JPH10195529A - Ferritic stainless steel in which cu is uniformly precipitated and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce ferritic stainless steel in which problems in the production such as hot cracks do not occur and whose antibacterial properties do not deteriorate even if it is worn by polishing or a long period of use and to provide a method for producing the same. SOLUTION: This ferritic stainless steel in which Cu is uniformly precipitated can be obtd. by subjecting a ferritic stainless stell added with Cu to hot rolling, subjecting this hot rolled product to long time annealing at 750 to 850 deg.C for >=2hr to uniformly precipitate Cu into the structure, executing cold rolling and subjecting the cold rolled product to short time annealing at 800 to 900 deg.C for 1 to 10min not so as to reenter Cu into solid solution. The amt. of Cu to be added to the ferritic stainless steel is regulated to 1 to 3%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ferritic stainless steel in which Cu is uniformly precipitated and a method for producing the same, and more particularly to a ferritic stainless steel in which the antibacterial property is increased by the precipitation of Cu and a method for producing the same.

[0002]

2. Description of the Related Art It is known that in an environment where Cu is used, an antibacterial effect can be obtained by elution of Cu ions. The antibacterial effect of antibacterial stainless steel is similar. In this case, in a state where Cu is solid-dissolved in the stainless steel as the base material, the elution of Cu ions is suppressed due to the stainless steel film. Therefore, it is considered effective to precipitate a large amount of Cu as a foreign phase in the structure in order to enhance the antibacterial property of ferritic stainless steel.

[0003] However, when the content of Cu increases, the precipitation amount of Cu also increases. However, when the content of Cu is too large, there is a problem in manufacturing that cracks occur during hot rolling.

There is also a method of forming a Cu-enriched layer on the surface by performing a sulfuric acid treatment. However, in this case, there is a disadvantage that when the surface is polished, the Cu-enriched layer disappears and the antibacterial effect is lost. Practically, if Cu can be uniformly precipitated as a heterogeneous phase in the structure, the antibacterial property does not decrease because Cu always exists on the surface even when subjected to abrasion due to polishing or long-term use.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a ferritic stainless steel which does not cause manufacturing problems such as hot tearing and which does not lose its antibacterial property even when subjected to abrasion due to polishing or long-term use. It is an object to provide steel and a method for manufacturing the same.

[0006] Such a problem can be obtained by increasing the Cu content in a range where hot cracking or the like does not occur and controlling the annealing conditions so that they are uniformly precipitated in the entire region of the material. The present invention has been found to be solved by ferritic stainless steel, and has completed the present invention.

[0007]

In order to solve the above-mentioned problems, the present invention provides a hot-rolled ferritic stainless steel to which Cu has been added and annealed the hot-rolled product at 750 to 850 ° C. for 2 hours or more. Cu is uniformly precipitated in the structure, and after cold rolling, the cold-rolled product is 800 to 800 so that Cu does not form a solid solution again.
Provided is a ferritic stainless steel in which Cu obtained by annealing for a short period of time at 900 ° C. for 1 to 10 minutes is uniformly precipitated.

[0008] By long-time annealing at 750 to 850 ° C for 2 hours or more, Cu is uniformly and uniformly precipitated in the structure. The internal stress due to cold rolling is 800-900 ° C.,
It is removed by short-time annealing for 10 minutes to 10 minutes, and workability and machinability are also improved. Under this condition, the Cu uniformly precipitated in the structure does not re-dissolve in the cold-rolled product, so that the manufactured ferritic stainless steel contains Cu uniformly and uniformly precipitated in the material.

According to a second aspect of the present invention, in the ferritic stainless steel according to the first aspect, wherein Cu is uniformly precipitated, the amount of Cu added to the ferritic stainless steel is 1 to 3% by weight. It is characterized by.

[0010] When the Cu content is 3% by weight or less, no rolling cracks occur during hot rolling, so that there is no production problem.

[0011] A second aspect of the present invention is a step of hot rolling a ferritic stainless steel to which Cu is added, and a step of annealing a hot-rolled product at 750 to 850 ° C for 2 hours or more for a long period of time. A step of uniformly depositing Cu, a step of cold rolling to form a cold rolled product, and a short time annealing of the cold rolled product at 800 to 900 ° C. for 1 to 10 minutes so that Cu is not dissolved again. And a method for producing a ferritic stainless steel in which Cu is uniformly deposited, the method comprising:

According to a fourth aspect of the present invention, there is provided a method of producing a ferritic stainless steel according to the third aspect, wherein Cu is uniformly precipitated.
Is 1 to 3% by weight.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a ferritic stainless steel according to the present invention in which Cu is uniformly precipitated and a method for producing the same will be described with reference to the illustrated preferred embodiments.

[0014] The method for producing a ferritic stainless steel in which Cu is uniformly precipitated according to the present invention generally comprises a hot rolling step, a long annealing step, a cold rolling step, and a short annealing step. And a process.

