JPH0672282B2 - Low decarburized spring steel - Google Patents

Description

Description: [Object of the invention] (Field of industrial application) The present invention relates to a spring steel used for manufacturing a spring having excellent fatigue strength, particularly during hot rolling (product of coil or bar material). The present invention relates to a low decarburized spring steel in which decarburization during rolling is extremely small.

(Prior Art) Conventionally, spring steels used for manufacturing springs have various chemical components (for example, Metal Handbook, Revised 4th Edition).
December 20, 1982, published by Maruzen Co., Ltd., pages 811 to 813
However, among these, JIS SUP6, SUP7 and SAE925
The spring steel specified in 4 has a high Si composition so that sufficient strength and sag resistance can be obtained.

(Problems to be solved by the invention) However, since Si added to this type of spring steel is an α-forming element, it increases the α ratio at high temperatures, so the γ → α transformation occurs during hot rolling. It is a steel type that is extremely susceptible to decarburization during the process. This is called ferrite decarburization, and since it contains almost no carbon, it significantly affects the spring characteristics.

Therefore, if a decarburized layer is formed on the surface of spring steel, the fatigue strength of the spring will be significantly reduced.Therefore, it is necessary to remove the formed decarburized layer or prevent the decarburized layer from forming itself. However, it is extremely troublesome to remove the decarburized layer, and it is difficult to prevent the formation of the decarburized layer itself, which greatly hinders the productivity of the spring and reduces the yield. There was a problem that the decrease was large.

(Object of the Invention) The present invention has been made in order to solve such a conventional problem, and particularly when the amount of Si is increased so as to obtain sufficient strength and sag resistance, hot working It is an object of the present invention to provide a low decarburized spring steel in which a ferrite decarburized layer hardly occurs during rolling.

[Structure of the Invention] (Means for Solving Problems) The low decarburized spring steel according to the present invention has a C: 0.40 to 0.75% by weight.
%, Si: 1.0 to 2.5%, Mn: 0.5 to 1.0%, Sb: 0.005 to 0.3
%, And, if necessary, Cr: 0.1 to 1.0%, and if necessary, one or two of V: 0.003 to 0.3% and Nb: 0.003 to 0.3%, and if necessary, Ni: 0.2 to 1.0%, Cu: 0.2〜
One or two of 1.0% is contained, and the balance is Fe and impurities.

Next, the reasons for limiting the component range (wt%) of the low decarburized spring steel according to the present invention will be described.

C (Carbon); C is an element effective in increasing the strength of steel, but 0.40
If it is less than 0.1%, the required strength as a spring cannot be obtained, and if it exceeds 0.75%, reticulated cementite is likely to occur and the fatigue strength of the spring is impaired, so the range was made 0.40 to 0.75%.

Si (Si); Si is an element effective in improving the strength of steel and the sag resistance of springs, but if it is less than 1.0%, the sag resistance required for springs can be obtained. If it exceeds 2.5%, the toughness deteriorates, so the range was made 1.0 to 2.5%.

Mn (manganese); Mn is an element that is effective for deoxidizing steel and for preventing damage by S. For this purpose, it is necessary to contain 0.5% or more, but 1.0% If it exceeds the range, segregation is likely to occur during ingot formation, and this segregation may cause uneven strength, so the range was made 0.5 to 1.0%.

Sb (antimony); Sb produces Sb oxide that is denser than Fe oxide on the surface at high temperature, and elements contained in steel, such as C (carbon), escape from the surface of the steel. It is an element effective in preventing ferrite decarburization from occurring during hot rolling by blocking with a substance. In order to obtain such an effect, it is necessary to contain 0.005% or more, but if it exceeds 0.3%, the toughness deteriorates.
The range was 0.005 to 0.3%.

Cr (Chromium); Cr is an element effective in preventing graphitization of carbides, but if it is less than 0.1%, these effects cannot be sufficiently expected, and if it exceeds 1.0, the toughness deteriorates. , 0.1-1.
The range was 0%.

V (vanadium), Nb (niobium); V and Nb are elements that improve the spring characteristics by the effect of precipitation hardening during quenching and tempering of steel and the grain refinement action.

However, if it is less than 0.003%, the above effect cannot be expected so much, and if it exceeds 0.3%, the spring characteristics are not so improved, so the respective ranges are made 0.003 to 0.3%.

Ni (nickel), Cu (copper); Ni and Cu are effective elements for preventing ferrite decarburization, and therefore, 0.2% or more may be contained to obtain such an effect. However, even if it exceeds 1.0%, the effect is not so much improved, so the range is set to 0.2 to 1.0%.

