JP2677910B2 - Stainless steel for springs with excellent dimensional stability during low temperature annealing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel material for springs, and more particularly to a steel material for springs such as a steel wire for springs, a steel plate for leaf springs, etc. For springs with small changes and excellent dimensional stability during low temperature annealing
Regarding stainless steel materials.

[0002]

2. Description of the Related Art A steel material for springs is a spring material (steel wire, steel plate shape, etc.) such as a coil spring and a leaf spring, and a steel material that has been solution treated or annealed (hereinafter referred to as solution treatment) is used as a raw material. It is formed into a predetermined shape and dimension.
Generally, the forming process is performed by repeating cold working such as wire drawing and annealing. At the end of the repetition, a cold working process is performed to secure the spring property, so that the spring steel material is in a so-called cold working finished state. For example, a steel wire for a coil spring is produced by heating a wire to 1150 ° C., cooling it with water, annealing it, pickling it, and then wire-drawing it into a steel wire for a spring. Incidentally, the solution treatment is a treatment for heating a metal such as steel to solidify an alloy element into a matrix, while
The annealing treatment is a treatment for heating metal to remove work strain and the like, strictly speaking, both are different from each other in metallurgy, but since the former solution treatment can remove work strain and the like, in this document, Both are treated as synonyms, and both are called solution treatment.

The spring steel material is formed into a spring shape, and then subjected to low-temperature annealing treatment for the purpose of removing residual strain and improving the elastic limit, thereby forming a spring. At this time, it is well known that dimensional changes occur due to annealing.

For example, a so-called spring steel wire such as a piano wire, a hard steel wire, and a stainless steel wire is formed into a coil spring, and then the piano wire or the hard steel wire is annealed at 250 to 400 ° C., and the coil spring is annealed by the annealing. The outer diameter of the
It is known that the outer diameter is increased by annealing at a temperature of 300 to 400 ° C (see page 314 of "Spring" edited by Japan Spring Association (published by Maruzen Co., Ltd.)).

For a torsion spring, a tension spring, or the like having straight portions or hooks at both ends of the coil, the crossing angle changes due to annealing after the spring is formed, and in the case of a piano wire or hard steel wire, the crossing angle at both ends. Increase and open, and those made of stainless steel wire close. Also in the forming material, the dimensions of the forming material change considerably due to annealing after forming, depending on its shape. Cold rolled steel plate for springs, SUS301CSP, SUS30
In the case of stainless steel sheets for springs such as 4CSP, and sheet steel sheets for leaf springs such as thin sheets formed by rolling piano wire and stainless steel wire, their dimensions change considerably due to annealing after bending.

[0006]

As described above, the spring steel material undergoes dimensional changes due to annealing after spring forming. Therefore, the operator takes into consideration such changes before forming. For example, in the case of coil springs, piano wires and hard steel wires are formed into springs with an outer diameter larger than the finished dimensions as specified, and stainless steel wires are formed into smaller springs, and dimensional changes occur due to low temperature annealing. We have devised a spring that has the specified dimensions.

However, since the above-mentioned amount of dimensional change has a delicate difference, it is generally difficult to rely on many years of experience, which is a serious problem. Is preformed by low temperature annealing in advance, various preliminary tests to grasp the amount of dimensional change are conducted, and the actual production is based on the results,
Therefore, there is a problem that the preliminary test requires time and the spring manufacturing efficiency is reduced accordingly, and improvement thereof is desired. Further, even if the main production is carried out based on the preliminary test as described above, the spring dimension after annealing is not constant and often varies, which makes it difficult to improve the spring dimension. Is also desired.

[0008] From the above, the above problems can be solved if a steel material for springs which is unlikely to undergo dimensional change during low temperature annealing treatment after spring forming can be solved. Therefore, the realization of such a steel material for springs is eagerly desired in the art. There is no point in saying.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a stainless steel material for springs which is unlikely to cause a dimensional change during the low temperature annealing treatment after the spring forming, thereby improving spring productivity. In addition to trying to improve the precision of the spring dimensions, it is intended to be used.

