KR101030912B1 - Manufacturing Method of steel wheel rim - Google Patents

Abstract

The present invention relates to a method for manufacturing a steel wheel rim. The present invention is carbon (C) 0.18 ~ 0.30wt%, manganese (Mn) 0.5 ~ 2.0wt%, silicon (Si) 0.5wt% or less, sulfur (S) 0.02wt% or less, phosphorus (P): 0.014 wt% or less , Molybdenum (Mo) 0.05 ~ 0.5wt%, Chromium (Cr) 0.1 ~ 0.5wt%, Boron (B) 0.001 ~ 0.01wt%, Steel blanks with alloy composition of remaining iron (Fe) and other unavoidable impurities 880 ~ 970 It is put in a heating furnace at ℃ ℃ and maintained for a set time to obtain a single-phase austenite structure, the austenitic steel sheet blank is rolled through a rolling roll with the upper and lower rolls are arranged symmetrically, and then the roll The formed steel sheet blank is welded at both ends to have a steel wheel rim shape, cooled to room temperature, and then subjected to annealing.

The present invention can secure a high strength and durability of more than 100kg without increasing the thickness of the steel sheet material, which can contribute to fuel economy saving through light weight of the vehicle and can replace expensive aluminum wheel rims, thereby reducing the burden on consumers. There is an advantage.

Steel Wheel Rim, High Strength, Durable, Light Weight

Description

Manufacturing Method of Steel Wheel Rim

The present invention relates to a method for manufacturing a steel wheel rim, and more particularly to a method for manufacturing a steel wheel rim that is fitted to the inside of the automobile tire.

1 is a perspective view showing the appearance of a general steel wheel, Figure 2 is a process chart showing a manufacturing method of a conventional steel wheel rim.

As shown in FIG. 1, a wheel m of a vehicle is composed of a wheel disc m2 that is bolted to a hub, and a wheel rim m1 welded to the outside of the wheel disc m2 to support a tire. do. The wheel (m) serves to directly transfer the driving force and the braking force to the road surface while supporting the weight of the vehicle, the occupant and the luggage together with the tire.

Types of wheels include steel wheels made of steel, aluminum wheels made of aluminum alloys, and magnesium wheels made of magnesium alloys. In recent years, wheels have been replaced by aluminum wheels due to improved fuel efficiency, performance, and aesthetics. .

Among them, aluminum wheel rims have a lower strength than steel wheel rims, but the weight cannot be 1/3 of the steel wheel rims, so that the weight can be reduced by the difference in weight, and various shapes can be manufactured through the casting method.

However, aluminum wheel rims have a disadvantage in that the flange portion of the wheel rims are easily broken due to brittleness, which is inherent in nature, and it is a burden for consumers to use because they are relatively expensive. Accordingly, the general consumer mainly uses a steel wheel rim that is less expensive to manufacture than an aluminum wheel rim without breaking the flange portion, which is a disadvantage of the aluminum wheel rim.

The manufacturing method of the conventional steel wheel rim is as follows.

That is, the steel sheet rim is passed through a rolling roll in which the upper and lower rolls are symmetrically formed to form an appearance of the steel wheel rim. Then, the steel sheet is rolled into a cylindrical shape to interview the corresponding end and then welded to the steel wheel rim. (m) is manufactured.

At this time, the rolling roll is subjected to welding after roll forming the steel sheet material so that the upper roll exerts a force on the lower roll to form flanges on both sides of the steel wheel rim. This manufacturing process, as shown in Figure 2, proceeds to the process of the steel sheet material (s) transfer (S1)-roll forming (S2)-welding (S3)-completion (S4).

However, the above-described conventional techniques have the following problems.

In other words, steel wheel rims are less expensive than aluminum wheel rims and are manufactured through roll forming, which requires less process cost.However, the main material is steel, which is relatively heavy, resulting in higher overall vehicle weight. There is a disadvantage.