The stainless steel used is a ferritic stainless steel containing about 16% or more of Cr, so that as much Cu as possible can be precipitated, but 1 to 3% by weight so as not to cause rolling cracks during hot rolling. The one to which Cu is added is used. When the addition amount of Cu is 1% by weight or less, Cu
The desired antimicrobial properties cannot be obtained due to the small amount of the precipitate. In particular, 1
In the case of using a ferritic stainless steel to which の 2% by weight of Cu is added, rolling crack does not occur, and 750-8%
At any temperature of 50 ° C., a sufficient amount of Cu precipitates in the grain boundaries and grains by the long-time annealing.

A hot-rolled product (band or plate) manufactured by hot rolling is annealed at 750 to 850 ° C. for 2 hours or more for a long time. By the long-time annealing of 2 hours or more, Cu can be uniformly and uniformly deposited over the entire range of the material. If the annealing time is short, Cu near the surface to be cooled first
Is increased, and conversely, the amount of Cu deposited in the central portion is reduced. Thus, when abrasion is caused by polishing or long-term use, a portion where the amount of Cu precipitated is small may be exposed and antibacterial properties may be reduced.

An appropriate annealing temperature is 750 to 850 ° C. This is because if the annealing temperature is set to 750 ° C. or lower, the recrystallization becomes incomplete because the annealing temperature is too low, and the hot rolled structure is inherited, and the mechanical properties of the thin plate deteriorate. Conversely, if the annealing temperature is set to 850 ° C. or higher, Cu precipitated in the structure becomes a solid solution because the annealing temperature is too high, and the antibacterial property of the thin plate is reduced or lost. In addition, there is an adverse effect that the crystal grains become coarse and the mechanical properties of the thin plate deteriorate.

A material in which Cu is uniformly precipitated in the structure by long-time annealing is cold-rolled to obtain a cold-rolled product (band or plate). Ferritic stainless steel is generally 600 to 80
When exposed to a temperature of 0 ° C. for a long time, a sigma phase is precipitated and brittleness is reduced. This decrease in sigma brittleness is removed in the subsequent short annealing step to restore toughness. Thereby, workability and machinability are improved. The cold rolling process itself,
Since this is a conventionally well-known process, a detailed description thereof will be omitted.

The next short annealing step is 800 to 90
It is performed within a relatively short time of 1 to 10 minutes at a temperature of 0 ° C. Under this condition, Cu uniformly precipitated in the structure does not re-dissolve in the cold-rolled product, so that the Cu uniformly and uniformly precipitated in the material by the long-time annealing step remains in the material as it is. The annealing temperature is particularly preferably 850 to 900 ° C. from the viewpoint of eliminating a decrease in sigma brittleness.

In the ferritic stainless steel thus obtained, Cu is uniformly and uniformly deposited in the entire region of the material, and is always constant and sufficient even when subjected to polishing or abrasion due to long-term use. Is deposited on the surface. Due to this, the antibacterial property on the exposed surface is
A constant and desired degree is always maintained.

[0021]

Example 1 A production test was performed using a ferritic stainless steel having a Cu content of 1.5%. Table 1 shows the chemical components of this test material.

[Table 1]

The test material was prepared by heating a 5 kg steel ingot by high frequency melting to a temperature of 1100 ° C., performing hot rolling, and obtaining a sheet thickness of 3 mm.
I made it. In the range of Cu content of 1 to 2%, no crack occurred during hot rolling. If the Cu content exceeds 3%, cracks occur during hot rolling. Thereafter, the hot-rolled product was annealed for three hours at a temperature of 750 ° C., 800 ° C., and 850 ° C. for 3 hours, and the microstructure of the cross section was observed, and the amount of Cu precipitated in the structure was investigated. As a result, in Test Material 1,
Although it is considered that Cu is precipitated at the grain boundary and in each of the grains, it is considered to be slightly insufficient. A large amount of Cu was precipitated.

FIG. 1 shows that a steel ingot having a Cu content of 1.5% by weight was heated to a temperature of 1100 ° C., hot-rolled, and then this hot-rolled product was annealed at a temperature of 850 ° C. for 3 hours. 7 is a cross-sectional microphotograph in the case of performing. On the other hand, FIG. 2 shows a cross-sectional microphotograph of a hot-rolled product under the same conditions, which was annealed at 1060 ° C. for 2 minutes, as a comparative example. The normal material listed as a comparative example has Cu precipitates (dot-like foreign substances) in the structure.
Is only slightly recognized. On the other hand, in the long-time annealed material of the hot-rolled product according to the method of the present invention shown in FIG. 1, a large amount of precipitates of Cu are recognized at the grain boundaries and in the grains. Note that the large black foreign matter found in both is due to the contamination of impurities.

