KR20190064898A - High strength steel wire having sulfide stress cracking resistance properties and method of manufacturing the same - Google Patents

Abstract

The present invention relates to a high strength steel wire having excellent sulfide stress cracking (SSC) resistance properties and a method for manufacturing the same. In one embodiment of the present invention, provided are a high strength steel wire having excellent SSC resistance properties and a method for manufacturing the same, wherein the high strength steel wire comprises: 0.3-0.6 wt% of carbon (C); 0.5-1.0 wt% of manganese (Mn); 0.1-0.5 wt% of silicon (Si); 0.1-0.5 wt% of chromium (Cr); 0.01-0.15 wt% of vanadium (V); 0.2-.0.8 wt% of nickel (Ni); and the remainder consisting of iron (Fe) and inevitable impurities. Moreover, a microstructure includes pearlite, and a distance of pearlite layers is less than 100 μm. A ratio of an area of a cross section and an average thickness is 1 : 0.2-0.6.

Description

TECHNICAL FIELD [0001] The present invention relates to a high strength steel wire having excellent SSC resistance characteristics and a manufacturing method thereof. BACKGROUND OF THE INVENTION 1. Field of the Invention [0002]

The present invention relates to a high strength steel wire having excellent SSC resistance characteristics and a manufacturing method thereof.

The armor cable is a reinforcing material that supports the load applied to a flexible pipe that transports crude oil at sea, and it requires high strength and resistance in a corrosive environment.

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 that increase the strength of the steel. A representative example of the strengthening element of the steel is carbon. As the carbon content increases, the fraction of cementite, which is a hard phase, increases in the wire material, and the strength of the material increases as the lamellar spacing of the pearlite structure becomes finer.

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

Second, it is a method of drastically improving the strength by drawing the wire rod and imparting work hardening. The drawing material is obtained by drawing and drawing a rolled wire material into a final wire material. When such a wire drawing process is carried out, the workpiece hardening can be imparted due to the reduction of the lamella spacing, the increase of the work hardening coefficient, .

Third, the strength can be improved by increasing the fresh strain rate of the material. At this time, since the fresh strain of the material is closely related to the ductility of the material, it is advantageous to improve the strength as the material itself is easily processed without breaking during drawing.

However, the above-described methods have limitations in improving the strength by independently controlling the alloying composition, the manufacturing conditions, the structure, and the like because they mutually change the strength of the steel material. In addition, the above methods are not considered in terms of corrosion resistance of the high strength steel wire, and there is a limit in improving the corrosion resistance.

On the other hand, Patent Document 1 is disclosed as a technique for improving corrosion resistance together with high strength. Patent Document 1, by controlling the fraction of the C, Si, Mn, Cr, P, an alloy such as S composition control, and controlling the microstructure in acicular martensite, and at the same time _{(Fe, Cr, Mn) 23} C 6 carbide There is a problem that it is difficult to secure the improvement of the SSC resistance characteristic in terms of the technique for improving the high strength and the corrosion resistance, or the alloy composition and the microstructure control.

Korean Patent Registration No. 10-1767822

One aspect of the present invention is to provide a steel wire having excellent SSC resistance characteristics in addition to high strength and a manufacturing method thereof.

An embodiment of the present invention is a method of manufacturing a semiconductor device, comprising: 0.3 to 0.6% carbon, 0.5 to 1.0% manganese, 0.1 to 0.5% silicon, 0.1 to 0.5% chromium, 0.01 to 0.15% of vanadium (V), 0.2 to 0.8% of nickel (Ni), balance iron (Fe) and unavoidable impurities, the microstructure includes pearlite, , A high strength steel wire having excellent SSC resistance characteristics with a ratio of the width of the cross section and the average thickness of 1: 0.2 to 0.6.

Another embodiment of the present invention is a method of manufacturing a semiconductor device, comprising: 0.3 to 0.6% carbon; 0.5 to 1.0% manganese; 0.1 to 0.5% silicon; 0.1 to 0.5% chromium; 0.01 to 0.15% of vanadium (V), 0.2 to 0.8% of nickel (Ni), the balance iron (Fe) and unavoidable impurities; Obtaining a steel wire by cold drawing the wire rod; Cold rolling the steel wire; And heat treating the cold-rolled steel wire at 300 to 400 ° C. The present invention also provides a method of manufacturing a high-strength steel wire having excellent SSC resistance characteristics.

