CN110029279B

CN110029279B - Steel with yield strength of 390MPa grade for high-speed rail bogie frame and preparation method thereof

Info

Publication number: CN110029279B
Application number: CN201910362422.6A
Authority: CN
Inventors: 王纯; 余伟; 刘敏; 陈雨来; 何春雨; 程知松
Original assignee: University of Science and Technology Beijing USTB
Current assignee: University of Science and Technology Beijing USTB
Priority date: 2019-04-30
Filing date: 2019-04-30
Publication date: 2020-12-01
Anticipated expiration: 2039-04-30
Also published as: CN110029279A

Abstract

The invention discloses steel with yield strength of 390MPa for a high-speed rail bogie frame and a preparation method thereof, wherein the steel comprises the following chemical components in percentage by mass of 0.07-0.12% of C, Mn: 0.50 to 1.00%, Si: 0.15-0.35%, P is less than or equal to 0.020%, S is less than or equal to 0.01%, and Ni: 0.20-0.50%, Cr: 0.30-0.80%, Cu: 0.2-0.05%, Ti: 0.015 to 0.025%, Nb: 0.01-0.04%, V: 0 to 0.07 percent of Ca and 0.001 to 0.002 percent of Ca. The balance of Fe and inevitable impurities. After smelting and casting the components, heating the components at 1200 ℃, carrying out hot processing to the required size, and then controlling and cooling. The microstructure of the steel is ferrite and pearlite, the yield strength is 390 MPa-460 MPa, the tensile strength is 520 MPa-620 MPa, the elongation after fracture is more than or equal to 20 percent, the V-notch impact energy at minus 40 ℃ is more than or equal to 120J, the carbon equivalent CEQ of the steel is less than or equal to 0.35 percent, and the crack resistance sensitivity index Pcm is less than or equal to 0.20 percent. The steel grade has the characteristics of low cost, excellent comprehensive mechanical property, easiness in welding, corrosion resistance and the like.

Description

Steel with yield strength of 390MPa grade for high-speed rail bogie frame and preparation method thereof

Technical Field

The invention discloses steel for a high-speed rail bogie frame with 390 MPa-level yield strength and a preparation method thereof, belonging to the field of metal materials.

Background

With the sixth major speed increase of railways in China, China has advanced the era of high-speed railways. The steel for the high-speed train bogie is required to have certain strength and higher toughness, and also has good welding performance, fatigue resistance and corrosion resistance. The steel for the bogie used at present, such as Q345 series steel and S355 steel, has low strength and poor low-temperature toughness, and the steel for the bogie of the high-speed rail adopts European standards at present. Therefore, the development of the novel steel for the high-speed train bogie with independent intellectual property rights has very practical significance.

355 MPa-grade low-temperature toughness thick plate steel in the Chinese invention patent CN 105063485A adopts low carbon (% C is less than or equal to 0.14%) and niobium-vanadium microalloying, strictly controls the content of phosphorus and sulfur, and finally obtains the Charpy transverse impact energy of more than or equal to 365MPa, more than or equal to 500MPa and more than or equal to 100J at minus 60 ℃ by adopting a TMCP (thermal mechanical control processing) process. In addition, 355 MPa-level large heat input welding steel in the Chinese invention patent CN 104498827A adopts low carbon (% C is less than or equal to 0.10%) and low carbon equivalent, adds a proper amount of Nb and Ti, improves the rolling reduction rate in the recrystallization zone at the rolling stage, optimizes the TMCP process, controls the final cooling temperature, obtains the yield strength which is more than or equal to 355MPa, the tensile strength which is more than or equal to 510MPa, the elongation which is more than or equal to 20%, and obtains the average value of normal impact power of 1/4 and the center part which is at minus 40 ℃ which is more than or equal to. Both methods have the defects of high content of carbon and manganese elements in steel, complicated process and the like.

