JPH08176741A - Long service life c hook for pickling - Google Patents

Abstract

PURPOSE: To manufacture a long service life C hook for pickling enabling continuous use for long term by hot-forging a steel having a specific composition regulating the contents of Ni, Cr and Mo and executing machining. CONSTITUTION: A steel ingot composed of, by wt.%, <=0.08% C, <=1.00% Si, <=2.00% Mn, <=0.030% P, <=0.030% S, <=3.00% Cu, 10.0-15.0% Ni, 15.0-19.0% Cr, 1.0-4.0% Mo, <=0.010% O and the balance Fe with impurity elements is hot-forged into a specific shape at about 1000-1250 deg.C and >=3 forging ratio. Successively, after executing solid solution heat treatment, the last finish working is applied by machining and the surface roughness after machining is desirable to be <=3μm Rmax . By this method, in a pickling apparatus used to both of acid solution and salt solution, the C hook obviating the exchange is obtd. at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pickling C hook which is used as a hanging tool for steel during a pickling process for the purpose of removing oxide scale on the surface after heat treating a steel.

[0002]

2. Description of the Related Art Steel materials are heat-treated under various conditions and methods suitable for each steel type and intended use in order to secure necessary properties. Usually, the heat treatment is performed in an environment in which the material to be heat treated is in contact with the atmosphere except in special cases. At this time, since it is heated to a high temperature, a scale that is an oxide of Fe is naturally generated on the surface. Since the presence of this scale impairs the performance as a product, scale removal treatment is usually performed by pickling.

The pickling is a method of using an acid solution such as hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid or a salt solution, and immersing the steel material in these solutions to remove the scale and improve the surface properties.
A steel material is hung on a special hook called a hook and immersed in a pickling solution.

As the conventional C-hook for pickling, when used in the above-mentioned line containing only the acid solution, a C hook made of iron (often used SS material) and FRP-coated is used. . However, when both an acid solution and a salt solution are used as in the pickling equipment for stainless steel, the C hook made of iron is weak against acid, and the FRP coating cannot withstand high temperatures, so an acid solution is used. FR when
It is called Hastelloy C (Hastelloy C) when it is used while replacing it with P-coated iron C hook, and when using salt solution, it is replaced with iron C hook without FRP coating. 16% Cr-
It is usual to use a C hook manufactured by casting using an extremely expensive alloy such as a 17% Mo-2.5% Co-4% W-Ni alloy or a 28% Cr-13% Ni alloy.

[0005]

The above-mentioned conventional C-hook for pickling has the following problems. That is, as described above, the FRP-coated C hook made of iron cannot withstand immersion at 400 to 500 ° C. like salt, and therefore can be used only in a pickling line using only an acid solution. If the iron C hook is used in a pickling line including the use of salt, it is necessary to exchange the C hook with FRP coating and the C hook without FRP coating as described above. , Extra space and dedicated switching equipment are required. Also, if the C hook is not replaced, an acid resistant alloy such as Hastelloy C is used as it can withstand acid and salt, but it is significantly more expensive than the iron C hook. In addition, it has a problem that it is expensive but its life is not sufficient, and it must be replaced within a short period of time.

The present invention has been made to solve the above problems, and its purpose is to eliminate the need for replacement even in a pickling equipment using both an acid solution and a salt solution. , Has a life that can be used continuously for a long period of time,
Moreover, it is an object of the present invention to provide a new C hook which is cheaper than the conventional one.

[0007]

Means for Solving the Problems The present inventor has sought a cheapest possible material among materials having both acid resistance and heat resistance capable of withstanding immersion in both an acid solution and a salt solution, The present invention has been completed as a result of examining including the manufacturing method and confirming the effect at the actual manufacturing site.

It is a well known fact that austenitic stainless steel has excellent corrosion resistance.
It is well known that materials containing a large amount of i, Cr, Mo, etc. have better corrosion resistance. However, the more these elements are added, the higher the cost becomes, and it is difficult to manufacture an inexpensive C hook even if the performance is improved. The present inventors have conducted experiments with various components to find a component range in which expensive elements are suppressed to a necessary minimum amount, and corrosion resistance and long service life can be secured without problem in use as C hooks.
I investigated it in detail.

