JPS62127453A - High-efficiency rail excellent in toughness and ductility and its production - Google Patents

Abstract

PURPOSE:To manufacture a high-efficiency rail having high toughness and ductility with maintaining required strength, by subjecting a steel having a specific composition consisting of C, Si, Mn, Nb, and Fe to cold rolling under proper conditions. CONSTITUTION:The steel having a composition consisting of, by weight, 0.60-0.90% C, 0.4-1.5% Si, 0.5-1.5% Mn, 0.01-0.05% Nb, and the balance Fe with inevitable impurities and further containing, if necessary, 0.1-0.3% Cr and/or 0.02-0.15% V is cold-rolled at <=800 deg.C at >=10% reduction in area, so that high-efficiency rails excellent in toughness and ductility can be obtained without causing reduction in strength. In the above-described method, a rail head can be made highly strengthened and highly ductile to a greater extent by subjecting it to accelerated cooling directly after the above rolling until pearlite transformation is finished.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-performance rail with excellent ductility and toughness (hereinafter referred to as ductility) and a method for manufacturing the same.

[Conventional technology]

Conventionally, rails have only been designed to have high strength from the viewpoint of wear resistance and transfer fatigue resistance.

However, in recent years, the conditions for using rails have become increasingly strict as railway transport speeds have increased and axle loads have increased.
Excellent ductility and toughness with no risk of breakage even under such severe usage conditions? Increasingly, there is a demand for rails with However, from the viewpoint of wear resistance, the rail (0.60
Pearlite steel is required to contain ~0.90% C' (H), and improving the ductility of such as-rolled pearlite steel without reducing strength is a very difficult technical problem. It is.

Generally, the following methods are known as methods for improving the ductility of as-rolled steel.

■ Decrease in C#S stiffness ■ Low-temperature rolling ■ Accelerated cooling after rolling [Problems to be solved by the invention] However, when these methods are applied to the production of rails, they each have the following problems.

That is, in the method (2), there is a problem in that the strength decreases even if the amount of C is simply lowered, and even if the decrease in strength is compensated for by alloying elements, the decrease in wear resistance cannot be compensated for.

In addition, method (2) is a method in which the structure is refined by low-temperature rolling. This method is very effective in improving the strength and ductility of low-carbon steels, but it is not easy to improve both properties at the same time in high-carbon steels such as rails. In high carbon steel, if the austenite grains are refined by low-temperature rolling, the hardenability decreases, and the strength decreases due to mineralization in the lamellar intervals. In the rail,
If the strength decreases even if the ductility is improved, the value of the product will be halved, and therefore this method cannot be applied simply.

Method (2) is a method in which the steel is transformed at a low temperature by accelerated cooling after rolling to refine the structure. This method is also very effective for low carbon steels, but for high carbon steels such as rails, although the strength and ductility are improved, the toughness is comparable to that of ordinary rails. In other words, even if this method is simply applied to rails, the toughness will not be improved at all.

The present invention was made in view of such conventional problems,
The present invention aims to provide a high-performance rail that has excellent ductility while ensuring desired strength, and a method for manufacturing the same.

[Means to solve the problem]

For this reason, the basic feature of the present invention is the following structure: (1) C: 0.60 to 0.90 wt%, Si:
0.4-1.5wt%.

Mn: 0.5-1.5wt%, Nb: 0.0
High performance rail with excellent ductility and toughness consisting of 1 to 0.05 wt%, balance F, and unavoidable impurities (2) C: 0.60 to 0.90 wt%, Si:
0.4-1.5wt%, MH: 0.5-1.5w
t%%Nb: 0.01S-0.05wt%, further Cr: 0.1-0.3 wt% and V: 0.02-0
．． A high-performance rail with excellent ductility and toughness, containing 15 wt% of one or more kinds, and the balance being Fe and unavoidable impurities.

(3) C: 0.60-0.90 wt%, Si:
0.4-1.5wt%, Mn: 0.5-1.
5wt%, Nb: 0.01~%-0.05wt%,
A method for producing a high-performance rail with excellent ductility and toughness, characterized by rolling steel consisting of Fe and unavoidable impurities at a low temperature of 800° C. or lower and an area reduction of 10% or higher.