Disclosure of Invention

The invention relates to steel for a high-speed rail bogie frame with 390 MPa-level yield strength, which meets the requirements of light weight of high-speed rails, service in alpine regions, easiness in welding and corrosion resistance.

The steel for the bogie frame of the high-speed rail with the yield strength of 390MPa grade comprises the following chemical components in percentage by mass of 0.07-0.12% of C, Mn: 0.50 to 1.00%, Si: 0.15-0.35%, P is less than or equal to 0.020%, S is less than or equal to 0.01%, and Ni: 0.20-0.50%, Cr: 0.30-0.80%, Cu: 0.2-0.5%, Ti: 0.015 to 0.025%, Nb: 0.01-0.04%, V: 0 to 0.07 percent of Ca and 0.001 to 0.002 percent of Ca. The balance of Fe and inevitable impurities.

The preparation method of the steel for the high-speed rail bogie frame with the yield strength of 390MPa level comprises the following preparation steps: smelting and casting according to the chemical components, heating a casting blank to 1150-1220 ℃ for complete austenitizing, then rolling, wherein the rough rolling finishing temperature is more than or equal to 1020 ℃, the finish rolling starting temperature is less than or equal to 950 ℃, the finish rolling termination temperature is 800-880 ℃, cooling to 550-650 ℃ at the speed of 5-10 ℃/s after rolling, and then air cooling or slowly cooling to room temperature.

The microstructure of the steel is ferrite and pearlite, the yield strength is 390 MPa-460 MPa, the tensile strength is 520 MPa-620 MPa, the elongation after fracture is more than or equal to 20%, the V-notch impact energy under the condition of minus 40 ℃ is more than or equal to 120J, and the ductile-brittle transition temperature reaches minus 60 ℃. The carbon equivalent CEQ of the steel is less than or equal to 0.35 percent, and the crack resistance sensitivity index Pcm is less than or equal to 0.20 percent.

The 390MPa grade high-speed rail bogie steel is adopted, so that the mechanical property of the steel plate can be improved, and the use requirement of high-speed rail in extremely cold weather can be met; the alloy and microalloying method can be adopted to improve the industrial atmosphere and coastal atmosphere corrosion resistance of the steel, so that the service life of the bogie can meet the requirement that the service life of the vehicle is consistent with that of the vehicle, and the maintenance cost of the vehicle is greatly reduced. Consider the strength grade of 390MPa grade high-speed railway bogie steel, and the required low-temperature service performance, corrosion resistance and welding performance. The following elements and their effects are considered in the composition design:

c: c is a gap strengthening element and has a remarkable effect of strengthening the gap of steel. When the product is added into hypoeutectoid steel, cementite in the steel can be separated out, the potential difference of micro-areas of the steel in a corrosive environment is increased, and the corrosion resistance of the steel is not good. Meanwhile, C affects the welding performance, the stamping performance, the impact toughness and the like of the steel.

Cu: cu is a solid-solution strengthening element in steel, and produces a precipitation strengthening effect when the content is high. When 0.2-0.4% of Cu is added into the steel, the alloy has corrosion resistance superior to that of common carbon steel in rural atmosphere, industrial atmosphere or marine atmosphere. Cu can be enriched on the surface of steel and in the rust layer to promote the anodic passivation of steel, and can form a barrier layer which takes Cu and P as main components between the matrix and the rust layer, and the barrier layer is firmly combined with the matrix, thereby having better protection effect. In addition, Cu has a remarkable effect of counteracting the harmful effect of S in steel, and the higher the S content in steel, the more remarkable the relative effect of the alloying element Cu in reducing the corrosion rate, which is thought to be caused by the formation of insoluble sulfides by Cu and S.

