Ti microalloyed weldable low cost bainitic non-quenched and tempered steel, manufacturing process and application thereof

Abstract

The application provides a Ti micro-alloying easy-to-weld low-cost bainite non-quenched and tempered steel and a manufacturing process and application thereof, the composition of the steel is as follows: C 0.05-0.12%, Si 0.80-1.50%, Mn 2.00-2.50%, Cr 0.20-0.40%, Al 0.030-0.050%, P ≤0.008%, S 0.010-0.030%, Ti 0.035-0.10%, T.O 8-12ppm, [N] 30-60ppm, and the rest is Fe and inevitable impurity elements; 30xC+10xSi+30xMn+15xS+20xCr+10xAl+40xTi+30xV+35xT.O ≤500, and Ceq ≤0.60; the application does not need air cooling treatment in the forging process through suitable element proportioning, the consistency of the performance of the part and the process window are improved, and the product has excellent performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of non-tempered steel, and particularly relates to a Ti micro-alloyed low-cost bainite non-tempered steel and a manufacturing process and application thereof, and is suitable for manufacturing high-quality automobile parts. BACKGROUND

[0002] Non-tempered steel has become the focus of green manufacturing due to its characteristics of canceling the tempering treatment and reducing carbon emissions. According to statistics, about 0.19 KWh of electricity is consumed and about 0.1976 kg of CO2 is emitted for every kilogram of tempered steel for tempering treatment. Taking a truck as an example, the steel consumption of each truck is about 10 tons, and the CO2 emission can be reduced by 1.98 tons for each truck, accounting for about 60% of the carbon emission in the vehicle manufacturing process. At the same time, the tempering process produces serious pollution problems such as oil pollution and water pollution, and the quenching deformation, oxidation decarburization and other problems in the quenching process of parts also lead to low yield of finished parts, which results in low production cost of tempered steel parts and great environmental pressure. Therefore, using non-tempered steel to replace tempered steel to manufacture automobile parts is one of the key materials for future automobile part manufacturing, and is also conducive to improving the comprehensive competitiveness of enterprises.

[0003] Traditional non-tempered steel is ferrite-pearlite type non-tempered steel, which obtains high mechanical properties by adding a large amount of micro-alloying elements (Nb, V), but its tensile strength is about 900 MPa. The high content of alloying elements in the martensitic non-tempered steel and the narrow process window lead to poor matching in large-scale process production, which is difficult to mass produce and apply. The bainite type non-tempered steel has become the focus of future automobile and engineering machinery parts due to its good strength and toughness and low alloy cost.

[0004] Traditional bainite non-tempered steel is usually strengthened by micro-alloying elements such as Nb, Ti and V to improve its strength and toughness. Chinese patent CN111118403A discloses a Ti micro-alloyed high strength and toughness bainite non-tempered steel, which has a tensile strength of ≥1000 MPa, a yield strength of ≥700 MPa, an elongation after fracture of ≥18%, and a room temperature impact energy KU2 of ≥65 J.

[0005] In addition, the controlled forging and controlled cooling process is another important factor that determines the performance of the non-quenched and tempered steel. The traditional bainite non-quenched and tempered steel adopts rapid cooling after forging to control the material organization and performance. The patent with the publication number CN111118403A disclosed on May 8, 2020 discloses a Ti micro-alloyed high strength and toughness bainite non-quenched and tempered steel and its controlled forging and controlled cooling process and production process, which adopts strong air cooling treatment after forging, and the cooling rate is 0.8℃ / s~2.4℃ / s. The patent with the publication number CN103952626A disclosed on July 30, 2014 discloses a method for regulating and controlling the performance of bainite non-quenched fastener steel, which mainly controls the strength through large deformation and controlled cooling after forging, and the steel involved in the patent is mainly applied to cold heading steel wire products, which cannot meet the performance requirements of hot rolled round steel for automobile forgings. In the production process of the part, due to the limitation of the complexity of the part structure and the gas flow, the strong wind treatment cannot guarantee the consistency of the part performance and the stability of the batch production.

