steel billet for the crash box to ensure that it has high strength and sufficient toughness;

[0021] (3) The steel billet prepared according to the method of the present invention has the advantages of low cost and high quality, which can be directly used by users. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Various other advantages and benefits will become apparent to those skilled in the art by reading the following detailed description of the preferred embodiment.The accompanying drawings are only for the purpose of illustrating the preferred embodiment and are not to be considered as limiting the present invention.

[0023] Figure 1 This is the metallographic structure of the steel billet after normalizing of the present invention. DETAILED DESCRIPTION

[0024] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0025] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are understood to include any and all subranges subsumed therein.

[0026] The technical solution of the present invention is to design a steel for railway locomotive crash boxes. By optimizing the design of conventional components and their contents such as carbon, silicon, manganese, phosphorus, sulfur, hydrogen, oxygen, and adding a small amount of elements such as chromium and vanadium, the strength and low-temperature impact performance of the steel billet are effectively improved by virtue of the synergistic effect between specific elements in specific contents, thereby well meeting the processing requirements of the crash box.

[0027] Specifically, the steel for a railway locomotive crash box of the present invention comprises, by weight percentage, the following: C: 0.16-0.20%, Si: 0.20-0.40%, Mn: 1.30-1.50%, P≤0.015%, S: ≤0.010%, Cr: 0.10%-0.20%, V: 0.03%-0.05%, and the remainder being Fe and unavoidable impurities.

[0028] The main component design ideas and control ranges of the present invention are:

[0029] Carbon: This material is designed with low carbon steel based on performance requirements and cost considerations, and achieves good strength and toughness through normalizing heat treatment. Therefore, the material of the present invention requires that the carbon content in the steel be controlled at 0.16% to 0.20%, preferably 0.16% to 0.19%.

[0030] Silicon: Silicon is a ferrite-forming element, and is essential for achieving good deoxidation of molten steel and controlling the type of inclusions. In order to achieve good deoxidation of molten steel, the silicon content in the steel is controlled at 0.20% to 0.40%, preferably 0.25% to 0.35%.

[0031] Manganese: Manganese is added to steel primarily to form MnS compounds with sulfur, which prevent hot brittleness, improve the steel's forgeability, and refine the pearlite structure. The manganese content in the material of the present invention is controlled to be between 1.30% and 1.50%, preferably between 1.35% and 1.45%.

[0032] Chromium: The addition of trace amounts of chromium to steel primarily increases the strength and hardness of the steel, and also improves its corrosion resistance. The chromium content in the material of the present invention is controlled within a range of 0.20% to 0.30%, preferably 0.18% to 0.28%.

[0033] Vanadium: Trace amounts of vanadium are added to steel primarily to refine grains, improve strength and yield ratio after normalizing, and enhance low-temperature properties. However, excessive addition should be limited, as this can increase the steel's core deformation resistance and lead to severe core porosity. In the material of this invention, the vanadium content is controlled between 0.03% and 0.05%, preferably between 0.035% and 0.045%.

[0034] Phosphorus and sulfur: Phosphorus and sulfur are generally impurity elements in steel. The lower their levels, the better. However, they are elements that cannot be completely removed during the production process. In the material of the present invention, the phosphorus content is controlled to ≤0.015%, and the sulfur content is controlled to ≤0.010%. Preferably, the phosphorus content is controlled to ≤0.010%, and the sulfur content is controlled to ≤0.005%.

[0035] On the other hand, the present invention also provides a method for preparing the above steel, comprising:

[0036] (1) Rough refining

[0037] Molten iron and scrap steel are added into an electric furnace to smelt crude molten steel, the chemical composition of the molten steel (by weight percentage) being: C 0.05-0.10%, Si≤0.10%, Mn≤0.10%, P≤0.020%, and S≤0.035%.

[0038] When tapping, 3.5-4.0 kg of aluminum shot per ton of steel, 7.5-8.0 kg of silicon manganese alloy per ton of steel, 6.2-6.7 kg of low manganese alloy per ton of steel, 7-7.5 kg of lime per ton of steel, and 2.5-3.0 kg of synthetic slag per ton of steel are added along with the steel flow.

