JPS61136612A - Production of high-si clean steel for spring - Google Patents

Abstract

PURPOSE:To produce a high-Si clean steel for springs having good fatigue resistance by subjecting a steel contg. a specific compsn. ratio each of C, Si and Mn to a molten steel treatment under the addition of a slag forming agent thereto so that the adequate slag compsn. is obtd. after the end of the treatment. CONSTITUTION:The high-Si clean steel for springs which contains essentially 0.50-0.70wt% C, 1.00-2.50% Si and 0.40-1.50% Mn is subjected to the molten steel treatment operation in such a manner that the slag compsn. in the ending stage of the molten steel treatment satisfies the condition range >=65% CaO+ SiO2, <=0.8 CaO/SiO2 and <=0.34 Al2O3/SiO2 in the stage of producing said steel by subjecting the steel to the molten steel treatment entailing the addition of the slag forming treatment. The non-ductile Al2O3 inclusion is thus decreased and the inclusion is made finer, by which the ductility of the inclusion is improved and the fatigue resistance characteristic of the resulting high-Si clean steel for springs is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing clean steel for high-Si steel with good fatigue resistance, and more specifically, to a method for producing molten steel that can achieve fine inclusions. This relates to a processing method.

[Faculty's technology]

The characteristics required for steel materials are becoming increasingly detailed and strict depending on the field of application. Clean steel for high-Si springs is no exception; for example, copper for valve springs for engines needs to be able to withstand increasingly harsh operating environments, so it is particularly resistant to fatigue! Required characteristics regarding gender tend to become stricter. We have responded to these demands by reducing the proportion of non-metallic inclusions and making individual inclusions finer, but conventional steelmaking technology cannot meet even more demands. The situation has become a trap where people are unable to respond to their demands.

Means for reducing inclusions in clean steel for high-81 springs can be classified into the following two types.

(4) Suppressing re-oxidation of molten steel by upgrading ladle bricks, implementing slag control, and implementing atmospheric control.1. A method of further adding molten steel treatment using strong stirring to promote flotation and separation of deoxidized products.

This method is considered to be particularly effective for AI deoxidized steel, and is practiced by various companies.

(6) A method of controlling the composition of the deoxidized product to produce inclusions that exhibit electrical properties during hot rolling. With this method, the inclusions that crack during hot rolling are also rolled out, so the inconvenience caused by the inclusions is greatly reduced. The technology belonging to this category is Japanese Patent Application Laid-open No. 53-76916.
(Mainly related to cleaning steel for steel cords)
, JP-A-58-130215 (mainly related to deoxidation of stainless steel for thin plate spring material) 1 special meeting Sho. 52-174
90- (Concerning inclusion control of coarse-grained carbon steel wire)
.

Japanese Patent Publication No. 54-7252 (Increasing wire drawability by making carbon steel inclusions into spesalite composition), No. 41 Publication No. 57-35
243 (in which CaO-containing flux is injected during production of steel for steel cords), etc. are known.

[Problems to be solved by the invention] The present inventors have been conducting research in the direction of improving the rollability of inclusions, and have developed a new method for the technology classified in (6) in the previous section. High S by providing
This is intended to meet the highly required characteristics for clean steel for i-springs.

[Means for solving problems]

The present invention provides a high 81 spring clean steel that essentially contains c: o, so to 0.70, Si: 1.00 to 2.50, Mn: G, 40 to 1.50%. When producing molten steel through molten steel treatment involving the addition of additives, the key point is to carry out the molten steel treatment operation so that the slag composition at the end of the molten steel sensitive layer satisfies the following condition range.

CaO+510g≧65chi CaO1510g≦0.8 A 1g0n / S 10 t≦0.34 [Function] First, the target steel of the present invention is JIS G4801
Composition of spring steel materials specified by KSUP6.5
Focusing on silicomanganese steels such as UP7, we comprehensively judged the composition of each of these steels and found that mechanical properties (yield strength, tensile strength, elongation, drawing strength, hardness, etc.) must be good. The conditions were determined as follows, taking into account the following conditions. That is, a steel that does not satisfy the following composition cannot be used as a whirling spring steel.

C: 0.50-0.70 Si: 1.00-2.50% Mn: 0.40-1.50 '16 Further, alloy components other than the above include Cr (x, z).

), Mo, vtNbt'rtscutNt eB
, N, O, etc. (all 0.5$1-1'), and trace amounts of p, s, and sb as impurities.

Inclusion of As etc. should be allowed.

In the steel type mentioned above, even if only a few orders of AI are mixed in, the A1 is a fast-moving A1 based on the existence of the person 1. O, is formed. On the other hand, the steel of the present invention, as mentioned above, contains a large amount of Si and Mn, so if the oxygen potential in the molten steel is increased, many SIO! It is expected that the amount of . produced will be competitively reduced, or that the produced A 1 t Os will be diluted by other inclusions, and the disadvantages caused by A 1 * OiK will be alleviated. Adding a slag-forming agent to supply oxygen to molten steel can be considered for various reasons, but if the oxygen supply capacity is too high, the total amount of inclusions will increase.
10. It was thought that it would be appropriate to add a 7 lux system, or a Sin, -CaO system.

By the way, the molten steel processing 11 of the present invention uses the Ar bubbling method, the DHfl vacuum processing method, the RH vacuum processing method, and the ladle refining method (ASEA-8KF method, VAII method).

