JP5375406B2 - Precipitation hardening stainless steel for strain generating body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a precipitation hardening stainless steel for an elastic body which is excellent in strength, toughness and corrosion resistance, and also is excellent in elastic body performance. <P>SOLUTION: The precipitation hardening stainless steel has a composition comprising, by mass, 0.010 to 0.060% C, &le;1.0% Si, &le;1.0% Mn, &le;0.05% P, &le;0.03% S, 2.0 to 4.0% Cu, 2.5 to 5.0% Ni, 13.0 to 17.0% Cr, &le;1.0% Mo, &le;0.030% Al, &le;0.020% O and 0.010 to 0.050% N, and comprising 0.10 to 0.40% Nb, and the balance Fe with inevitable impurities, and in which C+N: 0.025 to 0.095%, Cu+Ni: &le;8.5%, and &alpha;value shown by formula; &alpha;=1320([C]+[N])+52[Ni]+14[Cu]+10[Cr]+20[Mo]+26[Mn]+20[Si] is &le;510. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a precipitation hardening type stainless steel for a strain generating body.

  Conventionally, in a pressure sensor, a weight sensor, a load cell, and the like, a strain generating body is used as a member that generates strain by an external force. Generally, nickel chrome molybdenum steel or stainless steel is known as a material of the strain generating body. In an environment where the corrosion is relatively mild, martensitic stainless steels such as SUS410 and SUS420J2 are used. Hardened stainless steel is used.

  Among the above stainless steels, the cold-worked material of austenitic stainless steel can be applied to a flexure body having a simple shape such as a plate shape. However, for a strained body having a complicated shape, the required strength may not be obtained, and when welding or the like is performed, the strength is reduced at the welded portion. In addition, the strength cannot be improved by performing a heat treatment after welding. Therefore, SUS630, which is a precipitation hardening stainless steel, is often used for strained bodies with complicated shapes and strained bodies with welding.

In addition, in Patent Document 1, as precipitation hardening stainless steel applied to a pressure sensor or the like, by mass%, C: more than 0.005% and 0.10% or less, Si: more than 0.50 2.0% or less, Mn: 0.6% or less, S: 0.005% or less, Ni: 5.5 to 7.5%, Cr: 13.0 to less than 15.0%, Mo and W Mo + 0.5 × W exceeding 1.5% to 3.0% or less, Cu: 0.2 to 1.0%, N: 0.05% or less, Al: 0.001 to 0.05%, Ti: 0 to 0.05%, B: 0.0005 to 0.01%, further containing one or more selected from Nb, V and Ta in a total range of 0.05 to 1.0%, and the balance Is substantially Fe, and the A value represented by the formula (1) is 21 or less, the B value represented by the formula (2) is 21 or less, and the C value represented by the formula (3) is 20 Precipitation hardening stainless steel is above is disclosed.
A value = −20 × (% C) + (% Si) −0.1 × (% Mn) −1.25 × (% Ni) + 1.8 × (% Cr) + 1.4 × (% Mo) +0 0.7 × (% W) −0.5 × (% Cu) + 2.5 × (% Nb) + 1.5 × (% V) + 0.75 × (% Ta) + 1.8 × (% Ti) −24 × (% N) (1)
B value = (% Ni) + 0.7 × (% Cr) + 0.98 × (% Mo) + 0.49 × (% W) + 1.05 × (% Mn) + 0.35 × (% Si) +0.48 X (% Cu) + 0.15 x (% Nb) + 0.75 x (% V) + 0.6 x (% Ta) + 0.3 x (% Ti) + 12.5 x (% C) + 10 x (% N ) ... (2)
C value = (% Cr) + 3.3 × (% Mo) + 1.65 × (% W) + 30 × (% N) (3)

JP 2005-298840 A

  However, SUS630, which has been frequently used as a strain generating material, has had the following problems. That is, the stainless steel used for the strain generating body needs to be excellent in strength and toughness as a structure. Moreover, since it may be used in corrosive environment, it needs to be excellent in corrosion resistance.