[0010]

In order to achieve the above object, the spring stainless steel material according to the present invention has the following constitution. That spring stainless <br/> steel according to claim 1, wherein the Ri consists multiphase mixed structure comprising a face-centered cubic lattice phase and body-centered cubic lattice phase, raw materials of the steel in a state of solution treated < The amount of body-centered cubic lattice phase contained in the material is
Body-centered cubic lattice phase for the sum of the volume of and the face-centered cubic lattice phase
The volume ratio, which is the percentage of the volume ratio of
Dimensional stability at low-temperature annealing, which is a composed value
Excellent stainless steel material for springs.

The stainless steel material for springs according to claim 2 is
The spring stainless steel material is a coil spring and a spring stainless steel wire for a torsion spring . Further, the stainless steel spring according to claim 3, wherein the stainless steel for the spring is stainless steel sheet for leaf springs.

[0012]

[Operation] As mentioned above, in the conventional coil spring,
Due to the low-temperature annealing after forming the coil spring, the outer diameter of the piano wire or hard steel wire shrinks, while the stainless steel wire expands. In terms of metallographic structure and crystal structure, the former mostly consist of body-centered cubic lattice phase (hereinafter referred to as BCC phase) called ferrite or martensite.
Most of the latter stainless steels consist of face-centered cubic lattice phase (hereinafter FCC phase) called austenite. Therefore,
The dimensional changes due to low temperature annealing are inversely related to those of the FCC phase and those of the BCC phase.
Therefore, it is considered that in the case of a multi-phase mixed structure containing the FCC phase and the BCC phase, the two phases act to cancel each other out, making it difficult for dimensional changes to occur during low temperature annealing.

Based on this concept, the present invention molds various springs having a multi-phase mixed structure containing an FCC phase and a BCC phase, anneals them at a low temperature, and carefully examines the amount of spring dimensional change before and after annealing. This is based on the following findings obtained.

That is, a solution-treated (solution-treated or annealed) steel material (raw material) is repeatedly cold-worked and annealed to form a cold-worked spring steel material, Various springs were formed from steel for springs, annealed at low temperature, and the amount of spring dimensional change before and after annealing was measured.On the other hand, for the above raw materials, steel for springs, and springs after forming, BCC phase volume ratio (FCC phase and BCC phase) The percentage of the volume of the BCC phase with respect to the total volume of the phases) was calculated, and the relationship between these volume ratios and the spring dimensional change was investigated.

As a result, when the volume ratio of the BCC phase in the solution-treated steel material (raw material) is set to 30 to 70%, the amount of spring dimensional change before and after annealing can be surely made extremely small. Or, even in the spring after forming, when the work-induced martensite (hereinafter referred to as M ₀ phase), which is a kind of BCC phase, is not contained, when the volume ratio of the BCC phase is 30 to 70%, the same as above. It was found that the amount of spring dimensional change is small. Therefore, the necessary and sufficient condition for reducing the amount of spring dimensional change before and after annealing as described above is to set the volume ratio of the BCC phase in the case of not containing the M ₀ phase to 30 to 70%. It is necessary to set the volume ratio of BCC phase in solution-treated steel (raw material) to 30 to 70%, not the volume ratio of spring steel or spring that often contains ₀ phase.

Therefore, the stainless steel material for spring according to the present invention has a face centered cubic lattice phase (FCC phase) and a body centered cubic lattice phase (B
Together consist of multiphase mixed structure containing CC-phase) and, solution treatment
Body-centered cubic lattice phase contained in the raw material steel material in the treated state
The amount of the ferrite phase as
For volume sum with austenite phase as square lattice phase
Volume ratio, which is the percentage of the volume ratio of the ferrite phase
It is a stainless steel material having a value of 30 to 70% . Therefore, according to the spring stainless steel material of the present invention, the above necessary and sufficient conditions are satisfied, and the amount of change in the spring dimension due to the low temperature annealing after the spring forming can be surely made extremely small. Therefore, the productivity of the spring can be improved without the need for a preliminary test, and the spring dimension can be made highly accurate with little variation in the spring dimension after annealing.

