TW202221148A - Dual-phase steel wire rod and method of making the same - Google Patents

Abstract

The present invention provides a dual-phase steel wire rod and method of making the same. A rolling step, a cooling step, a temperature-maintaining step and a rapid cooling step with certain conditions are performed on steel billet with certain components to obtain a dual-phase steel wire rod having a certain volume ratio of ferrite and martensite. The dual-phase steel wire rod has high cold formability and high tensile strength, and thus can apply to produce fasteners with strengths like that of 8.8 grade bolts.

Description

Duplex steel wire rod and method of making the same

The present invention relates to a wire rod, especially a dual-phase steel wire rod and a manufacturing method thereof.

A screw fastener (such as a bolt) is an element that uses threads to generate friction to connect and fix two components without relative movement. Screw fasteners are often used for positioning, locking, adjusting and/or connecting mechanism components, etc. Among them, screw fasteners used for bridges, rails, and high-voltage equipment require greater strength to withstand greater loads.

Generally speaking, screw fasteners are made of medium carbon steel wire and are formed by cold punching. The above-mentioned medium carbon steel wire rod is based on fertilizer granulated iron, which is soft and conducive to cold deformation, but the strength of fertilizer granulated iron is low, so to obtain high-strength bolts, it is often necessary to perform quenching and tempering heat treatment. produce a phase transition.

In order to reduce cost and simplify processing, a wire rod with both high strength and high cold-strength is required. However, the wire rod prepared by the conventional method cannot meet the requirements of high cold-strength and high strength at the same time. Therefore, a method for manufacturing a dual-phase steel wire rod is urgently needed to solve the above problems.

Therefore, one aspect of the present invention is to provide a method for manufacturing a dual-phase steel wire rod, which utilizes a specific cooling rate to control the phase transformation of the disk element, thereby obtaining a dual-phase steel wire rod with both high strength and high cold-strength. .

According to the above aspect of the present invention, a method for manufacturing a dual-phase steel wire rod is provided. First, a steel blank is provided, wherein the steel blank may contain 0.06 wt % to 0.20 wt % carbon, 0.30 wt % to 1.00 wt % silicon, 1.00 wt % to 2.00 wt % manganese, and below 0.025 wt % of phosphorus, 0.025 wt% or less of sulfur, 0.003 wt% or less of boron, unavoidable impurities, and a balanced amount of iron.

Next, the steel billet is subjected to a heat treatment step to form a treated material having 100 volume percent (vol %) of the Wasserian iron phase. Then, a rolling step and a coiling step are performed on the treated material to obtain a disk element, and subsequently, a temperature holding step is performed on the disk element, so that the disk element has a fat iron phase.

After the temperature-maintaining step, the disk element is subjected to a quenching step to obtain a dual-phase steel wire, wherein the dual-phase steel wire may contain 80 vol% to 90 vol% of the ferric iron phase and 10 vol% to 20 vol% of hemp Scattered iron phase.

According to the above-mentioned embodiment of the present invention, the heat treatment step may, for example, raise the temperature of the steel billet to 1000°C to 1200°C.

According to the above-mentioned embodiment of the present invention, the rolling temperature of the rolling step can be, for example, greater than the _Ar3 temperature.

According to the above-mentioned embodiment of the present invention, the holding temperature of the holding step is from the temperature of _Ar1 to the temperature of _Ar3 .

According to the above-mentioned embodiment of the present invention, the temperature of _Ar3 can be, for example, 800°C to 830°C.

According to the above-mentioned embodiment of the present invention, the A _r1 temperature can be, for example, 730°C to 735°C.

According to the above-mentioned embodiment of the present invention, the time of the temperature-holding step may be, for example, 5 seconds to 15 seconds.

According to the above-mentioned embodiment of the present invention, the quenching step may be, for example, cooling the disk element to a temperature not greater than Ms at a cooling rate of not less than 20°C per second.

According to the above-mentioned embodiment of the present invention, the Ms temperature may be, for example, 420°C to 450°C.

According to the above aspect of the present invention, a dual-phase steel wire rod is proposed, which is obtained by the above-mentioned manufacturing method of the dual-phase steel wire rod, wherein the dual-phase steel wire rod is based on the ferrite-based structure, and the dual-phase steel wire rod The carbides can be dispersed in al-Qaeda, for example, in the form of island-shaped hemp iron.

