JP3474545B2 - Machine parts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] TECHNICAL FIELD The present invention is excellent in cold workability.
Wire or bar steel (hereinafter sometimes abbreviated as steel)
The present invention relates to a mechanical part obtained by using the method. The present invention
"Excellent in cold workability" in
The rise in deformation resistance in the heat generating area was suppressed. "
You. In other words, the present invention provides a hot pressure without a softening heat treatment.
Suppression of deformation resistance at room temperature and in the heat generation area of processing
Controlled linear or bar steel is used for cold forging and cold
It is obtained by performing cold working such as cold heading and cold rolling.
Bolts, screws, nuts, sockets, ball joins
G, inner tube, torsion bar, clutch case
, Cage, housing, hub, cover, case, seat
Gold, tappet, saddle, bulg, inner case, club
Switch, sleeve, outer race, sprocket, core
ー, stator, anvil, spider, rocker arm
System, body, flange, drum, fitting, connector,
Pulley, bracket, yoke, base, valve lifter, spa
Related to mechanical parts, electrical parts, etc.
is there. [0002] 2. Description of the Related Art Cold working is more efficient than hot working and cutting.
High productivity and good steel yield?
Bolts, screws, nuts, etc.
It is widely used as a method for efficient production. [0003] Therefore, steel used for such cold working
Is required to be inherently excellent in cold workability.
You. Specifically, the deformation resistance during cold working is low (working ratio
(Low weight) and high ductility (elongation, drawing)
It is. Tools used for cold working with high deformation resistance of steel
Life is shortened, while low ductility results in cold working
Occasionally, cracks easily occur, which causes defective products. Conventionally, a rolled wire or steel bar is pickled.
After descaling, coating, and cold drawing
After drawing and drawing (working rate 10-40%), cold working
It was common to do. However, this method
Is effective when the cold working rate is low and the working load is low.
However, as the processing load increases with the increase in the processing rate,
Tool life for machining is shortened and cannot be adopted
Was. Therefore, when the working load during cold working is high,
If cracks occur during cold working,
Heat treatment such as low-temperature annealing, annealing, and spheroidizing annealing
And thereby softened the steel and increased its ductility
A method of cold working in a state is widely used. However, the heat treatment requires several hours to several tens of hours.
With the problem of requiring long-term heat treatment
I have. Therefore, productivity improvement, energy saving measures,
Spheroidizing annealing, etc. for the purpose of cost reduction
Linear or excellent in cold workability that can omit heat treatment
The development of bar steel is eagerly awaited. [0007] SUMMARY OF THE INVENTION The present invention has arrived at the above circumstances.
The purpose was to achieve the spheroidizing annealing process.
Excellent cold workability with hot rolling even if the process is omitted
Bolts and high-strength steel
It is to provide machine parts such as nuts. [0008] A book which has solved the above-mentioned problems
In the mechanical part according to the present invention, the components in steel satisfy the following (A).
The structure is made of linear or bar steel satisfying the following (B)
The average area of dislocation cells is
0.18-0.50 μm^TwoHave a gist where
Things. (A) C: 0.05 to 0.40%, Si: 0.40%
Below (including 0%), Mn: 0.15 to 1.8%, so
l. 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%), Ti, Nb
And at least one of V and Nb and V in total
0.080% or less, Ti: suppressed to 0.020% or less
B: 0.0055% or less, Zr: 0.
035% or less, and
N: 0.0005-0.0070%
In addition, B, Zr and N satisfy the following formula, and -0.0010 ≦
[N] -1.3 [B] -0.15 [Zr] ≦ 0.0020 (wherein [
 ] Represents the content of each element) balance: substantially iron
The (B) Substantially ferrite structure or ferrite and par
It has a mixed structure of light, and ranges from the center to the diameter / 8 of the rolled material
The ferrite grain number in the surrounding ferrite structure is 4 to
No. 9 in the ferrite structure in the outermost layer of the rolled material
The ferrite grain size number is 4 to 10 and the highest
Ferrite grain number in the ferrite structure in the surface layer
Ferrite structure in the range from center to diameter / 8 of the rolled material
The difference in the ferrite grain size numbers in the table is 0 to 1. In the present invention, the above-described bolt, screw,
Including mechanical parts such as nuts and electrical parts, etc.
Products ". The "cell" of the above "dislocation cell" is gold
When you look at a genus tissue with a microscope or an electron microscope, it looks like a cell
The term "dislocation cell" is a generic term for what appears to be a shape.
The part that is entangled in the mesh has almost no dislocation
It means the processing structure in the enclosed state. By cold working or forging
Dislocations enter the steel crystal, but these dislocations
By having a non-uniform cell structure rather than mating,
Become stable. In measuring the average area of a dislocation cell,
As will be described later, a TEM
(Transmission electron microscope, magnification 15,000 times)
Average value of the area of dislocation cells at the structure observation position shown in Fig.
Is calculated. [0012] BEST MODE FOR CARRYING OUT THE INVENTION
In order to provide steels with excellent cold workability, especially at room temperature
Reduction of shape resistance and deformation resistance in the heat generating area
To improve cold workability. "
We have been studying hard. Deformation resistance especially in cold workability
Focused on deformation resistance at room temperature governed by initial strength
In addition, the behavior of strain aging due to solid solution C and solid solution N
Because it also affects the deformation resistance in the heating area
is there. As a result, the results are as follows.