  Further, in addition to the above, it is required not to deteriorate the strain generating body performance. In this regard, the conventional component system of SUS630 (17Cr-4Ni-4Cu-Nb) contains about 10% by volume of residual austenite phase in the structure after heat treatment in which aging treatment is performed after solution treatment. Therefore, when this is used for a strain body, there is a problem that the soft retained austenite phase yields slightly during use of the sensor, the hysteresis increases, the reference point gradually fluctuates, and the strain body performance deteriorates. .

  The present invention has been made in view of the above circumstances, and the problems to be solved by the present invention are not only excellent in strength, toughness, and corrosion resistance, but also precipitation hardening for strain-generating bodies excellent in strain-generating body performance. Is to provide type stainless steel.

The precipitation hardening stainless steel for strain-generating bodies according to the present invention is in mass%, C: 0.010 to 0.060%, Si: 1.0% or less, Mn: 1.0% or less, P: 0.00. 05% or less, S: 0.03% or less, Cu: 2.0 to 4.0%, Ni: 2.5 to 5.0%, Cr: 13.0 to 17.0%, Mo: 1.0 %: Al: 0.030% or less, O: 0.020% or less, N: 0.010 to 0.050%, and Nb: 0.10 to 0.40%, with the balance being Fe and It consists of inevitable impurities, and is summarized as C + N: 0.025 to 0.095%, Cu + Ni: 8.5% or less, and the α value represented by the following formula is 510 or less.
α = 1320 ([C] + [N]) + 52 [Ni] +14 [Cu] +10 [Cr] +20 [Mo] +26 [Mn] +20 [Si]

  Here, the precipitation hardening stainless steel for strain generating body preferably has a structure in which the amount of retained austenite is 2.0% by volume or less.

  Moreover, the precipitation hardening type stainless steel for strain-generating bodies is one or two selected from mass%, Co: 0.05 to 1.0%, and W: 0.05 to 1.0%. The above may be further contained.

  Moreover, the precipitation hardening type stainless steel for strain generating bodies is in mass%, V: 0.005 to 0.20%, Ti: 0.005 to 0.10%, Ta: 0.005 to 0.10%. And one or more selected from Zr: 0.005 to 0.10% may be further contained.

  Moreover, the precipitation hardening type stainless steel for strain generating bodies is mass%, B: 0.0005 to 0.0100%, Mg: 0.0005 to 0.0100%, and Ca: 0.0005 to 0.00. You may further contain 1 type, or 2 or more types selected from 0100%.

  Precipitation hardening type stainless steel for strain generating bodies according to the present invention includes, in particular, C and N alone and in total, Cu and Ni alone and in total, and Cr and Nb alone in a specific range. By controlling the amount of the component to a specific amount or less, the strength, toughness and corrosion resistance are excellent. Furthermore, by setting the α value defined by the specific formula to 510 or less, the Ms point during the solution heat treatment increases, and the amount of retained austenite can be reduced. For this reason, even when repeated stress is applied when used as a strain generating body, it is possible to suppress microyield. Therefore, the precipitation hardening stainless steel for strain generating bodies according to the present invention is not only excellent in strength, toughness, and corrosion resistance, but also excellent in strain generating body performance.

  Here, when the amount of retained austenite has a structure of 2.0% by volume or less, it becomes easy to suppress microyield and to improve the strain generating body performance.

  Further, when a specific amount of one or more selected from Co and W is further contained, it can contribute to improvement of corrosion resistance. Moreover, it becomes easy to suppress the increase in a retained austenite amount, and it can contribute to suppression of the strength fall after an aging treatment, and the suppression of the fall of a strain body performance.

  Further, when a specific amount of one or more selected from V, Ti, Ta and Zr is further contained, it is possible to suppress the grain coarsening during the solution heat treatment and contribute to the improvement of toughness. . Moreover, it can contribute to improvement of hot workability and suppression of strength reduction after aging treatment.