(4) C: 0.60-0.90wt%, St
: 0.4-1.5wt%, Myl: 0.5-1.
5 wt%, Nb: 0.01 to 0.05 wt%,
Furthermore, Cr: 0.1 to 0.3 wt% and V: 0
．． 02 to 0.15 wt% of one type or 28 or more,
A method for producing a high-performance rail with excellent ductility and toughness, characterized by rolling steel consisting of Fe and unavoidable impurities at a low temperature of 800° C. or lower and an area reduction of 10% or higher.

(51C: 0.60-0.90wt% %Si:
G, 4~1.5wt'Iy, Mn: 0.5~1.
5 wt%, Nb: 0.01 to 0.05 wt%, balance Fe and unavoidable impurities.
A method for manufacturing a high-performance rail with excellent ductility and toughness, characterized by low-temperature rolling with an area reduction of 10% or more, and immediately after the rolling, the rail head is acceleratedly cooled until pearlite transformation is completed.

(61C: 0.60-0.90wt%, Si: 0
．． 4-1.5wt%, Mn: 0.5-1.5wt%
, Nb: 0.01 to 0.05 wt%, further Cr
: 0.1~0.3wt% and 72002~015w
A steel containing one or more of t% and the remainder Fe and unavoidable impurities is low-temperature rolled at 80°C or less and an area reduction of 10% or more, and immediately after the rolling, the rail head is accelerated until the entire pearlite transformation is completed. A method for manufacturing a high-performance rail with excellent ductility and toughness, characterized by cooling.

The reason for limiting the component system of the present invention will be explained below.

C is an effective component for increasing the strength, hardness, and wear resistance of the rail. If it is less than 0.60 wt, desired properties such as wear resistance cannot be obtained.

On the other hand, if C exceeds 0.90 wt%, a large amount of pro-eutectoid cementite will be produced, which will significantly embrittle the steel. For this reason%
C is set at 0.60 to 0.90 wt%.

Si is one of the main elements that characterizes the present invention. In order to ensure wear resistance, the rail steel has a C: 0.60 to 0.
It is a pearlite steel with a content of 90 wt %, and exhibits a 100% brittle fracture surface when subjected to a destructive test at the temperature at which the rail is used.

A sufficient improvement in toughness cannot be achieved simply by making the structure finer.

Under such conditions, the addition of St has been found to have a significant effect of improving toughness. In other words, Si is an effective component for increasing the toughness of the rail, and 0.4 wt.
%, no significant toughness improvement effect is observed. On the other hand, S
When i exceeds 1.5 wt% gold, the ductility deteriorates significantly;
It also tends to become brittle. From such a thing,
The content of Si is 0.4 to 1.5 wt%.

Mn is a component for improving hardenability and rail strength, and if it is less than 0.5 wt%, the desired strength cannot be ensured. On the other hand, if Mn exceeds 1.5 wt%, martensite will be generated in the segregated portion during rail welding, which will impair weldability. Therefore, Mn is 05 to 1.5 wt%
Let it be Mn.

Nb is added with the primary purpose of improving the ductility of the rail. The second purpose of adding islands is to completely prevent a decrease in strength during low-temperature rolling, and to ensure strength equal to or higher than normal rolling. If Nb is less than 0.01 wt%, the above purpose cannot be achieved; on the other hand, if Nb is less than 0.05 wt%
%, coarse Nb carbonitrides are generated during rolling heating,
It has a negative impact on the rail by making the steel extremely brittle and becoming a starting point for cracks such as shelling damage. For this reason, Nb is added in an amount of 0.01 to 0.05 wt. Cr and V are added singly or in combination to increase the overall strength of the rail. By increasing the hardenability of Cr, V becomes V.
The overall strength is increased by precipitation strengthening of carbonitrides. Cr is 0.1
When the content of ■ is less than 0.02 wt%, no significant increase in strength is observed.

On the other hand, if Cr exceeds 0.3 wt% and ■ exceeds 0.15 wt%, the ductility-improving effects of Si and Nb are lost.

In the above-mentioned component system containing Si and Nbi, sufficient rolling toughness can be obtained by normal rolling, but the strength can be reduced by low-temperature rolling at a temperature of 800°C or lower and an area reduction of 10 factors or higher. The ductility is further improved without any moreover.

