JP4153650B2 - Manufacturing method of high weldability rail - Google Patents

Description

【００２１】
【表２】

【００２２】
【発明の効果】
以上述べたように本発明によれば、ロングレール化に必要なフラッシュバット溶接部の硬さが母材レールと同等の値を示して不連続性をなくし、使用中の摩耗が均一となり、騒音、振動などの問題を解決できる低強度レールを提供することができるので、産業上の効果は大きい。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high weldability pearlite rail for railways that is used as a long rail mainly by flash butt welding.
[0002]
[Prior art]
In recent years, railway rails have been made longer by welding from the viewpoints of simplifying track maintenance and inspection, suppressing noise and vibration, and improving riding comfort. The welding methods used include flash butt welding, gas pressure welding, enclosed arc welding, and thermite welding.
[0003]
Among these welding methods, flash butt and gas pressure welding are indispensable techniques for lengthening the rail, as shown in the literature (iron and steel, Vol. 70, No. 10, 1984). ing. In the case of these joints, the rails are joined to each other and a new thermal history is received by welding. Therefore, the hardness of the welded part is different from that of the base metal rail, resulting in a large discontinuity in the welded part. As the passing tonnage overlaps, uneven wear occurs, causing noise and vibration. On the other hand, in recent years, a method of correcting a non-uniform shape by grinding has been employed. However, in this case, there is a problem that a great amount of cost is required for introduction and maintenance of a grinding machine.
[0004]
[Problems to be solved by the invention]
Long railing is an important technology from the viewpoint of reducing track maintenance and ensuring safety in high-speed trains. Among them, maintaining the uniformity of the hardness of flash butt welds used for general purposes Of particular importance. In general, pearlite steel having a hardness of HB220 to 300 is used as a general-purpose rail, and the production method thereof is reduced in cost by suppressing the amount of expensive alloy added and keeping the rolling without heat treatment. . That is, the hardness of such a general-purpose rail is determined by the cooling rate (0.5 ° C./s or less) and the steel component as it is allowed to cool as determined by the size of the rail cross section.
[0005]
On the other hand, the flash butt weld has a cooling rate of 1 to 2.5 ° C / s after welding. Accordingly, there is a difference in hardness between the hardness obtained in the rail manufacturing process and the welded portion hardness after welding.
An object of the present invention is to provide a rail in which the hardness of a base metal rail and the hardness after flash butt welding are similar, and unevenness in the hardness of a welded long rail can be prevented.
[0006]
[Means for Solving the Problems]
The present invention is similar to the hardness of the base rail and the hardness of the welded portion after flash butt welding, and can prevent unevenness of the hardness of the welded long rail. %: C: 0.60 to 0.95%, Si: 0.10 to 1.20%,
Mn: 0.20 to 1.50%, Cr: 0.01 to 0.50%, Mo: 0.01 to 0.20%,
Co: 0.1 to 2.0%, Cu: 0.05 to 1.00%,
Ni: 0.05-1.00%, V: 0.005-0.20%,
Nb: 0.005-0.05%, Ti: 0.005-0.05%
Containing one or more of
Ceq = C + Si / 10 + Mn / 6 + Cr / 5 + Mo / 4 + Co / 5 Ceq obtained by satisfying 0.6 to 1.0, the balance being iron and inevitable impure, and after product rolling, 800 to It is a manufacturing method of a high weldability rail characterized by receiving accelerated cooling of 1 to 2.5 ° C./s between 500 ° C. and having a hardness of HB220 to 300.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below. First, the reasons for limiting the content components will be described. C is an element necessary for satisfying the strength that the rail should have and for obtaining a pearlite structure stably. C is required to be contained in an amount of 0.60% or more as an effective component for generating pearlite and ensuring wear resistance. However, at a high content exceeding 0.95%, a large cementite structure is precipitated at a cooling rate of 2.5 ° C./s or less, and the ductility is significantly reduced. Therefore, the content range is set to 0.60 to 0.95%.
[0008]
Si is an element that increases the hardness (strength) of the rail head by hardening a solid solution to the ferrite phase in the pearlite structure in addition to being added as a deoxidizer to clean steel, but less than 0.10% However, the effect cannot be expected sufficiently, and if it exceeds 1.20%, a lot of surface flaws are generated during hot rolling, and weldability is lowered due to the generation of oxides. Limited to -1.20%.
[0009]
Mn is an element that contributes to increasing the strength by lowering the pearlite transformation temperature and increasing the hardenability, and further suppresses the formation of proeutectoid cementite structure, but with a content of less than 0.20%, The effect is small, and it is difficult to secure the hardness required for the rail head. On the other hand, if it exceeds 1.50%, the hardenability is remarkably increased, the martensite structure is easily formed, segregation is promoted, and a pro-eutectoid cementite structure that is harmful to the toughness of the rail is easily formed in the segregated part. Therefore, the amount of Mn was limited to 0.20 to 1.50%.
[0010]
Further, one or more of Cr, Mo, and Co can be added as a strengthening element of pearlite within the range shown below.
Cr is an element that raises the equilibrium transformation point of pearlite and, as a result, refines the pearlite structure and contributes to increasing the strength, and at the same time improves the wear resistance by strengthening the cementite phase in the pearlite structure. If the amount is less than 0.01%, the effect is small. If excessive addition exceeding 0.50% is performed, a large amount of martensite structure is generated and the toughness of the rail is lowered. Limited to 50%.
