JP2002340701A - Method for manufacturing magnetostrictive torque sensor shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a magnetostrictive torque sensor shaft which has hysteresis characteristics greatly improved by an inexpensive method. SOLUTION: By the method for manufacturing the magnetostrictive torque sensor shaft, a torque which is larger than a maximum torque that the shaft is loaded with is applied as prestrain to the shaft material of the magnetostrictive sensor in the same direction as the twisting direction of the shaft when the torque sensor is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetostrictive torque sensor shaft used for magnetically detecting an elastic torque applied to a shaft to be measured.

[0002]

2. Description of the Related Art Conventionally, in the field of a magnetostrictive torque sensor,
A method has been used in which a magnetic steel is used as a shaft to be measured, and an elastic torque applied to the shaft is magnetically detected by utilizing a magnetostrictive effect of the magnetic steel. FIG. 1 shows an output characteristic diagram of the torque sensor. The characteristics of the torque sensor include the slope S (hereinafter, referred to as sensitivity) of the output voltage with respect to the elastic torque (input signal),
Deviation of output voltage from initial value after removing elastic torque
h (hereinafter referred to as hysteresis)
The larger the (S in FIG. 1) and the smaller the hysteresis (h in FIG. 1), the better the torque sensor characteristics. Since the shaft of such a magnetostrictive torque sensor requires structural hardness as well as magnetism, structural steel such as JISSK material, SCM material and SNCM material is conventionally used. Steel is preferably used because it has the magnetostrictive effect of Fe and is inexpensive. However, structural steels that have been used in the past have a problem in that accurate torque detection cannot be performed because the relative permeability and magnetostriction are small, so that sensitivity is small and hysteresis is large.

[0003] In order to solve the above-mentioned problems, many studies have been made on shaft materials and shaft manufacturing methods. For example, Japanese Patent No. 2132909 discloses that in mass% C: 0.1 to 0.5%, Si: 1.0%.
% Or less, Mn: 2.0% or less, Ni: 5.0% or less, one or both of Cr: 5.0% or less, and a technique using a material having a composition of Fe and inevitable impurities as a balance as a torque sensor shaft is disclosed. ing. Patent 2697846 also has a composition obtained by further improving the material of Patent 2132909, C: 0.1 to 1.5%, Si: 0.5 to
4.0%, Mn: 0 and 3.0% or less, Al: 0 and 3.0% or less, N
A technique is disclosed in which one or both of i: 5.0% or less and Cr: 5.0% or less, and the balance is made of a material having a composition of Fe and inevitable impurities as a torque sensor shaft. These technologies ensure the strength and hardness of the material by the addition of alloying elements, and take advantage of the characteristics of each added element to make JIS SK, S
This is an excellent material technology in that the alloy composition is adjusted so that the sensitivity is higher than the CM material, SNCM material, etc. and the hysteresis is small.

[0004] As a conventional technique for examining a manufacturing method, Japanese Patent No. 2781071 discloses a technique for reducing hysteresis by performing a predetermined heat treatment on a torque sensor shaft and then performing shot peening. This proposal is an excellent manufacturing technique in that not only the material of the shaft to be measured but also the surface treatment is used to reduce the hysteresis.

[0005]

As described above, as a method of reducing the hysteresis conventionally performed, a method of adjusting a chemical composition of a material used for a shaft or a method of simply adding a strain near a material surface is used. Although it is possible to reduce the hysteresis, it is not enough to completely remove it to near zero. An object of the present invention is to provide a method for manufacturing a magnetostrictive torque sensor shaft in which the hysteresis characteristics are dramatically improved by an inexpensive method.

[0006]

The present inventor has studied a method of removing the hysteresis of the magnetostrictive torque sensor shaft to near zero, and as a result, after applying a distortion to the entire shaft in advance, it is necessary to apply a pre-distortion method. Predistortion), found that no new hysteresis occurs for strains in the same direction as the predistortion and smaller than the given predistortion. It has been found that the characteristics can be greatly improved. Then, the optimum chemical composition for the purpose was examined, and it was found that a hard material having high sensitivity could be selected as the material of the shaft, and the present invention was reached.