And reduction of deformation resistance in the heat-generating region "
In order to control the deformation resistance,
To fix solid solution C and solid solution N
Or ferrite structure that constitutes the internal structure of bar-shaped steel
Or ferrite-pearlite
By suppressing the strengthening due to the refinement of crystal grains,
Tensile strength is reduced, deformation resistance at room temperature is also reduced,
It was found that the cold workability was improved. Like this
The initial tensile strength to reduce the deformation resistance at room temperature
At the same time as reducing the deformation resistance in the heat generating area.
To achieve the task of improving cold workability in the meaning
It is more effective to keep the ferrite grain size
That is, in the range from the center of the rolled material to the diameter / 8
Ferrite grain number in a certain ferrite structure is 4-9
Blow in the ferrite structure in the outermost layer of the rolled material
The particle size number is 4 to 10 and the center of the rolled material is
Ferrite grain size in ferrite structure in the range of diameter / 8
It is effective to make it larger than the number "
Previously unknown and first discovered by the present inventors
It is a good finding. As in the present invention, the spheroidizing annealing treatment is omitted.
Even so, the method of producing steel with excellent cold workability is
Although previously proposed, the technology of the present invention described above
The idea is neither disclosed nor suggested. [0015] For example, Japanese Patent Publication No.
Solid solution C and solid solution by controlling the rolling and cooling conditions
N to reduce work hardening caused by strain aging
A method for reducing the shape resistance is disclosed. However, in steel
With regard to the component composition of, increase in deformation resistance due to strain aging
A for the purpose of preventing strain aging due to solid solution N
l to precipitate N as AlN.
It is merely described. Japanese Patent Application Laid-Open No. 57-63635 discloses A
Temperature below the c1 transformation point, not less than 50 ° C from the Ac1 transformation point
By holding the cementite for at least 5 hours.
As well as controlling the amount of Al to fix solid solution N.
With this, the bar steel for cold forging, which has a longer tool life,
A manufacturing method is disclosed. This publication states that “After hot rolling,
If the temperature is kept within the specified range, cementite will coagulate and precipitate.
The strength can be reduced at least. "
It was made based on the "
When cracks occur, cracks are likely to occur during cold forging. "
From the viewpoint of controlling the composition of steel and preventing the steel from becoming coarse
The initial strength is low in that it must contain Al, etc.
From the viewpoint of reducing the deformation resistance at room temperature
Coarse (rather than finer) ferrite grains
For this purpose, the distance between the center of the rolled material and the diameter / 8 is
Ferrite grain number in ferrite structure
Between Ferrite Grain Number in Ferrite Structures in Japan
It has a completely different technical idea from the present invention controlled by
Things. Japanese Patent Application Laid-Open No. Hei 8-260047 discloses a cooling method.
N to reduce the amount of solute N that causes strain aging during cold forging
Hot rolling by specifying aluminum and Al / N; hot rolling
In the final stage, plastic deformation of 50% or more in the specified temperature range
Thermo-mechanical heat treatment process to add processing; cooling after thermo-mechanical heat treatment
After that, heat to a temperature range of 300 to 400 ° C for 3 hours or more.
Method of manufacturing bar steel wire for cold forging including overaging treatment
Is disclosed. This gazette states, "Overaging after cold rolling.
In order to improve the strain aging resistance by processing, the ferrite particle size
It is effective to reduce
Adjusting the temperature to give a specific degree of processing
Refinement of grain size, thereby suppressing strain aging and improving ductility
Has a critical effect on
"Straining ferrite grain size
It is very effective in suppressing the occurrence of effects ''
I'm sure. However, the present inventors have considered
However, when the ferrite grain size is reduced as in the above method,
In this case, the occurrence of strain aging is suppressed.
Deformation resistance is reduced, but tensile strength is increased.
As a result, the deformation resistance at room temperature rises,
It was found that the cold workability decreased. As in the present invention
"The initial strength is reduced and the deformation resistance at room temperature is reduced.
To improve cold workability. "
If the ferrite grain size is reduced as described in the above publication,
The method is not preferred, but rather, contrary to miniaturization, ferrite
It is more effective to increase the grain size. Such meaning
And both have completely different technical ideas.
is there. Hereinafter, each requirement for specifying the present invention will be described.
I will tell. As described above, the linear or bar steel of the present invention
Suppresses the increase in strength due to the refinement of ferrite grains.
Technology has improved cold workability.
It has a thought. In order to embody such a technical idea, a line
The internal structure of bar or bar steel can be controlled as follows:
Recommended. Substantially ferrite structure or ferrite
And a mixed structure of pearlite and the center of the rolled material to the diameter /
Ferrite grain size number in ferrite structure in the range of 8
Is the 4th to 9th ferrite group on the outermost layer of the rolled material
The ferrite grain number in the weave is 4 to 10 and the rolling
Ferrite grain size number in the ferrite structure in the outermost layer of the material
No. and the ferrite in the range from the center to the diameter / 8 of the rolled material
The difference in the ferrite grain number in the microstructure is 0 to 1. First, in the present invention, the ferrite
Weave or have a mixed structure of ferrite and pearlite
Is necessary. For the purpose of the present invention, comparable to spheroidized material
In order to ensure deformability and deformation resistance, use the above structure
It is essential. The percentage of pearlite is large.
