JPH06100940A - Production of soft magnetic stainless steel - Google Patents

Abstract

PURPOSE:To obtain soft magnetic stainless steel excellent in corrosion resistance and secondary workability by subjecting the hot rolled sheet of Cr series stainless steel to intermediate cold rolling and finish cold rolling at specified drafts including process annealing and thereafter executing magnetic annealing at a specified temp. CONSTITUTION:The intermediate stock of Cr series stainless steel having a compsn. contg., by weight, <0.12% C, >1.0 to 3.5% Si, 0.10 to 2.0% Mn, 11 to 23% Cr, 0.20 to 3.0% Ni and <0.12% N and in which the value of A expressed by A=(Ni+0.5Mn+35C+40N)-0.31 (Cr+1.5Si) lies in the range of -2.7 to 0 is subjected to intermediate cold rolling at 25 to 55% draft, is subjected to process annealing, is subjected to finish cold rolling at 8 to 20% draft and is thereafter subjected to magnetic annealing at 650 to 850 deg.C. The soft magnetic stainless steel sheet excellent in corrosion resistance as well as good in workability and used in a corrosive environment can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing soft magnetic stainless steel having excellent corrosion resistance and secondary workability. In particular, it is a method for producing soft magnetic stainless steel having excellent performance as an iron core component of various relay mechanisms including electromagnetic valves.

[0002]

2. Description of the Related Art Generally, a soft magnetic material is also called a high magnetic permeability material, and its basic characteristic is that the initial magnetic permeability is large and the coercive force is small, and in some cases, it is also required that the saturation magnetic flux density is large. These soft magnetic materials are used in many fields such as magnetic valves, various motors and various relays as metal parts driven by the magnetism in response to magnetism generated by an electromagnetic coil. Electromagnetic soft iron and silicon steel sheets are known as the most general soft magnetic materials, and grain-oriented silicon steel sheets having excellent magnetic properties only in the rolling direction are also known as silicon steel sheets.

However, these iron-based materials are very susceptible to rust, and it was difficult to use them as they are in a corrosive environment. Therefore, when used in a corrosive environment, Ni plating is applied to the parts after processing, but Ni plating is very expensive, which increases the cost of the parts, and the effect of rust prevention was not good enough.

By the way, Cr-based stainless steel is known as a material which is excellent in corrosion resistance and inexpensive, and in recent years, it has been studied as an alternative to the iron-based material. However, these Cr-based stainless steels have a problem that they are inferior in magnetic properties or the secondary workability such as press molding is inferior to the above-mentioned iron-based materials, which is an obstacle to practical use.

Although various proposals have been made to improve the properties of Cr-based stainless steels in the past, a material satisfying all of corrosion resistance, secondary workability, and magnetic properties and a manufacturing method thereof have been found. The current situation is that there are none.

[0006]

The object of the present invention is to improve the magnetic properties of a Cr-based stainless steel having both corrosion resistance and secondary workability, and to provide an excellent soft magnetic material for use in a corrosive environment. It is to provide a method of manufacturing soft magnetic stainless steel. It should be noted that the improvement of the magnetic properties referred to here is to improve the initial permeability, that is, the magnetic flux density in a weak magnetic field. More specifically, the magnetic flux density B
₂ to obtain soft magnetic stainless steel having a high magnetic flux density at a magnetizing force of ₂ Oe.

[0007]

As a result of various investigations on materials having both corrosion resistance and secondary formability, the present inventors have focused on the Cr-based stainless steel of Japanese Patent Application Laid-Open No. 61-296135 previously filed. As a result of various investigations while changing the cold rolling condition before the magnetic annealing and the magnetic annealing condition, the magnetic flux densities B ₁ and B ₂ in the rolling roll direction were remarkably increased and the directional softness It has been found that magnetic stainless steel can be obtained. The present invention has been made based on such findings, and the summary thereof is as follows.

