WO2018105944A1 - High strength steel wire having excellent corrosion resistance and method for manufacturing same - Google Patents

Abstract

The present invention relates to a high strength steel wire and, more specifically, to a steel wire and a method for manufacturing the same, which can skip a heat treatment and have a high corrosion resistance as well as a high strength.

Description

High strength steel wire with excellent corrosion resistance and manufacturing method thereof

The present invention relates to a high strength steel wire, and more particularly to a high strength steel wire excellent in corrosion resistance and a method for manufacturing the same.

Armor cables are reinforcements that support loads on flexible pipes that transport crude oil at sea. They require high strength and resistance to corrosion.

The method for obtaining the required physical properties of the armor cable is as follows.

First, it is a method of increasing the strength of the material itself by adding a large amount of elements to increase the strength of the steel. Representative examples of the strength-reinforcing elements of the steel include carbon. As the carbon content increases, the fraction of hard cementite inside the wire increases, and the strength of the material improves as the lamellar spacing of the pearlite structure becomes finer.

However, carbon is effective in improving strength, but because it inhibits corrosion resistance, there is a limit to select an appropriate content according to the use environment.

Secondly, it is a method of greatly improving the strength by drawing the wire and giving work hardening. The drawing material is drawn and heat-treated the rolled wire and processed into final wire. In this way, drawing work can give work hardening due to miniaturization of lamellar spacing, increase in work hardening coefficient, and dislocation accumulation. .

Third, the strength can be improved by increasing the fresh strain of the tire cord material. In this case, since the strain rate of the raw material is closely related to the ductility of the raw material, disconnection does not occur in the raw material itself during the fresh processing, and it may be advantageous to improve the strength as it is easily processed.

However, the above-described methods are to change the strength of the steel material by the alloy composition, manufacturing conditions, structure, etc. are interrelated, there is a limit to improve the strength by controlling each independently. In addition, the above-described methods have no consideration in terms of corrosion resistance of high strength steel wires, and there is a limit in improving corrosion resistance.

An aspect of the present invention is to provide a steel wire having a high corrosion resistance and high corrosion resistance while the heat treatment can be omitted, and a method of manufacturing the same.

One aspect of the present invention, in weight%, carbon (C): 0.07 ~ 0.15%, manganese (Mn): 2.7 ~ 3.5%, silicon (Si): 0.10 ~ 0.50%, chromium (Cr): 0.8% or less ( 0%), titanium (Ti): 0.01% to 0.02%, boron (B): 0.001% to 0.003%, the balance contains iron (Fe) and unavoidable impurities, and has excellent corrosion resistance including a bainite phase as a microstructure. Provide high strength steel wire.

Another aspect of the invention, the step of manufacturing a wire rod that satisfies the above-described alloy composition; Manufacturing cold drawn wire by cold drawing the wire with a total reduction of 40 to 80%; And cold rolling the cold drawn wire with a total reduction rate of 50 to 90% to produce a cold rolled material.

According to the present invention, not only the steel wire having a high strength can be provided even if the LP heat treatment step is omitted, and the steel wire of the present invention has an effect of ensuring excellent corrosion resistance.

Accordingly, the steel wire of the present invention has an effect that can be advantageously applied to applications requiring high strength and high corrosion resistance.

The present inventors have studied in depth to provide a steel wire that can be suitably used in an environment requiring high strength as well as high corrosion resistance. As a result, it was confirmed that by optimizing the alloy composition and manufacturing conditions of the steel, it is possible to provide a steel wire having a microstructure that is advantageous in ensuring excellent high strength and high corrosion resistance at the same time, and came to complete the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The high-strength steel wire having excellent corrosion resistance according to an aspect of the present invention is a weight%, carbon (C): 0.07 to 0.15%, manganese (Mn): 2.7 to 3.5%, silicon (Si): 0.10 to 0.50%, chromium (Cr ): 0.8% or less (including 0%), titanium (Ti): 0.01 to 0.02%, boron (B): 0.001 to 0.003% is preferably included.

Hereinafter, the reason for controlling the alloy composition of the steel wire provided in the present invention as described above in detail. In this case, unless otherwise specified, the content of each element means weight%.

C: 0.07 ~ 0.15%

Carbon (C) is an element that is advantageous for improving the strength of the steel wire, when the content of C is less than 0.07%, there is a problem in that the strength is lowered. On the other hand, when the content of C exceeds 0.15%, the strength is improved, but there is a problem that the ductility is reduced. In particular, the corrosion resistance of the steel wire tends to decrease as the content of C increases.