  Moreover, when 1 type or 2 types or more selected from B, Mg, and Ca are contained further in specific amount, it can contribute to the improvement of hot workability.

  Hereinafter, the precipitation hardening stainless steel for strain-generating bodies according to an embodiment of the present invention (hereinafter sometimes referred to as “the present stainless steel”) will be described in detail. This stainless steel contains the following elements, and the balance consists of Fe and inevitable impurities. Further, the α value defined by the specific formula is equal to or less than the specific value.

  The type, content, reason for limitation, and technical significance of each formula in each stainless steel are as follows. In addition, the unit of content is mass%.

C: 0.010 to 0.060%
C is effective in reducing the amount of δ-ferrite. C combines with Nb and N to form a carbonitride, prevents crystal grain coarsening during solution heat treatment, and contributes to improved toughness and ductility. In order to obtain the effect, the lower limit of the C content is set to 0.010% or more. The lower limit of the C content is preferably 0.020% or more, more preferably 0.030% or more.

  However, excessive addition of C tends to reduce the solid solution Cr of the parent phase due to the formation of Cr-based carbides and to reduce the corrosion resistance. In addition, the Ms point is decreased to increase the amount of retained austenite, which causes a decrease in strength after aging treatment and a decrease in strain generating body performance. Therefore, the upper limit of the C content is set to 0.060% or less. The upper limit of the C content is preferably 0.045% or less, more preferably 0.040% or less.

Si: 1.0% or less Si is effective as a deoxidizing element. However, when the amount increases, the amount of δ-ferrite is increased and the strength after the aging treatment is decreased. Further, excessive addition of Si lowers the Ms point and increases the amount of retained austenite, leading to a decrease in strength and aging of the strain body after aging treatment. Therefore, the upper limit of the Si content is 1.0% or less. The upper limit of the Si content is preferably 0.5% or less.

Mn: 1.0% or less Mn is effective as a deoxidation and desulfurization element. It is also effective in reducing the amount of δ-ferrite. However, excessive addition of Mn lowers the Ms point and increases the amount of retained austenite, leading to a decrease in strength after aging treatment and a decrease in strain body characteristics. Therefore, the upper limit of the Mn content is 1.0% or less. The upper limit of the Mn content is preferably 0.6% or less.

P: 0.05% or less P is an impurity element of a steel material. Since excessive addition of P reduces hot workability and toughness, it is preferably reduced as much as possible. However, an excessive reduction of P causes an increase in cost. Therefore, the upper limit of the P content is 0.05% or less. The upper limit of the P content is preferably 0.03% or less.

S: 0.03% or less Since excessive addition of S decreases hot workability, toughness, and corrosion resistance, it is preferably reduced as much as possible. However, reduction of S more than necessary causes an increase in cost. Therefore, the upper limit of the S content is 0.03% or less. The upper limit of the S content is preferably 0.01% or less.

Cu: 2.0 to 4.0%
Cu is an essential component as a precipitation hardening component, and is also effective in improving corrosion resistance. It is also effective in reducing the amount of δ-ferrite. In order to obtain the effect, the lower limit of the Cu content is set to 2.0% or more. The lower limit of the Cu content is preferably 2.7% or more, more preferably 2.9% or more.

  However, excessive addition of Cu decreases the Ms point and increases the amount of retained austenite, leading to a decrease in strength after aging treatment and a decrease in strain-generating body performance. Moreover, hot workability is reduced. Therefore, the upper limit of the Cu content is 4.0% or less. The upper limit of the Cu content is preferably 3.5% or less, more preferably 3.2% or less.

Ni: 2.5-5.0%
Ni is effective in reducing the amount of δ-ferrite and is effective in improving corrosion resistance. In order to obtain the effect, the lower limit of the Ni content is set to 2.5% or more. The lower limit of the Ni content is preferably 3.0% or more, more preferably 3.5% or more.

  However, excessive addition of Ni decreases the Ms point and increases the amount of retained austenite, leading to a decrease in strength after aging treatment and a decrease in strain-generating body performance. Moreover, hot workability is reduced. Therefore, the upper limit of the Ni content is 5.0% or less. The upper limit of the Ni content is preferably 4.0% or less, more preferably 3.9% or less.

