JP2001172746A - Strain-induced martensitic steel with high hardness and high fatigue strength, and steel strip using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a strain-induced martensitic steel having high hardness and high fatigue strength and a steel strip composed of the strain-induced martensitic steel. SOLUTION: The strain-induced martensitic steel with high hardness and high fatigue strength has a composition which consists of, by mass, 0.01-0.10% C, <=3.0% Si, >5.0-10.0% Mn, 1.0-12.0% Ni, 4-18% Cr, either or both of Mo and W in amounts within the range satisfying Mo+1/2W=0.1 to 4.0%, <=5.0% (including 0%) Cu, <=0.15% (including 0%) N, <=0.10% Al, <=0.005% O and the balance essentially Fe and in which the value of A represented by equation A=Ni+0.65Cr+0.98Mo+0.49W+1.05Mn+0.35Si+Cu+12.6(C+N) (where unadded elements among selective elements are figured as zero) is regulated to 13-27%. Further, this steel has a structure containing >=30 vol.% martensitic phase in austenite after cold working.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high hardness suitable for use in members requiring high hardness and high fatigue strength, such as power transmission belts used in continuously variable transmissions for automobiles and the like. The present invention relates to a work-induced martensitic steel having high fatigue strength and a steel strip made of the work-induced martensite steel having high fatigue strength.

[0002]

2. Description of the Related Art Conventionally, members of high strength, such as parts for rockets, parts for centrifuges, parts for aircrafts, parts for continuously variable transmissions of automobile engines, molds and the like are mainly used at around 2000 Mpa. Maraging steel with very high tensile strength is used, and its typical composition is
18% Ni-8% Co-5% Mo-0.4% Ti-0.1% Al-bal.Fe.
This maraging steel contains a large amount of expensive elements such as Co and Mo as strengthening elements, and the material price is extremely expensive, so that it is used for the above-mentioned special limited uses.

[0003]

Generally, not only high hardness and tensile strength but also high fatigue strength and toughness are required for high-strength steels used for applications requiring high strength. . When the tensile strength is about 1200 MPa or less, the fatigue strength tends to increase in proportion to the hardness and the tensile strength, but for high strength steel with a hardness of about 400 Hv or more and a tensile strength of about 1200 MPa or more, Even if hardness and tensile strength increase, fatigue strength does not increase. This is not the case with the above-mentioned maraging steel, and the fatigue strength is not high for a high tensile strength.
Therefore, there has been a demand for an inexpensive and new high-strength steel having high fatigue strength and replacing conventional maraging steel.

[0004] Therefore, the present inventors have intensively studied various high-strength steels as novel high-strength steels replacing the above-mentioned maraging steels. First, as a relatively inexpensive high-hardness material, there is a hardened martensitic stainless steel of 13% Cr-based mainly containing about 0.5% of C. This type of stainless steel is manufactured by applying cold working to a predetermined size in a state of being softened by annealing, and then performing a heat treatment of quenching and tempering. Since a hard martensite phase containing C is obtained by this heat treatment, very high hardness can be obtained. However, since heat treatment called quenching and tempering is required to obtain high hardness, there are many material processes to obtain a desired article, the manufacturing process is complicated, and heat treatment deformation due to quenching from a high temperature is large. There was a problem. In addition, the weldability was not always easy because of the relatively high content of C.

[0005] Next, JIS SUS631 is well known as a type of stainless steel transformed into martensite by cold working. When SUS631 is subjected to solution treatment, cold-worked, and then subjected to aging treatment, a hardness of about 490 HV can be obtained. However, SUS631 has a problem that characteristics such as hardness are very sensitive to the composition and heat treatment conditions, and the characteristics tend to vary. High hardness can also be obtained by cold working austenitic stainless steel such as JIS SUS304 or SUS201. However, in these austenitic stainless steels, since the austenite phase is stable, a part of the austenite phase undergoes work-induced martensitic transformation even when subjected to heavy working, and most are work-hardened austenite phases. There was a problem that a sufficiently high hardness could not be obtained. An object of the present invention is to provide a work-induced martensitic steel having high hardness and high fatigue strength and a steel strip made of the work-induced martensite steel.

