Provided are a non-heat-treated steel wire rod with excellent cold forgeability and a method of manufacturing the same, the non-heat-treated steel wire rod including carbon: 0.20 to 0.40 wt %, silicon: 0.10 to 0.30 wt %, manganese: 1.30 to 1.60 wt %, phosphorus: more than 0 wt % and up to 0.05 wt %, sulfur: more than 0 wt % and up to 0.05 wt %, chromium: 0.02 to 0.30 wt %, nickel: 0.02 to 0.30 wt %, molybdenum: 0.02 to 0.30 wt %, vanadium: 0.01 to 0.15 wt %, niobium: 0.01 to 0.05 wt %, aluminum: 0.005 to 0.060 wt %, titanium: 0.005 to 0.020 wt %, copper: 0.01 to 0.30 wt %, boron: 0.0001 to 0.0020 wt %, nitrogen: 0.005 to 0.015 wt %, and a balance of iron and other unavoidable impurities, wherein a sum of Nb and V is 0.02 to 0.2 wt %, and wherein the non-heat-treated steel wire rod satisfies a tensile strength of 900 MPa or more.
Legal claims defining the scope of protection, as filed with the USPTO.
. A non-heat-treated steel wire rod, the non-heat-treated steel wire rod comprising: carbon (C): approximately 0.20 wt % to 0.40 wt %, silicon (Si): approximately 0.10 wt % to 0.30 wt %, manganese (Mn): approximately 1.30 wt % to 1.60 wt %, phosphorus (P): more than 0 wt % and up to approximately 0.05 wt %, sulfur(S): more than 0 wt % and up to approximately 0.05 wt %, chromium (Cr): approximately 0.02 wt % to 0.30 wt %, nickel (Ni): approximately 0.02 wt % to 0.30 wt %, molybdenum (Mo): approximately 0.02 wt % to 0.30 wt %, vanadium (V): approximately 0.01 wt % to 0.15 wt %, niobium (Nb): approximately 0.01 wt % to 0.05 wt %, aluminum (Al): approximately 0.005 wt % to 0.060 wt %, titanium (Ti): approximately 0.005 wt % to 0.020 wt %, copper (Cu): approximately 0.01 wt % to 0.30 wt %, boron (B): approximately 0.0001 wt % to 0.0020 wt %, nitrogen (N): approximately 0.005 wt % to 0.015 wt %, and a balance of iron (Fe) and other unavoidable impurities,
. The non-heat-treated steel wire rod of, wherein the non-heat-treated steel wire rod comprises a composite precipitate with a diameter of approximately 50 nm or less, and
. The non-heat-treated steel wire rod of, wherein the composite precipitate has an austenite grain size of number 10 or above.
. A method of manufacturing a non-heat-treated steel wire rod, the method comprising:
. The method of, wherein the temperature region above the A3 transformation point is approximately 750° C. to 900° C.
. The method of, wherein, in the forming of the wire rod, cooling is performed at a cooling rate of approximately 2° C./s or less after preforming the rolling.
. The method of, wherein, in the cold drawing of the wire rod, a drawing reduction rate is approximately 30% to 50%.
. The method of, wherein, in the forming of the wire rod, a speed of a conveyor for transporting the wire rod after being rolled is controlled to approximately 0.2 m/s to 0.7 m/s to control an overlap density of the wire rod transported by the conveyor.
. The method of, wherein the wire rod manufactured after the cold forging satisfies a tensile strength of approximately 900 MPa or more.
Complete technical specification and implementation details from the patent document.
This application is a continuation of International Application No. PCT/KR2023/013084 filed on Sep. 1, 2023, which claims under 35 U.S.C. § 119(a) the benefit of Korean Patent Application No. 10-2022-0183546 filed on Dec. 23, 2022, the entire contents of which applications are incorporated by reference herein.
The present disclosure relates to a non-heat-treated steel wire rod with excellent cold forgeability and a method of manufacturing the same, and more particularly, to a non-heat-treated steel wire rod capable of achieving excellent strength and toughness without heat treatment, and a method of manufacturing the same.
Heat-treated steel wire rods, which are quenched and tempered in the austenite region after cold forging to enhance material strength and toughness, are commonly used for the mechanical structure of vehicle parts.
As shown in, a typical heat-treated steel wire rod is manufactured through a raw material manufacturing step S, and a parts processing step Sfor processing the manufactured wire rod into parts. Specifically, the raw material manufacturing step Sincludes a steelmaking and continuous casting step S, a bloom reheating step S, a billet rolling step S, a wire rod rolling step S, and a wire rod manufacturing step S. The wire rod manufactured through the above-mentioned steps is post-processed according to product specifications to ultimately manufacture non-heat-treated wire rod products. The post-processing refers to the parts processing step S, and the parts processing step Sincludes a cold drawing step S, a spheroidization step S, a cold forging step S, a quenching/tempering step S, a processing step S, and a product manufacturing step S.
