CN114574771A

CN114574771A - High-elongation-flange-performance and fatigue-resistant special steel for wheels and production process

Info

Publication number: CN114574771A
Application number: CN202210211639.9A
Authority: CN
Inventors: 李洪波; 任志鑫; 高振伟; 赵亚飞; 孟凡超; 孙晶磊; 李君彦; 李世伟
Original assignee: Wuan Yuhua Iron And Steel Co ltd
Current assignee: Wuan Yuhua Iron And Steel Co ltd
Priority date: 2022-03-04
Filing date: 2022-03-04
Publication date: 2022-06-03

Abstract

The invention relates to the technical field of steel products, and provides wheel special steel with high extending flange performance and fatigue resistance, which comprises the following chemical components in percentage by weight: c: 0.05% -0.09%, Mn: 0.70% -0.85%, P: less than or equal to 0.015 percent, S: less than or equal to 0.012 percent, Als: 0.020% -0.040%, Ti: 0.015% -0.020%, Nb: 0.008% -0.015% and the balance of Fe and inevitable impurity elements. Through the technical scheme, the problem that the strength, the forming and fatigue performance and the surface quality of steel in the prior art cannot meet the service condition of the automobile wheel is solved.

Description

Special wheel steel with high extending flange performance and fatigue resistance and production process

Technical Field

The invention relates to the technical field of steel, in particular to wheel special steel with high extension flange performance and fatigue resistance and a production process thereof.

Background

The development of automobile technology has higher and higher requirements on the structure of wheels and the performance of steel used by the wheels. The wheels are important safety parts for the running of the automobile and are also main factors influencing the performance of the whole automobile. The rim and the spoke of the rolling wheel are combined into the wheel. Compared with the traditional profile steel wheel for the vehicle, the profile steel wheel for the vehicle does not need an inner tube, and has the advantages of reasonable structure, high precision, safety, reliability, material saving, light weight, good dynamic balance, long fatigue life and the like, thereby being widely applied to the vehicle. However, the manufacturing process of the roll-type wheel is complex, the acceptance conditions are strict, and the requirements on the hot rolled steel plate used as the wheel material are very strict. The rolling wheels are adopted for cars, minivans, light-duty vehicles with small tonnage, trucks with medium tonnage and the like; in order to improve the overall performance of the truck, the wheels of the truck also tend to adopt a rolling forming process. At present, the international wheel steel is developed towards specialization and serialization, and the wheel steel is produced and forms a series according to the strength grade according to the requirements of different vehicle types. With the introduction of advanced models of cars and light vehicles in China, the demand of corresponding steel grades in China is large according to the requirement of a wheel production line introduced in a matched mode, and the development of the steel plate for automobile wheels in China is undoubtedly promoted. With the rise of domestic automobile industry, especially car industry, and the localization of various wheels, the development and application of steel plates for rolling wheels with high quality requirements are imperative. The steel for wheels in China is restricted by strict requirements on thickness tolerance and depends on import for a long time, and particularly, the steel for wheels of a large batch of car production lines introduced from the United states, Japan, Germany and France depends on import all before 95 years. A plurality of wheels in China are made of Q235, Q195, 08Al and other non-special steels, but the steels have many problems, large raw material consumption, poor flash welding performance and high scrap flushing rate.

The technical requirements for the materials used in the manufacturing process of the automobile wheel and the service conditions of the wheel are very strict, and the automobile wheel is required to have good comprehensive mechanical properties such as stretch flangeability, cold formability, flash weldability, fatigue property and the like, good surface quality and dimensional tolerance for ensuring the air tightness of the wheel and not generating large rotary oscillation or unbalance during the operation of the wheel. The production of the rolling wheel must solve the technical problems of forming, welding and the like. The processes of spoke forming with complex shape and long fatigue life, rim forming of flaring rolling after flash welding, welding synthesis of spokes and rims and the like all depend on proper components and good comprehensive performance of steel plates. The wheel steel has excellent comprehensive mechanical properties such as strength, forming and fatigue, and also has good surface quality and strict thickness tolerance.

Disclosure of Invention

The invention provides a wheel special steel with high extending flange performance and fatigue resistance and a production process thereof, which solve the problem that the strength, the forming and fatigue performance and the surface quality of steel in the prior art cannot meet the service condition of an automobile wheel.