According to an aspect of the present invention, there can be provided a steel wire having excellent strength and SSC resistance characteristics and a manufacturing method thereof.

The present inventors have studied depth to provide a steel wire that can be suitably used in environments requiring high strength as well as high corrosion resistance. As a result, it has been found that a steel wire having a microstructure advantageous for securing both high strength and high corrosion resistance at the same time can be provided by optimizing the alloy composition and manufacturing conditions of the steel, and thus the present invention has been accomplished.

Hereinafter, the present invention will be described. First, the alloy composition of the present invention will be described. The content of the alloy component mentioned below means% by weight.

Carbon (C): 0.3 to 0.6%

The carbon (C) is an element favorable for improving the strength of the steel wire. If the content of C is less than 0.3%, the strength is lowered. On the other hand, when the content of C exceeds 0.6%, the strength is improved while the ductility is decreased. In particular, the corrosion resistance of the steel wire tends to decrease as the content of C increases. Therefore, the content of C is preferably controlled to 0.3 to 0.6% in terms of securing strength and corrosion resistance of the steel wire.

Manganese (Mn): 0.5 to 1.0%

Manganese (Mn) is an element favorable for securing the intended microstructure as well as improving the entrapment of the steel wire. If the content of Mn is less than 0.5%, there is a problem that it is difficult to secure the entrapment property and the desired microstructure and strength can not be obtained. On the other hand, when the content of Mn exceeds 1.0%, center segregation is promoted and the ductility is greatly reduced. Therefore, the content of Mn is preferably controlled to 0.5 to 1.0%.

Silicon (Si): 0.1 to 0.5%

Silicon (Si) is an element favorable for the deoxidation effect and is preferably added at 0.1% or more in order to obtain a sufficient deoxidation effect. If the content of Si is less than 0.1%, the effect of deoxidation is insufficient and there is a possibility that the inclusions increase, and the ductility and the corrosion resistance are likely to be weakened therefrom. On the other hand, when the content of Si exceeds 0.5%, there is a problem that drawability and plate rolling property are deteriorated. Therefore, it is preferable to control the content of Si in the range of 0.1 to 0.5%.

Chromium (Cr): 0.1 to 0.5%

Chromium (Cr) is a useful element for improving the corrosion resistance. For this purpose, it is preferable to add Cr at 0.1% or more. However, if the content exceeds 0.5%, the incombustibility is greatly increased, thereby increasing the heat treatment time during the steel wire manufacturing process, thereby deteriorating the productivity. Therefore, it is preferable that the content of Cr is in the range of 0.1 to 0.5%.

Vanadium (V): 0.01 to 0.15%

V is an element that increases the strength through precipitation of V-carbide. However, when the content is less than 0.01%, there is almost no precipitation strengthening effect, and when it exceeds 0.15% It can aggravate. Therefore, it is preferable that the content of V is in the range of 0.01 to 0.15%.

Nickel (Ni): 0.2 to 0.8%

Ni plays a role of accelerating decomposition of cementite by making the pearlite layer interface unstable and also increasing the number of operable slip systems of cementite in pearlite to increase plastic deformation. In order to sufficiently obtain the above effect, it is preferable to add 0.2% or more of Ni, but if it exceeds 0.8%, the manufacturing cost increases considerably, and therefore the content of Ni is preferably in the range of 0.2 to 0.8%.

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.

The microstructure of the steel wire according to the present invention includes pearlite, wherein the interval on the pearlite layer is preferably 100 탆 or less. As described above, by controlling the interval on the pearlite layer, the strength of the steel wire and the sectional reduction ratio can be improved at the same time. On the other hand, when the pearlite layer-shaped spacing is more than 100 탆, the initial strength and work hardening rate of the wire rod are decreased to decrease the strength of the steel wire and decrease the ductility, Lt; / RTI >

It is also preferable that the pearlite has a colloidal size of 10 탆 or less. By controlling the colloidal size of pearlite as described above, it is possible to obtain the same effect of suppressing the generation of cracks when the colloid is rotated and elongated in the rolling direction during the drawing process. On the other hand, when the pearlite has a colloidal size of more than 10 mu m, cracking may be promoted at the time of drawing to cause delamination.