In the present invention, it is preferable to control the content of C to 0.07 to 0.15% in terms of securing the strength and corrosion resistance of the steel wire. More preferably, it may contain 0.09 to 0.13%.

Mn: 2.7-3.5%

Manganese (Mn) is an element that is advantageous for securing the intended microstructure as well as improving the hardenability of the steel wire. If the Mn content is less than 2.7%, it is difficult to secure hardenability, and thus there is a problem in that the target microstructure and strength cannot be obtained. On the other hand, when the content of Mn exceeds 3.5% there is a problem that ductility is greatly reduced.

Therefore, in the present invention, it is preferable to control the content of Mn to 2.7 to 3.5%. More preferably, it may comprise 2.8 to 3.3%.

Si: 0.10 to 0.50%

Silicon (Si) is an element advantageous for the deoxidation effect, and in order to obtain a sufficient deoxidation effect, it is preferable to add Si at 0.10% or more. If the content of Si is less than 0.10%, there is a possibility that the deoxidation effect is insufficient and the inclusions may increase, and thus the ductility and corrosion resistance may be inferior. On the other hand, when the content of Si exceeds 0.50% there is a problem that the fresh workability and sheet rolling property is lowered.

Therefore, in the present invention, it is preferable to control the content of Si to 0.10 to 0.50%, more preferably to 0.15 to 0.40%.

Cr: 0.8% or less

Chromium (Cr) is an element that is advantageous in securing bainite phase as a microstructure of steel wire by securing hardenability, and is also an element that is advantageous in improving strength.

In the present invention, the Cr may be further included for the above-described effect, but if the content thereof exceeds 0.8%, there is a concern that the martensite phase may be formed as a microstructure to deteriorate the fresh workability.

Therefore, in the present invention, when the Cr is added, the content is preferably controlled to 0.8% or less, and even if the Cr is not added, there is no difficulty in securing the intended microstructure and strength, and includes 0%.

Ti: 0.01 ~ 0.02%

Titanium (Ti) is the most reactive element with nitrogen (N) and forms nitride in steel. In the present invention, by adding Ti to form TiN, most of the nitrogen in the steel is exhausted, thereby minimizing boron (B) reaction with N to form BN. That is, by making B exist in a soluble state, hardenability improvement can be obtained advantageously.

For the above-described effect, it is preferable to add Ti in an amount of 0.01% or more, but when the content exceeds 0.02%, coarse nitride is formed, which causes a problem of deteriorating mechanical properties.

Therefore, in the present invention, it is preferable to control the content of Ti to 0.01 ~ 0.02%. More preferably, it is controlled at 0.012 to 0.07%.

B: 0.001-0.003%

Boron (B) is an element that is advantageous in improving the hardenability of steel, and has the effect of suppressing the formation of ferrite during cooling and diffusing into the austenite grain boundary and increasing the hardenability.

In order to fully acquire the effect mentioned above, it is preferable to add B in 0.001% or more. However, if the content exceeds 0.003%, the effect is not only saturated, but boron-based nitride is precipitated and grain boundary strength is lowered, resulting in inferior hot workability.

Therefore, in the present invention, it is preferable to control the content of B to 0.001 to 0.003%.

The remaining component of the present invention is iron (Fe). However, in the conventional manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably mixed, and thus cannot be excluded. Since these impurities are known to those skilled in the art, all of them are not specifically mentioned in the present specification.

On the other hand, as described above, the nitrogen (N) forming TiN is the upper limit in order to allow boron (B) in the steel to remain in solid solution rather than precipitates (ex, BN) to sufficiently exhibit the effect of improving hardenability. It is desirable to limit to 0.005%.

In addition, since sulfur (S) forms a low melting point emulsion, inhibits hot rolling property, and deteriorates fresh workability, it is preferable to limit the upper limit to 0.015%.

The steel wire of the present invention that satisfies the above-described alloy composition preferably includes bainite single phase as a microstructure.

In the present invention, instead of forming a pearlite phase having a fine lamellar spacing in order to ensure high strength of the steel wire in general, by providing a uniform bainite phase with a microstructure, a steel wire having high strength and high corrosion resistance characteristics, There is a technical significance that can omit the existing LP heat treatment process.

In addition to the above-mentioned alloy composition, the steel wire of the invention having a bainite phase in the microstructure is the corrosion resistance to the yield strength and less to have a tensile strength of at least 1200MPa, as well as high strength, ² · h sulfate corrosion decrease 800g / mm or more 1100MPa Has an excellent effect.

Hereinafter, a method of manufacturing a high strength steel wire excellent in corrosion resistance which is another aspect of the present invention will be described in detail.

