JP2001303189A - Wire-shaped or bar-shaped steel whose rise in deformation resistance in heat generating region by working as well as at room temperature is suppressed, and machine parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a wire-shaped or bar-shaped steel excellent in cold workability in an as-hot-rolled state even if spheroidizing annealing treatment is omitted. SOLUTION: In the wire-shaped or bar-shaped steel, the refinement of ferrite crystal grains is suppressed by providing a composition which contains at least either of <=0.0055% B and <=0.035% Zr and also contains 0.0005-0.0070% N and in which B, Zr and N satisfy the following inequality: -0.0010<=[N]-1.3[B]-0.15[Zr]<=0.0020 (where each symbol of element in brackets represents the content of the element).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear or bar steel (hereinafter, sometimes abbreviated as steel) excellent in cold workability, and a mechanical part obtained by using the steel. In the present invention, "excellent in cold workability" means:
It means that "the increase in deformation resistance in the room temperature and the heat generation region of the processing is suppressed". That is, the present invention provides bolts, screws,
Nut, socket, ball joint, inner tube, torsion bar, clutch case, cage, housing, hub, cover, case, washer, tappet, saddle, bulg, inner case, clutch, sleeve, outer race, sprocket, core, stator , Anvils, spiders, rocker arms, bodies, flanges, drums, fittings, connectors, pulleys, fittings, yokes, bases, valve lifters, spark plugs, mechanical parts, electrical parts, etc., cold forging, cold forging, In manufacturing by cold working such as cold rolling, the present invention relates to a linear or rod-shaped steel and a machine part in which an increase in deformation resistance in a room temperature and a heat generation region of a working is suppressed even when hot rolling is performed without performing softening heat treatment. Things.

[0002]

2. Description of the Related Art Cold working is more efficient than hot working and cutting, and has a good yield of steel. Therefore, it is possible to efficiently manufacture mechanical parts such as bolts, nuts and screws, and electrical parts. It is widely used as a method for doing this.

[0003] Therefore, the steel used for such cold working is required to be essentially excellent in cold workability. Specifically, it is necessary that deformation resistance during cold working is low (working specific gravity is low) and ductility (elongation, drawing) is high. If the deformation resistance of steel is high, the life of a tool used for cold working is reduced, while if the ductility is low, cracks are liable to occur during cold working, which causes defective products.

Conventionally, cold rolling is performed after descaling a rolled wire or a steel bar by pickling, coating, drawing a wire by cold drawing (a working ratio of 10 to 40%). Was common. However, this method is effective when the cold working rate is low and the working load is low. However, as the working rate increases, the working life of the tool for cold working is shortened when the working load increases, and this method can be adopted. Did not.

[0005] Therefore, when the working load during cold working is high or when cracks occur during cold working, heat treatment such as low-temperature annealing, annealing, and spheroidizing annealing is performed before cold working. Accordingly, a method of cold working in a state where the steel material is softened and the ductility is enhanced by that is widely used.

However, the above heat treatment has a problem that a long heat treatment of several hours to several tens of hours is required. Therefore, for the purpose of improving productivity and energy saving measures, and further reducing costs, there is a strong demand for the development of a linear or rod-shaped steel excellent in cold workability that can omit heat treatment such as spheroidizing annealing. I have.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an excellent cold workability as hot rolling even if the spheroidizing annealing treatment is omitted. It is an object of the present invention to provide a linear or rod-shaped steel and mechanical parts such as bolts and nuts obtained by using the linear or rod-shaped steel.

[0008]

SUMMARY OF THE INVENTION A wire or rod-shaped steel excellent in cold workability in the sense that the increase in deformation resistance in the room temperature and the heat generating region of the work according to the present invention which has solved the above-mentioned problems is suppressed. , B: 0.0055% or less, Zr:
By containing at least one of 0.035% or less, and containing N: 0.0005 to 0.0070%, and B, Zr and N satisfy the following formula, refinement of ferrite crystal grains Has a gist where it is suppressed. -0.0010≤ [N] -1.3 [B] -0.15 [Z
r] ≦ 0.0020 (where [] represents the content of each element)

This is because in order to exhibit desired characteristics,
In fixing solid solution C and solid solution N, which govern the increase in deformation resistance, ferrite grains are not refined.
It has been identified based on the finding that the addition of Zr or Zr is effective.
This means that it is effective not to add ferrite crystal grain refining elements such as i, Nb, and V as much as possible. In this sense, at least one of Ti, Nb and V is contained, and Nb and V are 0.080 in total.
% Or less (including 0%), Ti: 0.020% or less (0%
Are preferred embodiments of the present invention.

