Spring steel and method for producing the same
View Patent ↗A spring steel according to the present embodiment has a chemical composition consisting of, in mass %, C: 0.4 to 0.7%, Si: 1.1 to 3.0%, Mn: 0.3 to 1.5%, P: 0.03% or less, S: 0.05% or less, Al: 0.01 to 0.05%, rare earth metal: 0.0001 to 0.002%, N: 0.015%, O or less: 0.0030% or less, Ti: 0.02 to 0.1%, with the balance being Fe and impurities. In the spring steel, the number of oxide inclusions having an equivalent circular diameter of equal to or greater than 5 μm is equal to or less than 0.2/mm 2 , the oxide inclusions each being one of an Al-based oxide, a complex oxide containing REM, O and Al, and a complex oxysulfide containing REM, O, S, and Al. Further, a maximum value among equivalent circular diameters of the oxide inclusions is equal to or less than 40 μm.
1. A spring steel having a chemical composition consisting of,
in mass %,
C: 0.4 to 0.7%,
Si: 1.1 to 3.0%,
Mn: 0.3 to 1.5%,
P: equal to or less than 0.03%,
S: equal to or less than 0.05%,
Al: 0.01 to 0.05%,
rare earth metal: 0.0001 to 0.002%,
N: equal to or less than 0.015%,
O: equal to or less than 0.0030%,
Ti: 0.02 to 0.1%,
Ca: 0 to 0.0030%,
Cr: 0 to 2.0%,
Mo: 0 to 1.0%,
W: 0 to 1.0%,
V: 0 to 0.70%,
Nb: 0 to less than 0.050%,
Ni: 0 to 3.5%,
Cu: 0 to 0.5%, and
B: 0 to 0.0050%, with the balance being Fe and impurities,
wherein a number of oxide inclusions having an equivalent circular diameter of equal to or greater than 5 μm is equal to or less than 0.2/mm 2 , the oxide inclusions each being one of an Al-based oxide, a complex oxide containing REM, O and Al, and a complex oxysulfide containing REM, O, S, and Al, and
wherein a maximum value among equivalent circular diameters of the oxide inclusions is equal to or less than 40 μm.
2. The spring steel according to claim 1 ,
wherein the chemical composition includes Ca: 0.0001 to 0.0030%.
3. The spring steel according to claim 1 ,
wherein the chemical composition includes one or more selected from the group consisting of,
Cr: 0.05 to 2.0%,
Mo: 0.05 to 1.0%,
W: 0.05 to 1.0%,
V: 0.05 to 0.70%,
Nb: 0.002 to less than 0.050%,
Ni: 0.1 to 3.5%,
Cu: 0.1 to 0.5%, and
B: 0.0003 to 0.0050%.
4. The spring steel according to claim 2 ,
wherein the chemical composition includes one or more selected from the group consisting of,
Cr: 0.05 to 2.0%,
Mo: 0.05 to 1.0%,
W: 0.05 to 1.0%,
V: 0.05 to 0.70%,
Nb: 0.002 to less than 0.050%,
Ni: 0.1 to 3.5%,
Cu: 0.1 to 0.5%, and
B: 0.0003 to 0.0050%.
5. A method for producing a spring steel, the method comprising the steps of:
refining molten steel having the chemical composition according to claim 1 ;
producing a semi-finished product from the refined molten steel by a continuous casting process; and
hot working the semi-finished product,
wherein the step of refining the molten steel includes the steps of:
performing ladle refining on the molten steel;
deoxidizing the molten steel using Al subsequent to the ladle refining; and
deoxidizing the molten steel using REM for at least 5 minutes after the deoxidation with Al, and
wherein the step of producing the semi-finished product includes the steps of:
stirring the molten steel within a mold to swirl the molten steel in a horizontal direction at a flow velocity of 0.1 m/min or faster; and
cooling the semi-finished product being cast at a cooling rate of 1 to 100° C./min.