As a result, regarding corrosion resistance, SUS3, which is the most used austenitic stainless steel, is used.
It was found that 04 is not sufficient, and at least the same level of corrosion resistance as SUS316 is required. In addition, as a result of examining the relationship with the life, the influence of the manufacturing method is very large, that the life by the hot forging is longer than that by casting, and the working ratio is set to a certain value or more during the hot forging. The present invention has been completed by finding that the manufactured product has a longer life, and that the machined surface has a smaller surface roughness so that pitting corrosion is less likely to occur and a longer life can be obtained.

The long-life C-hook for pickling of the present invention obtained as a result of the above explanation has a weight ratio of C: 0.08% or less and Si: 1.0.
0% or less, Mn: 2.00% or less, P: 0.030% or less, S: 0.030% or less,
Cu: 3.00% or less, Ni: 10.0 to 15.0%, Cr: 15.0 to 19.0%,
Steel containing Mo: 1.0-4.0%, O: 0.010% or less, and balance Fe and impurity elements is hot forged into a predetermined shape at a working ratio of 3 or more, and then subjected to final finishing by machining. It is characterized by having done. And, it is preferable to set the surface roughness after machining to Rmax: 3 μm or less. As will be described later, when C is not reduced to 0.02% or less, it is necessary to perform solution heat treatment after hot forging.

It is also possible to add a machinability improving element to facilitate machining after hot forging. In this case, S: 0.030 to 0.400%, Pb: 0.40% or less, Se: 0.40% or less, Te: 0.40% or less, Bi: 0.40% or less, Ca: 0.0005 to 0.100%
Of these, one kind or two or more kinds may be contained. Next, the reasons for limiting the component composition of the C hook material used in the present invention will be described below.

C: 0.08% or less C is an element that stabilizes the austenite phase and contributes to high strength by forming a solid solution, but is also an element that impairs corrosion resistance. Therefore, in order to secure the corrosion resistance withstanding the acid solution, it is preferable to further reduce it, and the upper limit was made 0.08%. In the case of emphasizing more excellent corrosion resistance, it is desirable that it is as low as possible, and if it is 0.02% or less, the solution heat treatment can be omitted, which is advantageous.

Si: 1.00% or less Si is an element necessary as a deoxidizing agent and stabilizes the ferrite phase. It is also an element effective in improving the oxidation resistance, work hardening property and age hardening property. However, 1.00%
If added above, the toughness is impaired, so the upper limit was made 1.00%.
It is preferably 0.50% or less. The lower limit is not specified, but the content of 0.10% or more is necessary for deoxidation.

Mn: 2.00% or less Mn is an element that stabilizes the austenite phase and is effective in improving work hardenability. The lower limit is not particularly defined, but preferably 1.00% or more is contained. However,
Even if a large amount is contained, the effect will be saturated, so the upper limit is 2.00%.
And

P: 0.030% or less P is an element that impairs hot workability and needs to be reduced as much as possible, so the upper limit was made 0.030%.

S: 0.030% or less or S: 0.030 to 0.400% S is an element that impairs corrosion resistance, but is also an element that improves machinability. Therefore, when importance is attached to corrosion resistance,
It has to be reduced, and the upper limit was made 0.030%. Especially when importance is placed on corrosion resistance, it is preferable to set S to 0.010% or less.
In addition, when the machinability is more important than the corrosion resistance, it is preferable to add a small amount, and it is possible to add it in the range of 0.030 to 0.400%.

Cu: 3.00% or less Cu is an element effective in improving the corrosion resistance, but if it is contained in a large amount, the hot workability deteriorates and it becomes difficult to manufacture the C hook by hot forging, so the upper limit is set. It was 3.00%.

Ni: 10.0 to 15.0% Ni is a basic element for ensuring the corrosion resistance of stainless steel,
It is also an element that improves hot workability and cold workability. In order to achieve the object of the present invention, it is indispensable to secure corrosion resistance for C hooks to be used for a long period of time, and at least 10.0% or more, preferably 12.0% or more. However, even if contained in a large amount, the life improving effect is saturated, so the upper limit was made 15.0%.

