JP2003013179A - Round steel material for bearing element parts with excellent hot workability - Google Patents

Abstract

(57) [Summary] [Problem] To provide a round steel material excellent in hot workability suitable for use in bearing element parts. SOLUTION: C: 0.8-1.2%, Si: 0.2-2.0%, Mn: 0.2
-1.5%, Cr: 0.5-2.0%, P: 0.005-0.025%, S: 0.0
03 to 0.015% P (%) + 2S (%): 0.020 to 0.040%, A
l: 0.01-0.05%, N: 0.005-0.012%, Cu ≦ 1.0%, Ni
≦ 2.0%, the balance is made of Fe and impurities, and is a round steel material with Ti ≦ 0.002% and O (oxygen) ≦ 0.0015% in the impurities. (R /
In the segregation zone existing in the region up to 10),
The width of the region where the Cr content exceeds 1.3 times the Cr content is
Round steel material for bearing element parts with excellent hot workability that is 0.0003 to 0.003 times the diameter of the round steel material.

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] The present invention is excellent in hot workability.
The present invention relates to a round steel material for bearing element parts. More details
Bearing elements such as ru, roller, needle, shaft, race
Concerning round steel materials with excellent hot workability suitable for parts applications
The [0002] [Background Art] Balls, rollers, needles, shafts,
As a material steel for bearing element parts such as
High carbon chromium shafts such as SUJ2 steel standardized by G 4805
Steel is widely used. The so-called “bearing steel” described above is hot rolled, etc.
After being processed into round steel materials such as steel bars and wire rods,
Finishing the various element parts using the method described in (a) or (b)
Often lost. (A) By hot cutting or forging
Is formed into a shape close to the element part, and then softening is aimed at
Subjected to targeted spheroidizing annealing, followed by cutting,
In addition, after heat treatment by quenching and tempering at low temperature,
Given the desired mechanical properties. (B) Subjected to spheroidizing annealing for the purpose of softening
Then, by cold forging, cold drawing, cutting, etc.
Are molded into element parts, and further quenched and tempered at low temperatures.
The desired mechanical properties are imparted by the heat treatment. Among these, the method (a) is an element in hot working.
Because it is molded into a shape close to the part, it is suitable for cold forging.
It is also applicable to element parts with more complex shapes,
It can reduce the amount of cutting in costly cutting
The Therefore, in recent years, the bearing element has been
Parts are often manufactured, hot forging dies and heat
Hot workability that can improve the life of blades for hot cutting
The demand for excellent bearing steel
The [0007] The present invention is based on the above situation.
The purpose was to add a special element.
Without tools such as hot forging dies and hot cutting blades
Can extend the life, ball, roller, need
Suitable for bearing element parts such as rails, shafts and races
It is to provide a round steel material excellent in hot workability. Here, “hot workability” means “for hot work”.
It is good when the tool life is long.
Hot torsion test, i.e. the length and diameter of the parallel part
Each 50 mm and 10 mm test pieces are 1050 ° C., 1
After holding at 100 ° C and 1150 ° C for 15 minutes,
When performing a hot torsion test at a speed of 300 rpm,
The average value of the number of twists until breakage is 84 times or less.
And aim. It is also used for various industrial machines and automobiles.
Since high surface pressure acts repeatedly on the bearings used, the shaft
Round steel for receiving element parts is rolling fatigue in the examples described later.
1.0 × 10 in the test⁷ Has more rolling fatigue life
The goal is to. [0009] The gist of the present invention is as follows.
It is a round steel material for bearing element parts with excellent hot workability. That is, “mass%, C: 0.8 to 1.
2%, Si: 0.2-2.0%, Mn: 0.2-1.5
%, Cr: 0.5-2.0%, P: 0.005-0.0
25%, S: 0.003 to 0.015% and P (%) + 2
S (%): 0.020 to 0.040%, Al: 0.01
-0.05%, N: 0.005-0.012%, Cu:
1.0% or less, Ni: 2.0% or less, with the balance being F
e and impurities, Ti in impurities is 0.002%
Hereinafter, O (oxygen) is a round steel material of 0.0015% or less.
