JPS59173250A - Free cutting spring grade steel and preparation thereof - Google Patents

Abstract

PURPOSE:To obtain spring grade steel excellent in free cutting property, by containing C, Si, Mn, Cr, Si, Te and Al, V and Nb in a predetermined ratio. CONSTITUTION:Free cutting spring grade steel consists of, on a wt. basis, 0.4- 0.75% C, 1-2.5% Si, 0.5-1% Mn, 0.1-1% Cr, S<=0.4% and Te<=0.16% and further additionally contains 0.01-0.1% Al, 0.03-0.3% V and 0.01-0.3% Nb and the ratio of Te/S thereof is limited to 0.04-0.4. This steel is excellent in free cutting property.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a free-cutting spring copper having excellent machinability such as machinability and grindability, and a method for manufacturing the same.

Conventionally, JIS 5UP6゜5UP was used as copper for splashing.
7, etc., but one of the factors that reduces the machinability of such copper for splashing is the presence of hard giant integrants present in the steel (Article A, o3).

S i02 , Cr203 ) and carbonitrides (Nb(C,N), V(C,N), Zr(C,'N)
It is already known that these inclusions wear cutting tools or abrasive grains by an abrasive mechanism. In addition, S combines with Mn in steel to form MnS, which is effective in improving the machinability of steel, but this MnS is released in the working direction by plastic working such as rolling or forging. It has been said that the drawback is that it stretches into a long and thin strip, resulting in anisotropy in strength. Therefore, the actual situation is that the improvement in machinability by MnS is not very desirable.

On the other hand, in the manufacturing process of springs, there are many processes such as cutting using a peel-link machine, which is seen in taper coil springs, center drilling when the grip part of torsion bars, etc., is serrations or splines, and cutting the outer diameter. Because it involves cutting, the machinability of copper for springs is poor.
There are extremely strong demands for the second. This means that
The same applies to grinding.

However, conventional copper for springs has problems in that it does not have sufficient rigidity such as machinability and grindability, and is not very desirable in terms of machining accuracy, tool life, productivity, etc.

The present invention has been made to address these conventional problems, and has been developed to improve machinability by expanding sulfides such as MnS contained in steel into elongated strips during hot working by adding Te. The object of the present invention is to provide a copper for springs with improved properties.

The free-cutting spring copper according to the present invention has a weight percentage of C.0.4.
0-0.75%, Si:1. O~2.5%, Mn: 0.
5~l', o%, Cr:O,l-1,0%, S
: 0.4% or less, Te: 0.16% or less, and Te (%
)/S (%) is 0.04 or more''20, including an amount of 4 or less,
Furthermore, depending on the purpose of use, A, Q: 0.01-0.1%
, ■2 0.03-0.3%, Nb: O, Of ~0
．． 3% or more, and Pb: 0.3% or less, B i: 0, 3% or less, and Se: 0.3% or less.

Contains one or more of Ca:O, 01% or less,
The remainder consists of Fe and impurities, and is characterized by uniformly dispersed spherical sulfides.

Further, the method for producing copper for free-cutting springs according to the present invention includes C: 0.40 to 0.75%, Si: 1.0 to 2.0% by weight.
5%, Mn+0.5~1.0%, Cr:O, 1~10%
is the basic component, and if necessary, Ni: 0.2 to 25%
, MO・0.1~06%, Zr:0.01~0.12%
, TiO, 02-012%, W: 0.05-1.0%,
Cu: 0.2-3.0%, B: 0.0005-0.01
%, REM: 0.3% or less, co.

005-08%, Be: 0.01-1.0%, etc., as free-cutting elements, S: 0.4% or more, Te: 0.16
% or less, Pb: 0.3% or less, Bi
: 0.3% or less, Se: 0.3% or less, Ca・0.01
% or less, and if necessary, lQ:
o, 01-0.1%, V: 0.03-0.3%, NbO
, 01 to 0.3%, in order to produce copper for free-cutting springs containing 01 to 0.3%, molten steel in which the above basic components and S are adjusted to a predetermined content in advance in a furnace or ladle is subjected to degassing treatment,
Sentence A above if necessary.

After adding V and Nb, non-oxidizing scum is introduced into the molten steel in a container such as a ladle or tundish, and by force stirring, large non-metallic inclusions are floated and separated into two parts. It is characterized in that Te and Pb, Bi, Se, and Ca selected as necessary are added to the molten steel flow during pouring and are uniformly dispersed.

Next, the reason for limiting the content range (% by weight) of the copper for free-cutting blades according to the present invention will be explained.

C (carbon): C is an element effective for increasing the strength of steel, or 0.
If it is less than 40%, it will not be possible to obtain the necessary strength as a spring, and if it exceeds 0.75%, reticular cementite will be likely to appear and the fatigue strength of the spring will be impaired.
．． The range was set at 75%.

