KR101239496B1 - Low nickel stainless steel for automobile break and manufacturing method for the same - Google Patents

Abstract

The present invention is a low-nickel stainless steel for automobile brakes that can secure corrosion resistance and formability equivalent to conventional steel sheets (high-nickel stainless steel) using low-nickel stainless steel manufactured by controlling cold reduction rate and annealing temperature, and the manufacture thereof. It is about a method. Low-nickel stainless steel for automobile brakes according to the present invention and a method for manufacturing the same are steps of manufacturing a primary cold rolled steel sheet through hot annealing of the hot rolled steel sheet; Cold rolling the primary cold rolled steel sheet to manufacture a secondary cold rolled steel sheet; And cold rolling the secondary cold rolled steel sheet again to produce a final cold rolled steel sheet. However, the second cold rolled steel sheet is rolled at a reduction ratio of 60% to 80% during each cold rolling, and then annealed at 1030 to 1050 ° C. By this configuration, it is possible to replace the existing expensive steel sheet can reduce the cost.

Low Nickel, Austenitic, Stainless Steel, Corrosion Resistance, Formability, Cold Rolling Rate

Description

Low nickel stainless steel for automobile break and manufacturing method for the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to low nickel stainless steel for automobile brakes and a method for manufacturing the same, and more particularly, to low nickel stainless steel for automobile brakes and a method for manufacturing the same, which can ensure corrosion resistance and formability equivalent to that of high nickel stainless steel. .

In general, a brake mounted on a vehicle is used to decelerate a vehicle while driving or to maintain a stopped or stopped state, and converts kinetic energy during driving into thermal energy by a mechanical friction device to release its frictional heat into the air to perform a braking action. do. According to such a brake structure, it can be divided into drum type brake and disc type brake. Disc type brake is to obtain the braking force by strongly pressing the disk-shaped disc that rotates with the wheel with the pads on both sides. Used for the front axle.

Recently, disc brakes are mainly used as automobile brakes, and the application trend is expected to intensify in the future. Disc brakes are also referred to as pad types, and the brake pads must be repeatedly torqued every time the braking action, and therefore have excellent durability in all parts.

In particular, the brake pad spring is a component that acts as a guide when moving back and forth during pad operation, and durability is particularly important. The pad spring should be secured by the friction pad pad sliding reference plane to increase the adhesion of the guide part, the vehicle vibration absorption and the friction pad pad to prevent the deviation of the operation position and there should be no sticking phenomenon due to the rust of the pad sliding portion.

As such, since the durability and corrosion resistance as a structural material is required, the steel sheet mainly used is STS301 steel, and a steel sheet having high strength through appropriate cold rolling reduction rate is used instead of a simple annealed state to improve durability. The reason why high-nickel stainless steel is used is not only excellent work hardening ability but also a high ductility area, so that moldability can be secured even in a required high strength area.

However, high nickel stainless steel is a burden on the user side in terms of material unit price due to the surge in nickel prices, one of the major alloying elements. Accordingly, there is an urgent need to develop a new alternative steel grade with excellent durability and corrosion resistance that can replace the existing high nickel stainless steel for pad springs of automobile brakes.

Accordingly, an object of the present invention is to ensure the corrosion resistance and formability equivalent to conventional steel sheets (high nickel stainless steel) by using a low nickel stainless steel manufactured by controlling the cold reduction rate and annealing temperature for the pad spring of the automobile brake. The present invention provides a low nickel stainless steel for automobile brakes and a method of manufacturing the same.

Method for producing a low nickel stainless steel for automobile brakes according to the present invention comprises the steps of manufacturing a primary cold rolled steel sheet through hot annealing of the hot rolled steel sheet; Cold rolling the primary cold rolled steel sheet to manufacture a secondary cold rolled steel sheet; And cold rolling the second cold rolled steel sheet again to produce a final cold rolled steel sheet. The cold rolled steel sheet is rolled at a reduction ratio of 60% to 80% during each cold rolling, followed by annealing at 1030 to 1050 ° C. .