[0006] At the same time, due to the complex structure of the automobile forging part, it is difficult to be formed by one-time forging, and often needs to be connected by welding. However, there is no report on the welding performance of bainite non-quenched steel, which affects the popularization and application of non-quenched steel. The traditional bainite non-quenched steel mainly faces three difficulties: first, it is difficult to balance the alloy cost and performance, and the higher micro-alloying element leads to little difference between the cost and the cost of quenched steel; second, the part performance consistency is poor, the forging process window is narrow, and the cooling condition after forging is harsh, which leads to large fluctuation of part performance after batch production of parts; third, there is no report on bainite non-quenched steel with good welding performance. SUMMARY

[0007] The purpose of the present application is to provide a Ti micro-alloyed easy-to-weld low-cost bainite non-quenched steel and its manufacturing process. Based on the Si-Mn-Cr alloy system, the present application inhibits the formation of bainite through the comprehensive action of Si and Ti elements, increases the bainite content, and at the same time realizes the refinement of M / A island, realizes the refinement of material organization and the improvement of toughness. In addition, by introducing an appropriate amount of Ti2O3 particles as the nucleation core of soft phase (retained austenite, ferrite), the toughness of the material is improved. In addition, by suitable element ratio, the material does not need special air cooling treatment during forging, which greatly improves the consistency of part performance and process window, and speeds up the market promotion of non-quenched steel. The final product has a tensile strength of 900MPa~1000MPa, a yield strength of 650~760MPa, an elongation after fracture of ≥17%, a reduction of area of ≥45%, a yield ratio of ≥0.76, a room temperature impact energy (KU2) of ≥60J, a rotary bending fatigue strength of ≥430MPa, and a Ceq of ≤0.60%.

[0008] Another objective of this invention is to provide an application of Ti microalloyed easy-to-weld, low-cost bainitic non-quenched and tempered steel for automobile manufacturing.

[0009] Specific technical solution of the present invention:

[0010] A Ti microalloyed, weldable, low-cost bainitic non-quenched and tempered steel comprises the following components by weight percentage:

[0011] C: 0.05-0.12%, Si: 0.80-1.50%, Mn: 2.00-2.50%, Cr: 0.20-0.40%, Al: 0.030-0.050%, P: ≤0.008%, S: 0.010-0.030%, Ti: 0.035-0.10%, TO: 8-12ppm, [N]: 30-60ppm, with the remainder being Fe and unavoidable impurity elements.

[0012] The composition of the Ti microalloyed easy-to-weld, low-cost bainitic non-quenched and tempered steel satisfies the following formula: X = 30 × C + 10 × Si + 30 × Mn + 15 × S + 20 × Cr + 10 × Al + 40 × Ti + 30 × V + 35 × TO, X ≤ 500. Where C, Si, Mn, S, Cr, Al, Ti, and V are in wt%, and TO is in ppm.

[0013] The composition of the Ti microalloyed easy-to-weld low-cost bainitic non-quenched and tempered steel satisfies the following formula: Ceq=C+Si / 24+Mn / 6+Cr / 5+V / 14, Ceq≤0.60%, where C, Si, Mn, Cr, and V are in wt%. For welded parts, the Ceq parameter also needs to be controlled.

[0014] The composition of the Ti microalloyed easy-to-weld, low-cost bainitic non-quenched and tempered steel satisfies Ceq≤0.60%.

[0015] The microstructure of the Ti microalloyed easy-to-weld, low-cost bainitic non-quenched and tempered steel is bainite + M / A islands, with a bainite area ratio content ≥90% and an M / A island size ≤25μm.

[0016] The Ti microalloyed easy-to-weld, low-cost bainitic non-quenched and tempered steel has a tensile strength of 900-1000 MPa, a yield strength of 650-760 MPa, an elongation after fracture ≥17%, a reduction of area ≥45%, a yield strength ratio ≥0.76, a room temperature impact energy (KU2) ≥60 J, and a bending fatigue strength ≥430 MPa.

[0017] The present invention provides a manufacturing process for a Ti microalloyed easy-to-weld, low-cost bainitic non-quenched and tempered steel, comprising the following process flow: smelting - refining - RH vacuum treatment - continuous casting of round billets / square billets - rolling - forging - air cooling.

