JPH03114625A - Production of sulphur double layered free cutting steel with continuous casting - Google Patents

Abstract

PURPOSE:To improve machinability of a core part by pouring molten steel with T.Al and Si contents adjusted into a mold and continuously charging iron-coated S-packing wire in a cast slab formed with solidified shell to incorporate S into the core part. CONSTITUTION:Molten steel containing 0.01-0.60% C, 0.30-1.60% Mn, <=0.040% P, <=0.035% S and adjusted in the range <=0.005% T.Al and 0.04-0.10% Si, is poured into the mold. By using a submerged nozzle, which does not execute gas blowing, casting is executed. Into the cast billet formed with solidified shell, the iron coated S-packing wire is continuously charged from upper part of the mold to incorporate 0.040-0.300% S in the core part. By this method, the free cutting steel having good surface quality and excellent machinability of the core part can be produced with continuous casting method.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing sulfur multilayer free-cutting steel by continuous bloom billet casting.

Conventional technology Traditionally, sulfur multilayer free-cutting steel was manufactured by the ingot-forming method. That is, rimmed steel or gapped steel is injected into a mold by the top pouring method or bottom pouring method, a rim layer of a predetermined thickness is solidified by a rimming action, and then Fe is poured from above the mold.
- By adding -5 and Fe-Mn, a core portion with high S and Mn concentrations is formed inside the rim layer. This core portion solidifies like guild steel due to the rimming action suppressing effect of S and Mn. In addition, the thickness of the rim layer can be adjusted by adjusting the capping time (from the end of injection to Fe-3 and Fe-3).
This is done by adjusting the time until Mn addition.

The rimmed sulfur multilayer free-cutting steel produced in this way has few surface defects and has excellent machinability in the core, so it is used for welding nuts and the like. A welding nut is produced by, for example, drawing a wire rod into a rectangular shape, shearing it, and then cold forging to form the outer shape of the nut.

Next, the central part of the cross section is punched out and threaded by tapping. In this way, steel materials for weld nuts require cold workability and weldability on the surface, and machinability on the core.
Sulfur multilayer free-cutting steel is the most suitable.

Conventionally, regarding the manufacture of this type of sulfur multilayer free-cutting steel by continuous casting, Japanese Patent Application Laid-Open No. 82-142053 describes a manufacturing method in which sulfur is added to the core portion using an iron-coated sulfur-filled wire.

Problems to be Solved by the Invention In the production of sulfur multi-layer free-cutting steel using the ingot-forming method, there are two problems: the thickness of the rim layer is thicker at the bottom of the ingot and thinner at the top, and the S concentration in the core is lower due to segregation. There is a problem in that it varies depending on the location, and as a result, there is a drawback that poor tapping and cold processing cracks are likely to occur during processing into nuts. Furthermore, in the ingot casting method, the consistent yield from steel ingot to finished product is low, so establishing a manufacturing method using continuous casting has been a long-standing challenge.

In addition, in the method for manufacturing pseudo-rimmed sulfur multilayer free-cutting steel in JP-A No. 82-142053, C0.20% or less, Nn0.30-2.00%, P 0.040% or less, So, 035% Thereafter, molten steel with a composition of 0.070 to 600 ppm is poured into a mold, and S is added to the position of the slab after the lower end of the mold where a partially solidified shell is formed using an iron-coated S-filled wire to reduce S to 0.001 ppm. ~0, 60~0.40
A continuous casting process for sulfur free-cutting steel with 0% core is described.

However, when casting rimmed steel, there is generally a problem in the formation of CO pores on the ingot surface and/or under the surface layer during solidification, and the O concentration in the molten steel must be adjusted to below the critical 0 concentration at which CO pores are not generated. known to be necessary. For example, the results of small-scale unidirectional solidification experiments regarding CO pore formation during iron solidification, "Hashibe, Mori: Tetsu to Hagane, 70 (1984), p. 44.
According to 2J, the critical O concentration for CO pore formation is C in molten steel.
Varies depending on concentration, approximately 45 ppm for 0.06% C steel
, about 40 ppm for 0.08% C steel, 0.12
% or more, it is kept constant at about 30 ppm.

In addition, the results of a survey on the formation of CO pores in slabs produced using a continuous caster, “Propensity,” Fujii et al.: Tetsu to Hagane, Ef9 (19
83), p 101-0, 607J, the CO pore generation limit is organized by C concentration and O concentration in molten steel, and 0.0
At 6-0.20% C, the critical O concentration is said to be 55 ppm.