P: p is a gap strengthening element, but decreases the low temperature toughness of the steel. P is also one of the most effective alloy elements for improving the atmospheric corrosion resistance of steel, and the corrosion resistance is the best when the content of P is 0.08-0.15%. When P is added to the steel in combination with Cu, a better recombination effect is shown. Under the condition of atmospheric corrosion, P in the steel is an anode depolarizer which can accelerate the uniform dissolution of the steel and the oxidation rate of Fe2+ in the steel, and is helpful for forming a uniform alpha-FeOOH rust layer on the surface of the steel and promoting the generation of an amorphous iron oxyhydroxide FeOx (OH)3-2x dense protective film, thereby increasing the resistance and becoming a protective barrier for a corrosive medium to enter a steel matrix so as to prevent the interior of the steel from atmospheric corrosion. P also acts as a corrosion inhibitor when it forms PO 43-.

Cr: cr is a solid solution strengthening element, has slightly lower solid solution strengthening capability than Mn, and has no obvious influence on the toughness of the material. Cr can form a compact oxide film on the surface of steel, and the passivation capability of the steel is improved. The Cr content in the weathering steel is generally 0.4-1.0% (maximum 1.3%). When Cr and Cu are added into steel at the same time, the effect is particularly obvious. Researches indicate that the increase of the Cr content is beneficial to refining the alpha-FeOOH, and when the Cr content in the alpha-FeOOH of the rust layer/metal interface exceeds 5 percent, corrosive anions, particularly Cl < - > can be effectively inhibited from invading; meanwhile, the Cr element is added to prevent the conversion of Fe3+ to Fe2+ during drying in the process of alternation between dry and wet, thereby improving the weather resistance of the steel. However, in areas with high Cl-content, the addition of Cr is considered to be detrimental.

Mn: the effect on corrosion resistance is not consistently known, and many researchers believe that Mn improves the corrosion resistance of steel to the marine atmosphere, but has little effect on corrosion resistance in industrial atmospheres. The Mn content in the weathering steel is generally 0.5-2%.

Si: si is a substitutional solid solution strengthening element, and is beneficial to improving the yield limit and the strength of steel. The use of the alloy and other elements such as Cu, Cr, P and Ca can improve the weather resistance of the steel, and the higher Si content is beneficial to refining alpha-FeOOH, thereby reducing the overall corrosion rate of the steel.

Ni: is a relatively stable element, and the Ni alloying is also beneficial to improving the low-temperature impact toughness of the steel. The addition of Ni can change the self-corrosion potential of the steel to the positive direction, and the stability of the steel is increased. The atmosphere exposure test shows that when the Ni content is about 4%, the atmospheric corrosion resistance of the seaside weathering steel can be obviously improved.

Al: al is a substitutional solid solution strengthening element, and can form AlN precipitates with N in steel, so that a certain degree of fine crystal strengthening and precipitation strengthening effects are generated. Al forms a stable spinel-type complex oxide (FeAl 2O 4) mainly in the spinel oxide (Fe 3O 4) of the rust layer, and provides cation selectivity to the rust layer to suppress Cl — -intrusion. Si-Al alloying has been used in recent years to develop low cost weathering steels.

S: the content of the residual element is controlled to be less than 0.04%.

Ca: the trace Ca added into the weathering steel can not only obviously improve the overall atmospheric corrosion resistance of the steel, but also effectively avoid the phenomenon of rust liquid sagging when the weathering steel is used. And a trace amount of Ca is added into the weathering steel, so that the alkalinity of a corrosion interface is increased, the corrosivity of the corrosion interface is reduced, and the rust layer is promoted to be converted into compact alpha-FeOOH with good protection. Jeong [34] et al indicate that Ca is more effective when used in combination with Si.

Nb: nb element can change the form of the rust layer, improve the corrosion potential and reduce the corrosion rate of steel. Research shows that after the steel is treated by niobium in a solid solution mode, the corrosion resistance of the steel in a marine atmospheric corrosion environment can be improved. Nb addition is generally chosen as the primary microalloying element to refine grain and improve strength. Research shows that Nb can obviously inhibit the precipitation of Mo and Cr in the 13Cr of the super martensitic stainless steel, prevent the occurrence of Mo-poor and Cr-poor areas and improve the pitting corrosion resistance of the steel.