Considering that it becomes difficult to increase the deformation resistance
If you take into account, even if it may increase by the amount of C,
It is recommended to keep it below 40%. In the present invention, the “outermost layer” refers to a rolled material
Means the layer of the surface portion excluding the range from the center to the diameter / 8,
The ferrite particle size number can be found in JIS G 0552
Measured based on the cellite grain size test method.
You. According to this test method, the ferrite grain size number is large.
The ferrite grain size becomes smaller when
Particle size number 4 has a particle size of 90 μm and ferrite particle size number 9
No. is 16 μm, and No. 10 is 11
μm means each. Therefore, the above ferrite grain size
If the number is expressed in terms of ferrite grain size,
Ferrite grains in ferrite structure in the range of diameter / 8
The diameter is 16-90 μm, and the diameter of the
The ferrite grain size in the light structure is 11 to 90 μm.
You. As described above, the steel of the present invention is made of ferrite.
By suppressing the increase in strength due to the refinement of crystal grains,
Reduce the initial tensile strength, and
It has a technical idea where deformation resistance is suppressed.
is there. Therefore, the ferrite constituting the internal structure of the steel of the present invention.
Blow of light structure or ferrite / pearlite structure
Particle size is refined as before to improve strength
Rather, in order to suppress the increase in strength by suppressing the miniaturization,
The lower limit has been specified. In the present invention, the roll on the outermost layer of the rolled material is used.
The ferrite grain number in the ferrite structure is the center of the rolled material.
Ferrite in ferrite microstructure in the range of ~ diameter / 8
It becomes larger than the particle size number. The reason is in rolling
Cooling is performed by applying water or air to the steel surface to cool it.
Of course, the outermost layer tends to have a higher cooling rate than the center,
This is because the time for growing the crystal grains is shortened.
Here, the ferrite grain number of the outermost layer of the rolled material is
Of ferrite grain number in the range of center to diameter / 8
The size of the rolled material depends on the size of the rolled material.
And the cooling conditions, etc.
Compared to the ferrite grain size number in the range of diameter / 8, it is almost 0
It is recommended to increase the size by about one. Further, on the assumption that the above relationship is satisfied,
In addition, in the present invention, the range from the center of the rolled material to the diameter / 8
The ferrite grain size number in the ferrite structure is 4 to 9
First, the ferrite structure in the outermost layer of the rolled material
It is necessary to control the particle size number from 4 to 10
It is. Thus, in the present invention, the ferrite particle size number
The range from the center of the rolled material to the diameter / 8, and the outermost layer of the rolled material
And the upper limit is slightly different (ie, ferrite
The lower limit of the particle size is different). First, rolling
In the range from the center of the material to the diameter / 8, the solute N bonds with Al
Grain size due to pinning effect of AlN produced
In the present invention, as a nitride-forming element,
Effectively exerts the effect of B and Zr added (described later)
It is necessary to exert the pressure;
A after cooling_r1After quenching to below the point,
Recrystallizing makes it easier to refine, so the parts other than the outermost layer
The lower limit of the ferrite grain size needs to be lowered.
Is based on considering both perspectives
From this point of view, the lower limit of the ferrite grain size of the outermost layer
Is strictly set. Preferably the center of the rolled material
Ferrite in ferrite microstructure in the range of ~ diameter / 8
Particle size is 16μm or more (ferrite particle size number 9 or less),
Ferrite grains in the ferrite structure in the outermost layer of rolled material
Diameter is 11μm or more (ferrite particle size number 10 or less)
is there. As described above, in the present invention, the ferrite crystal grains
In order to suppress the increase in strength due to miniaturization,
Although the lower limit of is specified as above,
If the particle size becomes too large,
There is a risk of causing adverse effects such as cracking. Therefore, in the present invention,
Even if the upper limit is in the range from the center of the rolled material to the diameter / 8,
No.4 ferrite grain size on the outermost layer of rolled material
(Ferrite particle size: 90 μm). Good
More preferably, the ferrule in the range from the center to the diameter / 8 of the rolled material
The ferrite grain size in the site structure is 64 μm or less (ferrite
Grain size number 5 or more), ferrite on the outermost layer of rolled material
The ferrite grain size in the microstructure is 45 μm or less (ferrite
(Granularity number 6 or more). Next, it is preferable to obtain such a desired tissue.
New steel components will be described. As described above, the present invention relates to the method of “initial tensile strength”.
While reducing the degree of deformation to reduce the deformation resistance at room temperature,
In the sense of reducing the deformation resistance in the heat generation area
In order to achieve the task of improving cold workability,
It is more effective not to make the crystal grain size finer. ''
From the viewpoint, the ferrule in the range from the center of the rolled material to the diameter / 8
The ferrite grain number in the
In relation to the ferrite grain size number in the ferrite microstructure
It has technical significance where you control it.