In the above-mentioned Japanese Patent Application Laid-Open No. 62-142053, the 0 concentration is set to 70~
It is specified as 0.01 to 0.600 ppm, and when compared with the above results, it is a component system that generates CO pores. Therefore, it is impossible to obtain a good slab without CO pores.

In the method of casting rimmed equivalent steel by continuous casting method, there is generally a low aluminum guild steel with approximately 0.05 to 0.020% of T-M added.
In order to inject into a billet continuous casting mold of 12 mm x IE 12 mm, it is necessary to use a small-diameter immersion nozzle with an outer diameter of 90 mmφ and an inner diameter of 40 mmφ, for example. However, in this case, M2O3, a deoxidation product, adheres and grows on the inner wall of the nozzle, which tends to cause nozzle blockage.Therefore, as a preventive measure, there is a method of blowing Ar gas into the submerged nozzle, but
There is a problem that pinhole defects caused by r occur frequently, and maintenance using a machine scarf or the like is required.

As a method to prevent clogging of the immersion nozzle without blowing Ar gas, Ca is added and suspended in molten steel.
An effective method is to control the form of 3 into a low melting point CaO-M2O+ type oxide. However, in the case of sulfur multi-layer free-cutting steel, an iron-coated S-filled wire is put into the mold and the core part is S-filled.
Since a large amount of is added, dissolved Ca and S tend to react and produce CaS with a high melting point, which poses a problem of significantly reducing the machinability of the steel material.

Therefore, it is difficult to apply aluminum guild steel or aluminum killed Ca-treated steel to bloom billet continuous casting of sulfur multilayer free-cutting steel, and improving the deoxidization method of molten steel is an important issue.

Means for Solving the Problems The present invention solves the above problems. That is, the present invention provides co, ot ~ o, eo%, Mn 0.30 ~
1.60%, P 0.040% or less, S 0.035%
Molten steel containing the following components is injected into the mold, and an iron-coated S-filled wire is continuously introduced from above the mold into the slab to form a solidified shell, so that the core part has an S of 0.040 to 0.30.
In continuous casting of bloom billets for multi-layer free-cutting steel containing 0% sulfur, the deoxidizing element concentration in the molten steel is T
・Al: 0.005% or less, Si: 0.04-0.10
% range, and then inject and solidify the molten steel using a submerged nozzle that does not inject gas, producing free-cutting steel with few surface defects and excellent machinability in the core. This is a method for manufacturing sulfur multilayer free-cutting steel by continuous casting.

The reason why the concentration of each component in molten steel is specified in the present invention will be explained below.

Since steel materials are used for various structural parts, C should be in the range of 0.01 to 0.60% in order to be able to select according to the required strength, cold workability, and hot workability. do.

If Mn is less than 0.30%, hot workability decreases;
If it exceeds 0.01 to 0.60%, cold workability and machinability will deteriorate, so the range is set to 0.30 to 1.60%.

P is set to 0.040% or less to ensure cold workability.

The reason for setting S to 0.035% or less is to ensure cold workability and prevent cracking during welding. Also, the core part S is 0
．． The reason for setting S to 0.040% to 0.300% is that S is 0.040%.
This is because adding 2% or more improves machinability, and adding more than 0-300% reduces cold workability and hot workability.

Further, M is added and adjusted for the purpose of deoxidation so that the O concentration in the molten steel is lower than the critical O concentration at which CO pores are not generated.

The reason why T-M is 0.005% or less is that 0.005%
If it exceeds M2O3 suspended in molten steel during continuous casting,
This is because M2O3 adheres and grows on the inner wall of the immersion nozzle, causing nozzle blockage, and because M2O3 is a hard inclusion, it forms a built-up edge on the cutting tool, which adversely affects the finished surface roughness and the life of the cutting tool. It is.

Furthermore, 0.04 to 0.0.
Add 10%. The reason for containing 0.04% or more of Si is that even if the O concentration in the molten steel is adjusted to 30 to 55 pp+w or less by M deoxidation, O will concentrate in the interdendritic trees during the solidification process of the molten steel, and the surface layer of the slab will Since CO pores are formed in
This is for the purpose of secondary deoxidation of O, which has become concentrated between the trees due to the addition of Si, during the solidification process. However, the effect is 0.04%
The above is sufficient; if it exceeds 0.10%, machinability is adversely affected, so it is specified to be 0.10% or less.