[0018] The smelting process employs an electric furnace / converter to reduce the phosphorus content in the steel to ≤0.05%.

[0019] The RH vacuum treatment utilizes precise control of the blowing volume during the RH vacuum degassing process to adjust the oxygen content to the target value. By controlling the oxygen content during vacuum degassing, the strength and toughness of the gear steel are improved.

[0020] The rolling process involves heating the round steel at a temperature ≥1230℃ for a heating time ≥300min; starting rolling at a temperature ≥1180℃; finishing rolling at a temperature 600~900℃; and then using an insulation cover or slow cooling pit for slow cooling after rolling.

[0021] The forging process is carried out at a forging heating temperature of 1180–1250°C, an initial forging temperature of 1100–1200°C, and a final forging temperature of 900–1000°C.

[0022] The air cooling process involves air cooling the forging process to below 400°C, followed by stack cooling to room temperature.

[0023] This invention provides an application of Ti microalloyed easy-to-weld, low-cost bainitic non-quenched and tempered steel for automobile manufacturing.

[0024] The design concept of this invention is as follows:

[0025] Carbon (C): Carbon is the most basic element in steel, essential for achieving high strength and hardness. While a high C content is beneficial for increasing steel strength (therefore, the C content should be ≥0.05%), a high carbon content also leads to decreased toughness and increases the likelihood of a decarburized layer, resulting in a lower strength-to-yield ratio and reduced fatigue performance. This is especially problematic for weldable materials, as a high carbon content reduces weldability and hinders their application. Therefore, a C content ≤0.12% is recommended, thus establishing a C content range of 0.05–0.12%.

[0026] Si (Si): Si is a strong oxidizing element in steel, which can increase the activity of carbon (C) and effectively inhibit the coarsening of carbides in steel, thus improving the yield strength and yield strength ratio. Furthermore, Si can improve the hardenability of steel and lower the bainitic transformation initiation temperature, thereby increasing the forging process window of parts and improving the consistency of part performance. Therefore, the Si content should be ≥0.80%; however, a higher Si content can easily lower the bainitic transformation termination temperature of steel, deteriorating the impact energy and toughness. Therefore, the Si content should be ≤1.50%. Thus, the Si content range is determined to be 0.80–1.50%.

[0027] Mn: Mn is a bainite-forming element, which can expand the bainite transformation region. Mn is also an austenite-forming element, which is beneficial for improving the strength and toughness of steel. Therefore, the Mn content is ≥2.00%. However, Mn is a segregating element, and higher Mn content can easily lead to the formation of coarse, blocky austenite in the steel. This not only hinders the consistency of part performance but also reduces the yield strength ratio and worsens the fatigue performance of the steel. Therefore, the Mn content is ≤2.50%. Thus, the Mn content range is determined to be 2.00–2.50%.

[0028] Cr: Cr can improve the hardenability and strength of steel and introduce an appropriate amount of ferrite, thereby improving the toughness of the material. In addition, Cr combines with carbon in steel to form fine carbides, which improves the yield strength ratio and fatigue performance of the material. Therefore, the Cr content is ≥0.20%. However, higher Cr content tends to increase the decarburization tendency of the steel surface, which is not conducive to obtaining high fatigue strength. Therefore, the Cr content is ≤0.40%. Thus, the Cr content range is determined to be 0.20~0.40%.

[0029] Ti readily combines with C and N in steel to form Ti(C,N) precipitates. On one hand, during forging, the residual heat and stress conditions of forging facilitate precipitation, improving the tensile strength and yield strength of the steel. On the other hand, Ti combines with C / N in the steel to form nanoscale Ti(C,N) particles. These particles cannot act as nucleation sites for ferrite, inhibiting ferrite precipitation and promoting bainite formation, thus refining the bainite and MA island structures. Furthermore, for steels with high weldability requirements, Ti and its oxide Ti₂O₃ act as nucleation sites in the molten pool, which is beneficial for improving the strength and toughness of the weld-affected zone, resulting in parts with good overall performance. Therefore, the Ti content is ≥0.0350%. However, a high Ti content easily leads to the formation of harmful inclusions TiN in the steel, reducing its fatigue strength. Therefore, the N content is ≤0.10%. Thus, the Ti content range is determined to be 0.035%–0.100%.