That is, according to the present invention, a torque larger than the maximum torque applied to the shaft is applied to the shaft member of the magnetostrictive torque sensor in the same direction as the torsion direction of the shaft when the torque sensor is used. A method for manufacturing a magnetostrictive torque sensor shaft, characterized in that: Preferably, the shaft material of the magnetostrictive torque sensor is a method of manufacturing a magnetostrictive torque sensor shaft made of precipitation-hardened Fe-based martensitic steel having a mass% of less than C: less than 0.1%, and more preferably a magnetostrictive torque sensor. The shaft material is C: less than 0.1% by mass%, Si: 2.0% or less, Mn: 2.0% or less,
Ni: 2.0 to 10.0%, Cr: 10.0 to 20.0%, (C
u: 0.5-5.0%, Al: 0.1-2.0%, Ti: 0.1-2.0%, Nb + Ta: 0.0
(5% to 2.0%), and a magnetostrictive torque sensor shaft including at least one of Fe and the balance substantially made of Fe.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, an important feature of the present invention is that a manufacturing method for introducing prestrain to the entire shaft is employed as a method for removing hysteresis of a magnetostrictive torque sensor shaft. Hereinafter, the reasons for the definition in the present invention will be described.

The present inventors have speculated that hysteresis is caused by dislocation movement within the elastic limit. Conversely, it was speculated that hysteresis could be eliminated if dislocations inside the torque sensor shaft were difficult to move. The reason for adopting the manufacturing method of introducing the prestrain to the entire shaft in the present invention is that, when the prestrain is introduced to the entire shaft, the dislocation in the shaft is fixed in the direction in which the prestrain was introduced, and it becomes difficult to move. It is.

Here, the direction of the pre-strain introduced into the shaft is defined to be the same as the torsional direction of the shaft when the torque sensor is used, in order to utilize the effect of the dislocation fixed in the pre-strain direction. For example, if you twist the shaft in the direction opposite to the prestrain direction,
The dislocation fixed by the pre-strain is not fixed to the strain in the opposite direction and is easily moved, so that a new hysteresis occurs, and it is difficult to obtain the effect of the pre-strain. For the above reasons, the direction in which the prestrain is introduced is the same as the direction of the torsion of the shaft when the torque sensor is used. In addition, as an application in which the torque sensor shaft manufactured by the manufacturing method of providing a pre-strain of the present invention is used, strain is added only in a certain direction,
For example, application to electric assist bicycles, machine tools, and the like is desirable.

The reason why the magnitude of the prestrain is set to be equal to or more than the maximum torque applied to the shaft when the torque sensor is used is to utilize the effect of the dislocation fixed by the prestrain as in the case described above. For example, when a larger amount of strain is applied than the pre-strain, the dislocation fixed by the pre-strain has no effect on the larger strain, so that the dislocation in the axis moves and new hysteresis occurs. It will be. For the above reasons, the magnitude of the pre-strain to be introduced is set to be equal to or greater than the maximum torque applied to the shaft when the torque sensor is used. In the present invention, the pre-strain may be introduced a plurality of times as needed.

Next, as a preferable material of the shaft manufactured by the above-mentioned method, a precipitation hardening type F having a C content of less than 0.1% by mass is used.
The reason specified for e-base martensitic steel is described. In the manufacturing method of the present invention, the hysteresis of the shaft is removed not by the shaft material but by pre-strain, so that a material having high sensitivity and high hardness can be selected as the shaft material. Here, as a magnetic and hard material, a Fe-based martensitic steel can be considered, but a martensitic steel of a type that contains a large amount of C, fixes dislocations by dispersing carbides, and obtains a high hardness is obtained. Since the relative permeability of the shaft cannot be sufficiently increased, it is difficult to remarkably increase the sensitivity of the shaft.

Therefore, in the present invention, attention was paid to the fact that the C content of the shaft material was reduced and the hardness of the shaft material was obtained by precipitation hardening by precipitating and dispersing an appropriate element or compound instead of dispersing carbide. The amount of C required for that purpose is less than 0.1% by mass%, and when C is 0.1% or more, the relative permeability of the shaft material is significantly reduced. Therefore, C in the present invention is less than 0.1%.

Next, the reason why the content of elements other than C is specified as a preferable composition of the shaft member will be described below. Si: 2.0% or less, Mn: 2.0% or less Both Si and Mn are elements that act as deoxidizing elements in the steelmaking process. The above range may be included as a range that does not particularly affect the sensitivity and hysteresis characteristics of the shaft. In addition, the preferred upper limits of Si and Mn are each 1.5% or less,
It is better to be in the range of 1.0% or less.