In addition, the cold rolling temperature is maintained at 1030 ~ 1050 ℃.

The final cold rolled steel sheet is rolled at a reduction ratio of 20% to 30% after annealing.

In addition, the final cold-rolled steel sheet by weight, Cr: 15 ~ 17, Mn: 8 ~ 10, Ni: 0.2 ~ 0.3, N: 0.2 ~ 0.3, C: 0.02 ~ 0.04, the balance Fe and inevitably contained elements Include.

Low-nickel stainless steel for automobile brakes according to the present invention, in weight percent, Cr: 15-17, Mn: 8-10, Ni: 0.2-0.3, N: 0.2-0.3, C: 0.02-0.04, balance Fe and inevitable And cold rolling is carried out twice at a reduction ratio of 60% to 80%, and after tempering at 1030 ° C to 1050 ° C, temper rolling is further performed at a reduction rate of 20% to 30%. It has a tensile strength of 1100 ~ 1150MPa and a yield strength of 750MPa or more.

As described above, according to the present invention By using cold nickel stainless steel manufactured by controlling cold reduction rate and annealing temperature for pad springs of automobile brakes, it can not only secure corrosion resistance and formability equivalent to that of conventional steel sheets (high nickel stainless steel), but also improve final part performance. By securing the satisfactory physical properties, it is possible to replace the existing expensive steel sheet can reduce the cost.

Hereinafter, with reference to the drawings showing an embodiment of the present invention will be described in detail a low nickel stainless steel for automobile brakes and a method of manufacturing the same according to the present invention.

1 is a schematic view showing a disc brake for an automobile, and FIG. 2 is a perspective view showing a pad spring.

Referring to FIGS. 1 and 2, generally, a disc brake for an automobile includes a caliper body 1, a torque member 2, a cylinder 10, a pair of pad plates 7, a disc rotor 6 and a pair The pad spring 11 of the. The caliper body (1) is fixed to the axle, the torque member (2) is axially coupled to the inside of the caliper body (1) and at the same time the pad plate (7) is inserted into the guide groove (4) to enable the sliding movement Is formed. The cylinder 10 engages with a hole formed at one side of the caliper body 1 and generates hydraulic pressure according to the pressure of the brake pedal, and the pair of pad plates 7 are guide grooves 4 of the torque member 2. Protruding jaw (9) is formed so as to be inserted into the one side is provided with a pair of friction pads (8) in contact with the cylinder (10).

Then, the disc rotor (6) is located between the pad plate (7) is formed a disc plate (5) which is rubbed by the pad plate 7 and rotates together with the wheel of the vehicle, a pair of pad spring 11 ) Has a bent portion (elastic support portion) to be fitted to the guide groove 4 in the state of receiving the projection jaw (9), the engaging projection 105 is fixed to the inside of the torque member (2) is formed inside. .

Particularly, the pad spring 11 is interposed between the torque member 2 and the pad plate 7, and as shown in FIG. 2, an elastic support part for supporting a part of the outer circumferential surface of the pad plate 7 is provided. 101, a two symmetrical vertical portion 100 in which a pad guide portion 102 in which the pad plate 7 is slidably moved, and a caliper fixing portion 103 which is inserted into and fixed to the protrusion 3 of the caliper are sequentially formed. It is connected by the connection part 200.

Resilient support 101 is a protruding shape to form a suitable curvature so that the end portion can cover the edge of the pad plate (7), the pad guide portion 102 and the caliper fixing portion 103 share one side. In addition, the pad guide portion 102 and the caliper fixing portion 103 are formed with guide protrusions 104 for facilitating sliding movement and assembly of the pad plate 7, and the elastic support portion 101 or the caliper fixing portion ( The inside of the 103 is a projection protrusion 105 is formed.

