JPS60408B2 - Method for manufacturing non-magnetic hot rolled steel sheet with excellent cold workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a non-magnetic hot-rolled steel sheet with excellent cold workability, which has a thin plate thickness of 12 willow or less, mainly 6 ribs or less, has a high degree of magnetic permeability, and has excellent magnetic permeability. The object of the present invention is to provide a method that can appropriately produce a high MnE magnetic hot rolled steel sheet having good ductility and toughness, especially bending workability, at low cost.

Fe-C-Mn austenitic non-magnetic steel has recently been developed to replace conventional austenitic stainless steel, and this is attracting attention as a mass-consumable non-magnetic steel.)
The fields that require such non-magnetic materials are gradually expanding, from structural members of magnetic levitation high-speed railways to various electrical components. However, among these parts, many of the electrical parts, such as transformer covers, are thin plates with a thickness of 6 sides or less, and are extracted from Osaka as gong plates.
Moreover, although the sheet material is formed into a predetermined shape by bending or the like, it is difficult to manufacture such a thin sheet material using a plate rolling mill, and so-called hot rolling is generally performed using a hot strip mill. In addition, for plates with a thickness of 9 to 12 sides, even if they can be manufactured using a plate rolling mill, the above-mentioned hot rolling is much more productive than thick plate rolling, and it is possible to produce the desired product at a low cost. However, as such a relatively thin non-magnetic material, there is no existing hot rolling technology for high-manganese non-magnetic steel sheets that have particularly excellent cold workability as described above. That is, in the case of hot rolling, since a slow cooling effect is provided by the winding process, there is decomposition of austenite, precipitation of carbides, and deterioration of material properties based on this, making production difficult. The present invention was devised after repeated studies in view of the above-mentioned circumstances, and it is based on the basics of high Mn steel regarding the decomposition of austenite during the processing-thermal cycle in the hot rolling process, the precipitation behavior of carbides, and the material relationship. As a result of a detailed study of the effects of C, Mn and other components and hot rolling conditions, we found that a thin non-magnetic material with sufficient plowing properties, especially lining workability, can be used at low cost in place of conventional expensive products. We succeeded in obtaining high-manganese nonmagnetic hot-rolled steel sheets with excellent properties.

In addition, the non-magnetic steel sheet referred to in the present invention is one whose magnetic permeability is 1.01% or less after bending or other cold working conditions, and is equivalent to or higher than conventional non-magnetic steel. be.

In addition, the actual usage conditions are that it is non-magnetic, that is, has low magnetic permeability, and has sufficient rut spreadability, especially cold workability, which meets JIS 18.
The object is those that have a minimum bending radius of lt or less in the 00 bending test. According to previous reports on the changes in properties of high-Mn non-magnetic steel due to constant temperature holding as described above, the isovalue curves of magnetic permeability and Charpy value often become C-shaped curves with a nose around 600°C. This change is generally understood to be due to the precipitation of carbides, which are ferromagnetic substances.

In addition, since hot rolling involves a winding and slow cooling process, it is expected that carbide precipitation and material deterioration will occur to some extent.
The present inventors conducted extensive studies on the component composition and hot rolling conditions, and found conditions that were excellent not only in magnetic permeability but also in the basic performance of cold workability, and established a preferred method for producing hot rolled steel sheets.
(According to the present invention) To explain more specifically, the reasons for limiting the component composition in the present invention are as follows.

That is, C is an important element for stabilizing austenite, and by increasing its amount, other austenitizing elements,
In particular, it reduces the amount of Mn, resulting in lower costs, and is effective as an austenite-strengthening element.

That is, if this C is less than 0.1%, a large amount of Mn is required to stabilize the austenite so that not only the magnetic permeability but also the critical bending radius is less than lt, which is disadvantageous from a practical economical point of view, so this is set as the lower limit. do. On the other hand, if the amount of C is too large, deterioration of bending performance due to carbide precipitation cannot be avoided even under the hot rolling and winding conditions of the present invention as described later. This relationship is as shown in Figure 1, and 650o
The relationship between the bending properties and C content of Fe-C-25%Mn steel of 6 skin thickness wound at
．． Minimum bending radius which is the basic objective of the present invention in the range of 4% 1. Satisfy the melon. C: If it is less than 0.1%, it becomes unstable austenite, and if it exceeds 0.4%, the bending properties will be significantly deteriorated due to the precipitation of carbides. This is because C is a fundamental element that controls bending properties through the precipitation of carbides.
has the effect of stabilizing austenite, and even if 25% of this Mh is contained to improve bending workability through stabilizing the austenite, if the amount of C is too large, it may be difficult to obtain appropriate bending workability. Since this is not possible, the upper limit of C was set at 0.4%. Mm' Well, it is a cheaper and more effective element than other elements as a stabilizing element for austenite, and basically this M
n amount is determined.