When the radius is R, (R /
In the segregation zone existing in the area up to 10),
Region where the Cr content exceeds 1.3 times the Cr content of
The width is 0.0003 to 0.003 of the diameter of the round steel material
Round steel for bearing element parts with excellent hot workability
Wood. It is. The "round steel material" as used in the present invention means hot
The cross-sectional shape machined in is a wire rod, steel bar or billet
The `` cross section '' refers to the rolling direction and the forging axis.
A surface cut directly. Also, "Cr content in round steel material" means round steel
Specimen is collected at the part (R / 2) from the center of the cross section of the material
And the value analyzed by the usual method. Furthermore, "Heat
When the tool life for hot working is long,
“Good” is as described above. The inventors of the present invention have reported that the center segregation and segregation of round steel materials.
Effects of alloying elements on tool life in hot working
As a result, the following knowledge was obtained. (A) In general, drawing during a hot tensile test
Cracks and cracks do not occur during hot working when the
Therefore, it is said that hot workability is good.
For the material steel of bearing element parts
The drawing value of a tensile test at 1000 to 1250 ° C. is almost
100%, general hot such as hot forging and hot rolling
The possibility of cracking or cracking during processing is extremely small
Yes. (B) In a torsion test in the hot state,
The number of twists to break is determined by the bearing element parts according to the present invention.
Even in the case of material steel, a large difference often occurs. And this
The number of twists has a large correlation with the tool life for hot working,
Lowering the number of twists will increase the tool life for hot working.
become longer. (C) In the hot torsion test in (b) above
In order to reduce the number of twists until rupture of P and S,
Increasing the content, as well as the amount of center segregation such as Cr, C, etc.
In the case of round steel material, from the center of the cross section to (R / 10)
Increase the amount of Cr and C in the segregation zone
It is effective. (D) On the other hand, the bearing element parts have a large rolling fatigue.
In order to ensure a working life, low P and S content
Reducing the amount of central segregation such as Cr and C
It is valid. (E) From the above (b) and (c),
Long tool life and good for bearing element parts
In order to ensure a good rolling fatigue life,
Amount and center segregation amount of Cr, C, etc. within a certain range
It is important to control. (F) C, Mn and Cr are easily segregated in the center.
Among these elements, of these, until the fracture in the hot torsion test
It is C and Cr that greatly affect the number of twists. Only
C is a light element and it is difficult to accurately quantify segregation.
Therefore, a method for quantitatively evaluating the segregation of Cr is effective.
The The present invention has been completed based on the above findings.
It is a thing. [0021] DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below.
To do. In addition, “%” of the content of chemical components is “mass%”.
means. (A) Chemical composition of round steel C: 0.8 to 1.2% Steel for bearings by heat treatment by quenching and tempering at low temperature
Giving the desired mechanical properties to the material (bearing element parts)
However, when the C content is less than 0.8%, the quenching and tempering is performed.
Later hardness is low, the desired rolling fatigue life (in the examples below)
1.0 × 10 in rolling fatigue test<sup>7</sup> More rolling fatigue
Labor life) is not obtained. On the other hand, the C content is 1.2%.
Otherwise, huge carbides are likely to be generated during solidification of the steel.
In order to ensure the target rolling fatigue life,
Cost, because it will be necessary to perform long-term homogenization heat treatment
Becomes bulky. Therefore, the content of C is 0.8 to
1.2%. The C content is 0.8 to 1.0%.
If it is 0.8 to 0.9%, it is more
preferable. Si: 0.2 to 2.0% Si is an element effective for increasing the rolling fatigue life.
