JP3422277B2 - Method of manufacturing martensitic stainless steel cold-rolled steel strip for leaf spring and leaf spring - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a martensite system for leaf springs, which is excellent in weldability and secondary workability (workability when forming from a cold rolled steel strip into a predetermined leaf spring product shape). The present invention relates to a stainless cold-rolled steel strip and a method for manufacturing a leaf spring from the steel strip. Note that weldability refers to deformation.
The joint strength of the welded part .

[0002]

2. Description of the Related Art JIS G 4313 defines the following three types of cold-rolled stainless steel strips for thin leaf springs that have been conventionally used. That is, austenitic stainless steel strips SUS301-CSP, SUS304
-CSP, SUS4 of martensitic stainless steel strip
20J2-CSP and S of precipitation hardening stainless steel strip
US631-CSP.

The austenitic stainless steel strip for springs is subjected to finish temper rolling in order to impart desired mechanical properties and spring properties. Strength is adjusted by changing the rolling reduction in this rolling. SU
Four types of material strength levels are specified in S301-CSP and three types of material strength level in SUS304-CSP.

However, in a steel strip in which the spring characteristics are improved by utilizing work hardening in the cold rolling process, the material strength in the width direction is higher than that in the cold rolling direction, and the spring limit value becomes large. There will be directionality. As a result, the spring characteristics change depending on the direction of the load applied to the spring.

Further, austenitic stainless steel has a large coefficient of thermal expansion as compared with ferritic stainless steel and martensitic stainless steel. Therefore, it is not suitable for applications such as springs for electronic parts that require strict dimensional accuracy maintenance in a relatively high temperature environment.

SU, a precipitation hardening stainless steel for springs
S631-CSP has enhanced material strength by martensitic transformation by precipitation hardening heat treatment and precipitation of Ni-Al compound. The structure is a structure containing a small amount of ferrite phase in the base of austenite phase, and the distribution and size of this ferrite phase influence the material properties. Therefore, when producing a spring from precipitation hardening stainless steel, it is necessary to pay attention to the chemical composition, heat treatment conditions, etc., and as a result, an expensive spring is obtained.

[0007] SUS420J2-CSP, which is a martensitic stainless steel for springs, is a steel strip cold-rolled to a predetermined plate thickness, formed into a desired spring shape by a processing maker, and then quenched to obtain a material strength. At the same time, the spring property is enhanced by utilizing the aging effect of the tempering process.

The martensitic stainless steel strip for springs, which is improved in spring characteristics by utilizing quenching treatment and age hardening heat treatment, does not have anisotropy in material strength and spring characteristics.
Excellent material anisotropy. That is, in the quenching process, the work strain generated in the material in the cold rolling process is erased because it is once heated to a temperature exceeding the softening heat treatment temperature. Further, martensitic stainless steel for springs has a property that the coefficient of thermal expansion is also small.

However, SUS420J2-CSP, which is a martensitic stainless steel for springs, has a drawback in that when it is joined to another member by resistance welding, the welded portion is cracked due to external deformation and is easily broken. That is,
The part that was exposed to a high temperature above the transformation point during welding is rapidly cooled, resulting in a particularly hard martensitic structure that significantly embrittles, impairs the ductility of the welded part, and reduces the volume accompanying the martensitic transformation during cooling. Because it changes.
Further, in this SUS420J2-CSP, since the material strength is excessively increased and the ductility is lowered by the quenching treatment,
There was a drawback that the subsequent secondary workability was poor.

Japanese Patent No. 2756549 discloses a method for producing a high-strength multi-layered stainless steel strip having excellent spring characteristics. This manufacturing method, as an essential component,
C: 0.01 to 0.15% by weight, Cr: 10 to 20% by weight, and stainless cold-rolled steel containing 0.10 to 4% by weight of one or more of Ni, Mn or Cu. This is a method in which the strip is heated to a temperature range where the ferrite phase and the austenite phase are made into two phases, and then rapidly cooled to obtain a stainless steel strip having a composite structure of the ferrite phase and the martensite phase, and then aging treatment.

This method is a method utilizing a quenching treatment in which the ferrite phase and the austenite phase are heated to a two-phase temperature range. Also in this method, stainless steel for springs having excellent weldability and secondary workability in resistance welds is also used. Cold rolled steel strip cannot be manufactured.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a cold-rolled stainless steel strip having excellent resistance weldability and secondary workability, and a method for producing a leaf spring from the steel strip. It is in.