Meanwhile, a non-heat-treated steel wire rod is a steel produced by omitting heat treatment during the above-mentioned post-processing. Specifically, the spheroidization step Sto be performed after the cold drawing step S, and the quenching/tempering step Sto be performed after the cold forging step Smay be omitted.
Unlike the heat-treated steel, tensile strength and impact toughness similar to those of the heat-treated steel may be achieved without the above-mentioned heat treatment processes. Thus, process simplification and cost savings may be enabled to achieve economic feasibility, and heat treatment defects and warping may be prevented to produce products that require straightness.
However, because the above-mentioned heat treatment processes are omitted for the non-heat-treated steel wire rod, work hardening continuously occurs during the cold drawing step Sand the cold forging step S. This leads to an increase in product strength but also a continuous decrease in ductility and toughness as well as a reduction in mold life during cold forging. As a result, the benefits of omitting heat treatment may diminish.
In addition, because the non-heat-treated steel wire rod does not undergo heat treatment during the parts manufacturing process and thus the mechanical properties of the raw material affect the final parts properties, variations in mechanical properties may pose a significant risk.
The present disclosure provides a non-heat-treated steel wire rod with excellent cold forgeability, which preferably can achieve excellent strength and toughness without heat treatment and exhibits at least substantially no variation in tensile strength, and a method of manufacturing the same. However, the above description is an example, and the scope of the present disclosure is not limited thereto.
According to an aspect of the present disclosure, there is provided a non-heat-treated steel wire rod preferably with excellent cold forgeability, the non-heat-treated steel wire rod including carbon (C): approximately 0.20 wt % to 0.40 wt %, silicon (Si): approximately 0.10 wt % to 0.30 wt %, manganese (Mn): approximately 1.30 wt % to 1.60 wt %, phosphorus (P): more than 0 wt % and up to approximately 0.05 wt %, sulfur(S): more than 0 wt % and up to approximately 0.05 wt %, chromium (Cr): approximately 0.02 wt % to 0.30 wt %, nickel (Ni): approximately 0.02 wt % to 0.30 wt %, molybdenum (Mo): approximately 0.02 wt % to 0.30 wt %, vanadium (V): approximately 0.01 wt % to 0.15 wt %, niobium (Nb): approximately 0.01 wt % to 0.05 wt %, aluminum (Al): approximately 0.005 wt % to 0.060 wt %, titanium (Ti): approximately 0.005 wt % to 0.020 wt %, copper (Cu): approximately 0.01 wt % to 0.30 wt %, boron (B): approximately 0.0001 wt % to 0.0020 wt %, nitrogen (N): approximately 0.005 wt % to 0.015 wt %, and a balance of iron (Fe) and other unavoidable impurities, wherein a sum of Nb and V is approximately 0.02 wt % to 0.2 wt %, and wherein the non-heat-treated steel wire rod satisfies a tensile strength of approximately 900 MPa or more.
In aspects, the non-heat-treated steel wire rod may include a composite precipitate with a diameter of approximately 50 nm or less, and the composite precipitate suitably may be a composite precipitate including one or more selected from Nb, V, Ti, and Al, or one or more selected from composite precipitates including TiN, VC, VN, NbC, NbN, AlN, and BN.
In aspects, the composite precipitate may have an austenite grain size of number 10 or above.
According to an aspect of the present disclosure, there is provided a method of manufacturing a non-heat-treated steel wire rod preferably with excellent cold forgeability, the method including forming a billet by reheating a steel material including carbon (C): approximately 0.20 wt % to 0.40 wt %, silicon (Si): approximately 0.10 wt % to 0.30 wt %, manganese (Mn): approximately 1.30 wt % to 1.60 wt %, phosphorus (P): more than 0 wt % and up to approximately 0.05 wt %, sulfur(S): more than 0 wt % and up to approximately 0.05 wt %, chromium (Cr): approximately 0.02 wt % to 0.30 wt %, nickel (Ni): approximately 0.02 wt % to 0.30 wt %, molybdenum (Mo): approximately 0.02 wt % to 0.30 wt %, vanadium (V): approximately 0.01 wt % to 0.15 wt %, niobium (Nb): approximately 0.01 wt % to 0.05 wt %, aluminum (Al): approximately 0.005 wt % to 0.060 wt %, titanium (Ti): approximately 0.005 wt % to 0.020 wt %, copper (Cu): approximately 0.01 wt % to 0.30 wt %, boron (B): approximately 0.0001 wt % to 0.0020 wt %, nitrogen (N): approximately 0.005 wt % to 0.015 wt %, and a balance of iron (Fe) and other unavoidable impurities, at approximately 1100° C. to 1350° C., wherein a sum of Nb and V is approximately 0.02 wt % to 0.2 wt %; forming a wire rod by rolling the reheated billet; cold drawing the wire rod; and performing cold forging after the cold drawing, wherein, in the forming of the wire rod, rolling is performed while heating in a temperature region above an A3 transformation point.
