JP6183037B2 - Oyster culture plated steel wire with excellent seawater resistance and scratch resistance - Google Patents

Description

  The present invention relates to a Zn-Al-plated steel wire having high corrosion resistance, particularly high corrosion resistance to seawater, and scratch resistance, and its main use is for seafood culture, particularly oyster culture. Further, the present invention relates to a plated steel wire that requires seawater resistance and scratch resistance.

There are roughly two conventional techniques for imparting high corrosion resistance to steel used in the sea.
One is a method for improving the corrosion resistance of the steel itself. For example, there is a technique disclosed in Patent Document 1. In order to improve the corrosion resistance of the steel itself in the sea, this technique is a technique for adding P, Cu, Cr to a low C system to form a fine oxide film on the surface or grain boundary to enhance the corrosion resistance. In the case of this technology, what is considered is corrosion resistance in a static environment, and it is difficult to exhibit regular performance in a dynamic environment. That is, in the case of this technique, application to oyster culture, which is a use of the present invention, has the following problems.

  In the case of oyster culture, oysters are suspended from steel wires and floated in the sea. Steel wires hanging oysters may encounter cases where adjacent steel wires or steel wires and oyster shells come into contact with each other due to wave motion in the sea.

  Furthermore, in the case of oyster culture, in order to confirm not only the harvest period but also the growth status of the oysters being cultured, the oyster suspension steel wire is pulled up and observed several times before harvesting. Also at this time, the steel wires may contact each other or the steel wire and the shell may be damaged. At this time, a part of the fine and dense oxide layer generated on the surface of the steel wire is peeled off, so that a local battery is formed in the part and pitting corrosion occurs. Since the corrosion of food progresses quickly, it breaks early.

  In order to prevent this problem, a method of covering the surface of the steel wire with plating has been adopted. For example, Patent Document 2 discloses a technique for improving the corrosion resistance by changing the pro-eutectoid phase generated in a lump shape to a form parallel to the interface of the steel wire by wire drawing in order to increase the corrosion resistance of the plating layer. Yes.

  However, the weak point of this technology is that the surface of the plated steel wire is cracked in the plating layer due to contact with the sharp shell used for oyster culture in the actual usage environment, as in the technology for improving the corrosion resistance of the bare steel wire. In this case, it is difficult to ensure the normal high corrosion resistance because local corrosion proceeds. Certainly, the alloy-plated steel wire of the prior art has a high corrosion resistance of about 3 to 7 times that of hot dip galvanizing, but these results are only performance achieved in a static environment. is there. In particular, depending on the ocean currents such as oyster culture, it is necessary to consider the case where the surface of the plating steel wire for aquaculture is damaged by the edge of the shell used for aquaculture. For this reason, the inventors have a new viewpoint of increasing the hardness of the plating layer in order to ensure that the plating layer itself has the effect of protecting the plating layer to improve the conventional target performance against alloy plating. Tried evaluation.

Japanese Patent Publication No. 02-025977 Japanese Patent No. 4464880

  The object of the present invention is excellent in seawater resistance and scratch resistance, such as a plated steel wire for oyster culture that has an underwater corrosion life that can be used throughout the season from aquaculture to harvest even in harsh usage environments. A plated steel wire is provided.

In order to achieve the above object, the present invention is as follows.
[1]
It is a plated steel wire with a Zn plating layer formed on the surface of the ground iron,
The steel
% By mass
C: 0.35-0.40%,
Si: 0.15-0.30%
Mn: 0.60-0.90%
P: 0.020% or less,
S: 0.010% or less,
And the balance consists of Fe and impurities,
The plating layer contains, by mass%, Al: 3.5-12%, the balance is made of Zn and impurities,
An alloy layer of Fe-Zn-Al composition between the plating layer and the ground iron,
A plated steel wire for oyster culture having a tensile strength of 1150 to 1390 MPa and excellent seawater resistance and scratch resistance.
[2]
The plated steel wire for oyster culture excellent in seawater resistance and scratch resistance according to [1], wherein the plating layer has an adhesion amount of 90 to 130 g / m ² .
[3]
The plated steel wire for oyster culture excellent in seawater resistance and scratch resistance according to [1] or [2], wherein the surface hardness of the plating layer is 80 to 131 in terms of Vickers hardness.