[0013]

The gist of the present invention is as follows.

(1) C: 0.1 to 0.15 by weight%
%, Si: 0.5% or less, Mn: 0.25 to 0.8%,
Cr: 11.5-13%, Ni: 0-0.8% and C
u: 0 to 0.8%, the balance consisting of Fe and unavoidable impurities, and satisfying the following formulas (1) and (2) ,
A martensitic stainless cold-rolled steel strip for a leaf spring having excellent weldability and secondary workability, which has a structure containing a martensite phase of 40 to 80% by volume .

Ni + Mn + Cu ≦ 0.8 (1) (Ni + 0.5Mn + 0.3Cu + 35C + 40N) -0.31 (Cr + 1.5Si) = 0.5 to 3 (2) The element symbol in the formula indicates the content (% by weight) of each element.

(2) C: 0.1 to 0.15% by weight
%, Si: 0.5% or less, Mn: 0.25 to 0.8%,
Cr: 11.5-13%, Ni: 0-0.8% and C
u: 0 to 0.8%, balance Fe and unavoidable impurities
A cold-rolled steel strip made of a steel and satisfying the following formulas (1) and (2) within a temperature range of 930 to 1000 ° C.
By heating for 0 minutes or less and quenching, a structure containing 40 to 80% by volume of martensite phase is formed, and then secondary forming is performed into a target spring shape, and age hardening heat treatment is performed in a temperature range of 300 to 500 ° C. A method for producing a martensitic stainless steel plate spring having excellent weldability, which is characterized by being applied. Ni + Mn + Cu ≦ 0.8 ········ (1) (Ni + 0.5Mn + 0.3Cu + 35C + 40N) -0.31 (Cr + 1.5Si) = 0.5~3 ··· (2) In addition, the formula The element symbols in the table indicate the content (% by weight) of each element.
Shall be shown.

In order to improve the weldability and secondary workability of martensitic stainless steel for springs, the present inventors have
As a result of various experiments and studies on various conditions of the chemical composition and the manufacturing method, the present invention has been completed by obtaining the following knowledge.

A) The deterioration of the weldability and secondary workability of the martensitic stainless cold-rolled steel strip for springs is mainly caused by C
Due to the improper balance between the content and the content of other elements,
This is because the amount of martensite increases at the time of welding or quenching, or the martensite phase itself is strengthened so that the material hardness becomes particularly high and the ductility is impaired.

B) In order to improve the secondary workability and weldability, the balance of the contents of Ni, Mn, Cu, C, N, Cr and Si is important, and ( Ni + 0.5Mn + 0.3Cu + 35C + 40N) -0.31
When (Cr + 1.5Si) exceeds 3, weldability and secondary workability are impaired. On the other hand, if it is less than 0.5, the hardenability becomes insufficient, and the desired strength cannot be obtained.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The reason for limiting the chemical composition of the martensitic stainless cold-rolled steel strip of the present invention will be described below. In the description of the chemical composition,% is% by weight.

C: 0.1 to 0.15% C is a strong austenite stabilizing element, and an element that affects the austenite single-phase temperature range by its balance with the Cr content. This austenite single-phase temperature range is a heating temperature range in the quenching treatment which is indispensable in the manufacturing process of martensitic stainless steel. Further, C is an important element that affects the strength of the martensite phase after quenching and the spring characteristics.

As will be described later, when the lower limit of the Cr content is set to 11.5% in order to ensure the corrosion resistance of stainless steel, if the C content is too low, the temperature will rise to a high temperature in the solidification process or hot rolling process of the steel. When heated, the δ ferrite phase coexists in the austenite phase. This δ ferrite phase may not disappear even in the subsequent softening and annealing step, in which case it remains in the final product in a state of being elongated by rolling. Since the δ-ferrite phase has no quench-hardenability, when the secondary processing for forming into a predetermined spring shape is performed, cracks may occur in the bent portion and spring fatigue characteristics may be deteriorated.
Therefore, it is desirable to control the production amount of the δ ferrite phase after hot rolling within 5%, preferably within 2% of the whole, and for that purpose, the lower limit of the C content must be 0.1%. .