The temperature region above the A3 transformation point may be approximately 750° C. to 900° C.
In the forming of the wire rod, cooling may be performed at a cooling rate of approximately 2° C./s or less after preforming the rolling.
In the cold drawing of the wire rod, a drawing reduction rate may be approximately 30% to 50%.
In the forming of the wire rod, a speed of a conveyor for transporting the wire rod after being rolled may be controlled to approximately 0.2 m/s to 0.7 m/s to control an overlap density of the wire rod transported by the conveyor.
The wire rod manufactured after the cold forging may satisfy a tensile strength of approximately 900 MPa or more.
As referred to herein, the term billet is used in its customary usage, such as a steel material, which is still in the form of a rectangle or a metal bar or other configuration. Rectangular steel billets are also referred to as steel slabs or other term.
As referred to herein, yield strength (YP) and tensile stress (TS) and elongation (EL) can be measured using a commercially available tensile tester and according to the ISO standard ISO 6892-1, published in October 2009.
According to the present disclosure, a non-heat-treated steel wire rod with excellent cold forgeability, which achieves excellent strength and toughness without heat treatment and exhibits no variation in tensile strength, may be manufactured. The above effects of the present disclosure are examples, and the scope of the present disclosure is not limited thereto.
Hereinafter, the present disclosure will be described in detail by explaining embodiments of the disclosure with reference to the attached drawings. The disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the disclosure to one of ordinary skill in the art. Like reference numerals refer to like elements throughout. Further, various elements and regions in the drawings are schematically illustrated. Therefore, the scope of the present disclosure is not limited by the relative sizes or distances shown in the attached drawings.
The present disclosure relates to a method of manufacturing a non-heat-treated steel wire rod with excellent cold forgeability by controlling precision rolling conditions and a cooling rate during wire rod manufacturing, and the non-heat-treated steel wire rod with excellent cold forgeability will be described first before describing the manufacturing method.
The non-heat-treated steel wire rod with excellent cold forgeability according to an embodiment of the present disclosure includes carbon (C): approximately 0.20 wt % to 0.40 wt %, silicon (Si): approximately 0.10 wt % to 0.30 wt %, manganese (Mn): approximately 1.30 wt % to 1.60 wt %, phosphorus (P): more than 0 wt % and up to approximately 0.05 wt %, sulfur (S): more than 0 wt % and up to approximately 0.05 wt %, chromium (Cr): approximately 0.02 wt % to 0.30 wt %, nickel (Ni): approximately 0.02 wt % to 0.30 wt %, molybdenum (Mo): approximately 0.02 wt % to 0.30 wt %, vanadium (V): approximately 0.01 wt % to 0.15 wt %, niobium (Nb): approximately 0.01 wt % to 0.05 wt %, aluminum (Al): approximately 0.005 wt % to 0.060 wt %, titanium (Ti): approximately 0.005 wt % to 0.020 wt %, copper (Cu): approximately 0.01 wt % to 0.30 wt %, boron (B): approximately 0.0001 wt % to 0.0020 wt %, nitrogen (N): approximately 0.005 wt % to 0.015 wt %, and a balance of iron (Fe) and other unavoidable impurities.
The functions and contents of the components included in the non-heat-treated steel wire rod according to the present disclosure are as follows. In this case, the unit for the contents of the constituent elements is wt %.
C is an element that forms an Nb-or V-based precipitate and dissolves in the matrix to increase the strength of steel. Although approximately 0.20 wt % or more of C is required to ensure sufficient strength of steel, when the content of C increases to more than approximately 0.40 wt %, the increase in strength leads to significant decreases in toughness and ductility. Therefore, C is added at approximately 0.20 wt % to 0.40 wt % to ensure excellent strength and toughness of non-heat-treated steel.
Si is an element that contributes to high strength and is useful for enhancing fatigue deformation resistance by increasing softening resistance. However, when excessively added as an element that improves deformation resistance, Si may significantly deteriorate the cold forgeability of non-heat-treated steel for which spheroidization is omitted. Considering this, Si is added at approximately 0.10 wt % to 0.30 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure.