Cr: 13.0 to 17.0%
Cr is an essential element as an element for improving the corrosion resistance. In order to obtain the effect, the lower limit of the Cr content is set to 13.0% or more. The lower limit of the Cr content is preferably 13.5% or more, more preferably 14.0% or more.

  However, when the amount increases, the amount of δ-ferrite is increased and the strength after the aging treatment is decreased. Further, excessive addition of Cr lowers the Ms point and increases the amount of retained austenite, leading to a decrease in strength after aging treatment and a decrease in strain body characteristics. Therefore, the upper limit of the Cr content is 17.0% or less. The upper limit of the Cr content is preferably 16.0% or less, more preferably 14.5% or less.

Mo: 1.0% or less Mo is effective in improving corrosion resistance. However, when the amount increases, the amount of δ-ferrite is increased and the strength after the aging treatment is decreased. Further, excessive addition of Mo decreases the Ms point and increases the amount of retained austenite, leading to a decrease in strength after aging treatment and a decrease in strain body characteristics. Therefore, the upper limit of the Mo content is 1.0% or less. The upper limit of the Mo content is preferably 0.5% or less.

Al: 0.030% or less Al is effective as a deoxidizing element. However, when the amount increases, the amount of δ-ferrite is increased and the strength after the aging treatment is decreased. Moreover, coarse nitrides are easily formed, leading to a decrease in toughness. Therefore, the upper limit of the Al content is 0.030% or less. The upper limit of the Al content is preferably 0.010% or less.

O: 0.020% or less Since excessive addition of O reduces hot workability, toughness, and corrosion resistance, it is preferably reduced as much as possible. However, reducing O more than necessary causes an increase in cost. Therefore, the upper limit of the O content is 0.020% or less. The upper limit of the O content is preferably 0.010% or less.

N: 0.010 to 0.050%
N is effective in reducing the amount of δ-ferrite. N combines with Nb and C to form a carbonitride, prevents crystal grain coarsening during solution heat treatment, and contributes to improvement in toughness and ductility. In order to obtain the effect, the lower limit of the N content is set to 0.010% or more. The lower limit of the N content is preferably 0.020% or more, more preferably 0.025% or more.

  However, excessive addition of N reduces toughness. In addition, the Ms point is decreased to increase the amount of retained austenite, which causes a decrease in strength after aging treatment and a decrease in strain generating body performance. Therefore, the upper limit of N content is 0.050% or less. The upper limit of the N content is preferably 0.035% or less, more preferably 0.030% or less.

Nb: 0.10 to 0.40%
Nb combines with C and N to form carbonitrides, prevents crystal grain coarsening during solution heat treatment, and contributes to improved toughness and ductility. Further, since the solute C and N are reduced, the Ms point is increased, which is effective for reducing the amount of retained austenite. In order to obtain the effect, the lower limit of the Nb content is 0.10% or more. The lower limit of the Nb content is preferably 0.15% or more.

  However, excessive addition of Nb impairs hot workability, increases the amount of δ-ferrite, and decreases the strength after aging treatment. Therefore, the upper limit of the Nb content is set to 0.40% or less. The upper limit of the Nb content is preferably 0.35% or less.

C + N: 0.025 to 0.095%
The total amount of the C content and the N content affects the toughness after aging treatment. In order to obtain good toughness, the lower limit of the total amount of C content and N content is 0.025% or more. The lower limit of the total amount of C content and N content is preferably 0.045% or more, more preferably 0.050% or more.

  However, excessive addition of these elements decreases the Ms point and increases the amount of retained austenite, leading to a decrease in strength after aging treatment and a decrease in strain-generating body performance. Therefore, the upper limit of the total amount of C content and N content is set to 0.095% or less. The upper limit of the total amount of C content and N content is preferably 0.075% or less, more preferably 0.065% or less.

