KR102406078B1 - Steel for stabilizer with excellent corrosion resistance, stabilizer using the same, and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a steel material for a stabilizer having excellent corrosion resistance, a stabilizer using the same, and a method for manufacturing the same, and more particularly, it proposes an austenite stabilization index for controlling the residual austenite ratio in the microstructure of the steel, and The present invention relates to a steel material for a stabilizer with improved strength and excellent corrosion resistance by shot peening, a stabilizer using the same, and a method for manufacturing the same.

Description

A steel material for a stabilizer with excellent corrosion resistance, a stabilizer using the same, and a method for manufacturing the same. {STEEL FOR STABILIZER WITH EXCELLENT CORROSION RESISTANCE, STABILIZER USING THE SAME, AND MANUFACTURING METHOD THEREOF}

The present invention relates to a steel material for a stabilizer having excellent corrosion resistance, a stabilizer using the same, and a method for manufacturing the same, and more particularly, it proposes an austenite stabilization index for controlling the residual austenite ratio in the microstructure of the steel, and The present invention relates to a steel material for a stabilizer with improved strength and excellent corrosion resistance by shot peening, a stabilizer using the same, and a method for manufacturing the same.

The present invention relates to a solid material for a stabilizer bar in a vehicle suspension system. The stabilizer bar is a kind of torsion bar spring, which is an important part that affects the NVH performance of a car.

Recently, as the weight of the vehicle increases, the load applied to the stabilizer bar is gradually increasing. In the case of the stabilizer bar, it is a part that is very sensitive to interference with peripheral parts. will occur In addition, in the case of a stabilizer bar, it is a part that is directly exposed to the outside and is easily exposed to a corrosive environment.

The conventional solid stabilizer bar material is generally SUP9D, which has a tensile strength of 1300 MPa. After that, the situation is that the shot peening is performed twice. In the case of existing materials, as shot peening is performed twice to secure material strength, there is a problem in that the process time increases and the cost rises.

In another prior art, in order to secure strength, there are cases in which the strength is secured by reducing the tempering temperature in the heat treatment step. There is a problem that may cause breakage. In addition, when the painting is peeled off by gravel or the like, there is a problem in that the possibility of damage due to corrosion may increase.

Japanese Patent Laid-Open No. 2006-089783 (2006.04.06)

The present invention has been devised to solve the above problems, and proposes an austenite stabilization index for controlling the residual austenite ratio in the microstructure of steel for stabilizers, and improves strength and corrosion resistance by performing shot peening on the surface An object of the present invention is to provide an excellent steel material for a stabilizer, a stabilizer using the same, and a method for manufacturing the same.

The method of manufacturing a stabilizer having excellent corrosion resistance according to an embodiment of the present invention, (a) by weight, C: 0.50 to 0.54%, Si: 0.15 to 0.35%, Mn: 1.50 to 1.70%, Cu: 0.10 to 0.30% , Cr: 0.80 to 0.90%, Ni: 0.20 to 0.30%, Mo: 0.10 to 0.30%, Ti: 0.03 to 0.06%, Sn: heating the steel containing 0.10 to 0.30%; (b) hot forming into a stabilizer shape; (c) a heat treatment step of tempering after quenching; may be included.

In addition, the content of Mn, Ni, and Mo of the steel is austenite according to the following Equation 1

It may be characterized in that the stabilization index A value is determined within a range of greater than 3.3 and less than 5.6.

[Equation 1]

A=1.2*[Mn]+5*{[Ni]+[Mo]} ([ ] is the weight % of each component)

In addition, the residual austenite in the microstructure after the heat treatment in step (c) may be characterized in that the area ratio is more than 20%, less than 35%.

In addition, the method may further include the step of shot-peening the heat-treated surface of the stabilizer.

In addition, the shot peening may be characterized in that it is performed once.

The steel material for a stabilizer excellent in corrosion resistance according to an embodiment of the present invention is, by weight, C: 0.50 to 0.54%, Si: 0.15 to 0.35%, Mn: 1.50 to 1.70%, Cu: 0.10 to 0.30%, Cr: 0.80 to 0.90%, Ni: 0.20 to 0.30%, Mo: 0.10 to 0.30%, Ti: 0.03 to 0.06%, Sn: 0.10 to 0.30%.