Si (silicon).

Si is an effective element for increasing the strength of steel and improving the fatigue resistance of springs; however, if it is less than 0%, it is not possible to obtain the fatigue resistance necessary for springs. , 2.5%
Since toughness deteriorates when the content exceeds 1.0% to 2.5%.

Mn (Mankan): Mn is an element that is effective in deoxidizing steel and improving the hardenability of steel, and for this purpose, Mn is an element that is effective in deoxidizing steel and improving the hardenability of steel.
- Although it is necessary to contain it, if it exceeds 10%, hardenability becomes excessive and toughness deteriorates, and it is likely to cause deformation during quenching, so the content was set in the range of 0.5 to 1.0%. .

Cr (Chromium) Cr is an effective element for preventing decarburization and graphitization of high carbon steel, but if it is less than 0.1%, these effects cannot be fully expected; Since toughness deteriorates when the content exceeds 0.1% to 1.0%.

S (Sulfur), Te (Tellurium) S is an element that improves machinability such as machinability and grindability of steel, and by containing it in combination with Te, the effect of improving machinability is further enhanced. It is possible to make it "direct". However, if it is contained in a large amount, the hot workability and strength of the steel will be reduced, so it is set at 0.4% νF.

Te suppresses internal cracking of steel slabs in steel containing S in a range of 0.54% or less, and also improves plastic workability such as rolling and forging by spheroidizing sulfides such as M n S. It is an effective element for preventing the occurrence of strength anisotropy in steel later.

In order to achieve such an effective effect, Te(%
)/S(%) or 0.04 or more.

However, if a large amount of Te is contained, it will impair the hot workability of the steel.
) is set to be 0.4 or less.

AIC aluminum), ■ (vanadium), Nb (
Niono).

An, V, and Nb have a large grain refining effect during low-temperature rolling, and can improve spring characteristics and increase reliability. Also, V and Nb have a significant effect on precipitation hardening during quenching and tempering. also contributes. Therefore, depending on the purpose of use, in addition to the above ingredients, sentence A, ■.

It is also possible to contain one or more types of Nb. At this time, for A text, if it is less than 0.01%, the effect of crystal grain refinement is small, and if it exceeds 0.1%, it will cause scratches, so it was set in the range of 0.01 to 01%. Also,
With regard to
If it exceeds 0.03, it becomes difficult to handle the steel.
The range was set to 0.3%. Furthermore, Nb(N b +T
Regarding (a), if it is less than 0.01%, the effect of crystal grain refinement and precipitation hardening cannot be expected much, and the effect of suppressing crystal grain coarsening during quenching heating cannot be obtained sufficiently, and 0.3% If it exceeds this value, carbide (N b C) and ringer-like substances are formed during agglomeration, which does not become a solution during normal blooming and is difficult to dissolve during subsequent heat treatment, resulting in poor spring properties as a product. Therefore, it was set in the range of 0.01 to 0.3%.

Pb (lead), Bi (bismuth), Se (selenium), Ca (calcium); Pb, B'i, Se, and Ca are all effective elements for further improving the machinability of steel. , one or more of these may be contained depending on the purpose of use. However, if contained in large amounts, the fatigue strength and hot workability of the steel will be reduced, so Pb is 0.3% or less, Bi is 0.3% or less, and Bi is 0.3% or less.
% or less, Se to 0.3% or less, and Ca to 0.01% or less.

Note that 0 (oxygen) produces moltenite-based inclusions, which may become the starting point of fatigue failure, so depending on the purpose of use, it is also desirable to keep this limit to 0.0015% or less. . Furthermore, since B (holon) is an effective element for increasing the hardenability of steel, it may be added in a range of 0.0005 to 0.01% depending on the purpose of use, such as large diameter springs.

When manufacturing copper for springs with such components, the basic components of steel and S are prepared in advance in a furnace or ladle.
After degassing the molten steel that has been adjusted to a predetermined content and adding the aforementioned Ai, V, and Nb as necessary, non-oxidizing gas is introduced into the molten steel in a container such as a ladle or tundish. By force stirring, large nonmetallic inclusions are floated and separated, and Te and optionally selected Pb are added to the molten steel during stirring or the molten steel flow during pouring.

At least one of Bi, Se, and Ca is added and dispersed uniformly, so that a structure in which spherical sulfides are uniformly dispersed can be obtained even after plastic working such as rolling and forging.

