JPH03138337A - Soft magnetic stainless steel for cold forging - Google Patents

Abstract

PURPOSE:To combinedly provide the stainless steel with good magnetic characteristics and electric characteristics as well as excellent cold forgeability by reducing the content of C and N in a steel and incorporating a specified amt. of Al thereto. CONSTITUTION:The compsn. of the soft magnetic stainless steel is formed from, by weight, <=0.008% C, <0.20% Si, <=0.35% Mn, <=0.005% S, 11 to 13% Cr, <=0.008% N, <=0.015% C+N, 0.22 to 0.83% Al and the balance Fe with impurity elements. By this compsn., the electromagnetic characteristics are improved and the cold forgeability is improved. If required, one or more kinds among 0.10 to 0.30% Pb, <=0.040% S, <=0.040% Se and 0.0020 to 0.0200% Ca are incorporated into the above steel, by which the machinability is improved. Furthermore, at the time of incorporating one or more kinds of S and Se, preferably, one kind of 0.002 to 0.040% Te and 0.02 to 0.15% Zr is incorporated and the total of S+Se+Te is regulated to <=0.050%.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is for cold forging with excellent cold forgeability, electromagnetic properties, and corrosion resistance for use in electromagnetic valves, electromagnetic clutches, electronic fuel injection devices for internal combustion engines, etc. Regarding soft magnetic stainless steel.

(Prior art) Conventionally, the properties required of soft magnetic stainless steel include magnetic properties such as magnetic flux density and coercive force, as well as electrical resistance and corrosion resistance.In order to obtain particularly excellent magnetic properties, 25i-
13Cr steel, I5i~0.20Al-13Cr steel, etc. have been developed and some of them are in practical use.

In recent years, the development of applications for soft magnetic stainless steel has progressed, and it has come to be applied to parts with complex shapes such as the body and core of electronic fuel injection devices. development was required.

For the above requirements, for example, I5i~0.20Al-
Steels such as 13Cr steel in which the C content is reduced to about 0.01χ have been developed and are used in some cases.

(Problem to be solved) However, these steels also have a tensile strength of 44°5k.
g f/IImt, reduction of area 74χ1, limit processing rate 47
It is difficult to cold forge parts with complex shapes such as the body and core of the electronic fuel injection device, and it is difficult to cold forge parts with complex shapes such as the body and core of the electronic fuel injection device. There was a desire to develop soft magnetic stainless steel with electromagnetic properties.

(Means for Solving the Problems) The present invention was made in view of the drawbacks of conventional steels, and the inventors have investigated the effects of various alloying elements on the electromagnetic properties and cold forgeability of 13 Cr steel. As a result of our investigation,
The magnetic properties are improved by adding Al and making the CAN extremely low, and the electrical properties are significantly improved by adding Al.
On the other hand, it has been found that cold forgeability is improved by reducing C+N and S.

It is known that Al, together with Si, is an element that improves electromagnetic properties, solid solution hardens the matrix in 13Cr-based ferrite, and impairs cold forgeability.

The problem of the present invention is to achieve both cold forgeability and electromagnetic properties, and the goal is to discover an element in which when a certain element is added, the rate of increase in electrical resistance due to the addition is much larger than the increase in tensile strength. . As a result of detailed investigation of the influence of alloying elements by the present inventors, we found that Al is the most effective, and obtained a soft magnetic stainless steel with an unprecedented balance of excellent cold forgeability and electromagnetic properties. The present invention has been completed.

Based on these findings, the present invention has developed C
+N content is 0.015% or less, and 0.2
It contains 2 to 0.832 Al to significantly improve electromagnetic properties, and furthermore, the C+N content is 0.01.
By setting the S content to 5% or less and the S content to 0.005% or less, cold forgeability is significantly improved.

Therefore, the steel of the present invention has a magnetic flux density (B
2°) and 1.00. It has the following coercive force and excellent magnetic properties, and has excellent electrical properties with an electrical resistance of 55 μΩ-cm or more, and has a tensile strength of 38 μm for cold forgeability.
kg f/m+m” or less, the limit machining rate is 65% or more,
This is a soft magnetic stainless steel for cold forging with excellent cold forging properties, making it suitable for electromagnetic valves, electromagnetic clutches, electronic fuel injection devices for internal combustion engines, etc.

That is, the steel of the present invention has co, oos% or less, Si less than 0.20χ, Mn less than 0.35%, S
0.005% or less, Cr 11-13! , N0.
008% or less, C+N 0.015X or less, Al 0.008% or less, C+N 0.015X or less, Al 0.
22 to 0.83χ, and the remainder consists of Fe and impurity elements, and the second invention further includes Pb in the first invention.
0.10-0.30%, S 0.040% or less, Se
0.040X or less, Ca 0.0020-0.0200
'&, and contains one or more of S,
When containing one or more types of Se, Te 0.002
-0.040 In the invention, Mo 4.0% or less, Cu 0.50% or less, Ni 2.50% or less, Nb 0.20% or less, V
The fourth invention further improves the corrosion resistance of the first invention by containing one or more of 0.20 2.50χ or less, Nb 0.20X or less, V
The corrosion resistance of the second invention is further improved by containing one or more of the above in an amount of 0.20% or less.

The reasons for limiting the composition of the steel of the present invention will be explained below.

C is an element that impairs cold forgeability due to its solid solution strengthening effect and also has an adverse effect on magnetic properties, and in the present invention, it is desirable to reduce it as much as possible, and its upper limit is set to 0.008χ.

Si is an element necessary for deoxidation during steel manufacturing, but it is also an element that impairs cold forgeability due to its solid solution strengthening effect.The present invention places the utmost importance on cold forgeability, and the upper limit of Si is It was set to less than 0.20χ.

Like Si, Mn is an element necessary for deoxidation during steel manufacturing, but the upper limit was set to 0.35χ so as not to impair magnetic properties.

S is an element that improves machinability, but on the other hand, it is also an element that impairs cold forgeability, and its upper limit was set to 0.005χ.

Cr is a basic element that imparts corrosion resistance to stainless steel, and must be contained in a small amount (at least 11χ). However, as its content increases, magnetic properties such as magnetic flux density are impaired, so the upper limit was set at 13χ.

Like C, N is an element that impairs cold forgeability due to its solid solution strengthening effect, and in the present invention, it is desirable to reduce it as much as possible, and its upper limit is set to o, oosχ.

Both C+N are elements that impair cold forgeability due to solid solution strengthening action. In the present invention, the tensile strength is 38 k.
The purpose is to obtain excellent cold forgeability with a limit workability of 65% or more, and C1N.
It is necessary to reduce the content as much as possible, and the upper limit was set at 0.015χ.

Al is the most important element in the present invention, and is an element that inhibits cold forgeability less than Si and improves magnetic and electrical properties, and must be contained in an amount of at least 0.22%. However, as the content increases, cold forgeability is impaired, so the upper limit was set at 0.83χ.

Pb, S, Se, and Ca are all elements that improve machinability.

pb is at least 0.1 to obtain excellent machinability.
It is necessary to contain 0% or more. However, since a large content impairs cold forgeability and hot workability, the upper limit was set at 0.30'l.

If large amounts of S and Se are contained, cold forgeability and corrosion resistance are impaired, so the upper limit thereof was set at 0.040χ.

Ca is at least 0.002 to obtain excellent machinability.
It is necessary to contain 02 or more. However, even if a large amount is contained, the effect is saturated, so the upper limit was set to 0.0200χ.

Te has the effect of neutralizing the adverse effects of S and Se on cold forgeability, and must be contained at least 0.002χ. However, if it is contained in a large amount, cold forgeability will be impaired, so the upper limit was set at 0.40X.

Furthermore, the main purpose of the present invention is to obtain excellent cold forgeability, and the upper limit of the sum of S+Se+Te is set to o and osoχ.

Zr is an element that spheroidizes MnS and improves cold forgeability, and must be contained in an amount of at least 0.02%. However, if a large amount of Zr is contained, the amount of inclusions increases and cold forgeability is impaired, so the upper limit was set at 0.152.

Mo, Cu, Ni+Nb, and V are elements that improve corrosion resistance.

However, Mo is 4.0%, Cu is 0.50%, and Ni is 2.
．． If Nb and V are contained in an amount exceeding 0.20%, the magnetic properties and cold forgeability will be impaired, so the upper limit is set at 4.0% for Mo, 0.50% for Cu, and 0.50% for Ni.
was set to 2.5o%, and Nb and ■ were set to 0.20χ.

(Example) Next, the characteristics of the present invention will be clarified through examples in comparison with comparative steel and conventional steel.

Table 1 shows the chemical composition of these test steels.

(Left below) In Table 1, steels 1 to 30 are the invention steels, 1 to 8 are the first invention steels, 9 to 14m are the second invention steels, and 15m are the second invention steels.
~25 steel is the third invention steel, and 26~30 steel is the fourth invention steel. Further, Steels 31 to 35 are comparative steels, and Steel 36 is a conventional steel.

Table 2 shows the test steel in Table 1 at 900°CX211
This figure shows the tensile strength, limit processing rate, magnetic flux density, coercive force, corrosion resistance, electrical resistance, and machinability of steels 1 to 36 that were heat-treated at a cooling rate of 100°C/Hr. .

The tensile strength was measured using a JIS No. 4 test piece.

Regarding the limit work rate, based on the cold forging subcommittee standards of the Japan Society for Plasticity Working, and the cold upsetting test method (temporary standard),
A compression test was conducted using a test piece with a diameter of 141φ, a height of 21mm, and a notch, and the upsetting rate at a cracking rate of 50χ was measured.

Regarding the magnetic properties, a DC type Bl+) racer was used as a test piece with an outer diameter of 24 + yo + φ and an inner diameter of 16 mm φ.
A ring with a thickness of 16 mm was prepared, and the magnetic flux density and coercive force were measured.

Regarding corrosion resistance, we conducted a salt spray test using a 5χ NaC1, 25°C aqueous solution and measured the rusting rate, and those with a rusting rate of 5% or less were ◎, those with a rusting rate of over 5~25χ were ○, and 2
Those with a value of more than 5 to 50χ were designated as Δ, and those with more than 50χ were designated as ×.

The electrical resistance was measured by the Wheatstone bridge method using a 1.2 mmφ x 500 mm wire as a test piece.

For machinability, a test piece with a thickness of 10 mm was used at a rotation speed of 725 r, p, m, and a drill SKI 5 mmφ.
A drilling test was conducted under a load of 4 kg, and the time required to drill the hole was measured.

(Left below) As is clear from Table 2, steel 31, which is the comparison steel, has a C
Due to the high r content, the magnetic flux density is as low as 12,800G, and the tensile strength and limit workability are poor, resulting in poor cold forgeability.32 steel has low Cr content, so the cold forgeability is poor. is excellent, but its corrosion resistance is very poor, and 33 steel has a low limit machining rate of 61χ due to its high Al content.
It is also inferior in tensile strength and magnetic flux density, and 34 steel has a low limit processing rate of 58χ due to its high Si content.
It is also inferior in magnetic flux density, and because of its high C+N content, 35 steel has an extremely low limit processing rate of 52X, and is also extremely inferior in tensile strength, coercive force, and corrosion resistance.

In addition, the conventional steel 36m has excellent electrical resistance and machinability, but the limit machining rate is 47% and the tensile strength is 45%.
kg f/mm2, which is very poor in cold forgeability, and the magnetic properties are also poor.

On the other hand, the steel of the present invention, 1 to 30 m, has C,
The content of elements that deteriorate cold forgeability due to solid solution strengthening effects such as N and Si is reduced as much as possible, and the A1 content is 0.22 to 0.83% and the Cr content is 11 to 13χ.
By doing so, the tensile strength is 38 kg f/mm”
It has excellent cold forging properties with a limit working rate of 65m or more, and its magnetic properties are as follows: magnetic flux density 13.000
G or more, and the coercive force is 1.00. It is excellent in the following, and is also excellent in corrosion resistance, electrical resistance, and machinability.

(Effects of the invention) As mentioned above, the steel of the present invention has excellent cold forgeability and good magnetic and electrical properties by reducing the content of C and N as much as possible and by using old steel. , and furthermore, S
+ P b + T e + S e + Z r +
The combined addition of Ca improves machinability without impairing cold forgeability, and the inclusion of an appropriate amount of Cr also improves corrosion resistance. This is a cold-forging soft magnetic stainless steel suitable for fuel injection devices, etc., and has high practicality.

Claims (4)

[Claims] (1) C0.008% or less by weight, Si0.20
%, Mn 0.35% or less, S 0.005% or less, C
r11-13%, N0.008% or less, C+N0.01
5% or less, containing 0.22 to 0.83% Al, the balance F
A soft magnetic stainless steel for cold forging characterized by comprising e and impurity elements. (2) C0.008% or less by weight, Si0.20
%, Mn 0.35% or less, Cr 11-13%, N0
．． 008% or less, C+N0.015% or less, Al0.2
Contains 2-0.83% and further contains Pb0.10-0.3
0%, S 0.040% or less, Se 0.040% or less, C
When containing one or more of a0.0020 to 0.0200% and one or more of S and Se, Te0.002 to 0.040% and Zr0.02 to
Contains one of 0.15% and further contains S+Se+Te
A soft magnetic stainless steel for cold forging, characterized in that the iron content is 0.050% or less, and the remainder consists of Fe and impurity elements. (3) C0.008% or less by weight, Si0.20
%, Mn 0.35% or less, S 0.005% or less, C
r11-13%, N0.008% or less, C+N0.01
5% or less, Al 0.22 to 0.83%, further Mo 4.0% or less, Cu 0.50% or less, Ni 2.50
% or less, Nb 0.20% or less, V 0.20% or less, and the balance is Fe and impurity elements. (4) C0.008% or less by weight, Si0.20
%, Mn 0.35% or less, Cr 11-13%, N0
．． 008% or less, C+N0.015% or less, Al0.2
Contains 2-0.83% and further contains Pb0.10-0.3
0%, S 0.040% or less, Se 0.040% or less, C
When containing one or more of a0.0020 to 0.0200% and one or more of S and Se, Te0.002 to 0.040% and Zr0.02 to
Contains one of 0.15% and further contains S+Se+Te
0.050% or less, Mo4.0% or less, C
u0.50% or less, Ni2.50% or less, Nb0.20
% or less, V0.20% or less, and the remainder is Fe and impurity elements.