JPH0770716A - Soft magnetic stainless steel having cold forgeability, corrosion resistance and weldability - Google Patents

Abstract

PURPOSE:To provide the soft magnetic stainless steel with which four characteristics including cold forgeability, corrosion resistance, magnetic characteristics and weldability are reconciled. CONSTITUTION:This stainless steel consists of a compsn. contg., by weight, <=0.02% C, <=0.30% Si, <=0.35% Mn, <=0.005% S, 15.0- -20.0% Cr, <=0.01% Al, <=0.02% N, <=0.0060% O, <=0.03% C+N, one or >=2 kinds among 0.02%-0.20% Ti, 0.02-0.40% Nb and 0.05-0.30% v, contg. one or two kinds of (1), (2) of (1) 0.05-0.50% Mo and (2) 0.015-0.045% Pb and 0.015-0.045% Bi and consisting of the balance Fe and impurity elements.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention requires excellent properties in terms of cold forgeability, corrosion resistance, weldability and magnetic properties, and is suitable for, for example, automobile ABS sensors, speed sensors, solenoid valves, etc. The present invention relates to soft magnetic stainless steel excellent in corrosion resistance and corrosion resistance.

[0002]

2. Description of the Related Art Conventionally, pure iron has been used as a material for parts that require soft magnetism such as electronic fuel injection devices, solenoid valves, and magnetic sensors, and Ni-P plating is applied to the surface to prevent corrosion. Was there. This is because pure iron has an excellent soft magnetic property to some extent, a very good cold forging property, and is inexpensive. However, the Ni-P plating applied on the surface has the drawbacks that the valve may be peeled off during use and the valve may be clogged, the electrical resistance is low, and the magnetic response is poor.

As a conventional soft magnetic cold forging stainless steel, Fe-13Cr-1Si-0.25Al steel has been already developed and used, but it has a considerably higher tensile strength than the pure iron. Since it is high, it is inferior in cold forgeability and is a material that is extremely difficult to cold forge into a predetermined shape as compared with iron. On the other hand, depending on the application, it may be welded, and in addition to cold forgeability, corrosion resistance and magnetic properties, stainless steel excellent in weldability has been strongly desired.

Recently, various studies have been conducted to solve the above-mentioned problems of pure iron and Fe-13Cr-1Si-0.25Al steel. For example, there is a soft magnetic stainless steel for cold forging described in JP-A No. 2-15143. This steel has a weight ratio of C: 0.015% or less, Si: 0.20% or less, Mn: 0.35% or less, S: 0.
010% or less, Cr: 8 to 13%, Al: 0.020% or less, O: 0.0070% or less, N: 0.0100% or less, C + N: 0.020% or less, and the balance Fe
And an impurity element.

[0005]

Recently, with regard to soft magnetic stainless steel for cold forging, it is a material used for ABS sensors, speed sensors, solenoid valves, etc. of automobiles, etc. There is an increasing tendency to require excellent corrosion resistance. That is, there has been a strong demand for the development of steel having improved corrosion resistance without deteriorating the cold forgeability and magnetic properties.

[0006] In response to this requirement, pure iron and Fe-13Cr-
The 1Si-0.25Al steel cannot satisfy the requirement because either the corrosion resistance or the cold forgeability is significantly inferior. Further, the steel described in Japanese Patent Laid-Open No. 2-15143 can meet the above requirements to some extent because it has excellent cold forgeability and magnetic properties, but since it has poor corrosion resistance, it does not meet the requirements. It is impossible to satisfy. On the other hand, as described above, there is a demand for a component design that also considers weldability.

In many cases, the four characteristics of cold forgeability, corrosion resistance, weldability, and magnetic characteristics are in a contradictory relationship, and if one of the four characteristics is prioritized and developed, the other characteristics deteriorate and the four characteristics The current situation is that the development of steel grades that have all the properties compatible with each other has not been fully developed. An object of the present invention is to solve the above problems and to provide a soft magnetic stainless steel having excellent cold forgeability, corrosion resistance, weldability, and magnetic properties.

[0008]

In view of the above-mentioned drawbacks of conventional steels, the present inventors have found a component system for improving corrosion resistance without deteriorating cold forgeability, weldability and magnetic properties. As a result of repeated intensive research, it was completed and is based on the following new findings.

[0009] By lowering (C + N) into a ferrite single phase, Si,
By lowering Mn, S, and O to the limit, excellent cold forgeability can be obtained, and by containing 8 to 13% of Cr, it is possible to obtain somewhat excellent corrosion resistance without deteriorating the cold forgeability. It is made clear by Japanese Patent Laid-Open No. 2-15143. However, since the steel described in the prior application emphasizes cold forgeability and regulates the upper limit of Cr to 13%, there is a limit to improvement in corrosion resistance.

Therefore, the present inventors have investigated in detail how the cold forgeability and the corrosion resistance are affected when the Cr content is changed. As a result, by containing 15.0% or more, the corrosion resistance is greatly improved as compared with the case where Cr is contained only up to 13%, and if the content is up to 20.0%, the above-mentioned cold forgeability improvement measures are taken. In some cases, it has been found that, although the strength is slightly increased, the cold forgeability does not deteriorate to the extent that actual cold forging becomes difficult, and excellent properties can be secured. Further, they have found that by strictly limiting the upper limit of Al, it is possible to improve the penetration state during welding and the bead appearance.

That is, the cold forgeability, corrosion resistance, and
The first invention of the soft magnetic stainless steel excellent in weldability is C: 0.02% or less by weight ratio, Si: 0.30% or less, Mn: 0.35% or less,
S: 0.005% or less, Cr: 15.0 to 20.0%, Al: 0.01% or less, N: 0.
02% or less, O: 0.0060% or less, C + N: 0.03% or less and Ti: 0.02
~ 0.20%, Nb: 0.02-0.40%, V: 0.05-0.30% 1
One or more kinds are contained, and the balance is Fe and impurity elements, and the second invention contains 0.05 to 0.50% of Mo in addition to the first invention steel in order to further improve the corrosion resistance. In the third and fourth inventions, in order to improve machinability, in addition to the first and second invention steels, Pb: 0.015 to 0.045%, Bi:
It contains 0.015 to 0.045% of 1 type or 2 types.

The reasons for limiting the components of the soft magnetic stainless steel excellent in cold forgeability, corrosion resistance and weldability according to the present invention will be described below. C: 0.02% or less C is an element that impairs cold forgeability and adversely affects magnetic properties because it increases deformation resistance by solid solution strengthening. In addition, when Cr carbonitride is formed by combining with Cr, Cr
The effect of improving the corrosion resistance of is impaired. Therefore, it is necessary to reduce it as much as possible, and the upper limit was set to 0.02%. In order to obtain more excellent corrosion resistance, magnetic properties, and cold forgeability, it is desirable that the content be 0.01% or less.

Si: 0.30% or less Si, like C, is an element that impairs cold forgeability by solid solution strengthening. In the present invention, since the cold forging property is given the highest priority, it is necessary to reduce it as much as possible, and the upper limit was made 0.30%. If possible, even better properties can be obtained by limiting the content to 0.15% or less.

Mn: 0.35% or less Mn is an element that significantly impairs corrosion resistance, magnetic properties, and cold forgeability, and it is necessary to reduce it as much as possible. Therefore, in the present invention, the upper limit is set to 0.35%. Desirably, it is 0.20% or less.

S: 0.005% or less S is usually contained as an impurity in steel and is an element that deteriorates both cold forgeability, magnetic properties and corrosion resistance due to the formation of MnS. Has a large effect on the above. Therefore, in the present invention, since it is necessary to reduce the amount from the amount normally contained as an impurity, the upper limit is set to 0.
It was set to 005%.

Cr: 15.0 to 20.0% Cr is an element that improves corrosion resistance and magnetic properties, and is the most important element for the present invention. The present invention attaches importance to corrosion resistance as well as cold forging property, and in order to obtain excellent corrosion resistance, it is necessary to contain Cr in an amount of 15.0% or more. However, if contained in a large amount, cold forgeability and magnetic properties deteriorate, so the upper limit was made 20.0%.

Mo: 0.05 to 0.50% Mo is an element having an effect of improving the corrosion resistance, and can be added as necessary to improve the corrosion resistance of the steel of the present invention. In order to obtain the above effect, it is necessary to contain at least 0.05%. However, if the content exceeds 0.50%, the hardness increases and the cold forgeability decreases, so the upper limit was made 0.50%.

Al: 0.01% or less Al is an element that improves electric resistance, but is also an element that deteriorates cold forgeability by solid solution strengthening. Further, when Al is added, the penetration depth during welding is lowered, the molten metal flow of the molten steel is deteriorated, and the bead appearance is deteriorated. In the present invention, since the weldability as well as the cold forgeability is important, it is desirable to reduce it as much as possible, and the upper limit was made 0.01%.

N: 0.02% or less N exists as an impurity in steel, and is an element which, like C, enhances strength by solid solution strengthening, reduces cold forgeability, and adversely affects magnetic properties. Therefore, it is desirable to reduce N as much as possible, and the upper limit was made 0.02%.
It should be 0.01% or less.

O: 0.0060% or less O is an element which is mixed as an impurity from the atmosphere during melting and forms an oxide inclusion or an interstitial solid solution to deteriorate cold forgeability and corrosion resistance. Therefore, it is desirable to reduce it as much as possible, but the upper limit was set to 0.0060% in consideration of actual productivity.

C + N: 0.03% or less In order to make the ferrite single phase and to keep the tensile strength low,
It is necessary to reduce the total content of C and N as much as possible.
Therefore, in the present invention, the upper limit is set to 0.03%. Desirably, it should be 0.015% or less.

Ti: 0.02 to 0.20%, Nb: 0.02 to 0.40%, V: 0.05 to 0.30% Ti, Nb, and V significantly improve the magnetic properties such as magnetic flux density and coercive force, and combine with C and N. Since it fixes C and N by forming fine carbonitrides, it is an element effective in preventing the deterioration of cold forgeability due to solid solution strengthening of C and N. Further, when added with Mo, it also has the effect of eliminating the adverse effect of Mo on the magnetic properties. Therefore, Ti, Nb, V
It is necessary to add at least one of them, Ti is 0.02% or more, Nb is 0.02%, and V is 0.05% or more.
However, if contained in a large amount, the carbonitride formed will become coarse, or the limit workability will decrease due to the reduction of the drawing due to the presence of a single substance, and precision cold forging will become difficult, so the upper limit of Ti is 0.
20%, Nb 0.40%, V 0.30%.

Pb: 0.015 to 0.045%, Bi: 0.015 to 0.045% Pb and Bi are elements improving the machinability, and can be added if necessary. To obtain this effect, Pb,
It is necessary to contain at least 0.015% or more of Bi.
However, even if added in a large amount, the above effect is saturated and the weldability is impaired, so the upper limits were made 0.045% respectively.

[0024]

[Function] The soft magnetic stainless steel excellent in cold forgeability, corrosion resistance, and weldability of the present invention is made into a ferrite single phase by lowering (C + N), and Si, Mn, S, and O are reduced to the maximum. As a result of strict regulation of the upper limit of Al by containing Cr in an amount of 15.0 to 20.0%, which is the limit amount that does not significantly reduce cold forgeability, cold forgeability, corrosion resistance,
Excellent properties were obtained for all four of the weldability and magnetic properties.

[0025]

EXAMPLES Next, the characteristics of the steels of the present invention will be clarified by examples in comparison with comparative steels and conventional steels. Tables 1 and 2 show the chemical components of the test materials used in the examples. In Tables 1 and 2, 1 to 40 steels are steels of the present invention, 1 to 10 steels are the first invention, and 11 to
The 20th steel is the second invention, the 21-30th steel is the third invention, and the 31-40th steel is the fourth invention.
It is steel that corresponds to the invention. Steels 41 to 54 are comparative steels, some of which are out of the scope of the present invention, and steels 55 and 56 are conventional steels. Among the conventional steels, 55 steel is pure iron, 56 steel is JP-A-2-
It is a steel within the composition range described in Japanese Patent No. 15143.

[0026]

[Table 1]

[0027]

[Table 2]

The test steels shown in Tables 1 and 2 were held at 900 ° C. for 2 hours, and then heat-treated at a cooling rate of 100 ° C./hour to obtain tensile strength, critical working rate, magnetic flux density, coercive force, and electrical strength. The resistance, corrosion resistance, weldability and machinability were evaluated. The evaluation results are shown in Tables 3 and 4.

The tensile strength was measured by a Shimadzu 25ton autograph using a JIS No. 4 test piece. For the limit working rate, the method based on the cold forging subcommittee standard of the Japan Plastic Working Society
It was evaluated using 14 mm, height 21 mm, and notch, and the upsetting rate was measured when the crack occurrence rate reached 50%.

Regarding the magnetic characteristics, a DC BH tracer was used, and the test piece had an outer diameter of 24 mmφ, an inner diameter of 16 mmφ, and a thickness of 16 mm.
Was manufactured and the magnetic flux density and coercive force were measured. The electrical resistance was measured by the Wheatstone bridge method using a 1.2 mmφ × 500 mm wire as a test piece. Regarding corrosion resistance, the corrosion weight loss was measured after continuous immersion in a 5% NaCl + 2% H ₂ O ₂ aqueous solution at 40 ° C for 24 hours, and when the corrosion weight loss was less than 0.7 g / m ² hr ◎ , 0.
7 g / m ² hr or more, ○ the case of less than ^{1.2g / m 2 hr, 1.2g /} m 2 hr
The above cases are shown as x in Tables 3 and 4.

Regarding the weldability, TIG welding was used for licking (without insert) under the conditions of a current of 80 A, an Ar flow rate of 10 liter / min, and a welding speed of 180 mm / min, and the bead appearance was observed and the penetration depth and the bead width were compared. evaluated. In Tables 3 and 4, those having a problem in one of the bead appearance and the penetration depth were marked with X, and those having good results were marked with ◯. The evaluation of the ratio of the penetration depth D to the bead width W was judged to be good if D / W was 0.2 or more.

The machinability was evaluated only for the invention steels 21 to 40 and the comparative steels 46 and 54 and the conventional steels containing Pb and Bi as the machinability improving elements. For the cutting test, a test piece with a thickness of 10 mm was used, the rotation speed was 759 rpm, and the material of the drill was SKH.
51 with 5mmφ straight shank drill, no cutting oil,
It was carried out by performing a perforation test under the condition of a load of 72 kg.
The test data was organized by the time required for drilling and by the value of each drilling time when the drilling time of SUS403 was 1. And, those having a value of less than 1.2 are indicated by ◯, and the other values are indicated by x, which are shown in Tables 3 and 4.

[0033]

[Table 3]

[0034]

[Table 4]

As is clear from Tables 3 and 4, when the comparative steels 41 to 54 are compared with the steels 1 to 40 which are the examples of the present invention, the 41 steel has a high Ti content, so that the limit working The ratio is inferior, and 42 and 50 steels have high Cr content, so cold forgeability,
The magnetic flux density is poor, and the 43 and 51 steels have a high Al content, so the tensile strength is slightly high and the weldability is poor.
In addition, since the 44 and 52 steels have high S content,
Magnetic properties and corrosion resistance are inferior, and 45 and 53 steels are inferior in cold forgeability due to high Mo content, and 46 and 54 steels are inferior.
Weldability is poor due to high Pb or Bi content, 47 steel has high C content, so cold forgeability, magnetic properties, and corrosion resistance are poor, and 48 steel has Cr content. Since it is low, corrosion resistance and magnetic properties are inferior, and since 49 steel has a high Nb content, cold forgeability is inferior.

Among the conventional steels, 55 steel, which is pure iron, is excellent in cold forgeability and magnetic flux density, but is significantly inferior in other evaluation items, and 56 steel is coercive force, corrosion resistance and cutting ability. It is inferior in sex.

On the other hand, the 1-40 steels of the present invention are
Although the cold forgeability is slightly lower than that of conventional steel, it is only a change that does not cause any problems in actual processing, and it has succeeded in improving corrosion resistance without deteriorating magnetic properties and weldability. is there. Furthermore, Pb and Bi were added.
It was confirmed that the 21-40 steels can obtain excellent machinability without deteriorating cold forgeability, magnetic properties, corrosion resistance, and weldability.

[0038]

As described above, the soft magnetic stainless steel excellent in cold forgeability, corrosion resistance and weldability according to the present invention has a low
(C + N) to obtain a ferrite single phase, and Si, Mn,
By reducing S and O as much as possible, excellent cold forgeability is secured, and by adding an appropriate amount of Cr and strictly controlling the upper limit of Al, it is possible to obtain excellent characteristics in corrosion resistance and weldability. It was Furthermore, the steel of the present invention is also excellent in magnetic properties, so it is suitable for use in parts such as automobile ABS sensors, speed sensors, solenoid valves, etc., where excellent corrosion resistance is required to improve service life, and is highly practical. Is to have.

Claims (4)

[Claims] 1. A weight ratio of C: 0.02% or less, Si: 0.30% or less, Mn: 0.35% or less, S: 0.005% or less, Cr: 15.0 to 20.0%,
Al: 0.01% or less, N: 0.02% or less, O: 0.0060% or less, C + N: 0.
03% or less, Ti: 0.02 to 0.20%, Nb: 0.02 to 0.40%, V:
A soft magnetic stainless steel excellent in cold forgeability, corrosion resistance, and weldability, characterized by containing 0.05 to 0.30% of one or more kinds, and the balance being Fe and impurity elements. 2. A weight ratio of C: 0.02% or less, Si: 0.30% or less, Mn: 0.35% or less, S: 0.005% or less, Cr: 15.0 to 20.0%,
Mo: 0.05-0.50%, Al: 0.01% or less, N: 0.02% or less, O: 0.0
060% or less, C + N: 0.03% or less, Ti: 0.02 to 0.20%, Nb:
Soft magnetic stainless steel with excellent cold forgeability, corrosion resistance and weldability, characterized by containing one or more of 0.02 to 0.40% and V: 0.05 to 0.30%, with the balance being Fe and impurity elements. . 3. A weight ratio of C: 0.02% or less, Si: 0.30% or less, Mn: 0.35% or less, S: 0.005% or less, Cr: 15.0 to 20.0%,
Al: 0.01% or less, N: 0.02% or less, O: 0.0060% or less, C + N: 0.
03% or less, Ti: 0.02 to 0.20%, Nb: 0.02 to 0.40%, V:
One or two of 0.05 to 0.30%, Pb: 0.015 to 0.045%, Bi:
Soft magnetic stainless steel excellent in cold forgeability, corrosion resistance, and weldability, characterized by containing one or more of 0.015 to 0.045% and the balance being Fe and impurity elements. 4. A weight ratio of C: 0.02% or less, Si: 0.30% or less, Mn: 0.35% or less, S: 0.005% or less, Cr: 15.0 to 20.0%,
Mo: 0.05-0.50%, Al: 0.01% or less, N: 0.02% or less, O: 0.0
060% or less, C + N: 0.03% or less, Ti: 0.02 to 0.20%, Nb:
0.02 to 0.40%, V: 0.05 to 0.30%, one or more, and Pb: 0.015 to 0.045%, Bi: 0.015 to 0.045%, one or two, with the balance being Fe and impurity elements. A soft magnetic stainless steel with excellent cold forgeability, corrosion resistance, and weldability.