JPH0333775B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a free-cutting spring steel that has excellent machinability such as machinability and grindability. Conventionally, JIS SUP6 and SUP7 were used as spring steels.
However, factors that reduce the machinability of spring steels include hard giant oxides (Al ₂ O ₃ , SiO ₂ , Cr ₂ O _{3 ,} etc.) and Carbonitrides (Nb(C,N), V(C,N), Zr
(C, N) are mentioned, and 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 elongated in the processing direction by plastic processing such as rolling or forging. The drawback has been that it stretches and causes anisotropy in strength. Therefore, the actual situation is that the improvement in machinability by MnS is not very desirable. On the other hand, the manufacturing process of springs involves cutting using a peeling machine, which is seen in tapered coil springs, etc., and cutting, such as center hole drilling and outer diameter cutting, when the grip part of torsion bars, etc. is serration or spline. Therefore, there is an extremely strong demand for improving the machinability of spring steel. This also applies to grinding. However, conventional spring steels have had problems in that machinability such as machinability and grindability is not sufficient, and machining accuracy, tool life, and productivity are not very favorable. The present invention was made by focusing on such conventional problems, and by adding Te to sulfides such as MnS contained in steel, it is made spherical instead of elongated during hot working. The object of the present invention is to provide a spring steel with improved machinability without anisotropy in strength. The free-cutting spring steel according to claim 1 of the present invention has C: 0.40 to 0.75% and Si: 1.0 to 1.0% by weight.
2.5%, Mn: 0.4-1.0%, Cr: 0.1-1.0%, S: 0.4% or less, Te: 0.16% or less, and Te
(%) / S (%) includes an amount of 0.04 or more and 0.4 or less,
The remainder consists of Fe and impurities, and is characterized by uniformly dispersed spherical sulfides. In addition, the terms for free-cutting springs of the second steel according to the present invention are: C: 0.40 to 0.75% in weight%;
Si: 1.0~2.5%, Mn: 0.4~1.0%, Cr: 0.1~1.0
%, S: 0.4% or less, Te: 0.16% or less, and Te (%) / S (%) is 0.04 or more and 0.4 or less, and further Al: 0.01 to 0.1%, V: 0.03 to 0.3 %,
Nb: Contains 0.01 to 0.3% of one or more types,
The remainder consists of Fe and impurities, and is characterized by uniformly dispersed spherical sulfides. Furthermore, the free-cutting spring steel according to claim 3 of the present invention has C: 0.40 to 0.75% in weight%;
Si: 1.0~2.5%, Mn: 0.4~1.0%, Cr: 0.1~1.0
%, S: 0.4% or less, Te: 0.16% or less, and Te (%) / S (%) is 0.04 or more and 0.4 or less, Pb: 0.3% or less, Bi: 0.3% or less,
Se: 0.3% or less, Ca: 0.01% or less type 1 or 2
Contains more than one species, the remainder consists of Fe and impurities,
It is characterized by uniformly dispersed spherical sulfides. Furthermore, claim 4 according to the present invention
The free-cutting spring steel mentioned above has C: 0.40-0.75%, Si: 1.0
~2.5%, Mn: 0.4~1.0%, Cr: 0.1~1.0%, S: 0.4% or less, Te: 0.16% or less, and Te
(%) / S (%) includes an amount of 0.04 or more and 0.4 or less,
Furthermore, Al: 0.01~0.1%, V: 0.03~0.3%, Nb:
0.01-0.3% of one or more types, and Pb:
0.3% or less, Bi: 0.3% or less, Se: 0.3% or less,
Contains one or more types of Ca: 0.01% or less,
The remainder consists of Fe and impurities, and is characterized by uniformly dispersed spherical sulfides. Next, the reason for limiting the composition range (weight %) of the free-cutting spring steel according to the present invention will be explained. C (carbon): C is an effective element for increasing the strength of steel, but if it is less than 0.40%, it will not be possible to obtain the strength necessary for a spring, and if it exceeds 0.75%, reticular cementite will easily form. Since this would impair the fatigue strength of the spring, it was set in the range of 0.40 to 0.75%. Si (silicon): Si is an element effective in improving the strength of steel and the fatigue resistance of springs, but at 1.0%
If it is less than 2.5%, it will not be possible to obtain the necessary fatigue resistance as a spring, and if it exceeds 2.5%, the toughness will deteriorate, so it is set in the range of 1.0 to 2.5%. Mn (manganese): Mn is an element that is effective in deoxidizing steel and improving the hardenability of steel, and for this purpose it is necessary to contain it at 0.4% or more, but 1.0 If it exceeds %, the hardenability becomes excessive, deteriorating the toughness, and tends to cause deformation during hardening. 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.
If it exceeds 1.0%, the toughness will deteriorate, so 0.1 to 1.0
% range. S (sulfur), Te (tellurium) S is an element that improves the machinability of steel, such as machinability and grindability, and by containing it in combination with Te, it has the effect of improving machinability. This can be further improved. However, if it is contained in a large amount, the hot workability and strength of the steel will be reduced, so it is limited to 0.4% or less. Te suppresses internal cracking of steel slabs in steel containing S in a range of 0.4% or less, and also
It is an effective element for spheroidizing sulfides such as MnS, preventing the occurrence of strength anisotropy in steel after plastic working such as rolling and forging, and increasing rotary bending fatigue strength. In order to obtain such an effect, it is necessary to contain Te in such a range that Te (%)/S (%) is 0.04 or more. However, if a large amount of Te is contained, it will impair the hot workability of the steel, so the content should be 0.16% or less and Te (%)/
The range was set so that S (%) was 0.4 or less. Al (aluminum), V (vanadium), Nb (niobium); Al, V, and Nb have a large grain refinement effect during low-temperature rolling, and can improve spring characteristics and reliability. , V, and Nb also contribute to precipitation hardening during quenching and tempering. Therefore, in addition to the above ingredients, depending on the purpose of use,
