JPH075960B2 - Method for manufacturing cold forging steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a cold forging steel used as a material for a machine structural steel part, for example, a mechanical part such as a spindle, a joint or a gear. The manufacturing method,
More specifically, the cold forgeability is improved by reducing the Si and Mn contents of the medium and low carbon low alloy steel, and B
The present invention relates to a method for producing a cold forging steel in which the hardenability is guaranteed by adding Ti and Ti, and the cold forgeability is further improved by controlling the heating temperature and the finishing temperature of hot rolling.

[Conventional technology]

Cold forging of steel is more productive than conventional hot forging and cutting, suitable for mass production, and has good dimensional accuracy of products. Further, it has been widely applied to the production of machine structural parts because it has a high material yield and can meet the demands of automation and high speed of the process. In particular, recently, there has been a demand for application to a part having a large shape and a complicated shape and a large workability.

By the way, in order to improve the cold forgeability of the steel and increase the life of the forging die, it is desirable that the C content of the steel is low. However, when the C content is reduced, there is a problem that the induction hardenability is deteriorated and desired surface hardness and hardened layer depth cannot be obtained. Therefore, improvement of the cold forgeability of steel having a high C content has been demanded because of the necessity of increasing the size of the cold forged product and ensuring the induction hardenability.

The cold forging steel of Japanese Examined Patent Publication No. 1-38847 was proposed to solve such problems in cold forging of steel, and the cold forgeability is reduced by reducing the contents of Si and Mn. , And by adding B and Ti, the hardenability is guaranteed.

[Problems to be solved by the invention]

The present invention has been made to further improve the previously proposed cold forging steel of Japanese Examined Patent Publication No. 1-38847, and further improves the cold forgeability as compared with the previous proposal and carburizes and quenches. An object of the present invention is to provide a method for producing a steel for cold forging which is applicable to case hardening alloy steel and toughened and tempered tough alloy steel.

[Means for solving problems]

As a result of intensive studies by the inventors to solve the above problems, the cold forging property is further improved by rolling the cold forging steel according to the previous proposal at a low temperature, and the carbon steel is induction hardened. The present invention has been completed by newly finding that it can be applied not only to case hardening alloy steel for carburizing and quenching and toughening alloy steel for quenching and tempering.

The method for producing the cold forging steel of the present invention is C: 0.10% by weight.
0.65%, Si: 0.15% or less, Mn: less than 0.50%, B: 0.0005 to 0.
0050%, Ti: 0.050% or less, SolAl: 0.015 to 0.050% is contained, and if necessary, Ni: 2.0% or less, Cr: 1.5% or less, Mo: 0.4
% Or less, one or more kinds are contained, and more desirably, Cu: 0.30% or less, P: 0.030% or less, S: 0.035% or less, N: 0.010% or less, O: 0.0020% or less , Pb: 0.30% or less, Te: 0.10 if necessary to improve machinability
% Or less, Ca: 0.005% or less, Bi: 0.10% or less, and one or more types are added. Nb: 0.05% or less, Ta: 0.05% or less, Zr as necessary for grain refinement. : 0.05% or less,
Cold forgeability, characterized in that one or more of these are added and the balance is steel consisting essentially of Fe and hot-rolled under the conditions of heating temperature: 1100 ° C or less and finishing temperature: 1000 ° C or less. And a method for producing cold forging steel having excellent hardenability.

The steel for cold forging to which the present invention is applied has good cold forgeability by reducing the Si content and the Mn content even when the C content is increased, and particularly lowers the Mn content. As a result, the initial amount of ferrite in the as-rolled material and the pearlite lamellar spacing are increased to reduce hardness,
The hardness after spheroidizing annealing is also reduced to improve the cold forgeability, and the addition of B and Ti reduces the hardenability due to the reduction of the Si content and the Mn content. In order to ensure the quenching depth, the tendency of crystal grain coarsening due to B addition is
The feature is that the addition of lAl was used to prevent it.

Hereinafter, the reasons for limiting the component range (% by weight) of the cold forging steel excellent in cold forgeability and hardenability produced by the present invention will be described.