In addition, the microstructured retained austenite may be characterized in that the area ratio is greater than 20% and less than 35%.

In addition, the content of Mn, Ni, and Mo may be characterized in that the austenite stabilization index A value according to Equation 1 is determined within the range of greater than 3.3 and less than 5.6.

[Equation 1]

A=1.2*[Mn]+5*{[Ni]+[Mo]} ([ ] is the weight % of each component)

The stabilizer having excellent corrosion resistance according to the embodiment of the present invention may be manufactured according to the above-described manufacturing method.

In addition, the stabilizer may be characterized in that the tensile strength is 1800Mpa or more, and the elongation is 18% or more.

The present invention proposes an austenite stabilization index, thereby controlling the content of the austenite stabilizing element, and increasing the retained austenite ratio, thereby improving the strength of the steel material for the stabilizer.

In addition, the heat-treated surface of the stabilizer is subjected to shot peening, thereby improving strength and increasing corrosion resistance.

In addition, as the proportion of retained austenite in the microstructure increases, the shot peening process is reduced to one step, thereby reducing process time and cost.

1 is a view showing a stabilizer bar applied to a vehicle;
2 is a photograph showing the austenite ratio in the microstructure according to the austenite stabilization index proposed in the present invention.
Figure 3 is a graph showing the depth of the corrosion pit according to the content of Cu in the present invention.
4 is a graph showing the initial austenite size according to the content of Ti in the present invention.
5 is a graph showing the depth and tensile strength of the corrosion pit according to the content of Sn in the present invention.
Figure 6 is a photograph showing a change in the microstructure according to the shot peening process in the present invention.
7 is a photograph comparing the residual austenite ratio of the existing material (SUP9D) and the developed material according to an embodiment of the present invention.
8 is a flowchart illustrating a method for manufacturing a stabilizer having excellent corrosion resistance according to an embodiment of the present invention.

The terms or words used in the present specification and claims should not be limited to their ordinary or dictionary meanings, and the principle that the inventor may appropriately define the concept of the term in order to best describe his or her invention It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the Therefore, the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and do not represent all the technical spirit of the present invention, so at the time of the present application, various equivalents that can replace them It should be understood that there may be water and variations. In addition, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the gist of the present invention will be omitted. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Table 1 relates to the content of the steel material of the present invention. The steel material for a stabilizer excellent in corrosion resistance according to the present invention has Fe as a main component, C: 0.50 to 0.54%, Si: 0.15 to 0.35%, Mn: 1.50 to 1.70 %, Cu: 0.10 to 0.30%, Cr: 0.80 to 0.90%, Ni: 0.20 to 0.30%, Mo: 0.10 to 0.30%, Ti: 0.03 to 0.06%, Sn: 0.10 to 0.30%. At this time, the content of each component is weight %, and unless otherwise specified, the following percentages also indicate weight %.

ingredient C Si Mn Cu Cr Ni Mo Ti Sn development
(wt%) 0.50 to 0.54 0.15 to 0.35 1.50 to 1.70 0.10 to 0.30 0.80 to 0.90 0.20 to 0.30 0.10 to 0.30 0.03~0.06 0.10 to 0.30

Next, the reason for limiting the content of each component in the present invention will be described.

C: 0.50 to 0.54 wt%

C is one of the main elements determining strength and hardness in special steel, and in the present invention, it is preferably included in an amount of 0.50 to 0.54% by weight. If it is less than 0.50 wt%, the steel of the present invention may have a decrease in strength below the required strength, and if it exceeds 0.54 wt%, brittleness increases and toughness against impact cannot be secured.

Si: 0.15 to 0.35 wt%

Si is a component added to deoxidize and secure strength. The content of Si in the present invention is preferably 0.15 to 0.35% by weight. If the Si content is less than 0.15% by weight, it is difficult to deoxidize and secure strength, and if the Si content exceeds 0.35% by weight, there is a problem that the formability may be deteriorated due to excessive increase in strength.