It is also possible to contain one or more of Al, V, and Nb. At this time, for Al, 0.01
If it is less than 0.1%, the effect of grain refinement will be small.
If it exceeds 0.01%, it may cause ground scratches.
The range was set at ~0.1%. Also, regarding V,
If it is less than 0.03%, the above-mentioned grain refinement and precipitation hardening effects cannot be expected, and if it exceeds 0.3%, handling in steelmaking becomes difficult.
The range was set at ~0.3%. Furthermore, Nb (Nb+Ta
If it is less than 0.01%, the effect of crystal grain refinement and precipitation hardening cannot be expected, and the effect of suppressing crystal grain coarsening during quenching heating cannot be sufficiently obtained, and if it exceeds 0.3%, When lumping, carbide (NbC) is formed in the form of stringers,
This content is set in the range of 0.01 to 0.3% because it does not become a solution during normal blooming rolling and is difficult to dissolve during subsequent heat treatment, reducing the spring properties of the product. Pb (lead), Bi (bismuth), Se (selenium), Ca (calcium); Pb, Bi, Se, and Ca are all effective elements for further improving the machinability of steel, so they are used. One or more of these may be contained depending on the purpose. However, if it is contained in large amounts, it will reduce the fatigue strength and hot workability of the steel.
It is necessary to keep Pb below 0.3%, Bi below 0.3%, Se below 0.3%, and Ca below 0.01%. Note that O (oxygen) produces oxide-based inclusions,
This can be the starting point for fatigue failure, so
Depending on the purpose of use, etc., it is desirable to keep the upper limit to 0.0015% or less. In addition, B (boron) is an effective element for increasing the hardenability of steel, so depending on the purpose of use, such as large diameter springs, it is
It is also good to add in a range of %. When manufacturing spring steel with such components, molten steel in which the basic components and S of the steel have been adjusted to a predetermined content is degassed in advance in a furnace or ladle, and if necessary, the Al ,V,Nb
After adding non-oxidizing gas to the molten steel in a container such as a ladle or tundish, large non-metallic inclusions are floated and separated by forced stirring, and then the molten steel is stirred or poured. In the molten steel flow, Te and optionally selected Pb, Bi,
At least one of 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 degassing 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 float and 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 stirring or the molten steel flow during pouring and casting, the yield of these additions can be significantly improved. At the same time, uniform dispersion becomes possible, which greatly contributes to improving the spring characteristics and its reliability. Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. First, the molten steel is melted in an arc furnace to adjust the chemical components of the steel other than Te, Pb, Bi, Se, and Ca to a predetermined amount, and then the molten steel is transferred to a vacuum degassing treatment container and degassed. Gas treatment is performed, and Al, Nb, and V are added at this time as necessary.Then, the molten steel is transferred to a ladle with a porous plug at the bottom, and non-oxidizing gas is blown into the molten steel through the porous plug. While performing forced stirring, add Te so that the value of Te (%)/S (%) is 0.04 or more and 0.4 or less according to the amount of S in the molten steel, and further add Pb, Bi, Se, and Ca. In some cases, a predetermined amount of one or more of these was added in conjunction with the addition of Te. In addition, Al,
V, Nb, Pb, Bi, Se, and Ca may be added to the molten steel flow when transferring it into a ladle equipped with a gas blowing device after vacuum degassing treatment. Next, each of the above molten steel was produced into a 2.5 ton steel ingot by the pouring method. Next, each steel ingot was sufficiently soaked at a temperature of 1260℃, then bloomed and then billet heated at a temperature of 930~
Hot rolling is performed at 980℃, rolling temperature at the final rolling roll: 900℃ or less, rolling reduction at the final rolling roll: 5% or more, and cooling to the Ar ₁ transformation point after rolling is performed at 30℃/ Perform controlled rolling at a cooling rate of min or more to make the shape of the sulfide spheroidal, and produce a spring steel material in which the spherical sulfide is uniformly dispersed.
A sample material was 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/0.5 to 0.6 m/m into a 480 x 370 mm mold via a tundish.
It was continuously cast at a drawing speed of min, and hot rolled after soaking. Next, in order to investigate the shape of the sulfide for each sample material, we examined the long axis L of the sulfide within a certain microscope field of view.
(μ) is 10 μ or more, measure its length L and short axis W (μ), and measure the proportion (percentage) of sulfides with a long/short axis ratio L/W of 5 or less in the measured sulfides. I looked into it. The results are also shown in Table 1. As shown in Table 1, all comparative steels
It was found that the amount was less than 15%, and the amount of sulfides with a length ratio of more than 5, that is, elongated sulfides that were not spheroidized, was quite large. On the other hand, in the steel of the present invention, the ratio exceeds 80% in all cases, and the majority of the sulfides have a length ratio of 5 or less, which means that the sulfides in the steel of the present invention are substantially spherical. It was found that almost no intensity anisotropy occurs. 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 significantly lower amounts of giant oxides and carbonitrides than the comparative steel, and it is possible to improve spring properties and increase reliability. I realized that I am getting used to it. This clearly shows the effects of degassing treatment and forced stirring using non-oxidizing gas on molten steel.