[0010] Further, the steel of the present invention contains C as a basic component.
: 0.001 to 0.40%, Si: 0.40% or less (including 0%), Mn: 0.15 to 1.8%. Al: 0.01 to 0.06
%, Cr: 0.01 to 0.50% P: 0.001 to 0.015%, S: 0.015%
It is preferable to contain the following (including 0%). In addition to the above components, steels containing other trace components and the like within a range that does not impair the function of the present invention are also included in the technical scope of the present invention.

[0011] Machine parts obtained by using the above-mentioned linear or rod-shaped steel are also included in the scope of the present invention.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In order to provide a steel excellent in cold workability as it is hot-rolled, the inventors of the present invention have been particularly concerned with "increase in deformation resistance at room temperature and reduction of deformation resistance in a heat-generating region." The cold workability is improved by reducing the rise. " Of the cold workability, the focus on deformation resistance was not only the deformation resistance at room temperature, which is governed by the initial strength, but also the deformation aging behavior due to solid solution C and solid solution N, Also has an effect.

As a result, in order to achieve both the problem of “reducing the increase in deformation resistance at room temperature and reducing the increase in deformation resistance in the heat-generating region”, it is necessary to reduce the increase in deformation resistance in cold workability. In fixing the dominant solid solution C and solid solution N, ferrite crystal grains such as Ti, Nb, and V are not added, but ferrite crystal grains are not refined (rather, they are coarsened). It has been found that when B or Zr is added, the strengthening due to the refinement of ferrite crystal grains is suppressed, the tensile strength is reduced, and the increase in deformation resistance at room temperature is also reduced. As a result, the cold workability is improved.
Therefore, the present invention has a technical idea that, in fixing solid solution C and solid solution N, an optimum carbide / nitride forming element is selected and added from the viewpoint of miniaturization of ferrite crystal grains. Things.

As described above, it is possible to achieve the object of improving cold workability in the sense of reducing the increase in deformation resistance at room temperature by reducing the initial strength and reducing the increase in deformation resistance in the working heat generating region. For this purpose, it is more effective not to make the ferrite crystal grain size smaller;
Instead of adding carbide and nitride forming elements non-selectively and randomly, or from the viewpoint of precipitation strengthening, for the purpose of fixing solid solution C and solid solution N as in the prior art, ferrite crystal grains are refined. From the viewpoint of suppression of strengthening, it is effective to appropriately select the type of carbide / nitride forming element to be added '' is not conventionally known, and is a finding first found by the present inventors. is there.

[0015] As in the present invention, a method for producing steel excellent in cold workability even when the spheroidizing annealing treatment is omitted is as follows.
Although proposed so far, the above-described technical idea of the present invention is neither disclosed nor suggested.

For example, Japanese Patent Publication No. 61-35249 discloses a method of reducing the solid solution C and the solid solution N by controlling the rolling conditions and cooling conditions, suppressing the work hardening caused by strain aging, and reducing the deformation resistance. Is disclosed. However, regarding the composition of the components in the steel, in order to prevent an increase in the deformation resistance due to the strain aging, A is used for the purpose of suppressing the strain aging due to solid solution N.
It merely describes a general description such as adding l and precipitating N as AlN.

Japanese Patent Application Laid-Open No. 57-63635 discloses A
_c1 transformation point, dissipate sufficiently aggregated cementite by 5 hours or more to a temperature not less than 50 ° C. from the transformation point A _c1, by fixing dissolved N by controlling the Al content, the machining tool life A method of making an enhanced cold forged bar is disclosed. This gazette is based on the knowledge that "if the temperature after hot rolling is maintained within a predetermined range, cementite can be coagulated and precipitated, and the strength can be reduced." From the viewpoint that cracking during cold forging is likely to occur when it occurs, it is necessary to control the components in the steel and to include Al or the like that prevents the steel from coarsening. Ferrite grains are coarsened (instead of refined) from the viewpoint of reducing the deformation resistance at room temperature by reducing the ferrite grains. The present invention has a completely different technical idea from the present invention in which the grain size number is controlled in relation to the ferrite grain size number in the ferrite structure in the outermost layer of the rolled material.

