KR101328338B1 - Wire rod and heat treated wire rod for drawing and high strength stell wire - Google Patents

Abstract

The present invention relates to a wire rod and heat treatment material and a high-strength steel wire that can be used for tire cords, wire ropes, piano wire, bridge steel wire, etc., in weight%, C: 0.84-1.0%, Mn: 0.1-0.6%, Si: 0.1 ~ 0.5%, Cr: 0.1 ~ 0.5%, B: 0.001 ~ 0.01%, N: 0.01% or less (excluding 0), balance Fe and other unavoidable impurities. Provided is a wire rod for drawing including a microstructure consisting of less than 1% pearlite or cementite cementite, a heat treatment material obtained therefrom, and a high strength steel wire.
According to the present invention, by appropriately controlling the alloying component can provide a wire for the wire and heat treatment material that can give excellent strength during the wire processing, it is possible to provide a high strength steel wire using this wire or heat treatment material.

Description

Wire rod, heat treatment material and high strength steel wire for wire drawing {WIRE ROD AND HEAT TREATED WIRE ROD FOR DRAWING AND HIGH STRENGTH STELL WIRE}

The present invention relates to a wire rod and heat treatment material and a high strength steel wire, and more particularly to a wire rod and heat treatment material and high strength steel wire that can be used, such as tire cords, wire ropes, piano wire, bridge steel wire.

In general, there are three methods for obtaining high strength wire for drawing.

First, it is possible to increase the strength of the material itself by adding a large amount of reinforcing elements. Representative examples of such reinforcing elements include carbon. As the strength of the required wire rods gradually increased, the carbon content increased gradually from the vacancy zone to the vacancy zone and from the vacancy zone to the supervacancy zone. As described above, when the carbon content is increased, the fraction of hard cementite in the wire rod increases and the strength of the material may be improved as the lamellar spacing of the pearlite structure becomes dense.

Secondly, the wire rod for drawing is drawn and heat-treated to the final wire after the rolled wire, the strength can be significantly improved by the work hardening during processing. When the wire is processed, the lamellar spacing of the pearlite structure can be miniaturized, the work hardening coefficient increases, the work can be hardened due to the accumulation of dislocations, and the like.

Third, the strength can be improved by increasing the fresh strain of the material separately from the above. The fresh strain of the material is closely related to the ductility of the material, and as the material itself is easily disconnected during wire drawing, the easier it is to improve the strength.

However, since these methods do not all work independently but are related to each other to change the strength of the wire rod, it is difficult to increase the strength by controlling them independently.

That is, when a large amount of alloying elements are simply added to improve the strength of the wire, problems such as disconnection may occur due to poor ductility of the wire in the subsequent steel wire manufacturing process after wire rod rolling. Therefore, in order to improve the strength of the wire rod, it is necessary to consider various factors from various viewpoints.

An object of the present invention is to provide a wire rod and heat treatment material excellent in drawability by appropriately controlling the component system and a high strength steel wire obtained therefrom.

One embodiment of the present invention is a weight%, C: 0.84 ~ 1.0%, Mn: 0.1 ~ 0.6%, Si: 0.1 ~ 0.5%, Cr: 0.1 ~ 0.5%, B: 0.001 ~ 0.01%, N: 0.01% or less (Excluding 0), the balance Fe and other unavoidable impurities, and provides a wire for a fresh wire having a microstructure comprising more than 99 area% of pearlite and less than 1% of the cornerstone ferrite or cornerstone cementite.

Another aspect of the present invention is by weight, C: 0.84-1.0%, Mn: 0.1-0.6%, Si: 0.1-0.5%, Cr: 0.1-0.5%, B: 0.001-0.01%, N: 0.01% or less (Except 0), the balance Fe and other unavoidable impurities, and is incubated to provide a fresh heat treatment material having a microstructure containing more than 99 area% of the upper bainite and less than 1% pearlite or cementite cementite. .

Another aspect of the present invention is by weight, C: 0.84-1.0%, Mn: 0.1-0.6%, Si: 0.1-0.5%, Cr: 0.1-0.5%, B: 0.001-0.01%, N: 0.01% or less (Except zero), balance Fe and other unavoidable impurities, providing a steel wire comprising a microstructure consisting of at least 99 area% of upper bainite and less than 1% of pearlite or cementite cementite.

According to the present invention, by appropriately controlling the alloying component can provide a wire for the wire and heat treatment material that can give excellent strength during the wire processing, it is possible to manufacture a high strength steel wire using this wire or heat treatment material.