[0006]

Generally, in high-strength steel,
For example, as disclosed in the Transactions of the Japan Society of Mechanical Engineers, A64, pp. 2536-2541, when fatigue fracture occurs in the low cycle region, it is known that fatigue fracture is caused by crack initiation and propagation starting from the surface. . In addition, in the ultra-high cycle region exceeding 10 7 times, which was conventionally considered as the fatigue limit,
It is known that fatigue fracture does not originate from the surface but originates from internal inclusions. In conventional maraging steel, inclusions existing at the fatigue fracture starting point of the internal origin are
It is known to be TiN (or Ti (C, N)). Therefore, eliminating inclusions of TiN (or Ti (C, N)) is effective for improving fatigue strength, and it is considered that high-strength steel containing no Ti has high fatigue strength.

Therefore, the present inventors have proposed a precipitation strengthening element.
We focused on work-induced martensitic stainless steel that can achieve high hardness without using Ti. However,
This work-induced martensitic stainless steel is
The characteristics are easy to vary like JIS SUS631, especially this SUS
While 631 has the disadvantage of poor weldability due to the inclusion of 1 mass% Al, the work-induced martensitic stainless steel has high hardness without adding expensive Co like maraging steel. Therefore, there is an advantage that the price can be greatly improved. Furthermore, since the means for obtaining high hardness and the finished shape is cold plastic working, it does not require quenching from a high temperature in a finished shape such as quenched martensitic steel, and has the advantage of no heat treatment deformation. is there.

The inventors of the present invention have conducted intensive studies on various alloying elements and their optimal addition amounts so as to eliminate the disadvantages while maximizing the above advantages.
A steel having a composition range including less than the region of the work-induced martensitic stainless steel and the region of 10% or more of the work-induced martensitic stainless steel (hereinafter, the region of the work-induced martensitic stainless steel and (This is referred to as work-induced martensitic steel as a general term for the type of martensitic steel), with the proper addition of specific alloying elements, and in particular, the aging of Mo, Cu, etc. to this work-induced martensite steel. By adding a hardening element, it has been found that when aging treatment is performed after cold plastic working, higher strength can be obtained. The inventors of the present invention aim to provide a work-induced martensitic steel with a strength, high hardness, and high fatigue strength that can be applied to a power transmission belt used in, for example, a continuously variable transmission for automobiles. After intensive studies, the present invention has been reached.

That is, in the first invention of the present invention,
C: 0.01 to 0.10%, Si: 3.0% or less, Mn: more than 5.0%, 10.0%
In the following, Ni: 1.0 to 12.0%, Cr: 4 to 18%, one or two types of Mo or W are 0.1 to 4.0% at Mo + 1 / 2W, and Cu: 5.0% or less (0
%), N: 0.15% or less (including 0%), Al: 0.10% or less, O: 0.005% or less, balance substantially consisting of Fe, and
An A value represented by the formula (1) is 13 to 27%, and a high hardness and high fatigue strength containing 30% or more by volume of a martensite phase in austenite after cold working. It is steel. A = Ni + 0.65Cr + 0.98Mo + 0.49W + 1.05Mn + 0.35Si + Cu + 12.6 (C + N) ... (1)

In the second invention, C: 0.01 to 0.10% by mass.
%, Si: 3.0% or less, Mn: more than 5.0% and 7.0% or less, Ni: 3.0 ~
11.0%, Cr: 4-16%, one or two of Mo or W are Mo
0.5 to 3.0% at + 1 / 2W, Cu: 4.0% or less (including 0%), N: 0.
15% or less (including 0%), Al: 0.05% or less, O: 0.003 or less,
The balance is substantially composed of Fe, and the A value represented by the equation (1) is
This is a work-induced martensitic steel having a high hardness and high fatigue strength of 19 to 25%, which contains 30% or more by volume of a martensite phase in austenite after cold working.