  The present invention provides a plated steel wire for oyster culture that stabilizes the aquaculture activity in one season and has an underwater life that can be used without disconnection just before harvesting. The present invention has the effect of stabilizing the yield of oyster culture yield.

It is a graph which shows the relationship between the amount of Al of a plating composition, and the hardness of a plating layer. It is a graph which shows the relationship between plating adhesion amount, plating peeling, and a crack. It is a graph which shows the disconnection generation | occurrence | production area | region in seawater real environment.

  The present inventors examined a method for reducing damage caused by oscillating in the sea and coming into contact with an adjacent oyster-suspended steel wire as in the case of a plated steel wire that suspends an oyster when cultivating oysters.

  First, it is necessary to improve the scratch resistance so that the plated layer of the plated steel wire is not easily scraped or peeled off by a mechanical external force. The present inventors examined a method for hardening the plating layer in order to improve the scratch resistance. FIG. 1 is a graph showing the relationship between the Al content in the plating layer and the Vickers hardness of the plating layer. It can be seen that the hardness of the plated layer is increased by adding Al to the hot dip galvanized layer.

  In addition, in order to form a Zn plating layer containing Al on a steel wire, a sufficient adhesion force between the steel material and the plating layer is obtained simply by immersing the steel wire (metal) in a zinc molten bath containing Al. Cannot be obtained. Therefore, a two-bath plating method is suitable for applying to an Al-containing plated steel material. That is, the first bath is a zinc bath, and the steel material (metal) is plated with zinc, and then the second bath is immersed in an Al-containing zinc bath. Thereby, an Al-containing plating layer with high adhesion can be obtained. At this time, an Fe—Zn—Al alloy layer is formed between the plating layer and the ground iron. This alloy layer is a thin but hard layer, which also contributes to improving the scratch resistance.

Next, steel wires for oyster farming have the work of attaching and removing oysters, or lifting and hanging steel wires carrying oysters, so steel wires should be more workable and flexible. . For example, it is necessary to suppress plating surface cracking and plating peeling during these operations. The inventors of the present invention have studied an optimum amount of plating for that purpose. FIG. 2 shows the result of investigating the relationship between the amount of plating and the peelability of plating. Own diameter wrapped result of the test, as shown in FIG, less was coating weight most peeling is an area of 90~130g / m ^2. If the adhesion amount is less than that, cracking occurs and the corrosion resistance also decreases. Conversely, it has been found that if the amount of adhesion is too much, cracking or peeling is likely to occur.

  In addition, the present inventors assumed that the quality of the plating layer simply dominates the fracture during the evaluation with various investigations in order to elucidate the cause of the early disconnection. It was also found that the plating layer of the present invention is divided into those that break early and those that do not break. In other words, this suggests that the internal performance of the steel itself may affect the early disconnection of corrosion fatigue in the sea. Efforts were made to identify sex. The results are shown in FIG.

  As shown in FIG. 3, it is shown that P and S of steel components affect the corrosion fatigue life in the sea. The x mark in the figure indicates that there is a disconnection at the harvest stage, the ■ mark indicates that there is no disconnection, but the plating layer has cracked, and the ○ mark indicates that there is no disconnection and plating cracks. Indicates what was missing.

By combining the above results, it has become possible to extend the life in the sea. The present invention is described in detail below. In the present invention, “%” for the composition of the base metal and the plating layer means mass%.

  C is an element used for properly imparting the strength of the wire and the steel wire. The lower limit is set to 0.35% because when the wire diameter of the steel wire is taken into consideration, the stress level applied to the steel wire at the time of cultivation cannot be supported below this. The upper limit is set to 0.40% because the strength becomes too high above this, the ductility of the steel wire itself deteriorates, and the steel wire breaks due to the bending of the oyster being lifted or suspended. This is because workability is deteriorated.

  Si is used not only as a deoxidizing element for steel, but also for stabilizing the plating performance during hot dip galvanizing. The lower limit is set to 0.15% because if it becomes less than this, it becomes a region where the formation of an alloy layer at the time of plating suddenly occurs, so that plating peeling or plating burn occurs and the plating performance deteriorates. . Even if the upper limit is set to 0.30%, Si affects the plating performance and plating burns easily occur.