The pad spring 11 according to the present invention is contained in weight percent of Cr: 15 to 17, Mn: 8 to 10, Ni: 0.2 to 0.3, N: 0.2 to 0.3, C: 0.02 to 0.04, balance Fe and inevitably. Low nickel stainless steel containing the element to be. It is manufactured by maintaining the cold reduction rate at 60% to 80% during cold rolling to control the spring characteristics and durability, and controlling the annealing temperature to 1030 ~ 1050 ℃. As a result, corrosion resistance and formability equivalent to those of existing steel sheets (high nickel stainless steel) can be secured, and physical properties satisfying final part performance can be secured. The cost can be reduced by lowering the nickel content in the existing expensive steel sheet, it is rich in work hardening characteristics and ductility, and can satisfy the fatigue characteristics as a pad spring.

Low-nickel stainless steel used in the present invention is a high grade stainless steel to reduce the expensive Ni content, and instead increase the low Mn content.

Hereinafter, the composition range of the present invention and the reason for limitation thereof will be described in more detail.

If Cr is low in content, the corrosion resistance is lowered. If the content is too high, the corrosion resistance is improved, but the strength is high and the elongation is low, which lowers the workability. Therefore, the content is limited to 15 to 17%.

Since Mn is an essential element for increasing the strength and stabilizing the austenite phase, 8% or more of Mn is added. However, Mn is limited to 10% or less because MnS elutes to lower pitting resistance.

Ni improves the mechanical properties such as ductility and impact energy, but when the addition amount exceeds 4.0%, the addition effect is saturated. Therefore, it is preferable to limit the addition amount of Ni to 0.2 to 0.3% in consideration of economic aspects. .

If N is excessive, the lower the lower limit is 0.3% because the lower the better, the excessive limit leads to an increase in refining cost, so the lower limit is limited to 0.2%.

C suppresses the formation of ε (epsilon) -martensite and increases the stability of austenite even when the lamination defect energy is increased, and is added at least 0.02%, and when the content is more than 0.04%, the lamination defect energy is too high. It is preferable to limit the content of carbon to 0.02 to 0.04% or less since the effect of twinning does not occur and carbides are excessively precipitated beyond the austenite phase solid solution limit.

The following describes the manufacturing conditions of the present invention and the reason for the limitation thereof.

In the present invention, after cold-rolling the steel sheet twice at a reduction ratio of 60% to 80%, annealing at 1030 ℃ to 1050 ℃ and then tempered rolling at a reduction ratio of 20% to 30% to the final crude pressure Manufactured by soft material.

Here, when the cold rolling rate is less than 60%, there is a problem that the number of cold rolling should be added to reach the final target gauge (Gauge), and if it exceeds 80%, the rolling equipment according to the increased rolling amount by high strength steel There is a problem with the limitations.

In addition, when annealing at less than 1030 ℃, there is a problem that the decomposition of carbonitride is insufficient to cause corrosion resistance, and when annealing above 1050 ℃, grain size growth is excessive to cause soft nitriding There is a concern that the pad spring strength specification may not be satisfied and the orange peel phenomenon may be intensified due to coarse grain size at the bending part when manufacturing the pad spring stamping.

In addition, if the rolling reduction ratio during temper rolling after two cold rolling is less than 20%, there is a problem that the pad spring strength spec is not satisfied, and when it exceeds 30%, the pad spring elongation spec is not satisfied. .

In order to confirm whether the final steel sheet of low nickel stainless steel manufactured through such a composition range and manufacturing conditions satisfies the required characteristics of the pad spring, various performance and durability tests are required and can be confirmed through the following examples.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example)

The present inventors compared the mechanical properties and formability of the STS204M steel sheet and the STS301L steel sheet in the annealed state in terms of securing durability and strength of low nickel stainless steel as an automobile structural material.

3 is a graph showing a comparison of the mechanical properties of the STS204M steel sheet used in the present invention and the existing STS301L steel sheet.