Mn is an element that is useful for deoxidizing steel, and dissolves in the matrix to effectively increase and ensure the strength of non-heat-treated steel. Mn lowers the transformation point to contribute to intermediate pearlite refinement and enhance toughness. When the content of Mn is less than approximately 1.30 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure, sufficient strength may not be ensured, and when the content of Mn is greater than approximately 1.60 wt %, the increase in strength may result in a decrease in toughness.
P is an element that easily segregates to impair the toughness of steel, and has an excellent solid solution strengthening effect to enhance the strength of steel with only a small amount added. P may be added at a content ratio of more than 0 wt % and not more than approximately 0.05 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure. When the content of P is greater than approximately 0.05 wt %, the toughness of steel may decrease.
S is an element that impairs workability and material properties. S segregates at the grain boundaries to impair the ductility of steel, and forms sulfides which are the primary cause of the deterioration in delayed fracture resistance and stress relaxation properties. Therefore, S may be added at a content ratio of more than 0 wt % and not more than approximately 0.05 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure. When the content of S is greater than approximately 0.05 wt %, martensite grain boundaries may fracture, hot workability may decrease, and surface defects such as cracks may occur due to the formation of coarse inclusions.
Cr not only increases the strength of steel but also enhances hardenability and strength as a ferrite stabilizing element. Cr may be added at a ratio of approximately 0.02 wt % to 0.30 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure. When the content of Cr is less than approximately 0.02 wt %, the strength enhancement effect may be insufficient, and when the content of Cr is greater than approximately 0.30 wt %, the improved hardenability may lead to the formation of low-temperature structures during cooling, and cold drawability and forgeability may decrease.
Ni contributes to increasing hardenability and enhancing toughness. Ni may be added at approximately 0.02 wt % to 0.30 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure. When the content of Ni is less than approximately 0.02 wt %, the effect of Ni addition may be insignificant, and when the content of Ni is greater than approximately 0.30 wt %, the costs may increase.
Mo contributes to enhancing strength and toughness. Mo may be added at approximately 0.02 wt % to 0.30 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure. When the content of Mo is less than approximately 0.02 wt %, the effect of Mo addition may be insignificant, and when the content of Mo is greater than approximately 0.30 wt %, hardness may increase to reduce workability, and the manufacturing costs of non-heat-treated steel may increase significantly.
V is an element that reacts with C and N to form an NbV (carbide/nitride) composite precipitate and contributes to strength enhancement through precipitation hardening. V acts as a ferrite nucleation site during wire rod rolling to increase the fraction of ferrite and enhance strength and toughness. Considering this, V may be added at approximately 0.01 wt % to 0.15 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure. When the content of V is less than approximately 0.01 wt %, the effect of V addition is insufficient, and when the content of V is greater than approximately 0.15 wt %, the precipitation hardening effect is insignificant and ineffective.
Like V, Nb is an element that reacts with C and N to form Nb (carbide/nitride). The Nb-based precipitate is an element that enables precipitation hardening and prevents grain boundary coarsening of steel. Like V, Nb acts as a ferrite nucleation site during wire rod rolling to increase the fraction of ferrite and enhance strength and toughness. However, the increase in Nb raises the solutioning temperature, and Nb which does not dissolve during raw material rolling forms a coarse precipitate. The formation of the coarse precipitate does not effectively impede the movement of dislocations, and thus the effect on fatigue life improvement is insignificant. As such, to increase the formation of a fine precipitate by dissolving Nb as much as possible during raw material rolling, Nb may be added at approximately 0.01 wt % to 0.05 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure.
Meanwhile, the sum of Nb and V may be approximately 0.02 wt % to 0.2 wt %. Nb and V are elements that form carbides or nitrides. Although the individual content ranges of these elements are also important, because the two are interchangeable and excessive addition may lead to the formation of a coarse precipitate, the total amount of both elements needs to be appropriately controlled in the present disclosure.
Al primarily acts as a deoxidizer, and combines with oxygen in steel to form oxides. Al remaining after reacting with oxygen combines with nitrogen to form AlN. Herein, AlN prevents grain boundary coarsening to enhance the toughness of the product. Al may be added at approximately 0.005 wt % to 0.060 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure. When the content of Al is less than approximately 0.005 wt %, Al is insufficient to form AlN, and when the content of Al is greater than approximately 0.060 wt %, a deterioration in mechanical properties may occur.