In order to control the microstructure, solid solution C and solid solution
Non-selection of carbide / nitride forming elements for the purpose of fixing N
Selectively and randomly, or from the perspective of precipitation strengthening
Rather than adding, strengthen by ferrite grain refinement
From the viewpoint of suppressing the formation of carbides,
It is effective to select the type of element appropriately. Therefore,
Regarding the components in steel, ferrite such as Ti, Nb, V
Ferrite crystals instead of adding grain refinement elements
B or Zr that does not refine (rather coarsens) the grains
It is preferred to add. Of these, the nitride forming element is B
  : 0.0055% or less, Zr: 0.035% or less
At least one of them, and N: 0.000
B, Zr and N
It is recommended to control to satisfy the following formula. −0.0010 ≦ [N] −1.3 [B] −0.15 [Z
r] ≦ 0.0020 (In the formula, [] represents the content of each element.) As described above, in the present invention, the nitride-forming element
As for the addition of ferrite grain refining elements such as Ti
Instead, do not refine the ferrite grains (rather
B) and / or Zr are added.
You. Therefore, the above element hardens B, for example, as in the prior art.
Instead of being added as an improving element, BN
/ ZrN to reduce the dynamic strain aging during cold working
In addition to suppressing the solid solution strengthening of N,
Ferrite crystal grains are refined due to precipitation of 1N and strength
Is added for the purpose of suppressing an increase in the temperature.
In order to exhibit such an effect effectively, B is added to 0.00
05% or more (more preferably 0.0010% or more), Z
r is 0.005% or more (more preferably 0.010% or less)
Above) It is recommended to add. However, B is 0.00
Addition of more than 55% adversely affects cold workability.
It will be like. More preferably 0.0040% or less
You. Similarly, when Zr is added in excess of 0.035%,
Deformability decreases, which adversely affects cold workability.
You. More preferably, it is 0.025% or less. The above B and Zr are each added alone.
May be added, or both may be added.
It is added only for the purpose of immobilizing solid solution N. Follow
Therefore, the above elements basically correspond to the finally contained N.
It is preferable to adjust the content appropriately. if,
If N in steel can always be suppressed to 0.0020% or less
It is not necessary to actively add these elements.
No. Even if such a small amount of N is present,
It is thought that there is little risk of adversely affecting the workability.
is there. Here, N is 0.0005 to 0.007.
It is recommended to control in the range of 0%. N is Ferai
Causes a solution aging during cold working
Therefore, it is preferable to use as little as possible.
Therefore, the upper limit was set to 0.0070%. More preferred
Is 0.0050% or less. On the other hand, 0.0005%
If it is full, it will be difficult to produce industrially worth the cost
It is. More preferably, it is 0.0010% or more. Further, in the present invention, the above B, Zr and N are
It is recommended that the formula be satisfied. −0.0010 ≦ [N] −1.3 [B] −0.15 [Z
r] ≦ 0.0020 (In the formula, [] represents the content of each element.) This is because the solid solution N by B and / or Zr
This is an expression provided to effectively exert the fixing action.
First, the lower limit of the above equation is B and B, which fix the necessary minimum N.
And Zr, and the lower limit is -0.0010
If above, B was excessively added to fix N.
Does not contribute to the hardenability, and Zr
Is added in excess to fix N
Precipitates as carbides and carbides.
It has been confirmed that it has no adverse effect. More preferred
Specifically, the lower limit of the above equation is -0.0005. The upper limit of the above equation is determined by the amount of N added.
The upper limit is specified in relation to the B amount and the Zr amount,
If the upper limit exceeds 0.0020, excess N becomes Br / Z.
and the number of AlNs other than r increases,
It will be thinner. The upper limit of the above formula is 0.0020 or less
If, for example, N combines with Al to form AlN
Even in hot rolling, ferrite grains are refined.
Without hot rolling, and even when hot-rolled
Deformation resistance is reduced to the same level as the annealed steel to ensure deformability
That you can do it. More preferably,
The upper limit of the above equation is 0.0015. The above are the nitride-forming elements used in the present invention.
Is an explanation of the elements involved in
Is related to carbonitride forming elements that are conventionally widely used,
It is recommended to control as follows. Including at least one of Ti, Nb and V
Nb and V in a total of 0.080% or less (including 0%
), Ti: 0.020% or less (including 0%)
The elements i, Nb and V are all carbonitride forming elements.
Yes, effective for fixing C and N, but precipitation strengthening
And increase in strength due to strengthening by grain refinement;
Addition contributes to grain refinement after hot rolling
From the purpose of the present invention, "reducing the initial tensile strength,
Cold workability by reducing deformation resistance at room temperature
It is a rather harmful element in "improving". Follow
Therefore, it is preferable that the addition amount of the above elements be as small as possible.
From such a viewpoint, Nb and V are set to 0.080% in total.
Or less (including 0%), Ti: 0.020% or less (0%
Including). In particular, Ti
Among them, it is most easily combined with N, and when combined with B, it is quenched.
In order to achieve the effect of improving
Is recommended. More preferably, Nb and V are combined.