Applying the dual-phase steel wire rod of the present invention and the manufacturing method thereof, the dual-phase steel wire rod is prepared from a steel billet with a specific composition under specific cooling conditions, wherein the dual-phase steel wire rod has a specific volume ratio of fertilizer particles Iron phase and Ma Tian scattered iron phase. Due to both the fertilizer grain iron phase and the Matian loose iron phase, the above-mentioned dual-phase steel wire has a low yield ratio and high strength, so it can be used in the manufacture of cold-rolled processed products (such as fasteners with strength such as 8.8-grade screws) and does not require adjustment. Quality heat treatment.

Continuing from the above, the present invention provides a dual-phase steel wire rod and a method for manufacturing the same, wherein the steel embryo disc containing a specific composition is firstly rolled into a disc element, and then the phase transformation is controlled by different cooling rates, so as to obtain dual-phase steel wire. Phase steel wire. This dual-phase steel wire has a specific proportion of ferrite iron phase and hemp iron phase, so it has high strength and high cold beatability.

Please refer to FIG. 1 , which is a flowchart of a method 100 for manufacturing a dual-phase steel wire rod according to an embodiment of the present invention. First, step 110 is performed to provide a steel blank. The "steel billet" is a primary product formed by pouring liquid iron into a mold, and the billet can be divided into large billets and small billets according to specifications. Generally speaking, screw fasteners are made from wire, and the wire is made from small billets.

In one embodiment, the steel billet may include 0.06 weight percent (wt %) to 0.20 wt % carbon, 0.30 wt % to 1.00 wt % silicon, 1.00 wt % to 2.00 wt % manganese, and 0.025 wt % or less phosphorus , 0.025 wt% or less of sulfur, 0.003 wt% or less of boron, unavoidable impurities, and iron in balance.

The above steel billets belong to low carbon steel. Carbon will form carbides during the transformation of the steel billet, thereby increasing the hardness of the steel billet, but it will reduce the cold playability of the steel billet. Therefore, if the carbon content of the steel billet is higher than 0.20 wt%, it is easy to generate excessive carbides, thereby reducing the cold-drawability of the formed dual-phase steel wire.

The addition of silicon and manganese is beneficial to the formation of the iron phase of fertilizer granules. Among them, silicon can stabilize the iron phase of fertilizer granules and expand the temperature range where the iron phase of fertilizer granules exists, thereby reducing the production of ferrous carbon. Manganese can reduce the phase transition temperature of the iron phase of the Vostian, so it is beneficial to the residual of the iron phase of the Vostian, and delay the formation of the bleed iron phase. Therefore, if the silicon content and/or the manganese content in the steel billet is too low, it is difficult to obtain enough ferrite iron phase as the base tissue. However, silicon and manganese can increase the hardness of the steel billet, so if the silicon and/or manganese content is too high, the resulting dual-phase steel wire will have poor cold workability.

Generally speaking, phosphorus and sulfur are regarded as harmful elements, among which phosphorus reduces the cold beatability of the steel billet, and sulfur easily causes the steel billet to break during high temperature treatment (eg, rolling step). Accordingly, the content of phosphorus and sulfur in the steel billet should not be too high. Secondly, although the addition of boron helps to improve the compactness and hot-rollability of the steel billet, boron will also increase the hardness of the steel billet, resulting in a decrease in cold playability, so the boron content in the steel billet should not be too high. In one embodiment, the phosphorus content may be, for example, less than 0.025 wt %, the sulfur content may be, for example, less than 0.025 wt %, and the boron content may be, for example, less than 0.003 wt %, according to the specification for a grade 8.8 bolt.

Next, the steel billet is subjected to a heat treatment step, as shown in step 130 , so that 100 volume percent (vol %) of the iron phase in the steel billet is transformed into a Worcesterian iron phase, thereby obtaining a treated material. In one embodiment, the heat treatment step may, for example, raise the temperature of the steel billet to 1000°C to 1200°C to ensure that the treated material is completely transformed into the Worcesterian iron phase. For example, the heat treatment step is to raise the temperature of the steel billet to 1150°C.

Then, a rolling step and a coiling step are performed on the processed material, as shown in step 150, to obtain a disk element, wherein the rolling temperature of the rolling step can be, for example, greater than the _Ar3 temperature. The above A _r3 temperature represents the temperature at which the Wostian iron phase begins to transform into a fertile iron phase during the cooling process. Therefore, if the rolling temperature is not controlled to be higher than the _Ar3 temperature, part of the Wostian iron phase will be transformed into a fertile iron phase, resulting in the inconsistency of the grains of the steel billet after the rolling step (after rolling). uniform, resulting in inconsistent strength of the prepared disc elements. In general, the _Ar3 temperature will vary due to the different composition of the steel billet. In one embodiment, the _Ar3 temperature of the steel blank of the present invention can be, for example, 800°C to 830°C.

