JPS60110809A - Manufacture of cast steel having high toughness and weather resistance - Google Patents

Abstract

PURPOSE:To manufacture a cast steel having high toughness and weather resistance by carrying out composite deoxidation treatment using specified amounts of Al, a rare earth element and Ca in a stage for refining a cast steel contg. specified percentages of C, Si, Mn, P, S, Cu and Cr. CONSTITUTION:A cast steel having a composition consisting of, by weight, C; 0.11-0.16%, Si; 0.25-0.50%, Mn; 0.60-1.00%, P; 0.080-0.150%, S; <=0.010%, Cu; 0.30-0.60%, Cr; 0.45-0.85% and the balance Fe with inevitable impurities is refined. In the refining stage, composite deoxidation treatment is carried out using Al; 0.08-0.12% and 0.10-0.20% at least one between a rare earth element and Ca.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing cast steel having high toughness and high 111 weatherability, which is suitable for structural members such as bridges under atmospheric corrosive environments.

In general, as an inexpensive 11ij weathering cast steel corresponding to the standard value of JIS SC464 or SC/l, P, Cu and Cr, which are effective in imparting weather resistance, are used.
P-Cu-Cr type 5 steel containing an appropriate amount of P-Cu-Cr is known.

However, the above-mentioned P-containing cast steel has absorption energy (21111
11V notch, 0℃ Charpy fiJ9R value.

same as below. ) is 2.8 ky·m or less, and there is a problem that the toughness is low.

The present inventors have conducted intensive research in order to solve the above-mentioned problems and develop a method for manufacturing cast steel that has high toughness and excellent weather resistance.

In conventional P (Cu-Cr) cast steel, P is an element that significantly inhibits notch toughness, so second phases such as pearlite and inclusions have a negative impact on toughness, especially when pearlite content is reduced. In the case of low C-containing cast steel, the toughness is significantly affected by the distribution and amount of inclusions.In addition, since P is an element that has a large solidification segregation, the segregation of inclusions and P The effect of the interaction is thought to be particularly significant.

Furthermore, in the conventional cast steel mentioned above, due to At deoxidation treatment, sulfides tend to precipitate between the branches of dendrites with a significant concentration of P and at grain boundaries, and furthermore, due to the low C, notch effects occur. Since H-type sulfides with a tendency to precipitate,
The interaction between sulfide and P segregation depends on /f%I,
This is considered to be the main cause of the extremely low toughness value.

Therefore, the present inventors investigated P and Cu, which are weather resistance promoting elements.
and Cr in the same range as conventional P-Cu-Cr cast steel, and has a component composition with the content of C, Si, Mn and S limited to a specific range, and as a deoxidizer, It has been found that a cast steel with high toughness and excellent weather resistance can be obtained by performing composite deoxidation using At in a specific range and at least one of a rare earth element and Ca.

This invention was made based on the above findings, and C2O,J, 1-0.16 wt, %.

Si: 0.25-0.50wt, %.

Mn: 0.60-1.00 wt, %.

p: o, o s o~O-150wt, %.

S: 0.010 wt, less than chi.

Cu　2　0.3　0　-　0.6　0　wt,%　.

Cr: 0.45-0.85 wt, %.

Remaining: Fe and inevitable impurities.

Color fx ru, 5'jJI4, deoxidizer,! : AzfO, (18~0.12wt, %) and at least one of rare earth elements and Ca at 0.10~0.20%.
It is characterized by complex deoxidation using wt, %.

Next, the reason why the composition range of cast steel is limited as described above in this invention will be explained.

(1) Since C has no effect on weather resistance, a lower content is desirable for increasing toughness and reducing solidification segregation of P.
If the content exceeds 0.16 wt.%, the toughness will decrease. On the other hand, if the C content is less than 0.11 wt, deoxidation will be insufficient and desulfurization will be difficult to perform. Therefore, the content of C is 0.11 wt·ra 0.16 wt,%
limited within the range of

f21 5i Si is an element necessary for deoxidation, but when its content i exceeds 0.50 wt.%, it causes a decrease in toughness. On the other hand, when the Si content is less than 0.25 wt.%,
This results in poor deoxidation. Therefore, the Si content was limited to a range of 0.25 to 0.50 wt%.