Immediately after such low-temperature rolling, the rail head is acceleratedly cooled until pearlite transformation is completed, thereby making it possible to further increase the strength and ductility of the rail head.

〔Example〕

Table 1 shows the chemical composition of the test steel.

Among the stiff steels, A-C steel types are comparative steels.

A steel type is ARli: A standard rail steel, B steel type and Ct@
The seeds are 1. Owt% Sl, 0.02
It is a steel with a single wt% island addition. D-F steel type is the steel of the present invention.

Table 2 shows rolling conditions and strength.

To see the effect of low temperature rolling on ductility.

Six levels of finishing temperature are used. Rolling l (abbreviation: S
l) ~ Rolling 3 (83) is the conventional level of rolling for rails. Rolling 5 (SS) to rolling 6 (86) correspond to the low-temperature rolling adopted by the method of the present invention.

Table 3 shows the accelerated cooling conditions performed immediately after rolling.

Figure 1 shows the relationship between the finishing rolling temperature, 0.2% proof stress, and reduction of area of each extrusion, and from this figure, the characteristics of each alloy component can be understood. In other words, A$.

As shown qualitatively in the 1980 Symposium Text P, 113 of the High Temperature Deformation Subcommittee of the Iron and Steel Institute, the strength decreases with low temperature rolling, whereas Nb# processed steel (
Steels C, D, E, and F) do not show any decrease in strength even when subjected to low-temperature rolling.

The reduction of area improves for all steel types as it is rolled at a lower temperature. However, since steel B (1, O3i single aff & processed steel) shows a lower reduction of area than steel A at all rolling levels, Si deteriorates the ductility. It turns out that it does. On the other hand, C steel (0.02w
Since the steel with only t% island addition shows a better reduction of area than steel A, it is clear that Nb completely improves ductility. On the other hand, the steels E and F, which are the steels of the present invention, exhibit better ductility than steel A because of the addition of Nb even though they are supplemented with Sl, which causes a total deterioration of ductility. Furthermore, the reduction of area value is even superior to that of 85 rolling (area reduction rate of 10% at 800° C. or lower).

Figure 2 shows the Charpy impact absorption energy (vEo) at 0°C and the rolling finishing temperature of each steel type.

This shows the relationship with the plane strain fracture toughness value (klc), which shows that St significantly improves toughness. In pearlite steel, v4, which was hardly improved even if the structure was refined like C steel, was found in B steel, D steel,
By adding 5i-pfA like E steel and F steel, it is clearly improved at all rolling levels. Further, in E steel and F steel, vEo is further improved by S5 rolling. The value of Klc is also Sl rolling (normal rolling level), A steel: 110
Kg/11/'', E steel: improved to 160 and 47m''. For example, this value is 1oK9/
20 due to Peng's axial tensile residual stress and vehicle wheel load.
This means that under conditions where a tensile stress of Kf/1111' is applied, steel A can withstand surface defects up to a depth of 3 m, whereas steel E can withstand up to a depth of 7 m.

FIG. 3 shows the relationship between the added amount of Sl and Klc.

According to this, a significant improvement in KIC is observed between 0.4 wt% and 1.5 wt%. In particular, 0.5 to 1
．． KIC > 150 in the range of 3 wt s Si
It shows a very high value of 0.3.

FIG. 4 shows changes in strength, ductility, and toughness of E steel and F steel depending on the presence or absence of accelerated cooling after rolling. By accelerated cooling, the strength and ductility are significantly improved, and the toughness is also 1c.
> la oKg7J”, showing a high value.

As described above, the component system mainly consisting of the combined addition of St and Nb, which is a feature of the present invention, significantly improves the ductility of as-rolled rail steel. Also.

In the above component system, by performing low-temperature rolling, even more excellent rolling toughness can be obtained without a decrease in strength, and furthermore, by performing accelerated cooling after such rolling, high toughness is maintained.

Strength and ductility are significantly improved.

Table 4 shows the strength, ductility, and
This shows the toughness.

Examples (1) to (5) of the present invention correspond to the first to fifth inventions of the present application, respectively.