On the other hand, if the C content is too high, when it is joined to other members by resistance welding at the time of use, the rapidly cooled region becomes a particularly hard martensitic structure after being exposed to a high temperature near the melting temperature. Ductility of the weld and the heat-affected zone around it is reduced. Furthermore, there is a risk of cracking in the weld due to the volume change accompanying the transformation from the austenitic structure to the martensitic structure during cooling. In order to prevent these, the upper limit of the C content must be 0.15%. Therefore, the C content is 0.1 to 0.15%
And

In order to investigate the influence of the C content, the present inventors changed the C content to 0.05 to 0.3%, and added Cr,
A martensitic stainless cold-rolled steel strip was prepared in which the contents of Si and Mn were adjusted within the ranges specified in the present invention, and each steel strip had a thickness of 0.8 mm, a width of 20 mm, and a length of 10.
A 0 mm bending test piece was sampled, two test pieces having the same chemical composition were joined by resistance welding, and then a 180-degree bending test of a welded portion was performed to measure the number of times of bending until breakage.

FIG. 1 is a diagram showing a bending test result of a resistance welding portion. From FIG. 1, it is effective to secure the weldability of the resistance weld zone because the carbon content of 0.15% or less significantly increases the number of bends until the fracture of the welded portion. I understand.

Si: 0.5% or less Si has a function of lowering the austenite single phase temperature range in martensitic stainless steel. Therefore, the amount of δ ferrite phase generated increases during heating in the solidification process and the hot rolling process, and as a result, cracking occurs in the bent portion due to secondary working and spring fatigue properties deteriorate. In order to avoid these adverse effects, it is desirable that the Si content be as low as possible, and the upper limit was made 0.5%.

Mn is an element added as a deoxidizing element during the melting of stainless steel, and is usually contained industrially at least 0.2%. Further, Mn has a function of fixing S, which is a chemical component that adversely affects hot workability, as a sulfide, so it is desirable to contain Mn to some extent. In order to obtain these effects, it is necessary to contain 0.25% or more, so the lower limit of the Mn content was set to 0.25%. on the other hand,
Mn is an austenite stabilizing element, and if contained in a too large amount, the amount of martensite formed after quenching increases and the ductility decreases, so the upper limit of the Mn content is set to 0.8%.
did.

Cr: 11.5 to 13% Cr is an important element for ensuring the corrosion resistance of stainless steel. For example, JIS G0203 is a steel containing 11% or more chromium as the definition of stainless steel. Is stipulated. Cr for the purpose of obtaining sufficient corrosion resistance
The lower limit of the content was 11.5%.

Generally, the higher the Cr content is, the more stable the corrosion resistance becomes, but if the Cr content is increased too much, the austenite single phase temperature range which is the quenching temperature becomes narrow. As described above, when the upper limit of the C content is limited to 0.15% for the purpose of ensuring the weldability of the resistance welded portion, when the Cr content exceeds 13%, the austenite single-phase temperature range rapidly increases. It becomes narrower and proper quenching process cannot be performed. Therefore, the upper limit of the Cr content is 13%.

Ni: 0 to 0.8% Ni is an austenite stabilizing element and is an element to be contained if necessary for the purpose of enhancing strength. But,
If it is contained in a large amount exceeding 0.8%, the hardness becomes excessively high and the ductility decreases, so the upper limit of the content is set to 0.
8%. Cu: 0 to 0.8% Cu is also an austenite stabilizing element and is an element to be contained if necessary for the purpose of increasing strength. But,
If it is contained in a large amount exceeding 0.8%, the hardness becomes excessively high and the ductility decreases, so the upper limit of the content is set to 0.
8%. Ni + Mn + Cu: ≦ 0.8% Mn, Ni, and Cu are both austenite stabilizing elements and have a function of stabilizing the austenite single-phase temperature range. However, if these elements are contained in too much amount, annealing treatment is performed. Since the progress is slowed down, the time required for the softening annealing before cold rolling becomes longer and the production efficiency is lowered.

Further, when the austenite phase is stabilized, there is a risk that the weldability and the secondary workability in the resistance welded portion deteriorate. In order to prevent these, Mn + Ni + C
The upper limit of the total amount of u was 0.8%.