(3) Mn 1νIn is an element necessary for deoxidation and improving toughness, and the toughness improving effect is better as the Mn/C ratio is larger. However, the content of 1 Vin is 1.00, w
If it exceeds t,%, the strength becomes too high and the desired effect of the above-mentioned reduction in toughness cannot be obtained. Therefore, M
The content of n was limited within the range of 0.60 to 1.00 wt%.

(4) SS Since S lowers the absorbed energy, it is desirable that its content be as low as possible. That is, increasing the toughness of cast steel in the present invention is achieved mainly by controlling inclusions (spheroidization and uniform dispersion), and the smaller the S H, the more effectively the above control is performed. Figure 1 is shown below.
It is a graph showing the absorbed energy of cast copper produced according to the component composition and deoxidation conditions shown in the table. As is clear from Figure 1, when the S content exceeds 0.10 wt.
Absorbed energy is significantly reduced. Therefore, the S content m
, is limited to 0.10 wt.% or less, which can be reduced relatively inexpensively and reasonably by ordinary steel manufacturing methods based on FIG.

[51P, Cu, CrP, Cu and Cr are lower in content than conventional P-Cu-C to promote weather resistance.
As with r-series cast steel, P is sail 080 to 0.150wt,
Within the range of %, Cu sails from 30 to 0.60 wt, % of 9
(Within 1z range, Cr is 0.45 to 0.80 wt, %
Each was limited within the range of That is, if the content of P, Cu, and Cr is less than the lower limit of each range of -1:He, the weather resistance is not sufficient; Even if the 2 limit is exceeded, the 111ij weatherability that matches M to 1:1 will not improve, and on the contrary, a problem will occur in which the toughness will decrease.

Next, as a deoxidizing agent, At and at least one of a rare earth element and Ca were determined as K15Ji as described above.
1! Explain about mountains.

(a) At At is a rare earth element and Ca to be deoxidized and added.
It is an essential element for the control of inclusions by at least one of the following. However, the addition ji7j is (1
, 08 wt, 'I), the desired effect cannot be obtained in the above action, while, on the other hand, if the amount added exceeds 0.12 wt, %, a problem arises in that non-metallic inclusions increase.

Therefore, the amount of At added was changed from 0.08 to 0.12wt,
% within the range.

(b) Rare earth elements and Ca Rare earth elements and Ca, in combination with At, have the effect of making inclusions spherical and uniformly dispersed, thereby reducing the influence of inclusions by 11 degrees. The addition may be either a rare earth element or Ca, or a combination of both. Figure 2 shows the results when 10 wt% of Ate O was added as a deoxidizer and rare earth elements and Ca were added in varying amounts to cast steel having the composition shown in Table 2 below. It is a graph showing absorbed energy.

In Figure 2, the circle indicates the case where rare earth elements are added in combination with ca (however, the rare earth elements are constant at 057wt and %).
, Δ marks are when Ca is added, and X marks are when rare earth elements are added. As is clear from Fig. 2, the addition amount of at least one of rare earth elements and Ca is 0.05 w.
t,% or more can increase absorption eorgy, but the effect is unstable and 0.10 wt,
% or more can stabilize the increase in absorbed energy.

- Addition of at least one of rare earth elements and Ca: 1;° exceeds (1.20 wt.%), a problem arises in which non-metallic inclusions increase. The amount of one addition is 0.10 to 0.20
It was limited within the range of wt,%.

As mentioned above, in this invention, as a deoxidizing agent,
By adding a predetermined range of At and at least one of a rare earth element and Ca in combination, relatively small inclusions in the steel can be dispersed into spherical and uniform shapes. Therefore, the influence of inclusions can be reduced, and the micro- and macro-segregation of P is reduced due to the refinement of the solidified structure, so the interaction between sulfide and P segregation mentioned above is eliminated, and the toughness is significantly improved. It is possible to make it "direct".

Furthermore, according to the method of the present invention, the transition temperature is lowered by regulating the amount of S and by the combined deoxidation, and the synergistic effect of this effect and the above-mentioned increase in absorbed energy results in a remarkable improvement in toughness. It can be said that it is effective.

Next, this invention will be further explained by examples.