It is also an element necessary as a deoxidizer. Si is steel
It is also an element that enhances hardenability. But its content is
If it is less than 0.2%, it is difficult to obtain the above effect. On the other hand, including Si
When the content exceeds 2.0%, after hot rolling or spheroidizing annealing
In addition, since it takes a long time to descal,
Incurs a significant drop. Therefore, the Si content is 0.2.
To 2.0%. The Si content is 0.2 to 1.
0% is preferable, and 0.2 to 0.6%
Even more preferred. Mn: 0.2 to 1.5% Mn improves the hardenability of steel and at the same time due to S
It is an element necessary for preventing hot brittleness. It produces these effects
In order to volatilize, it is necessary to contain 0.2% or more of Mn
is there. On the other hand, if the content of Mn exceeds 1.5%, Mn
The center segregation of Cr becomes remarkable, and the center segregation of Cr is described below.
The rolling fatigue life is significantly reduced even if controlled to
Rolling fatigue life (rolling fatigue test in examples described later)
And 1.0 × 10<sup>7</sup> No more rolling fatigue life)
Become. Therefore, the Mn content is 0.2 to 1.5%.
It was. In addition, the desirable range of Mn content is 0.2 to
1.0%, more desirable if 0.2-0.8%
Yes. Cr: 0.5 to 2.0% Cr improves the hardenability of steel and at the same time hot working
It is an effective element to increase the tool life. Shi
However, if the content is less than 0.5%, C
Even if the center segregation of r is controlled within the range described later,
In the torsion test, it is difficult to achieve the desired number of twists of 84 times or less.
Therefore, it is difficult to extend the tool life for hot working. one
On the other hand, if it exceeds 2.0%, the center segregation of Cr and C becomes prominent.
As a result, the rolling fatigue life is significantly reduced, and the desired rolling fatigue is achieved.
Labor life (1.0% in rolling fatigue test in examples described later)
× 10<sup>7</sup> The above rolling fatigue life) cannot be obtained. Shi
Therefore, the Cr content is set to 0.5 to 2.0%. Na
The Cr content is preferably 0.7-1.5%.
If it is 0.7 to 1.2%, it is more preferable. P: 0.005 to 0.025% P is combined with S to increase the tool life for hot working
Is an effective element. However, its content is 0.005
Less than 84%, the above-mentioned hot torsion test is not less than 84 times desired.
The number of twists below is unlikely, so hot working tools
It is difficult to extend the service life. On the other hand, P segregates at the grain boundary and
Is an element that easily causes embrittlement, and its content is 0.025.
%, The reduction in rolling fatigue life becomes remarkable and desired.
Rolling fatigue life (rolling fatigue test in examples described later)
And 1.0 × 10<sup>7</sup> No more rolling fatigue life)
Become. Therefore, the P content is 0.005 to 0.0.
25%. The content of P is P (%) + 2S
(%) Must satisfy 0.020-0.040%
The S: 0.003 to 0.015% S is combined with P to increase the tool life for hot working
Is an effective element. However, its content is 0.003
Less than 84%, the above-mentioned hot torsion test is not less than 84 times desired.
The number of twists below is unlikely, so hot working tools
It is difficult to extend the service life. On the other hand, S combines with Mn to form Mn
An element that forms S and reduces the rolling fatigue life.
In particular, if its content exceeds 0.015%, it is coarse
As a result, the rolling fatigue life is reduced.
The desired rolling fatigue life (in the examples below)
1.0 × 10 in the rolling fatigue test<sup>7</sup> More rolling fatigue life
Life) is not obtained. Therefore, the S content is 0.00
It was set to 3 to 0.015%. The S content is P
(%) + 2S (%) satisfies 0.020-0.040%
There is a need to. P (%) + 2S (%): 0.020-0.
040% As mentioned above, P and S are combined and the tool life for hot working
Improve life. However, the value of P (%) + 2S (%) is
In the case of less than 0.020%, the hot torsion test described above
Therefore, it is difficult to achieve the desired number of twists of 84 times or less.