Further, Japanese Patent Application Laid-Open No. Hei 8-260047 discloses that in order to reduce solute N which causes strain aging in cold forging, N
And hot rolling with specifying Al / N; a thermomechanical heat treatment step of performing plastic working of 50% or more in a predetermined temperature range in the final stage of hot rolling; and 300 to 400 after cooling following the thermomechanical heat treatment. There is disclosed a method for producing a bar material wire rod for cold forging, which includes an overaging treatment of heating to a temperature range of 3 ° C. for 3 hours or more. This gazette states, "In order to increase the strain aging resistance by overaging after cold rolling, it is effective to reduce the ferrite grain size. Giving a degree of work has a critical effect on the refinement of ferrite grains and the resulting suppression of strain aging and improvement of ductility. Is very effective in suppressing the occurrence of strain aging. " However, the present inventors have studied that, when the ferrite grain size is reduced as in the above method, the occurrence of strain aging is suppressed, and the deformation resistance at a high temperature of 150 to 300 ° C. is reduced, but the tensile strength is increased. Therefore, it was found that the deformation resistance at room temperature increased, cracks and the like were remarkably generated, and the cold workability was reduced. From the viewpoint of "reducing the initial strength and increasing the cold workability by reducing the deformation resistance at room temperature" as in the present invention, from the viewpoint of reducing the ferrite grain size as described in the above-mentioned publication, It is not preferable, but rather, it is more effective to make the ferrite grain size coarser, contrary to the miniaturization. In this sense, both have completely different technical ideas.

Further, Japanese Patent No. 2599466 discloses that Ti
Is added in the range of (Ti-3.4N) / C = 4 to 6 to fix C and N to make them non-ageing, thereby preventing the yield ratio after cold working from increasing. A specific structural steel is disclosed. This publication has excellent non-aging properties,
In addition, in order to satisfy a low yield ratio and to secure a predetermined strength level, the properties of the ferritic single-phase steel are utilized to the utmost. Immobilization of C and N by Ti from the viewpoint that immobilization of C and N which are the type solid solution atoms is essential (that is, immobilization of C and N by adding Ti or more equivalents of C and N). On the other hand, if Ti is added excessively, coarsening of TiC occurs, and precipitation strengthening by TiC cannot be used, and it is difficult to increase the strength. Accordingly, the above publication only discloses "immobilization of solid solution C by adding Ti; as a result, an increase in strength due to precipitation strengthening of the resulting TiC".
No technical idea is disclosed in which a nitride-forming element such as N or B is added to suppress the refinement of ferrite crystal grains and to suppress strengthening due to the refinement. Moreover, since Ti, which is the most important component in the above publication, is a precipitation strengthening element,
"Increase in deformation resistance at room temperature due to initial strength decrease →
In order to solve the problem of the present invention of "improvement of cold workability", it is necessary to reduce the addition amount of Ti as much as possible,
The composition in steel is completely different from the above-mentioned publication in which Ti is actively added (compared with the present invention) in a large amount.

On the other hand, in JP-A-3-287743, instead of adding Ti as described above, Nb is converted to Nb / Nb.
A low carbon non-aging wire controlled to (C + N) ≧ 7 is disclosed. This gazette states that "Ti added for the purpose of suppressing aging of C and N is simultaneously reduced in S which is effective for machinability.
Reacts with Ti to form TiS or Ti ₂ S, and S is fixed, so that the effect of S is not sufficiently exhibited. ” It has been proposed with the aim of suppressing the wire and having excellent machinability. Therefore, even if the above publication is carefully examined, there is no disclosure at all of the addition of a nitride-forming element such as Zr or B in order to suppress the refinement of ferrite crystal grains as in the present invention. Moreover, since Nb, which is the most important component in the above publication, is a precipitation strengthening element,
"Increase in deformation resistance at room temperature due to initial strength decrease →
In order to solve the problem of the present invention of "improving cold workability", it is necessary to reduce the amount of Nb added as much as possible.
The composition in steel is completely different from that in the above publication in which Nb is actively added (compared to the present invention) in a large amount.