In the same table, looking at the improvement in mechanical properties of the inventive example over the comparative example, 1 inventive example (1) has an aperture value of 24.5'14.
33.2%, vEo is 0.5) w·ffi −+0.
8 edges/m, Klc is 110 Kg/wJ”→t s
2 Kf/■"", and in the example (2) of the present invention, it was improved to 0.
sl proof stress increased from 50.5KI/- to 5 & 1114/-, aperture value increased from 24.5% to 37.7%, vEg increased to Q,
5 K4- m-+1. Q Kg 'm, Ni 1c has improved from IILIKg7ms" to l80 K4/J'. Examples (3) and (4) of the present invention are 65.5 Kg/w
I? While having a 0.2% yield strength.

Invention example (1) (23) shows excellent ductility, which is on the same level as in invention example (23).In addition, in invention example (5), the 0.2 strength is 79.1/'sw!, and the aperture value is The toughness was improved to 43.2%, and shows excellent toughness at the same level as Examples (1) to (4) of the present invention.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a high-performance rail having excellent ductility while ensuring desired strength.

[Brief explanation of drawings]

@1 Figures (a) to (d) show the relationship between the finishing rolling temperature, 02% proof stress, and reduction of area of each steel type in Examples. FIG. 2 similarly shows the relationship between each type of rolling finishing temperature, Charpy impact absorption energy (VEO) at 0, and plane strain fracture toughness value (K+c). FIG. 3 shows the relationship between the amount of st added and KIC. Figure 4 shows E steel in Example 1. Strength of F steel with or without accelerated cooling after rolling. This shows changes in ductility and toughness. Patent Applicant: Nippon Kokan Co., Ltd. Inventor: Kazu 1) Norihiro Misato
Fuku 1) Kozo 2nd figure Lm type] = star &('C) (a) 1 figure (b) (C) 1 figure (d) Procedural amendment (!King”) Show + [lbO year! year February 2nd, 2007, the 78th Office filed a complaint with the Uga Michibu Department (Mr. γr1 in charge) 1, Indication of the case Relationship with the Showa bO year Patent Application No. 26-3727 case Applicant (412) Japan M-Kan Co., Ltd. N4 4 Agent 5, Date of amendment order 6, Subject of amendment Contents 1 The "Scope of Claims" of the present application is corrected as follows. r (1) C: 0.6 C1~0.9 Q wt%,
Si: 0.4-1.5wt, Mn: 0.5
~1.5wt%, Nb: 0.01~0.05wt%
A high-performance rail with excellent ductility and toughness, consisting of , the balance being Fe and unavoidable impurities. (21C: 0.60-0.90wt%, St: 0
．． 4-1.5wt%, Mn: U, 5-1.5wt%
, Nb: 0.01 to 0.05 wt%, and further Cr:
0.1-0.3 wt% and ■: 0.02-0.15 w
A high-performance rail with excellent ductility and toughness, containing one type of tfb or 28i steel, with the balance being Fe and unavoidable impurities. (3) C: 0.60-0.90 wt%, Si:
0.4-1.5wt, Mn: 0.5-1.5wt
%, Nb: 0.01-0.05wt%, balance Fe
A method for manufacturing a high-performance rail with excellent ductility and toughness, which comprises rolling steel containing unavoidable impurities at a low temperature of 800° C. or lower and an area reduction of 10% or higher. (4 N C: 0.60-0.90 wt excellent, Sl: 0
．． 4-1.5wt%, Mn: 0.5-1.5w
t%, Nb: 0.01 to 0.05wt%, and further C
r: 0.1~G, 3wt% and V: 0.02~0.
Steel containing one or two types +→ of 15wt pot and the balance consisting of Fe and unavoidable impurities was heated at 800°C or less with an area reduction rate of 1.
A method for manufacturing a high-performance rail with excellent ductility and toughness, characterized by low-temperature rolling at a coefficient of 0 or higher. (5) C: 0.60~0.90wt%, Si: 0.4~
1.5wt%, Myl: 0.5-1.5wt%
, Nb: 0.01 to 0.05 wt%, the balance being Fe and unavoidable impurities.礒□' = energy ratio y and film 1 ≦ friend me] yu (7) C: 0.60 to 0.90wt%%Si
: 0.4 to 1.5wt2 At the beginning of page 4, line 17, in the specification of the present application, the phrase ``let it go down'' is corrected to ``let it go down''. 3. In the circular, page 5, line 7, the phrase ``mineralization of intervals'' is corrected to read ``widening of r intervals''. Medical circular, page 7, line 14 lcor soo℃ or less, area reduction rate 1
Delete the text "low temperature above 0%". S [Correct the 3rd and 4th lines of page 8 as follows. ``The steel consisting of and unavoidable impurities is rolled and the steel is rolled.'' The following is added between lines 7 and 8 on page 8 of the same book. "Also, the embodiments of (5) and (61) above are characterized by rolling at a low temperature of 800°C or less and an area reduction rate of 10% or more." Ibid., page 11, lines 1 to 3 Correct up to the line as follows: "The ductility is further improved without any complications. In addition, by accelerating the cooling of the rail head immediately after rolling until the end of pearlite transformation, JS Ibid. No. 18
In the negative 9th line, "at male" is corrected to "at 0°C." 9 "rfRa diagram, Figure 4" in the attached drawings of this application is corrected as shown in the attached sheet. /θ In the specification of the present application, on page 6, line 14, the phrase "one or more types" is corrected to read 11 types or 2 typesj. /ll On page 7 of the same book, the word “sexuality” is corrected to “type 1 or type 2.” / Correct the phrase "one or more kinds" in the second line of page 8 of the second edition to "one or more kinds."