Note that as the scum removal treatment performed in this manufacturing method, conventionally known methods such as the DH method and the RH method are employed. By degassing the molten steel and forcibly stirring the molten steel using non-oxidizing gas, it becomes possible to sufficiently separate large inclusions that are harmful to the machinability of the steel and the strength of the spring. It becomes possible to significantly improve the characteristics and reliability thereof. Furthermore, by adding Te and, if necessary, Pb, Bi, Se, and Ca to the molten steel during IW stirring or the molten steel flow during pouring and casting, the additive yield can be significantly improved. At the same time, uniform dispersion becomes possible, which greatly contributes to improving the spring characteristics and its reliability.

Hereinafter, this invention will be explained in more detail with reference to Examples and Comparative Examples.

First, melting is performed in an arc furnace to remove Te among the chemical components of steel.
, Pb, Bi, Se, and other alloy components other than Ca are adjusted to predetermined amounts, and then the molten steel is transferred to a vacuum degassing treatment vessel to perform vacuum degassing treatment, and if necessary, Al
, Nb, and V are added, and then the molten steel is transferred into a ladle with a porous plug at the bottom, and non-oxidizing scum is blown into the molten steel through the porous plug, and Te is added while forcibly stirring.
The value of Te (%)/S (%) is 0 depending on the amount of S in the molten steel.
04 or more and 0.4 or less, and Pb
, Bi, Se, and Ca, one or more of these was added in a predetermined amount in conjunction with the addition of Te. In addition, A sentence, V, Nb.

Pb, Bi, Se, and Ca may be added to the molten steel flow when it is transferred into a ladle equipped with a gas blowing device after the vacuum degassing treatment. Next, the above molten steel was poured into 2 parts by pouring method, respectively.
Manufactured into a 5 ton steel ingot. Next, each steel ingot was heated to 1260°C.
After thorough soaking at a temperature of Second, hot rolling is carried out, followed by controlled rolling using Ar after rolling and cooling at a cooling rate of 30°C/min or more to the transformation point to make the shape of the sulfide spheroidal. A spring steel material in which sulfides were uniformly dispersed was manufactured, and test materials were taken from this spring steel material.

Table 1 shows the chemical components of each sample material. In addition, in Table 1, No. 14 is 0°5 to 0.6 m/m into a 480 x 370 mm mold through Kundi and Shu.
It was continuously cast at a drawing speed of 1.5 in. and hot rolled after soaking.

Next, in order to investigate the shape of sulfide for each sample material,
Within a certain microscope field, the long axis L (pL) of the sulfide crab 0
The length L and breadth W (river) of the specimens larger than 100 cm were measured, and the ratio (percentage) of sulfides with a length ratio L/W of 5 or less in the measured sulfides was investigated. The results are also shown in Table 1. As shown in Table 1, in all comparative steels, the content was 15% or less, and it was found that there was a considerable amount of elongated sulfides that were not spheroidized and had a length ratio of more than 5. On the other hand, in the steel of the present invention, all 8
0%, and most of the sulfides have a length ratio of 5 or less, which indicates that the sulfides in the steel of the present invention are substantially spherical, and there is no difference in strength. It was found that almost no polarization occurred.

In addition, in order to investigate the amount of giant oxides and carbonitrides in each sample material, the area percentage occupied by giant oxides and carbonitrides within a certain microscope field of view was measured. The results are also shown in Table 1. As shown in Table 1, it is clear that the steel of the present invention has a significantly lower amount of giant oxides and carbonitrides than the comparative steel, and it has improved spring characteristics and reliability. I found out that it is. This clearly shows the effects of degassing treatment and forced stirring using non-oxidizing gas on molten steel.

／ ／ ／″ 7′ ／′ ／ 7, / Next, in order to examine the machinability of each test material, we used test pieces with a diameter of 11 mm that had been annealed to form a spheroid. Automatic lathe cutting was carried out under the cutting conditions shown in Table 2. The results are shown in Table 3. This evaluation of machinability was carried out by measuring the flank face wear of the tool when cutting 500 pieces. but,
As shown in Table 3, it is clear that the steels of the present invention have less wear and better machinability than the comparative steels, and the effects of the addition of S and Te, as well as Pb.

The effects of adding Bi, Se, and Ca are clear.

Furthermore, in order to investigate the grindability of each sample material, each sample material was subjected to grinding processing under the grinding conditions shown in Table 4 after performing the machinability test described in Section 2. The power consumption during grinding was measured. The results are shown in Table 3.

As shown in Table 3, the grinding voltage consumption of the steel of the present invention is generally lower than that of the comparison steel.

It is clear that it also has excellent grindability.

Furthermore, in order to investigate the fatigue strength of each sample material, test pieces with a diameter of 11 mm were prepared, and each test piece was subjected to spheroidizing annealing, cutting, and then quenching and tempering. The hardness of the test piece was adjusted to HRC45-48, and then a fatigue test was conducted on the young sample using an Ono rotary bending fatigue tester.