The inventors of the present invention while researching to develop a wire rod that can be manufactured into a steel wire having excellent drawability and high strength after drawing, the alloy composition, in particular, if the content of B and the microstructure of the wire rod is properly controlled, the above problem I realized that I can solve the problem. In general, the B is known to have little effect of suppressing formation of calcite cementite and improving hardenability in the roughened steel. However, according to the present inventors, when control of the microstructure and addition of B are performed simultaneously, contrary to the previously reported research results, it is possible not only to give the wire rod excellent freshness but also to increase the strength of the steel wire after processing. It has been found to increase significantly, and the present invention has been devised.

In one embodiment, the present invention provides, in weight percent, C: 0.84-1.0%, Mn: 0.1-0.6%, Si: 0.1-0.5%, Cr: 0.1-0.5%, B: 0.001-0.01%, N: 0.01 It is composed of less than% (excluding 0), balance Fe and other unavoidable impurities, and provides a wire rod for drawing having a microstructure including more than 99 area% of pearlite and less than 1% of cornerstone ferrite or cornerstone cementite.

Hereinafter, the component system of this invention is demonstrated.

C: 0.84-1.0 wt%

C is a key element in securing strength. However, if the content exceeds 1.0%, the cross-sectional reduction rate (RA) of the wire rod is reduced, and ultimately, the strength increase due to fresh processing cannot be expected. On the other hand, if it is added less than 0.84%, it may be difficult to secure the target strength. Therefore, the content of C is preferably controlled in the range of 0.84 ~ 1.0% by weight.

Mn: 0.1-0.6 wt%

The Mn is an element effective for increasing the hardenability, and it is preferable to add 0.1% or more to obtain the effect. However, if it exceeds 0.6%, central segregation may occur, and since the grain boundary of the tissue on the surface of the material is easily oxidized during heat treatment, it may adversely affect the product characteristics, so the content does not exceed 0.6%. desirable. Therefore, the content of Mn is preferably controlled in the range of 0.1 to 0.6% by weight.

Si: 0.1-0.5 wt%

Si is an element that plays a role of not promoting the formation of cementite cementite in the pore-forming composition range and at the same time exerts an effect of solid solution strengthening. The Si is used as a deoxidizer in the steelmaking process, but may be included in the steel in a small amount, in the present invention, it is preferable to add 0.1% or more in order to improve the strength and ductility in addition to the formation of the above-described cementite cementite. However, if it is added in excess of 0.5% decarburization easily occurs on the surface of the material when reheating and fresh workability may be reduced.

Cr: 0.1-0.5 wt%

Cr is an element effective in securing strength and ductility by miniaturizing the pearlite layer spacing. When the Cr is added less than 0.1% may not be sufficient to refine the layered structure, if the content exceeds 0.5% may slow down the constant temperature transformation rate to reduce productivity. Therefore, the content of Cr preferably has a range of 0.1 to 0.5% by weight.

B: 0.001-0.01 wt%

B is an element capable of suppressing the formation of cementite cementite and segregating at grain boundaries to improve quenchability. It is preferable to add 0.001% or more for the above effect, but when it exceeds 0.01%, the fresh workability may be deteriorated, so the content of B is preferably controlled to have a range of 0.001 to 0.01 wt%.

N: 0.01 wt% or less (excluding 0)

N is an element present as an impurity in steel, but in the present invention, N has an effect of slightly improving strength. Since the N may deteriorate the fresh workability when a large amount is added, the upper limit is preferably controlled to 0.01%, more preferably 0.006% or less.

The wire rod of the present invention preferably has a microstructure having a pearlite single-phase structure, through which the microstructure can be easily controlled after heat treatment, and further, it can impart excellent tensile strength to the steel wire manufactured by drawing. On the other hand, the microstructure of the wire rod of the present invention is preferably made of a single phase of pearlite, but inevitably, impurity structures such as cornerstone ferrite or cornerstone cementite may be formed. In this invention, it is preferable to control so that such an impurity structure may be less than 1%.

The wire rod that satisfies the component system and microstructure as described above is then subjected to heat treatment such as lead patenting (LP) before being manufactured into steel wire through drawing. As described above, the wire rod through LP heat treatment may be incubated to change to the desired microstructure.

On the other hand, the wire rod or constant temperature heat treatment may use a manufacturing method commonly used in the art, and those skilled in the art, considering the alloying components of the wire rod during heat treatment, without appropriate difficulty in cooling and cooling stop temperature By setting, desired microstructure can be obtained.

In the present invention, the wire rod is incubated as described above, so that the structure of the heat-treated wire rod (hereinafter also referred to as 'heat treatment member') has an upper bainite single phase. In this way, the microstructure can be controlled by the upper bainite single phase to reduce the tensile strength of the heat treatment material, thereby improving the drawability. In addition, the tensile strength of the steel wire is significantly increased after drawing. On the other hand, the microstructure of the heat treatment material of the present invention is preferably made of an upper bainite single phase, impurity can be inevitably formed in the process. The impurity structure may be pearlite or salty cementite, and in the present invention, it is preferable to control the pearlite or salty cementite structure to be less than 1%.