[0011] In the third invention, C: 0.01 to 0.10% by mass.
%, Si: less than 1.0, Mn: more than 5.0% and 7.0% or less, Ni: 3.0-1
1.0%, Cr: 4-16%, one or two types of Mo or W are Mo
0.5 to 3.0% at + 1 / 2W, Cu: 4.0% or less (including 0%), N: 0.
15% or less (including 0%), Al: 0.05% or less, O: 0.005% or less, balance substantially consisting of Fe, and A represented by the formula (1)
It is a work-induced martensitic steel having a value of 19 to 24% and having a high hardness and high fatigue strength containing 30% or more by volume of a martensite phase in austenite after cold working. A fourth invention of the present invention provides a steel composition according to any one of the first invention to the third invention, wherein one or more of V, Ti, and Nb contain 0.2% or less in total of high hardness and high fatigue. It is a work-induced martensitic steel having strength. A fifth invention of the present invention provides the steel composition according to any one of the first invention to the fourth invention,
It is a work-induced martensitic steel having high hardness and high fatigue strength containing at least 0.10% of one or more of B, Mg, and Ca.

According to a sixth aspect of the present invention, there is provided a steel strip made of a work-induced martensitic steel having high hardness and high fatigue strength according to any one of the first to fifth aspects of the present invention. This is a work-induced martensitic steel strip having high hardness and high fatigue strength with a Vickers hardness of 455 or more. A seventh invention of the present invention is directed to a work-induced martensitic steel strip having a high hardness and high fatigue strength according to the sixth invention, wherein a nitride layer is formed on a surface of the work-induced martensitic steel strip, and a compressive residual stress is applied to the surface. It is a martensitic steel strip. The eighth invention of the present invention is the first invention
A steel strip made of a work-induced martensitic steel having high hardness and high fatigue strength according to any one of the inventions to the fifth invention, wherein a nitrided layer is formed on the surface of the steel strip, and This is a work-induced martensitic steel strip to which a compressive residual stress is applied. Further, the work-induced martensitic steel strip of the present invention using the above-described work-induced martensitic steel has a nitrided layer formed on the surface by an appropriate nitriding treatment to impart compressive residual stress to the surface. Can be.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to the ease of work-induced martensitic transformation and N
It is necessary to optimize the addition amounts of i, Cr, Mo, W, Mn, Si, Cu, C, and N. And Ni, Cr, Mo, W, Mn, Si, Cu,
The elements C and N not only satisfy the individual component ranges,
In order to obtain high hardness, specified in the steel of the present invention (1)
It is necessary to satisfy the formula. The A value shown in the equation (1) is the value of the present invention.
It shows the Ni equivalent, and the magnitude of the A value in this equation is an important index that affects the easiness of forming a work-induced martensite phase. The A value is obtained by adding a value obtained by adding a coefficient according to the effect of each element to the mass% of each element that affects the ease of transformation into work-induced martensite. In the steel of the present invention, if the A value is less than 13, a large amount of martensite structure is generated by cooling after the solution treatment, and the amount of martensite generated by work-induced transformation is reduced, so that it is difficult to obtain a sufficiently high hardness. . On the other hand, if the value exceeds 27, the austenite phase is too stabilized, so that work-induced martensite is hardly generated by cold plastic working, and it becomes impossible to obtain a sufficiently high hardness. ~ 27%
And Preferably, it is 19 to 25%, and more preferably, 19 to 24%.

The action of each element of the steel of the present invention will be described below. C is an austenite-forming element and is effective for obtaining an austenite structure after the solution treatment. In addition, it is effective for strengthening the martensitic structure that has been transformed by cold working and increasing the hardness, but 0.10%
If added in excess of, the austenite phase becomes too stable due to solid solution in the matrix, making it difficult for process-induced transformation to occur.
Since work hardening is increased, cold working becomes difficult. On the other hand, if the content is less than 0.01%, not only is it not possible to obtain sufficient hardness after cold working, but also delta ferrite is generated and reduces hardness and hot workability, so the content of C is reduced.
0.01% to 0.10%.

[0015] Si is added in a small amount for deoxidation.
No further improvement effect is seen even if added over
3.0% or less. Desirably, it is less than 1.0%. Mn is an austenite-forming element and is effective for obtaining an austenite structure after a solid solution treatment.In addition, in controlling the Ni equivalent defined by the A value, a part of Ni can be replaced with Mn to increase Mn. Therefore, there is also an advantage that the cost can be reduced by adding a large amount of Mn, which is a cheaper material than Ni. In addition, it increases the solid solubility of N in the austenite phase and facilitates the addition of N. In other words, it is very effective for stably adding N (that is, not producing casting defects due to N). In N-containing steels, it is necessary to increase Mn, but if added over 10.0%, cold workability deteriorates, but at 5.0% or less, sufficient effect cannot be obtained, so it exceeds 5.0% and 10.0% or less And Desirably, it is more than 5.0% and not more than 7.0%.