(Ni + 0.5Mn + 0.3Cu + 35C + 40N) -0.31 (Cr + 1.5S
i): 0.5 to 3 This formula is an empirical formula obtained by repeated tests, and can evaluate the austenite stabilization region necessary for determining the quenching temperature. As this value increases, the austenite stabilization region expands, but if it exceeds 3, the strength after quenching becomes excessively high and ductility is impaired. On the contrary, when this value becomes small, the austenite stabilization region becomes narrow, and
If it is less than 5, the effect of quenching is lost.

[0033] Note that N in the formula is an impurity,
Considering that it is an element that affects the stabilization of tenite.

Next, the manufacturing method will be described. The cold-rolled steel strip used in the production method of the present invention may be produced by an ordinary method. That is, a steel ingot or a slab obtained by the ingot making method or the continuous casting method is made into a hot rolled stainless steel strip by forging or hot rolling, then subjected to softening annealing, pickling, and then cold rolling and intermediate annealing. (600-850
C)) and is repeated.

1) Heating conditions: 10 at 930 to 1000 ° C.
The heating of the stainless cold-rolled steel strip to 930 to 1000 ° C. for minutes or less is for quenching. For this heating, it is preferable to use continuous annealing pickling equipment or continuous bright annealing equipment.

The heating temperature is set to 930 to 1000 ° C., which is the lower limit of the austenite single phase temperature range. If it is less than 930 ° C, quenching cannot be performed, while if it exceeds 1000 ° C, the effect of quenching is saturated. Therefore, the heating temperature was set to 930 to 1000 ° C.

The heating time is set to 10 minutes or less because if the heat treatment time is lengthened to exceed 10 minutes, the material strength excessively increases and the subsequent secondary workability is impaired.

2) Quenching By heating at the above temperature and then quenching and quenching, hardness is increased and material strength is improved. This rapid cooling is cooling at a cooling rate higher than forced air cooling. 3) Martensite structure of 40 to 80% by volume When a martensite structure is formed by rapid cooling, the martensite phase occupies 40 to 80% by volume. 40%
Below, the target strength and spring characteristics cannot be obtained,
On the other hand, if it exceeds 80%, impair ductility too hard turned into by,
Since the secondary workability is deteriorated, the martensite structure is 40 to 80%. This amount of martensite can be adjusted by the chemical composition and the quenching conditions.

4) A secondary formed leaf spring is obtained by cutting a cold-rolled steel strip into a size required for obtaining a final spring product by machining, and then finishing the final spring product shape by bending or the like. can get.
The process for finishing this product shape is the secondary forming process.

5) Age hardening heat treatment temperature: 300 to 500
By performing age hardening heat treatment at a temperature in the range of 300 to 500 ° C. after the secondary molding process at 0 ° C., the spring characteristics represented by the spring limit value are significantly improved.

In order to investigate the influence of the aging heat treatment temperature on the hardness and the spring limit value, from the martensitic stainless cold-rolled steel strip having the chemical composition specified in the present invention,
A test piece for aging treatment is prepared, and the aging treatment temperature is 100-
Aging treatment was carried out by changing variously within a temperature range of 750 ° C., and Vickers hardness and spring limit value were measured.

FIG. 2 shows the results of these measurements. It can be seen from FIG. 2 that a heat treatment temperature of 300 to 500 ° C. is appropriate in order to obtain the spring characteristic improving effect while ensuring the hardness after the aging heat treatment. This effect appears even in a short aging heat treatment of 3 minutes, and the effect is saturated even if the heat treatment time is extended more than that, but if it is desired to make the spring characteristics uniform among a large number of members, it is 20 minutes to 1 minute. It is desirable to take a heat treatment time of time.

If the steel strip after the age hardening heat treatment is subjected to forming, the spring characteristics at the worked portion may be significantly deteriorated. It is necessary to carry out after the molding process to

By the above method, a martensitic stainless steel leaf spring having excellent weldability can be obtained.

[0045]

Example A slab having a chemical composition indicated by symbol e in Table 1 was continuously cast in an actual machine, the slab was heated to 1200 ° C. and hot-rolled to obtain a hot-rolled steel strip having a plate thickness of 3 mm. This steel strip is subjected to a softening heat treatment of holding it at a heating temperature of 800 ° C. for 6 minutes and gradually cooling it using a continuous annealing pickling facility, pickling it, and then cold rolling it to 0.8 mm thick cold rolling. A steel strip was used. After that, using a continuous annealing pickling equipment, after holding at a heating temperature of 950 ° C. for 6 minutes, a heat treatment for forced air cooling is applied,
Hardened.