The technical scheme of the invention is as follows:

the special steel for the wheel with high extending flange performance and fatigue resistance comprises the following chemical components in percentage by weight: c: 0.05% -0.09%, Mn: 0.70% -0.85%, P: less than or equal to 0.015 percent, S: less than or equal to 0.012 percent, Als: 0.020% -0.040%, Ti: 0.015% -0.020%, Nb: 0.008% -0.015% and the balance of Fe and inevitable impurity elements.

As a further technical scheme, the weight percentage of chemical components is as follows: c: 0.07%, Mn: 0.79%, P: 0.012%, S: 0.008%, Als: 0.024%, Ti: 0.017%, Nb: 0.010% and the balance of Fe and inevitable impurity elements.

The invention also provides a production process of the wheel special steel with high extending flange performance and fatigue resistance, which comprises molten iron pretreatment desulfurization, converter smelting, LF refining, continuous casting, heating, high-pressure water descaling, rough rolling, finish rolling and coiling.

As a further technical scheme, the inclusion is driven to float upwards by adopting a bottom argon blowing process, and the inclusion is gradually combined and agglomerated in the upward floating process, so that the size of the inclusion is increased, the inclusion is adsorbed by metallurgical slag to react, and the homogenization of the components of the molten steel is promoted.

As a further technical scheme, the molten iron is fully desulfurized by a KR stirring method.

Sulfur is an element which seriously influences the plasticity and toughness of steel, and the reduction of the content of sulfur is beneficial to reducing the inclusion and hot cracking tendency of steel, and obviously improves the grade and toughness level of the inclusion. Therefore, the molten iron is fully desulfurized by adopting a KR stirring method, and the sulfur content in the molten iron is greatly reduced.

As a further technical scheme, the heating time is 120-180 min, and the temperature of furnace gas in a soaking section is 1200 +/-20 ℃.

The heating quality of the plate blank directly influences the performance of the product, and in order to obtain uniform heating temperature and avoid remarkable growth of austenite grains, the heating time needs to be ensured, and the temperature is not suitable to be too high.

As a further technical scheme, the finish rolling temperature is 820-850 ℃.

As a further technical scheme, the outlet temperature of the laminar flow is 580-630 ℃ during laminar flow cooling.

As a further technical scheme, the cooling mode adopts continuous and rapid cooling of the front section after rolling.

The invention has the beneficial effects that:

1. the invention better solves the matching of strength and plasticity by optimizing components, microalloying niobium and titanium, thermally simulating static and dynamic CCT curves in a laboratory, adopting low-carbon medium-manganese microalloying niobium and titanium, TMCP and a front-section continuous rapid cooling process, develops the special steel for the wheel with higher strength, toughness, plasticity, fatigue resistance, wear resistance and thermal crack resistance, and is particularly suitable for special rims. The tensile properties are statistically shown in the following table:

Rel(MPa)	Rm(MPa)	A％
			372～415	458～479	28～31

2. the invention comprises the following components:

[C] hardly dissolved in ferrite, has an effect of improving tensile strength, and the more finely and dispersedly precipitated carbides have a significant effect of improving strength and reducing plasticity. In addition, the carbon content has obvious effects on the overheating sensitivity, the corrosion resistance and the hardenability. For formability and flash weldability, the invention adopts low carbon of 0.05-0.07%.

The [ Mn ] atoms are dissolved in austenite, ferrite and cementite, and in addition to directly playing a role in strengthening, since Mn lowers the transformation temperature at the time of transformation of austenite to pearlite, formed ferrite and pearlite are refined, and again contribute to strength. In the aspect of process, Mn is a deoxidizer and a desulfurizer in smelting, has the function of purifying steel, reduces or does not form FeS with low melting point existing in a grain boundary in a film form, and improves the red brittleness in hot processing of steel. But the ductile MnS inclusions increase the directionality of the material. Because Mn expands a gamma region to coarsen gamma grains, excessively high Mn content increases hardenability and overheating sensitivity, and is also unfavorable for welding, the invention comprehensively considers strength and economy, and the Mn content is controlled to be 0.70-0.85%.

[P][S]Phosphorus is easily precipitated in steel and forms Fe₃P, thereby increasing the brittleness of the steel, and in addition, its diffusion rate in alpha iron and gamma iron is small, segregation is easily formed, thereby increasing the level of the band structure, and it is difficult to lighten the level and eliminate it by the heat treatment method. Sulfide inclusions and brittle phosphides along the rolling direction cause the anisotropy of a steel sheet to be increased, S is easy to form MnS inclusions and segregate in the steel, so that an internal banded structure is formed by heating and rolling in the production process, and the plasticity, cold formability and impact toughness of the steel are reduced. Therefore, the invention controls the phosphorus to be less than or equal to 0.015 percent and the sulfur to be less than or equal to 0.012 percent, improves the purity of molten steel and improves the hot cracking property of steel.

