JPH0530883B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to ductility and toughness (hereinafter referred to as ductility).
The present invention relates to a method for manufacturing high-performance rails. [Prior Art] Conventionally, rails have only been designed to have high strength from the viewpoint of emphasis on wear resistance and rolling fatigue resistance. However, in recent years, the operating conditions for rails have become increasingly strict as railway transport speeds up and the axle load increases, and rails with excellent ductility and toughness that are free from breakage even under such harsh operating conditions are needed. Increasingly, there is a demand for rails with However, from the viewpoint of wear resistance, the rail is required to be made of pearlite steel containing about 0.60 to 0.90% C, and it is difficult to improve the ductility of such as-rolled pearlite steel without reducing its strength. This is a technically extremely difficult problem. Generally, the following methods are known as methods for improving the ductility of as-rolled steel. Decreasing the amount of C added Low temperature rolling Accelerated cooling after rolling [Problems to be solved by the invention] However, these methods have the following problems when applied to the production of rails. That is, in the method (2), there is a problem that simply reducing the amount of C causes a decrease in strength.
Furthermore, even if the decrease in strength is compensated for by alloying elements, the decrease in wear resistance cannot be compensated for. Another method is to refine the structure by low-temperature rolling. This method is very effective in improving strength and ductility in low carbon steels, but in high carbon steels such as rails, it is not easy to improve both properties at the same time. In high carbon steel, when the austenite grains are refined by low-temperature rolling, the hardenability decreases, and the strength decreases due to the widening of the lamella spacing. For rails, even if ductility is improved, if the strength is reduced, the value of the product will be halved, so this method cannot be simply applied. This method involves accelerating cooling after rolling to transform the steel at a low temperature and 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 these conventional problems, and it is an object of the present invention to provide a method for manufacturing a high-performance rail that has excellent ductility while ensuring desired strength. [Means for Solving the Problem] Therefore, the present invention is characterized by the following configuration. (1) C: 0.60-0.90wt%, Si: 0.4-1.5wt%,
Steel consisting of Mn: 0.5-1.5wt%, Nb: 0.01-0.05wt%, balance Fe and unavoidable impurities was heated to 800℃.
A method for producing high-performance rails with excellent ductility and toughness, characterized by low-temperature rolling at a reduction rate of 25% or more and a finishing temperature of 700°C or more. (2) C: 0.60-0.90wt%, Si: 0.4-1.5wt%,
Mn: 0.5-1.5wt%, Nb: 0.01-0.05wt%,
Excellent ductility and toughness characterized by low temperature rolling of steel consisting of Cr: 0.1 to 0.3 wt%, balance Fe and unavoidable impurities, with an area reduction of 25% or more at 800°C or lower and a finishing temperature of 700°C or higher. A method for manufacturing high-performance rails. (3) C: 0.60-0.90wt%, Si: 0.4-1.5wt%,
Mn: 0.5-1.5wt%, Nb: 0.01-0.05wt%,
V: 0.02 to 0.15wt%, balance Fe and unavoidable impurities, the steel is low-temperature rolled with an area reduction of 25% or more at 800°C or lower and a finishing temperature of 700°C or higher. Excellent ductility and toughness. A method for manufacturing high-performance rails. (4) C: 0.60-0.90wt%, Si: 0.4-1.5wt%,
Mn: 0.5-1.5wt%, Nb: 0.01-0.05wt%,
Cr: 0.1-0.3wt%, V: 0.02-0.15wt%, balance
A method for producing high-performance rails with excellent ductility and toughness, which comprises rolling steel consisting of Fe and inevitable impurities at a low temperature of 25% or more in area reduction at 800°C or lower and at a finishing temperature of 700°C or higher. (5) C: 0.60-0.90wt%, Si: 0.4-1.5wt%,
Steel consisting of Mn: 0.5-1.5wt%, Nb: 0.01-0.05wt%, balance Fe and unavoidable impurities was heated to 800℃.
