JP2007107059A - Method for manufacturing base material having excellent cold forgeability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a base material which has a reduced cost due to a shortened annealing period of time, and shows high deformability while being cold-forged. <P>SOLUTION: The method for manufacturing the base material comprises the steps of: forging a steel material containing, by mass%, 0.1-0.6% C, at 200°C to 820°C, while imparting a distortion of 0.3 or more to the steel material; and then annealing it at 600°C to 780°C. The steel material further includes 0.03-0.6% Si, 0.1-1.0% Mn, 0.1-1.5% Cr, 0.01-0.5% Mo, 0.01-3% Ni, 0.01-0.5% Al and 0.003-0.03% N, as needed; and still further one or more elements of 0.001-0.01% Ti, 0.0005-0.0020% B and 0.01-0.09% Nb, in some cases. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a material having a low deformation resistance during cold forging and a high deformability and excellent cold forgeability.

For example, when manufacturing mechanical structural parts, conventionally, steel is hot forged (for example, the heating temperature is 1000 to 1200 ° C.) and then subjected to spheroidizing annealing (SA), followed by cold forging. Then, it was molded into a shape close to the final product, and then finished by machining.
Here, the spheroidizing annealing treatment spheroidizes carbides (cementite) in the lamellar structure of pearlite and disperses them finely, and it takes a long time for the heat treatment.
However, conventional spheroidizing annealing does not sufficiently spheroidize and disperse carbides, and therefore, when cold forging is performed at a high processing rate, there is a problem that processing cracks are likely to occur. It was.

The reason why such a crack occurs during cold forging is that the carbide does not spheroidize sufficiently and pearlite lamellar remains, and strain concentrates on the long and narrow lamellar, which becomes the starting point of the crack.
As countermeasures, it is possible to reduce the cooling rate during slow cooling during the spheroidizing annealing process. In this case, the time required for the spheroidizing annealing process becomes longer, which increases the manufacturing cost. It was a big factor.

The present invention has been devised to solve such problems.
As a prior art for the present invention, there is one disclosed in Patent Document 1 below.
However, the one disclosed in Patent Document 1 is different in manufacturing conditions such as a hot forging temperature of 800 ° C. or higher, and a structure as in the present invention cannot be obtained.

JP-A-6-299241

  In the background of the above circumstances, the present invention can simplify or shorten the heat treatment time required for the annealing treatment to reduce the cost, and has high deformability at the time of cold forging and excellent cold forgeability. It was made for the purpose of providing the manufacturing method of a raw material.

  Thus, the manufacturing method of claim 1 is forging a steel material containing C: 0.1 to 0.6% by mass at a temperature of 200 ° C. or higher and 820 ° C. or lower and a strain of 0.3 or higher, and then 600 ° C. or higher and 780 ° C. or lower. It is characterized by annealing at a temperature of

  The manufacturing method of claim 2 is C: 0.1-0.6%, Si: 0.03-0.6%, Mn: 0.1-1.0%, Cr: 0.1-1.5%, Mo: 0.01-0.5%, Ni: 0.01- 3%, Al: 0.01-0.5%, N: 0.003-0.03% steel is forged at a temperature of 200 ° C to 820 ° C and strain of 0.3 or more, and then annealed at a temperature of 600 ° C to 780 ° C It is characterized by doing.

  The manufacturing method according to claim 3 contains one or more of Ti: 0.001 to 0.01%, B: 0.0005 to 0.0020%, Nb: 0.01 to 0.09% in addition to each component of Claim 2 in mass%. The forged steel material is forged at a temperature of 200 ° C. or higher and 820 ° C. or lower and a strain of 0.3 or higher, and then annealed at a temperature of 600 ° C. or higher and 780 ° C. or lower.

Effects and effects of the invention

  As described above, the present invention involves forging a steel material containing C: 0.1 to 0.6% at a temperature of 200 ° C. or higher and 820 ° C. or lower and a strain of 0.3 or higher, and thereafter annealing at a temperature of 600 ° C. or higher and 780 ° C. or lower. is there.

