JPS6393846A - Non-heattreated-type hot-forging steel excellent in toughness and machinability - Google Patents

Abstract

PURPOSE:To manufacture a non-heattreated-type hot-forging steel excellent in machinability as well as in toughness, by incorporating specific amounts of Pb and N to a steel having a specific composition in which V and Ti are added in combination for improving toughness. CONSTITUTION:The hot-forging steel has a composition consisting of, by weight, 0.20-0.45% C, 0.01-1.5% Si, 0.80-2.0% Mn, 0.01-0.20% V, 0.003-0.010% Ti, <=0.009% S, 0.04-0.35% Pb, N in an amount satisfying an inequality, and the balance Fe. In this steel, S has a machinability-improving function but, when its content exceeds 0.009%, deterioration in toughness and toughness anisotropy are brought about. Pb is added for improving machinability in place of S and improves machinability while causing practically no deterioration in toughness and, as to its additive quantity, an amount of >=0.04% is required, but, even if Pb is added by the amount exceeding 0.35%, an effect corresponding to the additive quantity cannot be expected. Moreover, required strength cannot be obtained when Ti/N is 2.5 or above and, when 2.5% or below, required toughness cannot be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a non-thermal hot forging steel having excellent toughness and machinability.

[Conventional technology and its problems]

Traditionally, hot forged materials were subjected to quenching and tempering after hot working to ensure strength and toughness, but in recent years, this refining has been omitted from the perspective of energy saving, and tempered steel has been made as hot forged. A non-tempered steel with properties equivalent to that of steel has been developed.

Various proposals have been made to date for this type of steel, but most of them are aimed at improving toughness, which is a disadvantage of non-tempered steel.
-It is made of Ti composite added steel. Such proposals include, for example, JP-A-56-169723 (V alone addition), JP-A-59-9122 (mainly ■ alone addition), JP-A-61-56235 (V, Ti and N
However, in such conventional steels, in the hope of improving 81j resistance, for example, in JP-A-56-169723, S was added to 0.
Since it is added in the range of 0.02 to 0.12 Wtqb, 0.05 wt % or less in JP-A-59-9122, and o, s wt % or less in JP-A-61-56235, it is harmful to toughness. This has a major disadvantage in that the amount of MnS increases, resulting in a decrease in toughness and an increase in anisotropy.

The present invention was made in view of these conventional drawbacks.
The object of the present invention is to provide a non-thermal hot forging steel with excellent toughness and machinability.

[Means to solve the problem]

Therefore, in the present invention, C: 0.20 to 0.45 wt%,
Si: 0.01~1.5wt'4, Mn:
0.80-2.0wt%, V: 0.01-0.2
0wt%, Ti: 0.003-0.010wt
俤, S: 0.009wt or less, Pb: 0.04~
Its basic characteristics are that it contains 0.35 wtes, N so as to satisfy 0.2 < Ti/N < 2.5, and the remainder consists of Fe and unavoidable impurities.

Hereinafter, the details of the present invention will be explained together with the reasons for its limitations.

C functions to ensure strength, and if it is less than 0.20 wt%, it is economically disadvantageous to have to increase the amount of Mn, etc. added in order to ensure the required strength. on the other hand.

If C exceeds 0.45 wt%, the required strength will be greatly exceeded, which is not preferable. Therefore, C is 0.20 to 0.4
5 wt chi.

St is an element necessary as a deoxidizer or to increase strength, and if it is less than 0.01 wt%, its effect is insufficient. However, if the content exceeds 1.5 wt%, a structure that is unfavorable in terms of toughness may appear. For this reason, Si
is 0. O1 to 1.5wt.

Mn is required to be at least 0.5% or sowt% to ensure strength, but if the content is 2.5% or more. If it exceeds 0.8 wt%, an undesirable structure may appear in terms of toughness, so Mn is 0.8
0-2. Let's say 0wt.

(2) is an element necessary to bring about an increase in strength through precipitation hardening, and for this purpose, 0.01wt1 or more is required. However, even if it is added in an amount exceeding 0.20 wt%, an effect commensurate with the amount added cannot be obtained, and on the contrary, it impairs economic efficiency. For this reason V
is 0.01 to 0.20 wt%.

Ti is an element necessary to improve toughness by refining austenite grains, and it is necessary to add 0.003 wt% or more, but adding more than 0.010 wt% will cause problems in strength properties. Therefore, Ti
is o, ooa to 0.010wt.

Is S an element that improves the machinability of steel?

If the S content exceeds 0.009 wt %, the toughness value will decrease and the anisotropy of toughness will increase. Therefore, in the present invention, we do not expect any improvement in machinability due to S, and the content is set to 0.009 wt %.
less than or equal to

PB is added for the purpose of improving machinability instead of S, and has the effect of improving machinability without impairing toughness. S
A major feature is that this Pb is added in an optimal manner instead of PB to improve machinability without impairing toughness. In order to obtain such an effect, it is necessary to add Pb in an amount of 0.04 wt% or more, but even if it is added in excess of o,aswt*, it cannot be expected that the effect will be commensurate with the amount added, and on the contrary, it will be less economical. This results in damage to the Therefore, pb is 0.04 to 0.35 w
It is assumed to be t%.

N is an element necessary to form nitrides with V and strengthen precipitation, but in terms of relative value to Ti, Ti/N≧2.
．． 5, the amount of N combined with V becomes too small due to TiN formation, and the necessary strength cannot be obtained, and conversely, Tl/N < 0
．． In No. 2, the formation of TiN is too small and the necessary toughness cannot be obtained. Therefore, N is 0.2 < Ti/N < 2.5
Is there a need to make it a wholesaler?

〔Example〕

Invention steel A having the chemical components shown in Table 1.

B and comparative steels C, D, E, F, G, H, and I were melted in a 150 mm melting furnace and rolled into a 60 mm thick plate.

These steel plates were heated to 1200°C and rolled to simulate hot forging in 3 baths to a thickness of 30 fins to obtain test materials. Then, while still rolling, tensile and impact test pieces were taken from the center of the plate thickness in the rolling direction (hereinafter abbreviated as the down direction), and impact test pieces were taken from the center of the plate thickness in the direction perpendicular to the rolling direction (hereinafter abbreviated as the C direction). The specimens were sampled and tested using JIS No. 4 for tensile strength and JIS No. 3 for impact leather.

Figure 1 shows the machinability of the sample steel of this example, organized by drill life in drill cutting, and shown in terms of the ratio of the impact values in the C direction and the L direction. , the steel of the present invention has improved both toughness anisotropy and machinability, and instead of reducing the toughness anisotropy by reducing the S content to 0.009 w1j or less and not expecting any improvement in machinability due to S. The effect of improving machinability by adding Pb is fully evident.

In addition, Figure 2 shows the toughness values of the test steels organized by the impact values in the L direction and their relationship with the amount of S.
: It can be seen that the toughness is greatly improved at 0.009 wt% or less.

〔Effect of the invention〕

According to the present invention described above, not only can heat treatment after hot forging be omitted, but also excellent toughness including anisotropy,
Moreover, it has excellent machinability and can provide steel suitable as a material for hot forged parts.

[Brief explanation of the drawing]

Figure 1 shows the machinability (drill life) of the test steel in the example.
is shown in relation to the ratio of the impact values in the C direction and the L direction. Figure 2 also shows the toughness of the test steel (impact value in the L direction).
is shown in relation to the amount of S. Patent applicant: Nippon Kokan Co., Ltd. Inventor: Satoshi Ishizaki Between the lines
White God Tetsu Unexplored
Hirotada Osuzu, Patent Attorney
Masato Yoshihara, Masato Tomabechi, Attorney Hiroko Yoshihara (Jl.
o (J1 Doril Island Life Imm
l

Claims (1)

[Claims] C: 0.20 to 0.45 wt%, Si: 0.01 to 1.
5wt%, Mn: 0.80-2.0wt%, V: 0.0
1-0.20wt%, Ti: 0.003-0.010w
t%, S: 0.009wt% or less, Pb: 0.04-0
．． 35wt% and N to satisfy 0.2<Ti/N<2.5, with the remainder being Fe and unavoidable impurities. Non-thermal heat treatment with excellent toughness and machinability. Steel for forging.