Therefore, it is difficult to extend the tool life for hot working. On the other hand, P
When the value of (%) + 2S (%) exceeds 0.040%,
The contents of Toe P and S are each 0.010 to 10
Even if it is 0.025%, 0.003-0.015%,
Desirable rolling fatigue life due to significant decrease in rolling fatigue life
(In a rolling fatigue test in Examples described later, 1 × 10<sup>7</sup>
The above rolling fatigue life) cannot be obtained. Therefore, P
The value of (%) + 2S (%) is 0.020 to 0.040%
did. Al: 0.01 to 0.05% Al has a deoxidizing action. Furthermore, Al combines with N
Action to prevent AlN formation and coarsening of crystal grains
Have However, if the Al content is less than 0.01%
Such an effect is difficult to obtain. On the other hand, Al is a non-metallic inclusion.
It is an element that causes the rolling fatigue life to decrease and, in particular,
If its content exceeds 0.05%, coarse non-metallic media
As it becomes easier to form natural objects, the rolling fatigue life is significantly reduced.
The desired rolling fatigue life (in the examples described later,
1.0 × 10 in dynamic fatigue test<sup>7</sup>The above rolling fatigue life)
It can no longer be obtained. Therefore, the content of Al is 0.01
˜0.05%. The Al content is 0.01 to
It is preferable to set it as 0.04%, 0.01-0.03
% Is more preferable. N: 0.005 to 0.012% N combines with Al to form AlN, resulting in coarse crystal grains
It has the effect | action which prevents doing. However, the N content is
If it is less than 0.005%, this effect is difficult to obtain. On the other hand, including N
As the amount increases, coarse AlN is likely to occur,
Limiting the content of Ti as an impurity element to the range described below
However, coarse TiN is likely to occur, and the rolling fatigue life is increased.
It will decline. In particular, its content exceeds 0.012%
In other words, the rolling fatigue life is significantly reduced and the desired rolling
Fatigue life (In rolling fatigue tests in the examples described later,
0x10<sup>7</sup> The above rolling fatigue life) cannot be obtained. did
Therefore, the N content is 0.005 to 0.0012%.
It was. The bearing element component having excellent hot workability according to the present invention.
For round steel materials for use, either Cu or Ni
Either or both of them can be selectively contained. You
In other words, Cu and Ni elements are added as optional additional elements.
And may be included. Hereinafter, C as an optional additive element
u and Ni will be described. Cu: 1.0% or less If Cu is added, it has the effect of enhancing the corrosion resistance. this
The effect can be obtained even with a content level of impurities,
In order to obtain the effect more remarkably, Cu is 0.05% or more.
The content is preferable. But its content is
If it exceeds 1.0%, it segregates at the grain boundary, and it is split rolled and hot.
Generation of cracks and flaws during hot working such as rolling and hot forging
Becomes prominent. Therefore, the Cu content is 1.0% or more.
Below. In addition, Cu content is preferable when added
The range is 0.05-1.0%. Ni: 2.0% or less If Ni is added, it will solidify in the martensite after quenching.
It has the effect of melting and increasing toughness. This effect is due to impurity levels.
Although it can be obtained even with a bell content, the effect is more prominent.
To obtain fruit, Ni should be 0.2% or more.
Is preferred. However, even if it exceeds 2.0%,
The above effects are saturated and the cost is increased. did
Therefore, the Ni content is set to 2.0% or less. Please note that
When Ni is added, the preferable range of Ni content is 0.2-2.
0%. In the present invention, T as an impurity element
The contents of i and O (oxygen) are limited as follows. Ti: 0.002% or less Ti combines with N to form TiN, and has a rolling fatigue life.