Ti: ti is added into the steel, can form carbonitride with C, N, is precipitated in the hot rolling process of steel, refines austenite grains, achieves the aim of precipitation strengthening, and simultaneously can form compounds with S in the steel, and is precipitated at high temperature, thereby avoiding forming MnS to reduce the corrosion resistance. In addition, the coexistence of Ti also reduces the size of the α -FeOOH crystals.

V: the V or VN alloying can effectively reduce the corrosion rate of the weathering steel, so that the weathering steel has excellent pitting corrosion resistance, the corrosion can be more uniformly carried out on the surface of a steel matrix, the charge conduction resistance of a rust layer is improved, and the insulating property is enhanced. The analysis of the rust layer of the VN alloyed weathering steel shows that the content of alpha-FeOOH is higher, and the value of alpha-FeOOH/gamma-FeOOH is larger, which again shows that the VN alloying is favorable for generating the rust layer with stable thermodynamics. In addition, V has precipitation strengthening and fine grain strengthening effects, VN particles precipitated at high temperature in VN alloyed low-carbon steel show good precipitation strengthening and fine grain strengthening effects, and the sum of the two effects has a contribution rate of reaching more than 70% to yield strength.

A plurality of alloy elements can meet different performance requirements of steel, but the alloy elements can really play a role, simultaneously give consideration to factors such as alloy cost, subsequent processing performance and the like, and have a plurality of alloying combination modes. After the factors are considered, the steel for the bogie frame of the high-speed rail with the yield strength of 390MPa grade is developed by combining the requirements of high strengthening, high toughness of service in alpine regions, easy welding in the processing process and corrosion resistance in the service process.

The invention has the beneficial effects that:

1) compared with the existing S355 and Q345 steel, the steel for the high-speed rail bogie frame with the yield strength of 390MPa grade has the advantages that the yield strength is improved by one grade, the lightweight index of iron can be improved, and the energy consumption of vehicle operation is reduced.

2) The V-shaped notch of the steel for the bogie frame of the high-speed rail with the yield strength of 390MPa grade has the low-temperature impact energy of-40 ℃ to more than 120J, the ductile-brittle transition temperature reaches-60 ℃, and the safe operation of the high-speed rail under extremely cold weather can be met.

3) The 390MPa grade steel for the bogie frame of the high-speed rail has the advantages of improving the industrial atmosphere and coastal atmosphere corrosion resistance of the steel due to the mechanical property, welding property and corrosion resistance, ensuring that the service life of the bogie is consistent with the service life cycle of a vehicle, and greatly reducing the maintenance cost of the vehicle.

4) The steel for the 390 MPa-grade high-speed rail bogie frame has the advantages that the carbon equivalent CEQ is less than or equal to 0.35 percent, the crack resistance sensitivity index Pcm is less than or equal to 0.20 percent, and the welding performance is excellent.

Drawings

FIG. 1 shows the microstructure of the steel grade according to the invention, ferrite + a small amount of pearlite, observed under a scanning electron microscope.

Detailed Description

A steel for a high-speed railway bogie frame with a yield strength of 390MPa grade, wherein the chemical compositions of example steel grades are shown in Table 1.

Heating the casting blank to 1150-1220 ℃ for complete austenitizing, then rolling, wherein the rough rolling and final rolling temperature is more than or equal to 1020 ℃, the finish rolling start temperature is less than or equal to 950 ℃, the finish rolling termination temperature is 800-880 ℃, cooling to 550-650 ℃ at the speed of 5-15 ℃/s after rolling, and then air cooling or slowly cooling to room temperature. The mechanical properties of the hot-worked steel sheet are shown in Table 2.