Referring to Figure 3, it can be seen that the STS204M steel sheet of the present invention is superior in strength and elongation of about 10% or more compared to the existing STS301L. For this reason, first, when the nitrogen content of the STS204M alloy element is deformed to more than 2000ppm solid solution strengthening is activated can lead to a sharp increase in strength from the initial deformation. In addition, since STS204M has higher phase stability than STS301L, phase transformation due to deformation occurs more consistently, thus showing excellent characteristics in terms of ductility.

division Thickness (mm) Width (mm) Length (mm) Weight loss rate
(mg) Immersion time
(hr) Corrosion rate
(g / ㎡hr) 204M 1.91 24.78 49.72 34.48 6 2.09 24 3.20 301L 1.82 24.80 49.70 50.19 6 3.06 24 4.93

Table 1 evaluates the corrosion resistance of STS204M, and it can be seen that the corrosion resistance is superior to STS301L when immersed in 6% FeCl3 solution. This confirms that the requirement for preventing the sliding of the pad sliding part, which is a required characteristic of the brake pad spring component, is not disadvantageous compared to STS301L. In other words, the immersion time was tested for 6 hours and 24 hours. In the case of STS204M, the corrosion rates were 2.09 g / m 2 hr and 3.20 g / m 2 hr, respectively. In the case of STS301L, the corrosion rates were 3.06 g / m 2 hr and 4.93 g / m, respectively. It can be seen that m 2 hr is higher than STS204M.

division Reduction rate
(%) Yield strength
(Kg / mm2) The tensile strength
(Kg / mm2) Elongation
(%) Lanford Index (R) Marten
Fraction 204M 0 38 80 53.8 0.87 0 10 65 99 35 0.81 1.1 20 81 116 25.4 0.78 7.8 30 102 134 19 - 21.5 301L 0 34.5 73.7 46.5 0.94 0.44 10 55 85 35 0.77 1.4 20 73 98 27 0.73 7.6 30 94 111 16 - 22.4

Table 2 shows the change in mechanical properties of STS204M and STS301L according to the cold rolling rate change. In relation to the role of the actual repeating guide (Guide), an important characteristic required for the pad spring, the cold reduction rate was changed to increase the spring coefficient and to improve the durability, and the values as shown in [Table 2] were measured. As can be seen in [Table 2], it can be seen that STS204M appears to have a greater work hardening due to an increase in reduction ratio compared to STS301L. That is, as the reduction ratio of STS204M increases, the yield strength and tensile strength of STS301L increase gradually, and the elongation decreases gradually, thereby improving work hardening characteristics.

In the pad spring processing having the shape of FIG. 2 of the present invention, in the 90 ° bending region, when the grain size of the steel sheet is too large, a surface roughness called orange peel may appear. In order to prevent this, in the present invention, the hot rolled steel sheet is cold rolled twice at a reduction ratio of 60% to 80%, and then subjected to annealing at 1030 ° C to 1050 ° C to set cold rolling conditions such that an average particle size is 20 μm or less. It was.

4 is a photograph showing the particle size of the surface according to the material processing temperature.

Referring to FIG. 4, when the steel sheet was processed at annealing temperature of 1040 ° C. according to the present invention, the grain size was not coarsened, but when the steel sheet was processed at 1070 ° C. and 1100 ° C. outside the annealing temperature range of the present invention, the particles were grained. It can be seen that is not suitable as a material of the pad spring is coarse.

5 is a flow chart showing the manufacturing process of the raw material according to the present invention.

The pad spring parts may show a slight difference depending on the type of vehicle, but most of the thickness of the steel sheet is about 0.4 to 0.5 mm in the present invention. Referring to FIG. Examine the manufacturing process of steel sheet.

