JP2008163410A - Steel for high-speed cold working and method for production thereof, and method for producing part formed by high-speed cold working - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel for cold working which exhibits good cold workability during working and also exhibits high hardness after working. <P>SOLUTION: The steel for high-speed cold working contains C: 0.03 to 0.15% (by mass), Si: 0.005 to 0.6%, Mn: 0.05 to 2%, P: ≤0.05% (excluding 0%), S: ≤0.05% (excluding 0%), and N: ≤0.04% (excluding 0%), with the remainder being iron and inevitable impurities and the amount of dissolved nitrogen in the steel being ≥0.006%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to cold work steel, particularly cold work wire or bar steel, useful for producing machine parts such as bolts and nuts, particularly automobile parts. The present invention also provides a cold work part obtained from the cold work steel.

  Cold processing (for example, processing of steel in an atmosphere of 200 ° C. or lower) has advantages such as higher productivity, better dimensional accuracy, and better steel yield than hot processing and warm processing. Therefore, it is widely used for manufacturing various parts. In addition, in order to further improve productivity, there is a trend toward high-speed machining.

  Against such a background, steel used for cold working needs to have low deformation resistance during cold working, and the deformability is not lowered during working. This is because if the deformation resistance of steel is high, the life of a tool used for cold working is reduced, while if the deformability is low, cracks are likely to occur during cold working.

  In order to reduce the deformation resistance of steel and improve the deformability, it is known that additive elements such as C (carbon), Si, and Mn may be reduced. However, if the additive element is simply reduced and the deformation resistance is lowered, the tool life can be improved, but there is a problem that the required component strength cannot be obtained after machining. Therefore, conventionally, after cold working the steel into a predetermined shape, heat treatment such as quenching and tempering has been performed to ensure a predetermined hardness.

  However, if the heat treatment is performed after the parts are processed, the dimensions of the parts will change, so that the parts must be further processed. In order to improve productivity and save energy, there is a demand for a solution that can prevent heat treatment and subsequent processing while ensuring a predetermined hardness.

  Under the background as described above, in order to suppress an increase in deformation resistance during processing, Patent Document 1 precipitates fine nitrides in ferrite grains and precipitates carbides such as cementite using this as a nucleus. Is disclosed. From this, it is disclosed that solid solution nitrogen and solid solution carbon are fixed as nitrides and carbides to suppress an increase in deformation resistance by suppressing dynamic strain aging during processing.

  Patent Document 2 discloses N and sol. It discloses that age hardening by carbon and nitrogen is suppressed by controlling the amount of Al to fix N as AlN and further precipitating carbon as carbides by aging treatment.

  In the methods of Patent Documents 1 and 2 above, in order to suppress dynamic strain aging and suppress an increase in deformation resistance, solid solution nitrogen and solid solution carbon are fixed as nitrides and carbides in ferrite grains. . In order to fix solute nitrogen and solute carbon, it is necessary to add Al. If Al is 0.039 to 0.045% as in the examples, even if the nitrogen amount is 0.015%, it is considered that there is almost no solid solution nitrogen.

  Patent Document 3 discloses a method for reducing deformation resistance during cold working by lowering the hardness of a steel material due to softening by solid solution by adding Cr and fixing solute nitrogen by adding Al. However, in this method, since solid solution nitrogen is fixed by adding Al, it is considered that there is almost no solid solution nitrogen as in Patent Documents 1 and 2 above.

In cold-worked parts after cold working, hardening heat treatment, for example, quenching and tempering, may be performed to ensure a predetermined hardness, but as described above, quenching and tempering are performed from the viewpoint of productivity improvement and energy saving. There is a need to omit it. For example, Patent Document 4 discloses that aging treatment (quenching and tempering) after cold forging can be omitted by cooling from a heat generation temperature after cold forging to room temperature at a cooling rate of 50 to 70 ° C./hr. Yes.
Japanese Patent No. 3515923 JP 60-82618 Japanese Patent Publication No.57-60416 JP 2003-266144 A

  Cold workability (deformation resistance and deformability) and hardness after cold work are contradictory properties, and conventionally, a steel for cold work that is good in both of these has not been obtained. Accordingly, an object of the present invention is to provide a cold work steel, particularly a cold work wire or a bar steel, which is excellent in cold workability during working and exhibits good hardness after working.