The steel wire of the present invention can be produced by producing a wire rod that satisfies the above-described alloy composition, and then going through the step of drawing the wire rod.

The wire rod may be manufactured through various wire rod manufacturing techniques commonly known in the art, but it is preferable to manufacture the wire rod through a series of processes described below.

First, it is preferable to produce a billet that satisfies the above-described alloy composition, and then undergo a heating step to homogenize it.

It is preferable to make the microstructure of the billet become austenite single phase through the heating process.

For this purpose, it is preferable to heat in the temperature range of 1000-1100 degreeC. If the heating temperature is less than 1000 ° C., it is difficult to secure the temperature range during the subsequent wire rolling, whereas if the temperature exceeds 1100 ° C., the austenite grains are coarse to form a difficult level of strength. .

It is preferable to wire-roll the billet heated according to the above, and then to cool the wire.

At this time, it is preferable to perform finish hot rolling in the wire rod rolling in the temperature range of 950-1100 degreeC. If the finish hot rolling temperature is less than 950 ℃ there is a problem that the roll life is reduced by the increase of the rolling load. On the other hand, if the temperature exceeds 1100 ℃ grain size may be coarse to reduce the ductility, there is a fear that excessive decarburization occurs to deteriorate the fresh workability.

Thereafter, it is preferable to produce a wire having a bainite phase by cooling at a cooling rate of 1 to 3 ° C / s. If the cooling rate is less than 1 ° C / s, there is a fear that a structure such as pearlite in addition to the bainite phase as a microstructure, while the martensite phase is formed when it exceeds 3 ° C / s.

Steel wire can be manufactured by drawing the wire rod manufactured as mentioned above. In the present invention, the LP heat treatment that is generally performed before the wire is drawn can be omitted.

According to the present invention, since the wire drawing process is performed on a wire rod having a uniform bainite phase without a ferrite structure, it is possible to secure homogeneity and high work hardening rate without performing a separate LP heat treatment.

More specifically, the wire rod can be cold drawn immediately without the LP heat treatment process, in which case it is preferable to cold drawn to a reduction ratio of 40 to 80% to prepare a cold drawn wire.

If the reduction rate during cold drawing is less than 40%, the processing amount is insufficient to secure sufficient strength, whereas if the reduction rate exceeds 80%, cracking may occur.

The cold drawn material cold drawn according to the above preferably has a yield strength of 1000 MPa or more and a tensile strength of 1100 MPa or more.

Subsequently, it is preferable to cold roll the cold drawn material, and in this case, it is preferable to cold roll to a total reduction rate of 50 to 90% to prepare a cold rolled material.

The cold rolling is for obtaining a steel wire having a plate-shaped shape. If the reduction rate is less than 50%, the processing amount is insufficient to secure sufficient strength, whereas if it exceeds 90%, cracking may occur.

The cold rolled material cold rolled according to the above preferably has a yield strength of at least 1100 MPa and a tensile strength of at least 1200 MPa.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, it is necessary to note that the following examples are only for illustrating the present invention in more detail, and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.

(Example)

After preparing the billet having the alloy composition shown in Table 1, the billet was heated at 1000 ~ 1100 ℃, and then hot-rolled at 1000 ℃ to prepare a wire rod. Thereafter, the wire rod was cooled to 500 ° C. at a cooling rate of 1 to 3 ° C./s, and then air cooled to room temperature.

Thereafter, for the inventive steels 1 to 6 satisfying the alloy composition proposed by the present invention, the steel wire was manufactured by cold rolling at a total reduction of 50 to 90% after the fresh processing with a total reduction of 40 to 80%. For LP, heat treatment was performed, followed by fresh processing (total reduction of 40 to 80%) and cold rolling (total reduction of 50 to 90%).

Tensile properties of each wire rod and steel wire prepared above were evaluated by a tensile test at room temperature, and corrosion loss was measured by immersing the steel wire in 5% sulfuric acid solution for each steel wire. The results are shown in Table 2 below.

division	Alloy composition (% by weight)
	C	Si	Mn	Cr	S	Ti	B	N
Inventive Steel 1	0.11	0.15	3.0	-	0.004	0.015	0.002	0.004
Inventive Steel 2	0.11	0.15	3.0	0.5	0.004	0.015	0.002	0.004
Inventive Steel 3	0.12	0.16	3.1	-	0.004	0.016	0.002	0.004
Inventive Steel 4	0.13	0.13	3.3	-	0.003	0.012	0.002	0.004
Inventive Steel 5	0.10	0.16	2.8	0.6	0.004	0.013	0.002	0.003
Inventive Steel 6	0.10	0.14	2.7	0.4	0.003	0.017	0.002	0.005
Comparative Steel 1	0.35	0.20	0.7	-	0.004	-	-	0.006
Comparative Steel 2	0.32	0.24	0.8	-	0.005	-	-	0.007
Comparative Steel 3	0.38	0.17	0.6	-	0.005	-	-	0.006
Comparative Steel 4	0.33	0.18	1.3	-	0.011	0.03	0.07	0.008