0.015% or less in total, Ti: 0.010% or less
Even more preferably, Nb and V are 0.01
0% or less, Ti: 0.005% or less. In order to embody the technical idea of the present invention,
Although the components in steel were described, in the present invention,
It is recommended that the elements be controlled as follows. [0040]C: 0.001 to 0.40% C is an element essential for imparting the necessary strength of steel.
You. If it is less than 0.001%, the desired strength cannot be obtained.
In addition, trying to control to such a low concentration is costly industrially.
Expensive and not economical. Preferably 0.003% or less
Above, more preferably 0.005% or more, even more preferred
At least 0.01%, particularly preferably at least 0.05%
is there. On the other hand, if it exceeds 0.40%, the pearlite fraction is high.
And the desired deformability cannot be obtained. Preferably 0.3
5% or less. [0041]Si: 0.40% or less (including 0%) Si is a useful element as a deoxidizer, but it is added in excess.
In addition, the processing load (deformation)
Not only increases resistance, but also decreases deformability.
It is preferable to use as little as possible because it may cause
From the viewpoint, the upper limit is set to 0.40%. 0.
When added in excess of 40%, the deformability is significantly reduced.
This is because that. It is more preferably at most 0.25%. [0042]Mn: 0.15 to 1.8% Mn is useful not only for deoxidation and desulfurization but also for cold working
Improves quenching and tempering softening resistance during subsequent heat treatment
It is a useful element for Effectively exhibiting such action
For this purpose, it is preferable to add 0.15% or more. Yo
More preferably, it is 0.20% or more. However, excessive addition
Then, ferrite / pearlite growth rate after hot rolling
And bainite, which is harmful to cold workability, is likely to occur.
Therefore, the upper limit was set to 1.8%. More preferred
Is 1.5% or less. The amounts of C, Si and Mn described above are just good.
Anything outside the above range that is within the preferred range
Is not to be included in the scope of
Needless to say. For example, JIS C 2503, JIS
G4051, JIS G4106, JIS G35
06, JIS G 3507 etc. in the present invention
Can be applied, and the component range specified in JIS cannot be excluded
If there are special circumstances, the scope specified in JIS
It is recommended to add within the box. However, immediately after cold working
Strength after cold working and quenching and tempering.
If you want to make it out of the range of ingredients specified in JIS
You can do it. [0044]sol. Al: 0.01 to 0.06% Al is an element useful for deoxidation. However, Al
Easy to form nitride (AlN) next to r, Ti, B, Nb
No. When the amount of AlN increases, the crystal grains become finer.
For the purpose of the present invention, AlN is produced as much as possible.
It is preferable not to do so, so that the amount of Al added can be
Should be as small as possible, but it should be added without departing from the spirit of the above.
May be added. From such a viewpoint, in the present invention, the lower limit is set to 0.
It was set to 01%. However, if added in excess, the above effect will
Not only does it saturate, but it also
Since the crystal grain refining effect is remarkable, the upper limit is set to 0.
06%. More preferably 0.015% or more,
It is 0.05% or less. [0045]Cr: 0.01 to 0.50% Cr promotes ferrite-pearlite transformation during hot rolling
To precipitate carbide without significantly contributing to the increase in strength.
It is an effective element for producing
In order to demonstrate, the lower limit was set to 0.01%. More preferred
Or 0.03% or more. However, over 0.50%
If added, the tensile strength becomes too high. More preferred
Is 0.30% or less. Further, the following elements can be added.
You. [0047]P: 0.001 to 0.015% (including 0%
Mu) P is effective as a hardenability improving element, and
In order to effectively exert the lower limit, the lower limit was set to 0.001%.
However, if added over 0.015%, micro
(B) segregation at the grain boundaries during hot rolling and embrittlement of the grain boundaries
As a result, the possibility of cracking during cold working increases. Yo
More preferably, it is 0.010% or less. [0048]S: 0.015% or less (including 0%) S mainly forms sulfide-based inclusions of MnS and is hot-rolled.
Occasionally segregation at grain boundaries embrittles the grain boundaries and causes
The upper limit is set at 0.015%
I did. It is more preferably at most 0.010%. The steel of the present invention contains the above components, and the balance:
Although qualitatively iron, the effects of the present invention can be
An acceptable component that is acceptable as long as it is not damaged may be added.
And impurities. Next, the wire or bar according to the present invention is manufactured.
A method for performing the above will be described. In order to obtain a predetermined tissue which is the object of the present invention,
Heats the billet to the range of 800-1100 ° C.,
After rolling to a predetermined wire diameter in the range of 0 to 1100 ° C,
At a cooling rate of 600 to 6000 ° C./min.
Temperature cooled to 00-800 ° C and recovered by reheating
(Adjustment cooling start temperature) to 750-875 ° C
Is necessary. Hereinafter, each requirement will be described. [0052]Heating temperature of billet: 800-1100 ° C This heating temperature suppresses the miniaturization of ferrite grain size
However, it is set to reduce the deformation resistance.
Here, the "heating temperature of the slab" is measured by a radiation thermometer.
It is measured, and strictly speaking, "surface temperature of billet"
Means When heated above 1100 ° C, ferrite
Crystal grain size becomes too large and ductility decreases
You. Preferably it is 1050 ° C. or less, more preferably 100 ° C.
0 ° C. or less. On the other hand, the heating temperature becomes lower than 800 ° C.