Cr: 15.0 to 19.0% Cr is a basic element indispensable for corrosion resistance of stainless steel. To ensure excellent corrosion resistance that can withstand the environment of repeated immersion in acid solution, 15.0%
It is necessary to contain the above. Further, it is preferable to contain 16.0% or more. However, even if it is contained in a large amount, the life improving effect saturates and the cost increases, so the upper limit was made 19.0%. More preferably the upper limit is 18.0%
It is good to

Mo: 1.0 to 4.0% Mo is an element that suppresses the precipitation of carbonitrides, improves rust resistance, and is effective in improving age hardening. In order to improve rust resistance when it is repeatedly immersed in an acid solution and to obtain an excellent life, the content must be 1.0% or more, preferably 2.0% or more. However, if it is contained in a large amount, δ ferrite will increase and the production by hot forging will be affected, so the upper limit was made 4.0%. More preferably, the upper limit is 3.0%.

O: 0.010% or less O is an element which is mixed in from the atmosphere when dissolved and is inevitably contained as an impurity. However, its content hinders the hot workability, so that it is preferable to limit the upper limit to 0.010% or less when it is desired to secure more excellent hot workability.

S: 0.030 to 0.400%, Pb: 0.40% or less, Se: 0.4
0% or less, Te: 0.40% or less, Bi: 0.40% or less, Ca: 0.0005 to 0.
In the present invention, in order to improve the life as a C hook,
Finally, it is machined to reduce the surface roughness. Therefore, when it is necessary to improve machinability, the above S: 0.030 to 0.400%, Pb: 0.40% or less, Se: 0.40% or less, Te: 0.40% or less, Bi: 0.40% or less, Ca: 0.0005 to 0.100%
Of these, it is preferable to contain one kind or two or more kinds.
In particular, in order to obtain a sufficient effect, it is preferable to add 0.03% or more of Pb, Se, Te, and Bi.

Next, the reasons for limiting the manufacturing conditions in the C hook manufacturing method will be described. First, a steel ingot melted and refined into the components defined in the above range is hot forged at a temperature of 1000 to 1250 ° C. At this time, setting the training ratio to 3 or more is a point for obtaining a long life. If the forging ratio is less than 3, a uniform structure cannot be obtained, so that a sufficient life improving effect cannot be obtained. If the training ratio is as high as 3 or more, the performance can be sufficiently exhibited, and it is more preferably 4 or more.
The higher the training ratio, the better, so the upper limit is not specified. Further, the wrought ratio described in the present invention means the ratio between the cross-sectional area before forming and the cross-sectional area after forming of the portion on which the steel material is applied.

The hot forged C-hook is subjected to solution heat treatment in order to form a solid solution with carbide. However, as mentioned above,
When the C content is reduced to 0.02% or less, the solid solution heat treatment can be omitted because the carbide does not precipitate at the grain boundaries even after natural forging after hot forging.

Finally, it is an important point to improve the life of the product that it is machined to finish the product to reduce the surface roughness as much as possible. This is because if the surface roughness is large, pitting corrosion easily occurs and an excellent life cannot be secured.
The surface roughness Rmax is preferably 3 μm or less.

[0026]

[Operation and effect] In the present invention, the required corrosion resistance is obtained with a cheaper material than Hastelloy C or 28Cr-13Ni alloy, which has been used as a material for C-hook which can be conventionally used with both acid solution and salt solution. The range of possible ingredients was found. In addition, the forging ratio during hot forging is set to 3 or more, and the surface roughness is reduced by finishing to improve the life. As a result, the cost can be significantly reduced compared to the conventional Hastelloy C and 28Cr-13Ni alloy C hooks, and at the same time, the life can be remarkably improved.

Further, since it is not necessary to replace the case of immersing in an acid solution and the case of immersing in salt solution like an iron C hook, it is not necessary to install an extra space or a device for replacement. Therefore, it becomes possible to reduce the cost of pickling the steel material as compared with the conventional case.

[0028]

EXAMPLES The features of the C hook of the present invention will be clarified below with reference to examples. Table 1 shows the chemical composition of the test materials used as examples.

[0029]

[Table 1]

In Table 1, steels 1 and 2 are steels that satisfy the conditions of the composition range of the present invention, and steels 3 and 4 are comparative steels in which some components do not satisfy the conditions of the present invention, and 5 steels are SUS304. Is. Further, 6 alloy and 7 steel are conventional C hook material, 6 alloy is Hastelloy C alloy, and 7 steel is 28Cr-13Ni steel.