Therefore, use of a high strength steel sheet for weight reduction is required. However, when using high strength steel sheet for light weight, due to the formability problem of the steel wheel rim, the high strength steel sheet of more than 60kg is not applicable. As a result, the strength of the final part is low, and the thickness of the steel sheet is increased to secure rigidity and durability, thereby increasing the weight of the entire vehicle.

In addition, the conventional roll forming operation has a problem that the workability is often deteriorated due to the poor processing of the steel wheel rim due to the deformation (Springback) and the bursting phenomenon due to the elongation is reduced.

The present invention is to solve the conventional problems as described above, an object of the present invention is to use steel as the material of the wheel rim, high-strength thermosetting material to enable the light weight of the steel wheel rim without increasing the thickness of the steel sheet material It is to provide a method of manufacturing a steel wheel rim to secure the high strength by applying.

The present invention is to solve the conventional problems as described above, the present invention is carbon (C) 0.18 ~ 0.30wt%, manganese (Mn) 0.5 ~ 2.0wt%, silicon (Si) 0.5wt% or less, sulfur ( S) 0.02 wt% or less, phosphorus (P): 0.014 wt% or less, molybdenum (Mo) 0.05 to 0.5 wt%, chromium (Cr) 0.1 to 0.5 wt%, boron (B) 0.001 to 0.01 wt%, remaining iron ( A steel sheet blank having an alloy composition of Fe) and other unavoidable impurities was put in a heating furnace at 880 to 970 ° C. and maintained for a set time to obtain a single-phase austenite structure. After roll forming through a symmetrically arranged rolling roll, the roll-formed steel sheet blank is welded at both ends to have a steel wheel rim shape, cooled to room temperature, and then subjected to annealing.

The holding time in the furnace is in the range of 3 to 10 minutes.

The steel sheet blank is subjected to both the roll forming and welding within 25 seconds after heating.

The cooling is carried out at a cooling rate of 25 ~ 100 ℃ / s.

The annealing heat treatment is reheated to 450 ~ 550 ℃ to maintain for 20 to 40 minutes, air-cooled to room temperature.

The present invention produces a 'steel wheel rim' that was produced through the conventional roll forming at room temperature through hot roll forming. Therefore, it is possible to secure a high strength of 100kg or more without increasing the thickness of the steel sheet material.

In addition, the 'steel wheel rim' of the present invention is hardly blown and springing phenomenon occurs when forming a high-temperature steel sheet at room temperature as the molding at high temperature.

In addition, the 'steel wheel rim' of the present invention is subjected to annealing heat treatment after forming the hot steel wheel rim to remove the stress inside the material due to hot roll forming, phase transformation to martensite, welding. Therefore, sufficient durability to withstand external forces such as high loads is secured.

Accordingly, the 'steel wheel rim' of the present invention can secure high strength and durability without increasing the thickness of the steel sheet material. Therefore, the fuel economy can be expected to be reduced by reducing the weight of the vehicle.

Hereinafter, a preferred embodiment of the method for manufacturing a steel wheel rim according to the present invention will be described in detail.

Figure 3 is a process chart showing a method of manufacturing a steel wheel rim according to the present invention, Figure 4 is a microscopic tissue photograph showing the structure of the steel wheel rim prepared by the present invention in comparison with the prior art.

According to the present invention, the steel is improved by hardening by adding boron (B), molybdenum (Mo), chromium (Cr), etc. to a high temperature of about 900 ° C. above Ac3 transformation point, and completely austenitizing the steel sheet. In the roll forming process, high-temperature molding into a part shape at one time and martensite through rapid cooling to manufacture high-strength automotive parts.

As is well known, the steel sheet is excellent in ductility when heated to a high temperature compared with the cold-formed steel sheet is excellent in formability and very high strength can greatly contribute to the weight reduction of the automobile.

As shown in Figure 3, the steel wheel rim of the present invention is steel sheet blank (s) heating (S1)-roll forming (S2)-welding (S3)-quenching (S4)-annealing heat treatment (S5)-finished (S6) It is prepared in the order of.