Mn: 1.50 to 1.70 wt%

Mn lowers the martensite formation temperature and increases the amount of retained austenite produced during Q/T (Quenching/Tempering) heat treatment. It also improves the hardenability and strength of steel. Therefore, the content of Mn in the present invention is preferably 1.50 to 1.70% by weight. If the content of Mn is less than 1.50 wt%, it is difficult to achieve a sufficient amount of retained austenite, and if the content of Mn exceeds 1.70 wt%, there is a problem that may act as a factor impairing the toughness of carbon steel.

Cu: 0.10 to 0.30 wt%

Cu is dissolved in ferrite at room temperature and exhibits a solid solution strengthening effect to increase strength and hardness. In addition, it is possible to significantly improve the corrosion resistance of the steel. In the present invention, Cu is preferably 0.10 to 0.30% by weight. If Cu is less than 0.10% by weight, the effect of increasing strength is small, and when it exceeds 0.30% by weight, the strength is increased, but toughness is lowered and there is no economic effect due to increase in manufacturing cost, which is not preferable.

Cr: 0.80 to 0.90 wt%

Cr improves the mechanical strength of carbon steel and improves corrosion resistance. And the spacing between the layers of pearlite of carbon steel is refined. Therefore, the content of Cr in the present invention is preferably 0.80 to 0.90% by weight. In the present invention, if the content of Cr is less than 0.80 wt%, it is difficult to secure sufficient corrosion resistance, and if the content of Cr exceeds 0.90 wt%, there is a problem that the ductility of carbon steel may be weakened.

Ni: 0.20 to 0.30 wt%

Ni refines the structure of steel and strengthens the matrix because it is also well-dissolved in austenite and ferrite. In addition, since it is an austenite stabilizing element, it increases the amount of retained austenite generated during Q/T heat treatment in combination with Cr. The content of Ni in the present invention is preferably 0.20 to 0.30% by weight. When the content of Ni is less than 0.20% by weight, the austenite stabilization effect is small, and when it is excessively added in excess of 0.30% by weight, the economic effect is reduced by increasing the manufacturing cost.

Mo: 0.10 to 0.30 wt%

Mo increases the hardenability of steel and is an austenite stabilizing element together with Ni.

The content of Mo in the present invention is preferably 0.10 to 0.30% by weight. When the content of Mo is less than 0.10% by weight, the austenite stabilizing effect is small, and when it is excessively added in excess of 0.30% by weight, the economic effect is reduced by increasing the manufacturing cost.

Ti: 0.03 to 0.06 wt%

Ti refines the grains and increases the corrosion resistance of steel. The content of Ti in the present invention is preferably 0.03 to 0.06% by weight. When the content of Ti in the present invention is less than 0.03% by weight, the effect of refining the grains is small, and when it is excessively added in excess of 0.06% by weight, the economic effect is reduced by increasing the manufacturing cost.

Sn: 0.10 to 0.30 wt%

Sn increases the tensile strength and yield strength of steel, reduces elongation and impact value, and improves corrosion resistance. The content of Sn in the present invention is preferably 0.10 to 0.30% by weight. If the content of Sn is less than 0.10% by weight, there is no effect of sufficient strength increase, and conversely, if it is excessively added in excess of 0.30% by weight, there is a problem that causes red-hot brittleness during hot working, tempering brittleness, low-temperature brittleness, and the like.

In addition, the remainder of the steel of the present invention is Fe, and unavoidable impurities may be further included.

In the steel material for a stabilizer having excellent corrosion resistance according to the present invention including these compositional components, it is preferable that the ratio of retained austenite in the microstructure is greater than 20% and less than 35% by area ratio. In order to control the ratio of retained austenite in the microstructure, the present invention proposes an austenite stabilization index A value according to the content of austenite stabilizing elements. In the present invention, the value of A in the following Equation 1 should satisfy the ranges of more than 3.3 and less than 5.6, and it is preferable that the contents of Mn, Ni, and Mo are respectively determined within the range.