[0039] (2) LF refining

[0040] The crude molten steel is poured into the LF ladle refining furnace for refining.

[0041] In the ladle refining furnace, the slag is adjusted to high basicity, with a target slag basicity ratio (CaO / SiO2) of 1.4-1.8. A bottom-blown argon flow rate of 800-1600 liters / minute is used for stirring and reduction. The composition is then fine-tuned by adding 0.75-0.85 kg / ton of ferrovanadium. Once the chemical composition meets the following requirements, the steel is tapped.

[0042] The chemical composition of the refined steel liquid (by weight percentage) is: C≤0.16~0.19%, Si: 0.20~0.40%, Mn: 1.30~1.50%, P≤0.015%, S: ≤0.010%, Cr: 0.20%~0.30%, V: 0.03%~0.05%, and the rest is Fe and unavoidable impurities.

[0043] Through LF refining, S≤0.005% and free oxygen≤0.0005% in steel are achieved, and the remaining components hit the target.

[0044] (3) VD refining

[0045] The holding time under VD high vacuum is 15 to 20 minutes, and the online setting [H] is ≤ 1.5ppm. The calcium feed line is 2.0 to 2.5 kg / ton of steel, and the soft stirring time is 15 to 20 minutes.

[0046] Through VD refining, [H] in steel is ≤ 0.00015% and the steel is pure.

[0047] (4) Die Casting

[0048] During the casting process, argon gas is used to protect the pouring, and the pouring temperature and pouring speed are controlled at the same time.

[0049] Taking 8.4t ingot as an example, the pouring temperature is 1560-1570℃, the pouring time for the first batch of ingot body is 15-17 minutes, the pouring time for the cap is 9-11 minutes, the pouring time for the second batch of ingot body is 13-15 minutes, and the pouring time for the cap is ≥6.5 minutes.

[0050] The die casting solidifies under slow cooling conditions, and the center shrinkage and porosity level are low; the 8.4t steel ingot has a large cross-section and a large molding compression ratio, which can well ensure the dense internal structure and high flaw detection pass rate.

[0051] (5) Heating of steel ingots

[0052] The steel temperature of the heating furnace is: 1270~1290℃, and the holding time is 210~270 minutes.

[0053] The heating temperature can achieve smooth rolling and the implementation of large reduction passes, and the holding time is to ensure that the temperature of the surface and core of the ingot is consistent.

[0054] (5) Rolling mill

[0055] After leaving the heating furnace, the steel ingot is rolled into finished square billets on the rolling mill.

[0056] Taking 8.4t ingot as an example, the rolling process must ensure a maximum reduction of 90 to 100mm on the vertical surface of the ingot in two passes, and the cross-sectional specification of the finished billet is 260mm×260mm.

[0057] In another aspect, the present invention further provides a use of the above steel in preparing a crash box.

[0058] The metallographic structure obtained after normalizing the steel billet of the present invention is as follows Figure 1 The normalizing process can be carried out in a conventional manner, and the present invention does not impose any specific limitation thereto.

[0059] Preferably, the crash box is a railway locomotive crash box.

[0060] In practice, the stainless steel billet prepared according to the method of the present invention has the advantages of high strength, good toughness and low cost, and meets the strength and low-temperature impact performance requirements of the production and use of railway locomotive crash boxes.

[0061] Example

[0062] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. In the following examples, the experimental methods without specific conditions are based on conventional methods and conditions.

[0063] Example 1

[0064] (1) Rough refining

[0065] 72.3 tons of molten iron and 13.5 tons of scrap steel were added to an electric furnace, oxygen was blown, and phosphorus was removed by oxidation to smelt crude molten steel. The chemical composition of the molten steel (by weight percentage) was: C 0.07%, Si 0.03%, Mn 0.08%, P 0.008%, S≤0.023%, and the rest was Fe and unavoidable impurities.

[0066] When the steel is tapped, 304kg of aluminum shot, 608kg of silicon manganese alloy, 514kg of low manganese alloy, 580kg of lime and 210kg of synthetic slag are added along with the steel flow.

