JP5307684B2 - Method for manufacturing chassis component having better long-term durability limit and chassis component - Google Patents

Description

  The present invention relates to a method of manufacturing a chassis component having a better long-term durability limit and a chassis component manufactured by such a manufacturing method.

  When manufacturing automotive chassis components, such as chassis torsion sections, not only are there high demands on mechanical properties, including long-term endurance limits of the final product, but also for process and cost optimization. High demands are imposed.

  In the current state of the art, a mechanical method called surface hardening is used to obtain the required periodic strength for the chassis components. Such a method is described, for example, in German Offenlegungsschrift 102004018586. In this case, the surface of the component is hardened by projecting the projection material.

  The disadvantage of this method is that only the surface of the part is cured and the thickness of the cured layer is small. Further, in the case of a part having a complicated structure, the hardening of the surface that has entered inside is troublesome or partially impossible by this method. Further, if the projection is too strong, the surface may be damaged, and there may be a problem in terms of fatigue strength. Furthermore, it has been found that the projection process on relatively thin walls always gives bad results.

  In addition, as a method for producing a high-strength structural part, use of hardened steel and heating, hardening and forming processes of the hardened steel are known. This method is described, for example, in German Offenlegungsschrift 10339119. The disadvantage of this production method is that the structural parts must be molded by cold forming after the curing process has been completed. Therefore, more energy must be input into the cold forming process, and the stress induced by the cold forming increases. In addition, this manufacturing method may require stress relief annealing subsequent to cold forming to remove stresses induced during cold forming.

German Patent Application No. 102004018586 German Patent Application No. 10339119

  The object of the present invention is to simplify the manufacture of chassis components and at the same time to obtain chassis components with a long service life.

  Accordingly, the present invention relates to a method for manufacturing a chassis component in which a semi-finished product is formed by cold forming as viewed from the first viewpoint of the problem. This method is characterized by nitriding a semi-finished product after cold forming.

1 is a process progress diagram of a first embodiment of a method according to the invention. FIG. 4 is a process progress diagram of a second embodiment of the method according to the invention.

  In the present invention, the chassis component is made of steel. The semi-finished product referred to in the present invention means a hollow steel such as a tube or a thin plate. These semi-finished products are given the shape of the final product to be manufactured by pressing, bending or other forming methods in the cold forming process. By nitriding the molded semi-finished product, the surface of the molded semi-finished product is cured. Compared with purely mechanical surface hardening by surface projection such as shot peening, the depth of the hardened layer by surface hardening can be appropriately adjusted in thermochemical treatment, that is, nitriding treatment. This nitriding treatment can be performed in a double chamber type furnace or a continuous heating furnace.

  In the case of nitriding, a basic structure such as a ferrite structure remains in the central portion of the steel semi-finished product. In addition, nitrogen permeation prevents austenite from forming near the surface. A very hard surface compound layer is formed on the surface of the molded semi-finished product (hereinafter referred to as incomplete product) by nitrogen permeation. Under this compound layer, an infiltration zone is formed, where nitrogen is deposited into a basic metal matrix (eg, ferrite metal matrix) to a certain depth. Nitrogen deposited in this solid solution improves the long-term endurance limit of unfinished products. Furthermore, the formation of precipitates in the vicinity of the surface provides wear resistance and extends the service life during cyclic loading. The nitriding process provides a long-term endurance limit (also referred to as a fatigue limit) of the unfinished product that ensures the end product or chassis component lifetime during cyclic loading. Since the surface of the unfinished product is formed with a layer with excellent strength and wear resistance due to nitridation, the strength required for the final product, i.e. As a result of which the demand for material as well as the weight of the chassis components can be reduced.

  Nitriding is usually performed at 400 to 600 ° C. This treatment temperature eliminates stresses induced in the unfinished product during cold forming. Thus, the nitriding process performed in accordance with the present invention replaces the stress relief annealing process that is separately required for cold-formed parts, resulting in a shortened overall manufacturing process and cost optimization. It is. Furthermore, since nitriding is generally performed under vacuum conditions, there is no oxide on the surface of the unfinished product, and there is no need for a process of cleaning and projecting the surface before the coating process. As a result, the entire manufacturing process can be shortened and the cost can be optimized.