[0030] Al: Al is an effective deoxidizer and combines with nitrogen in steel to form AlN precipitates, refining the austenite grains and simultaneously improving both strength and toughness. When the Al content is below 0.030%, its effect is not significant; above 0.050%, it easily forms coarse inclusions, deteriorating the steel's properties. Therefore, the timing of Al addition during steelmaking should be adjusted to ensure the Al content is controlled between 0.030% and 0.050%.

[0031] Sulfur (S) readily combines with manganese (MnS) in steel to form MnS inclusions, causing hot brittleness. However, adding a small amount of S, without affecting product performance, allows the appropriate amount of MnS inclusions to liquefy during cutting, resulting in fragmented cutting and preventing iron filings from scratching the tool surface, thus improving the material's machinability. Therefore, the S content should be ≥0.010%. However, higher S content can easily lead to the deterioration of sulfide morphology in steel, which in turn worsens the steel's machinability. Moreover, excessively high S content can reduce the plasticity of the weld-affected zone. Therefore, the S content should be ≤0.030%. Thus, the S content range is determined to be 0.010–0.030%.

[0032] P: P is an element with a strong tendency to segregate, increasing the cold brittleness of steel, reducing plasticity, and being detrimental to the uniformity of product microstructure and properties. P should be controlled to ≤0.008%.

[0033] [N]: [N] can form compounds with Ti, Al, etc., refining the grain size. A reasonable Al / [N] ratio has a significant effect on grain refinement, while excessive [N] can lead to defects such as bubbles and TiN inclusions. Therefore, the [N] content should be controlled between 30-60 ppm.

[0034] TO (Oxygen) is the main source of inclusions in steel; therefore, controlling oxygen levels is crucial for determining the properties of non-quenched and tempered steel. For ordinary steel grades, lower oxygen levels are preferable. However, in this invention, precise control of oxygen content during the RH smelting process maintains an appropriate oxygen content in the non-quenched and tempered steel. This promotes the combination of Ti and O in the steel to form Ti₂O₃. MnS can nucleate around Ti₂O₃, refining sulfide sizes, improving inclusion ratings and machinability. Furthermore, it can form Mn-depleted regions around Ti₂O₃ inclusions, serving as limited nucleation areas for ferrite. A small amount of ferrite in the steel can coordinate material deformation, thereby improving the steel's toughness. Therefore, the TO content is ≥8 ppm. However, excessive oxygen can lead to an increase in the number of oxide inclusions and worsen Class D inclusions; therefore, TO ≤12 ppm. Thus, the TO content is controlled between 8 and 12 ppm.

[0035] This invention controls the X value to increase the bainite content and refine the M / A island size, thereby improving the material's strength and toughness and broadening its forging process window. This invention refines the bainite and M / A island size through the inhibitory effect of Si on carbon diffusion. Simultaneously, the combined effects of elements such as C, Si, Mn, S, Cr, Al, Ti, and TO in the steel, along with the precipitation of second phases such as Ti(C, N) and Ti2O3, enhance the steel's strength and toughness. Furthermore, to improve the material's weldability, good weldability is achieved through Ceq control. For automotive forging steel, the process window is one of the key factors determining the uniformity of part performance. Air cooling effectively avoids the "uneven surface" problem caused by air cooling. Therefore, to achieve the performance described in this patent, the total composition needs to be matched, and the elements must satisfy the following formula: X = 30×C + 10×Si + 30×Mn + 15×S + 20×Cr + 10×Al + 40×Ti + 30×V + 35×TO, X ≤ 500. The units for C, Mn, Si, S, Cr, Al, and V are wt%, and the unit for TO is ppm.