Conventionally, in order to stabilize austenite, a regression equation of the lowest Mn content with respect to the C content was calculated, and the higher the C, the lower the Mm content, but in the case of the hot-rolled material of the present invention, bd Minimum Mh that guarantees bending properties in the range of 0.1-0.4%
The amount of C remains almost unchanged at 22%. Figure 2 shows 0.
12%C "0.25%C and 0.45%C systems show the relationship of minimum bending radius with Mn content, but for 0.12%C and 0.25%C, which is within the scope of the present invention, Mn: 22 % or more, a minimum bending radius of less than lt is guaranteed.On the other hand, 0.4
In the 5% C system, austenite is stabilized when Mn is about 18% or more, and the magnetic permeability is as low as 1.01 or less, but the bending properties are not so good, and even if the Mn content is increased, the lt Since the following minimum bending radius cannot be guaranteed, the lower limit of Mn in the present invention is set to 22%. On the other hand, Mn basically has no effect on material properties in stable austenite, but if it exceeds 30%, not only does it increase costs, but hot workability deteriorates, causing many problems in actual operation. Therefore, we set this as the upper limit. N
If it is less than 0.005%, the stability of austenite may be lost, so this is set as the lower limit, while excessive N impairs the hot workability of copper, so the upper limit is set as 0.04%.

In addition, in the present invention, Cr is effective for strengthening austenitic manganese steel, and by adding 2% or less of Cr, high strength can be achieved without impairing the feature of the present invention, that is, cold workability. May be used.

When hot rolling steel having the above components using a hot strip mill, it is important to pay particular attention to the coiling temperature, and the hot rolling conditions will be described in detail below.

That is, first, the heating temperature of the steel ingot or slab is preferably 122,000 or less in order to prevent hot cracking. The finishing temperature of rolling must be at a temperature where the final recrystallized structure is achieved, and it is necessary to avoid finishing at a high temperature and ending the rolling at the recrystallization temperature. However, as long as the usual hot rolling schedule is investigated, the finish is not particularly specified because the above-mentioned slab heating temperature, the relationship between the slab thickness and the finished rolled dimensions will result in a finish of 90,000 or less, which is a recrystallization region for the steel of the present invention. The steel plate rolled as described above is cooled on a runout table and then coiled, and the coiling temperature must be 650 degrees or higher.

Figure 3 shows the relationship between the minimum bending radius and coiling temperature in a 180o bending test with 6 ribs for 0.24%-25%Mn steel. When the coiling temperature is lower than 650°C, the bending properties deteriorate. It is clear that it deteriorates. Steel sheets covered and rolled at temperatures below 650°C have a structure in which the crystal grains are elongated in the rolling direction, and carbide precipitation is observed at the grain boundaries, whereas steel sheets rolled at temperatures above 650q0 show considerable recrystallization. It exhibits a developed structure, with many carbides precipitated within the crystal grains. This means that when the component steel of the present invention is in a normal hot-rolled finished state, the crystal grains are approximately deformed and elongated as described above, and this state is brought to the coiling temperature by cooling on the runout table and then rolled. After rolling, recrystallization has progressed. Therefore, if the coiling temperature is low, recrystallization will not progress, and the final structure will remain the stretched unrecrystallized structure immediately after rolling, and grain boundaries will not move. Therefore, grain boundary carbides that precipitate within a relatively short period of time remain as grain boundary carbides and have an adverse effect on the material quality. However, in the coiling temperature range specified in the present invention, although the carbide precipitation nose (dish se) is close to each other, recrystallization progresses and carbide precipitation progresses almost simultaneously, so even if carbides are present at grain boundaries from time to time, Even if precipitated, the grain boundaries move due to the progress of recrystallization, and eventually the carbide precipitated location is no longer a grain boundary, and the influence of carbide precipitation becomes extremely small. In addition, in order to prevent this carbide precipitation from occurring, the coiling temperature must be extremely low, such as 400 qo or less, which would place an excessive load on the coiler and be impractical. Moreover, the material is in an unrecrystallized state and becomes hard, making it impossible to achieve the object of the present invention. On the other hand, the upper limit of the winding temperature is 750 qo, and this winding temperature is 75 qo.
At temperatures above 0°C, the rate of recrystallization increases and recrystallization ends before the precipitation of carbides. As a result, carbides preferentially precipitate at recrystallized grain boundaries, which is the final structure, resulting in poor workability. It will cause deterioration. Furthermore, in general, when high temperature winding is performed, the secondary scale becomes thick and easily peels off, and considering this surface quality, it is necessary to wind up at a temperature of 750 mm or less. As described above, according to the present invention, it is possible to precisely obtain a non-magnetic steel sheet with excellent cold workability in hot rolling at a low cost, which was considered difficult to manufacture in the prior art due to the relationship with carbide precipitation behavior. Can be done. The characteristics of the present invention will be further clarified by describing specific examples (methods of the present invention) as follows. That is, the present inventors have proposed the following first
Using steel types A to L as shown in the table, each of these steels was heated to 1200 qo and finished into 6 ribs at 850 qo.