The steel for high-speed cold working of the present invention that has achieved the above object is:
C: 0.03 to 0.15% (meaning mass%, the same shall apply hereinafter)
Si: 0.005 to 0.6%,
Mn: 0.05-2%
P: 0.05% or less (excluding 0%),
S: 0.05% or less (not including 0%), and N: 0.04% or less (not including 0%)
The balance consists of iron and inevitable impurities,
The amount of dissolved nitrogen in the steel is 0.006% or more.

  In order to secure the amount of dissolved nitrogen at 0.006% or more, it is desirable that N: 0.007% or more.

  In addition to the above components, it is also effective to further contain Al: 0.1% or less (not including 0%) in the steel for high-speed cold working according to the present invention.

  In the steel for high-speed cold working of the present invention, in addition to the above components, if necessary, Zr: 0.2% or less (excluding 0%), Ti: 0.1% or less (including 0%) Nb: 0.1% or less (not including 0%), V: 0.5% or less (not including 0%), Ta: 0.1% or less (not including 0%), and Hf : It is also effective to contain at least one selected from the group consisting of 0.1% or less (not including 0%).

  In addition to the above components, the steel for high-speed cold working according to the present invention may further include B: 0.0015% or less (not including 0%) and / or Cr: 2% or less (including 0%) as necessary. It is also effective to contain at least one selected from the group consisting of:

At this time, it is recommended that the above components satisfy the following formula (1).
[N]-(27 [Al] /14+47.9 [Ti] /14+92.9 [Nb] /14+50.9 [V] /14+91.2 [Zr] /14+10.8 [B] /14+180.9 [Ta ] /14+178.5 [Hf] / 14) ≧ 0.006 (1) Formula [In Formula (1), [] represents the total content (mass%) of each element in steel. ]

  In addition to the above components, it is also effective to further contain Cu: 5% or less (not including 0%) in the steel for high-speed cold working according to the present invention.

  In the steel for high speed cold work of the present invention, in addition to the above components, Ni: 5% or less (not including 0%) and / or Co: 5% or less (not including 0%) as necessary. It is also effective to contain.

  In the steel for high-speed cold working of the present invention, in addition to the above components, Mo: 2% or less (not including 0%) and / or W: 2% or less (not including 0%) as necessary. It is also effective to contain.

  In the steel for high-speed cold working of the present invention, in addition to the above components, if necessary, Ca: 0.05% or less (not including 0%), rare earth elements (hereinafter abbreviated as “REM”) : 0.05% or less (not including 0%), Mg: 0.02% or less (not including 0%), Li: 0.02% or less (not including 0%), Pb: 0.1% It is also effective to contain at least one selected from the group consisting of the following (not including 0%) and Bi: not more than 0.1% (not including 0%).

  The steel for high-speed cold working of the present invention is recommended to be used for high-speed cold working under the condition that the working temperature is 200 ° C. or less. Moreover, it is recommended to use it for high-speed cold working under the condition that the strain rate is 100 / sec or more.

  Note that the strain rate is obtained by dividing the true strain by the unit time.

As a method for producing high-speed cold working steel of the present invention, a steel having the above component composition, heated to Ac ₃ point + 30 ° C. or higher, and hot working in the subsequent Ac ₃ point + 30 ° C. or higher temperature range Then, a method of cooling to 500 ° C. or lower at a cooling rate of 0.5 ° C./s or higher is recommended as a preferred embodiment.

As a method for producing high-speed cold working steel of the present invention, a steel having the above component composition, heated to Ac ₃ point + 30 ° C. or higher temperatures, 500 ° C. or less in the subsequent 0.5 ° C. / s or more cooling rate A method of cooling to a low temperature is recommended as a preferred embodiment.

  Since the steel for high-speed cold working of the present invention contains (a) solute nitrogen in a predetermined amount or more, even if quenching and tempering after cold working is omitted, the hardness of the steel part after cold working is reduced. Can be improved. The steel for high-speed cold working of the present invention is limited to (b) high-speed cold working (preferably cold working with a strain rate of 100 / second or more), and (c) chemical Since the component amount is optimized, it shows good cold workability.