  Mn is an element that contributes to strength in addition to being used as a deoxidizing element for steel. The lower limit of the present invention is set to 0.60% because if it is less than this, the strength is lowered and the surface properties of the wire and the steel wire may be deteriorated due to insufficient deoxidation. On the other hand, the reason why the upper limit is set to 0.90% is that when the content exceeds this upper limit, the quenching performance is improved and the strength is increased more than necessary.

  P is an impurity in the present invention. If the upper limit of P is set to 0.20%, the fluctuations inevitably caused by wave motion in the sea according to the data collected in the real field that affects the oyster culture in the sea by the inventors It was found that the breakage occurred early from the grain boundary in the low cycle fatigue stress field caused by. As can be seen from this result, the influence of P was found to be extremely large. Although there is no particular lower limit, it is preferably about 0.005% except for an economical viewpoint.

S is an impurity in the present invention. S, like P, affects corrosion fatigue. S is an element involved in the ductility of steel, and the ductility deteriorates if grain boundary such as MnS occurs. Further, if MnS is exposed on the surface of the steel wire, it becomes easy to form a local battery at the location in the sea and iron elution is likely to occur. Therefore, the upper limit of S is set to 0.010% or less.
The above is an explanation of the composition of steel (metal).

  Next, the plating layer mainly composed of Zn in the present invention will be described.

  The reason for limiting the Al concentration of the plating layer will be described. The reason why the lower limit of the Al concentration is set to 3.5% is that if it is less than this, the basic corrosion resistance of the plating layer itself is inferior, so that the competitiveness with ordinary hot dip galvanizing is lost. Further, when Al is further added to the plating layer, the hardness of the plating layer is increased and the scratch resistance is improved. However, the upper limit is set to 12% because if a large amount of Al is added, a large amount of oxidized dross is generated in the plating bath, so that it is impossible to control the drawing when it is pulled up from the plating bath, and there is no oxidized dross on the plating surface. It is because it adheres and the surface property of plating deteriorates remarkably.

  From the above two viewpoints, the Al content in the plating layer is limited to 3.5 to 12%. If the Al content is in this range, Mg may be added in an amount of 0.1 to 5%, or Si may be added in a range of 0.0005 to 2% in order to further improve the corrosion resistance.

  Next, the reason for limiting the plating hardness will be described. In the present invention, an increase in plating hardness is significant because it plays a role of protecting the plating layer when an external force is applied. The reason why the lower limit is limited to 80 in terms of Vickers hardness is that if it is less than this, the decrease in hardness becomes large and the predetermined plating protection ability cannot be maintained. Further, the upper limit is set to 131 because it is necessary to further increase the Al content in the plating layer to increase the upper limit, which leads to the deterioration in quality due to the increase in oxidized dross described above.

The reason for limiting the adhesion amount of the plating layer will be described. The lower limit of the coating amount of the plating layer was set to 90 g / m ² from the corrosion resistance. If it is less than this, the basic performance of the corrosion resistance itself of the plating layer is lowered, and the competitiveness with normal hot dip galvanizing is lost. The reason why the upper limit is limited to 130 g / m ² is that when the amount of adhesion is larger than this, the plating layer becomes thick and plating peeling occurs in the self-diameter winding evaluation.

  Next, the reason for limiting the strength of the plated steel wire will be described. In the present invention, the reason why the lower limit of the strength of the plated steel wire is limited to 1150 MPa is to eliminate the risk of disconnection due to insufficient tension that supports the total weight of the oysters at the time of harvest. The upper limit of the strength of the plated steel wire was set to 1390MPa. This is a manual process of fixing the plated steel wire by locally bending or twisting it when fixing the plated steel wire to a culture rod instead of increasing the strength more than necessary. In addition to an increase in the load, the ductility is inevitably deteriorated, so that the workability described above is remarkably lowered, and the upper limit is set to 1390 MPa.