And the hot deformation resistance becomes too high,
Wear, trips of the rolling motor, etc.
May cause harm. Preferably it is 850 ° C or higher. [0053]Rolling temperature: 750 to 1100 ° C This temperature is the same as during the billet heating during rolling,
Suppress ferrite crystal grain size reduction and reduce deformation resistance
It is set to aim at. Here, "rolling temperature
"Degree" is measured by a radiation thermometer,
Strictly, it means “surface temperature of billet”. 1100 ° C
When rolling beyond this, the ferrite grain size increases.
Too long and the ductility decreases. Preferably 1050 ° C
Or less, more preferably 1000 ° C. or less. On the other hand, pressure
When the rolling temperature is lower than 750 ° C, the ferrite grain size becomes
Ferrite grains
Unnecessary dislocations easily remain in the steel, increasing the strength after rolling
You. Preferably it is 850 ° C or higher. In addition, the rolling roll
Considering increased load, reduced dimensional accuracy, prevention of surface flaws, etc.
Then, in practice, the rolling temperature is about 875 to 975 ° C.
Is recommended. [0054]Adjusted cooling start temperature: 750-875 ° C The adjusted cooling start temperature means that water is mainly used as a medium after the final rolling.
And the highest surface temperature at a cooling rate of 600 to 6000 ° C / min.
Is cooled to at least 500-800 ° C,
Holding a billet while being wound on a belt (cooling conveyor)
It means the temperature that is recovered by heat (recuperation). 875 ° C
At higher temperatures, the scale becomes thicker and subsequent removal
Not only is it easy for trouble to occur in the scale process,
Since the cooling time becomes longer, productivity is hindered. Preferably
850 ° C or lower. On the other hand, lower than 750 ° C
And the martensite in the surface layer generated during cooling
Therefore, it does not recover and tempered martensite is formed,
It is not suitable for cold working because it becomes a brittle and brittle steel. Actual operation
The preferred level is 775 ° C or higher. [0055]Cooling rate: 0.05-5 ° C / sec (600 ° C
Until) This is at 600 ° C. after reaching the adjusted cooling start temperature.
It specifies the cooling rate when cooling to
You. As in the present invention, the structure is ferrite or ferrite.
In order to control the light-perlite structure, the cooling rate must be reduced.
It is preferable to use pearlite
(Lamellar structure of ferrite and cementite)
The spacing may be wide, resulting in a less ductile tissue
Therefore, the lower limit was set to 0.05 ° C./sec. For industrial production,
Considering quality stability, etc., 0.2 ℃ / sec or more, 3 ℃
/ S or less is recommended. According to the present invention, the wire rod as hot rolled or
Although excellent cold workability can be obtained with steel bars,
Immerse steel bars in a bath of acid (hydrochloric acid, sulfuric acid, etc.)
After removing the scale by mechanically applying distortion, etc.
Pre-drawing treatment for zinc oxide film, calcium phosphate film, lime, etc.
Wire drawing and cold using metal soap etc. as lubricant
The same excellent cold work is applied to rolled steel wire.
Workability is obtained. The mechanical part of the present invention is preferably a linear or rod-shaped part.
It is obtained using steel. Here, the flatness of the dislocation cell
Average area is 0.18 ~ 0.50μm^TwoWhat is preferred
It is a mode that is not good. As described above, in the present invention, solid solution C and
In fixing solid solution N, fine ferrite grains
From the viewpoint of suppressing the formation of steel, the internal structure of linear or
Constituting ferrite structure or ferrite parlor
Control the ferrite grains in the microstructure
Does not refine ferrite grains (rather
Identify carbide / nitride forming elements)
Is thereby introduced into the steel during cold working
The dislocation is the above-mentioned carbide / nitride forming element, solid solution C, solid solution N
Formed to progress without being fixed by
The dislocation cell becomes larger. However, the average area of the dislocation cells is 0.18
~ 0.50 μm^TwoOut of the range, deformation resistance at room temperature
And high deformation resistance in the heat generating area,
Will decrease. A more preferred lower limit is 0.19 μm.^Two
(Even more preferably 0.20 μm^Two) And better
A good upper limit is 0.45 μm^Two(Even more preferably, it is 0.
40 μm^Two). Hereinafter, the average area of the dislocation cells will be measured.
The method will be described. First, compressed at a predetermined compression rate
In the test piece, a sample was taken from the tissue observation position shown in FIG.
And a thin film sample is prepared by electrolytic polishing. This
The dislocation cells present in the thin film sample of
Observation with a scanning electron microscope (magnification: 15000)
Shoot. Next, the average area was calculated from the dislocation cell photograph.
Put out. Since the shape of dislocation cells is generally close to a rectangle,
To determine the area of the dislocation cell accurately, multiply the long side and the short side.
The area was determined by combining them. Specifically, dislocation
A straight line (4
(Length equivalent to ５5 μm) by 5
Count the number of dislocation cells cut by the line,
The average area of the dislocation cells was determined by the equation. Average area of dislocation cells S = (L1 / I1) × (L2 / I
2) In the formula, L1: the length of a straight line drawn in the longitudinal direction of the dislocation cell
Sum (5 lengths) L2: Total length of lines orthogonal to L1 (length of 5 lines) I1: Total number of dislocation cells cut by L1 I2: Total number of dislocation cells cut by L2 However, when counting dislocation cells, if the cells are not clear
Count (if not a cell surrounded by dislocations)
, And the straight line also subtracted that part. Incidentally, the average area of the dislocation cells should be within the range of the present invention.