Ni: 2.0 to 10.0% Ni has the effect of increasing the magnetostriction and the sensitivity of the shaft material in the Fe-based martensitic steel, as well as enhancing the hardenability of the shaft material and changing the structure to martensite. It is an important element of the present invention which is effective. If an appropriate heat treatment temperature is selected, Al
It also has the effect of forming a compound with Ti and Ti and increasing the hardness by precipitation hardening. However, when the content is less than 2.0%, the effect is small. On the contrary, when the content is more than 10.0%, the structure of the shaft becomes austenite, which deviates from the preferable metal structure of the shaft of the present invention. . Desirably 3.0 to 8.0
% Range.

Cr: 10.0 to 25.0% Cr is an important element for securing the corrosion resistance of the shaft material and improving the hardenability similarly to Ni to make the structure of the shaft material martensite. However, if it is less than 10.0%, the effect of securing corrosion resistance is small, and if it exceeds 25.0%, the workability of the shaft material is significantly deteriorated. The preferred Cr content is in the range of 12.0-20.0%.

Next, Cu, Al, Ti, and Nb + Ta were selected as the selected elements, and one or more of these elements were selected because these elements reduced the hardness of the shaft material by precipitation hardening. This is because it has the effect of raising. The purpose of precipitation hardening can be achieved by adding one of these elements or by adding two or more of these elements in combination. Hereinafter, the reason for defining the effect and the range of the content of each element will be described. Cu: 0.5 to 5.0% Cu has a low solid solubility in martensite and easily forms a supersaturated solid solution in martensite. Therefore, precipitation of Cu by aging contributes to hardening of martensite. However,
If it is less than 0.5%, the effect is small, and if it exceeds 5.0%, the workability of the shaft material is deteriorated.

Al: 0.1 to 2.0% Al forms an intermetallic compound with Ni by aging treatment, and contributes to the hardening of martensite by precipitation hardening. However, 0.
If it is less than 1%, the effect is small. On the contrary, if it exceeds 2.0%, the workability of the shaft material is deteriorated. Ti: 0.1 to 2.0% Ti, like Al, forms an intermetallic compound with Ni by aging treatment and contributes to the hardening of martensite by precipitation hardening. Also, since a small amount of C is fixed, it is also effective in increasing the relative magnetic permeability of the shaft material and thus the sensitivity. However, if the content is less than 0.1%, the effect is small, and if it exceeds 2.0%, the workability of the shaft material deteriorates.

Nb + Ta: 0.05-2.0% Since Nb and Ta fix a small amount of C, similarly to Ti, they are effective in increasing the relative magnetic permeability of the shaft material and, consequently, the sensitivity. However, 0.05%
If the content is less than 2.0%, the effect is small, and if the content is more than 2.0%, the workability of the shaft material is deteriorated. In the present invention, the elements other than the above-mentioned elements are not particularly specified, and the remainder may be substantially Fe. However, naturally, impurities inevitably contained are contained in a small amount. However, if excessively contained, the characteristics of the torque sensor shaft material are degraded. Therefore, P, S,
N and O may each be contained in a range of 0.1% or less as a range that does not particularly deteriorate the sensitivity and the hysteresis characteristics.

As a desirable manufacturing procedure of the torque sensor shaft of the present invention, a material having a preferable composition of the present invention is first melted, and then heated to 1050 to 1200 ° C. to perform hot working to obtain a target dimension. Good to finish. Next, after the heat-processed torque sensor shaft material is heat-treated at 600 to 800 ° C. and softened, it is processed into a magnetostrictive torque sensor shaft shape, and then
Rapid cooling is performed from a temperature range of 1000 to 1100 ° C, and the metal structure of the shaft material is changed to a martensitic structure. Further, aging treatment is performed in the range of 400 to 600 ° C. to increase the hardness of the torque sensor material by precipitation hardening. Next, the above-described magnetostrictive torque sensor material is provided with a torque having a magnitude equal to or greater than the maximum torque applied when the torque sensor shaft is used as a pre-strain in the same torsion direction as in use, and the magnetostrictive torque of the present invention is obtained. What is necessary is just to make it a type torque sensor shaft.