[Equation 1]

A=1.2*[Mn]+5*{[Ni]+[Mo]}

In this case, [ ] is the weight% of each component, [Mn]=IF(Mn<1.0,0.5*Mn,IF(Mn<=1.5,1.0*Mn,IF(Mn<=1.7,1.5*Mn,IF(Mn<=1.7,1.5*Mn,IF( Mn>1.7,1.7*Mn)))), [Ni]=IF(Ni<=0.3,1.0*Ni,IF(Ni>0.3,1.1*Ni)), [Mo]=IF(Mo<=0.3, 1.0*Mo,IF(Mo>0.3,1.1*Mo))

The austenite stabilization index A in the present invention is an effective value during quenching/tempering heat treatment after heating the steel including each of the above-described alloy components to the austenite region, and the residual austenite in the microstructure thus generated will be described later. Since there is an effect of increasing strength and toughness as it transforms into processed martensite through shot peening, it is to control the component content of the austenite stabilizing element to obtain adequate retained austenite in the heat treatment step.

The austenite stabilization index A value is preferably greater than 3.3 and less than 5.6, and as shown in Table 2 below, the content of Mn, Ni, and Mo components is preferably adjusted in this range. When the A value is 3.3 or less, the residual austenite after the heat treatment becomes 20% or less in area ratio, so there is no effect of generating sufficient retained austenite to obtain processing-induced martensite. This is because the proportion of retained austenite in the microstructure is 35% or more in terms of area, so there is a problem in that the deformation and distortion of the material increases due to the increase in volume during the transformation to processing-induced martensite during shot peening.

division C Si Mn Cu Cr Ni Mo Ti Austenite stabilization index [A] Residual austenite amount after Q/T heat treatment (%) Existing Goods (SUP9D) 0.58 0.25 0.85 - 0.85 - - - 0.51 5 Development material (Example) 0.52 0.25 1.6 0.2 0.85 0.25 0.2 0.04 5.13 30 Comparative Example 1 0.52 0.25 0.85 0.2 0.85 0.25 0.2 0.04 2.76 20 Comparative Example 2 0.52 0.25 1.5 0.2 0.85 - - 0.04 1.8 18 Comparative Example 3 0.52 0.25 1.75 0.2 0.85 0.3 0.3 0.04 8.1 -

Table 2 shows the austenite stabilization index according to each Example and Comparative Example, and the residual austenite ratio in the microstructure after quenching and tempering heat treatment as an area ratio. Looking at the existing material (SUP9D), the developed material (Example), and Comparative Examples 1 and 2, when only Mn is added or when only Ni and Mo are added, the austenite stabilization index is at a maximum of 2.7, which is less than the standard value of 3.3. could check In the case of Mn, when added in an amount of 1.7 wt% or more, the toughness of the material deteriorates rapidly, so it should be managed at 1.7 or less. should be

In addition, in the present invention, Cu, Ti, and Sn were added to improve corrosion resistance, and as shown in FIGS. 3 and 4, Cu is 0.1 to 0.3% to improve corrosion resistance by suppressing corrosion pits on the surface of the material. can be added. As shown in FIGS. 4 and 5, Ti may be added in an amount of 0.03 to 0.06% to prevent coarsening of the initial austenite. As shown in FIGS. 5 and 6, Sn may be added in an amount of 0.1 to 0.3% to prevent corrosion by forming an oxide film of SnO2 on the surface. However, in the case of Sn, as can be seen from Table 6, the corrosion prevention effect is improved when 0.4% or more is added, but there is a problem in that physical properties are deteriorated due to a marked decrease in tensile strength, so the amount is preferably limited to 0.3%. do.

Next, a stabilizer excellent in corrosion resistance and a manufacturing method thereof according to an embodiment of the present invention will be described.

The stabilizer and its manufacturing method in the present invention are manufactured by applying the above-described steel material for the stabilizer. Preferably (a) in wt%, C: 0.50 to 0.54%, Si: 0.15 to 0.35%, Mn: 1.50 to 1.70%, Cu: 0.10 to 0.30%, Cr: 0.80 to 0.90%, Ni: 0.20 to 0.30% %, Mo: 0.10 to 0.30%, Ti: 0.03 to 0.06%, Sn: heating the steel containing 0.10 to 0.30% (S100); (b) hot forming into a stabilizer shape (S200); (c) a heat treatment step (S300) of tempering after quenching; may be included.