  Furthermore, nitriding not only improves the long-term durability limit of the chassis components, but also improves corrosion resistance and creates a wear protection layer.

  In one preferred embodiment of the invention, the raw material of the semi-finished product is steel with a carbon content (C) of 0.30% by weight or less. Thus, it has been found that sufficient surface hardness can be obtained by nitriding even if the carbon content is small. Unlike nitrided steel, which normally has a carbon content of 0.3-0.4% by weight, the method according to the invention makes it possible to produce chassis components that can be processed for automotive applications. For example, a chassis component manufactured in accordance with the present invention can be joined to other components by welding.

  In one preferred embodiment, the semi-finished product is given a final shape by cold forming, i.e. before nitriding. By final shape is meant the shape and dimensions that the chassis component has before being attached to the chassis or joined to other components. This ensures that the surface that will be exposed to mechanical loads in the final product can be cured. Furthermore, since it is not necessary to further mold the surface-cured part, it is not necessary to destroy the surface hardened layer generated by nitriding.

  Nitriding is nitriding mainly by plasma nitriding. In the present invention, nitriding of the molded semi-finished product is performed by gas nitriding or plasma nitriding (also called ion nitriding). However, since the nitriding treatment time can be shortened to several hours, plasma nitriding is prioritized. An excellent advantage of plasma nitriding and gas nitriding is that even a component having a complicated structure can be reliably processed. In particular, in the case of a hollow steel often found in chassis components, the surface entering the inside can be easily hardened, so that the strength of the entire part is improved. No additional processing after nitriding on the surface-hardened part is necessary. Thus, further optimization is achieved compared to methods such as bath nitriding.

  In a further embodiment, a process of projecting the projection material onto at least a part of the surface of the molded semi-finished product after nitriding is added. By subjecting the surface already hardened by nitriding to surface hardening by projection, the compound layer formed at the time of nitriding becomes harder by mechanical hardening. As a result, the service life of the parts is further extended. Furthermore, local intensity | strength raise can be performed appropriately by projecting on a part of surface. In addition, the relatively small surface wrinkles produced by the previous process are removed upon projection onto the molded semi-finished product, thus improving the long-term durability limit.

  The final product after the nitriding treatment is not sent to a further molding process or heat treatment process except for an intensity projection process that is performed in some cases. In other words, no additional heat treatment or mechanical treatment is required. Thereby, the structure (the surface strength and the viscosity of the central part are high) generated in the part at the time of nitriding and the intensity projection to be added depending on the case is reliably maintained. In addition, this manufacturing process requires fewer steps and therefore requires less time, saving time and costs. Further, since there is little or no distortion or deformation during nitriding, a molded semi-finished product to be subjected to nitriding can be made to the dimensions as completed. During cold forming, the various final dimensions of the vehicle can be reliably and easily adjusted within tolerances.

  Microalloy steel and tempered steel can be used as raw materials for semi-finished products. The advantages of these raw materials over nitrided steel are that the manufacturing cost is low and the carbon content is low, so that processing (particularly welding) is possible in the final product state.

  Steel that can be used in the method according to the invention is, for example, tempered steel sold by Bentler AG under the trade name BTR165. This steel used as a raw material has, in addition to iron and contaminants resulting from melting, for example, any one of the three combinations shown in Table 1 in alloy elements (% by weight).

In one embodiment, the semi-finished raw steel consists of (wt%):
Carbon (C): 0.22 to 0.25%
Silicon (Si): 0.20 to 0.30%
Manganese (Mn): 1.20 to 1.40%
Phosphorus (P): 0.020% or less Sulfur (S): 0.010% or less Aluminum (Al): 0.020 to 0.060%
Boron (B): 0.0020 to 0.0035%
Chromium (Cr): 0.10 to 0.20%
Titanium (Ti): 0.020 to 0.050%
Molybdenum (Mo): 0.35% or less Copper (Cu): 0.10% or less Nickel (Ni): 0.30% or less Remaining: Iron and contamination caused by melting

  It has been found that the surface hardness obtained by nitriding these alloys has a long-term durability limit sufficient as a chassis component of an automobile. Furthermore, these steel alloys can be produced at low cost and can be welded because of their low carbon content.