The above-mentioned coiling step can be performed, for example, using a conventional coiling method. In one embodiment, the coiling step is performed using a coiling machine to coil the rolled steel billets into coils, and the coils are scattered on the cooling bed.

In one embodiment, between the rolling step and the coiling step, a water tank can be used to cool the rolled steel billet to a temperature of _Ar3 , so as to ensure the transformation of the ferrite iron phase.

Next, step 170 is performed, which is to perform a temperature holding step on the disk element, so as to make the disk element produce a ferrite phase transformation. The method of the above temperature maintaining step is not limited. For example, a closed space (eg, a cover) can be formed on the cooling bed to block the outside air, and the disk elements can be heated evenly, thereby avoiding uneven heating of the disk elements. Since the disk elements are arranged in a partially overlapping manner on the cooling bed, if the disk elements are not isolated from the outside world, not only the result of phase transformation cannot be controlled, but also problems such as uneven crystal grains caused by inconsistent temperature of the disk elements.

In one embodiment, the temperature of the temperature-holding step may be, for example, the temperature of Ar1 to temperature of _Ar3 , wherein the temperature of _Ar1 is defined as the temperature at which the Worcester iron phase begins to transform into _blebir during the cooling process. Therefore, controlling the holding temperature from Ar1 temperature to _Ar3 temperature can promote the transformation of part of the _Wostian iron phase into the fertile iron phase, and will not produce other iron-carbon phases. The size of the A _r1 temperature will vary according to the composition of the steel blank, wherein the A _r1 temperature of the steel blank of the present invention can be, for example, 730°C to 735°C. In addition, the process of the above-mentioned phase transformation is accompanied by a carbon emission effect, which can increase the hardening energy of the untransformed Vostian iron phase. In some embodiments, the holding temperature of the holding step may be 730°C to 805°C.

In one embodiment, the time of the temperature-holding step may be, for example, 5 seconds to 15 seconds, so that a part of the Worcester iron phase can form ferrite iron.

After step 170, a quench step (shown as step 190) is performed to obtain a dual phase steel wire. In the quenching step, the Panyuan system is rapidly cooled to a temperature not greater than Ms, where the Ms temperature is defined as the temperature at which the Worcester iron phase begins to transform into a loose iron phase during cooling. By rapidly cooling to a temperature not higher than Ms, the remaining Wostian iron phase can be completely transformed into a matian loose iron phase without producing other iron-carbon phases. Ms temperature will vary depending on the composition of the steel billet. In one embodiment, the Ms temperature of the steel billet of the present invention may be, for example, 420°C to 450°C. In one embodiment, the "quick cooling" may be, for example, a cooling rate of not less than 20°C per second.

The above-mentioned dual-phase steel wire rod contains 80 vol% to 90 vol% of ferrite iron phase and 10 vol% to 20 vol% of loose iron phase, so the dual-phase steel wire rod has high strength and high cold strikeability. The above-mentioned Matian scattered iron phase is dispersed in the dual-phase steel wire in the form of island-shaped Matian scattered iron phase, wherein the island-shaped Matian scattered iron phase is formed by the carbides that move to the grain boundary with the carbon expulsion effect in the temperature holding step. .

The "high strength" refers to high tensile strength, where tensile strength refers to the maximum stress a material can withstand before breaking. In one embodiment, the high strength may be greater than 540 MPa, for example. The above-mentioned "cold punchability", also known as "cold workability", refers to the property that the wire can be shaped at room temperature (eg 10°C to 40°C). Generally speaking, a material with a high yield ratio, which is defined as the ratio of yield strength to tensile strength, has better cold workability, and yield strength is the stress required to initiate plastic deformation of the material. In one embodiment, the high cold resistance may be, for example, a yield ratio of less than or equal to 0.65.

Several embodiments are used below to illustrate the application of the present invention, but they are not intended to limit the present invention. Those with ordinary knowledge in the technical field of the present invention can make various changes and modifications without departing from the spirit and scope of the present invention. retouch.

The steel billet composition and process conditions listed in Table 1 were used in conjunction with the above-mentioned manufacturing method of the dual-phase steel wire rod to manufacture the wire rod, so as to obtain the wire rods of the Examples and Comparative Examples. As shown in Table 1, the difference between the embodiment and the comparative example is that the cooling step performed is different, and the temperature holding step is not performed in the comparative example. [Table 1]

The wires were observed with an optical microscope, as shown in Figures 2A and 2B, wherein Figures 2A (Example) and Figure 2B (Comparative Example) are optical micrographs of wires obtained by different cooling methods. As shown in FIG. 2A , the wire rod of the embodiment has an island-shaped hemp field scattered iron phase interspersed in the fertilizer granulated iron phase. On the contrary, as shown in FIG. 2B, the wire rod of the comparative example is a mixture of the bleb iron phase and the ferrite phase. It follows that the manner in which the cooling step is performed can affect the composition of the microstructure.