For example, FIGS. 1 to 4 are diagrams demonstrating this, and FIG. 1 shows a BCC at the raw material stage of steel for springs.
The volume ratio of the phases, and shows the relationship between the volume fraction of M ₀ phase in the steel spring of cold working up state, the outer diameter change ratio before and after low-temperature annealing after the coil spring forming and (Db) . still,
Db was calculated by the following formula.

Db (%) = 100 × (D ₁ −D ₂ ) / D ₁ --- In the formula, D ₁ is the outer diameter (mm) after coil spring molding,
D ₂ is the outer diameter (mm) after low temperature annealing.

As can be seen from FIG. 1, when the BCC phase volume ratio in the raw material stage is in the range of 30 to 70%, the spring steel material is
Db is as small as 0.25% or less regardless of the volume fraction of the M ₀ phase (generated by processing from the raw material), and even if a large volume fraction of the M ₀ phase is contained, as a result, in the spring steel material. BCC
Db is small even if the volume ratio of the phase reaches 100%. On the other hand, when the volume ratio of BCC phase at the raw material stage is small,
By generating a M ₀ phase 30 the volume ratio of BCC phases with steel spring
It can be 70%, but even then, Db cannot be reduced,
On the contrary, it grows.

FIG. 2 shows the results in the case of a tension spring, and in the BCC phase volume ratio of 30 to 70% at the raw material stage,
The crossing angle of both end hooks is small regardless of the M ₀ phase volume ratio in the spring steel. Further, the same tendency was obtained for the torsion spring.

FIG. 3 shows the results for the formed product, and the dimensional change of L shown in the figure is small at the BCC phase volume ratio of 30 to 70% at the raw material stage. Further, as shown in FIG. 4, even in the case of a leaf spring, the change amount of the V angle is small at the BCC phase volume ratio of 30 to 70% at the raw material stage.

As described above, the solution treatment and the annealing treatment are treated as synonyms in the present invention.
Therefore, the solution treatment is a solution treatment or an annealing treatment.

[0023]

[Examples] Spring steels (wires and plates) made of Cr-Ni-Si-based steels with various components were manufactured, and various springs were manufactured from these, and BCC phase volume ratio and dimensional change due to low temperature annealing, etc. Was measured. The details will be described below.

Example 1 A wire having a diameter of Φ5.5 mm was solution treated at 1100 ° C., pickled and coated, drawn to a diameter of Φ3.0 mm, and further solution treated at 1100 ° C. This was used as a raw material (raw wire), and after pickling and coating, wire drawing was performed at a speed of 120 m / min to make a spring wire material. At this time, the wire drawing amount, the BCC phase volume ratio and chemical composition of the original wire, and the M ₀ phase volume ratio of the spring wire rod were variously changed as shown in Table 1.

Next, using the above wire for spring, the number of windings is 15
It was wound and formed into a coil spring with spring index D / d: 10. Here, D is the outer diameter of the coil spring, and d is the wire diameter. After that, low-temperature annealing was performed at 300 ° C. for 10 minutes, and the change rate Db of the outer diameter of the spring before and after annealing was determined. Table 3 shows the results. A negative Db value means that the outer diameter has contracted.

The above wire for spring is used and the number of turns is 45.
Winding, forming into a tension spring with D / d: 10, annealing similar to the above, obtaining the amount of change in hook crossing angle before and after annealing, and forming a torsion spring with 6 turns and D / d: 10 Then, similarly, the diagonal change amount before and after annealing was obtained. Further, a forming material similar to that shown in FIG. 3 was molded, and the dimensional change of L before and after annealing was similarly obtained. Table 3 shows the results. A negative value means that the angle or L has decreased.