[0067] (2) LF refining

[0068] The crude molten steel is poured into the LF ladle refining furnace for refining.

[0069] In the ladle refining furnace, the slag was adjusted to a high basicity slag with a basicity of 1.52, and the bottom-blown argon flow rate was 1100 liters / minute for stirring and reduction. The composition was then fine-tuned, and 300 kg of ferromanganese and 62 kg of ferrovanadium were added.

[0070] The chemical composition of the refined steel liquid (by weight percentage) is: C: 0.17%, Si: 0.28%, Mn: 1.47%, P: 0.009%, S: 0.001%, Cr: 0.22%, V: 0.05%, and the rest is Fe and unavoidable impurities.

[0071] (3) VD refining

[0072] Evacuate to a maximum vacuum of 50 Pa, maintain high vacuum for 16 minutes, break the air, and set the [H] level online to 0.5 ppm. Feed the calcium wire at 2.5 kg / ton of steel, stir softly with argon for 20 minutes, and add a covering agent to tap the steel.

[0073] (4) Mold casting

[0074] The casting ingot is 8.4t steel ingot, argon protection casting is used, and the molten steel temperature is: 1562℃.

[0075] Casting speed: the first batch of 5 ingots: 15 minutes 55 seconds for the ingot body and 9 minutes 20 seconds for the cap; the second batch of 4 ingots: 13 minutes 52 seconds for the ingot body and 7 minutes 15 seconds for the cap.

[0076] (5) Ingot heating

[0077] The steel temperature of the heating furnace is: 1280℃, and the holding time is 240 minutes.

[0078] (6) Rolling mill

[0079] After leaving the heating furnace, the steel ingot is rolled into finished square billets on the rolling mill. The two vertical surfaces of the middle pass of the steel ingot adopt a large reduction of 95mm and 100mm respectively. The cross-sectional specification of the finished square billet is 260mm×260mm.

[0080] Example 2

[0081] (1) Rough refining

[0082] 72.6 tons of molten iron and 13.1 tons of scrap steel were added to an electric furnace, oxygen was blown, oxidized and dephosphorized, and smelted into crude molten steel. The chemical composition (weight percentage) of the molten steel was: C 0.06%, Si 0.03%, Mn 0.06%, P 0.004%, S≤0.026%.

[0083] The rest is Fe and inevitable impurities.

[0084] When the steel is tapped, 300 kg of aluminum shot, 608 kg of silicon manganese alloy, 521 kg of low manganese alloy, 590 kg of lime and 205 kg of synthetic slag are added along with the steel flow.

[0085] (2) LF refining

[0086] The crude molten steel is poured into the LF ladle refining furnace for refining.

[0087] In the ladle refining furnace, the slag was adjusted to a high basicity slag with a basicity of 1.57, and the bottom-blown argon flow rate was 1100 liters / minute for stirring and reduction. The composition was then fine-tuned, and 320 kg of ferromanganese and 62 kg of ferrovanadium were added.

[0088] The chemical composition of the refined steel liquid (by weight percentage) is: C: 0.16%, Si: 0.29%, Mn: 1.49%, P: 0.006%, S: 0.001%, Cr: 0.25%, V: 0.05%, and the rest is Fe and unavoidable impurities.

[0089] (3) VD refining

[0090] Evacuate to a maximum vacuum of 48 Pa, maintain high vacuum for 15 minutes, break the air, and set the [H] level online to 0.5 ppm. Feed the calcium wire at 2.5 kg / ton of steel, stir softly with argon for 16 minutes, and add a covering agent to tap the steel.

[0091] (4) Mold casting

[0092] The casting ingot is 8.4t steel ingot, argon protection casting is used, and the molten steel temperature is: 1566℃.

[0093] Casting speed: the first batch of 5 ingots: 16 minutes and 5 seconds for the ingot body and 9 minutes and 25 seconds for the cap; the second batch of 4 ingots: 13 minutes and 43 seconds for the ingot body and 7 minutes and 20 seconds for the cap.

[0094] (5) Ingot heating

[0095] The steel temperature of the heating furnace is: 1280℃, and the holding time is 240 minutes.

