JPS62274058A - Low decarburization spring steel - Google Patents

Abstract

PURPOSE:To prevent the occurrence of ferrite decarburization at the time of hot rolling, etc., and also to improve sag resistance as well as strength, by specifying the amounts of C, Si, Mn, Sb, Fe, Cr, etc. CONSTITUTION:This low decarburization spring steel has a composition consisting of, by weight, 0.4-0.75% C, 1-2.5% Si, 0.5-1% Mn, 0.005-0.3% Sb, and the balance Fe or containing, besides the above, 0.1-1% Cr or further containing, besides the above, 0.03-0.3% V and/or 0.003-0.3% Nb. On applica tion of the above steel, the dissipation of C, etc., contained in steel from steel surface to the outside can be inhibited at the time of gamma-alpha transformation in hot rolling, etc.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Object of the Invention] (Field of Industrial Application) The present invention relates to spring steel used for manufacturing springs with excellent fatigue strength, and particularly relates to spring steel that is used for manufacturing springs with excellent fatigue strength. This relates to low decarburization spring steel that exhibits significantly less decarburization (during product rolling of coil or bar material).

(Prior Art) Conventionally, spring steel used for manufacturing springs has various chemical compositions (for example, Metal Handbook, Revised 4th Edition).
December 20, 1981 Published by Maruzen Co., Ltd., No. 811
(pages 813 to 813) are especially JIS
Spring steels specified in 5UP6, 5UP7 and 5AE9254 have a high Si composition to provide sufficient strength and resistance to fatigue.

(Problem to be solved by the invention) However, Si added to this type of spring steel is
Since it is a forming element, it increases the α ratio at high temperatures, so
This is a steel type that is extremely susceptible to decarburization during the γ→α transformation during hot rolling.

This is called ferrite decarburization, and since it contains almost no carbon, it has a significant impact on the spring properties.

Therefore, if a decarburized layer is formed on the surface of spring steel, it will significantly reduce the fatigue strength of the spring, so it is necessary to remove the decarburized layer or prevent the formation of the decarburized layer itself. However, removing such a decarburized layer is extremely troublesome, and it is difficult to prevent the formation of the decarburized layer itself, which greatly impedes spring productivity and reduces yield. There was a problem that the decrease was also large.

(Purpose of the Invention) The present invention was made to solve these conventional problems, and even when the amount of Si is increased to obtain sufficient strength and fatigue resistance, The object of the present invention is to provide a low decarburization spring steel in which a ferrite decarburization layer is difficult to form during rolling.

[Structure of the Invention] (Means for Solving the Problems) The low decarburization spring steel according to the present invention has a C: 0.40 in weight%.
~0.75%, Si: 1.0~2.5%, Mn:
0, 5-1, 0%, Sb: 0.005-0.3%,
and Cr: 0.1-1.0% as necessary, V: 0.003-0.3%, Nb: 0.00 as necessary
One or two of 3 to 0.3%, Ni 0.2 to 1.0%, Cu: 0.2 to 1.0% as necessary.
It is characterized by containing one or two of these, with the remainder consisting of Fe and impurities.

Next, the composition range (weight%) of the low decarburization spring steel according to this invention
) will be explained.

C (carbon); C is an element effective in increasing the strength of steel, but 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 tend to form, impairing the fatigue strength of the spring, so 0.40~
The range was set at 0.75%.

St (silicon): Si is an effective element for improving the strength of steel and the fatigue resistance of springs, but if it is less than 1.0%, it will not have the fatigue resistance necessary for springs. 2.5%
Since toughness deteriorates when the content exceeds 1.0% to 2.5%.

Mn (manganese); Mn is an element that is effective in deoxidizing steel and preventing damage caused by S, and for this purpose it is necessary to contain it at 0.5% or more, but 1 If it exceeds 0.0%, segregation may occur during agglomeration, and this segregation may cause uneven strength, so it was set in the range of 0.5 to 1.0%.

sb (antimony): sb produces sb oxide on the surface at high temperatures, which is denser than Fe oxide, and contains elements contained in steel, such as C (carbon).
This is an effective element in preventing ferrite decarburization during hot rolling by preventing ferrite from being extracted from the steel surface by this dense sb oxide. In order to obtain such an effect, it is necessary to contain 0.005% or more, but if it exceeds 0.3%, the toughness decreases, so the content was determined to be in the range of o, oos 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 fully expected, and if it exceeds 1.0, the toughness decreases. deteriorates, so
It was made into the range of 0.1-1.0%.

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

However, if the content is less than 0.003%, the above-mentioned effects cannot be expected much, and if it exceeds 0.3%, the spring characteristics will not improve much, so each content is set in the range of 0.003 to 0.3%.