Each of the steels A to L as mentioned above is approximately 1.
It was cooled on a ramp table at a cooling rate of 0oC/sec and then wound up.

The coiling temperature of each of these steel types, the yield strength (YS), tensile strength (TS), elongation (EI) in the direction perpendicular to rolling, the minimum bending radius in the 1800 bending test according to JIS regulations, and The magnetic permeability after 50% cold working is shown in Table 2 below.

2. Obviously, each of the above-mentioned steels has a composition according to the present invention after hot rolling, that is, among the steel types shown in Table 1, E, F, G, J and K have the composition according to the present invention in terms of C content or Mn content. is not satisfied.

For example, in B-ltB-2, F-1, and K-1 villages, the C content exceeds the present invention's C content of 0.4%, and even though the magnetic permeability is sufficiently low, the bending workability is poor, and from the viewpoint of magnetic permeability. Although it is a stable austenite, it has poor cold workability. Steel G is known to have sufficient mechanical and magnetic properties when air-cooled after rolling, such as when rolled into a thick plate, but when hot-rolled, not only does it deteriorate in magnetic permeability, but it also has poor ductility to the point that it is almost unbendable. Also H-
One village has a low Mn content and becomes unstable austenite, which is extremely poor in terms of magnetic permeability, which is the basic performance of non-magnetic steel. For each steel type mentioned above, steel A, B, C, D, 1, J,
and L both satisfy the C-Mn range of the present invention.
However, only when the winding temperature is 650 qo or more, the bending properties become 1. It is clear that he is superior to his enemies. To explain further, when winding is performed at a low temperature, the strength generally increases, but at temperatures below 650°C, the EI and bending properties deteriorate more than the effect of increasing the strength, and the change in magnetic permeability due to the winding temperature is small. Even though these general trends exist, steels A to D each exhibit excellent magnetic permeability and cold workability, although the amount of C is varied within the composition range of the present invention. Steel 1, J
shows the influence of Mn at the same amount of C, and there is no fundamental effect of the amount of Mn on magnetic permeability and line workability. This, together with the results for material K-1, makes it clear that the amount of C controls the cold workability. Finally L-1
Although Mura is a Cn-added material, it can be seen that Cr has the effect of increasing YS especially compared to the 1-1 material. Note that the bending properties shown above are all in the C direction, but are also the same in the L direction, and the material properties of the steel of the present invention, especially cold workability, do not depend on the amount of S, inclusions, etc. This is basically based on the stability of austenite and the precipitation behavior of carbides, and the amount of C-Mn and the hot-rolling temperature have particularly important meanings.

According to the present invention as explained above, a high manganese non-magnetic steel sheet having excellent ductility, particularly line workability, and high magnetic permeability can be advantageously obtained by hot rolling with high productivity.
This product can be provided at a low cost, and can be economically adopted in fields of application such as various electrical components that require non-magnetic materials. Furthermore, as understood from the magnetic flux, 8
Even when cold-worked to 0% or more, its magnetic permeability hardly changes, and it has sufficient cold-workability in the above-mentioned non-magnetic materials, making it suitable for many uses such as cutting plates. This invention has the advantage of being able to be expanded over a period of time, and is a highly effective invention industrially.

[Brief Description of the Drawings] The drawings show the technical content of the present invention, and Fig. 1 is a chart showing the relationship between the minimum bending radius and C amount in the JIS1800 bending test, and Fig. 2 is a chart showing the relationship between the minimum bending radius and the amount of C in the JIS 1800 bending test. Radius and Mn
FIG. 3 is a chart showing the relationship between the same minimum bending radius and the winding temperature. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 C: 0.1-0.4%, Mn: 22-30%, N:
A cold-workable steel containing 0.005 to 0.04% and the remainder consisting of iron and unavoidable impurities is hot rolled in a hot strip mill and coiled at 650 to 750°C. A method for producing excellent non-magnetic hot-rolled steel sheets. 2C: 0.1-0.4%, Mn: 22-30%, N:
A steel containing 0.005 to 0.04% Cr and 2% or less of Cr, with the balance consisting of iron and unavoidable impurities, is hot rolled in a hot strip mill to a temperature of 650 to 750°C.
A method for producing a non-magnetic hot-rolled steel sheet with excellent cold workability, characterized by winding the steel sheet.