In addition, the step of shot-peening the surface of the stabilizer that has undergone the heat treatment step (S400) and the step of painting (S500) may be further included.

More specifically, the steel material having the above composition is heated to the austenite region. Thereafter, hot working is performed in the shape of a predetermined stabilizer. The processed stabilizer is quenched by quenching with water or oil, and then subjected to a tempering process to relieve stress. However, in the present invention, as described above, the austenite stabilizing elements Mn, Ni, Mo that have the austenite stabilization index A value in the range of more than 3.3 and less than 5.6, respectively, are 1.50 to 1.70%, 0.20 to 0.30%, 0.10 to By adding 0.30%, retained austenite of more than 20% and less than 35% in area ratio along with martensite was secured.

As shown in Fig. 2 (a), in the case of the existing material, as a result of adding only Mn to 0.85%, the austenite stabilization index A value was 0.51, and the residual austenite ratio (area ratio of the white part) after heat treatment was 5% It was confirmed that only .

On the other hand, FIG. 2(b) shows that by adding 1.6% of Mn, 0.25% of Ni, and 0.2% of Mo according to an embodiment of the present invention, A value of 5.13 is obtained, and the residual austenite ratio in the microstructure after heat treatment It can be confirmed that sufficient processing organic martensite can be obtained with 30% of this (area ratio of the white part). Conversely, in the case of FIG. 2(c), it can be seen that the retained austenite ratio (area ratio of the white part) is 40% when the A value is 6.0 out of the range of the present invention. In this case, there is a problem in that deformation and distortion of the material occur during shot peening later.

As described above, it is preferable to further include the step of shot peening on the surface of the stabilizer after the heat treatment step. In the present invention, the austenite remaining in the microstructure after the heat treatment step is meta-safe and is transformed into processing-induced martensite when subjected to external deformation. At this time, when the transformation occurs by processing, the work hardening index is high and the necking resistance is increased, and the compressive residual stress by shot peening is generated on the surface, which is uniform and fatigue generated on the surface by the action of repeated tension. Against this, the fatigue strength and fatigue life of parts are improved.

For such a shot peening process, as described above, in the prior art, since the retained austenite ratio was insufficient at 5%, a two-stage shot peening process was required to secure sufficient strength. However, in the embodiment of the present invention, as described above, the retained austenite after heat treatment is sufficiently secured to 30%, and accordingly, even if the shot peening process is performed only once, sufficient strength is obtained while transforming into processing-induced martensite according to processing. It has the effect of securing the strength improvement and excellent corrosion resistance by the residual compressive stress on the surface. As a result, there is an effect of reducing the time and cost of the shot peening process by reducing the shot peening process to one time compared to the prior art.

In an embodiment of the present invention, C: 0.52%, Si: 0.25%, Mn: 1.6%, Cu: 0.2%, Cr: 0.85%, Ni: 0.25%, Mo: 0.2%, Ti: 0.04%, After heating to 950° C., quenching, tempering at 500° C., followed by slow cooling, the amount of retained austenite in the microstructure and tensile strength elongation were measured, and the results are shown in Table 3. In the case of the existing material, as shown in FIG. 7 (a), the ratio of retained austenite is 5%, but in the embodiment of the present invention, as shown in FIG. 7 (b), it is confirmed that 30% of retained austenite is generated. In the example, by securing a tensile strength of 1800 Mpa and an elongation of 18%, the effect of an improvement in tensile strength of about 40% and an improvement of an elongation of about 50% compared to the conventional material (SUP9D) was confirmed. In the case of the existing material, as shown in FIG. 7 (a), the ratio of retained austenite is 5%, but in the embodiment of the present invention, as shown in FIG. 7 (b), it is confirmed that 30% of retained austenite is generated. did

steel grade Tensile strength (MPa) Elongation (%) Residual austenite content (%) Existing Goods (SUP9D) 1,300 12 5 Development material (Example) 1,800 18 30

In FIG. 6, 30% of retained austenite was secured in the steel according to the embodiment of the present invention in FIG.