Hereinafter, requirements for specifying the present invention will be described.

As described above, the linear or bar-shaped steel of the present invention has a technical idea in that cold workability is improved by suppressing an increase in strength due to refinement of ferrite crystal grains. In order to realize such a technical idea, it is necessary to control the components of the linear or bar steel as follows.

First, regarding the nitride-forming element, B:
0.0055% or less, Zr: 0.035% or less, and N: 0.0005 to
It contains 0.0070%, and B, Zr and N must satisfy the following formula. −0.0010 ≦ [N] −1.3 [B] −0.15 [Z
r] ≦ 0.0020 (where [] represents the content of each element)

As described above, in the present invention, instead of adding a ferrite grain refining element such as Ti as a nitride-forming element, B and / or Zr which do not refine (rather coarsen) ferrite grains are added. It is to be added. Therefore, the above element is not added as, for example, B as a quenching improving element as in the prior art, but is combined with N to form BN.
/ ZrN to suppress dynamic strain aging during cold working, suppress solid solution strengthening of N,
Since 1N is precipitated, it is added for the purpose of suppressing ferrite crystal grains from becoming finer and increasing the strength.
In order to exhibit such an effect effectively, B is added to 0.00
05% or more (more preferably 0.0010% or more), Z
It is recommended that r be added in an amount of 0.005% or more (more preferably 0.010% or more). However, B is 0.00
If added in excess of 55%, the cold workability will be adversely affected. More preferably, it is 0.0040% or less. Similarly, when Zr is added in excess of 0.035%,
Deformability is reduced, and adversely affects cold workability. More preferably, it is 0.025% or less.

The above-mentioned B and Zr may be added alone, or both may be added. In any case, B and Zr are added for the purpose of fixing solid solution N only. Therefore, basically, it is preferable to appropriately adjust the amount of the element to be added according to the finally contained N. if,
If N in steel is always suppressed to 0.0020% or less, there is no need to actively add these elements. This is because even if such a small amount of N exists, it is considered that there is little possibility that the cold workability is adversely affected.

Here, N is 0.0005 to 0.007.
It is recommended to control in the range of 0%. Since N forms a solid solution in ferrite and causes strain aging during cold working, it is preferable that N is as small as possible. From such a viewpoint, the upper limit is set to 0.0070%. More preferably, it is 0.0050% or less. On the other hand, if it is less than 0.0005%, it is difficult to perform industrial production commensurate with cost. More preferably, it is 0.0010% or more.

Further, in the present invention, it is recommended that B, Zr, and N satisfy the following expressions. −0.0010 ≦ [N] −1.3 [B] −0.15 [Z
r] ≦ 0.0020 (where [] represents the content of each element)

This is an equation provided to effectively exert the effect of immobilizing solid solution N by B and / or Zr.
First, the lower limit of the above expression specifies B and Zr that fix the necessary minimum N, and the lower limit is -0.0010
Above, even if B is excessively added to fix N, it does not contribute to hardenability, and Zr
It has been confirmed that even if N is excessively added to fix N, it precipitates as sulfides and carbides, and thus has no adverse effect on the improvement of cold workability. More preferably, the lower limit of the above formula is -0.0005.

The upper limit of the above equation specifies the upper limit of the amount of N to be added in relation to the amounts of B and Zr.
If the upper limit exceeds 0.0020, excess N becomes Br / Z.
The number of AlNs other than r increases and ferrite crystal grains are refined. If the upper limit of the above formula is 0.0020 or less, even if N combines with Al to form AlN, the ferrite crystal grains are not refined in hot rolling, and the hot rolling is not performed. It has been confirmed that the deformation resistance can be reduced to the same level as that of the spheroidized annealed material and the deformability can be ensured even as it is. More preferably,
The upper limit of the above equation is 0.0015.