It will decrease. Especially its content exceeds 0.002%
The rolling fatigue life is significantly reduced and the desired rolling
Fatigue life (In rolling fatigue tests in the examples described later,
0x10<sup>7</sup> The above rolling fatigue life) cannot be obtained. did
Therefore, the Ti content is set to 0.002% or less. Na
The content of Ti as an impurity element is as small as possible
Is desirable. O (oxygen): 0.0015% or less O forms oxide inclusions and reduces the rolling fatigue life.
I will let you. In particular, its content exceeds 0.0015%
The rolling fatigue life is significantly reduced and the desired rolling fatigue life
Life (1.0 × 1 in the rolling fatigue test in Examples described later)
0<sup>7</sup> The above rolling fatigue life) cannot be obtained. Therefore
Therefore, the content of O is set to 0.0015% or less. Note that
Minimize the content of O as a pure element
Is desirable. (B) Cr segregation in the cross section of round steel material
Band width In the present invention, from the center of the cross section of the round steel material (R / 1
In the segregation zone existing in the region up to 0),
Of the region where the Cr content exceeds 1.3 times the Cr content.
The width is 0.0003 to 0.003 times the diameter of the round steel material
Stipulate. “Cr content in round steel” is round steel.
Specimen is collected at the part (R / 2) from the center of the cross section of the material
However, it has already been mentioned that it refers to the value analyzed by the usual method.
It ’s exactly as it was. Here, from the center of the cross section of the round steel material (R /
The target of segregation bands existing in the area up to 10)
If we focus on the segregation zone in this area, the tool for hot working
The life of rolling and the rolling fatigue life of bearing element parts can be evaluated.
It is. From the center of the cross section of the round steel material (R /
In the segregation zone existing in the area up to 10),
Region where the Cr content exceeds 1.3 times the Cr content of
If the width is less than 0.0003 times the diameter of the round steel
In the hot torsion test, the desired number of twists (in the examples described later)
The twisting test was less than 84 times)
Therefore, the tool life for hot working is not extended. one
On the other hand, the area from the center of the cross section of the round steel material to (R / 10)
In the segregation zone present in the
The width of the region where the Cr content exceeds 1.3 times
When it exceeds 0.0030 times the diameter of steel, rolling fatigue
Decrease in work life becomes significant, and the desired rolling fatigue life (described later)
In the rolling fatigue test in Example 1, 1.0 × 10<sup>7</sup> Less than
The above rolling fatigue life) cannot be obtained. Here, “1.3% of Cr content in round steel material”
The width of the region where the Cr content exceeds double is, for example, round
After mirror-polishing the cross section of the steel material, a scanning electron microscope (hereafter
Energy dispersive X-ray segment attached to SEM)
It can be determined by the analyzer (hereinafter referred to as EDX)
Yes. Specifically, for example, the probe diameter of EDX is 1 μm.
And the center of the cross-section of the round steel material as the measurement start point "R
Line analysis of Cr up to / 10 ”
Using the measurement chart, the analysis value of Cr is C in round steel.
Among the locations where the r content was 1.3 times or more, the widest
The width of the wide part is “1.3 times the Cr content in round steel.
The width of the region having a Cr content exceeding 50% ”may be used. It should be noted that “from the center of the cross section of the round steel material (R /
In the segregation zone existing in the area up to 10),
Region where the Cr content exceeds 1.3 times the Cr content of
The width of the round steel product diameter is 0.0003 to 0.003
To `` double '', for example, the steel ingot before homogenization heat treatment
As a round shape, from the center of the cross section to (R / 10)
In the segregation zone present in the region, the Cr content in the steel ingot
The width of the region where the Cr content exceeds 2.0 times is round.
0.0002 to 0.002 times the diameter of the shaped steel ingot
In the case of 6-12 in the temperature range of 1200-1240 ° C.
Time homogenization heat treatment may be performed. Here, "With round steel material
"Cr content in steel ingot" as well as "Cr content in steel ingot"
Is (R / 2) from the center of the cross section of the round steel ingot
Specimens taken at
Point to. The chemical composition described in the above item (A) and the book (B)
A circle having the width of the Cr segregation band in the transverse section
Steel is processed by hot forging and hot cutting in the usual way.