In order to control the distance, a line satisfying the above-described requirements of the present invention
Or cold-rolled or bar-shaped steel with a strain of 0.2 or more
Forging is recommended. Combination of wire drawing and cold forging
If the amount of strain applied is less than 0.2, less dislocations are introduced.
This is because the desired strength cannot be obtained. More preferred
Is 0.4 or more, still more preferably 0.6 or more.
However, if the amount of strain exceeds 3, it becomes difficult to form mechanical parts.
Therefore, the upper limit should be controlled to 3, more preferably 2.5.
Is recommended. Here, the distortion amount of the wire drawing is calculated by the following equation.
The amount of strain during cold forging is
Table on page 158 of "Possible Forming Technology Series 4 (Corona)"
The logarithmic distortion described in 5.2 was used. ε = 2In (D1 / D2) In the formula, ε is strain, D1 is an initial wire diameter, and D2 is a wire after drawing.
Each means a diameter. Hereinafter, the present invention will be described in detail with reference to examples.
However, the following examples do not limit the present invention,
Changes may not be made without departing from the spirit of the preceding and following sections.
All are included in the technical scope of the present invention. [0064] EXAMPLE A test steel having the composition shown in Table 1 (in the table,
Is the mass%) and various production conditions shown in Tables 2 to 4 are used.
Various wire rods (Nos. 1 to 19) were obtained depending on the conditions. here
No. A, B and C are specified in JIS G 3507, respectively.
SWRCH10K, SWRCH20K, SWRCH
It is a 35K current process material. A1 is the spheroidizing firing of A.
Inventive steels B1-B3 produced for the purpose of omission of dulling treatment
Is a steel of the present invention which was produced for the purpose of omitting the spheroidization of B, C1
Means steel of the present invention which was melted for the purpose of spheroidization of C
And B5 to B8 are P and S (B5), N and Zr, respectively.
The sum (B8) of (B6), Ti (B7) and Nb + B is the book
It is a comparative steel outside the scope of the invention. Next, the above-mentioned wire rod was subjected to a compression test as shown in FIG.
Shape of the test specimen (Japanese Society for Plastic Working
Recommended shape for Engineering Technology Series 4 (Corona) p155 "
(Steel wire diameter x 1.5)
Use a constrained pressure plate with concentric grooves
Upsetting was performed using Incidentally, the deformation resistance was measured at room temperature at a compressibility of 60%.
The measurement was made at two levels: the case and the case of 300 ° C. of preheating. Ma
The deformability is No. A, A1, B, B-1 to B8 (N
o. For 1 to 16), test 30 pieces at a compression ratio of 80%
To determine the presence or absence of cracks; C and C-1
(Nos. 17 to 19) indicate the pressure from the viewpoint of the deformability of the working steel.
A test at a shrinkage of 70% was carried out in the same manner,
Nothing was determined. Further, No. 60% compression test of 1-19
Pieces and No. 5,6 20-80% compression test pieces
The average area of dislocation cells is calculated by the above-mentioned measurement method.
Issued. In addition, No. For 5 and 6, compressive strain and rolling
To check the relationship between the size of cell (average area), the compression ratio
In the range of 20 to 80% (compression strain of 0.27 to 2.23)
And change the average area of the dislocation cells in the same manner.
Calculations were performed (five for each compression test piece). The obtained results are also shown in Tables 2 to 4. still,
FIG. 2 shows the ferrite in the range from the center to the diameter / 8 of the rolled material.
Grain size number and deformation resistance (60% compression
FIG. 3 shows the relationship between the roll ratio and the room temperature).
Ferrite grain size number and deformation resistance (60
% Compression ratio, room temperature); FIG.
Ferrite grain size in ferrite structure in the range of diameter / 8
Number and deformation resistance (60% compression ratio, 300 ° C);
FIG. 5 shows the ferrite structure in the ferrite structure on the outermost surface of the rolled material.
Light particle size number and deformation resistance (60% compression ratio, 300 ° C)
Are graphed and shown. In addition, in FIGS.
◇, ferrite grain size number satisfies the requirements of the present invention
A book whose component composition also satisfies the preferred requirements of the present invention
Invention steel; △ indicates ferrite grain size number satisfies the requirements of the invention
However, the component composition does not satisfy the preferable requirements of the present invention.
Reference steel; ○: ferrite particle size number satisfies the requirements of the present invention
Not a comparative steel. FIG. 7 shows the average area and deformation of dislocation cells.
FIG. 8 shows the relationship between resistance (60% compression ratio and room temperature);
Average area and deformation resistance (60% compression ratio, 300 ° C)
The relationship is shown in a graph. Further, FIG. 5
And 6, the compressive strain and the average area of dislocation cells (N =
The relationship with 5) is shown in a graph. [0070] [Table 1][0071] [Table 2] [0072] [Table 3][0073] [Table 4]From the above results, the ferrite grain size number was
No. 4 to 9 in the range from the center of the rolled material to the diameter / 8, on the outermost surface
Spheroidizing annealing by controlling to 4 to 10
Without, almost to the deformation resistance level comparable to the spheroidization of the current steel
Could be reduced. Further control of ferrite grain size number
In addition, the component composition was also controlled within the preferred range of the present invention.