[0036] Compared with existing technologies, this invention, through compositional design and control of the matching of multiple elements, achieves an X value of 30×C + 10×Si + 30×Mn + 15×S + 20×Cr + 10×Al + 40×Ti + 30×V + 35×TO, with an X value ≤ 500. This increases the bainite content and refines the M / A island size, thereby improving the material's strength and toughness and broadening its forging process window. After forging, the material of this invention, air-cooled to 200–400℃, exhibits a tensile strength of 900–1000MPa, a yield strength of 650–760MPa, an elongation at break ≥ 17%, a reduction of area ≥ 45%, a yield strength ratio ≥ 0.76, a room temperature impact energy (KU2) ≥ 60J, a bending fatigue strength ≥ 430MPa, and a Ceq ≤ 0.60%. Attached Figure Description

[0037] Figure 1 This is a tissue diagram of Example 1;

[0038] Figure 2 This is an organizational diagram of Example 2;

[0039] Figure 3 This is a tissue diagram of Example 3;

[0040] Figure 4 This is a tissue diagram for Comparative Example 1. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to the embodiments.

[0042] Example 1

[0043] A Ti microalloyed, weldable, low-cost bainitic non-quenched and tempered steel comprises the following mass percentage composition as shown in Table 1. The balance not shown in Table 1 is Fe and unavoidable impurities.

[0044] The composition of the Ti microalloyed, weldable, low-cost bainitic non-quenched and tempered steel satisfies the following formula: X = 30 × C + 10 × Si + 30 × Mn + 15 × S + 20 × Cr + 10 × Al + 40 × Ti + 30 × V + 35 × TO = 388.1. Where C, Si, Mn, S, Cr, Al, Ti, and V are in wt%, and TO is in ppm. Ceq = 0.57.

[0045] The manufacturing process of the Ti microalloyed easy-to-weld low-cost bainitic non-quenched and tempered steel described in Example 1 includes the following process flow: smelting - refining - RH vacuum treatment - continuous casting of round billets / square billets - rolling - forging - air cooling.

[0046] The smelting process employs an electric furnace / converter to reduce the phosphorus content in the steel to ≤0.05%.

[0047] The RH vacuum treatment utilizes precise control of the blowing volume during the RH vacuum degassing process to adjust the oxygen content to the target value. By controlling the oxygen content during vacuum degassing, the strength and toughness of the gear steel are improved.

[0048] The rolling process involves heating the round steel at 1240℃ for 310 minutes; the initial rolling temperature is 1190℃, and the final rolling temperature is 850℃. After rolling, the steel is either covered with a heat preservation cover or placed in a slow cooling pit for slow cooling.

[0049] The forging process is carried out at a forging heating temperature of 1192℃, an initial forging temperature of 1126℃, and a final forging temperature of 921℃.

[0050] The air cooling process involves air cooling the forged material to 232°C, followed by stack cooling to room temperature.

[0051] Example 2

[0052] A Ti microalloyed, weldable, low-cost bainitic non-quenched and tempered steel comprises the following mass percentage composition as shown in Table 1. The balance not shown in Table 1 is Fe and unavoidable impurities.

[0053] The composition of the Ti microalloyed, weldable, low-cost bainitic non-quenched and tempered steel satisfies the following formula: X = 30 × C + 10 × Si + 30 × Mn + 15 × S + 20 × Cr + 10 × Al + 40 × Ti + 30 × V + 35 × TO = 417.0. Where C, Si, Mn, S, Cr, Al, Ti, and V are in wt%, and TO is in ppm. Ceq = 0.57.

[0054] The manufacturing process of the Ti microalloyed easy-to-weld low-cost bainitic non-quenched and tempered steel described in Example 1 includes the following process flow: smelting - refining - RH vacuum treatment - continuous casting of round billets / square billets - rolling - forging - air cooling.

[0055] The smelting process employs an electric furnace / converter to reduce the phosphorus content in the steel.

[0056] The RH vacuum treatment utilizes precise control of the blowing volume during the RH vacuum degassing process to adjust the oxygen content to the target value. By controlling the oxygen content during vacuum degassing, the strength and toughness of the gear steel are improved.