Production of high-performance rails with excellent ductility and toughness, characterized by low-temperature rolling with an area reduction of 25% or more and a finishing temperature of 700°C or more, and immediately after the rolling, the rail head is acceleratedly cooled until pearlite transformation is completed. Method. (6) C: 0.60-0.90wt%, Si: 0.4-1.5wt%,
Mn: 0.5-1.5wt%, Nb: 0.01-0.05wt%,
Steel consisting of Cr: 0.1 to 0.3wt%, balance Fe and unavoidable impurities is low-temperature rolled at a finishing temperature of 700℃ or higher with an area reduction of 25% or higher at 800℃ or lower, and the rail head undergoes pearlite transformation immediately after the rolling. A method for manufacturing a high-performance rail with excellent ductility and toughness, characterized by accelerated cooling until completion. (7) C: 0.60-0.90wt%, Si: 0.4-1.5wt%,
Mn: 0.5-1.5wt%, Nb: 0.01-0.05wt%,
Steel consisting of V: 0.02 to 0.15 wt%, balance Fe and unavoidable impurities is low-temperature rolled with an area reduction of 25% or more at 800°C or lower and a finishing temperature of 700°C or higher, and the rail head undergoes pearlite transformation immediately after rolling. A method for manufacturing a high-performance rail with excellent ductility and toughness, characterized by accelerated cooling until completion. (8) C: 0.60-0.90wt%, Si: 0.4-1.5wt%,
Mn: 0.5~1.5wt%, Nb: 0.01~0.05wt%,
Cr: 0.1-0.3wt%, V: 0.02-0.15wt%, balance
Steel consisting of Fe and unavoidable impurities is low-temperature rolled with an area reduction of 25% or more at 800°C or lower and a finishing temperature of 700°C or higher, and immediately after the rolling, the rail head is acceleratedly cooled until pearlite transformation is completed. A method for manufacturing high-performance rails with excellent ductility and toughness. The reason for the current decline in the composition of the present invention will be explained below. C is an effective component for increasing the strength, hardness, and wear resistance of the rail, and if it is less than 0.60 wt%, desired properties such as wear resistance cannot be obtained. On the other hand, C
If it exceeds 0.90wt%, a large amount of pro-eutectoid cementite will be produced, which will significantly embrittle the steel. For this reason, C
is 0.60 to 0.90wt%. Si is one of the main elements that characterizes the present invention. To ensure wear resistance of rail steel, C:
Pearlitic steel with a content of 0.60 to 0.90 wt% has 100
% brittle fracture surface, and sufficient improvement in toughness cannot be achieved simply by refining the structure. Under these conditions, the addition of Si was found to have a significant effect on improving toughness. In other words, Si is an effective component to increase the toughness of the rail, and 0.4wt
%, no significant toughness improvement effect is observed. On the other hand, if Si exceeds 1.5wt%, ductility deteriorates significantly and there is a tendency for embrittlement to begin. For this reason, Si is set at 0.4 to 1.5 wt%. Mn is a component to improve hardenability and rail strength, and if it is less than 0.5 wt%, the desired strength cannot be secured. On the other hand, when Mn exceeds 1.5wt%,
During rail welding, a problem arises in that martensite is generated in the segregated areas, impairing weldability. For this reason
Mn should be 0.5 to 1.5wt%Mn. Nb is added primarily to improve the ductility of the rail. The second purpose of adding Nb is to prevent a decrease in strength during low-temperature rolling and to ensure strength equal to or higher than that of normal rolling. Nb is
If it is less than 0.01wt%, the above purpose cannot be achieved, while if it exceeds 0.05wt%, it may cause coarse grains during rolling heating.
Nb carbonitrides are generated, which significantly embrittles the steel.
It can become a starting point for cracks such as shelling damage, which has a negative impact on the rail. For this reason, Nb
The content should be 0.01-0.05wt%. Cr and V are added singly or in combination to increase the strength of the rail. Cr improves hardenability, and V increases strength through precipitation strengthening of V carbonitrides. When Cr is less than 0.1wt% and V is less than 0.02wt%, no significant increase in strength is observed. On the other hand, Cr
When V exceeds 0.3 wt% and V exceeds 0.15 wt%, the ductility improving effect of Si and Nb is lost. In the above-mentioned composition system containing Si and Nb, 800
Area reduction rate of 25% or more at temperatures below ℃, finish rolling temperature 700
By performing low-temperature hot rolling at a temperature of .degree. C. or higher, the ductility is improved without a decrease in strength. In order to improve ductility and toughness, it is effective to refine the structure. Even in eutectoid steel such as rails, by rolling in the non-recrystallized region of austenite, a fine-grained pearlite structure is obtained and the ductility is improved. This is because by applying pressure to unrecrystallized fine austenite grains, the austenite grains are elongated as fine grains, increasing the austenite grain boundary area as a preferential nucleation site for pearlite, and increasing pearlite nucleation. It depends. In refining the pearlite structure through controlled rolling, the combined addition of Si and Nb is effective in improving the strength-toughness balance. Nb has a strong effect of suppressing austenite recrystallization and is effective in increasing the non-recrystallization temperature.