Cu + Ni: 8.5% or less When the total amount of Cu content and Ni content becomes excessive, the As point (starting temperature of austenite transformation at the time of heating) decreases, increasing the amount of retained austenite after aging treatment, The distortion performance is reduced. Therefore, the upper limit of the total amount of Cu content and Ni content is set to 8.5% or less. The upper limit of the total amount of Cu content and Ni content is preferably 7.5% or less, and more preferably 7.0% or less.

  The stainless steel contains at least the essential components. Here, this stainless steel has an α value defined by the following formula of 510 or less.

α = 1320 ([C] + [N]) + 52 [Ni] +14 [Cu] +10 [Cr] +20 [Mo] +26 [Mn] +20 [Si]
However, [X] represents mass% of the element X.

  The tendency to form retained austenite generated during the solution heat treatment is indicated by the α value. The lower the α value, the higher the Ms point during the solution heat treatment and the lower the amount of retained austenite. In the present invention, by setting the α value to 510 or less, an increase in hysteresis due to the micro-yield of the retained austenite phase is suppressed, and when used as a strain generating element, the reference point gradually increases even when repeated stress is applied. The strain generating body performance can be improved, such as being less likely to fluctuate. The α value is preferably 500 or less, more preferably 490 or less, from the viewpoint of improving the strain generating body performance.

  This stainless steel preferably has a retained austenite content of 2.0 vol% or less in its structure. This is because there are advantages such as easy suppression of micro-yield of the retained austenite phase and easy improvement of the strain generating body performance. The amount of retained austenite is more preferably 1.0% by volume or less.

  In addition to the essential elements described above, the present stainless steel may further contain one or more elements selected from Co and W as necessary. The component ranges of Co and W and the reasons for their limitation are as follows.

Co: 0.05-1.0%
Co is effective in improving corrosion resistance. It is also effective in reducing the amount of δ-ferrite. In order to obtain the effect, the lower limit of the Co content is set to 0.05% or more. The lower limit of the Co content is preferably 0.30% or more.

  However, excessive addition of Co leads to an increase in cost, and also lowers the Ms point and increases the amount of retained austenite, leading to a decrease in strength after aging treatment and a decrease in strain body characteristics. Therefore, the upper limit of the Co content is 1.0% or less. The upper limit of the Co content is preferably 0.80% or less.

W: 0.05-1.0%
W is effective for improving corrosion resistance. In order to obtain the effect, the lower limit of the W content is set to 0.05% or more. The lower limit of the W content is preferably 0.30% or more.

  However, excessive addition of W causes an increase in cost, and also lowers the Ms point and increases the amount of retained austenite, leading to a decrease in strength after aging treatment and a decrease in strain-generating body characteristics. Therefore, the upper limit of the W content is 1.0% or less. The upper limit of the W content is preferably 0.80% or less.

  The stainless steel may further contain one or more elements selected from V, Ti, Ta, and Zr as necessary in addition to the elements described above. The component ranges of V, Ti, Ta, and Zr and the reasons for their limitations are as follows.

V: 0.005-0.20%
V, like Nb, combines with C and N to form carbonitrides, prevents crystal grain coarsening during solution heat treatment, and contributes to improved toughness. In order to obtain the effect, the lower limit of the V content is set to 0.005% or more. The lower limit of the V content is preferably 0.05% or more.

  However, excessive addition of V impairs hot workability, increases the amount of δ-ferrite, and decreases the strength after aging treatment. Therefore, the upper limit of V content is 0.20% or less. The upper limit of the V content is preferably 0.12% or less.

Ti: 0.005-0.10%
Ti combines with C and N to form carbonitrides, prevents coarsening of crystal grains during the solution heat treatment, and contributes to improvement of toughness. In order to obtain the effect, the lower limit of the Ti content is set to 0.005% or more. The lower limit of the Ti content is preferably 0.01% or more.

  However, excessive addition of Ti impairs hot workability, increases the amount of δ-ferrite, and decreases the strength after aging treatment. Therefore, the upper limit of the Ti content is set to 0.10% or less. The upper limit of the Ti content is preferably 0.05% or less.