[0046]

[Table 1]

SUS30 having the chemical composition shown by symbol f in Table 1
Steel equivalent to 4-CSP is melted in a high frequency melting furnace to a thickness of 50
A 10 kg flat steel ingot of mm was obtained. After this steel ingot was hot-rolled to a thickness of 3 mm, it was subjected to softening heat treatment of keeping at a heating temperature of 1100 ° C. for 10 minutes and air cooling, and pickling. This hot rolled steel sheet was cold rolled to obtain a cold rolled steel strip having a thickness of 1.33 mm. This steel strip is again subjected to softening heat treatment and pickling, and then cold-finished and temper-rolled with a reduction rate of 40% to obtain a cold-rolled steel having a thickness of 0.8 mm corresponding to the SUS304-CSP steel strip. I got a belt.

Steels having chemical compositions other than the symbols e and f in Table 1 were melted in a high frequency melting furnace to obtain a 10 kg flat steel ingot with a thickness of 50 mm. After this steel ingot is hot-rolled to a thickness of 3 mm, it is held at 800 ° C. for 10 minutes for softening heat treatment for slow cooling and pickling, and then cold-rolled to a cold-rolled steel of 0.8 mm thickness. It was a belt. The cold-rolled steel strip thus produced was held at each quenching temperature shown in Table 2 for 10 minutes, and then subjected to a quenching treatment of forced air cooling.

[0049]

[Table 2]

For each of the quenched steel strips, the following spring characteristic test, hardness measurement, secondary workability test, and resistance welding bend test were carried out.

[0051] (a) the spring characteristic test (processing after molding spring limit test, spring fatigue characteristic test) from each cold-rolled steel strip after quenching, cut out a strip-shaped plate spring material and formed shape machining a press.

FIG. 3 is a perspective view showing the shape and dimensions of the molded spring 1. The leaf spring of SUS304-CSP steel of symbol f was subjected to batch aging heat treatment in which the leaf spring was maintained at 650 ° C. and the other leaf springs were kept at a heating temperature of 450 ° C. for 60 minutes.

Regarding the leaf spring which has been subjected to this aging heat treatment,
The same test as the moment type spring limit value test method defined in JIS H3130 was performed, and the spring characteristics were evaluated with a value corresponding to the Kb value.

Regarding the spring fatigue property test, bending was applied at a repetition rate of 50 Hz, and the spring fatigue property was determined by the maximum bending amplitude that did not cause cracks that penetrated the plate before that, based on the number of repetitions of 1 million times. Was evaluated. The results are shown in Table 2.

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

(B) Hardness measurement A test piece for hardness measurement was taken from the cold-rolled steel sheet after quenching to measure Vickers hardness. The results are shown in Table 2.

(C) Secondary workability evaluation test From the cold rolled steel strip after quenching, width 20 mm, length 100
The bending test piece of mm is sampled, and the bending radius of 1 mm is 90.
A bending test was carried out to evaluate the presence or absence of cracks in the bent portion. The results are shown in Table 3.

[0063]

[Table 3]

(D) Bending test of resistance welded portion From cold rolled steel strip after quenching, width 20 mm, length 100
mm bending test pieces were taken, and the test pieces taken from the same steel strip were overlapped and spot-welded to each other, and then a 180-degree repeated bending test of the welded portion was performed, and the number of times of repeated bending until breakage and its The strength of the resistance weld was evaluated by the fracture mode.

FIG. 4 is a view showing a fractured form of the test piece after the bending test . Welded and joined by spot weld 3
The state where the two test pieces 2 and 2 are broken by the bending test is shown. The fracture forms could be classified into the following types A to E.