The thickness of the primary cold rolled steel sheet through primary cold rolling, which has a rolling reduction ratio of 60% to 80%, based on the final thickness of the steel sheet (0.4 mm) based on the electric furnace-refining furnace-component adjustment-continuous casting, which is a general manufacturing process. To 1.4 mm. Thereafter, the thickness of the secondary cold rolled steel sheet is 0.47 mm through secondary cold rolling having the primary cold rolled steel sheet having a reduction ratio of 60% to 80%. After annealing, the annealing temperature is 1030 ℃ to 1050 ℃, the average particle size of the cold rolled steel sheet thus prepared is 20㎛ or less. Thereafter, the secondary cold rolled steel sheet is subjected to temper rolling at a reduction ratio of 20% to 30% to produce a final temper rolled material (0.39 mm). Tensile strength of the final rough rolled material is 1100 ~ 1150MPa, yield strength is 750MPa or more, elongation is 18% or more, hardness is 370 ~ 380.

division 204M, 0.39㎜ Physical Properties Final cold reduction rate Yield strength (Mpa) 1100
22% Tensile Strength (Mpa) 1170 Elongation (%) 24 Hardness (Hv) 380

By controlling the final cold rolling rate to 20% to 30% by using a thin cold rolled steel sheet obtained through such a process, the physical properties satisfying the durability of the pad spring can be secured as shown in the example of [Table 3]. Could.

division Test result Remarks Performance characteristic Airtight performance pass Hydraulic 70bar Drag performance pass After applying hydraulic 70bar Sliding performance pass Sliding direction sliding resistance Durability High pressure durability pass More than 100,000 times under normal temperature and pressure Vibration durability pass More than 5 million times

Table 4 shows the results of the performance and durability characteristics of the steel sheet developed by the brake pad spring through the present invention. It can be seen that the physical properties of the finally secured steel sheet satisfies the pad spring performance characteristics, and in the case of STS204M having the optimum steel sheet conditions, all the characteristics are satisfied. This means that the STS204M development steel of the present invention can secure suitable physical properties for automobile brake pad springs, and that an appropriate area exists.

As described above, according to the present invention, by using the low-nickel stainless steel manufactured by controlling the cold reduction rate and annealing temperature, as well as to ensure the corrosion resistance and formability equivalent to the existing steel sheet (high nickel stainless steel) as well as the final part By securing the physical properties satisfying the performance, it is possible to replace the existing expensive steel sheet can reduce the cost.

Although the technical spirit of the present invention has been described in detail according to the above-described preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

1 is a schematic view showing a disc brake for an automobile.

Figure 2 is a perspective view of the pad spring.

Figure 3 is a graph showing the comparison of the mechanical properties of the STS204M steel sheet used in the present invention and the existing STS301L steel sheet.

Figure 4 is a photograph showing the particle size of the surface according to the steel sheet processing temperature.

5 is a flow chart showing a manufacturing process of the steel sheet according to the present invention.

Claims (4)

Manufacturing a primary cold rolled steel sheet through hot annealing of the hot rolled steel sheet; Cold rolling the primary cold rolled steel sheet to manufacture a secondary cold rolled steel sheet; And Cold rolling the second cold rolled steel again to produce a final cold rolled steel sheet; including, After each cold rolling, rolling at a reduction ratio of 60% to 80%, followed by annealing at 1030 to 1050 ° C, The cold rolled steel sheet after the final annealing treatment, the manufacturing method of low nickel stainless steel for automobile brakes to be rolled at a reduction ratio of 20% to 30%. delete The method of claim 1, The cold rolled steel sheet in weight percent, Cr: 15 ~ 17, Mn: 8 ~ 10, Ni: 0.2 ~ 0.3, N: 0.2 ~ 0.3, C: 0.02 ~ 0.04, the balance Fe and inevitably contained elements Method for manufacturing low nickel stainless steel for brakes. % By weight, Cr: 15 to 17, Mn: 8 to 10, Ni: 0.2 to 0.3, N: 0.2 to 0.3, C: 0.02 to 0.04, balance Fe and inevitably contained elements; After cold rolling twice at a reduction ratio of 80% to 80%, annealing at 1030 ° C to 1050 ° C, followed by temper rolling at a reduction rate of 20% to 30% to obtain a tensile strength of 1100 to 1150 MPa or more and 750 MPa or more. Low-nickel stainless steel for automotive brakes with yield strength.

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