The salt spray corrosion rate of the steel of each example is reduced by more than 20 percent compared with the 09CuPTiRE steel.

TABLE 1 chemical composition of the steels of the examples and mechanical properties measured in the tests

Examples	C	Mn	Si	P	S	Ni	Cr	Cu	Nb	Ti	V	Ca
													No.1	0.11	1.12	0.35	0.007	0.015	0.27	0.33	0.4	0.03	0.028	0.061	0.001
No.2	0.099	1.03	0.3	0.006	0.015	0.25	0.3	0.38	0.031	0.015	≤0.01	0.001
													No.3	0.086	0.96	0.18	0.006	0.016	0.19	0.46	0.41	0.025	≤0.01	0.095	0.001
No.4	0.095	0.98	0.27	0.006	0.017	0.3	0.47	0.4	0.032	0.018	0.057	0.001
													No.5	0.081	1.04	0.28	0.006	0.017	0.32	0.38	0.41	0.026	0.013	0.060	0.001
No.6	0.076	0.66	0.32	0.006	0.003	0.29	0.45	0.36	0.03	0.015	0.051	0.001

TABLE 2 Hot working Process and mechanical Properties of the steels of the examples

Claims

1. The steel for the high-speed rail bogie frame with the yield strength of 390MPa grade comprises the following chemical components in percentage by mass: 0.07 to 0.12%, Mn: 0.50 to 1.00%, Si: 0.15-0.35%, P is less than or equal to 0.020%, S is less than or equal to 0.01%, and Ni: 0.20-0.50%, Cr: 0.30-0.80%, Cu: 0.2-0.5%, Ti: 0.015 to 0.025%, Nb: 0.01-0.04%, V: 0-0.07%, Ca:0.001-0.002%, and the balance of Fe and inevitable impurities;

the steel for the high-speed rail bogie frame is prepared by the following method: smelting and casting according to the chemical components, heating a casting blank to 1150-1220 ℃ for complete austenitizing, then rolling, wherein the rough rolling finishing temperature is more than or equal to 1020 ℃, the finish rolling starting temperature is less than or equal to 950 ℃, the finish rolling termination temperature is 800-880 ℃, cooling to 550-650 ℃ at the speed of 5-10 ℃/s after rolling, and then air cooling or slowly cooling to room temperature;

wherein the microstructure of the steel is ferrite and pearlite, the yield strength is 390 MPa-460 MPa, the tensile strength is 596 MPa-620 MPa, the elongation after fracture is more than or equal to 20 percent, the V-shaped transverse notch impact energy at minus 40 ℃ is more than or equal to 120J, the ductile-brittle transition temperature is minus 60 ℃, the carbon equivalent CEQ of the steel is less than or equal to 0.35 percent, and the crack resistance sensitivity index Pcm is less than or equal to 0.20 percent.

2. The preparation method of the steel for the high-speed railway bogie frame with the yield strength of 390MPa grade according to claim 1, which is characterized by comprising the following steps:

smelting and casting according to the chemical components, heating a casting blank to 1150-1220 ℃ for complete austenitizing, then rolling, wherein the rough rolling finishing temperature is more than or equal to 1020 ℃, the finish rolling starting temperature is less than or equal to 950 ℃, the finish rolling termination temperature is 800-880 ℃, cooling to 550-650 ℃ at the speed of 5-10 ℃/s after rolling, and then air cooling or slowly cooling to room temperature;

the microstructure of the steel is ferrite and pearlite, the yield strength is 390MPa to 460MPa, the tensile strength is 596MPa to 620MPa, the elongation after fracture is more than or equal to 20 percent, the V-shaped transverse notch impact energy at minus 40 ℃ is more than or equal to 120J, the ductile-brittle transition temperature is minus 60 ℃, the carbon equivalent CEQ of the steel is less than or equal to 0.35 percent, and the crack resistance sensitivity index Pcm is less than or equal to 0.20 percent.