Since Ni and Cu are elements effective in preventing ferrite decarburization, it is good to include them in an amount of 0.2% or more in order to obtain such an effect. Even if the content exceeds 0.0%, the effect is not significantly improved, so each content was set in the range of 0.2 to 1.0%.

In addition, B is an effective element for increasing the hardenability of steel, so it is recommended to add it depending on the purpose of use.
If it is less than 0.0005%, it is difficult to obtain the above effects;
Even if it exceeds 0.01%, the above-mentioned effects will not increase significantly, so when adding it, it is preferably in the range of o,oos to 0.01%.

In addition, S is an element that tends to impair the fatigue strength of springs, and the lower the S content, the more reliable the spring will be.
It is more desirable that it be 10% or less.

Furthermore, since 0 produces oxide-based inclusions, which may become the starting point of fatigue fracture, it is more desirable to set the content to 0.0015% or less depending on the purpose of use.

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

(Example) Steel having the chemical composition shown in the table was melted and then formed into an ingot.The steel ingot was then subjected to blooming rolling and wire rod rolling, and the depth of the decarburized layer of the obtained wire rod was measured by the IMA method. The results are also shown in the table.

As shown in the table, ferrite decarburization occurred in the wire rod after hot rolling in the comparative steels (No. 1.2.3), while in the invention steels (No. 4 to 16), In all cases, ferrite decarburization did not occur, and it was confirmed that even high-Si spring steel can effectively prevent ferrite decarburization during hot rolling. This means that sb
This shows that the addition of is very effective in preventing ferrite decarburization. Incidentally, there was virtually no negative effect on the spring properties due to the addition of sb.

〔Effect of the invention〕

As explained above, in the spring steel according to the present invention, C: 0.40-0.75%, Si: 1.0-2
．． 5%, high S with Mn: 0.5-1.0% as the basic component
T-spring steel should contain Sb: 0.005 to 0.3%, and if necessary, Cr: O, 1 to 1, 0%,
Similarly, V: 0.003 to 0.3%, Nb: as necessary.
One or two of 0.003 to 0.3%, and if necessary, Ni: 0.2 to 1.0%.

Cu: Since one or two of 0.2 to 1.0% is contained, C, etc. contained in the steel is prevented from flowing from the steel surface to the outside during γ→α transformation during hot rolling. By preventing extraction, it is possible to prevent the occurrence of ferrite decarburization during hot rolling, etc., even in high-Si spring steel, and unlike conventional methods, material yield is significantly reduced due to removal of the decarburized layer. It has the excellent effect of being a spring material that has excellent strength and fatigue resistance as well as excellent strength and fatigue strength without significantly impairing the manufacturability or quality of the spring.

Claims (1)

[Claims] (1) In weight%, C: 0.40 to 0.75%, Si: 1
．． 0-2.5%, Mn: 0.5-1.0%, Sb: 0.
A low decarburization spring steel characterized by containing 0.005 to 0.3%, with the balance consisting of Fe and impurities. (2) In weight%, C: 0.40-0.75%, Si: 1
．． 0-2.5%, Mn: 0.5-1.0%, Cr: 0.
1 to 1.0%, Sb: 0.005 to 0.3%, and the balance is Fe and impurities. (3) In weight%, C: 0.40-0.75%, Si: 1
．． 0-2.5%, Mn: 0.5-1.0%, Cr: 0.
1 to 1.0%, and one or two of V: 0.003 to 0.3%, Nb: 0.003 to 0.3%, and Sb: 0.005 to 0.0%.
A low decarburization spring steel characterized by containing 3% Fe and the balance consisting of Fe and impurities. (4) In weight%, C: 0.40-0.75%, Si: 1
．． 0-2.5%, Mn: 0.5-1.0%, Sb: 0.
005-0.3%, and Ni: 0.2-1.0%, C
u: Contains one or two of 0.2 to 1.0%,
A low decarburization spring steel characterized in that the remainder consists of Fe and impurities. (5) In weight%, C: 0.40-0.75%, Si: 1
．． 0-2.5%, Mn: 0.5-1.0%, Cr: 0.
1-1.0%, Sb: 0.005-0.3%, and N
A low decarburization spring steel characterized by containing one or two of i: 0.2 to 1.0%, Cu: 0.2 to 1.0%, and the balance consisting of Fe and impurities. (6) In weight%, C: 0.40-0.75%, Si: 1
．． 0-2.5%, Mn: 0.5-1.0%, Cr: 0.
1 to 1.0%, and one or two of V: 0.003 to 0.3%, Nb: 0.003 to 0.3%, and Sb: 0.005 to 0.0%.
3%, further Ni: 0.2-1.0%, Cu: 0.2-
A low decarburization spring steel characterized by containing one or two of 1.0% and the remainder consisting of Fe and impurities.