division chemical composition Pit Depth(㎛) Difference (μm) #One Remaining ingredients (Cu not added) 520 - #2 0.1Cu + rest of the ingredients 350 -170 #3 0.2Cu + rest of the ingredients 250 -100 #4 0.3Cu + rest of the ingredients 190 -60 #5 0.4Cu + rest of the ingredients 160 -30 #6 0.5Cu + rest of the ingredients 150 -10

division chemical composition Prior austenite grain size(㎛) note #One Remaining ingredients (Ti not added) 7 size large #2 0.01Ti + rest of the ingredients 5 Effect ○ #3 0.03Ti + rest of the ingredients 3~2 Effect ○ #4 0.06Ti + rest of the ingredients 2-1 Effect ○ #5 0.08Ti + rest of the ingredients ↑ effect × #6 0.10 Ti + rest of the ingredients ↑ effect ×

division chemical composition Pit Depth(㎛) Difference (μm) Tensile strength (MPa) #One Remaining ingredients (Sn not added) 520 - 1830 #2 0.1Sn+remaining ingredients 350 -170 1825 #3 0.2Sn+remaining ingredients 250 -100 1810 #4 0.3Sn+remaining components 190 -60 1800 #5 0.4Sn+remaining ingredients 160 -30 1630 #6 0.5Sn+remaining ingredients 150 -10 1440

The above-described embodiment is only a preferred embodiment that allows those of ordinary skill in the art (hereinafter referred to as 'person of ordinary skill in the art') to easily practice the present invention, and the above-described embodiment and the accompanying drawings Since it is not limited to, the scope of the present invention is not limited thereto. Accordingly, it will be apparent to those skilled in the art that various substitutions, modifications, and changes are possible within the scope of the present invention, and it is apparent that parts easily changeable by those skilled in the art are also included in the scope of the present invention. .

Claims (10)

(a) in wt%, C: 0.50 to 0.54%, Si: 0.15 to 0.35%, Mn: 1.50 to 1.70%, Cu: 0.10 to 0.30%, Cr: 0.80 to 0.90%, Ni: 0.20 to 0.30%, Mo : 0.10 to 0.30%, Ti: 0.03 to 0.06%, Sn: 0.10 to 0.30%, heating the steel containing the remaining iron and unavoidable impurities;
(b) hot forming into a stabilizer shape;
(c) a heat treatment step of tempering after quenching;
The content of Mn, Ni, and Mo of the steel is characterized in that the austenite stabilization index A value according to the following Equation 1 is determined within the range of more than 3.3 and less than 5.6,
After the heat treatment in step (c), the residual austenite in the microstructure is more than 20% and less than 35% by area ratio.
[Equation 1]
A=1.2*[Mn]+5*{[Ni]+[Mo]} ([ ] is the weight % of each component) delete delete The method of claim 1,
The method of manufacturing a stabilizer excellent in corrosion resistance further comprising the step of shot-peening the surface of the heat-treated stabilizer. 5. The method of claim 4,
The method of manufacturing a stabilizer excellent in corrosion resistance, characterized in that the shot peening is performed once. By weight%, C: 0.50 to 0.54%, Si: 0.15 to 0.35%, Mn: 1.50 to 1.70%, Cu: 0.10 to 0.30%, Cr: 0.80 to 0.90%, Ni: 0.20 to 0.30%, Mo: 0.10 to 0.30%, Ti: 0.03 to 0.06%, Sn: 0.10 to 0.30%, including the remaining iron and unavoidable impurities,
Retained austenite in microstructure is characterized in that the area ratio is greater than 20% and less than 35%,
The content of Mn, Ni, Mo is a steel material for a stabilizer with excellent corrosion resistance, characterized in that the austenite stabilization index A value according to the following Equation 1 is determined within the range of more than 3.3 and less than 5.6.
[Equation 1]
A=1.2*[Mn]+5*{[Ni]+[Mo]} ([ ] is the weight % of each component) delete delete A stabilizer with excellent corrosion resistance manufactured according to the manufacturing method of claim 1 or 6. 10. The method of claim 9,
The stabilizer is a stabilizer with excellent corrosion resistance, characterized in that the tensile strength is 1800Mpa or more, and the elongation is 18% or more.

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