  In a further embodiment, the alloying elements of the raw steel are within the range of the examples in Table 1, but increased by the aluminum content. For example, the aluminum content can be 0.020 to 0.100% by weight. When the aluminum content is increased, the hardness of the nitride layer composed of the compound layer and the permeation layer is further increased, and the wear resistance is further improved.

  In the present invention, it is additionally or alternatively possible to use steel having a vanadium (V) content of 0.100% by weight or less as a raw material. It is particularly preferable to use an alloy in which 0.100% by weight or less of vanadium (V) is added to steel having any composition in Table 1.

As a raw material for producing a semi-finished product, an alloy composed of iron and contaminants resulting from melting and the following alloy elements (% by weight) is also possible.
Carbon (C): 0.02 to 0.14%
Silicon (Si): 0.15% or less Manganese (Mn): 0.15-1.50%
Phosphorus (P): 0.035% or less Sulfur (S): 0.020% or less Aluminum (Al): 0.015-0.060%
Niobium (Nb): 0.020 to 0.120%
Titanium (Ti): 0.100% or less Vanadium (V): 0.100% or less Molybdenum (Mo): 0.10% or less

Further alloys that can be used as raw materials for semi-finished products according to the invention include the following alloying elements (wt%) in addition to iron and contaminants due to melting.
Carbon (C): 0.02 to 0.10%
Silicon (Si): 0.40% or less Manganese (Mn): 0.50 to 1.60%
Phosphorus (P): 0.025% or less Sulfur (S): 0.010% or less Aluminum (Al): 0.020% or more Niobium (Nb): 0.008 to 0.060%
Titanium (Ti): 0.008 to 0.060%
Vanadium (V): 0.008 to 0.060%

  Further, nitride forming elements (Al, Ti, V, Mo, Cr) can be added individually or in combination in a form deviating from the above-described alloy compositions (particularly the last alloy composition listed). .

  The steel alloys that can be used in the method according to the present invention include a low carbon content, appropriate amounts of nitride-forming elements (Al, Ti, V, Mo, Cr), and alloys thereof. It is particularly outstanding in terms of the good formability of steel, the low price of steel, and the availability of raw materials.

  In one embodiment, the semi-finished product is a hollow steel, which is also a particularly thin hollow steel. In the case of a hollow steel, especially a thin hollow steel, it is particularly important to ensure surface hardness and torsional flexibility that can withstand the requirements of cyclic loads in the final product, compared to non-hollow parts. If the method according to the invention is employed for the production of such semi-finished products, particularly great results are obtained.

  The production process according to the invention is mainly a continuous process. The continuous method is a method for mass production of chassis components, and the process times of the individual processes are adjusted to each other. In this case, this manufacturing process is integrated as one production chain, and a product that has finished one process is immediately sent to the next process. The advantage of this method is that the cost can be optimized since no relay storage is required. Furthermore, since the nitriding treatment time is short, it is not necessary to extend the manufacturing process step time employed in the conventional chassis component manufacturing method. In other words, nitriding can be incorporated into the manufacturing process without changing the process time.

  Viewed from another aspect, the invention relates to a chassis component manufactured according to the method according to the invention. As this chassis component, for example, a torsion section steel, a stabilizer (bent or straight), and other tubular components that are exposed to a cyclic load after being charged can be considered.

  Examples of chassis components include a cross member, a transverse link, a multi-link rear suspension, a semi-independent suspension, a front axle, a suspension link, a longitudinal or lateral traverse made of tubes or thin plates, a drive shaft, and the like.

  Since the method according to the invention provides a combination of excellent surface hardness and torsional flexibility, the method according to the invention (using the preferentially used steel alloy) is particularly suitable for all these chassis components. ing. It is also advantageous for these chassis components that the preferentially used alloys and the production method according to the invention are low-cost.

  The advantages and features mentioned for the method apply accordingly to the chassis component according to the invention, and vice versa. Furthermore, the advantages and features described in connection with one embodiment apply to other embodiments, but other embodiments do not necessarily have all the features of one other embodiment.