[0096] (6) Rolling mill

[0097] After leaving the heating furnace, the steel ingot is rolled into finished square billets on the rolling mill. The two vertical surfaces of the middle pass of the steel ingot adopt a large reduction of 95mm and 100mm respectively. The cross-sectional specification of the finished square billet is 260mm×260mm.

[0098] Performance Testing

[0099] The steel billets prepared in Examples 1 and 2 were tested, wherein the testing method can be carried out according to a conventional method. The test results are shown in Table 1.

[0100] Table 1 Performance of steel billets for railway locomotive crash boxes prepared in Example 1-2

[0101]

[0102] It can be seen from Table 1 that the steel billet prepared in the present invention meets the strength and low-temperature impact performance requirements for the production and use of railway locomotive crash boxes.

[0103] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art will appreciate that these embodiments are intended only to illustrate the present invention and are not to be construed as limiting the scope of the present invention. It should be noted that any equivalent variations and substitutions to these embodiments are to be considered encompassed within the scope of the claims of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope defined in the claims.

Claims

1. A steel for a crash box, characterized in that: Calculated by weight percentage, it includes: C: 0.16% to 0.20%, Si: 0.25% to 0.35%, Mn: 1.30% to 1.50%, P≤0.015%, S: ≤0.010%, Cr: 0.2% to 0.3%, V: 0.035% to 0.045%, and the rest is Fe and unavoidable impurities; The steel preparation method comprises: (1) adding molten iron and scrap steel into an electric furnace to smelt crude molten steel; (2) pouring the crude molten steel into a ladle for LF+VD refining; (3) after the molten steel composition is qualified, the molten steel is mold-casted, the steel ingot is heated to 1270-1290°C, and the temperature is kept at this temperature for 210-270 minutes, and then the steel ingot is vertically rolled twice with a large reduction of 90-100 mm to obtain a steel billet; The steel billet has an impact absorption energy KV2 of ≥69 J at -40°C and a yield strength ReH of 383-420 MPa.

2. The steel according to claim 1, characterized in that Calculated by weight percentage, it includes: C: 0.16%~0.19%, Si: 0.25%~0.35%, Mn: 1.35%~1.45%, P: ≤0.010%, S: ≤0.005%, Cr: 0.2%~0.3%, V: 0.035%~0.045%, and the rest is Fe and unavoidable impurities.

3. The method for preparing steel according to any one of claims 1 to 2, characterized in that: include: (1) Add molten iron and scrap steel into an electric furnace to smelt crude steel; (2) Pour the crude molten steel into the ladle for LF+VD refining; (3) After the molten steel composition is qualified, the steel billet is obtained through mold casting, ingot heating and rolling.

4. The preparation method according to claim 3, wherein Calculated by weight percentage, the crude molten steel comprises: C 0.05-0.10%, Si≤0.10%, Mn≤0.10%, P≤0.020%, and S≤0.035%.

5. The preparation method according to claim 3, characterized in that By weight percentage, when the crude steel is tapped, 3.5-4.0 kg of aluminum shot per ton of steel, 7.5-8.0 kg of silicon-manganese alloy per ton of steel, 6.2-6.7 kg of low-manganese alloy per ton of steel, 7-7.5 kg of lime per ton of steel, and 2.5-3.0 kg of synthetic slag per ton of steel are added along with the steel flow.

6. The preparation method according to claim 3, characterized in that During LF furnace refining, the basicity control target R (CaO / SiO2) is 1.4~1.8, the bottom blowing argon flow rate is 800~1600 liters / minute for stirring reduction, the composition is fine-tuned, and 0.75~0.85kg / ton of vanadium iron is added.

7. The preparation method according to claim 3, wherein During VD refining, the high vacuum is maintained for 15 to 20 minutes, [H] is set online to ≤1.5ppm, the calcium wire is fed 2.0 to 2.5 kg / ton of steel, and the soft stirring time is 15 to 20 minutes.

8. Use of the steel according to any one of claims 1 to 2 or the steel obtained by the preparation method according to any one of claims 3 to 7 in the preparation of a crash box.

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