LF method) etc. can be applied, and of course it is also possible to apply a combination of these, but in any case, when using these processing furnaces, for example, when processing AI deoxidized steel as a precharge, , fireproof wall KA1. During the molten steel treatment of the present invention, O, adheres to the slag (KIIJ) and further dissociates, increasing the amount of AI in the molten steel. In addition, this AI is oxidized in molten steel, and free-flowing AI, O, is formed, which causes defects. However, when the slag control of the present invention is carried out in accordance with the above considerations, the oxygen potential of the slag increases. Therefore, the dissociation reaction of AI, 03 from the slag into the molten steel (rightward reaction in the reaction equation below) (AI, 01) R(Al)+(0) is suppressed.

The present invention has determined the direction of slag control based on the above-mentioned theoretical considerations and predictions, but the slag from the previous charge adhering to the ladle refractory wall, etc. In consideration of the fact that the brick components constituting the fireproof wall may be mixed in by erosion, it was decided that the molten steel treatment was at the final stage. As mentioned in the discussion above, the slag composition at the terminal stage must have a relatively high oxygen potential. Therefore, as mentioned above, molten steel is treated by adding 72Tx containing a large amount of KCaO and Si (for example, wollastonite or a mere mechanical mixture), but the slag thus formed naturally contains KCaO and SiO. The ratio of , is high. The foundation for achieving the object of the present invention will be established only by performing control such that the height is 65- or more.

In addition to the above, the slag components include 20% or less Mg.
Q: There is no problem even if 10% or less of MnO, 5% or less of FeO, etc. are included.

On the other hand, the relationship between the slag components, specifically, ijCa
O/S i Ox and A It's/S i
Each abundance ratio represented by Ot"?' indicates the most direct and important influence on achieving the objective of the present invention. That is, CaO
/Si0g is the basicity index of slag, and when this ratio exceeds 0.8, the basicity balance shifts to the acidic side, and AI and O in the slag dissociate into the molten steel.
It increases I and becomes an obstacle to achieving the desired purpose. On the other hand, AI, 0. /S i O, is AI in slag
,0. If the c-o value exceeds 0.34, it becomes an indicator of the abundance ratio of A1 in the slag. The relatively large amount of O, increases the risk of it migrating into the molten steel, which becomes an obstacle to the present invention.

〔Example〕

Two types of 51-Mn deoxidizing pots shown in Table 1 were prepared.

(The remainder is S and unavoidable impurities.) After converter blowing or arc melting the above steel, it is transferred to a ladle, and wollastonite or 7 lux, which is a modified addition of some inorganic oxide, is added to the molten steel. A stirring process was performed. Table 2 shows the results. N12, 3, 5, and 9, which do not satisfy the conditions of the present invention, had many inclusions with large particle sizes and were evaluated as X. On the other hand, in Nll, 4, 6, 7, and 8, which satisfy the conditions of the present invention, the particle size of inclusions was generally small] and was evaluated as ◎.

No. 21! ! When examining the inclusion types for PJnl~4 of the experiments shown in ``Table 3'', it was found that Ugly 2 and N13 were mostly D type with many A 1 t O-s, and Chenl and Yang. 4 had many A types with A1.0.0 less.

Furthermore, when the thickness of inclusions in the manufactured steel bars for the same (Nnl-1 & 14) was investigated, the results as shown in Fig. 1 (surface layer) and Fig. 2 were obtained. 1,
In No. 4, the thickness of inclusions was obvious (small).

In addition, 25g of the above bar material was cut and removed and dissolved in silicic acid.
When the number of inclusions of 0 μm or more was calculated, the results shown in FIG. 3 were obtained (n number = 4), which indicates that the inclusions satisfying the present invention show good results. In addition, for the purpose of confirming the effect of improving fatigue resistance, we conducted a Nakamura type rotating bending fatigue test (wire diameter: 4.5 mm + φ, test weight: 80 kg) on swosc-v.
f/j), N12, 3, 5
, 9, cracks originating from inclusions or from the surface were observed after 2 × 10· to 6 × 10'passes];
In the case of hl, 4.6° 7.8, cracks originating from the surface were only observed after 10' cycles. O, system (A1xOs=
O~5chi) B: S i 02-Mn O-A 1 BO2 system (
A1zOi=5~20chi) C: S i O! -Mn O-A I 101 series (A
I, 0. =20~4096) D: SiO! -Mn O-A 120g series (
A1.0. =40~60qII) E: S i OH-Mn0-A 1101 series (A1
103260%) [Effects of the Invention] Since the present invention is configured as described above, the number of AI, O, and inclusions in the clean steel for high-Si springs is reduced, and the particle size of the inclusions is also reduced. Therefore, it is expected that the ductility of the inclusions during piezoelectricity will be improved, and that the fatigue resistance will be improved.

[Brief explanation of the drawing]

FIG. 1.2 is a graph showing the distribution of inclusion thickness, and FIG. 3 is a graph showing the number of inclusions of 20 μm or more.

Claims (1)

[Claims] Essentially contains C: 0.50 to 0.70% (same meaning as below) Si: 1.00 to 2.50% Mn: 0.40 to 1.50% In producing clean steel for high-Si springs through molten steel treatment accompanied by the addition of a slag-forming agent, the molten steel treatment operation is carried out so that the slag composition at the end of the molten steel treatment satisfies the following condition range. Manufacturing method of clean steel for Si springs. CaO+SiO_2≧65% CaO/SiO_2≦0.8 A1_2O_3/SiO_2≦0.34