Ni is an austenite-forming element like Mn, and is effective for obtaining an austenite structure after a solution treatment. If the content is less than 1.0%, a sufficient effect cannot be obtained.On the other hand, if the content is more than 12.0%, the austenite phase becomes too stable, and the work-induced martensitic transformation hardly occurs. From 1.0 to 12.0%. Desirably, the content is 3.0 to 11.0%. Cr is an important element for obtaining work-induced martensite.If it is less than 4.0%, the austenite phase becomes too stable.On the other hand, if it exceeds 18.0%, it becomes easy to form delta ferrite and deteriorates hot workability. 4.0
118.0%. Desirably, 4.0 to 16.0% is good.

Mo is an element effective for increasing the strength of work-induced martensite, and also has an effect on age hardening after cold working. Mo is desirably added as an essential element. W is also effective in increasing the strength similarly to Mo, but the effect of W alone is small. When W is added, a part of Mo is equivalent to W (1 / 2W is equivalent to equivalent Mo). Add in the form of substituting. If Mo + 1 / 2W is less than 0.1%, the effect of increasing strength cannot be expected, and if Mo + 1 / 2W exceeds 4.0%, delta ferrite is likely to be formed, and hot workability and cold working Therefore, the content is set to 0.1 to 4.0% because the property is deteriorated. Desirably, 0.5 to 3.0% is good.

[0018] Cu has the effect of reducing the workability index of the austenite phase and improving the cold workability. Also,
There is an effect of increasing strength by aging precipitation by aging treatment after cold working. Even if added in excess of 5.0%, no further improvement effect is seen and the hot workability deteriorates, so Cu was set to 5.0% or less. Desirably, it is 4.0% or less. However, when hardening only by cold working, Cu is not added (0%) because higher hardness is obtained if Cu is not present.
May be. N increases the hardness by forming a solid solution in the austenite phase and the martensite phase, increases the work hardening index, increases the hardening by cold working, and also increases the hardening by strain aging during aging treatment. It is an effective element. However, if added in excess of 0.15%, the soundness of the steel ingot is impaired and the manufacturability is deteriorated. In addition, when used in welding, a large amount of N inhibits weldability, so N is preferably lower,
It may not be added (0%).

Al is added in a small amount for deoxidation.
If the content is more than 10%, a large amount of Al ₂ O ₃ inclusions is formed and the fatigue strength is reduced. Therefore, the content of Al is set to 0.10% or less. Desirably 0.05%
The following is good. O is an impurity element that forms oxide-based inclusions and lowers toughness and fatigue strength. Therefore, O is set to 0.005% or less. Desirably, the content is 0.003% or less.

V, Ti, and Nb are not necessarily added, but are effective elements for forming primary carbides to refine crystal grains to improve hardness and ductility. The above is added as needed. When one or two or more of them add over 0.2% in total, they form nitride-based inclusions, lower the fatigue strength or form coarse primary carbides, and improve the cold workability. Because of harm, one or two or more kinds were set to 0.2% or less in total.

B, Mg, and Ca are not necessarily added, but by forming oxides and sulfides, it is possible to reduce S and O segregating at crystal grain boundaries and improve hot workability. Or one or more of them may be added as needed.
Even if one or more of B, Mg, and Ca are added in a total amount of more than 0.10%, no further improvement effect is obtained, and conversely, the cleanliness is reduced to reduce hot workability and cold workability. Since the workability is impaired, one or more of B, Mg, and Ca are added in a total amount of 0.1%.
It is better to be 0% or less. In addition, P and S, which are impurity elements, are not particularly specified because there is no problem as long as they can be mixed at a normal dissolution level.However, from the viewpoint of corrosion resistance and hot workability, a lower one is preferable, and P is 0.04%. Hereinafter, S may be 0.02% or less.

The steel of the present invention cannot achieve the desired high hardness and high fatigue strength only by satisfying the above-mentioned component ranges, and can be subjected to cold working such as cold rolling, cold drawing, and cold forging. In addition, it is necessary to generate a work-induced martensite phase. 30% by volume of martensite phase after cold working
If less, sufficient high hardness and high fatigue strength cannot be obtained, so the volume fraction of the martensite phase after cold working is 30
% Or more.