Ta: 0.005 to 0.10%
Ta combines with C and N to form carbonitrides, prevents coarsening of crystal grains during solution heat treatment, and contributes to improved toughness. In order to obtain the effect, the lower limit of the Ta content is set to 0.005% or more. The lower limit of the Ta content is preferably 0.05% or more.

  However, excessive addition of Ta impairs hot workability, increases the amount of δ-ferrite, and decreases the strength after aging treatment. Therefore, the upper limit of the Ta content is set to 0.10% or less.

Zr: 0.005 to 0.10%
Zr combines with C and N to form carbonitrides, prevents coarsening of crystal grains during solution heat treatment, and contributes to improvement of toughness. In order to obtain the effect, the lower limit of the Zr content is set to 0.005% or more. The lower limit of the Zr content is preferably 0.05% or more.

  However, excessive addition of Zr impairs hot workability, increases the amount of δ-ferrite, and decreases the strength after aging treatment. Therefore, the upper limit of the Zr content is 0.10% or less.

  In addition to the elements described above, the present stainless steel may further contain one or more elements selected from B, Mg, and Ca as necessary. The component ranges of B, Mg and Ca and the reasons for their limitation are as follows.

B: 0.0005 to 0.0100%
B is effective for improving hot workability. In order to obtain the effect, the lower limit of the B content is set to 0.0005% or more. The lower limit of the B content is preferably 0.0008% or more.

  However, excessive addition of B lowers the cleanliness and adversely affects hot workability. Therefore, the upper limit of the B content is set to 0.0100% or less. The upper limit of the B content is preferably 0.0030% or less.

Mg: 0.0005 to 0.0100%
Mg is effective in improving hot workability. In order to obtain the effect, the lower limit of the Mg content is set to 0.0005% or more. The lower limit of the Mg content is preferably 0.0008% or more.

  However, excessive addition of Mg reduces cleanliness and conversely affects hot workability. Therefore, the upper limit of the Mg content is 0.0100% or less. The upper limit of the Mg content is preferably 0.0030% or less.

Ca: 0.0005 to 0.0100%
Ca is effective in improving hot workability. In order to obtain the effect, the lower limit of the Ca content is set to 0.0005% or more. The lower limit of the Ca content is preferably 0.0010% or more.

  However, excessive addition of Ca reduces cleanliness and conversely affects hot workability. Therefore, the upper limit of the Ca content is 0.0100% or less. The upper limit of the Ca content is preferably 0.0080% or less.

  Specifically, the stainless steel described above can be suitably used as a strain generating body such as a pressure sensor, a weight sensor, a combustion pressure sensor diaphragm, and a load cell.

  Next, an example of the manufacturing method of this stainless steel is demonstrated. In order to obtain the above-described stainless steel, for example, the following may be performed.

  For example, in a melting furnace such as a vacuum induction furnace, a steel ingot having the above-described chemical composition is melted and subjected to hot working such as hot forging and hot rolling to obtain a steel material having a desired shape. Next, if the obtained steel material is subjected to solution heat treatment and aging treatment, this stainless steel can be obtained.

  Examples of the solution heat treatment include a method of heating to an optimal temperature corresponding to the composition of steel, holding the temperature for a certain time, and air cooling.

  The lower limit of the heat treatment temperature during the solution heat treatment is preferably 950 ° C. or higher, more preferably 1020 ° C. or higher. On the other hand, the upper limit of the heat treatment temperature during the solution heat treatment is preferably 1080 ° C. or lower, more preferably 1050 ° C. or lower.

  This is because if the heat treatment temperature during the solution heat treatment is within the above range, good cold workability, corrosion resistance, and strength after aging treatment can be obtained.

  Moreover, as said aging treatment, after heating to the optimal temperature according to the composition of steel, the method of hold | maintaining at the temperature for a fixed time and air-cooling etc. can be illustrated.