C: 0.10 to 0.65% C is an element necessary to secure the strength of machine structural parts, and 0.10 to maintain the toughness and strength of case hardening steel.
% Or more must be added. However, if it is too large, quench cracking tends to occur during induction hardening, so the content was limited to 0.65% or less.

Si: 0.15% or less Si is an element that acts as a deoxidizer during melting, but if it is contained as a normal deoxidizer, cold forgeability deteriorates, so cold forgeability is improved. Therefore, the content is limited to 0.15% or less.

Mn: less than 0.50% Mn is an element that acts as a desulfurizing agent at the time of melting and is an element that improves hardenability, but if added in an amount necessary to obtain sufficient hardenability, it becomes Si Similarly, since cold forgeability is deteriorated, in order to improve cold forgeability, it is limited to less than 0.50%.

B: 0.0005 to 0.0050% B is an element added to compensate for the deterioration of the hardenability due to the reduction of the Si content and the Mn content and to secure the necessary quenching depth. 0 to get the effect.
It is necessary to contain 0005% or more. However, if contained in a large amount, the crystal grains are coarsened and the toughness is lowered, so the content is limited to 0.0050% or less.

Ti: 0.050% or less Ti is an element added to ensure the improvement of the hardenability by adding B, but if it is too much, the toughness decreases, so it is 0.
Limited to 050% or less. Further, the more desirable content of Ti is 0.005 to 0.050%.

SolAl: 0.015 to 0.050% Al is an element that is effective in preventing the coarsening tendency of crystal grains due to the addition of B, improving the strength, and remarkably reducing the strain after quenching. At 0.015
% Or more. However, if it is too large, the crystal grains will be coarsened and the toughness of the steel will be reduced, so the content was limited to 0.050% or less.

Ni: 2.0% or less, Cr: 1.5% or less, Mo: 0.4% or less, Ni, Cr, Mo enhance the strength of the steel, and further supplement the hardenability improvement by adding B, and at the same time, provide a sufficient quenching depth by quenching. Since it is an element effective for obtaining the required amount, it may be added if necessary. However, if the amount is too large, the effect is saturated and the cold forgeability is deteriorated. Therefore, it is preferable to limit the composition range.

Cu: 0.30% or less Cu strengthens the dough, but since it is an element harmful to cold forgeability,
If necessary, it should be regulated to 0.30% or less.

P: 0.030% or less P content of too much impairs toughness and deteriorates cold forgeability, so 0.030% or less, more preferably 0.020% or less
It is good to regulate to less than%.

S: 0.035% or less If the S content is too large, the cold forgeability deteriorates, so
It is preferable to regulate it to 035% or less, more desirably 0.020% or less. However, if the S content is too low, the machinability is deteriorated. Therefore, if the machinability improving element described later is not added, it may be contained to the extent that the cold forgeability is not deteriorated. It is desirable to regulate the range.

N: 0.010% or less If the N content is too large, the deformation resistance increases and the cold forgeability deteriorates. Therefore, it is more preferable to control the content to 0.010% or less.

O: 0.0020% or less If the O content is too large, the amount of inclusions in the steel increases and the cold forgeability decreases, so it is more preferable to control the content to 0.0020% or less.

One or more of Pb: 0.30% or less, Te: 0.10% or less, Ca: 0.005% or less Pb, Te, Ca are elements effective for improving machinability,
Since it is effective in compensating for the decrease in machinability when the S content is considerably suppressed in order to improve the cold forgeability, it may be appropriately added within the above range if necessary.

One or two or more of Nb: 0.05% or less, Ta: 0.05% or less, and Zr: 0.05% or less. Nb, Ta, and Zr are elements that contribute to refine the crystal grains and improve the toughness. If necessary, it may be added within the above range.

The conditions for hot rolling were that the heating temperature was 1100 ° C or lower and the finishing temperature was 1000 ° C because deformation resistance was extremely low when cold forging the steel hot-rolled under these conditions, and the cold forgeability was excellent. This is because steel can be obtained. If hot rolling is performed at the heating temperature or higher and the finishing temperature or higher, the crystal grains after finishing the rolled product are coarsened and the cold forgeability is deteriorated. Therefore, the rolling conditions are set to the heating temperature and the finishing temperature or lower.