That is, in the present invention, in% by weight, C: 0.
12% or less, Si: more than 1.0% and 3.5% or less, Mn: 0.10 to 2.0
%, Cr: 11 to 23%, Ni: 0.20 to 3.0%, N: 0.12% or less, and A = (Ni + 0.5 Mn + 35C + 40N) -0.31 (Cr
+1.5 Si) The A value determined by the relational expression is in the range of -2.7 to 0, and the balance: Fe and a steel composition consisting of impurities
A method for producing a soft magnetic stainless steel, characterized in that, when an intermediate material of Cr-based stainless steel is finish-rolled and then magnetic-annealed, the finish-rolling rate is 8 to 20% and the magnetic annealing temperature is 650 to 850 ° C. Is.

Further, there is provided a method for producing a soft magnetic stainless steel, characterized in that after the intermediate material is subjected to intermediate rolling and intermediate annealing, the intermediate rolling rate is set to 25 to 55% in the subsequent finish rolling and magnetic annealing. . In the present invention, the rolling rate
(%) Is expressed by the reduction rate (%) of the plate thickness.

[0010]

In the method of the present invention, the reason why the composition ratio of steel and the manufacturing conditions are limited as described above will be explained below. In the present specification, unless otherwise specified, "%" indicating a composition ratio is% by weight.

C, N: C and N are all interstitial solid solution elements to strengthen the substrate and improve wear resistance.
N) is preferably contained at least 0.02%. However, if the amount of (C + N) becomes large, the secondary workability deteriorates accordingly, so the upper limits of C and N were made 0.12% respectively.
Preferably, (C + N) ≦ 0.14%.

Si: Si is the most important element in constituting the present invention, and is an element essential for improving wear resistance and secondary workability, and further improving magnetic performance. It is effective to add more than 1.0%. But 3.5
%, The toughness is significantly deteriorated and the manufacturability is impaired. Therefore, in the present invention, the content is limited to 3.5% or less. It is preferably 2.0 to 2.5%.

Mn: Mn is effective as a deoxidizing and desulfurizing agent in ordinary steelmaking and requires 0.10% or more. On the other hand, when the wear resistance is improved by substitutional solid solution strengthening as in the present invention, Si is used. Secondary workability can also be improved by the combined addition of and. However, if added in a large amount, hot workability is impaired, so the content is limited to 2.0% or less.

Cr: Cr is added in an amount of 11% or more in order to ensure the corrosion resistance as stainless steel. Preferably, 16% or more is added. Corrosion resistance improves as the amount of addition increases, but addition of too large amount causes cost increase.
A ferritic stainless steel satisfying the limitation of the value could not be obtained, so the upper limit was made 23%.

Ni: Ni is effective for improving the toughness of Si-added steel, and is necessary for improving the secondary workability of the hard rolled material by adding Si together. This effect is seen with addition of 0.20% or more, and the degree of improvement increases as the addition amount increases, but even if the addition amount exceeds 3.0%, the effect becomes saturated, and so much more is added. Since the addition of is expensive, the upper limit is 3.0%. Preferably, it is more than 0.6% and 2.0% or less.

Furthermore, according to a preferred embodiment of the present invention, at least one of the following additive components may be further added. Cu:
At least one selected from the group consisting of 1.0% or less, Mo: 3.0% or less, Nb: 1.0% or less, Al: 0.5% or less, and Zr: 0.5% or less, at least one of B, Ca, Mg, and a rare earth element. 0.01% or less for each. The action of these additional additive elements will be described below.

Cu: Cu is a desired additive element, Ni and Mn
Similar to the above, it is effective to improve the secondary workability of the hard material by the composite addition of Si. However, even if added in an amount exceeding 1.0%, the effect cannot be sufficiently exerted, and rather the hot workability is adversely affected, so 1.0% or less may be added if necessary.

Mo: Mo is a desired additive element, and is an element having an effect of improving corrosion resistance as much as or more than Cr. It also has the effect of improving the secondary workability and wear resistance of the hard material. However, the addition of Mo raises the cost, and the addition of a large amount embrittles the base material.
You may add 3.0% or less.