A: Fracture of the base metal portion unrelated to the welded portion B: Fracture of the base metal portion starting from the heat-affected zone C: Fracture reaching the base material portion starting from the periphery of the heat-affected zone D: Resistance welded portion Fracture E in Nugget E: Table 3 shows the fracture results in the heat-affected peripheral area. As is clear from Table 2, the symbols a to
In the example of the present invention indicated by e, the g
Comparative example (conventional example) of SUS420J2-CSP steel
And the performance was comparable. Designated by the symbol f here
In SUS304-CSP steel, the pressure from the effect of cold rolling
Limit value of spring after forming in the plate width direction compared to the elongation direction
A material anisotropy that increases the value is recognized. Also, the symbol h,
In the comparative examples indicated by i and k, austenite during quenching
Since the stabilization temperature range has moved to the high temperature side, the quenching temperature is increased.
The ratio indicated by the symbols h and i
In the comparative example, as compared with the example of the present invention, quenching hardness and after molding
This resulted in poor spring limit values. Furthermore, with the symbols h and k
In the comparative example shown, the spring fatigue property after forming is inferior,
Observation of the metallographic structure of these steels revealed that expanded δ-ferrite
A phase has been observed, which deteriorates spring fatigue properties.
It was speculated that As is clear from Table 3, symbols a to e
The example of the present invention indicated by is a comparative example (conventional example) with the symbol g.
Compared with SUS420J2-CSP steel,
The strength and secondary workability have been dramatically improved. Symbol f
The SUS304-CSP steel indicated by is inferior in secondary workability.
However, this is due to ductility due to work hardening in cold working.
Because I lost it. In addition, comparative examples indicated by symbols h and k
Is also inferior in secondary workability, but this is due to the residual δ ferrite phase.
It is due to. For these steels, resistance weld strength evaluation tests
In the test as well, fracture occurred along with fracture in the base metal. symbol
Comparative examples indicated by g and j are used for resistance weld strength evaluation test.
Although it breaks at the resistance weld rather than the base metal,
Heat affected zone during resistance welding has a particularly hard martensitic structure
The ductility is deteriorated.

[0067]

EFFECTS OF THE INVENTION The martensitic stainless cold-rolled steel strip for springs of the present invention maintains the features of the conventional martensitic stainless cold-rolled steel strip for springs, and has the drawback of resistance welding. It has improved weldability and sufficient secondary workability.

[Brief description of drawings]

Is a diagram showing FIG. 1 resistance welds bending trial Ken'yui results

FIG. 2 is a diagram showing a relationship between an aging heat treatment temperature, hardness, and a spring limit value.

FIG. 3 is a diagram showing a spring shape used in a spring limit value test and a spring fatigue characteristic test.

FIG. 4 is a diagram showing a fracture mode in a bending test of a resistance welding portion.

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-5-171282 (JP, A) JP-A-7-278758 (JP, A) JP-A-8-319519 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 6/00 C21D 9/02 C21D 9/46

Claims (2)

(57) [Claims] 1. C: 0.1 to 0.15% by weight, S
i: 0.5% or less, Mn: 0.25 to 0.8%, Cr:
11.5-13%, Ni: 0-0.8% and Cu: 0
Comprises 0.8%, the balance being Fe and unavoidable impurities, and satisfies the following formula (1) and (2), 40
Weldability and secondary processing excellent in martensitic stainless cold-rolled steel strip for leaf springs and said Rukoto to have a tissue containing 80 vol% of martensite phase. Ni + Mn + Cu ≦ 0.8 ・ ・ ・ ・ ・ ・ (1) (Ni + 0.5Mn + 0.3Cu + 35C + 40N) -0.31 (Cr + 1.5Si) ＝ 0.5〜3 ・ ・ ・ (2) The element symbols in the table indicate the content (% by weight) of each element. 2. C: 0.1 to 0.15% by weight, S
i: 0.5% or less, Mn: 0.25 to 0.8%, Cr:
11.5-13%, Ni: 0-0.8% and Cu: 0
~ 0.8%, the balance from Fe and unavoidable impurities
And quenching the cold-rolled steel strip satisfying the following formulas (1) and (2) within a temperature range of 930 to 1000 ° C. for 10 minutes or less to rapidly cool the martensite to 40 to 80% by volume. Manufacture of martensitic stainless steel plate spring having excellent weldability, which is characterized by having a structure containing phases, and then subjecting it to secondary forming into a target spring shape and subjecting it to age hardening heat treatment in a temperature range of 300 to 500 ° C. Method. Ni + Mn + Cu ≦ 0.8 ········ (1) (Ni + 0.5Mn + 0.3Cu + 35C + 40N) -0.31 (Cr + 1.5Si) = 0.5~3 ··· (2) In addition, the formula The element symbols in the table indicate the content (% by weight) of each element.
Shall be shown.