[0057] The rolling process involves heating the round steel at 1250℃ for 320 minutes; the initial rolling temperature is 1180℃, and the final rolling temperature is 700℃. After rolling, the steel is either covered with an insulation cover or placed in a slow cooling pit for slow cooling.

[0058] The forging process is carried out at a forging heating temperature of 1226℃, an initial forging temperature of 1146℃, and a final forging temperature of 943℃.

[0059] The air cooling process involves air cooling to 313°C after forging, followed by stack cooling to room temperature.

[0060] Example 3

[0061] A Ti microalloyed, weldable, low-cost bainitic non-quenched and tempered steel comprises the following mass percentage composition as shown in Table 1. The balance not shown in Table 1 is Fe and unavoidable impurities.

[0062] The composition of the Ti microalloyed easy-to-weld, low-cost bainitic non-quenched and tempered steel satisfies the following formula: X = 30 × C + 10 × Si + 30 × Mn + 15 × S + 20 × Cr + 10 × Al + 40 × Ti + 30 × V + 35 × TO = 449.1, where C, Si, Mn, S, Cr, Al, Ti, and V are in wt%, and TO is in ppm. Ceq = 0.57.

[0063] The manufacturing process of the Ti microalloyed easy-to-weld low-cost bainitic non-quenched and tempered steel described in Example 1 includes the following process flow: smelting - refining - RH vacuum treatment - continuous casting of round billets / square billets - rolling - forging - air cooling.

[0064] The smelting process employs an electric furnace / converter to reduce the phosphorus content in the steel.

[0065] The RH vacuum treatment utilizes precise control of the blowing volume during the RH vacuum degassing process to adjust the oxygen content to the target value. By controlling the oxygen content during vacuum degassing, the strength and toughness of the gear steel are improved.

[0066] The rolling process involves heating the round steel at 1250℃ for 300 minutes; the initial rolling temperature is 1180℃, and the final rolling temperature is 800℃. After rolling, the steel is either covered with a heat preservation cover or placed in a slow cooling pit for slow cooling.

[0067] The forging process is carried out at a forging heating temperature of 1242℃, an initial forging temperature of 1168℃, and a final forging temperature of 987℃.

[0068] The air cooling process involves air cooling the forged material to 384°C, followed by stack cooling to room temperature.

[0069] Comparative Example 1 uses 25Mn2CrVS with conventional heating and smelting processes; Comparative Example 2 uses the composition and smelting method of the present invention, but does not use the forging process of the present invention.

[0070] The components of each embodiment and comparative example are shown in Table 1, the forging parameters are shown in Table 2, and the properties are shown in Table 3. Among them, comparative example 1 does not meet the components of this patent, and comparative example 2 has the components of embodiment 1 of this invention, but does not meet the process conditions of this invention.

[0071] Table 1 Chemical composition of embodiments of the present invention (unit: TO, [N] are ppm, others are wt%)

[0072]

[0073]

[0074] Table 2 Forging process parameters

[0075] Heating temperature / °C Initial forging temperature / °C Final forging temperature / °C Down line temperature / °C Cooling process Example 1 1192 1126 921 232 On-line air cooling, stack cooling after off-line Example 2 1226 1146 943 313 On-line air cooling, stack cooling after off-line Example 3 1242 1168 987 384 On-line air cooling, stack cooling after off-line Comparative Example 1 1126 1020 813 120 On-line air cooling, stack cooling after off-line Comparative Example 2 1142 1032 834 115 On-line air cooling, stack cooling after off-line

[0076] Table 3 Mechanical properties, bending fatigue strength, and yield strength ratio of the examples and comparative examples.

[0077]

[0078] Examples 1-3 are non-quenched steels produced using the specific composition and smelting process of this invention. Comparative Example 1 is 25Mn2CrVS produced according to GB / T 15712 standard and using conventional smelting and rolling processes. Other smelting and rolling processes are the same for the examples and comparative examples. Table 2 shows the forging process parameters of the samples, and Table 3 shows the mechanical properties and rotational bending fatigue performance test results of the materials after forging treatment in the examples and comparative examples. Comparative Example 1 uses 25Mn2CrVS with conventional heating and smelting processes; Comparative Example 2 uses the composition and smelting method of this invention, but not the forging process of this invention.