Nb, Al, Zr: These elements have the effect of improving the secondary workability of ferritic stainless steel.
However, Nb exceeds 1.0%, and Al and Zr are each 0.
Even if added over 5%, its performance will be saturated, and inclusions such as nitrides will be scattered,
Secondary workability deteriorates instead. Therefore, if necessary, at least one of these elements, Nb of 1.0% or less, and Al and Zr of 0.5% or less may be added.

B, Ca, Mg, rare earth elements: B and Ca increase the strength and ductility at high temperatures even when added in a trace amount, and are effective in improving hot workability. It is also effective in improving wear resistance. However, if it exceeds 0.01%, it causes embrittlement, and therefore, if necessary added, the addition amounts of B and Ca are both limited to 0.01% or less. For the same reason,
Mg and rare earth elements are also limited to 0.04% or less.

Regarding the A value: When the A value is smaller than -2.7, the precipitation of the γ phase is reduced at high temperature, and the cold block cracking of the slab is caused. On the other hand, when the A value is larger than zero (0), the γ phase is formed. Too much, causing ear cracks during hot rolling,
Productivity is significantly impaired. Therefore, in the present invention, since it is a high Si material, this A value is limited to an appropriate range of -2.7 to 0.

The Cr-based stainless steel having such a steel composition is, after being melted, obtained, for example, by an ingot-making method, then undergoes slab rolling, rough hot rolling, and finish hot rolling, and then undergoes intermediate annealing. No. 2 which was subjected to intermediate and finish cold rolling while performing, and then subjected to finish annealing pickling and then light cold rolling.
A B-finished material is used, followed by cold rolling for obtaining magnetic properties and finally magnetic annealing to obtain a soft magnetic stainless steel. According to the present invention, the finish rolling rate in the cold rolling for obtaining the magnetic properties in the manufacturing stage is 8 to 20.
%, Limiting the magnetic annealing temperature to 650-850 ° C.

Further, according to a preferred embodiment of the present invention, the intermediate rolling rate in the cold rolling is 25 to 55%. Here, "intermediate rolling" refers to cold rolling performed prior to finish rolling, and intermediate annealing may be performed if necessary.

Finishing rolling ratio: The suitable range of finishing rolling ratio varies depending on the magnetic annealing conditions, but when the finishing rolling ratio is less than 8%, the magnetic flux density B ₂ decreases, and when it exceeds 20%, the magnetic flux density B ₂
Has a tendency to decrease, and is 8 to 20% from the viewpoint of workability. It is preferably 10 to 17%.

Magnetic annealing conditions: When the temperature exceeds 850 ° C, martensite precipitates in the steel, and the magnetic flux density B ₂ shows a low value at any finishing rolling rate. The characteristic does not appear. It is preferably 700 to 800 ° C. This is an annealing process of heating for a long time and then gradually cooling in order to grow crystal grains in a magnetic annealing atmosphere.

Intermediate rolling ratio: Magnetic properties are further improved by performing intermediate rolling and intermediate annealing. This is thought to be because the crystal orientation has more orientation, but if the intermediate rolling ratio is less than 25%, it is ineffective, and if it exceeds 55%, the magnetic properties deteriorate. In that case, the value and directionality of the magnetic flux density B ₁ are also remarkable, and are preferably 30 to 40%. Next, the function and effect of the present invention will be described more specifically based on Examples.

[0027]

[Example] A stainless steel having a composition shown in Table 1 and having a plate thickness of 1 mm and a No. 2B finished stainless steel defined by JIS G 4307 as a raw material. The rolling reduction was changed from 0 to 20%, and the magnetic annealing temperature was changed from 600 to 900 ℃.
The magnetic flux density was measured at each of three points in the ° direction. The magnetic measurement in this case was performed by a direct current magnetization characteristic test according to JIS C2550.