The above is a description of the elements involved in the nitride-forming element used in the present invention. In the present invention, the following commonly used carbonitride-forming elements can be controlled as follows. Recommended.

It contains at least one of Ti, Nb and V, and contains Nb and V in a total of 0.080% or less (including 0%), and Ti: 0.020% or less (including 0%). The element V is a carbonitride forming element, and is effective for fixing C and N.
The strength is increased due to precipitation strengthening or strengthening by grain refinement; since addition contributes to grain refinement after hot rolling, the purpose of the present invention is to reduce the initial tensile strength, It is a rather harmful element in improving cold workability by reducing deformation resistance at room temperature. " Therefore, it is preferable that the addition amount of the above elements is as small as possible.
It is up to 80% or less (including 0%) and Ti: 0.020% or less (including 0%). In particular, Ti is most easily bonded to N among the above-mentioned elements, and when added in combination with B, exhibits an effect of improving hardenability. Therefore, it is recommended that Ti be controlled in the above range. More preferably, Nb and V are 0.015% or less in total and Ti: 0.010% or less; even more preferably, Nb and V are 0.010% or less in total, Ti: 0.005% or less. It is.

The components in steel for embodying the technical idea of the present invention have been described above. In the present invention, it is recommended to further control the following elements as follows.

C: 0.001 to 0.40% C is an essential element for imparting the required strength of the steel material. If the content is less than 0.001%, the desired strength cannot be obtained, and if the concentration is controlled to such a low level, the cost is industrially high and the method is not economical. It is preferably at least 0.003%, more preferably at least 0.005%, even more preferably at least 0.01%, particularly preferably at least 0.05%. On the other hand, if it exceeds 0.40%, the pearlite fraction increases, and the desired deformability cannot be obtained. Preferably 0.3
5% or less.

Si: 0.40% or less (including 0%) Si is a useful element as a deoxidizing agent, but when added in excess, working load in cold working due to solid solution strengthening (generally synonymous with deformation resistance) ) Not only increases but also lowers the deformability. Therefore, the upper limit is set to 0.40% from the viewpoint that it is preferable to reduce as much as possible. 0.
This is because when the content exceeds 40%, the deformability is significantly reduced. It is more preferably at most 0.25%.

Mn: 0.15 to 1.8% Mn is an element useful not only for deoxidation and desulfurization but also for improving quenching and tempering softening resistance during heat treatment after cold working. In order to effectively exert such an effect, it is preferable to add 0.15% or more. More preferably, it is 0.20% or more. However, if added in excess, the growth rate of ferrite / pearlite after hot rolling is reduced, and bainite harmful to cold workability is likely to be generated. Therefore, the upper limit was set to 1.8%. More preferably, it is 1.5% or less.

It is needless to say that the amounts of C, Si and Mn are only preferable ranges, and that values outside the above ranges are not included in the scope of the present invention. For example, JIS C 2503, JIS
G4051, JIS G4106, JIS G35
06, JIS G 3507, etc. may be applied to the present invention. If there is a special situation that the component range specified in JIS cannot be deviated, it is recommended to be added within the range specified in JIS. Is done. However, as long as the strength immediately after cold working and the strength after cold working and after quenching and tempering are matched, the component range specified in JIS may be intentionally deviated.

Sol. Al: 0.01 to 0.06% Al is an element useful for deoxidation. However, Al
Nitride (AlN) is easily formed next to r, Ti, B, and Nb. Since the increase of AlN causes the crystal grains to be refined, it is preferable that AlN is not generated as much as possible from the point of the present invention. Therefore, it is preferable that the amount of Al added is as small as possible, but it does not deviate from the above point. You may add in the range. From such a viewpoint, in the present invention, the lower limit is set to 0.
It was set to 01%. However, if the addition is excessive, not only the above-mentioned effect is saturated, but also the ferrite crystal grain refining effect due to the formation of AlN becomes remarkable.
06%. More preferably 0.015% or more,
0.05% or less.

