A high-quality non-quenched and tempered steel and its preparation method and application

Abstract

The invention discloses a high-quality non-quenched and tempered steel, a preparation method and an application thereof. The high-quality non-quenched and tempered steel comprises the following components in weight percentage: C: 0.20-0.26%, Si: 0.20-0.40%, Mn: 1.80-2.10%, P≤0.015%, S: 0.015-0.045%, Cr: 0.40-0.60%, V: 0.05-0.15%, Nb: 0.02-0.05%, Al: 0.015-0.040%, Ti: 0.015-0.035%, Mg: 0.0015-0.0040%, O: 0.0005-0.0015%, N: 0.014-0.020%, H≤0.0002%, and the balance is Fe and unavoidable impurities. The front axle is manufactured through a process of converter blowing, LF furnace refining, RH vacuum treatment, continuous bloom casting, furnace heating, high-pressure water descaling, cogging, continuous rolling, cooling on a cooling bed, and slitting to length. Made from high-quality, non-quenched and tempered steel, the front axle boasts a yield strength of ≥700 MPa and a yield-to-strength ratio of ≥0.70. Intense shot blasting significantly improves stress distribution at sharp bends, resulting in a fatigue life of over 1.7 million cycles, meeting the performance requirements of various road conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of automobile materials, and in particular relates to high-quality non-quenched and tempered steel and a preparation method and application thereof. Background Art

[0002] As one of the main structures of commercial vehicles, the front axle assembly uses the swing of the steering knuckle to achieve vehicle steering, so it is also called the steering axle and front axle.

[0003] In recent years, with the increasing refinement of commercial vehicle operating scenarios, heavy trucks used for express delivery, coal transportation, industrial and daily necessities transport, etc., have relatively good road conditions and are rarely subjected to sudden, excessive impact loads. This is especially true for the front axle, where the loads are relatively stable, requiring only a yield strength that meets the design stress and safety factor requirements. Under these conditions, the use of bainitic non-quenched and tempered steel for commercial vehicle front axles offers significant advantages over traditional 42CrMo quenched and tempered steel. This significantly reduces production costs, improves processing efficiency, and effectively avoids potential risks such as microcracking associated with the 42CrMo quenched and tempered process.

[0004] As a key component in commercial vehicles, the front axle typically experiences a design stress of 500-600 MPa, requiring a yield strength of at least 700 MPa. Conventional bainitic, non-quenched and tempered steel has a tensile strength of 900-1050 MPa and a yield strength of 500-600 MPa, resulting in a yield-to-strength ratio of only 0.60. This severely restricts its widespread adoption across various tonnages.

[0005] Refining grains and metallographic structures is very effective in improving the yield strength of steel. By systematically optimizing the order and timing of alloy addition and the composition of the final refined slag, a large number of fine and dispersed Al2O3-MgO-TiO2 inclusions are formed in the molten steel, which serve as the nucleation core of intragranular ferrite. This is very necessary for refining the structure and smooth production. At the same time, using Nb+V+Ti composite strengthening instead of simple V strengthening, combined with controlled rolling and controlled cooling and controlled cooling after forging, to increase the number of precipitates such as Nb(C,N) and V(C,N), can not only effectively suppress the grain coarsening problem caused by high-temperature forging, but also significantly improve the yield strength of the steel. Therefore, combined with the current actual production equipment, optimizing the chemical composition, innovating process parameters and control, and developing a production method for high-yield ratio bainitic non-quenched and tempered steel front axles to fully replace quenched and tempered steels such as 42CrMo is imperative. Summary of the Invention

[0006] In response to the problems of low yield ratio and short fatigue life of bainitic non-quenched and tempered steel in the prior art, the present invention provides a high-quality non-quenched and tempered steel and its preparation method and application. By optimizing and adjusting the chemical composition, innovating process parameters and control, the role of fine dispersed Al2O3-MgO-TiO2 inclusions and precipitates such as Nb(C, N) and V(C, N) is fully utilized, so that the yield strength of the front axle is ≥700MPa and the yield strength ratio is ≥0.70, thereby realizing the low-cost production of high-quality non-quenched and tempered steel front axles.

[0007] The present invention is achieved through the following technical solutions:

[0008] A high-quality non-quenched and tempered steel comprises the following components in percentage by weight: C: 0.20-0.26%, Si: 0.20-0.40%, Mn: 1.80-2.10%, P≤0.015%, S: 0.015-0.045%, Cr: 0.40-0.60%, V: 0.05-0.15%, Nb: 0.02-0.05%, Al: 0.015-0.040%, Ti: 0.015-0.035%, Mg: 0.0015-0.0040%, O: 0.0005-0.0015%, N: 0.014-0.020%, H≤0.0002%, and the balance being Fe and unavoidable impurities.