[ Als ] can refine crystal grains, improve strength, combine with [ N ] to generate AlN, prevent strain aging, and be added into steel as a supplementary deoxidizer to improve the steel quality, but the excessive content can increase the alumina inclusion of the steel grade. Not only ensures the effect of subsequent calcium treatment, but also improves the purity of the molten steel; the method has the advantages of preventing the casting blank from being pulled and leaked, ensuring the smooth continuous casting, obviously refining the macrostructure of the slab casting blank, and ensuring that inclusions and precipitates in the casting blank are small in size and are uniformly distributed in a dispersed mode.

[Ti]A small amount of Ti element is added into the steel and combined with C, N to form fine and dispersed TiCN, which can prevent austenite grains from growing and refine the austenite grains, and further obtain fine ferrite grains when the structure is cooled and transformed; titanium and sulfur combine to form Ti₄C₂S₂The method can spheroidize sulfide inclusions in the steel, improve the hole expansion rate and the forming performance of the steel, and ensure that the content of Ti is 0.015-0.020%.

The Nb has important effects on phase transformation behavior, grain refinement, enrichment in austenite and nucleation of martensite, has certain inhibition effect on the phase transformation from austenite to ferrite in the cooling process, and can delay static and dynamic recrystallization in the thermal deformation process. When small carbonitrides are precipitated in combination, recrystallization can be delayed, grain growth is prevented, and the strengthening effect is obvious.

3. When the wheel steel obtained according to the chemical composition and the production process is used for a hole expansion experiment, the hole expansion rate lambda is 158-206%, the average value is 185%, and the hole expansion rate is high, so that the steel strip has good local elongation performance.

4. The steel ferrite of the wheel has fine crystal grains, and the grain size is 9.5-11 grades according to ASTM standard. Non-metallic inclusion observation is carried out, and long-strip MnS type inclusions and silicate type inclusions which are easy to form material directionality are difficult to find, and D type oxide inclusions are distributed in steel in a spherical mode.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIG. 1 is the static CCT curve for the steel of example 1;

FIG. 2 is the dynamic CCT curve for the steel of example 1;

FIG. 3 is a microstructure of undeformed and deformed austenite of the steel material of example 1 at different cooling rates, wherein (a) v is 0.5 ℃/s; (b) v is 15 ℃/s; (c) v is 30 ℃/s;

FIG. 4 shows the surface quality of steel material No. 1;

FIG. 5 shows the surface quality of Steel No. 2;

FIG. 6 is a scanning electron microscope photograph of steel product No. 1, wherein the upper view is the upper surface of the sample, and the lower view is the lower surface of the sample;

FIG. 7 is a cold bending test pattern of the wheel steel of example 2;

FIG. 8 is a photograph of the microstructure of example 3;

FIG. 9 is a metallographic structure of a weld joint according to example 4;

FIG. 10 is a graph showing the hardness distribution of the steel material of example 10 in the direction perpendicular to the weld.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any inventive step, are intended to be within the scope of the present invention.

Example 1

The special steel for the automobile wheel comprises the following chemical components: c: 0.07%, Mn: 0.79%, P: 0.012%, S: 0.008%, Als: 0.024%, Ti: 0.017%, Nb: 0.010% and the balance of Fe and inevitable impurity elements.

The production process comprises the following steps:

s1, pretreating and desulfurizing molten iron, and fully desulfurizing by adopting a KR stirring method;

s2, smelting in a converter;

s3, LF refining;

s4, continuous casting;

s5, heating for 150min, and controlling the temperature of furnace gas of a soaking section to be 1200 +/-20 ℃;

s6, descaling by high-pressure water;

s7, rough rolling;

s8, finish rolling, wherein the start temperature of the finish rolling is controlled to be 1020 +/-20 ℃, and the finish rolling temperature is controlled to be 820-;

s9, coiling, wherein the coiling temperature, namely the laminar flow outlet temperature, is mainly used for cooling and controlling the strip steel at the outlet of the finishing mill by a laminar flow cooling device; the rapid cooling can refine grains and improve the surface quality of the strip steel, but the low coiling temperature is easy to cause residual stress and loose coiling after the strip steel is coiled, the high coiling temperature is unfavorable for the texture performance and the surface quality, the outlet temperature of the control layer is controlled at 580-630 ℃, and the cooling mode adopts continuous rapid cooling of the front section after rolling.