Table 3 shows Examples Nα1 to 3 of the present invention and Comparative Example Nα
The chemical composition, amount of deoxidizing agent added, mechanical properties, and absorbed energy of 1-7 and conventional examples N111 and 2, as well as their mechanical properties and absorbed energy. Figure 3 is a graph showing the tensile strength and absorbed energy of each. It is.

In FIG. 3, ○ marks represent Examples Nα1 to 3 of the present invention, ψ marks represent Comparative Examples N[Ll to 3, and Δ marks represent Comparative Example Floors 4 to 6.
The ■ mark indicates Comparative Example No. 7, and the X mark indicates Conventional Example No. 1 to
2 are shown respectively.

In Table 3 and FIG. 3, Comparative Example NCLI~3 performs composite deoxidation, but the amount of S is higher than the range of the present invention.
Comparative Examples N14 to 6 have component compositions within the range of the present invention, but only At is used as a deoxidizing agent, and Comparative Example 7 performs composite deoxidation, but the C and S amounts are different from those of the present invention. This is an example of a wider range.

Furthermore, Conventional Examples] and 2 are examples in which the amounts of C and S are larger than the range of the present invention, and only At is used as a deoxidizing agent. The mechanical properties are those obtained after tempering at 9506C for 5 hours, tempering at 920°C for 2 hours, and cooling in air.

As shown in Table 3 and Figure 3, when the amount of S is larger than the range of the present invention, the absorbed energy is low even if composite deoxidation is performed, and even if the component composition is within the range of the present invention, the absorption energy is low. Only deoxidation could not increase the absorbed energy. When the amount of C and S ffi were greater than the range of j proposed in this paper, the absorbed energy further decreased regardless of whether or not composite deoxidation was performed. On the other hand, in the case of Example 1) 3, in which the component composition was within the range of the present invention described above and the composite deoxidation treatment was performed under the conditions described above, the toughness was
- Due to the correlation between light opening and inclusions, the absorbed energy was extremely high and the toughness could be significantly improved.

Table 4 further shows conventional P-Cu-Cr cast steel and Cu
-Mechanical properties of Cr-based cast steel and cast steel of the present invention and 0°C
This is a comparison of Charpy absorbed energy.

As is clear from Table 4, the cast steel produced by the method of the present invention (Example 1) is different from the conventional P-Cu-Cr cast steel (Conventional Example 3) and Cu-Cr cast steel (Conventional Example 4). Its toughness was significantly improved compared to

In this invention, the combined addition of a deoxidizing agent is carried out at the time of tapping the cast steel having the above-mentioned chemical composition.
After deoxidizing by adding At of 0.10 to 0.0%, at least one of a rare earth element and Ca is added in the ladle.
This was done by adding 20 wt.%.

As described above, according to the method of the present invention, the acceleration of embrittlement caused by micro and macro segregation of P and the orientation in the surface layer columnar crystal region, which are of practical importance in P-containing cast steel, are reduced. The toughness can be significantly improved, and the weather resistance is equal to or better than conventional P-CIl-Cr cast steel, and it can prevent cracks, gas defects, and casting cracks, and is inexpensive and easy to use. This brings about excellent industrial effects such as ease of manufacturing.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between S content and absorbed energy, Figure 2 is a graph showing the relationship between the amount of addition of rare earth elements and Ca and absorbed energy, and Figure 3 is an example of the present invention and a comparison. It is a graph showing the relationship between absorbed energy and tensile strength of the example and the conventional example. Applicant Nippon Casting Co., Ltd. Agent Natsuo Shioya (and 2 others) Figure 1 S content (Wj,'/-)

Claims (1)

[Claims] c: 0.11 to (1,16 wt, %. Si: 0.25 to Q, 50 wt, %. 811n: I), (i (1 to LOOwt-Daro. 1) : 0.08 (] ~ 0.15 'Owt, %. 820-010 wt, below Chi. Co: IL: 3 (1 ~ (1,6,0 wt, %. Cr: (1,/15 ~ 0.85 wt, part. The remainder is 1?C and unavoidable impurities. In the melting process, AA is melted at o, o s ~ 0.12 wt, and A method for manufacturing cast steel having high toughness and high weather resistance, in which at least one of a rare earth element and Ca is used as a sail 10 to 0.20.