  The steel for high speed cold work of the present invention has a great feature in that it contains solute nitrogen in a predetermined amount or more. With this feature, even if quenching and tempering is omitted after cold working, the hardness of the steel part after working can be increased. However, the inclusion of a relatively large amount of solute nitrogen can lead to an adverse effect that the deformation resistance of the steel material can be increased. Therefore, the present invention is characterized in that cold workability is maintained by performing cold work at high speed. That is, the steel of the present invention is one of the features that it is used for the purpose of high-speed cold working. Such technical idea, ie, (a) increasing the hardness after cold working by containing a predetermined amount or more of solid solution nitrogen, and (b) suppressing the harmful effects of solid solution nitrogen by high-speed cold working. Thus, the idea of maintaining good cold workability has never existed. Further, performing cold working at high speed contributes to improving the productivity of parts.

  The steel of the present invention is also characterized in that the amount of chemical component (c) is optimized in order to achieve good cold workability. Below, the component composition of steel and the amount of dissolved nitrogen are demonstrated first.

(C: 0.03-0.15%)
C (carbon) is an element necessary for ensuring the strength of steel. Therefore, the lower limit of the carbon content is set to 0.03%. A more preferred lower limit is 0.04%. On the other hand, if the amount of carbon is excessive, machinability and cold workability deteriorate. Therefore, the upper limit of carbon content was set to 0.15%. A more preferred upper limit is 0.12%.

(Si: 0.005-0.6%)
Si is an element used as a deoxidizer in the steelmaking process. If the amount of Si is too small, gas is generated during the solidification process, which tends to act as defects, and thus cracks may occur during cold working. Therefore, the lower limit of Si content is set to 0.005%. A more preferred lower limit is 0.008%. On the other hand, even if the amount of Si is excessive, the effect is saturated and the cold workability is lowered. Therefore, the upper limit of Si content is set to 0.6%. A more preferred upper limit is 0.5%.

(Mn: 0.05-2%)
Mn acts as a deoxidizer in the steel making process, just like Si. Mn is also an effective element as a desulfurizing agent. If the amount of Mn is too small, FeS precipitates in the form of a film at the crystal grain boundary, and the grain boundary strength is significantly reduced. obtain. Therefore, the lower limit of the amount of Mn is set to 0.05%. A more preferred lower limit is 0.1%. On the other hand, if the amount of Mn is excessive, cold workability is lowered. Therefore, the upper limit of the amount of Mn is set to 2%. A more preferred upper limit is 1%.

(P: 0.05% or less (excluding 0%))
P is an element that degrades the cold workability by strengthening the solid solution of ferrite, and is preferably reduced as much as possible. Therefore, it is recommended to reduce the amount of P to 0.05% or less, more preferably 0.03% or less. However, it is industrially difficult to reduce the P content to zero.

(S: 0.05% or less (excluding 0%))
S, together with Mn, is an element that forms MnS inclusions that act as starting points for cracks during cold working. Therefore, it is recommended to reduce the amount of S to 0.05% or less, more preferably 0.03% or less from the viewpoint of deformability. However, it is industrially difficult to reduce the amount of S to 0. Note that S has an effect of improving machinability. From the viewpoint of improving machinability, S is preferably contained in an amount of 0.002% or more, more preferably 0.006% or more.

(N: 0.04% or less (excluding 0%))
Nitrogen (N) has the effect of increasing the hardness of steel parts after cold working by solid solution in steel, and is an essential element in the present invention. However, if the total amount of nitrogen in the steel is excessive, the amount of dissolved nitrogen may also be excessive and cracks may occur during cold working, and further, internal defects in steel and slab cracking during continuous casting are likely to occur. . Therefore, the upper limit of the total nitrogen amount in the steel is set to 0.04% from the viewpoint of the deformability of the steel, the stability of the material, and the yield improvement during casting. A more preferred upper limit is 0.03%. On the other hand, the lower limit of the total nitrogen amount is not particularly limited as long as the lower limit of the solid solution nitrogen amount described later can be satisfied. However, in order to stably secure solid solution nitrogen, the lower limit of the total nitrogen amount is preferably 0.007%, more preferably 0.008%.