After being cold-worked as necessary,
Desired machine after heat treatment by tempering and tempering at low temperature
Precision after being finished into bearing element parts with special properties
Assembled into bearings as final products that are machine parts
The The following examples further illustrate the present invention.
Light up. [0042] EXAMPLES Example 1 J having the chemical composition shown in Table 1
3 tons of electricity using IS standard SUJ2 equivalent steel
Furnace melting, no homogenization, and 4-24 hours at 1240 ° C
When the four types of homogenization are performed,
Steel ingots with different deposition levels were prepared. Table 1 above
In the case of steel ii, the chemical composition satisfies the conditions specified in the present invention.
Steel. [0043] [Table 1] Next, the above steel ingots are hot forged by a normal method.
To make a steel slab, and then hot rolled to a diameter of 40 mm
Bar steel was used. Steel bar with a diameter of 40 mm obtained in this way
After mirror polishing the cross section of the EDX, attach it to the EDX attached to the SEM
Therefore, “1.3% of Cr content in a steel bar having a diameter of 40 mm.
The width of the region where the Cr content exceeds twice is as follows:
And investigated. That is, the EDX probe diameter is 1 μm.
And the center of the cross section of the steel bar as the measurement start point
Up to “R / 10” part (that is, about 2 mm from the center)
The line analysis was performed 3 times for Cr and the measurement was performed.
Using the chart, the Cr analysis value is the Cr content in the steel bar
The widest part among the parts that were 1.3 times more than
The width of the “Cr content in a steel bar having a diameter of 40 mm”
The width of the region where the Cr content exceeds 1.3 times "
Set. The steel bar having a diameter of 40 mm is made of 118
After heating to 0 ° C, shear cutting was performed with a P10 carbide blade.
When the cutting blade life was investigated. Furthermore, the diameter is 40mm
Machined parallel to the rolling direction from the center of the steel bar
Screws with parallel part length and diameter 50mm and 10mm respectively
Specimens for sampling tests were collected and 1050 ° C, 1100 ° C and
And at a temperature of 1150 ° C. for 15 minutes,
Hot torsion test at rpm, until breaking at the above 3 temperatures
The average value of the number of twists was determined. Further, from the central portion of the steel bar having a diameter of 40 mm.
Parallel to rolling direction, diameter 12mm, length by machining
Cut out a 22 mm test piece, quench the test piece,
Reversion treatment (holding at 820 ° C for 30 minutes, oil quenching,
Tempering at 160 ° C. for 1 hour) and subjected to a rolling fatigue test.
In other words, using a cylindrical rolling fatigue tester,
Using # 68 turbine oil, maximum Hertz contact stress is 5
900MPa, test piece loading frequency is 46000 times / minute
A rolling fatigue test was conducted. 10 specimens for each steel
Remove the surface and remove the surface first of the 10 test pieces.
The rotational speed at this time was defined as “rolling fatigue life”. Rolling fatigue
Working life is 1.0 × 10⁷ In these cases, rolling fatigue characteristics
Evaluated as excellent. Table 2 shows “Cr in steel bar with a diameter of 40 mm”.
Width of the region where the Cr content exceeds 1.3 times the content "
(In the table, described as “Cr segregation band width / diameter”), cutting
Blade life, that is, breaking load is 1.3 times the first one
Number of cuts at the time, twist to break at the above three temperatures
Average value (in the table, simply “number of twists until break”)
Listed) and rolling fatigue life survey results. [0048] [Table 2] From Table 2, it is clear that the chemical composition and
The width of the Cr segregation band in the cross section is defined by the present invention.
If the condition is satisfied, the desired number of twists of 84 times or less and 1.
0x10⁷ The above rolling fatigue life is obtained together.