Cr: 0.01 to 0.50% Cr is an element that promotes ferrite-pearlite transformation during hot rolling and precipitates carbide without significantly contributing to an increase in strength. The lower limit is set to 0.01% in order to effectively exert such effects. It is more preferably at least 0.03%. However, if it exceeds 0.50%, the tensile strength becomes too high. It is more preferably at most 0.30%.

Further, the following elements can be added.

P: 0.001 to 0.015% or less (0%
Including) P is effective as hardenability improving element, in order to develop this function effectively, defining the lower limit to 0.001%.
However, if added in excess of 0.015%, microsegregation occurs during solidification, segregates at the grain boundaries during hot rolling to embrittle the grain boundaries, and as a result, the risk of cracking during cold working increases. It is more preferably at most 0.010%.

S: 0.015% or less (including 0%) S mainly forms sulfide-based inclusions of MnS, segregates at the grain boundaries during hot rolling, embrittles the grain boundaries, and cools down. The upper limit was set to 0.015% because of the possibility of cracking during cold working. It is more preferably at most 0.010%.

The steel of the present invention contains the above-mentioned components, and the balance is substantially iron. However, other than the above-mentioned components, allowable components which are acceptable as long as the effects of the present invention are not impaired may be added. And impurities.

Next, a method for producing a wire or a rod according to the present invention will be described.

In order to obtain a desired structure intended in the present invention, a steel slab is heated to a temperature of 800 to 1100 ° C.
After rolling to a predetermined wire diameter in the range of 0 to 1100 ° C., cooling is performed mainly at a cooling rate of 600 to 6000 ° C./min by water flow.
It is necessary to cool to 00 to 800 ° C and control the temperature recovered by reheating (adjustment cooling start temperature) to 750 to 875 ° C. Hereinafter, each requirement will be described.

Heating temperature of steel slab: 800-1100 ° C. This heating temperature is set in order to suppress the refinement of the ferrite crystal grain size and reduce the deformation resistance.
Here, the "heating temperature of the slab" is measured by a radiation thermometer, and strictly speaking, "the surface temperature of the slab"
Means If the heating temperature exceeds 1100 ° C., the ferrite crystal grain size becomes too large, and the ductility is reduced. Preferably it is 1050 ° C. or less, more preferably 100 ° C.
0 ° C. or less. On the other hand, when the heating temperature is lower than 800 ° C., the hot deformation resistance becomes excessively high, which may cause abrasion of the rolling roll, a trip of the rolling motor, and the like, resulting in a production hindrance. Preferably it is 850 ° C or higher.

Rolling temperature: 750 to 1100 ° C. This temperature is the same at the time of rolling as at the time of heating the slab.
It is set to suppress the refinement of the ferrite crystal grain size and reduce the deformation resistance. Here, the "rolling temperature" is measured by a radiation thermometer,
Strictly, it means “surface temperature of billet”. 1100 ° C
When the rolling is performed beyond the range, the ferrite crystal grain size becomes too large, and the ductility is reduced. Preferably 1050 ° C
Or less, more preferably 1000 ° C. or less. On the other hand, when the rolling temperature is lower than 750 ° C., not only the ferrite crystal grain size becomes small, but also unnecessary dislocations are likely to remain in the ferrite grains without being completely recrystallized, and the strength after rolling increases. Preferably it is 850 ° C or higher. In consideration of an increase in the load of the rolling roll, a decrease in dimensional accuracy, prevention of generation of surface flaws, and the like, it is practically recommended to set the rolling temperature to about 875 to 975 ° C.

Adjusted cooling start temperature: 750 to 875 ° C. The adjusted cooling start temperature means that the outermost surface temperature is at least about 500 to 800 ° C. at a cooling rate of 600 to 6000 ° C./min mainly using water as a medium after final rolling. After being cooled to a temperature, the temperature recovered by the heat (recuperation) of the slab while being wound around a cooling zone (cooling conveyor). 875 ° C
At higher temperatures, the scale becomes thicker and not only is it easier for troubles to occur in the subsequent descaling process,
Since the cooling time becomes longer, productivity is hindered. Preferably it is 850 ° C or lower. On the other hand, when the temperature is lower than 750 ° C., martensite in the surface layer generated during cooling is not recovered by reheating, and tempered martensite is generated, and the steel becomes hard and brittle, which is not suitable for cold working. Preferred at practical operating levels is 775 ° C or higher.