(Soluted nitrogen: 0.006% or more)
In order to sufficiently secure the increase in hardening after cold working, in the present invention, the lower limit of the amount of dissolved nitrogen in the steel is set to 0.006%. A preferred lower limit is 0.007%. On the other hand, if the amount of dissolved nitrogen is excessive, cracks occur during cold working. Therefore, the amount of solid solution nitrogen is preferably 0.03% or less. Of course, the upper limit of the solid solution nitrogen amount does not exceed 0.04%, which is the upper limit of the total nitrogen amount in the steel. Here, the value of “the amount of solid solution nitrogen” in the present invention is based on JIS G 1228, and the amount of solid solution nitrogen in the steel is calculated by subtracting the amount of all nitride compounds from the total amount of nitrogen in the steel.

  (I) The total nitrogen amount in the steel uses an inert gas melting method-thermal conductivity method. A sample is cut from the test steel material, placed in a crucible, melted in an inert gas stream, extracted with nitrogen, transported to a thermal conductivity cell, and the change in thermal conductivity is measured.

  (Ii) Ammonia distillation separated indophenol blue absorptiometry is used to measure the total amount of nitrided compounds in steel. A sample is cut out from the test steel material, 10% AA electrolyte (non-aqueous solvent electrolyte that does not produce a passive film on the steel surface, specifically 10% acetylacetone, 10% tetramethylammonium chloride. , The remainder: methanol). About 0.5 g of the sample is dissolved, and the insoluble residue (nitride compound) is filtered through a polycarbonate filter having a hole size of 0.1 μm. The insoluble residue is decomposed by heating in sulfuric acid, potassium sulfate and pure Cu chips and mixed into the filtrate. After making this solution alkaline with sodium hydroxide, steam distillation is performed, and the distilled ammonia is absorbed by dilute sulfuric acid. Phenol, sodium hypochlorite and sodium pentacyanonitrosyl iron (III) are added to form a blue complex, and its absorbance is measured using a photometer.

  The amount of solute nitrogen in the steel is calculated by subtracting the total amount of nitrided compound from the total amount of nitrogen in the steel determined by the above method.

  The basic component composition of the steel of the present invention is as described above, and the balance is substantially iron. However, it is naturally allowed that inevitable impurities brought into the steel depending on the situation of raw materials, materials, manufacturing equipment, etc. are contained in the steel. Furthermore, the steel of this invention may contain the following arbitrary elements as needed.

(Al: 0.1% or less)
Al is an effective element as a deoxidizing element in the steel making process, and is also effective for crack resistance of steel. Therefore, it is recommended that Al is contained in an amount of preferably 0.001% or more, more preferably 0.005% or more, if necessary. However, Al has a strong affinity for nitrogen (N), and since Al nitride is formed to reduce the amount of dissolved nitrogen, the upper limit for the inclusion is set to 0.1%. The amount of Al is preferably 0.05% or less, more preferably 0.03% or less.

(From Zr: 0.2% or less, Ti: 0.1% or less, Nb: 0.1% or less, V: 0.5% or less, Ta: 0.1% or less, and Hf: 0.1% or less At least one selected from the group consisting of
Zr, Ti, Nb, V, Ta, and Hf are effective elements for forming nitrides together with nitrogen to refine crystal grains and increasing the toughness of parts obtained after cold working. Therefore, if necessary, Zr is preferably 0.002% or more, more preferably 0.004% or more, Ti is preferably 0.001% or more, more preferably 0.002% or more, and Nb is preferably 0.00. 001% or more, more preferably 0.002% or more, V is preferably 0.001% or more, more preferably 0.002% or more, Ta is preferably 0.003% or more, more preferably 0.006% or more , And Hf are preferably included in an amount of 0.002% or more, more preferably 0.004% or more.

  On the other hand, these elements have a strong affinity for nitrogen, and in order to form nitrides and reduce the amount of dissolved nitrogen, the upper limit amounts were determined as follows. The amount of Zr is preferably 0.05% or less, more preferably 0.03% or less, the amount of Ti is preferably 0.05% or less, more preferably 0.03% or less, and the amount of Nb is preferably 0.00. 06% or less, more preferably 0.04% or less, the V amount is preferably 0.1% or less, more preferably 0.05% or less, and the Ta amount is preferably 0.05% or less, more preferably 0. 0.03% or less, and the amount of Hf is preferably 0.05% or less, more preferably 0.03% or less.