Example 2

The special steel for the automobile wheel comprises the following chemical components: c: 0.09%, Mn: 0.70%, P: 0.015%, S: 0.012%, Als: 0.040%, Ti: 0.020%, Nb: 0.015% and the balance of Fe and inevitable impurity elements.

The production process comprises the following steps:

s2, smelting in a converter;

s3, LF refining;

s4, continuous casting;

s5, heating for 180min, and controlling the temperature of furnace gas of a soaking section to be 1200 +/-20 ℃;

s6, descaling by high-pressure water;

s7, rough rolling;

s9, coiling, controlling the temperature of the outlet of the control layer at 580-630 ℃, and adopting continuous and rapid cooling of the front section after rolling in a cooling mode.

Example 3

The special steel for the automobile wheel comprises the following chemical components: c: 0.05%, Mn: 0.85%, P: 0.005%, S: 0.008%, Als: 0.020%, Ti: 0.015%, Nb: 0.008% and the balance of Fe and inevitable impurity elements.

The production process comprises the following steps:

s2, smelting in a converter;

s3, LF refining;

s4, continuous casting;

s5, heating for 120min, and controlling the temperature of furnace gas of a soaking section to be 1200 +/-20 ℃;

s6, descaling by high-pressure water;

s7, rough rolling;

Example 4

The special steel for the automobile wheel comprises the following chemical components: c: 0.06%, Mn: 0.80%, P: 0.003%, S: 0.007%, Als: 0.032%, Ti: 0.018%, Nb: 0.011 percent and the balance of Fe and inevitable impurity elements.

The production process comprises the following steps:

s2, smelting in a converter;

s3, LF refining;

s4, continuous casting;

s6, descaling by high-pressure water;

s7, rough rolling;

Experimental example 1

Continuous cooling phase change and structure evolution laws of the thin slab continuous casting billets in the wheel steels of examples 1 to 4 were performed by using a Gleeble-1500 heat/force simulation experiment machine and an optical microscope.

FIG. 1 is a static CCT curve of the steel of example 1, and FIG. 2 is a dynamic CCT curve of the steel of example 1. Other embodiments have similar results and are omitted here.

The phase change area of the CCT curve under the undeformed and deformed conditions is divided into two parts: in a high-temperature transformation zone, phase transformation products are pro-eutectoid ferrite (F) and a small amount of pearlite (P), the phase transformation intervals under the undeformed condition are mostly between 530 ℃ and 765 ℃, and the phase transformation intervals under the deformed condition are mostly between 560 ℃ and 795 ℃; in the medium-temperature transformation zone, the phase transformation product is a bainite structure, the phase transformation temperature range of the bainite under the undeformed condition is 460-590 ℃, and the phase transformation temperature range of the bainite under the deformed condition is 480-610 ℃.

It can also be seen from FIGS. 1-2 that the gamma → alpha transition temperature decreases after deformation as the cooling rate increases. One is that since the tissue is in an unstable high free energy state after deformation, there is a tendency to recover toward a state of lower free energy before deformation, i.e., phase transformation occurs more easily. The temperature range of the gamma + alpha two-phase region of example 1 is between 70 and 90 ℃ and is significantly narrower than the transition range of continuous cooling during static transition.

The microstructure of the undeformed and deformed austenite of the steel material of example 1 at different cooling rates is shown in fig. 3, (a) ν is 0.5 ℃/s; (b) v is 15 ℃/s; (c) nu is 30 ℃/s.

In the cooling speed range (0.5-40 ℃/s) of the experiment, the microstructure of the experimental steel mainly comprises pro-eutectoid ferrite, pearlite and bainite. When the cooling speed is low, the pro-eutectoid ferrite exists in the structure of the experimental steel, when the cooling speed is increased to a certain degree, a bainite structure begins to appear in the steel, and the critical cooling speeds of the bainite of the experimental steel under the non-deformation condition and the deformation condition are respectively 5 ℃/s and 10 ℃/s. As the cooling rate increases, the content of ferrite and pearlite in the structure gradually decreases, ferrite grains become finer, and the content of bainite gradually increases.

Experimental example 2

No. 1 the steel material obtained by the method described in example 1, No. 2 is different from the method described in example 1 in the following table, and the other points are the same.