Steel wheel rim of the present invention is carbon (C) 0.18 ~ 0.30wt%, manganese (Mn) 0.5 ~ 2.0wt%, silicon (Si) 0.5wt% or less, sulfur (S) 0.02wt% or less, phosphorus (P): 0.014 wt% or less, molybdenum (Mo) 0.05 ~ 0.5wt%, chromium (Cr) 0.1 ~ 0.5wt%, boron (B) 0.001 ~ 0.01 wt%, the remaining iron (Fe) and other alloy composition of the inevitable impurities.

After the steel sheet is made of steel sheet blank (S1), hot roll molding is performed to process the steel wheel rim (S2). Hot roll forming is carried out by inserting a steel sheet blank in a heating furnace of 880 ~ 970 ° C atmosphere and maintaining it for a set time, and then passing through a rolling roll (not shown, but the steel sheet is transferred to a blank before hot roll forming to blanking). Process is performed.)

The holding time in the furnace is maintained for at least 3 minutes so that the austenite transformation of the steel blank can occur completely. However, if the holding time is excessively long, the scale layer is formed on the surface of both the non-plating and the plating material by the high temperature oxidation, so that the plating layer may be lost or problems such as surface defects such as surface defects may occur during roll forming. Do not.

Then, the hot rolled steel sheet blank becomes a shape in which the steel wheel rims are unfolded, and thus, the ends rolled into a cylindrical shape are welded to form a steel wheel rim shape (S3).

At this time, the steel sheet blank is heated to prevent cooling to a temperature (about 600 ° C.) at which martensite transformation occurs in the air, and then molded after welding within 25 seconds. This is because when the steel sheet blank is exposed to the air, cooling occurs at about 20 ° C. per second, and the formability of the steel sheet blank is lowered due to the lower austenite transformation temperature during hot roll forming.

After the welding is completed, cooling is performed (S4), and the cooling allows the steel wheel rim to have a high strength martensite structure.

Cooling is cooled to room temperature at a cooling rate of 25 ~ 100 ℃ / s. This cooling rate prevents austenite from transforming to pearlite or bainite. That is, if the cooling rate is slower than 25 ℃ / s martensite transformation is difficult due to perlite or bainite transformation, if faster than 100 ℃ / s may cause surface cracks or cracks due to thermal shock. At this time, the cooling time is maintained for 2 to 15 seconds to ensure maximum martensite structure.

After cooling, reheat to 450 ~ 500 ℃ again and heat treatment for 20 to 40 minutes. (S5) After the heat treatment is cooled to room temperature. This heat treatment improves the structure of the steel wheel rim by eliminating tissue unevenness and removing internal stress. In other words, the durability of the degraded material is compensated for by releasing the stress inside the material due to hot roll forming, phase transformation into martensite, and welding.

Since steel wheel rims are external parts, the parts hardened by martensite are softened by additional heat treatment to secure high durability. The final structure of the steel wheel rim thus becomes a tempered martensite structure.

The heat treatment temperature is increased to 450 ~ 500 ℃ strength, but more than that sharply decrease the heat treatment is preferably within the above range. If the heat treatment holding time is less than 20 minutes, the effect is insufficient, and if it exceeds 40 minutes, the strength of the steel wheel rim can be significantly lowered.

Hereinafter, the function and content of the alloying elements of the present invention will be described in detail.

Carbon (C) 0.18 ~ 0.30wt%

Carbon (C) is an indispensable element for imparting high strength to the steel sheet. However, in order to improve the heat treatment hardenability of the steel sheet it is necessary to control the appropriate carbon (C) content.

If the content of carbon (C) is less than 0.18wt%, the heat treatment hardenability of the steel is low, and thus the tensile strength through sufficient martensite formation cannot be obtained after the heat treatment. And when the content of carbon (C) is more than 0.30 wt% can secure sufficient tensile strength by improving the heat treatment hardenability, the strength before the heat treatment of the steel is increased, there is a difficulty in forming the product.