The In contrast, the segregation of Cr in the cross section.
If the width of the band is outside the conditions specified in the present invention,
The desired number of twists of 84 times or less and 1.0 × 10⁷ More rolling
Any of the fatigue lives has not reached the desired value. (Example 2) Three steels A to M having chemical compositions shown in Table 3 were used.
After melting in a 00kg vacuum furnace, 5 minutes of hot water in a 50kg mold
5 steel ingots (ingots) having the same chemical composition
Individually made. Steels B to D, G to H and M in Table 3
Is a steel whose chemical composition satisfies the conditions specified in the present invention.
On the other hand, steel A, E, F and I to L are any of the components.
In the steel of the comparative example deviating from the content range specified in the present invention.
is there. [0051] [Table 3]Four of the five steel ingots of steels A to M above
Next, homogenized heat treatment was performed using an electric furnace.
It was. Homogenization heat treatment conditions (heat pattern) are as follows
These four conditions. Condition W: heated to 1240 ° C. and held for 4 hours
After cooling outside the furnace, Condition X: heated to 1240 ° C. and held for 8 hours, then outside the furnace
Allowed to cool, Condition Y: after heating to 1240 ° C. and holding for 12 hours, furnace
Let cool outside, Condition Z: after heating to 1240 ° C. and holding for 24 hours, furnace
Allow to cool outside. Next, five steel ingots for each steel,
In other words, four steel ingots that have been subjected to the above-mentioned homogenization heat treatment and casting
A total of five steel ingots without any homogenization treatment were 1200
Heated to ℃ and hot forged at a finishing temperature of 950 ℃, then
The product was allowed to cool in the atmosphere to obtain a round bar having a diameter of 40 mm. like this
The segregation of Cr in the round bar with a diameter of 40 mm
The width of the strip was measured. That is, each round bar with a diameter of 40 mm
After mirror polishing the cross section of the EDX, attach it to the EDX attached to the SEM
Therefore, “1.3% of Cr content in a round bar with a diameter of 40 mm.
The width of the region where the Cr content exceeds twice is as follows:
And investigated. That is, the EDX probe diameter is 1 μm.
2 with the center of the cross section of the round bar as the measurement start point
The line analysis was performed 3 times for Cr up to the position of mm.
Using the measurement chart, the analysis value of Cr is Cr
The widest of the locations that were 1.3 times the content
The width of a large portion is the above-mentioned “Cr content in a round bar having a diameter of 40 mm.
The width of the region where the Cr content exceeds 1.3 times the amount "
Decided. Further, from the center of a round bar having a diameter of 40 mm.
Parallel to the forging axis, the length and diameter of the parallel part are machined.
Take 50 mm and 10 mm specimens for torsion testing, respectively.
Temperature at 1050 ° C, 1100 ° C and 1150 ° C
For 15 minutes and then hot torsion test at 300 rpm
The average value of the number of twists until rupture at the above three temperatures is obtained.
I tried. Also, from the center of the 40 mm diameter round bar
Parallel to the forging axis, diameter 12mm, length 2 by machining
Cut out a 2mm test piece, quench and temper this test piece
Treatment (holding at 820 ° C. for 30 minutes, oil quenching, 1
Tempering at 60 ° C. for 1 hour) and subjected to a rolling fatigue test. You
In other words, using a cylindrical rolling fatigue testing machine,
Using 68 turbine oil, maximum Hertz contact stress is 59
00MPa, test piece loading frequency of 46,000 times / minute
A rolling fatigue test was conducted. 10 specimens for each steel
Each of the 10 specimens was first peeled off.
The rotational speed at the time of rolling was defined as “rolling fatigue life”. Rolling fatigue
Life is 1.0 × 10⁷ Excellent rolling fatigue characteristics in these cases
It was evaluated that. In Tables 4-6, “With a round bar with a diameter of 40 mm,
Of the region where the Cr content exceeds 1.3 times the Cr content.