The hysteresis of the magnetostrictive torque sensor shaft manufactured by the method of the present invention is reduced to near zero by prestrain. Giving a pre-distortion is less expensive than providing a step such as shot peening, and also gives a distortion to the entire axis, so that the hysteresis can be more reliably reduced to near zero. Further, using a martensitic steel having a low C composition defined in the present invention,
When used in combination with the manufacturing method of the present invention, it is extremely effective as a torque sensor shaft having high sensitivity, low hysteresis, and structural rigidity. That is, the torque sensor using the torque sensor shaft of the present invention can perform highly accurate torque detection.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, it is important to first evaluate the hysteresis characteristics when a prestrain is applied to a torque sensor shaft and when no prestrain is applied. Also, the material of the torque sensor shaft manufactured by the method of giving a pre-strain becomes important. 10 kg of material was melted by vacuum melting. Table 1 shows the chemical composition of each test material. The breakdown of each material shown in Table 1 is as follows.

The compositions of Nos. 1 and 2 have a C content of 0.1% by mass.
And is a material for a magnetostrictive torque sensor that becomes a precipitation hardening type Fe-based martensitic steel by heat treatment. Among them, No. 1 is a material corresponding to the preferred composition range of the present invention. The compositions of Nos. 3 and 4 are magnetostrictive torque sensor materials which have a C content of 0.1% or more by mass% and become Fe-based martensitic steel by heat treatment. Of these, No. 3
Has been favorably used as a material for magnetostrictive torque sensors
Equivalent to JIS SK5 material. No. 4 corresponds to the material disclosed in Japanese Patent No. 2132909.

[0024]

[Table 1]

The melted steel ingot was heated to 1100 ° C. and hot worked to obtain a round bar having a diameter of 20 mm. For this round bar, material Nos. 1 and 2 with a C content of less than 0.1% are furnace-cooled at 700 ° C for 3 hours in the atmosphere, and material Nos. 3 and 4 with a C content of 0.1% or more are in the air. The softening treatment was performed under the conditions of medium 750 ° C-4h → 20 ° C / h → 650 ° C furnace cooling.

When the above-mentioned material is actually used as a magnetostrictive torque sensor shaft, the softened material is machined into the shaft shape of the magnetostrictive torque sensor, and then the shaft material is hardened. Heat treatment is performed, and a magnetostrictive torque sensor shaft is obtained through a process in which a torque larger than the maximum torque applied to the shaft is applied as pre-strain in the same direction as the torsion direction when the torque sensor is used.

An external torque (torsion) is applied to the magnetostrictive torque sensor shaft, but the surface layer of the shaft where a change in relative permeability (inductance) is detected is pulled at an angle of 45 degrees from the longitudinal direction of the shaft. Compressive stress is applied. That is, the sensitivity and hysteresis characteristics of the magnetostrictive torque sensor shaft can be simply evaluated by measuring the change in inductance of the magnetostrictive torque sensor shaft with respect to an externally applied tensile or compressive stress. The direction of the stress when evaluating the torque sensor axis may be either the tension or the compression direction.

Here, the relationship between the torque T when a round bar having a diameter D is twisted and the tensile stress σ generated on the surface of the round bar is generally expressed by the following relational expression (1). σ = 16T / (πD) ³ … (1) If D = 10 (mm) on the torque sensor axis, 100 (N
m), the tensile stress on the shaft surface is (1)
It can be estimated from the formula to be about 50 (MPa). When used as an actual magnetostrictive torque sensor, the maximum torque applied to the shaft is often about 500 (Nm) or less, and the tensile stress level can be evaluated in a stress range up to about 250 (MPa). It is enough. When the characteristics of the torque sensor shaft are evaluated by applying a tensile stress of 250 (MPa) for the above-described reason, the shaft material subjected to the above-described softening treatment and then subjected to the hardening heat treatment is subjected to 250 (MPa).
a) By giving the above-described tensile prestrain, this shaft becomes a torque sensor shaft manufactured by the manufacturing method of the present invention.

In this embodiment, a round bar test piece having a diameter of 10 mm and a length of 80 mm was sampled from the material subjected to the above-mentioned softening treatment by machining, and M10 screw processing was performed on both ends. Heat treatment was performed under the conditions to make the metal structure of the material a martensitic structure. By this heat treatment, the material of this example was a magnetostrictive torque sensor made of Fe-based martensite steel. Among them, No. 1-2 are precipitation hardening type having a C content of less than 0.1% by mass% as a preferred composition of the shaft material in the present invention.
Fe-based martensitic steel, No. 3-4 have a C content of 0.
Fe-based martensitic steel of 1% or more. Table 2 shows the heat treatment conditions of each material and the hardness after the heat treatment.