  The lower limit of the heat treatment temperature during the aging treatment is preferably 460 ° C. or higher, more preferably 470 ° C. or higher. On the other hand, the upper limit of the heat treatment temperature during the aging treatment is preferably 590 ° C. or lower, more preferably 570 ° C. or lower.

  This is because if the heat treatment temperature during the aging treatment is within the above range, the amount of retained austenite produced is small, and high strength and good strain-generating body performance can be obtained.

Hereinafter, the present invention will be described more specifically with reference to examples.
150 kg of steel ingots having various chemical components shown in Tables 1 and 2 were melted in a vacuum induction furnace and hot forged, and then hot rolled to produce a wire coil having a diameter of 18 mm. And after holding this wire coil in the temperature range of 1040 degreeC +/- 20 degreeC for 1 hour, the solution heat treatment which air-cools was performed. Then, after holding at 480 ° C. for 4 hours, an aging treatment (H900 treatment) for air cooling or an aging treatment (H1025 treatment) for air cooling after holding at 550 ° C. for 4 hours was performed. And the test shown below was implemented.

(Measurement of residual austenite)
A test piece was collected from the material after the aging treatment, and the amount of retained austenite was measured by an X-ray diffraction method.

(Tensile test)
A JIS No. 4 tensile test piece was collected from the material after the aging treatment, and 0.2% proof stress and elongation at break were measured using this specimen.

(Impact test)
A JIS No. 2 mm U notch impact test piece was collected from the material after the aging treatment, and the Charpy impact value was measured.

(Corrosion resistance test)
A test piece was collected from the material after the aging treatment, and subjected to a salt spray test for up to 96 hours at 35 ° C. in a 5% NaCl solution in accordance with JISZ2371, to confirm whether or not rust was generated. The case where there was no rust was indicated as “◯”, and the case where rust was generated was indicated as “X”.

(Distortion characteristics)
Than material after the aging treatment, 5.0 mm is the diameter of the parallel portion was taken a rod-shaped tensile test pieces of length 15 mm, this paste strain gauge, after loaded with 10 ^three times repeated load hysteresis ( The increase in deviation from the initial position when cyclic stress was applied in the elastic region was investigated. The result was compared with the comparative example 1 which is general SUS630 (commercially available material component). The case where the hysteresis was 1/10 or less as compared with Comparative Example 1 was evaluated as “◯”, and the case where the hysteresis was larger than Comparative Example 1 was evaluated as “X”.

  Tables 1 and 2 show chemical components of the strain-generating stainless steels according to Examples and Comparative Examples, and Tables 3 and 4 show test results.

  When the results in Tables 3 and 4 are evaluated relative to each other, the following can be understood.

  That is, the comparative example 1 is general SUS630. Therefore, the α value exceeds 510, and the structure after the solution treatment and the aging treatment contains 10% by volume or more of retained austenite phase. Therefore, it can be said that the reference point gradually fluctuates due to an increase in hysteresis due to the micro-yield of the retained austenite phase, and the strain generating body performance is likely to deteriorate.

  In Comparative Examples 2 to 4, C + N is less than the amount specified in the present application. In Comparative Example 5, C + N exceeds the amount specified in the present application. Therefore, Comparative Examples 2 to 5 have low elongation at break and impact value and are inferior in toughness.

  In Comparative Example 6, Cu + Ni exceeds the amount specified in the present application, and the α value exceeds 510. Therefore, 10% by volume or more of retained austenite phase is included in the structure after solution treatment and aging treatment, and the reference point is likely to change gradually due to an increase in hysteresis due to micro-yield of the retained austenite phase. Inferior performance.

  In Comparative Example 7, Cr exceeds the amount specified in the present application. Therefore, a decrease in strength after aging treatment and a decrease in strain body characteristics are observed.

  In Comparative Example 8, Cr is less than the amount specified in the present application. Therefore, it is inferior to corrosion resistance.

  In Comparative Example 9, C exceeds the amount specified in the present application, and the α value is also high. Therefore, it is easy to produce Cr carbide, and as a result, the amount of solid solution Cr in the parent phase is reduced, so that the corrosion resistance is poor.