Cooling rate: 0.05 to 5 ° C./sec (600 ° C.
Up to 600 ° C after reaching the adjusted cooling start temperature
The cooling rate at the time of cooling to the maximum is specified. As in the present invention, in order to control the structure to a ferrite structure or a ferrite-pearlite structure, it is preferable to reduce the cooling rate. Therefore, the upper limit is set to 5 ° C./sec. It is recommended that the temperature be 0.2 ° C./sec or more and 3 ° C./sec or less in consideration of quality stability in industrial production.

According to the present invention, excellent cold workability can be obtained even with a hot-rolled wire or steel bar. However, the wire or the steel bar can be dipped in an acid (hydrochloric acid, sulfuric acid, etc.) bath, After removing the scale by mechanically applying strain, etc., pre-drawing of zinc phosphate film, calcium phosphate film, lime, etc., and drawing using metal soap etc. as a lubricant, drawing, cold rolling etc. The same excellent cold workability can be obtained in the steel wire subjected to the above.

Hereinafter, the present invention will be described in detail with reference to examples.
However, the following examples do not limit the present invention,
All modifications and alterations without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

[0051]

EXAMPLES Using test steels having the component compositions shown in Table 1 (units in the table are mass%), wires were obtained under various production conditions shown in Tables 2-4. Here, No. A, B and C are each
WRCH10K, SW specified in JIS G 3507
RCH20K and SWRCH35K (current process materials). A1 is the one obtained by omitting the spheroidizing annealing treatment of A,
B1 to B4 were obtained by omitting the spheroidizing annealing treatment of B, C1
Means a product produced for the purpose of omitting the spheroidizing annealing of C, and B5 to B8 represent the total (B) of P and S (B5), N and Zr (B6), Ti (B7), and Nb + B, respectively.
8) is steel outside the preferred range of the present invention.

The wire obtained in this manner was shaped into a test piece for compression test as shown in FIG. 1 (the shape recommended by the Japan Society for Plastic Processing in “Forging and Plastic Working Technology Series 4 (Corona) p155)”. (Diameter of steel wire × 1.5), and this was used as an upsetting test piece, and upsetting was performed using a constrained pressure-resistant plate with concentric grooves as an upsetting platen.

The deformation resistance was measured at a compressibility of 60% and at two levels: room temperature and 300 ° C. for preheating. The deformability is No. For A, A1, B, B-1 to B8, 30 pieces were tested at a compression ratio of 80% to determine the presence or absence of cracks; C and C-1 were similarly tested at a compressibility of 70% from the viewpoint of the deformability of the current steel,
The presence or absence of cracks was determined.

The results obtained are shown in Tables 2 to 4. FIG. 2 shows that [N] -1.3 [B] -0.15 [Z
r]} and the deformation resistance (60% compression ratio, room temperature); FIG. 3 shows {[N] -1.3 [B] -0.15 [Z]
[r]} and the deformation resistance (60% compression ratio, 300 ° C.) are shown by graphs. In addition, in FIGS. 2 and 3, as for {}, the value of {[N] -1.3 [B] -0.15 [Zr]} satisfies the requirements of the present invention, and the component composition and rolling conditions of the present invention are also different. Examples of the present invention satisfying preferable requirements; {is a value of {[N] -1.3 [B] -0.15 [Zr]}, but satisfies the requirements of the present invention, but the component in steel or the rolling condition is not Reference example that does not satisfy the preferable requirements of the invention;
The value of -1.3 [B] -0.15 [Zr]} is a comparative example that does not satisfy the requirements of the present invention.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

[0058]

[Table 4]

From the above results, the following can be considered.

First, in Table 2, No. 3 is steel type A1 in Table 1.
[N] -1.3 [B]-
Since the value of 0.15 [Zr]} is controlled within the range of the present invention, the deformation resistance is reduced to the deformation resistance (No. 1 in Table 2) comparable to that of the current steel A without spheroidizing annealing. I was able to. In addition, No. omitting the spheroidizing annealing treatment of the working steel.
In the case of No. 2, since the deformation resistance at 300 ° C. is higher than the deformation resistance at room temperature, it can be seen that it is not suitable for cold forging in the working heat generation region.