In the case of a conventional manufacturing method in which annealing is performed after hot forging, the austenite grains are once flattened by hot forging as shown in the schematic diagram of FIG. The grains grow after being divided into grains and become large round austenite grains 10.
And it transforms by the subsequent air cooling and becomes ferrite pearlite grains 12.
In the figure, 14 indicates ferrite and 16 indicates pearlite.

Thereafter, when spheroidizing annealing (SA treatment) is performed, cementite forming the lamellar of pearlite 16 is spheroidized to form spherical carbides 18.
However, in the conventional manufacturing method, the cementite is not sufficiently spheroidized and dispersed by this spheroidizing annealing treatment, which does not give sufficient deformability to the material for cold forging, and cracks during cold forging. It was the cause.

On the other hand, when the steel material is forged at a temperature of 820 ° C. or less, preferably 780 ° C. or less, which is the recrystallization temperature of austenite according to the present invention, as shown in FIG. When the temperature is not higher than ° C., grains 22 composed of ferrite 14 and austenite 20 are formed, and then crushed by forging to become flat grains 24.
At this time, both the ferrite 14 and the austenite 20 are flat.

In the manufacturing method of the present invention, unlike the conventional manufacturing method, the flattened grains 24 are not recrystallized thereafter, and thus the flat shape is maintained as it is.
In the flattened grains 24, the austenite 20 is transformed into pearlite 26 by the subsequent air cooling.
In the figure, reference numeral 28 denotes a grain after flat pearlite transformation comprising pearlite 26 and ferrite 14 transformed by air cooling.

At this time, the flat particle 28 after transformation has a short lamellar length of the pearlite 26 after transformation as shown in FIG.
In addition, since the ferrite 14 has a flat shape and divides the lamellar, the length of the lamellar becomes shorter due to the division by the ferrite 14.
Therefore, when the annealing process is performed after that, the cementite in the lamellar structure is well spheroidized and dispersed due to the short lamellar structure, and it becomes a soft grain that does not leave much lamellar structure, resulting in a material with low deformation resistance and high deformability. give.

  The above is the case where the forging process is performed at a temperature of 780 ° C. or less at which ferrite precipitates, but even if the forging process is performed at a recrystallization temperature of 820 ° C. or less at an austenite recrystallization temperature, the forging Since the austenite grains keep a flat shape by processing and transformation is caused by subsequent cooling in that state, the length of the lamellar is similarly shortened, and the cementite is well spheroidized during the annealing treatment, and the material is deformed. Low resistance gives high deformability.

According to the present invention, even when the annealing time is shortened, a high deformability can be imparted to the material for cold forging, and the cost for manufacturing the material can be reduced.
Alternatively, when the annealing time is increased, higher deformability can be imparted to the material for cold forging than in the prior art.

  In the present invention, if necessary, the steel material contains one or more of Si, Mn, Cr, Mo, Ni, Al, N, or even Ti, B, Nb at the above-mentioned contents. (Claim 2, Claim 3).

Next, each chemical component and each reason for limitation of manufacturing conditions in the present invention will be described below.
C: 0.1-0.6%
The amount of C needs to be 0.1 to 0.6 so that the structure of the material for cold forging becomes a ferrite pearlite structure.

Si: 0.03-0.6%
Si needs to be contained by 0.03% or more in order to ensure the strength of the ferrite layer.
However, if the content exceeds 0.6%, the plastic workability deteriorates, so the upper limit is made 0.6%.

Mn: 0.1-1.0%
Mn is contained in an amount of 0.1% or more to make the pearlite layer lamellar fine.
However, if the content exceeds 1.0%, the plastic workability deteriorates, so the upper limit is made 1.0%.