[0030]

[Table 2]

From Table 2, it can be seen that each material has a hardness of 40 HRC or more, and the structural hardness is maintained. Next, in this example, the sensitivity and hysteresis characteristics of the torque sensor shaft composed of each shaft member were evaluated by the following method using a tensile tester and an LCR meter. After covering the above round bar test piece with a search coil with a coil length of 25 mm and 100 turns,
The test piece is connected to the tensile tester, and the search coil is connected to the LCR meter. The setting of the LCR meter is as follows: frequency f = 80 [kHz
z], the maximum applied magnetic field Hm = 40 [Am ^-1 ], and the initial value of the coil inductance L ₀ [μH] without applying a tensile stress.
Is measured. From this state, the loading and unloading of the tensile stress are repeated to gradually increase the magnitude of the tensile stress.

The tensile stress increases every 50 [MPa],
The test was performed up to a maximum load stress of 250 [MPa]. Maximum load stress is 25
The reason for setting it to 0 [MPa] is to take into account the maximum torque when used as an actual torque sensor as described above. Note that the inductance measured by the LCR meter is a value corresponding to the relative magnetic permeability μr of the material. From the inductance-stress characteristics described above, the sensitivity S ₀ and the hysteresis h ₀ of each material were defined by the following equations. Sensitivity: S ₀ [nH / MPa] = (L _load -L ₀ ) / Load stress… (2) Hysteresis: h ₀ [%] = 100 × (L _unload -L ₀ ) / L ₀ … (3 )

In the present embodiment, 25
The inductance-tensile stress characteristics after applying a tensile prestrain of 0 [MPa] were measured. By giving the tensile prestrain of 250 [MPa], the shaft members of Nos. 1 to 4 become the magnetostrictive torque sensor shafts manufactured by the manufacturing method of the present invention. In addition, the hardness of each shaft member of Nos. 1 to 4 showed the same value as in Table 2 even after the introduction of prestrain. FIG. 2 shows the characteristics of a magnetostrictive torque sensor shaft made of shaft material No. 1 as an example of measuring the inductance-tensile stress characteristics of the magnetostrictive torque sensor shaft manufactured by the manufacturing method of the present invention.

Next, as a manufacturing method of a comparative example, the inductance-tensile stress characteristics in a case where the shaft material was not subjected to a tensile prestrain while being in a hardening heat treatment state were measured. As an example of measuring the inductance-tensile stress characteristics of the magnetostrictive torque sensor shaft manufactured by the manufacturing method of the comparative example, FIG. 3 shows the characteristics of the magnetostrictive torque sensor shaft made of shaft material No. 1. Further, with respect to the magnetostrictive torque sensor shaft manufactured by the manufacturing method of the present invention and the magnetostrictive torque sensor shaft manufactured by the manufacturing method of the comparative example, each axis when a tensile stress of 250 [MPa] is applied and unloaded. Table 3 shows the sensitivity and hysteresis characteristics of the torque sensor shaft made of a material.

[0035]

[Table 3]

From Table 3, it can be seen that the magnetostrictive torque sensor shaft manufactured by the manufacturing method of the present invention has low hysteresis characteristics due to the effect of prestrain, but the magnetostrictive torque sensor shaft manufactured by the manufacturing method of the comparative example. It can be seen that the hysteresis of the axis is large. Further, it can be seen that in the magnetostrictive torque sensor shaft manufactured by the manufacturing method of the present invention, the hysteresis is reduced to around 0.1% or less near zero regardless of the material of the shaft. If the absolute value of the hysteresis of the torque sensor axis is 0.1% or less,
As a magnetostrictive torque sensor, a decrease in torque measurement accuracy due to hysteresis can be ignored. Also in mass%
The sensitivity of the torque sensor shaft composed of shaft materials No. 1 and 2 having C of less than 0.1% is higher than that of the torque sensor shaft composed of shaft materials No. 3 and 4 having C of 0.1% or more. It can be seen that a particularly high sensitivity is obtained with the torque sensor shaft made of the shaft material No. 1, which is a preferable composition range.