Width ”(in each table,“ Cr segregation band width / diameter ”
The average value of the number of twists to break at the above three temperatures
(In each table, simply describe as “Number of twists until break”)
The survey results of dynamic fatigue life are summarized. [0058] [Table 4][0059] [Table 5][0060] [Table 6] As is apparent from Tables 4-6, the steel of the comparative example
In the case of a test number using A and steels I to L, that is, including C
Test numbers 1 to 5 using steel A with an amount of less than 0.8%,
P content exceeds 0.025% and “P (%) + 2
Test using Steel I with a value of "S (%)" exceeding 0.040%
Test numbers 41-45, S content is over 0.015%,
And "P (%) + 2S (%)" exceeds 0.040%
Test number 46-50 using steel J, Ti content is 0.0
Test numbers 51-55 with steel K above 02%, and
Using steel L with O (oxygen) content exceeding 0.0015%
Test numbers 56 to 60 have a rolling fatigue life of 1.0 × 10
⁷ Has not reached times. Of the above, test numbers 41, 42, 46, 4
7, 51 and 56 have a "Cr segregation band width / diameter" of 0. 0.
Since it exceeds 0030, the rolling fatigue life is particularly short. Of the above, test numbers 4, 5, 53, 5
4, 59 and 60 have a "Cr segregation band width / diameter" of .0.
Since it is below 0003, the number of twists to break in the twist test
Even the target value has not been reached. Test number 21 using comparative steels E and F
˜30, “Cr segregation band width / diameter” is the
Although it is within the range, the value of “P (%) + 2S (%)” is
Since it is less than 0.020%, the twist until the break in the twist test
More than 84 times. Of the above, test numbers 24, 25, 29 and
30 is "Cr segregation band width / diameter" below 0.0003
Since it is turning, the number of twists is particularly large. Content range defined by the present invention for chemical composition
Even if the steel is in the test number 6, 11, 16, 3
1, 32, 36 and 37 are "Cr segregation band width / diameter"
Is over 0.0030, so the rolling fatigue life is 1.0 ×
10⁷ Has not reached times. Also, test numbers 9, 10,
14, 15, 20, 40, 64 and 65 are "Cr segregation.
Since the “width / diameter of the belt” is below 0.0003,
The number of twists until breakage in the bending test is more than 84 times. In contrast to the above comparative example, the conditions defined in the present invention.
Test Nos. 7, 8, 12, 1 which are examples of the present invention that satisfy the conditions
3, 17-19, 33-35, 38, 39, 61, 62
And 63, the desired number of twists of 84 times or less and 1.
0x10⁷ The above rolling fatigue life is obtained together.
The [0068] The round steel material of the present invention is excellent in “hot workability”.
(Ie, “long tool life for hot working”)
Also, the rolling fatigue life is long, so balls, rollers, and needles
As a material for bearing element parts such as
Can be used.

─────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme code (reference) F16C 33/62 F16C 33/62

Claims (1)

What is claimed is: 1. By mass%, C: 0.8 to 1.2%, Si:
0.2-2.0%, Mn: 0.2-1.5%, Cr:
0.5-2.0%, P: 0.005-0.025%,
S: 0.003 to 0.015% and P (%) + 2S
(%): 0.020-0.040%, Al: 0.01-
0.05%, N: 0.005 to 0.012%, Cu:
1.0% or less, Ni: 2.0% or less, with the balance being F
e and impurities, Ti in impurities is 0.002%
Hereinafter, O (oxygen) is a round steel material of 0.0015% or less, and when the radius is R, (R /
In the segregation zone existing in the region up to 10), the width of the region having a Cr content exceeding 1.3 times the Cr content in the round steel material is 0.0003 to 0.003 of the diameter of the round steel material.
Round steel material for bearing element parts with excellent hot workability characterized by being doubled.