These test steels were melted in an electric furnace and cast or hot forged to prepare test pieces of 50 mm square and 20 mm in plate thickness under the conditions shown in Table 2 and used as test materials. Using this test material, in order to reproduce the corrosive environment in an actual pickling equipment, hydrochloric acid with a concentration of 20% at 55 ° C for 40 minutes, salt solution at 450 ° C for 15 minutes, and concentration of 20% at 55 ° C were used. 40 minutes for hydrochloric acid, 5 minutes for nitric hydrofluoric acid with a concentration of 15% at 35 ° C, 2 for nitric acid with a concentration of 7% at room temperature
A repeated continuous immersion test was performed in the order of minutes, water washing, and drying (water washing is performed between and, and), and the amount of wear after one month was measured. Table 2 shows the test results. The numbers shown in Table 2 and Table 3 to be described later are the numbers of the test materials shown in Table 1.

[0032]

[Table 2]

As can be seen from Table 2, Comparative Steel 3,
The 4 steels have large amounts of wear due to low Ni and Mo contents, respectively. Even if the 1st and 2nd steels, which are the target steels of the present invention, are used, they can be manufactured by casting or by machining. It can be seen that the amount of wear increases if the final finish is not applied. Furthermore, although 5 steel is SUS304, which is the most widely used austenitic stainless steel,
When used as a hook, the corrosion resistance is slightly inferior and the amount of wear is increased.

Further, those produced by casting using 6 alloys and 7 steels, which have been used as materials for C-hooks that can be used with both acid solution and salt solution, are remarkably high alloys as compared with the steels of the present invention. However, the effect of the added element is not efficiently obtained, and the amount of wear is still largely inferior to that of the present invention even if the improvement is made by machining. Further, since 6 alloy and 7 steel are high alloys, their hot workability is poor and it is difficult to manufacture them by hot forging.

On the other hand, in the test material of the present invention, steel having an appropriate composition range is manufactured by hot forging and the surface roughness is improved by machining, so that the amount of wear after one month is only 0.2. It was able to be suppressed below mm. Further, it was confirmed that the one having the surface roughness within the above-mentioned preferable range can obtain more excellent performance.

Further, in order to confirm the effect of the present invention with an actual C hook, as shown in Table 3, the C of the present invention is used.
Hooks, conventional C hooks, and C hooks that do not meet some of the manufacturing conditions of the present invention are manufactured, and each C hook is used to periodically pickle the wire under exactly the same conditions.
The amount of wear for one year was investigated. In addition, the influence of the training ratio, which could not be evaluated with the test material, was also investigated.
The results are shown in Table 3. The life shown in Table 3 is estimated from the measured wear loss for one year.

[0037]

[Table 3]

As is clear from Table 3, the C hook of the present invention can be used for a long period of time as compared with the C hook manufactured by the conventional Hastelloy C alloy, the C hook which is not machined, and the like. I was able to confirm that. Also, it has been confirmed that the effect of the forging ratio during hot forging has a great influence on the performance, it is important to set the forging ratio to 3 or more, and the smaller the surface roughness, the better the performance obtained. did it. In this example, an example in which only S was added as a free-cutting element was shown, but similar tests were performed in the case of adding other free-cutting elements as described above, and as a result, excellent performance was obtained. Was confirmed.

Claims (4)

[Claims] 1. A weight ratio of C: 0.08% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.030% or less, S: 0.030% or less, Cu:
3.00% or less, Ni: 10.0 to 15.0%, Cr: 15.0 to 19.0%, Mo:
A steel containing 1.0 to 4.0%, O: 0.010% or less, and the balance of Fe and impurity elements was hot forged into a predetermined shape with a working ratio of 3 or more and then subjected to final finishing by machining. A long-life C hook for pickling characterized by. 2. C: 0.08% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.030% or less, Cu: 3.00% or less, Ni: 1 by weight.
0.0 to 15.0%, Cr: 15.0 to 19.0%, Mo: 1.0 to 4.0%, O: 0.
010% or less, S: 0.030 to 0.400%, Pb: 0.40% or less, Se: 0.4
0% or less, Te: 0.40% or less, Bi: 0.40% or less, Ca: 0.0005 to 0.
Steel containing 100% or less of 1 or 2 or more and the balance Fe and impurity elements was hot-forged into a predetermined shape at a working ratio of 3 or more and then subjected to final finishing by machining. A long-life C hook for pickling characterized by 3. After hot forging and solution heat treatment,
The long-life C-hook for pickling according to claim 1 or 2, which is subjected to final finishing by machining. 4. The surface roughness is Rmax: 3 by the final finishing process.
The long-life C-hook for pickling according to claim 1, wherein the hook is Cm or less.