The steel wire provided by the present invention has a SSC (SULFIDE STRESS CRACKING) resistance characteristic of 720 hours or more, excellent corrosion resistance, a yield strength of 1100 MPa or more, and a tensile strength of 1300 MPa or more. On the other hand, the SSC resistance characteristic means resistance to cracking and destruction caused by H ₂ S in an H ₂ S atmosphere.

On the other hand, since the steel wire of the present invention is produced by cold rolling, it has a shape which is close to a rectangle, that is, a ratio of the width of the cross section to the average thickness is 1: 0.2 to 0.6, instead of the circular shape of the ordinary steel wire.

Hereinafter, a method of manufacturing a steel wire according to the present invention will be described.

First, a wire material having the above-described alloy composition is manufactured.

At this time, the method of manufacturing the wire rod includes: preparing a billet; Heating the billet at 1000 to 1100 占 폚; Subjecting the heated billet to finish wire rolling at 950 to 1100 ° C to obtain a wire rod, and cooling the wire rod at a cooling rate of 1 to 3 ° C / s.

After preparing the billets as described above, it is preferable that the billets are subjected to a heating process for homogenizing the billets. It is preferable that the microstructure of the billet is made into an austenite single phase through the heating process. For this purpose, the billet is preferably heated at 1000 to 1100 캜. If the heating temperature is less than 1000 占 폚, it becomes difficult to secure a temperature region during subsequent wire rolling. If the temperature exceeds 1100 占 폚, austenite grains are formed coarsely and it becomes difficult to secure a desired level of strength .

Then, the heated billet is subjected to finish wire rolling at 950 to 1100 DEG C to obtain a wire rod. If the temperature during the final hot rolling is less than 950 ° C, there is a problem that the roll lifetime is reduced due to an increase in the rolling load. On the other hand, when the temperature exceeds 1100 ° C, the grain size becomes large and ductility may be reduced, and decarburization may occur excessively, which may deteriorate the drawability.

Thereafter, the wire rod is cooled at a cooling rate of 5 to 15 DEG C / s. It is preferable to produce a wire having pearlite structure through the cooling. If the cooling rate is less than 5 DEG C / s, corner stone cementite may be formed, whereas if it exceeds 15 DEG C / s, martensite structure may be formed.

The thus obtained wire rod is subjected to cold drawing to obtain a steel wire. The total reduction ratio during cold drawing is preferably in the range of 40 to 80%. If the total reduction ratio is less than 40%, the amount of drawing processing is insufficient and sufficient strength can not be secured. On the other hand, when the total reduction ratio exceeds 80%, cracks may occur.

Thereafter, the steel wire is cold-rolled. The cold rolling is to obtain a steel wire having a plate-like shape, and it is preferable that the reduction rate in the cold rolling is in the range of 50 to 80%. If the reduction rate is less than 50%, the processing amount is insufficient and sufficient strength can not be secured. On the other hand, when the reduction ratio exceeds 80%, cracks may occur.

Then, the cold-rolled steel wire is heat-treated at 300 to 400 ° C. The heat treatment is a step of recovering ductility by eliminating dislocations generated in drawing and cold rolling, and is necessary for improving SSC resistance characteristics. If the heat treatment temperature is lower than 300 ° C, aging may occur and the ductility may be drastically reduced. If the heat treatment temperature is higher than 400 ° C, the strength may be drastically decreased and it may be difficult to ensure high strength.

Hereinafter, the present invention will be described in detail with reference to Examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

(Example)

A billet having the alloy composition shown in Table 1 below was prepared. The billet was heated at 1050 占 폚 and then hot rolled at 1000 占 폚 to produce a wire rod. Thereafter, the wire rod was cooled to 500 deg. C at a cooling rate of 10 deg. C / s and then air-cooled to room temperature. The wire was subjected to cold drawing to obtain a steel wire, the steel wire was cold-rolled, and then heat-treated under the conditions shown in Table 2 to prepare a steel wire. The tensile properties of the prepared steel wire were evaluated by a tensile test at room temperature, and the pearlite layer spacing and the colloidal size were measured by microstructural analysis. The SSC resistance characteristics were measured and the results are shown in Table 2 below. The SSC resistance characteristic evaluation was performed by applying a stress of 85% of the yield strength to the specimen in an H ₂ S atmosphere to measure the time of destruction.