(B: 0.0015% or less and / or Cr: 2% or less)
B is an element that improves the deformability of steel by increasing the strength of grain boundaries. Similarly, Cr can improve the deformability of steel. Therefore, if necessary, B is preferably contained in an amount of 0.0001% or more, more preferably 0.0002% or more, and Cr is preferably contained in an amount of 0.1% or more, more preferably 0.2% or more. Recommended. However, B has a strong affinity for nitrogen, and forms B nitride to reduce the amount of dissolved nitrogen. Moreover, when B nitride becomes excessive, cold workability will fall. When Cr is excessive, deformation resistance is increased. Therefore, when these elements are contained, the B content is preferably 0.001% or less, more preferably 0.0008% or less, and the Cr content is preferably 1.5% or less, more preferably 1% or less. .

(Cu: 5% or less)
Cu has the effect | action which improves the intensity | strength of a steel component. Therefore, it is recommended to contain Cu in an amount of preferably 0.1% or more, preferably 0.5% or more. However, even if Cu is contained excessively, the effect is saturated, and the cold workability and the surface properties of the parts are deteriorated. Therefore, the upper limit of the amount of Cu in the case of inclusion is set to 5%. The amount of Cu is preferably 4% or less, more preferably 2% or less.

(Ni: 5% or less and / or Co: 5% or less)
Ni and Co are effective elements for strengthening steel. Ni also has an action of preventing surface defects of steel when Cu is contained. Therefore, it is recommended that Ni is contained in an amount of preferably 0.1% or more, preferably 0.5% or more, and Co is preferably contained in an amount of 0.1% or more, preferably 0.5% or more. However, even if the amount of Ni becomes excessive, the effect is saturated and the cold workability deteriorates. Further, when the amount of Co is excessive, the grain boundaries are deteriorated in the steel manufacturing process such as casting and rolling, and cracking is likely to occur. Therefore, the upper limit in the case of inclusion is set to 5%. The amount of Ni is preferably 4% or less, more preferably 2% or less, and the amount of Co is preferably 4% or less, more preferably 2% or less.

(Mo: 2% or less and / or W: 2% or less)
Mo and W have the effect of improving the hardness and toughness of the parts after cold working. Therefore, it is recommended that Mo is contained in an amount of preferably 0.04% or more, more preferably 0.1% or more, and W is preferably 0.04% or more, more preferably 0.1% or more. However, when these amounts are excessive, cold workability deteriorates. Therefore, the upper limit in the case of inclusion is set to 2%. The Mo amount is preferably 1.5% or less, more preferably 1% or less, and the W amount is preferably 1% or less, more preferably 0.5% or less.

(Ca: 0.05% or less, REM: 0.05% or less, Mg: 0.02% or less, Li: 0.02% or less, Pb: 0.1% or less, and Bi: 0.1% or less At least one selected from the group consisting of
Ca, REM, Mg, Li, Pb and Bi are elements that contribute to improving the machinability of steel. Ca, REM, Mg, and Li also have the effect of increasing the toughness of steel by spheroidizing sulfide inclusions such as MnS. Ca is preferably 0.005% or more, more preferably 0.01% or more, REM is preferably 0.005% or more, more preferably 0.01% or more, and Mg is preferably 0.005% or more, more preferably Is 0.008% or more, Li is preferably 0.001% or more, more preferably 0.005% or more, Pb is preferably 0.005% or more, more preferably 0.01% or more, and Bi is preferably It is recommended that the content be 0.005% or more, more preferably 0.01% or more.

  However, even if the amount of these elements is excessive, the effect is saturated. Then, the upper limit amount in the case of making it contain was defined as follows, respectively. The Ca amount is preferably 0.04% or less, more preferably 0.02% or less, the REM amount is preferably 0.02% or less, more preferably 0.01% or less, and the Mg amount is preferably 0.00. 015% or less, more preferably 0.01% or less, the Li amount is preferably 0.015% or less, more preferably 0.01% or less, and the Pb amount is preferably 0.08% or less, more preferably 0. 0.06% or less, and the Bi content is preferably 0.09% or less, and more preferably 0.08% or less.