The surface quality of the steel materials prepared in the

numbers

1 and 2 is shown in fig. 4 and 5, respectively, and red iron scale appears on the surface of fig. 5. Sampling is carried out on the steel coil with the number 1 in the direction perpendicular to the rolling direction, the cross section is ground into a metallographic sample, the appearance and the components of the iron oxide scale are observed on a scanning electron microscope, and the detection component result of the scanning electron microscope is shown in the following table.

FIG. 6 is a scanning electron micrograph of steel product No. 1, the upper drawing showing the upper surface of the sample, and the lower drawing showing the lower surface of the sample.

From the analysis of the test results, the iron sheet components of the upper surface and the lower surface of the experimental steel strip are Fe₃O₄And Fe and iron scale are compact, the thickness of the iron scale is obviously reduced compared with that before the experiment, red iron scale on the surface is successfully eliminated, and the wheel steel belt has high surface quality.

Experimental example 3

The wheel steels of examples 1 to 4 were subjected to 180 ° wide cold bending tests in which B was 35, 45, 60, 80mm, d was 0.5a, and d was 0.

FIG. 7 is a drawing of a cold bending test sample of the wheel steel of example 2, and it can be seen that no crack appears in the test sample, and the product is qualified. The other examples also did not show cracks, thereby indicating that the wheel steel has good cold bending properties.

Experimental example 4

The following table shows the results of gas content detection in the steels of examples 1-4, which are lower in gas content and pure in steel quality, and lay a good foundation for obtaining good cold-forming properties.

Sample (I)	O/ppm	N/ppm
			Example 1	32	45
Example 2	28	46
			Example 3	30	44
Example 4	31	48

Experimental example 5

The metallographic structure of examples 1 to 4 was observed by a metallographic microscope to be fine ferrite and a small amount of fine lamellar pearlite, and no distinct banded structure was observed, and fig. 8 is a photograph of the microstructure of example 3.

Experimental example 6

The steel for wheel of examples 1 to 4 was subjected to the flash weldability test:

flashing: the uneven surface, dirt and oxide of the workpiece are burnt and adjusted;

preheating: heating the surface of the workpiece by adopting multiple short circuits;

flash burning: continuing to heat the workpiece to prepare for upsetting;

upsetting: the workpiece is rapidly fed under a certain upsetting pressure, so that the workpiece interface gap is rapidly closed, and the end surface liquid metal and the oxidized slag are rapidly extruded.

In example 4, the metallographic structure of the welded joint is as shown in fig. 9, and the tensile test samples were cut out from the welded plate material of example 4, and the test results are as shown in the table below. The super steel has good welding performance and can completely ensure the strength of a heat affected zone.

The steel material of example 4 was subjected to a hardness test in a direction perpendicular to the weld bead direction, and a hardness profile 10 was obtained. The flash welding steel plate is not softened, so that necking cracking is not generated at a welding position when the rim is subjected to diameter expansion deformation, a hardened structure is not generated after the steel plate is welded, the hardness difference between a welding seam and a heat affected zone does not exceed 45HV5, and deformation cracking is not generated during roll forming, which shows that Yuhua steel produced wheel steel has excellent welding performance.

The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The special steel for the wheel with high extending flange performance and fatigue resistance is characterized by comprising the following chemical components in percentage by weight: c: 0.05% -0.09%, Mn: 0.70% -0.85%, P: less than or equal to 0.015 percent, S: less than or equal to 0.012 percent, Als: 0.020% -0.040%, Ti: 0.015% -0.020%, Nb: 0.008% -0.015% and the balance of Fe and inevitable impurity elements.

2. The special steel for the wheel with high extending flange performance and fatigue resistance as claimed in claim 1, wherein the chemical components in percentage by weight are as follows: c: 0.07%, Mn: 0.79%, P: 0.012%, S: 0.008%, Als: 0.024%, Ti: 0.017%, Nb: 0.010% and the balance of Fe and inevitable impurity elements.

3. A process for producing the high stretch flange performance and fatigue resistance steel for vehicle wheels according to claim 1 or 2, comprising molten iron pretreatment desulfurization, converter smelting, LF refining, continuous casting, heating, high-pressure water descaling, rough rolling, finish rolling, and coiling.

4. The production process of the special steel for the wheel as claimed in claim 3, wherein the heating time is 120-180 min, and the temperature of furnace gas in a soaking section is 1200 +/-20 ℃.

5. The production process of the steel special for the wheel according to claim 3, wherein the finish rolling temperature is 820-850 ℃.

6. The production process of the wheel-dedicated steel according to claim 3, wherein the laminar flow outlet temperature is 580-630 ℃ during laminar flow cooling.