It becomes possible to form rolled and elongated grains without recrystallizing the austenite grains even at temperatures as high as 0.degree. but,
Recrystallization tends to progress when rolling is completed at a temperature higher than 800°C. For this reason, when rolling is completed at a temperature higher than 800℃, it is difficult to obtain elongated austenite grains with high strain, and because the amount of pearlite nucleation decreases, grain refinement of the pearlite structure does not occur and high elongation toughness is obtained. do not have. For the above reasons, the present invention requires that rolling be completed at 800°C or lower, that is, perform low-temperature rolling at 800°C or lower. In addition, the minimum area reduction rate required to obtain the effect of unrecrystallized austenite elongation graining by low-temperature rolling at 800℃ or less is about 25%, and if the area reduction rate is less than this, the The above-mentioned effects obtained by rolling cannot be sufficiently obtained. Furthermore, since the effect of grain refinement of the pearlite structure cannot be obtained unless rolling is performed in the austenite region, the lower limit of the finishing temperature of rolling is set at 700°C. Moreover, by accelerating cooling of the rail head immediately after such low-temperature rolling until the completion of pearlite transformation, the rail head can be made even higher in strength and ductility. [Example] Table 1 shows the chemical composition of the test steel. Among these, A to C and M to O are comparison steels, steel type A is AREA standard rail steel, and steel types B and C are steels with the sole addition of 1.0 wt% Si and 0.02 wt% Nb, respectively. D to L steel types are the steels of the present invention. Table 2 shows rolling conditions, and six levels of finishing temperature are used to examine the effects of low-temperature rolling on strength and rolling toughness. Rolling 1 (abbreviation: S1)
~Rolling 4 (S4) is rail rolling. Table 2 shows the rolling conditions, and in order to see the influence of low temperature rolling on strength and rolling toughness, six levels of finishing temperature are used. Rolling 1 (abbreviation:
S1) to rolling 3 (S3) are the conventional level rolling of rails. Rolling 5 (S5) ~ Rolling 6 (S6)
This corresponds 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 rolling finishing temperature and 0.2% proof stress of each steel type.
This shows the relationship between the aperture value and allows you to understand the characteristics of each alloy component. In other words, A steel is the 1980 Iron and Steel Institute High Temperature Deformation Subcommittee Symposium Text P.113
As qualitatively shown in Figure 2, although the strength decreases with low-temperature rolling, Nb-added steel (C,
Steels 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 they are rolled at lower temperatures. However, since steel B (steel with only 1.0 Si added) shows a lower reduction of area than steel A at all rolling levels, it is clear that Si deteriorates ductility. on the other hand,
Steel C (steel with only 0.02 wt% Nb added) shows a better reduction of area than Steel A, which shows that Nb 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 despite the addition of Si, which degrades ductility. In addition, S5 rolling (800℃
It shows an even better level of aperture value than the 25% area reduction rate shown below. Figure 2 shows the relationship between the rolling finishing temperature of each steel type, the Shapey impact absorption energy (vE ₀ ), and the plane strain fracture toughness value (k ₁ 1c) at 0°C. It can be seen that it can be improved. In pearlite steel, vE ₀ was hardly improved even if the structure was refined like C steel.
However, by adding Si, as in B steel, D steel, E steel, and F steel, it is clearly improved at all rolling levels. In addition, for E steel and F steel, vE ₀ is further reduced by S5 rolling.
is improving. FIG. 3 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 were significantly improved, and the toughness also showed a high value of K ₁ C > 160 Kg/mm ^3/2 . As mentioned above, by performing low-temperature rolling under specified conditions, even more excellent ductility can be obtained with a component system mainly containing composite additions of Si and Nb without a decrease in strength.