  Next, the manufacturing method of the steel for high speed cold work of this invention is demonstrated. The steel of the present invention is characterized by containing solute nitrogen in an amount of 0.06% or more. In order to ensure this amount of dissolved nitrogen, (i) increasing the total amount of nitrogen in the steel, and (ii) increasing the amount of dissolved nitrogen by heating the steel to a predetermined temperature or higher. Is effective.

First, it will be explained from increasing the total amount of nitrogen in the steel. When the steel contains an element having a strong affinity for nitrogen such as Al, nitrogen forms a nitride with Al or the like, resulting in a decrease in the amount of dissolved nitrogen. However, if the total amount of nitrogen in the steel is large, a sufficient amount of solute nitrogen can be secured even if Al and the like all form nitrogen and nitride. More specifically, by securing a total nitrogen amount that satisfies the following formula (1), a solid solution nitrogen amount of 0.006% or more can be secured:
[N]-(27 [Al] /14+47.9 [Ti] /14+92.9 [Nb] /14+50.9 [V] /14+91.2 [Zr] /14+10.8 [B] /14+180.9 [Ta ] /14+178.5 [Hf] / 14) ≧ 0.006% (1) Formula [In the above formula (1), [] represents the total content (mass%) of each element in steel. . ]
The coefficient in the above formula (1) is obtained by dividing the atomic weight of an element (for example, Al) having a strong affinity with nitrogen (N) by the atomic weight of nitrogen (N).

In addition, when the amount of chemical components in the steel does not satisfy the above formula (1) and a large amount of nitride such as Al is formed, a sufficient amount of dissolved nitrogen cannot be ensured. After the steel is heated and held at a temperature at which the nitride dissolves in the solid solution, the solid solution heat treatment that suppresses the precipitation by quenching the steel can increase the amount of solid solution nitrogen. Specifically, after heating the steel to a temperature of Ac ₃ points + 30 ° C. or higher and then cooling to 500 ° C. or lower at a cooling rate of 0.5 ° C./s or higher, the amount of solid solution nitrogen in the steel is increased. Can do.

In order to increase the amount of dissolved nitrogen, the heating temperature is preferably Ac ₃ points + 30 ° C. or higher, more preferably Ac ₃ points + 50 ° C. or higher. The heating and holding time is preferably 10 minutes or longer, more preferably 30 minutes or longer. However, from the viewpoint of production cost, the heating temperature is preferably Ac ₃ points + 400 ° C. or lower, more preferably Ac ₃ points + 300 ° C. or lower. The heating and holding time is preferably 2 hours 30 minutes or less, more preferably 1 hour 30 minutes or less.

  During this heating and holding, hot working such as wire drawing, rolling, or pressing may be performed as appropriate. After heating and holding, preferably at a cooling rate of 0.5 ° C./s or more, more preferably 1 ° C./s or more, more preferably 5 ° C./s or more, up to 500 ° C. or less where solid solution nitrogen can stably exist Preferably, by cooling to 450 ° C. or lower, precipitation of nitrides can be suppressed and a sufficient amount of dissolved nitrogen can be secured.

  One feature of the present invention is that the steel containing the chemical composition and solute nitrogen is subjected to high-speed cold working. The steel of the present invention contains a relatively large amount of solute nitrogen. Nevertheless, in order to maintain good cold workability, the steel of the present invention is preferably 100 / second or more, more preferably Is recommended to be cold worked at a strain rate of 120 / sec or more, more preferably 140 / sec or more. On the other hand, if the strain rate is too high, an adiabatic temperature rise occurs and cracking tends to occur. Therefore, the upper limit value of the strain rate is preferably 300 / second, more preferably 280 / second, and even more preferably 260 / second. It is.

  Further, since the temperature at the time of processing also affects the cold workability, it is recommended that the upper limit value of the processing temperature is preferably set to 200 ° C, more preferably 180 ° C, and even more preferably 160 ° C. This is because if the processing temperature is too high, dynamic strain aging occurs during deformation and the deformation resistance increases. On the other hand, cold working is usually performed at room temperature. However, if the temperature is lower than 0 ° C., the deformation resistance becomes higher due to temperature dependence, and therefore the preferred lower limit of the working temperature is 0 ° C. The processing temperature refers to the atmospheric temperature during processing.

  The steel material (for example, wire rod or bar) manufactured as described above is then cold worked at high speed to become parts such as bolts and nuts and other machine parts. The cold working method here includes cold working such as cold forging, cold forging, cold rolling, cold punching and the like. Further, if necessary for the processing of the parts, processing such as wire drawing and rolling may be performed.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and may be implemented with appropriate modifications within a range that can meet the gist of the preceding and following descriptions. Of course, any of these is also included in the technical scope of the present invention.

  First, steels having the chemical composition shown in Tables 1 to 3 were melted by a converter, made into steel pieces by continuous casting, and then rolled into a φ12 mm wire.

  The obtained wire was subjected to heat treatment under the conditions shown in Table 4. After the heat treatment under the conditions shown in Table 4, it is desirable to provide a holding time of 10 minutes or longer, preferably 30 minutes or longer. Next, a test piece having a diameter of 4 mm and a length of 6 mm was cut out from the center of the wire subjected to the heat treatment. Tables 1 to 3 show whether or not each test piece satisfies the above formula (1). When the formula (1) is satisfied, “◯”, when the formula (1) is not satisfied Is marked with “x”. Further, in the table, “solid solution N” indicates the amount of solid solution nitrogen, and “N” indicates the total amount of nitrogen.

  Next, the test pieces described in Tables 1 to 3 were processed at a capacity of 200 kN under processing conditions of strain rate: 0.001 to 240 / second, processing temperature: 20 to 400 ° C., and compression rate: 20 to 80%. Forged using a Formaster tester and processed into parts. As the strain rate, an average value of strain rates during processing (plastic deformation) was used. About the obtained component, the surface was observed with the actual condition microscope with an observation magnification of 20 times, and the presence or absence of the crack was confirmed. Tables 5 to 7 show the processing conditions, presence / absence of cracks, and deformation resistance of each part.

  Also, using a Vickers hardness tester under the conditions of load: 1000 g, measurement position: D / 4 center of test piece cross section (D: component diameter), and number of measurements: 5 times (Vickers hardness ( Hv) was measured. Tables 5 to 7 show the hardness (Hv) of each part.

  In this example, it was determined that steel having no cracks in the part and having low deformation resistance of steel with respect to the part hardness (specifically, satisfying the following formula (2)) is excellent in cold workability.

In addition, it was determined that a component having a Vickers hardness (Hv) of 240 or more is excellent in strength. Tables 5 to 7 show whether or not each test piece satisfies the following formula (2). When the formula (2) is satisfied, “◯”, when the formula (1) is not satisfied Is marked with “x”.
H = (DR + 1000) / 6 (2) where H: hardness (Hv), DR: deformation resistance (MPa)

  From Tables 5 to 7, under preferable processing conditions (strain rate and processing temperature), the steel satisfying the requirements of the amount of chemical components and the amount of dissolved nitrogen specified in the present invention is excellent in cold workability and obtained from this. It can be seen that the parts are excellent in strength. On the other hand, those that do not satisfy the requirements defined in the present invention are inferior in cold workability or component strength, as described below.

Part No. Since 1 (steel No. 1A) has a small amount of carbon, the hardness (Hv) is less than 160 and the strength is insufficient.
Part No. No. 6 (steel No. 1F) had a large amount of carbon, and therefore cracked in the parts.
Part No. Since No. 7 (steel No. 1G) had a small amount of Si, cracks occurred in the parts.

Part No. Since No. 14 (steel No. 1N) had a large amount of Si, cracks occurred in the parts.
Part No. Since No. 15 (steel No. 1O) had a small amount of Mn, cracks occurred in the parts.
Part No. Since No. 24 (steel No. 1X) had a large amount of Mn, cracks occurred in the parts.

Part No. Since 25 and 26 (steel No. 1Y and 1Z) had a large amount of P, cracks occurred in the parts.
Part No. Since Nos. 27 and 28 (steel Nos. 2A and 2B) had a large amount of S, cracks occurred in the parts.
Part No. Since 29 (steel No. 2C) has a small amount of dissolved nitrogen, the deformation resistance (MPa) / hardness (Hv) exceeded 2.4, and the deformation resistance was large relative to the component hardness.

Part No. Since 31-34 (material No. 31, steel No. 2E) had a slow strain rate, the crack generate | occur | produced in components.
Part No. Since 37-38 (steel No. 2F-G) had high processing temperature, the crack generate | occur | produced in components.