  In Comparative Example 10, N exceeds the amount specified in the present application, and the α value is also high. Therefore, the elongation at break and impact value are low, and the toughness is poor. In addition, the retained austenite phase is likely to increase due to the decrease in the Ms point, and a decrease in strength after aging treatment and a decrease in strain-generating body properties are observed.

  In Comparative Example 11, Ni exceeds the amount specified in the present application, and the α value is also high. For this reason, the retained austenite phase is remarkably increased due to the decrease in the Ms point, and a decrease in strength after aging treatment and a decrease in characteristics of the strain body are observed.

  In Comparative Example 12, Ni is below the amount specified in the present application. For this reason, a decrease in strength after aging treatment and a decrease in characteristics of the strain-generating body are observed.

  In Comparative Example 13, Cu exceeds the amount specified in the present application, and the α value is also high. Therefore, a crack arises at the time of hot processing, and it is inferior to hot workability.

  In Comparative Example 14, Cu is less than the amount specified in the present application. Therefore, precipitation hardening is insufficient and the strength is poor. Moreover, the strain generating body characteristic is also low.

  Comparative Example 15 is SUS420J2. SUS420J2 was rusted and had low corrosion resistance.

  As described above, it can be seen that Comparative Examples 1 to 15 that do not satisfy the conditions specified in the present application are inferior in at least one of strength, toughness, corrosion resistance, and strain generating body performance.

  On the other hand, it turns out that Examples 1-25 which satisfy the conditions prescribed | regulated to this application are excellent in all of intensity | strength, toughness, corrosion resistance, and strain body performance. Therefore, if this is applied to a strain generating body, it becomes possible to obtain a sensor or the like with little fluctuation of the reference point. In particular, if the amount of retained austenite is 2.0% by volume or less, it becomes easy to suppress microyield and easily improve the strain generating body performance, so that a sensor having excellent reliability can be provided.

  As mentioned above, although the precipitation hardening type stainless steel for strain generating bodies concerning this invention was demonstrated, this invention is not limited to the said embodiment and Example at all, In the range which does not deviate from the summary of this invention, it is various. Can be modified.

Claims (5)

% By mass
C: 0.010 to 0.060%,
Si: 1.0% or less,
Mn: 1.0% or less,
P: 0.05% or less,
S: 0.03% or less,
Cu: 2.0 to 4.0%,
Ni: 2.5-5.0%,
Cr: 13.0 to 17.0%,
Mo: 1.0% or less,
Al: 0.030% or less,
O: 0.020% or less,
N: 0.010-0.050% and
Nb: 0.10 to 0.40% is contained, the balance consists of Fe and inevitable impurities,
C + N: 0.025 to 0.095%,
Cu + Ni: 8.5% or less,
A precipitation hardening stainless steel for a strain generating body, wherein the α value represented by the following formula is 510 or less.
α = 1320 ([C] + [N]) + 52 [Ni] +14 [Cu] +10 [Cr] +20 [Mo] +26 [Mn] +20 [Si]   A precipitation hardening type stainless steel for strain generating bodies, characterized in that the amount of retained austenite is 2.0 volume% or less. % By mass
Co: 0.05-1.0% and
W: 0.05-1.0%
The precipitation hardening stainless steel for strain generating bodies according to claim 1 or 2, further comprising one or more selected from the group consisting of: % By mass
V: 0.005 to 0.20%,
Ti: 0.005 to 0.10%,
Ta: 0.005 to 0.10%, and
Zr: 0.005 to 0.10%,
The precipitation hardening stainless steel for strain-generating bodies according to any one of claims 1 to 3, further comprising one or more selected from the group consisting of: % By mass
B: 0.0005 to 0.0100%,
Mg: 0.0005 to 0.0100%, and
Ca: 0.0005 to 0.0100%,
The precipitation hardening type stainless steel for strain generating bodies according to any one of claims 1 to 4, further comprising one or more selected from the group consisting of: