JPH01219148A - Non-thermal free-cutting steel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a non-thermal free-cutting steel, and particularly to a non-thermal free-cutting steel that has improved machinability without reducing strength.

(Background Art) Non-tempered steel has been known that can be made into a product by finishing processing such as cutting after hot working without performing thermal refining such as quenching and tempering. Since such non-heat treated steel does not require heat treatment such as quenching and tempering, it is very advantageous to use non-heat treated steel in terms of cost reduction and process simplification. It is. However, such non-tempered steel has to be cut in a hardened state, making it relatively difficult to process.
Conventionally, free-machining elements such as S and PB have been added for the purpose of improving the machinability of such non-tempered steel.

However, as the amount of these free-machining elements increases, the free-machinability of non-heat treated steel improves, but on the other hand, the problem arises that its strength decreases. It was. For this reason, the amount of free-machining elements added to -i had to be kept low.
In the end, it has been difficult to simultaneously obtain the required sufficient free machinability and strength in non-tempered steel.

(Problem to be solved) The present invention has been made against the background of the above-mentioned circumstances, and the problem to be solved is to obtain excellent machinability in non-thermal treated steel. Then,
The objective is to solve the problem of reduced strength, and to provide a non-thermal free-cutting steel that has sufficient strength and improved machinability.

(Solution Means) To solve this problem, the present invention provides carbon (C) up to 0.60%, silicon (Si) up to 2.5%, and manganese up to 2.0% on a weight basis. (Mn) and up to 0.5% vanadium (V) and 0.5%, respectively.
Contains up to 5% of one or two of niobium (Nb) and further contains 0.0040-0.0200% boron (B) and 0.0050-0.0500% nitrogen (N)
%N/%B is 0.5 to 4.0, and contains 0.0015% or less of oxygen (0), titanium (Ti),
The gist is a non-thermal free-cutting steel with excellent machinability characterized by containing 0.01% or less of zirconium (Zr) and rare earth elements (REM) in total.

In this way, in the present invention, in order to improve machinability, B and N are contained during melting of non-thermal steel, and in the subsequent solidification process and hot working process, free machinability is improved. This precipitates fine N (hexagonal boron nitride) that exhibits excellent effects. Moreover, such BN precipitates contain sulfides,
Compared to the free-machining element precipitates of Pb, their size is small and very fine, and they are also stable at high temperatures, which makes them superior to the mechanical properties (strength) of non-tempered steel. It will not deteriorate.

Furthermore, in the present invention, oxygen, which forms oxides with B and inhibits the precipitation of BN, and T, which has a strong tendency to form nitrides,
By reducing i, Z r % RE M to the utmost limit, it was possible to stably precipitate fine N inclusions.

Therefore, in the present invention, it was possible to produce a non-thermal free-cutting steel with excellent machinability without deteriorating its mechanical properties.

In addition, in the present invention, such B and N are not usually added as a BN compound. If BN itself is added to molten steel, since its specific gravity is small, there is a risk that it will float on top of the molten steel, and it will not be mixed uniformly.

By the way, the non-thermal free-cutting steel according to the present invention preferably has:
Nickel (Ni) up to 5.0% by weight, 5.0
% chromium (Cr), up to 3.0% molybdenum (
It further contains one or more of Mo), and by adding these elements, the strength can be further improved.

Further, in the present invention, preferably, on a weight basis, 0
．． up to 40% sulfur (S), up to 0.40% selenium (
Ss), up to 0.10% tellurium (Te), 0.40%
lead (Pb) up to 0.40%, bismuth (B i
), 1 of calcium (Ca) up to 0.01%
A seed or two or more kinds are further added, thereby further improving the free machinability.

By the way, the action of each alloy component of the non-tempered free-cutting steel according to the present invention and the reason for limiting the content thereof are as follows. Note that all percentages shown below are based on weight.

C: 0.60% or less C is an essential element to ensure strength, but if it is contained in a large amount it will reduce toughness, so the upper limit is 0.
．． It is said to be 60%. However, in order to ensure a certain degree of strength, the content is preferably 0.05% or more.

Si: 2.5% or less Si is an effective element as a deoxidizing agent and is necessary to prevent the occurrence of surface defects in copper ingots. is assumed to be 2.5%. However, in order to exhibit the effect of Si, 0
．． The content is preferably 0.02% or more.

Mn: 2.0% or less Mn is effective as a deoxidizing agent and desulfurizing agent, and has the effect of preventing hot embrittlement due to S by forming sulfides such as MnS. Since it deteriorates machinability, its upper limit is set at 2.0%. however,
In order to exhibit the effect of Mn, the lower limit is preferably 0.10%.

V: 0.5% or less Nb: 0.5% or less These elements form carbides and carbonitrides, and these compounds precipitate finely in the steel, thereby improving the strength of the steel. However, if they are included in large amounts, hot workability deteriorates, so the upper limit is 0.5 for each.
%. However, in order to ensure a certain degree of strength of the steel, it is preferable that each of them be contained in an amount of 0.01% or more.

B: O, OO40~0.0200%N: 0.0
050-0.0500% However, %N/%B: 0.5
~4.0 These elements precipitate in the steel as BN, which has the effect of free machinability, and improve the machinability. Moreover, since such BN precipitates finely, it does not reduce mechanical properties (strength). In order to fully utilize the effect, set B to 0,
It is necessary to add N by 0.0040% or more, and N by 0.0050% or more. However, when the B content exceeds 0.0200%, hot workability deteriorates, and when the N content exceeds 0.0500%, castability deteriorates. Furthermore, if %N/%B is less than 0.5, hot workability deteriorates, and if it exceeds 4.0, castability deteriorates.

0: O, 0O 15% or less 0 forms an oxide with B and inhibits the formation of BN, so
Its content is kept as low as possible, 0.0015% or less.

Ti+Zr+REM: 0.01% or less These elements form nitrides with N and inhibit the formation of BN, so the upper limit of their total amount is set to 0.01%.

In addition, REV is from La with atomic number 57 to 71 with atomic number
refers to one or more of the elements up to Lu.

Ni: 5.0% or less Cr: 5.0% or less Mo: 3.0% or less These elements are effective for improving strength, but
If the upper limits of each of these elements are exceeded, machinability deteriorates. However, in order to exhibit the effects of these elements favorably, they are preferably added at 0.3% or more, 0.1% or more, and 0.05% or more, respectively.

S: 0.40% or less Se: 0.40% or less Te: Q, lQ% or less Pb: 0.40% or less Bi: Q, 49% or less Ca: 0.10% or less These elements affect machinability However, if the upper limit of each of these elements is exceeded,
Strength and hot workability deteriorate. however,
In order to exhibit the effects of these elements satisfactorily, S and Se are preferably 0.01% or more and 0.01%, respectively.
As described above, Te is added in an amount of 0.005% or more, Pb is added in an amount of 0.01% or more, Bi is added in an amount of 0.01% or more, and Ca is added in an amount of o, oos% or more.

(Examples) Hereinafter, some examples of the present invention will be shown to clarify the present invention more specifically, but it is understood that the present invention is not limited in any way by the description of such examples. It goes without saying that this is not something you should accept.

In addition to the following embodiments and the above-described specific description, the present invention includes various changes, modifications, and changes based on the knowledge of those skilled in the art without departing from the spirit of the present invention. It should be understood that improvements and the like may be made.

First, cast steel having a composition consisting of the alloy components shown in Table 1 below (the remainder is Fe and unavoidable impurities) was heated to 2 t.
After melting in an on-arc furnace and refining in a refining furnace, it was made into a 1.3 ton ingot, which was then rolled into a bar with a diameter of 50 as+ and air cooled. Then, a cutting test and a tensile test were conducted on each of the obtained steels. Note that numbers 1 to 18 are cast steels according to the present invention, and A to F are comparison steels adjusted to have tensile strengths corresponding to the respective steels of the present invention.

By the way, as a cutting test, each steel was turned with a carbide tool, and the flank wear of the tool was 0.2.
The cutting time corresponding to mm was determined. And those values,
Comparison steel B was converted as a standard (1,0), and each was compared as a tool life ratio. In addition, the tensile test for measuring the strength was performed from near the surface layer of the 50 mmφ rolled material by JI
No. S4 tensile test specimens were taken and tests were conducted on each.

The results obtained are shown in Table 2 below.

Table 2 As is clear from the comparison between Tables 1 and 2, Invention Steel 1 and Comparative Steel A were adjusted to have a tensile strength of 60 kg f 7 mm'' class, and The present invention tli
i12. 3. 4 and comparative steels B, C, and D are 70 kg
f/mm'' class tensile strength, and the invention steel 5 and comparative steel E have been adjusted to have a tensile strength of 80 kg f/mm'' class.

Invention steels 6 to 8 have the same carbon level as invention steel 5 (
Invention steels 9 to 15 have the same carbon level and alloy composition as comparative fjJ4B, and comparative steel F has the same carbon level and alloy composition as comparative fjJ4B. A free-machining element was added to the steel, and the strength was made to be at the same level as Invention Steel 2 and Comparative W4B, respectively.

Furthermore, invention steels 16 to 18 were steels with the same carbon level and alloy composition as invention fas 6 to 8, with additional free-machining elements added to them, and the same level of strength as invention steels 6 to 8. It is something.

From the values of tool life ratio and tensile strength shown in Table 2, it can be seen that compared to comparative MA-E, invention steels 1 to 5 have a longer tool life without any decrease in tensile strength, that is, strength. The ratio, or machinability, has been significantly improved. Furthermore, compared to Inventive Steel 5, Inventive Steels 6 to 8 have strength-enhancing elements added, which advantageously improves the strength and also ensures good machinability. Furthermore, compared to Inventive Steel 2, Inventive Steels 9 to 15 have free-machining elements added thereto, which advantageously improves machinability and also ensures good strength. And invention steel 6~
Compared to Steel No. 8, Invention Steels Nos. 16 to 18 exhibited better strength and machinability due to the addition of strength-enhancing elements and free-machining elements.

(Effects of the Invention) As is clear from the above explanation, the non-thermal treated steel according to the present invention contains B and N, and precipitates fine N which exhibits an excellent effect on free machinability. B by forming an oxide
By minimizing oxygen, which inhibits N precipitation, and Ti, Zr, and REM, which tend to form nitrides, we were able to stably precipitate fine N inclusions. The machinability of non-tempered free-cutting steel could be significantly improved without deteriorating its mechanical properties, and this is where the great industrial significance of the present invention lies.

Claims (3)

[Claims] (1) Contains up to 0.60% carbon, up to 2.5% silicon, and up to 2.0% manganese, by weight;
and contains one or two of up to 0.5% vanadium and up to 0.5% niobium, and further contains 0.0
040-0.0200% boron and 0.0050-0.0200% boron.
Contains 0.500% nitrogen such that %N/%B is 0.5 to 4.0, and also contains 0.0015% or less of oxygen and 0.01% or less of titanium, zirconium, and rare earth elements in total. A non-thermal free-cutting steel with excellent machinability. (2) Up to 5.0% nickel, 5.0% by weight;
The non-thermal free-cutting steel according to claim 1, further comprising one or more of up to 3.0% of chromium and up to 3.0% of molybdenum. (3) Sulfur up to 0.40%, 0.40% by weight;
Claims further containing one or more of the following: selenium up to 0.10%, tellurium up to 0.10%, lead up to 0.40%, bismuth up to 0.40%, calcium up to 0.01% Non-thermal free-cutting steel according to item (1) or (2).