When satisfying the alloy composition and composition range and the microstructure as described above, the heat treatment material may have a tensile strength of 900 ~ 1100MPa, if less than 900MPa it may be difficult to obtain a high strength steel wire, if more than 1100MPa Workability may be lowered.

Thereafter, the heat treatment material may be drawn to manufacture a steel wire having excellent strength. At this time, the above-mentioned fresh working may use ordinary conditions. The steel wire produced as described above has a high tensile strength of 2400 MPa or more, more preferably 3300 MPa or more, and is thus very suitable for application to products requiring high strength such as tire cords, wire ropes, piano wires, and steel wires for bridges.

Hereinafter, the present invention will be described in detail with reference to Examples. However, the following examples are only for illustrating the present invention in more detail and do not limit the scope of the present invention.

(Example)

Ingot having a composition range as shown in Table 1 was hot-rolled at 1150 ℃ to prepare a wire having a pearlite structure of 99.9 area%. The wire rod was heated at 1200 ° C. for 30 minutes for normalization, followed by air cooling. Subsequently, the wire was heated at 1100 ° C. for 30 minutes, and then subjected to incubation to obtain a heat treatment material having various microstructures as shown in Table 1 below. After measuring the tensile strength of the heat treatment material thus obtained, the results are shown in Table 1 below. Then, after the heat treatment material is drawn to produce a steel wire until disconnection occurs, the tensile strength was also measured for this steel wire, and the results are shown in Table 1 below.

division Chemical composition (% by weight) Heat treatment Steel wire C Si Mn Cr B N Microstructure The tensile strength
(MPa) The tensile strength
(MPa) Inventory 1 0.92 0.2 0.3 0.2 0.004 0.0005 Upper bainite 1086 3321 Comparative Example 1 0.92 0.2 0.3 0.2 0.004 0.0005 Pearlite 1251 2302 Inventive Example 2 0.95 0.2 0.4 0.2 0.004 0.005 Upper bainite 1097 2445 Comparative Example 2 0.95 0.2 0.4 0.2 0.004 0.005 Pearlite 1273 2379 Comparative Example 3 0.90 0.2 0.3 0.2 - 0.0005 Pearlite 1123 2285 Comparative Example 4 0.90 0.2 0.3 0.2 - 0.0005 Upper bainite 1125 2328

As shown in Table 1, satisfying the alloy composition and composition range proposed by the present invention, and at the same time it is found that in the case of Inventive Examples 1 and 2 consisting of the upper bainite has a low tensile strength of less than 1100MPa Can be.

On the other hand, Comparative Examples 1 and 2, in which B is added and the pearlite microstructure, have a high strength of 1200 MPa or more, and Comparative Example 3, in which B is not added and the pearlite structure, has a strength of 1100 MPa or more. In other words, even if the component system proposed by the present invention is satisfied, it can be seen that the tensile strength of the heat treatment material is high when the microstructure is different. In the case of Comparative Example 4, but includes the microstructure of the present invention, B is not added, it can be seen that it has a high strength.

On the other hand, when the heat treatment of the heat treatment material, Comparative Examples 1 and 2 was only about 1050 ~ 1100MPa of the amount of increase in strength, Comparative Example 3 was only 1162MPa, Comparative Example 4 was only 1203MPa. However, Inventive Examples 1 and 2 had a strength increase amount of 1300 MPa or more, which is significantly higher than that of the comparative examples. In particular, Inventive Example 1, the increase in tensile strength was 2235 MPa, and it can be seen that the tensile strength was very high.

As described above, in the present invention, although the strength of the heat treatment material is low, when the steel wire is manufactured after drawing, the tensile strength is clearly increased.

Claims (5)

delete In weight%, C: 0.84-1.0%, Mn: 0.1-0.6%, Si: 0.1-0.5%, Cr: 0.1-0.5%, B: 0.001-0.01%, N: 0.01% or less (excluding 0), Consisting of balance Fe and other unavoidable impurities,
A heat treatment material for a fresh wire having a microstructure containing incubated at least 99 area% of upper bainite and less than 1% of pearlite or cementite cementite.
The method according to claim 2,
The heat treatment material is a fresh heat treatment material having a tensile strength of 900 ~ 1100MPa.
In weight%, C: 0.84-1.0%, Mn: 0.1-0.6%, Si: 0.1-0.5%, Cr: 0.1-0.5%, B: 0.001-0.01%, N: 0.01% or less (excluding 0), Consisting of balance Fe and other unavoidable impurities,
A steel wire comprising a microstructure consisting of at least 99 area% of upper bainite and less than 1% of pearlite or cementite cementite.
The method of claim 4,
The steel wire is a steel wire having a tensile strength of 2400MPa or more.