The tensile test was carried out according to the test method of Japanese Industrial Standards (JIS) No. Z3121, and the obtained mechanical properties are listed in Table 1, wherein the yield ratio is the ratio of yield strength to tensile strength. As shown in Table 1, compared with the comparative example in which the cooling step was performed by the slow cooling step, the wire rods of the examples treated by the temperature holding step and the quenching step had higher tensile strength and lower yield ratio. Due to the mixed structure of the fertilizer granulated iron phase and the loose iron phase, the wire rod of the embodiment can have both the good cold-beating properties of the fertilized granulated iron and the high strength of the loose iron. Accordingly, the present invention adjusts the phase transformation result of the wire rod by controlling the cooling rate, so as to obtain a dual-phase steel wire rod with high cold strikeability and high strength.

By applying the steel piece and its manufacturing method of the present invention, a dual-phase steel wire rod with both high cold-strength and high-strength can be obtained by using a specific steel billet composition and matching specific cooling conditions. This dual-phase steel wire can be used to produce fasteners, such as bolts with a strength of 8.8. The fasteners can have the required strength without quenching and tempering during the production process.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field to which the present invention pertains can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the appended patent application.

100: Manufacturing Method 110, 130, 150, 170, 190: Steps

In order to make the above and other objects, features, advantages and embodiments of the present invention more clearly understood, the detailed description of the accompanying drawings is as follows: [FIG. 1] It is a flow chart of a manufacturing method of a dual-phase steel wire rod according to an embodiment of the present invention. [ FIG. 2A ] and [ FIG. 2B ] are optical micrographs of wires obtained by different cooling methods, respectively.

Domestic storage information (please note in the order of storage institution, date and number) none Foreign deposit information (please note in the order of deposit country, institution, date and number) none

100: Manufacturing Method

110, 130, 150, 170, 190: Steps

Claims (10)

A method for manufacturing a dual-phase steel wire rod, comprising: A steel blank is provided, wherein the steel blank comprises: 0.06 weight percent (wt%) to 0.20 wt% carbon; 0.30 wt% to 1.00 wt% silicon; 1.00 wt% to 2.00 wt% of manganese; Phosphorus below 0.025 wt%; Sulfur below 0.025 wt%; Boron below 0.003 wt%; unavoidable impurities; and Balanced amount of iron; subjecting the steel billet to a heat treatment step to form a treated material having 100 volume percent (vol %) of the Wasserian iron phase; and A rolling step and a coiling step are performed on the treated material to obtain a coil; A temperature-holding step is performed on the disk element, so that the disk element has a fat iron phase; After the temperature-holding step is performed, a quenching step is performed on the disk element to obtain the dual-phase steel wire, wherein the dual-phase steel wire comprises 80 vol% to 90 vol% of the ferric iron phase and 10 vol% to 10 vol%. 20 vol% of Matian loose iron phase. The method for manufacturing a dual-phase steel wire rod as claimed in claim 1, wherein the heat treatment step is to heat the steel billet to 1000°C to 1200°C. The method for manufacturing a dual-phase steel wire rod according to claim 1, wherein one of the rolling temperatures in the rolling step is greater than the _Ar3 temperature. The method for manufacturing a dual-phase steel wire rod as claimed in claim 1, wherein one of the temperature-holding temperatures in the temperature-holding step is from A _r1 temperature to A _r3 temperature. The method for manufacturing a dual-phase steel wire rod as claimed in claim 3 or 4, wherein the _Ar3 temperature is 800°C to 830°C. The method for manufacturing a dual-phase steel wire rod as claimed in claim 4, wherein the A _r1 temperature is 730°C to 735°C. The method for manufacturing a dual-phase steel wire rod as claimed in claim 1, wherein one of the temperature holding steps is 5 seconds to 15 seconds. The method for manufacturing a dual-phase steel wire rod as claimed in claim 1, wherein the quenching step is to cool the disk element to a temperature not greater than Ms at a cooling rate of not less than 20°C per second. The method for manufacturing a dual-phase steel wire rod as claimed in claim 1, wherein the Ms temperature is 420°C to 450°C. A dual-phase steel wire rod, which is produced by the manufacturing method described in any one of claims 1 to 9, wherein the dual-phase steel wire rod is based on ferrite iron as a base structure, and the dual-phase steel wire rod is Carbides are scattered throughout the al-Qaeda in one form of island-like scatted iron.

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