Claims (6)

[Claims] (1) C: 0.60~0.90wt%, Si: 0.4~
1.5wt%, Mn: 0.5-1.5wt%, Nb: 0
．． A high-performance rail with excellent ductility and toughness, consisting of 0.01 to 0.05 wt%, the balance being Fe and unavoidable impurities. (2) C: 0.60~0.90wt%, Si: 0.4~
1.5wt%, Mn: 0.5-1.5wt%, Nb: 0
．． 01 to 0.05 wt%, further Cr: 0.1 to 0.3
A high-performance rail with excellent ductility and toughness, containing one or more of 0.02 to 0.15 wt% of wt% and V, and the balance being Fe and unavoidable impurities. (3) C: 0.60~0.90wt%, Si: 0.4~
1.5wt%, Mn: 0.5-1.5wt%, Nb: 0
．． A method for producing a high-performance rail with excellent ductility and toughness, which comprises rolling a steel consisting of 0.01 to 0.05 wt%, the balance being Fe and unavoidable impurities at a temperature of 800° C. or less and an area reduction of 10% or more. (4) C: 0.60~0.90wt%, Si: 0.4~
1.5wt%, Mn: 0.5-1.5wt%, Nb: 0
．． 01 to 0.05 wt%, further Cr: 0.1 to 0.3
wt% and V: 0.02 to 0.15 wt% of one or more types, and the balance consists of Fe and unavoidable impurities, and the steel is low-temperature rolled at 800°C or less and with an area reduction of 10% or more. A method for manufacturing high-performance rails with excellent ductility and toughness. (5) C: 0.60~0.90wt%, Si: 0.4~
1.5wt%, Mn: 0.5-1.5wt%, Nb: 0
．． A steel consisting of 01 to 0.05 wt%, the balance being Fe and unavoidable impurities is low-temperature rolled at 800°C or less with an area reduction of 10% or more, and immediately after the rolling, the rail head is acceleratedly cooled until the end of pearlite transformation. A method for manufacturing high-performance rails with excellent ductility and toughness. (6) C: 0.60~0.90wt%, Si: 0.4~
1.5wt%, Mn: 0.5-1.5wt%, Nb: 0
．． 01 to 0.05 wt%, further Cr: 0.1 to 0.3
A steel containing one or more of wt% and V: 0.02 to 0.15 wt%, the balance consisting of Fe and unavoidable impurities, is low-temperature rolled at 800 ° C. or less and with an area reduction of 10% or more,
A method for producing a high-performance rail with excellent ductility and toughness, characterized by accelerating cooling of the rail head immediately after rolling until the end of pearlite transformation.