division Alloy composition (% by weight) C Si Mn Cr V Ni Inventive Steel 1 0.45 0.2 0.7 0.3 0.05 0.3 Invention river 2 0.45 0.2 0.7 0.3 0.1 0.3 Comparative River 1 0.45 0.2 0.7 0.6 0.25 0.9 Comparative River 2 0.45 0.2 0.7 - 0.3 0.1 Comparative Steel 3 0.45 0.2 0.7 - - - Invention steel 3 0.45 0.3 0.8 0.4 0.13 0.3 Inventive Steel 4 0.50 0.4 0.6 0.5 0.12 0.6

division Steel grade Heat treatment
Temperature
(° C) Pearlite
Laminar spacing
(탆) Culloni
size
(탆) Yield strength
(MPa) The tensile strength
(MPa) Elongation
(%) SSC Resistance Characteristics
(time) Inventory 1 Inventive Steel 1 330 98 8 1161 1321 9.8 720 Inventory 2 Invention river 2 330 76 7 1223 1373 9.1 720 Comparative Example 1 Comparative River 1 330 103 11 1131 1221 4.9 367 Comparative Example 2 Comparative River 2 330 107 12 1096 1152 4.3 36 Comparative Example 3 Comparative Steel 3 330 132 19 1017 1142 7.8 14 Comparative Example 4 Invention steel 3 260 104 12 1092 1234 4.1 22 Comparative Example 5 Inventive Steel 4 480 141 14 1045 1189 8.7 456

As can be seen from Tables 1 and 2, Examples 1 and 2, which satisfy the alloy composition and manufacturing conditions of the present invention, satisfy the condition that the spacing on the pearlite layer is 100 μm or less and the colloidal size is 10 μm or less, The yield strength, the tensile strength, the elongation and the SSC resistance characteristics are secured.

However, in the case of Comparative Examples 1 to 3, which do not satisfy the alloy composition of the present invention, the strength, elongation and SSC resistance characteristics are lower than those of Examples 1 and 2.

Comparative Examples 4 and 5 satisfy the alloy composition of the present invention, but do not satisfy the manufacturing conditions of the present invention. Comparative Example 4 was lower than the heat treatment temperature range of the present invention, and the age hardening occurred and ductility decreased. In Comparative Example 5, the pearlite structure was decomposed and the strength was lowered as compared with the heat treatment temperature of the present invention.

Claims (8)

(Si), 0.1 to 0.5% of chromium (Cr), 0.1 to 0.5% of vanadium (V), 0.01 to 0.5% of vanadium (V) To about 0.15%, nickel (Ni): about 0.2 to about 0.8%, the balance iron (Fe) and unavoidable impurities,
The microstructure includes pearlite,
The interval on the pearlite layer is 100 mu m or less,
High Strength Steel Wire with Excellent SSC Resistance Characteristic with Cross Section Width and Average Thickness Ratio of 1: 0.2 ~ 0.6.
The method according to claim 1,
Wherein the pearlite has a colloidal size of 10 占 퐉 or less and has excellent SSC resistance characteristics.
The method according to claim 1,
The steel wire has excellent SSC resistance characteristics with an SSC resistance characteristic of 720 hours or more.
(Note that the SSC resistance characteristic means a time at which a stress of 85% of a yield strength is applied to a specimen in an H ₂ S atmosphere and is destroyed.)
The method according to claim 1,
The steel wire has superior SSC resistance characteristics with a yield strength of 1100 MPa or more and a tensile strength of 1300 MPa or more.
(Si), 0.1 to 0.5% of chromium (Cr), 0.1 to 0.5% of vanadium (V), 0.01 to 0.5% of vanadium (V) To about 0.15%, nickel (Ni): about 0.2 to about 0.8%, the balance iron (Fe) and unavoidable impurities;
Obtaining a steel wire by cold drawing the wire rod;
Cold rolling the steel wire; And
And heat treating the cold-rolled steel wire at 300 to 400 ° C.
The method of claim 5,
Wherein the step of fabricating the wire rod comprises:
Preparing a billet;
Heating the billet at 1000 to 1100 占 폚;
Finishing the heated billet at 950 to 1100 ° C to obtain a wire rod; and
And cooling the wire rod at a cooling rate of 5 to 15 占 폚 / s to obtain a high strength steel wire having excellent SSC resistance characteristics.
The method of claim 5,
Wherein the cold drawing is performed at a total reduction ratio of 40 to 80%.
The method of claim 5,
The cold-rolled steel sheet has excellent SSC resistance characteristics with a total reduction of 50 to 80%.