JPH059652A - Non-heat-treated steel for forging having excellent machinability - Google Patents

Abstract

PURPOSE:To provide non-heat-treated steel for hot forging imparting sufficiently high strength and toughness and satisfactory drillability to a product without carrying out heat treatment. CONSTITUTION:This non-heat-treated steel for hot forging consists of, by weight, 0.19-0.29% C, 0.05-0.5% Si, 1.0-3.0% Mn, 0.05-0.5% V, 0.29-0.79% Cr, >0.02-0.1% Al, 0.02-0.3% S, 0.02-0.3% Pb and the balance of Fe with impurity elements or further contains <=0.1% Nb and/or <=0.1% Ti and has >=90kgf/mm<2> tensile strength, 5kg f/cm<2> Charpy impact value 2UE20 deg.C and drillability made higher than that of other non-heat-treated steel having the same strength by >=20%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-heat treated steel for hot forging excellent in machinability, and particularly to a product having sufficient strength and toughness without being subjected to heat treatment such as quenching and tempering after hot forging. The present invention relates to a non-heat treated steel that is imparted and also has good machinability.

[0002]

2. Description of the Related Art Various structural parts have been used after being subjected to a tempering treatment such as quenching and tempering after forging to obtain the required strength and toughness according to the purpose and application. In this case, since a large amount of heat energy is required for the refining treatment, the refining treatment is expensive and the manufacturing cost is high.

On the other hand, from the viewpoint of energy saving and cost reduction, a non-heat treated steel capable of omitting the heat treatment has been developed and has already been put to practical use for structural parts.

[0004]

However, the conventional non-heat treated steel for hot forging has a tensile strength of 90 kgf.
Although a value of / mm ² or more can be obtained relatively easily, there is a problem in that the toughness is insufficient as compared with the tempered steel, and the machinability decreases as the strength increases.

In view of such a problem, the present invention is 90 k
An object of the present invention is to provide a non-heat treated steel for hot forging, which has good toughness and drill piercing property despite having a strength of gf / mm ² or more.

[0006]

[Means for Solving the Problems] The inventors of the present invention
90 kgf by adjusting C, Si, Mn, Cr, V for strength, C, Mn, Cr, V, Nb, Ti for toughness and S, Pb for machinability.
/ Mm ² or more, _2U E ₂₀ ℃ = 5kgf / cm
^The inventors have found that a structural non-heat treated steel having a toughness of ² or more and a drill piercing property improved by 20% or more as compared with the conventional non-heat treated steel having the same strength can be obtained, and thus the present invention has been completed. It is a thing.

That is, the non-heat treated steel for hot forging according to the first invention of the present application is "C: 0.19 to 0.29% Si: 0.05 to 0.5% Mn: 1 by weight ratio. 0.0 to 3.0% V: 0.05 to 0.5% Cr: 0.29 to 0.79% Al: more than 0.02 to 0.1% S: 0.02 to 0.3% Pb: 0.02 to 0.3%, the balance consisting of Fe and impurity elements, tensile strength of 90 kgf / mm ² or more, Charpy impact value _2U E
_It has a combined temperature of ₂₀ ° C = 5 kgf / cm ² or more, and further has improved drill piercing property by 20% or more compared to other non-heat treated steels having the same strength. "

Further, the non-heat treated steel for hot forging according to the second invention of the present application has "C: 0.19 to 0.29% Si: 0.05 to 0.5% Mn: 1 by weight ratio. 0.0 to 3.0% V: 0.05 to 0.5% Cr: 0.29 to 0.79% Al: more than 0.02 to 0.1% S: 0.02 to 0.3% Pb: 0.02 to 0.3%, Nb: 0.1% or less, Ti: 0.1% or less, one or two kinds, and the balance of Fe and impurity elements. 90 kgf / mm ² or more,
In addition to having a Charpy impact value of _2U E ₂₀ ° C = 5 kgf / cm ² or more, the drill piercing property was further improved by 20% or more compared to other non-heat treated steels having the same strength. "

[0009]

The reason why each component is limited as described above in the present invention will be described below. [C: 0.19 to 0.29%] C is effective for increasing the strength of steel, and it is necessary to add 0.19% or more in order to obtain 80 kgf / mm ² or more without tempering. . However, in order to secure the target toughness in the steel of the present invention, the upper limit is set to 0.29% in consideration of the relationship with other elements that affect the toughness (Mn, V, Cr, S). [Si: 0.05 to 0.5%] In addition to being added as a deoxidizing agent during melting, Si must be added in an amount of 0.05% or more to secure the strength. However, if it exceeds 0.5%, the toughness is lowered and the desired toughness cannot be obtained in the steel of the present invention, so the upper limit is made 0.5%. [Mn: 1.0 to 3.0%] Like Si, Mn is an element effective in improving strength and toughness in addition to being added as a deoxidizing agent during melting, and is effective in obtaining desired strength and toughness. Should be added in an amount of 1.0% or more in consideration of the correlation with other alloying elements. However, since Mn reduces machinability on the other hand,
In order to secure the desired machinability in the steel of the present invention, the upper limit is set to 3.0% in consideration of the relationship with other elements (C, P, V) that affect the machinability. [V: 0.05 to 0.5%] V is an important element for ensuring strength and toughness without hot forging, that is, without tempering, and its effect is remarkable at 0.05% or more. become. However, if it exceeds 0.5%, the effect is saturated, so the upper limit is made 0.5%. [Cr: 0.29 to 0.79%] Cr is an effective element together with V in order to secure the strength and toughness in the as-hot-forged state, and becomes remarkable at 0.29% or more. However, 0.79
%, The toughness decreases, so the upper limit is 0.7.
9%. [Al: more than 0.02 to 0.1%] Al is added as a deoxidizing agent during melting, and is also effective for refining crystal grains.
If it is 0.01% or less, the effect is small. Also, 0.1%
, The machinability will deteriorate, so the upper limit is 0.1.
% Or less. [S: 0.02 to 0.3%] In the steel of the present invention, it is necessary to add at least 0.02% or more in order to improve machinability. However, if it exceeds 0.3%, the hot workability deteriorates, problems in manufacturing occur, and the toughness also decreases, and the desired toughness cannot be obtained, so the upper limit is 0.3%.
And [Pb: 0.02 to 0.3%] Like S, Pb is an element effective for improving machinability, and its effect appears when 0.02% or more. However, if over 0.3%, the hot workability deteriorates, so the upper limit is made 0.3%.

[Nb: 0.1% or less, Ti: 0.1% or less] The second invention steel of the present application is the same as the first invention steel in addition to Nb.
And / or Ti is added, and it is completed for the purpose of making the grain size finer, particularly improving the toughness, and using it for parts requiring particularly high toughness. However, the effect does not increase even if both Nb and Ti are added in excess of 0.1%, so the upper limit is made 0.1% or less.

[0011]

EXAMPLES Steel having the components shown in Table 1 was melted using a 100 kg vacuum melting furnace. 1200 kg of steel ingot
By forging at φ65 and φ30 steel bars, and using this to make notch Charpy test pieces, tensile test pieces and test pieces for drill piercing properties, Charpy impact test, tensile test and drill piercing test ( Φ of SKH51 as a drill
8 JIS standard drill was used to measure the time required to perforate a depth of 10 mm at a load of 70 kgf and a rotation speed of 915 rpm. Here, Table 1 shows the chemical composition of each test material, and Table 2 shows the test results. Comparative steel No. 1,
2 and 3 are heat-treated steels, and comparative steels 4, 5, and 6 are non-heat-treated steels that have been used conventionally. In addition, comparative steel No. Nos. 7 to 11 are non-heat treated steels similar to the present invention steel.

[0012]

[Table 1]

[0013]

[Table 2]

According to the test results, no.
For 1 and 2, the toughness and drillability are 22.1 kg.
f / cm ² and 8.4 sec and 12.1 kgf / cm
² and 8.9 seconds are good, but strength is 69kgf
/ Mm ² and 76 kgf / mm ² , which is insufficient. Further, Comparative Steel No. 3, which is a tempered steel, is well balanced, but requires a large amount of heat energy for the tempering treatment, resulting in a high manufacturing cost.

Comparative steel Nos. 4 and 5 which are conventional non-heat treated steels
For, the toughness and drillability are 8.1 kgf / c
m ² and 10.1 sec and 5.1 kgf / cm ² and 10.4 sec are good, but strength is 76 kgf / m
m ² and 79 kgf / mm ² , which is insufficient. Similarly, Comparative Steel No. 6, which is a conventional non-heat treated steel, has an excellent strength of 92 kgf / mm ² , but has toughness and drillability of 3.7 kgf / cm ² and 13.0 s.
ec is not good.

Comparative steel N containing a small amount of Mn, Cr and V
o. 7 and 8, the tensile strength is 65 kgf / mm ²
And 75 kgf / mm ² and low, C, in the comparative steel No. 9 Cr amount is large, the tensile strength despite high as 112kgf / mm ^2, toughness becomes low as 2.7kgf / cm ^2. Further, in Nos. 10 and 11 not containing Pb and S, the drill piercing properties are 13.2 sec and 12.8 se.
c is inferior.

On the other hand, invention steel No. 12 to
No. 20 has a large strength of 90 kgf / mm ² or more, and has a Charpy impact value of _2U E ₂₀ ° C = 5 kgf / c.
It has excellent toughness with m ² or more. Furthermore, by adding Pb and S free-cutting elements, the drill piercing property could be improved by 20% or more in spite of the high strength compared to the non-added steel.

[0018]

INDUSTRIAL APPLICABILITY As described above, according to the non-heat treated steel for hot forging according to the present invention, sufficient strength and toughness and good drilling can be achieved without performing heat treatment such as quenching and tempering after hot forging. Since piercing properties can be imparted to the product, it becomes possible to apply it to parts for machine structures.

[Figure 1]

[Fig. 2]

Claims (2)

[Claims] 1. By weight ratio, C: 0.19 to 0.29% Si: 0.05 to 0.5% Mn: 1.0 to 3.0% V: 0.05 to 0.5% Cr: 0.29 to 0.79% Al: more than 0.02 to 0.1% S: 0.02 to 0.3% Pb: 0.02 to 0.3%, with the balance being Fe and impurity elements And has a tensile strength of 90 kgf / mm ² or more and a Charpy impact value of _2U E
_For hot forging with excellent machinability, which has a combined temperature of ₂₀ ° C = 5 kgf / cm ² or more and has improved drill piercing properties by 20% or more compared to other non-heat treated steels having the same strength. Non-heat treated steel. 2. A weight ratio of C: 0.19 to 0.29% Si: 0.05 to 0.5% Mn: 1.0 to 3.0% V: 0.05 to 0.5% Cr: 0.29 to 0.79% Al: more than 0.02 to 0.1% S: 0.02 to 0.3% Pb: 0.02 to 0.3%, and Nb: 0.1% Ti: 1% or less of 0.1% or less, the balance of Fe and impurity elements, and a tensile strength of 90 kgf / mm ² or more,
It has a Charpy impact value of _2U E ₂₀ ℃ = 5kgf / cm ² or more, and has improved drilling properties by 20% or more compared to other non-heat treated steels with the same strength. Excellent machinability. Non-heat treated steel for hot forging.