The results are summarized in FIGS. 1 and 2. FIG. 1 is a graph showing the magnetic flux density B ₂ in the relationship between the finish rolling rate and the magnetic annealing temperature. As the magnetic annealing temperature rises, the peak of the magnetic flux density B ₂ shifts to the low finishing rolling rate side and conversely 900 ° C. It can be seen that high magnetic flux density cannot be obtained when the distance is close. From this, it can be seen that the magnetic annealing temperature is good near 800 ° C.

FIG. 2 is a graph showing the magnetic flux density B ₂ in the roll direction, the width direction and the 45 ° direction with respect to the finish rolling rate when the magnetic annealing temperature is 800 ° C., where the finish rolling rate is 6%. It can be seen that the magnetic flux density B ₂ rises sharply and reaches a peak at 10 to 15%, and when it exceeds 15%, the magnetic flux density B ₂ gradually decreases. In this case, roll direction, width direction, 45
The difference in the ° direction is large, and it can be seen that the magnetic characteristics have directionality.

Next, in order to investigate the influence of the intermediate rolling and the intermediate annealing, first, when the material is subjected to the intermediate rolling, the rolling ratio is 0 to 0.
60% change, intermediate annealing is performed in a BA furnace at 800 ° C for 2 minutes by slow cooling, finish rolling is 10% reduction, magnetic annealing is 800 ° C, 3
The magnetic flux density was measured in three directions for 3 hours and gradually cooled.

The results are summarized in FIGS. 3 and 4. Fig. 3 shows roll direction, width direction, and 45
It is a graph in which the magnetic flux density B ₂ in the ° direction is taken, but it shows a higher value than the magnetic flux density of only finish rolling and magnetic annealing.
It turns out that it is desirable to perform the intermediate rolling at a rolling rate of%.

Similarly, FIG. 4 is a graph in which the magnetic flux density B ₁ is plotted. The magnetic flux density B ₁ has a large variation in measurement and is represented by the magnetic flux density B ₂ , but the results of this graph show that the magnetic flux density B ₁ in the roll direction is remarkably high at an intermediate rolling ratio of 30 to 35%. I found out that

Next, Table 2 shows the results of measuring the magnetic flux density B ₂ by changing the rolling and annealing conditions for the component compositions shown in Table 1. Table 3 shows the results of measuring the mechanical properties of A and C in Table 2 after finish rolling and magnetic annealing. As an electromagnetic component, secondary working such as press molding is performed after finish rolling, and then magnetic annealing is performed. From Table 3, the material of the present invention exhibits good Erichsen value and elongation, and is excellent in secondary workability. The hardness after magnetic annealing also shows a good value. Further, Table 4 shows the results of detailed examination of the magnetic characteristics of A to A in Table 2.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

[Table 4]

[0038]

From the above results, according to the present invention, it is possible to impart the magnetic characteristics to the Cr-based stainless steel, which is a material having excellent corrosion resistance, and also secure the secondary workability. Many uses are expected.

[Brief description of drawings]

FIG. 1 is a graph collectively showing the results of Examples of the present invention.

FIG. 2 is a graph collectively showing the results of the examples of the present invention.

FIG. 3 is a graph collectively showing the results of the examples of the present invention.

FIG. 4 is a graph collectively showing the results of the examples of the present invention.

Claims (2)

[Claims] 1. By weight%, C: 0.12% or less, Si: more than 1.0% and 3.5% or less, Mn: 0.10-
2.0%, Cr: 11-23%, Ni: 0.20-3.0%, N: 0.12% or less, and A = (Ni + 0.5 Mn + 35C + 40N) -0.31 (Cr + 1.
5 Si) The A value determined by the relational expression is in the range of −2.7 to 0, and the balance: the finish rolling rate during finish rolling and magnetic annealing of an intermediate material of Cr-based stainless steel having a steel composition consisting of Fe and impurities. 8 to 20
%, And a magnetic annealing temperature of 650 to 850 ° C. for producing a soft magnetic stainless steel. 2. The soft magnetic stainless steel according to claim 1, wherein intermediate rolling and intermediate annealing are performed before finish rolling and magnetic annealing, and the intermediate rolling rate at that time is set to 25 to 55%. Production method.