Next, in Table 3, No. Nos. 7 to 16 are examples using steel types B1 to B8 in Table 1, respectively. this house,
A steel material whose value of {[N] -1.3 [B] -0.15 [Zr]} satisfies the range of the present invention and whose steel component also satisfies the preferable range of the present invention, No. manufactured under preferable rolling conditions. In each of Nos. 6, 10 and 12, the deformation resistance (No. 4 in Table 3) could be reduced to the same level as the spheroidizing of the working steel B without performing the spheroidizing annealing.

On the other hand, in Table 3, No. 13 is B5 in which P and S are out of the preferred range of the present invention; 14 is N
And Br deviating from the preferred range of the present invention;
o. 15 is B7 in which Ti is out of the preferred range of the present invention.
No. No. 16 is an example using each of B8 whose sum of Nb + B is out of the preferable range of the present invention, and could not be reduced to a desired deformation resistance.

In addition, in Table 3, Nos. 7 to 9 are examples in which the rolling conditions do not satisfy the preferred steps of the present invention, and could not be reduced to the desired deformation resistance.

It should be noted that N for which the spheroidizing annealing treatment of the working steel was omitted.
o. In No. 15, since the deformation resistance at 300 ° C. is higher than the deformation resistance at room temperature, it can be seen that it is not suitable for cold forging in the working heat generation region.

Next, in Table 4, No. 19 is steel type C in Table 1.
This is an example of the present invention using No. 1 and Δ [N] −1.3 [B] −
Since the value of 0.15 [Zr]} is controlled within the range of the present invention, the deformation resistance is reduced to the deformation resistance (No. 17 in Table 4) comparable to that of the spheroidizing steel C without spheroidizing annealing. I was able to. It should be noted that N was obtained by omitting the spheroidizing annealing of the working steel.
o. In No. 18, since the deformation resistance at 300 ° C. is higher than the deformation resistance at room temperature, it can be seen that it is not suitable for cold forging in the working heat generation region.

[0066]

According to the present invention, as described above, even if the spheroidizing annealing treatment is omitted, it is possible to efficiently provide a linear or rod-shaped steel excellent in cold workability as it is in hot rolling. I was able to. In particular, the linear or bar steel of the present invention,
During cold working, it is extremely useful in that the deformation resistance in a temperature range (approximately 100 to 350 ° C.) caused by the heat generated by working can be reduced.

[Brief description of the drawings]

FIG. 1 is a view showing a shape of a test piece for a compression test used in an example.

FIG. 2 {[N] -1.3 [B] -0.15 [Zr]}
And the deformation resistance (60% compression ratio, room temperature).

FIG. 3 {[N] -1.3 [B] -0.15 [Zr]}
6 is a graph showing the relationship between the deformation resistance (60% compression ratio and 300 ° C.).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C21D 8/06 C21D 8/06 A

Claims (5)

[Claims] 1. A composition containing at least one of B: 0.0055% or less (mass%, the same applies hereinafter), Zr: 0.035% or less, and N: 0.0005 to 0.0070%. In addition, B, Zr, and N satisfy the following formulas, whereby the refinement of ferrite crystal grains is suppressed. Or bar steel. −0.0010 ≦ [N] −1.3 [B] −0.15 [Z
r] ≦ 0.0020 (where [] represents the content of each element) 2. It contains at least one of Ti, Nb and V, and Nb and V are suppressed to 0.080% or less (including 0%) in total and Ti: 0.020% or less (including 0%). The linear or bar-shaped steel according to claim 1, which is a steel. 3. C: 0.001 to 0.40%, Si:
0.40% or less (including 0%), Mn: 0.15 to 1.
The linear or bar-shaped steel according to claim 1 or 2, which contains 8%. 4. The sol. Al: 0.01 to 0.06%, Cr: 0.01 to 0.50% P: 0.001 to 0.015%, S: 0.015% or less (including 0%) The linear or bar-shaped steel according to any one of claims 1 to 3. 5. A machine part obtained by using the linear or bar steel according to claim 1.