In addition, B is an element effective for increasing the hardenability of steel, so it is preferable to add B according to the purpose of use.
If it is less than 0.0005%, the above-mentioned effect is difficult to obtain, and if it exceeds 0.01%, the above-mentioned effect does not increase so much. Therefore, when it is added, the range is preferably 0.0005 to 0.01%.

In addition, S is an element that tends to impair the fatigue strength of the spring, and the lower the S content, the higher the reliability as a spring. Therefore, the S content should be 0.01 depending on the purpose of use.
It is more desirable to set it to 0% or less.

Further, O forms an oxide-based inclusion, which may be the starting point of fatigue fracture. Therefore, the content thereof is more preferably 0.0015% or less depending on the purpose of use.

In springs made of steel with such component contents,
In order to improve spring properties such as sag resistance and fatigue strength, tempering such as quenching and tempering and controlled rolling are applied to the material after continuous casting or ingot formation and hot rolling (after product rolling). It is more desirable that the crystal grain size of the structure be No. 9 or more by applying the above.

(Example) A steel having the chemical composition shown in the table was melted and then ingot, then this steel ingot was slab-rolled and wire-rolled, and the depth of the decarburized layer of the obtained wire was measured by the IMA method. The results are also shown in the table.

As shown in the table, in the comparative steels (No. 1, 2, 3), ferrite decarburization occurs in the wire rod after hot rolling, whereas in the steels of the present invention (No. 4 to 16), It was confirmed that ferrite decarburization did not occur, and even high Si spring steel can effectively prevent the ferrite decarburization during hot rolling. This shows that the addition of Sb is very effective in preventing ferrite decarburization. In addition, the negative factor for the spring characteristics due to the addition of Sb was not substantially observed.

[Advantages of the Invention] As described above, in the spring steel according to the present invention, C: 0.40 to 0.75%, Si: 1.0 to 2.5%, and Mn: 0.5 to 1.0 by weight%.
% Si as a basic component in a high Si spring steel so as to contain Sb: 0.005 to 0.3%, if necessary Cr: 0.1 to 1.0%, and if necessary, V: 0.003 to 0.3%, Nb: 0.003 to One or two of 0.3%, Ni: 0.2-1.0%, if necessary
Cu: One or two of 0.2 to 1.0% is contained, which prevents C contained in the steel from escaping from the steel surface to the outside during the γ → α transformation during hot rolling. By doing so, it is possible to prevent the occurrence of ferrite decarburization even in high Si spring steel during hot rolling, etc., and the material yield is greatly reduced by removing the decarburized layer as in the past, and spring manufacturability is improved. It has a very excellent effect that it is a spring material which is excellent in strength and sag resistance and fatigue strength as well as does not significantly deteriorate the quality.

Claims (6)

[Claims] 1. C: 0.40 to 0.75% by weight, Si: 1.0 to 2.5
%, Mn: 0.5 to 1.0%, Sb: 0.005 to 0.3%, and a balance of Fe and impurities, which is a low decarburized spring steel. 2. C: 0.40 to 0.75% by weight, Si: 1.0 to 2.5
%, Mn: 0.5-1.0%, Cr: 0.1-1.0%, Sb: 0.005-0.3%
A low decarburized spring steel containing Fe and the balance Fe. 3. By weight%, C: 0.40 to 0.75%, Si: 1.0 to 2.5
%, Mn: 0.5 to 1.0%, Cr: 0.1 to 1.0%, and V: 0.003 to
Low decarburized spring steel, characterized in that it contains one or two of 0.3% and Nb: 0.003 to 0.3%, and further contains Sb: 0.005 to 0.3%, and the balance Fe and impurities. 4. In weight%, C: 0.40 to 0.75%, Si: 1.0 to 2.5
%, Mn: 0.5-1.0%, Sb: 0.005-0.3%, and Ni: 0.2-
1.0%, Cu: containing 0.2 to 1.0% of one or two,
Low decarburized spring steel characterized by the balance Fe and impurities. 5. By weight%, C: 0.40 to 0.75%, Si: 1.0 to 2.5
%, Mn: 0.5 to 1.0%, Cr: 0.1 to 1.0%, Sb: 0.005 to 0.3
%, Ni: 0.2 to 1.0%, Cu: 0.2 to 1.0%, and a balance of Fe and impurities, and a low decarburized spring steel. 6. By weight%, C: 0.40 to 0.75%, Si: 1.0 to 2.5
%, Mn: 0.5 to 1.0%, Cr: 0.1 to 1.0%, and V: 0.003 to
One or two of 0.3%, Nb: 0.003 to 0.3%, Sb: 0.005 to 0.3%, Ni: 0.2 to 1.0%, Cu: 0.2 to 1.0
% Low decarburized spring steel, characterized in that it contains one or two of the above, and the balance is Fe and impurities.