  The invention will be described below on the basis of possible embodiments and with reference to the accompanying drawings.

  FIG. 1A shows a tubular semi-finished product from which the chassis components are manufactured. This tube becomes a molded semi-finished product indicated by B after one or more molding processes. In this case, bending and other forming methods that do not depend on cutting are employed.

  The semi-finished product so formed is then sent to the processing chamber (FIG. 1C) for the nitriding process. In this processing chamber, the nitrogen-containing gas is ionized by, for example, an electric field in a vacuum state. As a result, a compound layer is generated on the surface of the unfinished product sent into the processing chamber, and in this compound layer, nitrides such as aluminum, chromium, molybdenum, vanadium, and titanium are formed in addition to iron nitride. Yes. Under this compound layer, a layer called a permeation layer is formed, and nitrogen exists in the form of fine nitride. The nitriding treatment can be performed using a continuous heating furnace instead of the treatment chamber.

  After the set processing time has passed, the unfinished product is taken out from the processing chamber as a final finished product (D).

  FIG. 2 shows another embodiment of the method according to the invention. In this case, the incomplete product nitrided in the processing chamber (C) is sent to the surface projection processing (FIG. 2E). In this process, the projection material is projected on the entire surface or a part of the surface, thereby generating a compressive stress on the surface. When the projection material is removed, the final finished product (FIG. 2D) is completed.

  A number of advantages are obtained by the present invention. In particular, chassis components with a long service life can be obtained at relatively low production costs. The reduction in manufacturing cost is due to the fact that a heat treatment such as stress relief annealing is unnecessary because of the nitridation process. The service life of these chassis components (particularly nitrided torsion section steel) corresponds to several times the service life of parts manufactured by known manufacturing methods. Furthermore, in view of the long-term durability limits obtained, the wall thickness of the chassis component can be made thinner than that produced by known production methods. As a result, the weight of the chassis component can be reduced. By using the method according to the present invention, even a steel alloy with a low content of alloy elements can be further reduced in cost because it is specially adjusted for the nitriding process.

Claims (9)

A method of manufacturing a chassis component in which a semi-finished product is formed by cold forming, and a nitriding treatment is applied to the formed semi-finished product after cold forming,
The semi-finished product is given a final shape by cold forming,
The nitriding treatment is nitriding by a plasma nitriding method,
It said method further comprises the step of processing for projecting blast material to at least a portion of the preformed semi-finished surface,
The raw material of the semi-finished product is as follows (wt%):
Carbon (C): 0.22 to 0.25%
Silicon (Si): 0.20 to 0.30%
Manganese (Mn): 1.20 to 1.40%
Phosphorus (P): 0.020% or less Sulfur (S): 0.010% or less Aluminum (Al): 0.020 to 0.060%
Boron (B): 0.0020 to 0.0035%
Chromium (Cr): 0.10 to 0.20%
Titanium (Ti): 0.020 to 0.050%
Molybdenum (Mo): 0.35% or less Copper (Cu): 0.10% or less Nickel (Ni): 0.30% or less Remaining: Steel made of iron and contaminants caused by melting Method. The method according to claim 1, wherein a process of projecting a projection material onto at least a part of the surface of the molded semi-finished product is performed after the nitriding process. The final product after the nitriding treatment is not subjected to further molding process or heat treatment process except for a process of projecting a projection material onto at least a part of the surface of the molded semi-finished product for increasing strength. The method according to claim 1 or 2. The method according to any one of claims 1 to 3, wherein the raw material of the semi-finished product is made of microalloy steel or tempered steel. The method according to claim 4, wherein the raw material has 0.020 to 0.100 wt% aluminum. The method according to claim 1, wherein the raw material has 0.100% by weight or less of vanadium (V). The method according to claim 1, wherein the semi-finished product is a thin hollow steel. 8. A method according to any one of the preceding claims, characterized in that the method is a continuous method. 9. Chassis components produced by the method according to claim 1, characterized in that they are torsion sections, stabilizers or other components that are subjected to cyclic loading after application. A chassis component.

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