The results are also listed in Table 3. As shown in Table 3, in the steel of the present invention, no significant strength deterioration was observed compared to the comparative steel, and the addition of S and Te, as well as Pb, Bi, Se,
It became clear that there were no problems in strength due to the addition of Ca.

7, / 7/'' / 2/' / Table 2 Table 3 Table 4 As explained above, the free-cutting spring steel according to the present invention has a carbon content of 0.40-075% and a Si of 1.0- 2.5%
, Mn+0.5~1.0%, Cr・0.1~1.0% as basic components, S: 0.4% or less, Te
: 0.16% or more and Te (%) / S (%) or 0.0
Depending on the purpose of use, one or more of AfL, V, and Nb may be included in order to further improve the splash characteristics and increase reliability. In order to further improve machinability.

Since it contains one or more of Pb, Bi, Se, and Cac7), sulfides such as MnS contained in the steel can be
By adding e, it is possible to make it spherical without elongating it during hot working, and it is possible to significantly improve machinability such as machinability and grindability without causing strength anisotropy. It is possible, and cutting processing with a peeling machine or 1.
- It is possible to perform center hole machining or grinding of the grip part with high precision and high efficiency, and has the remarkable effect of extending tool life and improving productivity. .

Furthermore, according to the method for producing copper for splinters according to the present invention, it is possible to add elements that improve machinability with a high yield, and at the same time, it is possible to add elements that improve machinability and spatter strength. Second, harmful large inclusions can be removed extremely efficiently, and high-quality free-cutting copper can be produced, which is a significant effect.

Representative Patent Attorney Yutaka Shio

Claims (5)

[Claims] (1) In weight%, C: 0.40-0.75%, Si: 1
．． 0-2.5%, Mn: 0.5-1.0%, Cr: 0.
Contains or has 1 to 1.0%, S2 0.4% or less, Te: 0
．． It is characterized by containing 16% or less and a Te (%) / S (%) of 0.04 or more and 0.4 or less, with the balance consisting of Fe and impurities, and spherical sulfides or uniformly dispersed. Copper for free cutting. (2) C: 0.40 to 0.75% by weight. Si: 1.0-2.5%, Mn: 0.5-1.0%, C
r: Contains O, l-1,0%, S204% or less, Te
: 0.16% or less, Te (%)/S (%) is 0.0
Contains an amount of 4 or more and 04 or less, Sarani A9. : 0, 0
1~O, i%, v20, 03~0, 3%, N
b: Copper for free-cutting blades containing one or more of 0, 01 to 0, 3%, the remainder consisting of Fe and impurities, and having spherical sulfides uniformly dispersed. . (3) 1% by weight, C: 0.40-0.75%, Si:
1. O-2.5%, Mn+0.5-1.0%, Cr:0
．． Contains 1 to 1.0%, S2 0.4% or less, Te: 0
．． 16% or less, including walls with Te(%)/S(%) of 0.04 or less, Pb: 0.3% or less, Bi: 0.3% or less, Se: 0.3% or less, Ca: 0
Contains 0.01% or less of one or more of the following, with the remainder being F.
Copper for free-cutting springs, which is composed of e and impurities, and is characterized by uniformly dispersed spherical sulfides. (4) In weight%, C: 0, 40-0.75%, Si
:1.0-2.5%, Mn+0.5-1.0%, Cr:
Contains 0.1 to 1.0%, S2 0.4% or less, Te:
0.16% or less Te(%)/S(%) is 0.04
"20, Contains an amount of 4 or less, and further A sentence: 0.01 ~
0.1%, ■=0.03~0.3%, Nb:0.01~
0.3% of one or more types, and Pb: 0.3
% or less, Ei: 0.3% or less, Se: 0.3% or less. Ca: 0.0]% or less of one or more types (1)
Copper for free-cutting splinters, characterized in that the balance consists of Fe and impurities, and spherical sulfides are uniformly dispersed. (5) wt% -, C: 0.40-0.7-5%, Si
:1.0-2.5%, Mn:0.5-1.0%, Cr.
01 to 10% is the main component, and S is the free cutting element.
04% or less, TeO, 16% or less, and P
b: 0.3% or less, Bi: 0.3% or less, Se: 0.3
% or less, Ca: 0.01% or less, and if necessary, A, Q: 0.01-0.1%. In producing free-cutting copper containing V: 0.03-0.3% and Nb: 0.01-03%, the above basic components and S are prepared in a predetermined content in a warming furnace or ladle. The molten steel adjusted to
After adding , V, and Nb, non-oxidizing gas is introduced into the molten steel in a container such as a ladle or tundish, and large non-metallic inclusions are removed by forced stirring. ! let me,
Te and optionally selected Pb and Bi are added to the molten steel during stirring or the molten steel flow during pouring. A method for producing copper for free-cutting splinters, characterized by adding and uniformly dispersing Se and Ca.