Part No. Since 42 (steel No. 2K) has a large amount of total nitrogen, cracks occurred in the parts.
Part No. 77 (steel No. 3T-1), part no. 81 and 82 (steel No. 3U-1 and 2), part no. 85 (steel No. 3V-1), part no. 89 and 90 (steel No. 3W-1 and 2), part no. 93 and 94 (steel No. 3X-1 and 2), part no. 97 (steel No. 3Y-1), part no. 101 and 102 (steel No. 3Z-1 and 2) and part no. Since 105 (steel No. 4A-1) had a small amount of dissolved nitrogen, the above formula (2) was not satisfied, and the deformation resistance was large with respect to the component hardness.

Claims (14)

C: 0.03 to 0.15% (meaning mass%, the same shall apply hereinafter)
Si: 0.005 to 0.6%,
Mn: 0.05-2%
P: 0.05% or less (excluding 0%),
S: 0.05% or less (excluding 0%), and
N: 0.04% or less (excluding 0%),
The balance consists of iron and inevitable impurities,
A steel for high-speed cold working characterized in that the amount of dissolved nitrogen in the steel is 0.006% or more.   N: The steel for high-speed cold work of Claim 1 containing 0.007% or more.   Furthermore, steel for high-speed cold work of Claim 1 containing Al: 0.1% or less (excluding 0%). further,
Zr: 0.2% or less (excluding 0%),
Ti: 0.1% or less (excluding 0%),
Nb: 0.1% or less (excluding 0%),
V: 0.5% or less (excluding 0%),
Ta: 0.1% or less (excluding 0%), and
Hf: 0.1% or less (excluding 0%)
The steel for high-speed cold work according to any one of claims 1 to 3, comprising at least one selected from the group consisting of:   The high-speed cold working according to any one of claims 1 to 4, further comprising B: 0.0015% or less (excluding 0%) and / or Cr: 2% or less (not including 0%). Steel. The steel for high speed cold work according to any one of claims 1 to 5, which satisfies the following formula (1).
[N]-(27 [Al] /14+47.9 [Ti] /14+92.9 [Nb] /14+50.9 [V] /14+91.2 [Zr] /14+10.8 [B] /14+180.9 [Ta ] /14+178.5 [Hf] / 14) ≧ 0.006 (1) Formula [In Formula (1), [] represents the total content (mass%) of each element in steel. ]   The steel for high-speed cold working according to any one of claims 1 to 6, further comprising Cu: 5% or less (not including 0%).   Furthermore, Ni: 5% or less (not including 0%) and / or Co: 5% or less (not including 0%) for high-speed cold working according to any one of claims 1 to 7 steel.   Further, Mo: 2% or less (not including 0%) and / or W: 2% or less (not including 0%), for high-speed cold working according to any one of claims 1 to 8 steel. further,
Ca: 0.05% or less (excluding 0%),
Rare earth element: 0.05% or less (excluding 0%),
Mg: 0.02% or less (excluding 0%),
Li: 0.02% or less (excluding 0%),
Pb: 0.1% or less (excluding 0%), and
Bi: 0.1% or less (excluding 0%)
The steel for high-speed cold work according to any one of claims 1 to 9, comprising at least one selected from the group consisting of:   A method for producing a high-speed cold-worked part, comprising high-speed cold-working the high-speed cold-working steel according to any one of claims 1 to 10 at a working temperature of 200 ° C or lower.   A method for producing a high-speed cold-worked part, comprising high-speed cold-working the steel for high-speed cold work according to any one of claims 1 to 10 at a strain rate of 100 / sec or more. After the steel having the component composition according to any one of claims 1 to 10, and heated to Ac ₃ point + 30 ° C. or higher temperatures, and hot working at Ac ₃ point + 30 ° C. or higher temperature range, 0. A method for producing steel for high-speed cold working, characterized by cooling to 500 ° C. or lower at a cooling rate of 5 ° C./s or higher. The steel material having the component composition according to any one of claims 1 to 10 is heated to a temperature of Ac ₃ point + 30 ° C or higher and then cooled to 500 ° C or lower at a cooling rate of 0.5 ° C / s or higher. A method for producing steel for high-speed cold working.