Next, when the steel strip of the present invention is used to form a steel strip, high hardness and high fatigue strength can be obtained by performing cold working. It is possible to obtain a desired amount of martensite after proper cold working. By adjusting to the amount of Vickers hardness
It can be 455 or more. Further, the steel strip using the steel of the present invention described above, ductility without lowering the hardness, in order to improve the spring properties, etc., if necessary, after cold working 400 ~ 600 ℃
The aging process can be performed by using.

Further, the steel of the present invention can be nitrided without lowering the hardness. When the steel of the present invention described above is formed in a belt shape and subjected to nitriding treatment under appropriate conditions so that it can be applied to, for example, a power transmission belt used as a component for a continuously variable transmission of an automobile engine, nitrides are almost completely eliminated. A nitride layer of about 20 to 40 μm can be formed on the surface without forming
A large compressive residual stress can be applied to the surface, and a higher fatigue strength can be obtained. It is preferable that the compressive residual stress on the surface is higher, but the control can be achieved by appropriately adjusting the thickness of the nitride layer and the hardness of the nitride layer.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
First, it was melted by vacuum melting to obtain a 10 kg steel ingot. Table 1 shows the chemical composition. Here, steel Nos. 1 to 15 are steels of the present invention in which the composition, A value and the amount of martensite phase after cold working are all within the scope of the present invention, and Nos. 31 to 36 are compositions, A values and No. 37 is JIS SUS420J2, a conventional quenched and tempered steel, in which any or some of the martensite phase after cold working is out of the limited range of the present invention. No. 1-3
The steel of No. 7 was formed into a plate having a thickness of 2 mm by hot forging and hot rolling, heated to 1050 ° C., and then subjected to an air-cooled solution treatment. After that, it is cold-rolled at a reduction rate of 50 to 70% into a steel strip,
Aging treatment was performed at 50 ° C. No. 36 steel was quenched from 950 ° C and then tempered at 300 ° C.

The amount of the martensite phase was measured by X-ray diffraction. The hardness was determined by measuring Vickers hardness in a longitudinal section of a cold-rolled sheet. In addition, the fatigue strength was measured by using a plate specimen of 0.2 mm thickness and 10 mm width, changing the span length at a bending angle of ± 25 ° and repeatedly performing a bending fatigue test at a repetition bending speed of 1000 cpm. The fatigue strength at 10 7 times was determined.

[0027]

[Table 1]

[0028]

[Table 2]

As can be seen from Table 2, the steels of the present invention No. 1 to 15
All show high Vickers hardness of 455 or more after cold working. Further, the steel of the present invention shows a high fatigue strength of 800 MPa or more from the results of the repeated bending fatigue test. On the other hand, the comparative steel No. 31 to 36 and the conventional steel No. 37 in which one or more of the composition, the A value, and the martensite phase amount after cold working deviate from the range specified in the present invention have a hardness of It can be seen that any of the properties of the fatigue strength in the repeated bending fatigue test is worse than that of the steel of the present invention. In particular, the comparative steels No. 32-35 in which the A value and the amount of martensite phase are out of the specified ranges
Has low hardness and cannot obtain high hardness.

When the Vickers hardness of the steel of the present invention in the solution treatment state was measured, the hardness was as low as 350 or less, the cold workability was good, and the cold forming was easy. further,
If the steel of the present invention is subjected to a nitriding treatment at a temperature lower than the aging treatment temperature after the aging treatment, or if a nitriding treatment is also performed together with the aging treatment, a nitrided layer having a depth of about 20 to 40 μm can be formed. The fatigue strength can be further increased by about 300 MPa due to the effect of the surface compressive residual stress caused by the stress.

[0031]

As described above, the work-induced martensitic steel of the present invention is high in hardness and excellent in fatigue strength. Therefore, members and components requiring both high hardness and fatigue strength, such as rockets, are required. Parts, centrifugal separator parts, aircraft parts, parts for continuously variable transmissions of automobile engines, molds, etc., the service life is improved, and furthermore, the steel strip is formed using the work-induced martensitic stainless steel of the present invention. Then, for example, if the power transmission belt is used as a component for a continuously variable transmission of an automobile engine, it has particularly favorable characteristics and has an industrially remarkable effect.