〔Example〕

Examples of the present invention will be described to clarify the effects of the present invention.

Steel with the chemical composition (% by weight) shown in Table 1 was melted in an electric furnace, subjected to external refining, cast into an ingot, slab-rolled, and then compact rolled to produce a rolled material with a diameter of 25 mm. .

In Table 1, No. 1 to No. 4 are steels of the present invention, and No. 5 to No.
No. 8 is a comparative steel. No. 1 is the steel of the present invention in which the amounts of Si and Mn of the comparative steel of No. 5 are regulated and B and Ti are added. As well
No. 2 is No. 6, No. 3 is No. 7, and No. 4 is invention steel corresponding to No. 8, respectively, in which the amounts of Si and Mn are regulated and B and Ti are added.

As for the rolling conditions of the rolled material, as shown in Table 2, two types of rolling were performed: a rolling condition according to the present invention and a rolling condition at a temperature higher than that of the present invention for comparison.

Then, a cold forged test piece having a diameter of 6 mm and a height of 12 mm was manufactured from each of the rolled pieces, and part of the cold forged test piece was subjected to spheroidizing annealing.

Subsequently, 60% cold upset forging was performed on the cold forged test piece as-rolled and the cold forged test piece subjected to spheroidizing annealing to forge a height of 4.8 mm, at that time. The deformation resistance of was investigated. The results are shown in Table 3.

In Table 3, No. 1 to No. 4 are examples of the present invention obtained by hot rolling the present invention steel under the rolling conditions of the present invention, and No. 5 to No. 8 are the present invention steels. It is a comparative example hot-rolled at a higher temperature, and No. 9 to No. 12 are comparative examples hot-rolled at a higher temperature than the rolling conditions of the present invention.

As shown in Table 3, No. 1 to No. 4 of the present invention have the same chemical composition but are deformed more than No. 5 to 8 with different rolling conditions, both the rolled material and the spheroidized annealing material. It is clear that the resistance is small and the cold forgeability is excellent. Further, N of the present invention example
o.1 to No.4 have the same C content and the same amount of Ni, Cr, Mo.
Compared with Comparative Examples No. 9 to No. 12 containing, both the rolled material and the spheroidized and annealed material have much smaller deformation resistance and are clearly superior in cold forgeability.

〔The invention's effect〕

The method for producing cold forging steel according to the present invention has a weight percentage of C: 0.10.
~ 0.65%, Si: 0.15% or less, Mn: less than 0.50%, B: 0.0005 ~
Contains 0.0050%, Ti: 0.050% or less, SolAl: 0.015 to 0.050%, Ni: 2.0% or less, Cr: 1.5% or less, Mo:
Steel containing one or more of 0.4% or less,
Since hot rolling is performed at a heating temperature of 1100 ° C or less and a finishing temperature of 1000 ° C or less, not only carbon steel for induction hardening but also case hardening alloy steel for carburizing and hardening and toughening alloy steel for quenching and tempering There is an excellent effect that the cold forgeability is remarkably improved and the hardenability is sufficiently ensured.

Claims (2)

[Claims] 1. C: 0.10 to 0.65% by weight: Si: 0.15% or less, M
n: less than 0.50%, B: 0.0005 to 0.0050%, Ti: 0.050% or less,
SolAl: 0.015 to 0.050%, the balance steel consisting essentially of Fe is hot-rolled at a heating temperature of 1100 ° C or less and a finishing temperature of 1000 ° C or less. Excellent cold forging steel manufacturing method. 2. C: 0.10 to 0.65% by weight% Si: 0.15% or less, M
n: less than 0.50%, B: 0.0005 to 0.0050%, Ti: 0.050% or less,
SolAl: 0.015 to 0.050%, Ni: 2.0% or less,
Cr: 1.5% or less, Mo: 0.4% or less, one or more types of steel is contained, and the balance consists essentially of Fe. Hot temperature: 1100 ° C or less Finishing temperature: 1000 ° C or less A method for producing a cold forging steel excellent in cold forgeability and hardenability, characterized by rolling.