division	LP heat treatment	Wire rod		LP material		Cold Rolled Wire (Steel Wire)		Corrosion loss (g / mm 2 · h)
		YS	TS	YS	TS	YS	TS
Inventive Steel 1	Not carried	480	757	-	-	1230	1331	527
Inventive Steel 2	Not carried	584	895	-	-	1344	1474	539
Inventive Steel 3	Not carried	483	762	-	-	1241	1332	532
Inventive Steel 4	Not carried	479	761	-	-	1232	1342	518
Inventive Steel 5	Not carried	596	901	-	-	1349	1489	548
Inventive Steel 6	Not carried	573	881	-	-	1330	1463	532
Comparative Steel 1	practice	293	327	451	687	1090	1187	1093
Comparative Steel 2	practice	287	319	448	673	1073	1163	1087
Comparative Steel 3	practice	312	334	467	692	1118	1203	1218
Comparative Steel 4	practice	332	347	505	714	1147	1198	1196

(In Table 2, YS means yield strength, TS means tensile strength, and its unit is MPa.)

As shown in Tables 1 and 2, it can be seen that the inventive steels 1 to 6 in which the alloy composition satisfies the present invention have improved strength (yield strength and tensile strength) of the wire compared to the comparative steels 1 to 4. In addition, it can be confirmed that the strength of the steel wire of the inventive steels 1 to 6 is also higher than that of the comparative steels 1 to 4 subjected to the LP heat treatment.

This is because, in the case of the inventive steels 1 to 6 having the bainite phase as a microstructure, the work hardening rate is high, and thus the target high strength can be achieved through drawing and cold rolling without performing the LP heat treatment compared to the comparative steels 1 to 4 having the pearlite phase. It can be secured.

In addition, the steel wires of the inventive steels 1 to 6 all had a corrosion loss of 550 g / mm ² · h or less.

This is a result showing that the corrosion resistance can be improved from removing the ferrite phase and forming the bainite phase, which adversely affects the corrosion resistance of the steel wire.

Claims (7)

1. By weight, carbon (C): 0.07 to 0.15%, manganese (Mn): 2.7 to 3.5%, silicon (Si): 0.10 to 0.50%, chromium (Cr): 0.8% or less (including 0%), titanium ( Ti): 0.01% to 0.02%, boron (B): 0.001% to 0.003%, the balance includes iron (Fe) and unavoidable impurities,

   High strength steel wire with excellent corrosion resistance including bainite phase as microstructure.
2. The method of claim 1,

   The steel wire is a high strength steel wire having excellent corrosion resistance of sulfuric acid corrosion loss of less than 800g / mm ² · h.
3. The method of claim 1,

   The steel wire is a high strength steel wire having excellent corrosion resistance having a yield strength of 1100 MPa or more and a tensile strength of 1200 MPa or more.
4. By weight, carbon (C): 0.07 to 0.15%, manganese (Mn): 2.7 to 3.5%, silicon (Si): 0.10 to 0.50%, chromium (Cr): 0.8% or less (including 0%), titanium ( Ti): 0.01% to 0.02%, boron (B): 0.001% to 0.003%, and the remainder is produced a wire rod containing iron (Fe) and unavoidable impurities;

   Manufacturing cold drawn wire by cold drawing the wire with a total reduction of 40 to 80%; And

   Manufacturing cold rolled material by cold rolling the cold drawn material with a total reduction ratio of 50 to 90%

   Method for producing a high strength steel wire excellent corrosion resistance comprising a.
5. The method of claim 4, wherein

   The step of manufacturing the wire rod, manufacturing a billet; Heating the billet at 1000 to 1100 ° C .; Rolling the heated billet at 950 ~ 1100 ℃ finish wire rod to produce a wire rod and cooling the wire at a cooling rate of 1 ~ 3 ℃ / s method of producing high strength steel wire having excellent corrosion resistance.
6. The method of claim 4, wherein

   The cold drawn material has a yield strength of 1000MPa or more and a tensile strength of 1100MPa or more of the high-strength steel wire having excellent corrosion resistance.
7. The method of claim 4, wherein

   The cold rolled material has a yield strength of 1100 MPa or more and a tensile strength of 1200 MPa or more to produce a high-strength steel wire excellent in corrosion resistance.