Manganese (Mn) 0.5 ~ 2.0wt%

Manganese (Mn) has a function to increase the hardenability of the steel sheet and to secure the strength of the steel sheet after quenching. Manganese must be added 0.5wt% or more to secure tensile strength of 1000MPa or more. However, when added more than 2.0wt% corrosion resistance and weldability is lowered, it is preferable not to add more than 2.0wt%.

Silicon (Si) 0.5wt% or less

Silicon (C) is an element remaining by a deoxidizer for removing oxygen in steel in the steelmaking process, and also has a function of improving quenchability. However, when excessively added, oxides are formed on the surface of the steel sheet, thereby inhibiting plating characteristics and increasing the viscosity of the molten metal in the part manufacturing process, thereby causing problems on the cut surface of the steel sheet. Therefore, the upper limit is limited to 0.5 wt% or less.

Sulfur (S) 0.02wt% or less

Sulfur (S) greatly reduces the weldability of the disk and the rim of the steel sheet by the generation of central segregation, so a trace amount control is required. Therefore, the upper limit thereof is limited to 0.02 wt% or less.

Phosphorus (P): 0.014 wt% or less

Phosphorus (P) is contained in the molten steel about 0.020wt% after the usual dephosphorization process. However, phosphorus deteriorates the hot workability of steel at high temperature, so trace amount control is required to improve the high temperature workability. It is possible to control less than 0.014wt% due to the recent development of steelmaking technology.

Molybdenum (Mo) 0.05 ~ 0.5wt%, Chromium (Cr) 0.1 ~ 0.5wt%

Molybdenum (Mo) and chromium (Cr) can improve the heat treatment hardenability of the steel to increase the toughness of the steel sheet, thereby increasing the impact energy absorption of the automotive member. When molybdenum and chromium are added in an amount less than 0.1 wt%, sufficient heat treatment hardenability cannot be obtained. When molybdenum and chromium are added in excess of 1.0 wt%, the heat treatment hardenability is not improved anymore, so both molybdenum (Mo) and chromium (Cr) It is preferable to design the sum of elements to 0.1 to 1.0 wt%. .

Boron (B) 0.001 ~ 0.01wt%

Boron (B) can greatly improve the heat treatment hardenability of the steel even with the addition of a small amount, it is possible to obtain a product of high tensile strength after heat treatment. Boron should be added more than 0.001wt% to increase the hardenability of the steel sheet. However, it is preferable to limit the upper limit to 0.01 wt% or less since the elongation decreases due to the increase of the solid solution boron, and the boron may diffuse on the surface, thereby degrading the plating property.

In addition to the above-described alloying elements, aluminum (Al), titanium (Ti), etc. may be contained in an amount of 0.1 wt% or less for the purpose of improving the strength.

The present invention includes the components of the alloy steel, the remainder is iron (Fe) and inevitable elements, and the elements contained in accordance with the situation of raw materials, materials, manufacturing facilities, etc. of the inevitable impurities such as nitrogen (N), oxygen (O) Fine incorporation is also allowed.

Hereinafter, the method of manufacturing the above-described steel wheel rim will be described in detail by way of examples.

Table 1 shows the present invention and the conventional alloy design divided into Comparative Examples and Inventive Examples, Table 2 shows the results of the mechanical properties of the steel wheel rim parts manufactured according to the alloy design of Table 1.