Next, examples will be described.
All the levels used were steel components produced by actual steel using a 250-ton converter. After being continuously cast into a slab having a cross section of 300 mm × 500 mm, it was rolled into a steel slab having a cross section of 122 mm square by lump rolling, and rolled to 5.5 mm and partly to a 5 mm wire at a wire rod factory. The heat treatment after rolling was cooled using both a DP level produced by blast heat treatment and a DLP level that was partially heat-treated in molten salt in-line to obtain a wire rod. By drawing this wire, the 5.5 mmφ wire was changed to a 2.18 mm steel wire, and the 5 mmφ wire was changed to a 2 mm steel wire.

  As for plating, Nos. 1 to 10 correspond to the present invention, which is a two-bath type plating method. In the first bath plating, normal hot dip galvanizing is performed, and in the second bath, Zn-AL alloy plating is performed. Was given. However, the effect on the present invention does not change even when electroplating is performed instead of the first bath plating. The composition of the second bath may be Zn—Al—Mg or Zn—Al—Mg—Si as described above. No. 11 to 19 are plating methods by the same two-bath method as described above, but are comparative methods in which the plating adhesion amount is larger than that of the present invention. In No11-19, S amount of bullion exceeds 0.010%. Nos. 20 to 28 are conventional methods, which are based on a one-bath plating method using only Zn, and the amount of plating adhesion is larger than the range of the present invention. For No20, 22-28, the amount of C in the bullion exceeds 0.40%. In No. 20 to 22, 24, 25, 27, and 28, the Mn content of the bare metal is less than 0.60%. In No20-28, P amount of bullion exceeds 0.02%. In No20 ~ 27, S amount of bullion exceeds 0.010%. In No. 20 to 28, the Al content of the plating layer is less than 3.5%.

  In order to grasp the performance of corrosion fatigue in the sea by carrying out self-winding using the plated steel wires produced by the above processes, observing the actual state of plating peeling and plating surface cracks, etc. The oyster culture period is one season in an environment where galvanized steel wires with levels of NO1 to 28 are actually used as oyster-suspended plated steel wires at the oyster farm near Hiroshima Bay in the Seto Inland Sea. The inside disconnection situation was observed.

Table 1 shows the results.

As a result of the self-winding winding test in Table 1, the mark ◯ indicates that there was no breakage, the mark Δ indicates that no breakage occurred, but a crack in the plating layer was observed, and the mark × indicates that breakage occurred.
Nos. 1 to 10 were at the level of the present invention, and good oyster harvesting was possible without disconnection. Further, Nos. 11 to 19 show the results of the comparative method. Although no disconnection occurred, cracks in the plating layer were observed. In No19, the Hv hardness of the plating layer exceeded 131. No. 20 to 28 were all disconnected. In Nos. 20 to 28, the Hv hardness of the plating layer was less than 80.

  From the above results, it is clear that in the actual environment, in the case of production without being aware of underwater corrosion fatigue of the plated steel wire, it is clear that the disconnection occurred at an early stage, which shows an adverse effect on the productivity of the aquaculture activity did. On the other hand, improvement of underwater corrosion fatigue can be confirmed by securing the hardness of the plating layer at least twice that of the conventional method as in the method of the present invention. Another point of view has been that the ductility of the plated steel wire itself can be secured by controlling the P and S components in the steel. It can be seen that the effect of the fact that the growth of No. 9 with low P and S is the best in the whole is actually shown. This suggests the possibility of improving characteristics such as low cycle fatigue due to waves.

Claims (3)

It is a plated steel wire with a Zn plating layer formed on the surface of the ground iron,
The steel
% By mass
C: 0.35-0.40%,
Si: 0.15-0.30%
Mn: 0.60-0.90%
P: 0.020% or less,
S: 0.010% or less,
And the balance consists of Fe and impurities,
The plating layer contains, by mass%, Al: 3.5-12%, the balance is made of Zn and impurities,
An alloy layer of Fe-Zn-Al composition between the plating layer and the ground iron,
A plated steel wire for oyster culture having a tensile strength of 1150 to 1390 MPa and excellent seawater resistance and scratch resistance. Adhering amount of the plating layer is 90~130g / m ^2, excellent oyster plated steel wire seawater abrasion resistance according to claim 1. The plated steel wire for oyster culture excellent in seawater resistance and scratch resistance according to claim 1 or 2, wherein the surface hardness of the plating layer is 80 to 131 in terms of Vickers hardness.