Cr: 0.1-1.5%
The strength can be ensured by adding 0.1% or more of Cr.
However, if the content exceeds 1.5%, the plastic workability deteriorates, so the upper limit is made 1.5%.

Mo: 0.01-0.5%
The strength can be secured by containing Mo in an amount of 0.01% or more.
However, if the content exceeds 0.5%, the plastic workability deteriorates, so the upper limit is made 0.5%.

Ni: 0.01 to 3%
Ni can be ensured in strength by containing 0.01% or more.
However, if the content exceeds 3%, the plastic workability deteriorates, so the upper limit is made 3%.

Al: 0.01-0.5%
By containing Al in an amount of 0.01% or more, the function of crystal grain refinement by AlN can be performed.
However, the effect is saturated at 0.5%, so the upper limit is 0.5%.

N: 0.003-0.03%
It is contained in an amount of 0.003% or more for the purpose of grain refinement by AlN.
On the other hand, since it is difficult to contain 0.03% or more, the upper limit is made 0.03%.

Ti: 0.001 to 0.01%
By containing 0.001 or more Ti, crystal grains can be refined.
However, the effect is saturated at 0.01%, so the upper limit is made 0.01%.

B: 0.0005-0.0020%
By containing B in an amount of 0.0005% or more, the crystal grains can be refined.
However, the effect is saturated at 0.0020%, so the upper limit is made 0.0020%.

Nb: 0.01-0.09%
By containing Nb in an amount of 0.01% or more, the crystal grains can be refined.
However, the effect is saturated at 0.09%, so the upper limit is set to 0.09%.

Forging temperature 820 ° C. or lower and 200 ° C. or higher:
It is necessary to forge at 820 ° C. or less in order to make austenite into an elongated form without being recrystallized during forging. Preferably, forging is performed at a temperature of 780 ° C. or lower where ferrite that divides the austenite structure is present.
In the present invention, the effect is exhibited by performing forging at a temperature of 820 ° C. or less. However, when the temperature during the forging process is low, the deformation resistance becomes high, so the temperature becomes 200 ° C. or more, which is a difficult temperature. Forging.

Strain of 0.3 or more Strain of 0.3 or more is necessary so that the lamellar of the pearlite structure is divided and the carbide is easily spheroidized. Here, the strain is a true strain and is defined by the following.
Strain = absolute value | ln (length after processing / length before processing) |

Annealing at 600 ° C. or higher and 780 ° C. or lower Since plastic processing is performed at 820 ° C. or lower, processing strain remains and is hard. In order to remove this processing strain, it is necessary to heat to 600 ° C. or higher.
On the other hand, when the annealing temperature is higher than 780 ° C., the spheroidized carbide is dissolved in austenite. In the present invention, annealing is performed at a temperature of 780 ° C. or lower in order to prevent the structure from becoming an austenite monolayer.

Next, embodiments of the present invention will be specifically described below.
A round bar having a diameter of 33 mm was manufactured by forging with a steel material having the chemical composition shown in Table 1.
Next, after machining into a round bar test piece of φ24 × 50 mm, various reductions shown in Table 2 at a surface reduction ratio of 20% (strain 0.2), 30% (strain 0.4), and 65% (strain 1.1). Forward extrusion (forging) was performed at the forging temperature.
Thereafter, an annealing treatment was performed under the conditions shown in FIG. 2 and processed into a tensile test piece. And the tension test was implemented using the test piece.

FIG. 2 (a) shows the extrudate raised to the respective annealing temperatures shown in Table 2, held for 3 hours, and then air-cooled, indicated by LA in Table 2.
On the other hand, FIG. 2 (b) shows that the extruded material was heated to various annealing temperatures shown in Table 2, held at that temperature for 5 hours, and then gradually cooled to 650 ° C. at a cooling rate of 20 ° C. per hour. Then, air cooling is performed, which is indicated by SA in Table 2.
Table 2 shows the results of the tensile test together with the forging temperature, the pattern of the annealing treatment, the annealing temperature, and the tensile strength and the drawing value in detail.