(Embodiment 2) A wire having a diameter of 5.5 mm similar to that of Embodiment 1 is rolled into a ribbon-shaped plate having a thickness of 3.0 mm, and then 11
Solution treatment was performed at 00 ° C. This was used as a raw material (raw plate), and after pickling, it was cold-rolled at the same processing rate as in Table 1 to make a spring plate material. Table 2 shows the processing rate, the BCC phase volume ratio in the original plate, and the M ₀ phase volume ratio in the spring plate material. Since the processing method is different from that in Table 1, the volume ratio of M ₀ phase is slightly different.

Next, using the above spring plate material, a plate spring similar to that shown in FIG. 4 (tip bending radius: 8 times the plate thickness)
Was molded and annealed in the same manner as in Example 1 to obtain the amount of diagonal change before and after annealing. Table 4 shows the results. A negative value means that the diagonal has decreased.

As can be seen from Tables 3 and 4, in any spring, the BCC phase volume ratio of the raw material (raw wire or raw plate): 30 to 7
At 0%, the amount of dimensional change (Db, amount of diagonal change, etc.) is extremely small compared to other cases, regardless of the volume ratio of the M ₀ phase in the spring steel material (spring wire rod or plate). .

Although the solution heat treatment is carried out at 1100 ° C. in the above-mentioned embodiment, the temperature is not limited to this temperature and may be a temperature at which the alloying element is solid-solved, for example, 1000 ° C. Further, when the alloying element has already been solid-soluted before such treatment and there is strain such as work strain, it is sufficient to heat to a temperature at which the strain can be removed and to anneal.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

[0034]

[Table 4]

[0035]

According to the stainless steel material for springs of the present invention, it is possible to surely reduce the amount of spring dimensional change due to low temperature annealing after spring forming, and therefore the spring can be eliminated without the need for preliminary tests. Can improve productivity in the manufacturing process ,
Also, put the product with a small variation of the spring dimensions after annealing
So it may play a precision of spring sizes that.

[Brief description of the drawings]

[Fig. 1] Volume fraction of body-centered cubic lattice phase (BCC phase) in the raw material (raw wire) of spring steel wire, and work-induced martensite (M in cold-worked steel wire for spring (M) FIG. 3 is a diagram showing a relationship between a volume ratio of ( ₀ phase) and an outer diameter change rate (Db) of a coil spring due to low temperature annealing.

FIG. 2 is a diagram showing the relationship between the volume ratio of the BCC phase in the original wire, the volume ratio of the M ₀ phase in the spring steel wire, and the amount of change in hook crossing angle of the tension spring due to low temperature annealing. .

[FIG. 3] Volume ratio of BCC phase in the original wire, volume ratio of M ₀ phase in the steel wire for spring, and L of the formed product by low temperature annealing
It is a diagram which shows the relationship with the amount of dimensional change.

FIG. 4 shows the volume ratio of the BCC phase in the raw material (raw plate), the volume ratio of the M ₀ phase in the spring plate material (after cold working), and the change amount of the V angle of the leaf spring due to low temperature annealing. It is a diagram showing a relationship.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area F16F 1/02 F16F 1/02 A

Claims (3)

(57) [Claims] 1. A Ri consists multiphase mixed structure comprising a face-centered cubic lattice phase and body-centered cubic lattice phase, raw materials in a state of solution treated
Of the body-centered cubic lattice phase contained in the steel material
Body-centered cubic for the sum of the volume of the lattice phase and the face-centered cubic lattice phase
30 to 7 in terms of volume ratio, which is the percentage of the volume ratio of the lattice phase
Dimension during low temperature annealing characterized by a value of 0%
Stainless steel material for springs with excellent stability . Wherein said stainless spring steel coil springs, stainless steel wire for spring which claim 1 spring scan with excellent dimensional stability at low-temperature annealing of the description of the torsion spring
Tenless steel material. 3. The stainless steel material for springs is a spring for leaf springs .
The dimensional stability during low temperature annealing according to claim 1, which is a stainless steel plate.
Stainless steel material for springs with excellent qualities.