Next, in the present invention, the magnitude and direction of the prestrain to be introduced and the method of introducing the prestrain are important. From the results in Table 3, the pre-strain was introduced by changing the pre-strain magnitude and direction and the method of pre-strain introduction for the torque sensor shaft made of the shaft material No. 1 with the highest sensitivity after the pre-strain introduction. After that, the sensitivity S and the hysteresis h when a tensile stress of 250 [MPa] was applied were measured. Table 4 summarizes the characteristic values of the predistortion direction, predistortion amount, sensitivity, and hysteresis.

[0038]

[Table 4]

The prestrain introducing methods a to f in Table 4 will be described. a to c are production methods of the present invention, in which after applying a tensile stress of 250 [MPa] or more as a pre-strain, a tensile stress of 250 [MPa] is applied to evaluate the sensitivity and hysteresis characteristics. d
To f are comparative examples. In method d, 150 [MPa] lower than 250 [MPa]
a) tensile stress was given as prestrain. In method e, 250
After applying a compressive stress of [MPa] as pre-strain, a tensile stress of 250 [MPa] was applied in the opposite direction to the pre-strain to evaluate the sensitivity and hysteresis characteristics. In method f, predistortion was introduced by shot peening. This method of introducing predistortion by shot peening corresponds to the technique disclosed in Japanese Patent No. 2780771.

As shown in Table 4, in the methods a to c of the present invention in which a tensile stress of 250 [MPa] or more was applied as a pre-strain, the absolute value of the hysteresis was 0.1% or less near zero. on the other hand,
According to the results of Comparative Examples d to f, there is no effect of removing the hysteresis for the strain in the direction opposite to the introduced pre-strain, and the hysteresis is also removed for the strain larger than the introduced pre-strain. It turns out that there is no effect. Further, although the hysteresis is reduced by shot peening as compared with the case without predistortion in Table 3, it can be seen that the effect of reducing the hysteresis is smaller than when prestrain is introduced by the manufacturing method of the present invention.

From the above experimental results, the magnetostrictive torque sensor shaft manufactured by the manufacturing method of the present invention has excellent low hysteresis characteristics, and when manufactured in combination with the shaft material having the preferred composition of the present invention, high sensitivity and high hardness can be obtained. It can be understood that the characteristics described above are particularly easy to use as a magnetostrictive torque sensor shaft. Furthermore, a magnetostrictive torque sensor using a shaft manufactured by this manufacturing method can accurately detect torque, and is particularly suitable for use in electric assist bicycles and machine tools, and further in the field of robots. .

[0042]

According to the manufacturing method of the present invention, the hysteresis characteristics of the magnetostrictive torque sensor shaft can be remarkably improved, and the manufacturing method combined with a shaft material having high sensitivity and hardness can be applied. , High sensitivity, low hysteresis,
A high-hardness magnetostrictive torque sensor shaft can be realized. The detection accuracy of the torque sensor can be enhanced by the magnetostrictive torque sensor shaft manufactured by the manufacturing method of the present invention. The present invention is an indispensable technique for practical use of a magnetostrictive torque sensor.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing output characteristics of a torque sensor.

FIG. 2 is an example showing inductance-tensile stress characteristics of a torque sensor shaft manufactured by the manufacturing method of the present invention.

FIG. 3 is an example showing inductance-tensile stress characteristics of a torque sensor shaft manufactured by a manufacturing method of a comparative example.

Claims (3)

[Claims] 1. A torque greater than a maximum torque applied to a shaft is applied to a shaft of a magnetostrictive torque sensor in the same direction as the torsion direction of the shaft when the torque sensor is used, as a pre-distortion. A method for manufacturing a magnetostrictive torque sensor shaft, characterized in that: 2. The shaft material of the magnetostrictive torque sensor is expressed in mass%.
2. The method for manufacturing a magnetostrictive torque sensor shaft according to claim 1, wherein the magnetostrictive torque sensor shaft is made of Fe: less than 0.1% precipitation hardening type Fe-based martensitic steel. 3. The shaft material of the magnetostrictive torque sensor is expressed in mass%.
C: less than 0.1%, Si: 2.0% or less, Mn: 2.0% or less, Ni: 2.0 to 10.0
%, Cr: 10.0 to 25.0%, and as a selected element (Cu: 0.5 to 5.0%,
Al: 0.1 to 2.0%, Ti: 0.1 to 2.0%, Nb + Ta: 0.05 to 2.0%), and the balance substantially consists of Fe. Or a method for manufacturing a magnetostrictive torque sensor shaft according to item 2.