【table】

[Table] Next, in order to examine the machinability of each sample material, 11 mm diameter test pieces that had not been spheroidized and annealed were machined using an automatic lathe under the cutting conditions shown in Table 2. I went there. The results are shown in Table 3. This evaluation of machinability was carried out by measuring tool flank wear during cutting of 500 pieces, and as shown in Table 3, the steel of the present invention showed less wear than the comparative steel, and It is clear that the machinability is excellent, and the effect of adding S and Te, as well as Pb, Bi,
The effect of adding Se and Ca is clear. Furthermore, in order to investigate the grindability of each sample material,
After performing the above machinability test, each sample material was subjected to grinding under the grinding conditions shown in Table 4, and the power consumption during grinding was measured. The results are shown in Table 3. As shown in Table 3, it is clear that the steel of the present invention has lower grinding voltage consumption overall than the comparative steel, and 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, each test piece was annealed to spheroidize, then cut, and then quenched and tempered. The hardness of the test piece is H _R C45 ~
48, and then a fatigue test was conducted on each specimen 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,
It became clear that there were no strength defects due to the addition of Se and Ca.

【table】

【table】

【table】

[Table] As explained above, the free-cutting spring steel according to the present invention contains C: 0.40 to 0.75%, Si: 1.0 to 2.5%,
Steel containing Mn: 0.4 to 1.0%, Cr: 0.1 to 1.0% as basic components, S: 0.4% or less, Te: 0.16% or less, and Te (%)/S (%) is 0.04 or more and 0.4 or less. In order to further improve spring characteristics and increase reliability, depending on the purpose of use,
In order to further improve machinability, Pb, Bi, Se,
Since one or more types of Ca are contained, the sulfides such as MnS contained in the steel can be made to have a spherical shape without being elongated during hot working by adding Te, thereby increasing the strength. It is possible to significantly improve machinability such as machinability and grindability without causing anisotropy, and it is possible to perform cutting with a peeling machine, center hole machining of the torsion bar grip part, or grinding with high precision. Moreover, it can be carried out with high efficiency, and has extremely excellent effects such as extending tool life and improving productivity.

Claims (1)

[Claims] 1% by weight, C: 0.40-0.75%, Si: 1.0-2.5
%, Mn: 0.4-1.0%, Cr: 0.1-1.0%,
S: 0.4% or less, Te: 0.16% or less, and Te
(%) / S (%) includes an amount of 0.04 or more and 0.4 or less,
A free-cutting spring steel characterized by the balance being Fe and impurities, with spherical sulfides uniformly dispersed. 2 Weight%: C: 0.40-0.75%, Si: 1.0-2.5
%, Mn: 0.4-1.0%, Cr: 0.1-1.0%,
S: 0.4% or less, Te: 0.16% or less, and Te
(%) / S (%) includes an amount of 0.04 or more and 0.4 or less,
Furthermore, Al: 0.01~0.1%, V: 0.03~0.3%, Nb:
A free-cutting spring steel containing 0.01 to 0.3% of one or more kinds, the remainder consisting of Fe and impurities, and having spherical sulfides uniformly dispersed therein. 3 In weight%, C: 0.40-0.75%, Si: 1.0-2.5
%, Mn: 0.4-1.0%, Cr: 0.1-1.0%,
S: 0.4% or less, Te: 0.16% or less, and Te
(%) / S (%) includes an amount of 0.04 or more and 0.4 or less,
Furthermore, Pb: 0.3% or less, Bi: 0.3% or less, Se: 0.3
% or less, Ca: 0.01% or less, the remainder is Fe and impurities, and is characterized by having spherical sulfides uniformly dispersed therein. 4 In weight%, C: 0.40-0.75%, Si: 1.0-2.5
%, Mn: 0.4-1.0%, Cr: 0.1-1.0%,
S: 0.4% or less, Te: 0.16% or less, and Te
(%) / S (%) includes an amount of 0.04 or more and 0.4 or less,
Furthermore, Al: 0.01~0.1%, V: 0.03~0.3%, Nb:
0.01-0.3% of one or more types, and Pb:
0.3% or less, Bi: 0.3% or less, Se: 0.3% or less,
Contains one or more types of Ca: 0.01% or less,
A free-cutting spring steel characterized by the balance being Fe and impurities, with spherical sulfides uniformly dispersed.