[0079] As shown in Tables 1-3, this invention proposes a non-quenched and tempered steel that meets the welding requirements of automobiles and engineering machinery through alloy design and production process control. Based on the Si-Mn-Cr alloy system, this invention, through the combined effect of Si and Ti elements, suppresses bainite formation, increases bainite content, and simultaneously refines M / A islands, thereby refining the material microstructure and improving toughness. Furthermore, by introducing an appropriate amount of Ti2O3 particles as nucleation sites for softening phases (retained austenite and ferrite), the toughness of the material is further enhanced. In addition, through appropriate elemental ratios, this invention eliminates the need for special air cooling during forging, significantly improving the consistency of part performance and the process window, thus accelerating the market promotion of non-quenched and tempered steel. Moreover, the alloy design and performance control concepts involved in this invention are also applicable to other non-quenched and tempered steels.

Claims

1. A Ti microalloyed, easy-to-weld, low-cost bainitic non-quenched and tempered steel, characterized in that, The Ti microalloyed, easy-to-weld, low-cost bainitic non-quenched and tempered steel comprises the following composition by mass percentage: C: 0.05-0.12%, Si: 0.80-1.50%, Mn: 2.00-2.50%, Cr: 0.20-0.40%, Al: 0.030-0.050%, P: ≤0.008%, S: 0.010-0.030%, Ti: 0.035-0.10%, TO: 8-12ppm, [N]: 30-60ppm, with the remainder being Fe and unavoidable impurity elements; The composition of the Ti microalloyed easy-to-weld, low-cost bainitic non-quenched and tempered steel satisfies the following formula: X = 30×C + 10×Si + 30×Mn + 15×S + 20×Cr + 10×Al + 40×Ti + 30×V + 35×TO, X ≤ 500; where C, Si, Mn, S, Cr, Al, Ti and V are in wt%, and TO is in ppm; The microstructure of the Ti microalloyed easy-to-weld, low-cost bainitic non-quenched and tempered steel is bainite + M / A islands, with a bainite area ratio content ≥90% and an M / A island size ≤25μm.

2. The Ti microalloyed, easy-to-weld, low-cost bainitic non-quenched and tempered steel according to claim 1, characterized in that, The composition of the Ti microalloyed easy-to-weld, low-cost bainitic non-quenched and tempered steel satisfies the following formula: Ceq=C+Si / 24+Mn / 6+Cr / 5+V / 14, Ceq≤0.

60.

3. The Ti microalloyed, easy-to-weld, low-cost bainitic non-quenched and tempered steel according to claim 1 or 2, characterized in that, The Ti microalloyed, easy-to-weld, low-cost bainitic non-quenched and tempered steel Tensile strength 900MPa~1000MPa, yield strength 650~760MPa, elongation after fracture ≥17%, reduction of area ≥45%, yield strength ratio ≥0.76, room temperature impact energy (KU2) ≥60J, flexural fatigue strength ≥430MPa.

4. A manufacturing process for the Ti microalloyed easy-to-weld, low-cost bainitic non-quenched and tempered steel according to any one of claims 1-3, characterized in that, The manufacturing process includes forging and subsequent air cooling.

5. The manufacturing process according to claim 4, characterized in that, The forging process is carried out at a heating temperature of 1180~1250℃, an initial forging temperature of 1100~1200℃, and a final forging temperature of 900~1000℃.

6. The manufacturing process according to claim 4 or 5, characterized in that, After forging, it is air-cooled to below 400°C, and then stacked and cooled to room temperature.

7. The manufacturing process according to claim 4 or 5, characterized in that, The manufacturing process also includes rolling, wherein the round steel is heated to a temperature ≥1230℃ for a heating time ≥300min; the initial rolling temperature is ≥1180℃; the final rolling temperature is 600~900℃; and after rolling, it is cooled by a heat preservation cover or placed in a slow cooling pit.

8. The application of the Ti microalloyed easy-to-weld, low-cost bainitic non-quenched and tempered steel according to any one of claims 1-3, characterized in that, Used in automobile manufacturing.

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