Like V and Nb, Ti forms carbonitrides to cause precipitation hardening and enhance strength and toughness. Ti may be added at approximately 0.005 wt % to 0.020 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure. When the content of Ti is less than approximately 0.005 wt %, the effect of Ti addition is insufficient, and when the content of Ti is greater than approximately 0.02 wt %, the manufacturing costs increase rapidly, and coarse alloy carbides increase and act similarly to non-metal inclusions, thereby deteriorating the fatigue properties and the precipitation hardening effect.
Cu is an element effective in increasing the strength and enhancing the toughness of steel. Cu may be added at approximately 0.01 wt % to 0.30 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure. When the content of Cu is less than approximately 0.01 wt %, the effect of Cu addition is insufficient, and when the content of Cu is greater than approximately 0.30 wt %, surface enrichment may be caused and cold drawability during a drawing process may decrease.
B is an element that segregates at the grain boundaries and enhances the ductility and toughness of steel. B may be added at approximately 0.0001 wt % to 0.0020 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure. When the content of B is less than approximately 0.0001 wt %, the effect of B addition is insufficient, and when the content of B is greater than approximately 0.0020 wt %, the hardenability of steel may increase and low-temperature structures may be caused during rapid cooling.
N combines with Al, V, and Nb to form nitrides such as AlN, VN, and NbN. These nitrides not only enable grain refinement through the grain boundary pinning effect, but also act as a ferrite nucleation site to increase the fraction of ferrite. N may be added at approximately 0.005 wt % to 0.015 wt % based on the total weight of non-heat-treated steel according to an embodiment of the present disclosure. When the content of N is less than approximately 0.005 wt %, the number of nitride particles formed may be insufficient, and when the content of N is greater than approximately 0.015 wt %, N may dissolve in the matrix to increase strength and decrease cold drawability.
The remaining component of the present disclosure is iron (Fe). However, because unintended impurities are inevitably introduced from the raw materials or the surrounding environment during general manufacturing processes, the addition of these impurities may not be completely prevented. Such impurities are known to any one of ordinary skill in the art and thus are not specifically described in this specification.
The non-heat-treated steel wire rod with excellent cold forgeability and the above-mentioned composition may satisfy a tensile strength of approximately 900 MPa or more.
The above-described non-heat-treated steel wire rod with excellent cold forgeability may include a composite precipitate with a diameter of 50 nm or less, and the composite precipitate may be a composite precipitate including one or more selected from Nb, V, Ti, and Al, or one or more selected from composite precipitates including TiN, VC, VN, NbC, NbN, AlN, and BN. By including the composite precipitate, grain refinement and ferrite fraction increase may be achieved and thus strength and toughness may be enhanced. For optimal effect, the composite precipitate may have a diameter of approximately 50 nm or less.
The grain refinement of the composite precipitate may be determined by measuring the austenite grain size (A, G, S). When the composite precipitate particles are finely dispersed, the austenite grain size may be number 10 or above. The grain refinement is a critical means of enhancing the strength and toughness of steel materials, and the principle thereof is based on the pinning effect by an MX precipitate, which inhibits grain growth. Therefore, the fine dispersion of the composite precipitate particles is crucial.
The fine dispersion of the composite precipitate particles in the non-heat-treated steel wire rod of the present disclosure may be determined based on the number of composite precipitate particles per approximately 100 μm. To achieve desired strength and toughness of steel materials, 1000 or more composite precipitate particles may be included per approximately 100 μm.
The above-described non-heat-treated steel wire rod according to an embodiment of the present disclosure may be manufactured as described below.
is a flowchart of a method of manufacturing a non-heat-treated steel wire rod, according to an embodiment of the present disclosure,is a schematic view specifically showing a wire rod rolling step shown in, andinclude schematic views of wire rods cooled on a cooling conveyor shown in.
Referring to, the non-heat-treated steel wire rod manufacturing method according to an embodiment of the present disclosure may be divided into two steps. The method includes a raw material manufacturing step Sfor manufacturing a wire rod by a steelmaker, and a parts processing step Sfor manufacturing parts by processing the wire rod manufactured through the raw material manufacturing step. In general, a heat-treated steel wire rod is manufactured by performing a raw material manufacturing step Sand then a parts processing step Sas shown in. The parts processing step Sincludes a cold drawing step S, a spheroidization step S, a cold forging step S, a quenching/tempering step S, a processing step S, and a product manufacturing step S.
Meanwhile, the non-heat-treated steel wire rod may be a steel produced by omitting heat treatment during the above-mentioned parts processing step S. For example, the spheroidization step Sto be performed after the cold drawing step S, and the quenching/tempering step Sto be performed after the cold forging step Smay be omitted.
Unknown
October 2, 2025
Browse 5M+ US patents with plain-English claim translations and AI-generated analysis.