In Table 2, Comparative Example A has a forging temperature of 1100 ° C., which is higher than the upper limit value of 820 ° C. of the present invention. Therefore, the annealing treatment (LA) of the pattern shown in FIG. However, the tensile strength is kept high and the squeezing value is low, so that it does not have sufficient deformability.
In Comparative Example B, the forging temperature is as high as 1150 ° C., so that even if annealing is performed thereafter, the tensile strength remains high and the drawing value is low, so that the deformability is insufficient.
In Comparative Example C, the same steel 5 as in Comparative Example B was used for forging at the same 1150 ° C. as in Comparative Example B, and thereafter the SA annealing treatment of FIG. The strength value is high and the aperture value is low, and the deformability is insufficient.

In Comparative Examples D and E, the same steel 5 as in Comparative Example C is used, and the forging temperature is set to a temperature within the range of the present invention, but the processing strain at that time is smaller than 0.3 which is the lower limit value of the present invention. Therefore, even if the LA treatment in FIG. 2A and the SA treatment in FIG. 2B are performed thereafter, the tensile strength value is high, the squeezing value is low, and the deformability is insufficient.
On the other hand, although Comparative Example F uses the same steel 5 and performs forging by applying a strain larger than the strain 0.3 specified in the present invention, the subsequent annealing temperature is the upper limit of the present invention. Since the temperature is higher than 780 ° C., both the tensile strength and the drawing value are poor, and the deformability is insufficient.
On the other hand, in Comparative Example G, although the forging and annealing conditions of the present invention are satisfied, the C content of the steel 8 used is higher than the upper limit of 0.6% of the present invention, so that the tensile strength is high. Both the aperture value is bad and the deformability is insufficient.

On the other hand, all of the examples of the present invention have excellent tensile strength and drawing values and excellent deformability during cold forging.
In the example of the present invention, as apparent from the comparison between the LA-treated and SA-treated, the SA-treated one has a lower tensile strength than the LA-treated one, and a higher aperture value. It shows a high deformability compared to that treated with LA.
That is, in the present invention, sufficient deformability can be imparted to the material for cold forging even when the processing time is shortened at a temperature lower than that of the SA treatment which is a conventional spheroidizing annealing treatment. At the same time, when the SA treatment is performed instead of the LA treatment, further excellent cold forgeability can be imparted to the material.

  Although the embodiment of the present invention has been described in detail above, this is merely an example, and the present invention can be implemented in variously modified forms without departing from the spirit of the present invention.

It is a schematic diagram explaining the effect | action of this invention compared with a comparative example. It is a figure showing the content of the annealing process in one Embodiment of this invention.

Claims (3)

  A steel material containing 0.1% to 0.6% C by mass% is forged at a temperature of 200 ° C or higher and 820 ° C or lower and strain of 0.3 or higher, and then annealed at a temperature of 600 ° C or higher and 780 ° C or lower. A method for producing a material having cold forgeability.   C: 0.1-0.6%, Si: 0.03-0.6%, Mn: 0.1-1.0%, Cr: 0.1-1.5%, Mo: 0.01-0.5%, Ni: 0.01-3%, Al: 0.01-0.5 %, N: 0.003 to 0.03% steel material is forged at a temperature of 200 ° C or higher and 820 ° C or lower and strain of 0.3 or higher, and then annealed at a temperature of 600 ° C or higher and 780 ° C or lower. A method for producing a material having cold forgeability.   A steel material containing one or more of Ti: 0.001 to 0.01%, B: 0.0005 to 0.0020%, and Nb: 0.01 to 0.09% in addition to each component of claim 2 at 200% to 820 ° C. A method for producing a material having excellent cold forgeability, characterized by forging at a temperature of the following and at a strain of 0.3 or more and then annealing at a temperature of 600 ° C to 780 ° C.

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