Furthermore, in the present invention, by injecting the molten steel adjusted as described above into a bloom/billet mold with a small cross-sectional size using a submerged nozzle that does not perform gas injection, This is intended to prevent bubble-like surface defects.

To add S to the core part, an iron-coated S-filled wire is continuously introduced from above the mold into the slab in which a solidified shell of a predetermined thickness has been formed, and the S concentration in the core part is adjusted to 0.040 to 0.300%. It is to be adjusted so that

By adjusting the working molten steel to the above composition system, even when casting into a small cross-sectional mold using a small-diameter submerged nozzle without gas blowing, the molten steel contains less M2O3-based oxides and Ca.
Since no processing is performed, there is no gas. Therefore, it is possible to manufacture sulfur multilayer free-cutting steel that is less likely to cause nozzle clogging and has excellent machinability in the core portion.

At the same time, by using a submerged nozzle without gas blowing, a slab with good surface quality is obtained with very few bubble defects caused by blowing gas.

Example 1 Rimmed steel equivalent to Al5I 1110 was melted in a 50mm converter, and the molten steel composition was reduced to 0.06% C-0.07 at RH.
%5iO150%Mm-0.025%F-0,012%
S-adjusted to 0,002% Al. In addition, the 0'a degree in the ladle self-melting steel was adjusted to 40 ppm using an oxygen concentration battery to prevent the formation of pore defects.

A billet with a cross-sectional size of 182 mm x 182 ff1 m was cast in a curved continuous casting machine with a radius of curvature of 12 m R using an integrated immersion nozzle with an inner diameter of 40 m + sφ at a casting speed of V.
It was cast at c=2-2m/win.

A wire feeder was used from above the mold to fill the mold with powdered sulfur from between the mold and the immersion nozzle so that the core sulfur concentration was o, oso%S.
Continuously supplies mild steel wire with a wall thickness of 1.0 mm,
Manufactured sulfur multilayer free-cutting steel.

0 As Comparative Example 1, 0.06% CO10 in converter and RH
1%Si-0,50%Mn-0,025%F-0,
After melting M-killed steel with 012%S-0,020%M, 20ppm of Ca was added to the molten steel in the ladle using a Ca wire to prevent nozzle clogging, and the molten steel was cast in the same manner. Manufactured layered free-cutting steel.

Figure 1 shows the S analysis value in the cross section of the obtained billet.
I am satisfied with 90%.

In addition, regarding rimmed sulfur multi-layer free-cutting steel using the conventional method,
For comparison, 0.10% c-o in converter and RH
,ot%5i-0,40%Mn-0,025%F-0
,012%S was melted free of M and Ca, and then Fe-3 and Fe-Mu were added from above the mold using an ingot-forming method.

The machinability test results of the billets are shown in Table 1, including the sulfur free-cutting steel produced by the agglomeration method as Comparative Example 2. Machinability was evaluated by drill life speed using tool 5KH57. The machinability of the present invention is significantly better than that of a comparative continuous cast free-cutting steel with Ca added, 1 and results comparable to the machinability of the ingot material have been obtained.

Further, when the sulfur multi-layer free-cutting steel of the present invention was rolled into a wire rod of 18 mm diameter and processed into a welding nut, although not shown in the figure, the same usage results as conventional agglomerates were obtained.

Table 1 As explained in detail about the invention, according to the method of the present invention, it is possible to produce free-cutting steel with good surface quality and excellent machinability in the core part by a continuous casting method, which is superior to the conventional ingot making method. The effect on cost reduction and quality stabilization is extremely large.

2

[Brief explanation of drawings]

FIG. 1 shows S in the billet cross section in an embodiment of the present invention.
It is a figure showing an analysis value.

Claims (1)

[Claims] C0.01-0, 60%, Nn0.30-1, 60%,
Molten steel containing components of P0.040% or less and S0.035% or less is injected into the mold, and an iron-coated S-filled wire is continuously introduced from above the mold into the slab to form a solidified shell to form the core part. In continuous casting of bloom billets for sulfur multilayer free-cutting steel containing 0.040 to 0.300% of S, the deoxidizing element concentration in the molten steel is T.Al of 0.00%.
After adjusting the Si content to 5% or less and in the range of 0.04 to 0.10%, molten steel is injected and solidified using a submerged nozzle without gas injection. A method for producing sulfur multilayer free-cutting steel by continuous casting, which is characterized by producing free-cutting steel with excellent properties.