[0009] Furthermore, the composition includes the following components in weight percentage: C: 0.24%, Si: 0.33%, Mn: 1.97%, P: 0.011%, S: 0.029%, Cr: 0.53%, V: 0.09%, Nb: 0.043%, Al: 0.024%, Ti: 0.027%, Mg: 0.0032%, O: 0.0012%, N: 0.0183%, H ≤ 0.00012%, and the balance is Fe and unavoidable impurities.

[0010] The invention discloses a preparation method of the above-mentioned high-quality non-quenched and tempered steel, which includes converter blowing, LF furnace refining, RH vacuum treatment, continuous casting of large square steel billets, heating in a heating furnace, high-pressure water descaling, cogging, continuous rolling, cooling on a cooling bed, cutting to length, and producing round steel.

[0011] Furthermore, the Mg content was adjusted by feeding a Mg-Si wire after LF refining, and the Ti content was adjusted by feeding a Ti wire before RH vacuum treatment. The time interval between feeding the Mg-Si wire and the Ti wire was 10-15 min.

[0012] Furthermore, during LF refining, the top slag is slaged by lime, fluorite, silicon carbide and aluminum particles, while ensuring that the composition of the final refining slag is CaO: 45-55%, SiO2: 15-25%, Al2O3: 15-25%, MgO: 4-8%, TFe+MnO≤1.0%, and the rest are P2O5 and TiO2, with a binary basicity R=CaO / SiO2=2~3.

[0013] Furthermore, the temperature of the blanking is 1120-1160℃, and water cooling is carried out after the blanking. The end temperature of the continuous rolling is 720-800℃, the cooling bed passes quickly, and enters the slow cooling pit for slow cooling. The pit entry temperature is 550-650℃, and the slow cooling time is 24~48h.

[0014] Furthermore, the heating temperature of the heating furnace is 1210-1250°C.

[0015] In the present invention, the application of the above-mentioned high-quality non-quenched and tempered steel in the preparation of automobile front axle materials is characterized in that the preparation process includes: sawing and blanking, induction heating, forging, trimming, correction, controlled cooling, slow cooling, strong shot blasting, machining, and inspection.

[0016] Furthermore, after the round steel is induction heated at 1220-1260℃, it is forged at a fast pace. After the correction is completed, the temperature is 960-1000℃. The front axle blank is controlled cooled and suspended in rapid cooling chambers 1 and 2. The temperature entering rapid cooling chamber 1 is 920-950℃, and the temperature exiting rapid cooling chamber 1 is 720-750℃. The time in rapid cooling chamber 1 is 6-10min. The temperature entering rapid cooling chamber 2 is 680-710℃, and the temperature exiting rapid cooling chamber 2 is 380-460℃. The time in rapid cooling chamber 2 is 3-5min. Finally, stacking cooling is carried out in the slow cooling chamber.

[0017] Furthermore, the surface compressive stress at the large bends on both sides of the front axle before strong shot blasting is ≥600Mpa.

[0018] The beneficial effects achieved by the present invention are:

[0019] (1) The front axle of the present invention, made of high-quality non-quenched and tempered steel, has a yield strength of ≥700 MPa and a yield strength ratio of ≥0.70. The strong shot blasting greatly improves the stress distribution at the large bend, so that the fatigue life of the front axle reaches more than 1.7 million times, which can meet the performance requirements of various road conditions;

[0020] (2) The high-quality non-quenched and tempered steel of the present invention does not require quenching and tempering, and potential risks such as microcracks caused by quenching can be completely avoided;

[0021] (3) The high-quality non-quenched and tempered steel of the present invention optimizes the chemical composition, innovates the process parameters and controls, and gives full play to the role of fine dispersed Al2O3-MgO-TiO2 inclusions and precipitates such as Nb(C, N) and V(C, N). The production and processing efficiency of the front axle is greatly improved, and the low-cost production of high-quality non-quenched and tempered steel front axles is achieved. DETAILED DESCRIPTION

[0022] The present invention will be described in further detail below by way of specific embodiments. In the following embodiments, many details are described in order to enable the present application to be better understood. However, those skilled in the art will readily appreciate that some of the features may be omitted in different situations, or may be replaced by other materials or methods.