After these materials are cold-rolled to a thickness of 1 mm, 800 ° C., 850 ° C., 900 ° C., 950 ° C. and 10 ° C.
Short-time annealing for 2 minutes was performed at a temperature of five conditions of 00 ° C.
Thereafter, the cross-sectional microstructure was observed, and the amount of Cu precipitated in the structure was investigated. FIG. 3 is a cross-sectional microphotograph when the long-annealed material of FIG. 1 is cold-rolled and subjected to short-time annealing at 900 ° C. for 2 minutes. On the other hand, FIG. 4 shows, as a comparative example, a cross-sectional microphotograph in the case where the normal material of FIG. 2 is cold-rolled and then subjected to short-time annealing at 1000 ° C. for 2 minutes.

The ordinary materials listed as comparative examples have C in their structures.
No precipitate of u (dot-like foreign matter) is observed. This is because Cu, which was slightly precipitated, re-dissolved in the structure due to the high annealing temperature. On the other hand, in the short-time annealed material of the cold-rolled product according to the method of the present invention shown in FIG. 3, a large amount of precipitates of Cu are recognized at the grain boundaries and in the grains. Note that the large black foreign matter found in both is due to the contamination of impurities.

Table 2 shows the amount of Cu precipitated after short-time annealing of cold rolled products.
Shown in Cu precipitation was detected by analyzing the cross-sectional structure with an electron microscope (EPMA). When the cold-rolled product was annealed at a temperature of 800 to 900 ° C. for a short time, it was confirmed that Cu precipitated by the long-time annealing of the hot-rolled product was not solid-dissolved in the structure but remained uniformly.

[Table 2]

FIG. 5 shows the cross-sectional hardness after cold-rolled product annealing.
From FIG. 5, it is confirmed that when the cold-rolled product is annealed at 900 ° C. or more for a short time, the structure of the stainless steel is recrystallized, thereby decreasing the Hv hardness.

From the above results, regarding this component system, 7
Anneal for a long time at a temperature of 50 to 850 ° C, and after cold rolling, 8
If the annealing is performed at 00 to 900 ° C. for a short time, a ferritic stainless steel satisfying the mechanical properties and having an antibacterial effect in which a large amount of Cu is uniformly precipitated in the structure can be produced.

[0029]

According to the ferritic stainless steel produced under the annealing conditions according to the present invention, a large amount of Cu is uniformly and uniformly deposited in the structure, and its surface is subject to abrasion due to polishing or long-term use. Constant and sufficient amount of C
Since u is precipitated, it has an effect of maintaining high antibacterial properties for a long time.

Therefore, it can be used in a wide range of fields where importance is placed on hygiene, such as medical equipment, food machines, furniture, and the like, and the use range of stainless steel is further expanded.

[Brief description of the drawings]

FIG. 1 is a photograph substituted for a drawing showing a cross-sectional microstructure of a long-time annealed material of a hot-rolled product according to the method of the present invention.

FIG. 2 is a photograph substituted for a drawing showing a cross-sectional microstructure of a normal material shown as a comparative example.

FIG. 3 is a drawing substitute photograph showing a cross-sectional microstructure of a short-time annealing material of a cold-rolled product according to the method of the present invention.

FIG. 4 is a drawing substitute photograph showing a cross-sectional microstructure of a normal material shown as a comparative example.

FIG. 5 is a graph showing a relationship between a cold-rolled product annealing temperature and a sectional hardness.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yasuhiro Hahara 1-30 Oyamacho, Sagamihara City, Kanagawa Prefecture Nippon Metal Industry Co., Ltd. Sagamihara Factory

Claims (4)

[Claims] 1. A hot-rolled ferritic stainless steel to which Cu has been added, and the hot-rolled product is annealed at 750 to 850 ° C. for 2 hours or longer to uniformly precipitate Cu in the microstructure. A ferritic stainless steel in which a cold-rolled product is uniformly annealed at 800 to 900 ° C. for 1 to 10 minutes for a short period of time so that Cu does not re-dissolve in the cold-rolled product, thereby uniformly depositing Cu. 2. The ferritic stainless steel according to claim 1, wherein the amount of Cu added to the ferritic stainless steel is 1 to 3% by weight. steel. 3. A step of hot-rolling a ferritic stainless steel to which Cu is added, and a step of annealing the hot-rolled product at 750 to 850 ° C. for 2 hours or more to uniformly precipitate Cu in the structure. And a step of cold rolling to a thin plate, and 800 to 900 ° C. so that Cu does not re-dissolve in the cold-rolled product.
And a step of annealing for a short time in 1 to 10 minutes, and a method for producing a ferritic stainless steel in which Cu is uniformly precipitated. 4. The method for producing a ferritic stainless steel according to claim 3, wherein the amount of Cu added to the ferritic stainless steel is 1 to 3% by weight. Manufacturing method of ferritic stainless steel.