(Unit: wt%, balance Fe) division C Si Mn P S Mo Cr B Comparative Example 1 0.059 0.02 0.34 0.012 0.008 0.311 - - Comparative Example 2 0.076 0.195 0.784 0.017 0.007 0.001 - - Comparative Example 3 0.076 0.024 0.935 0.017 0.007 0.044 - - Example 1 0.191 0.214 1.414 0.014 0.008 0.051 0.051 0.002 Example 2 0.224 0.247 1.261 0.014 0.007 0.371 0.371 0.001 Example 3 0.235 0.271 1.881 0.014 0.008 0.074 0.074 0.007

division Tensile Strength (MPa) Yield strength (MPa) Elongation (%) Comparative Example 1 437 298 23.3 Comparative Example 2 464 331 31.1 Comparative Example 3 603 425 22.8 Example 1 1156 894 11.7 Example 2 1188 899 12.3 Example 3 1116 836 12.9

Comparative Example of Table 2 was produced by roll forming and welding a steel sheet blank having the alloy design of Comparative Example of Table 1 at room temperature. And the Example of Table 2 heated the steel sheet blank which has the alloy design of the Example of Table 1 to about 900 degreeC, performed hot roll forming within 25 second, it welded, and cooled to room temperature. Thereafter, annealing was performed at 500 ° C. for 30 minutes, followed by air cooling.

Looking at Table 1 and Table 2, in the case of hot roll forming with the addition of boron (B), molybdenum (Mo), chromium (Cr) components, etc., the ultra-high strength of 1000MPa or more is secured by more than 2.5 times the strength compared to the comparative example You can see that.

In addition, it can be seen that the elongation is also secured by more than 10% durability.

And, looking at the tissue picture of Figure 4, the steel wheel rim of the present invention can be confirmed that the tissue forms a tempered Martensite (Tempered Martensite) structure is secured high strength and toughness. The tempered martensite tissue has a high hardness but lacks toughness, so the toughness does not significantly decrease and the toughness is greatly increased. Therefore, it is suitable for steel wheel rims that require high strength and durability. have.

And, although not shown, the simulation results also secured an application thickness reduction of 30% or more compared to the comparative example.

The hot roll forming performed by the above-described process may be applied to various steel sheets such as hot rolled steel sheet, cold rolled steel sheet, and plated steel sheet.

Within the scope of the basic technical idea of the present invention, many other modifications are possible to those skilled in the art, and the scope of the present invention should be interpreted based on the appended claims. will be.

1 is a perspective view showing the appearance of a typical steel wheel.

Figure 2 is a process diagram showing a method for manufacturing a conventional steel wheel rim.

Figure 3 is a process diagram showing a method for manufacturing a steel wheel rim according to the present invention.

Figure 4 is a microscopic tissue photograph showing the structure of the steel wheel rim prepared by the present invention in comparison with the prior art.

Explanation of symbols on the main parts of the drawings

m1: wheel rim m2: wheel disc

m: wheel

Claims (5)

0.18 to 0.30 wt% of carbon (C), 0.5 to 2.0 wt% of manganese (Mn), 0.5 wt% or less of silicon (Si), 0.02 wt% or less of sulfur (S), phosphorus (P): 0.014 wt% or less, molybdenum ( Mo) 0.05 ~ 0.5wt%, chromium (Cr) 0.1 ~ 0.5wt%, boron (B) 0.001 ~ 0.01wt%, steel sheet blank with alloy composition of remaining iron (Fe) and other unavoidable impurities Into the furnace of 880 ~ 970 ℃ and maintained for a set time to obtain a single-phase austenite structure, After roll forming the austenitic steel sheet blank through a rolling roll in which upper and lower rolls are symmetrically disposed, the roll formed steel sheet blank is welded at both ends to have a steel wheel rim shape, and then cooled to room temperature. Annealing heat treatment, The steel sheet blank is subjected to both the roll forming and welding within 25 seconds after leaving the heating furnace, The cooling method of manufacturing a steel wheel rim, characterized in that carried out at a cooling rate of 25 ~ 100 ℃ / s. The method according to claim 1, Method of manufacturing a steel wheel rim, characterized in that the set time in the heating range is 3 to 10 minutes. delete delete The method according to claim 1 or 2, The annealing heat treatment is reheated to 450 ~ 550 ℃ to maintain for 20 to 40 minutes, the method of manufacturing a steel wheel rim, characterized in that air-cooled to room temperature.

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