[0023] Composition of high-quality non-quenched and tempered steel: C: 0.20-0.26%, Si: 0.20-0.40%, Mn: 1.80-2.10%, P≤0.015%, S: 0.015-0.045%, Cr: 0.40-0.60%, V: 0.05-0.15%, Nb: 0.02-0.05%, Al: 0.015-0.040%, Ti: 0.015-0.035%, Mg: 0.0015-0.0040%, O: 0.0005-0.0015%, N: 0.014-0.020%, H≤0.0002%, the balance is Fe and unavoidable impurities;

[0024] The processing method of high-quality non-quenched and tempered steel front axle is as follows: converter blowing, LF furnace refining, RH vacuum treatment, continuous casting of large square billets, heating in a heating furnace, high-pressure water descaling, billet opening, continuous rolling, cooling on a cooling bed, cutting to length, round steel, sawing and blanking, induction heating, forging, trimming, correction, controlled cooling, slow cooling, high-pressure shot blasting, machining, and inspection.

[0025] Among them, aluminum iron is added at 1 / 3 of the converter tapping process, and the Mg content is adjusted by feeding the Mg-Si wire after the LF refining is completed. The Ti content is adjusted by feeding the Ti wire before the RH vacuum treatment. The time interval between feeding the Mg-Si wire and the Ti wire is 10-15 minutes.

[0026] During LF refining, the top slag is slaged by lime, fluorite, silicon carbide, and aluminum particles, while ensuring that the composition of the refined slag is CaO: 45-55%, SiO2: 15-25%, Al2O3: 15-25%, MgO: 4-8%, TFe+MnO≤1.0%, and the rest is P2O5 and TiO2. The binary basicity R=CaO / SiO2=2-3; the billet opening temperature is 1120-1160℃, and water cooling is carried out after billet opening. The rolling end temperature is 720-800℃. The cooling bed is fast-passed and then enters the slow cooling pit for slow cooling. The pit entry temperature is 550-650℃ and the slow cooling time is ≥24h. The heating temperature of the heating furnace is 1210-1250℃.

[0027] After induction heating of the round steel at 1220-1260℃, it is forged at a fast pace. After calibration, the temperature is 960-1000℃. The front axle blank is cooled in a controlled manner and suspended in rapid cooling chambers 1 and 2. The temperature entering rapid cooling chamber 1 is 920-950℃, and the temperature exiting rapid cooling chamber 1 is 720-750℃. The time in rapid cooling chamber 1 is 6-10 minutes. The temperature entering rapid cooling chamber 2 is 680-710℃, and the temperature exiting rapid cooling chamber 2 is 380-460℃. The time in rapid cooling chamber 2 is 3-5 minutes. Finally, it is stacked and cooled in a slow cooling chamber. The surface compressive stress at the large bend on both sides of the front axle is ≥600Mpa after strong shot blasting.

[0028] The following is described by specific examples:

[0029] (1) The process parameters of converter blowing, LF furnace refining, and RH vacuum treatment in Examples 1 to 6 are shown in Table 1 below:

[0030] Table 1

[0031]

[0032] (2) During LF refining, the top slag is slaged by lime, fluorite, silicon carbide and aluminum particles, and the composition of the final slag is ensured to be CaO: 45-55%, SiO2: 15-25%, Al2O3: 15-25%, MgO: 4-8%, TFe+MnO≤1.0%, and the rest is P2O5, TiO2, etc. At the same time, the binary basicity R=CaO / SiO2=2~3; the composition of the final slag of LF refining of Examples 1~6 is shown in Table 2 below:

[0033] Table 2

[0034]

[0035] (3) The heating temperature of the heating furnace is 1210-1250°C, the temperature of the blanking is 1120-1160°C, and water cooling is performed after the blanking. The rolling end temperature is 720-800°C, the cooling bed is fast, and the product enters the slow cooling pit for slow cooling. The pit entry temperature is 550-650°C, and the slow cooling time is ≥24h. The parameters of the heating furnace heating, blanking and continuous rolling processes of Examples 1 to 6 are shown in Table 3 below:

[0036] Table 3

[0037]

[0038] (4) After the round steel is induction heated at 1220-1260°C, it is forged at a fast pace to ensure that the temperature is 960-1000°C after the correction is completed. Then the front axle blank is controlled to cool and suspended in the rapid cooling chamber 1 and chamber 2. The temperature entering the rapid cooling chamber 1 is 920-950°C, the temperature exiting the rapid cooling chamber 1 is 720-750°C, and the time in the rapid cooling chamber 1 is 6-10 minutes. The temperature entering the rapid cooling chamber 2 is 680-710°C, the temperature exiting the rapid cooling chamber 2 is 380-460°C, and the time in the rapid cooling chamber 2 is 3-5 minutes. Finally, stack cooling is carried out in the slow cooling chamber. The temperature parameters and time of the cooling process of the front axle blanks of Examples 1 to 6 are shown in Table 4 below. The chemical composition of the high-quality non-quenched and tempered steel of Examples 1 to 6 is shown in Table 5 below:

[0039] Table 4

[0040]

[0041] Table 5

[0042]

[0043] (5) The mechanical properties and fatigue life of the automobile front axles prepared using high-quality non-quenched and tempered steel as raw materials in Examples 1 to 6 are shown in Table 6 below:

[0044] Table 6

[0045]

[0046] As can be seen from Table 6, the yield strength of non-quenched and tempered steel front axles is all ≥700 MPa, the yield strength ratio is ≥0.70, and the fatigue life is all ≥1.7 million times, which can meet the performance requirements of commercial vehicle front axles under various road conditions.

Claims

1. A high-quality non-quenched and tempered steel, characterized in that: The invention comprises the following components in weight percentage: C: 0.20-0.26%, Si: 0.20-0.40%, Mn: 1.80-2.10%, P≤0.015%, S: 0.015-0.045%, Cr: 0.40-0.60%, V: 0.05-0.15%, Nb: 0.02-0.05%, Al: 0.015-0.040%, Ti: 0.015-0.035%, Mg: 0.0015-0.0040%, O: 0.0005-0.0015%, N: 0.014-0.020%, H≤0.0002%, and the balance is Fe and unavoidable impurities; The preparation method of the high-quality non-quenched and tempered steel comprises: converter blowing, LF furnace refining, RH vacuum treatment, continuous casting of large square steel sheets, heating in a heating furnace, high-pressure water descaling, cogging, continuous rolling, cooling on a cooling bed, cutting to length, and producing round steel. The aluminum and iron are added at 1 / 3 of the converter tapping process, the Mg content is adjusted by feeding a Mg-Si wire after the LF refining is completed, and the Ti content is adjusted by feeding a Ti wire before the RH vacuum treatment, and the time interval between feeding the Mg-Si wire and the Ti wire is 10 to 15 minutes. During LF refining, the top slag is slaged by lime, fluorite, silicon carbide and aluminum particles, while ensuring that the composition of the final slag is CaO: 45-55%, SiO2: 15-25%, Al2O3: 15-25%, MgO: 4-8%, TFe+MnO≤1.0%, and the rest is P2O5, TiO2, and the binary basicity R=CaO / SiO2=2~3; The temperature of the blank is 1120-1160℃. After the blank is opened, it is water-cooled. The end temperature of continuous rolling is 720-800℃. The cooling bed passes quickly and enters the slow cooling pit for slow cooling. The pit entry temperature is 550-650℃ and the slow cooling time is 24~48h.

2. The high-quality non-quenched and tempered steel according to claim 1, characterized in that: The material includes the following components in weight percentage: C: 0.24%, Si: 0.33%, Mn: 1.97%, P: 0.011%, S: 0.029%, Cr: 0.53%, V: 0.09%, Nb: 0.043%, Al: 0.024%, Ti: 0.027%, Mg: 0.0032%, O: 0.0012%, N: 0.0183%, H≤0.00012%, and the balance is Fe and unavoidable impurities.

3. The high-quality non-quenched and tempered steel according to claim 1, characterized in that: The heating temperature of the heating furnace is 1210-1250°C.

4. Use of the high-quality non-quenched and tempered steel according to claim 1 or 2 in the preparation of automobile front axle materials, characterized in that: The preparation process includes: sawing, induction heating, forging, trimming, correction, controlled cooling, slow cooling, strong shot blasting, machining and inspection.

5. The use according to claim 4, characterized in that After the round steel is induction heated at 1220-1260℃, it is forged at a fast pace. After the correction is completed, the temperature is 960-1000℃. The controlled cooling of the front axle blank is carried out in the rapid cooling chamber 1 and the suspension chamber 2. The temperature entering the rapid cooling chamber 1 is 920-950℃, and the temperature exiting the rapid cooling chamber 1 is 720-750℃. The time in the rapid cooling chamber 1 is 6-10min. The temperature entering the rapid cooling chamber 2 is 680-710℃, and the temperature exiting the rapid cooling chamber 2 is 380-460℃. The time in the rapid cooling chamber 2 is 3-5min. Finally, it is stacked and cooled in the slow cooling chamber.

6. The use according to claim 4, characterized in that The surface compressive stress at the large bends on both sides of the front axle of the strong shot blasting is ≥600Mpa.

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