Is to reduce the deformation resistance of the current steel
Was completed. The average area of dislocation cells after cold forging is
By making it as large as the current steel, spheroidizing annealing
To reduce the deformation resistance to the same level as the spheroidized working steel
Conventional steel obtained by spheroidizing annealing
The hardness after compression also increased. On the other hand, the spheroidizing annealing
No. for which the processing was omitted. For 2, 5 and 18, the 300 ° C
The shape resistance increases compared to the deformation resistance at room temperature.
Are also miniaturized.
It turns out that it is not suitable for hot forging. FIG. 9 shows that the steel of the present invention (No. 6) was used.
When wire drawing and cold forging with a compression strain of 0.2 or more
In each case, the compression ratio was reduced to 80%.
0.20μm^TwoThe above average dislocation cell area is obtained.
On the other hand, in the comparative steel (No. 5), the compression ratio was 40%.
Even the average area of dislocation cells is 0.18 μm^TwoLess than
Sample occurred. For reference, no. At 10 and 16
Fig. 1 shows TEM (transmission electron microscope) photographs of the dislocation cells.
0 and FIG. No. 10 of the present invention
This is an example of the present invention forged using steel type B2 satisfying the requirements.
However, the size of the dislocation cell satisfying the requirements of the present invention (average
Area 0.24μm^Two) Is obtained. In contrast, B
8 is the ratio of forged using steel types that do not satisfy the requirements of the present invention.
This is a comparative example, but the average area of dislocation cells is small.
(0.12 μm^Two). [0079] The present invention is configured as described above.
Therefore, even if the spheroidizing annealing treatment is omitted, it is still hot-rolled.
Efficiently provide wire or bar steel with excellent cold workability
We were able to. In particular, the linear or bar steel of the present invention,
Temperature range caused by heat generated during cold working
(Approximately 100-350 ° C.)
This is extremely useful in that it can be used. Further, the present invention
The machine parts obtained by using steel or bar steel
Hardness after forging is high.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing the shape of a test piece for compression test used in Examples. FIG. 2 is a graph showing a relationship between a ferrite grain number in a ferrite structure in a range from the center of a rolled material to a diameter / 8 and deformation resistance (60% compression ratio, room temperature). FIG. 3 is a graph showing a relationship between a ferrite grain number in a ferrite structure on the outermost surface of a rolled material and deformation resistance (60% compression ratio, room temperature). FIG. 4 is a graph showing a relationship between a ferrite grain number in a ferrite structure in a range from the center to a diameter / 8 of a rolled material and deformation resistance (60% compression ratio, 300 ° C.). FIG. 5: Ferrite grain size number and deformation resistance in the ferrite structure on the outermost surface of the rolled material (60% compression ratio, 300 ° C.)
6 is a graph showing the relationship of. FIG. 6 is a schematic view showing a structure observation position for measuring an average area of a dislocation cell. FIG. 7 is a graph showing the relationship between the average area of dislocation cells and deformation resistance (60% compression ratio, room temperature). FIG. 8 is a graph showing the relationship between the average area of dislocation cells and deformation resistance (60% compression ratio, 300 ° C.). FIG. 9 is a graph showing the relationship between compressive strain and the average area of dislocation cells. FIG. 10 is a TEM (transmission electron microscope) photograph of the dislocation cell in FIG. FIG. 16 is a TEM (transmission electron microscope) photograph of the dislocation cell in No. 16.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-2001-192771 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00 C21D 8/06

Claims (1)

(57) [Claims] [Claim 1] The steel component satisfies the following (A) and the structure is
Obtained using a linear or bar steel satisfying the following (B)
That a mechanical component, the average area of dislocation cells are 0.18～0.50Myuemu ²
A mechanical part characterized by the following. (A) C: 0.05 to 0.40 %, Si: 0.40% or less (including 0%), Mn: 0.15 to 1.8%, 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%) , It contains at least one of Ti, Nb, and V. Nb and V are suppressed to 0.080% or less in total, Ti: 0.020% or less, B: 0.0055% or less, and Zr: 0.035. % Or less.
And N: 0.0005-0.0070%
In addition, B, Zr and N satisfy the following formula : -0.0010 ≦ [N] -1.3 [B] -0.15 [Zr] ≦ 0.0020 (where [] represents the content of each element) The rest: real
Manner is iron; (B) have a substantially ferritic structure, or ferrite and mixed structure of pearlite, the ferrite grain size number of ferrite in a range of center-diameter / 8 of the strip in 4-9 No. The ferrite structure number in the ferrite structure in the outermost layer of the rolled material is 4 to 10 and the ferrite grain in the outermost layer of the rolled material is
Difference in ferrite grain size number of ferrite in that the ferrite grain size number of ferrite tissue in a range of center-diameter / 8 of the rolled material is a 0-1 number.