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[Procedure amendment]

[Submission date] March 9, 2001 (2001.3.9)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

[0012] The sixth aspect of the present invention is a steel strip comprising a working induced electromotive type <br/> martensitic steel having high hardness and high fatigue strength according to any of the first invention through the fifth invention , of the steel band solid
It is a work-induced martensitic steel strip having high hardness and high fatigue strength with a Vickers hardness of 455 or more after the solution treatment . A seventh invention of the present invention is directed to a work-induced martensitic steel strip having a high hardness and high fatigue strength according to the sixth invention, wherein a nitride layer is formed on a surface of the work-induced martensitic steel strip, and a compressive residual stress is applied to the surface. It is a martensitic steel strip. Eighth of the invention
The invention is a steel strip made of a work-induced martensitic steel having high hardness and high fatigue strength according to any one of the first to fifth inventions, wherein a nitrided layer is formed on a surface of the steel strip,
This is a work-induced martensitic steel strip having a compressive residual stress applied to the surface of the steel strip. Further, the work-induced martensitic steel strip of the present invention using the above-described work-induced martensitic steel has a nitrided layer formed on the surface by an appropriate nitriding treatment to impart compressive residual stress to the surface. Can be.

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Claims (8)

[Claims] 1. In mass%, C: 0.01 to 0.10%, Si: 3.0% or less, Mn: more than 5.0% to 10.0% or less, Ni: 1.0 to 12.0%, Cr: 4
-18%, one or two of Mo or W is 0.1% at Mo + 1 / 2W
~ 4.0%, Cu: 5.0% or less (including 0%), N: 0.15% or less (0%
), Al: 0.10% or less, O: 0.005% or less, the balance being substantially composed of Fe, and the A value represented by the formula (1) is 13 to 27%. A work-induced martensitic steel having high hardness and high fatigue strength, characterized by containing at least 30% by volume of a martensite phase. A = Ni + 0.65Cr + 0.98Mo + 0.49W + 1.05Mn + 0.35Si + Cu + 12.6 (C + N) ... (1) 2. In mass%, Mn: more than 5.0% and 7.0% or less,
i: 3.0 to 11.0%, Cr: 4 to 16%, one or two of Mo or W
The species contains 0.5 to 3.0% of Mo + 1 / 2W, Cu: 4.0% or less (including 0%), Al: 0.05% or less, and the A value represented by the formula (1) is 19 to 25%. The process-induced martensitic steel having high hardness and high fatigue strength according to claim 1. 3. In mass%, Si: less than 1.0, Mn: more than 5.0% and 7.0% or less, Ni: 3.0 to 11.0%, Cr: 4 to 16%, Mo or W
One or two types are 0.5% to 3.0% Mo + 1 / 2W, Cu: 4.0%
2 (including 0%), Al: 0.05% or less, and the A value represented by the formula (1) is 19 to 24%. Work-induced martensitic steel. 4. One or more of V, Ti and Nb in mass%.
The work-induced martensitic steel having high hardness and high fatigue strength according to any one of claims 1 to 3, wherein the steel contains 0.2% or less in total of at least one kind. 5. The high hardness and high fatigue according to claim 1, wherein one or more of B, Mg, and Ca are contained in a total of 0.10% or less by mass%. Work-induced martensitic steel with high strength. 6. A steel strip made of a work-induced martensitic steel having a high hardness and high fatigue strength according to claim 1, wherein the Vickers hardness of the steel strip is 455 or more. A work-induced martensitic steel strip having high hardness and high fatigue strength. 7. A work-induced martensitic steel strip having high hardness and high fatigue strength according to claim 6, wherein a nitride layer is formed on a surface of the steel strip, and a compressive residual stress is formed on the surface of the steel strip. A work-induced steel strip, characterized by having been provided with. 8. A steel strip made of a work-induced martensitic steel having high hardness and high fatigue strength according to any one of claims 1 to 5, wherein a nitrided layer is formed on the surface of the steel strip.
A work-induced martensitic steel strip wherein a compressive residual stress is applied to the surface of the steel strip.