Furthermore, by performing accelerated cooling after rolling, strength and ductility are significantly improved while maintaining high toughness. Table 4 shows the strength, ductility, and toughness of each rail of the present invention example and comparative example.

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〔Effect of the invention〕

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

[Brief explanation of the drawing]

Figures 1a to 1d show the relationship between the rolling finishing temperature, 0.2% proof stress, and reduction of area of each steel type in Examples. FIG. 2 similarly shows the relationship between the rolling finishing temperature, the Charpy impact absorption energy (vE ₀ ) at 0° C., and the plane strain fracture toughness value (K ₁ c) for each steel type. Figure 3 shows E in the example.
Strength of steel and F steel depending on the presence or absence of accelerated cooling after rolling,
This shows changes in ductility and toughness.

Claims (1)

[Claims] 1 C: 0.60 to 0.90wt%, Si: 0.4 to 1.5wt%,
Mn: 0.5-1.5wt%, Nb: 0.01-0.05wt%, balance
A method for producing a high-performance rail with excellent ductility and toughness, which comprises rolling steel consisting of Fe and inevitable impurities at a low temperature of 25% or more in area reduction at 800°C or lower and at a finishing temperature of 700°C or higher. 2 C: 0.60-0.90wt%, Si: 0.4-1.5wt%,
Mn: 0.5-1.5wt%, Nb: 0.01-0.05wt%, Cr:
A steel with excellent ductility and toughness is produced by low-temperature rolling a steel consisting of 0.1 to 0.3 wt%, the balance being Fe and unavoidable impurities, with an area reduction of 25% or more at 800°C or less and a finishing temperature of 700°C or more. How to make performance rails. 3 C: 0.60-0.90wt%, Si: 0.4-1.5wt%,
Mn: 0.5-1.5wt%, Nb: 0.01-0.05wt%, V:
A steel with excellent ductility and toughness is produced by low-temperature rolling a steel consisting of 0.02 to 0.15 wt%, the balance being Fe and unavoidable impurities, with an area reduction of 25% or more at 800°C or less and a finishing temperature of 700°C or more. How to make performance rails. 4 C: 0.60-0.90wt%, Si: 0.4-1.5wt%,
Mn: 0.5-1.5wt%, Nb: 0.01-0.05wt%, Cr:
Steel consisting of 0.1 to 0.3 wt%, V: 0.02 to 0.15 wt%, balance Fe and unavoidable impurities is low-temperature rolled with an area reduction of 25% or more at 800°C or less and a finishing temperature of 700°C 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: 0.01-0.05wt%, balance
Steel consisting of Fe and unavoidable impurities is low-temperature rolled with an area reduction of 25% or more at 800°C or lower and a finishing temperature of 700°C or higher, and immediately after the rolling, the rail head is acceleratedly cooled until pearlite transformation is completed. 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: 0.01-0.05wt%, Cr:
Steel consisting of 0.1 to 0.3wt%, balance Fe and unavoidable impurities is low-temperature rolled at a finishing temperature of 700℃ or higher with an area reduction of 25% or higher at 800℃ or lower, and the rail head immediately after rolling is rolled until pearlite transformation is completed. A method for manufacturing high-performance rails with excellent ductility and toughness, characterized by accelerated cooling. 7 C: 0.60-0.90wt%, Si: 0.4-1.5wt%,
Mn: 0.5-1.5wt%, Nb: 0.01-0.05wt%, V:
Steel consisting of 0.02 to 0.15 wt%, balance Fe and unavoidable impurities is low-temperature rolled with an area reduction of 25% or more at 800°C or less and a finishing temperature of 700°C or more, and the rail head immediately after rolling is rolled until the end of pearlite transformation. A method for manufacturing high-performance rails with excellent ductility and toughness, characterized by accelerated cooling. 8 C: 0.60-0.90wt%, Si: 0.4-1.5wt%,
Mn: 0.5-1.5wt%, Nb: 0.01-0.05wt%, Cr:
Steel consisting of 0.1 to 0.3 wt%, V: 0.02 to 0.15 wt%, balance Fe and unavoidable impurities is low-temperature rolled at a reduction rate of 25% or more at 800°C or lower and a finishing temperature of 700°C or higher, and immediately after the rolling. A method for manufacturing a high-performance rail with excellent ductility and toughness, characterized by accelerating cooling of the rail head until the end of pearlite transformation.