[0011]
Mo, like Cr, is an element that increases the equilibrium transformation point of pearlite and, as a result, refines the pearlite structure, contributes to higher strength and improves wear resistance. When the excessive addition exceeds 0.20%, segregation is promoted, the pearlite transformation rate is further reduced, a martensite structure is formed in the segregated portion, and the toughness of the rail is reduced. It was limited to 0.01 to 0.20%.
[0012]
Co is an element that improves the strength by increasing the transformation energy of pearlite and making the pearlite structure fine, but if it is less than 0.1%, the effect cannot be expected, and an excess exceeding 2.0% Even if this addition is performed, the effect reaches the saturation region, so the Co content is limited to 0.1 to 2.0%.
[0013]
Further, for the purpose of improving the strength without impairing the ductility, either or both of Cu and Ni can be added within the range shown below.
Cu is an element that improves the strength without impairing the toughness of pearlite steel, and the effect is the largest in the range of 0.05 to 1.00%, and when it exceeds 1.00%, red heat embrittlement tends to occur. Therefore, the amount of Cu was limited to 0.05 to 1.00%.
[0014]
Ni is an element that improves the ductility and toughness of pearlite steel and at the same time increases the strength of pearlite steel by solid solution strengthening. However, if it is less than 0.05%, its effect is remarkably small, and 1.00% No further effect can be expected even if excessive addition is performed. Therefore, the amount of Ni is limited to 0.05 to 1.00%.
[0015]
Moreover, 1 type (s) or 2 or more types can be added in the range shown below as an intensity | strength improvement element by a precipitation effect among V, Nb, and Ti.
In the heat treatment of the rail head, V forms carbides and nitrides inside the rail head, which has a cooling rate slower than that of the rail head surface portion, and precipitates on the ferrite ground in the pearlite structure. Although it is an element that improves the hardness, if it is less than 0.005%, it becomes difficult to form carbide or nitride, and precipitation hardening of the pearlite structure inside the rail head becomes difficult. Moreover, since the effect beyond it cannot be expected even if it adds exceeding 0.20%, V amount was limited to 0.005-0.20%.
[0016]
Nb increases the strength by precipitation hardening with Nb carbide and Nb nitride like V, and further refines austenite grains by the action of suppressing the growth of crystal grains when heat treatment is performed at a high temperature. The austenite grain growth suppressing effect acts up to a temperature range higher than V (around 1200 ° C.), and improves the ductility and toughness of the pearlite structure. The effect cannot be expected if it is less than 0.005%, and no further effect can be expected even if excessive addition exceeding 0.05% is performed. Therefore, the Nb content is limited to 0.005 to 0.05%.
[0017]
Ti makes use of the fact that precipitated Ti carbide and Ti nitride do not dissolve during reheating during rail rolling, thereby reducing the austenite crystal grain size during rolling heating and improving the ductility and toughness of the pearlite structure. It is an effective ingredient. However, if the amount is less than 0.005%, the effect is small, and if added over 0.05%, coarse Ti carbide and Ti nitride are generated, which becomes the starting point of fatigue damage during use of the rail and generates cracks. Therefore, the Ti content is limited to 0.005 to 0.050%.
[0018]
Note that Ceq = C + Si / 10 + Mn / 6 + Cr / 5 + Mo / 4 + Co / 5 is an equation of carbon equivalent obtained empirically from the relationship between hardness and components.
Since the cooling rate after flash butt welding, which is the final heat history, is 1 to 2.5 ° C / s between 800 to 500 ° C, it is important that the cooling rate at the pearlite transformation of the base metal rail is the same cooling rate. At that time, in order to ensure the hardness of HB 220 to 300 for both the base metal rail and the welded portion, the value of Ceq needs to be 1.0 or less. On the other hand, C is required to be 0.60% or more from the viewpoint of ensuring wear resistance, and Ceq is also set to a lower limit of 0.6.
[0019]
【Example】
The effects of the present invention are specifically shown below by examples.
Using a test steel consisting of the chemical components shown in Table 1 and having a pearlite metal structure, a rail consisting of the base material accelerated cooling rate and base material hardness shown in Table 2 is manufactured, and flash butt welding is performed. The difference between the hardness of the later welded portion and the hardness of the base material was compared.
The rails 1 to 5 that meet the conditions of the present invention could all be rails having no difference between post-weld hardness and base metal hardness. On the other hand, in reference numerals 6, 7, and 9 that deviate from the cooling condition of the present invention, the difference (ΔHB) between the post-weld hardness and the base metal hardness was large. Moreover, in the code | symbol 8 using the steel D from which component conditions remove | deviated, although the hardness difference was small, base material hardness was out of the range of this invention.
[0020]
[Table 1]

[0021]
[Table 2]

[0022]
【The invention's effect】
As described above, according to the present invention, the hardness of the flash butt weld necessary for the long rail shows the same value as the base metal rail, eliminating discontinuity, uniform wear during use, noise Since a low-strength rail that can solve problems such as vibration can be provided, the industrial effect is great.

Claims (4)

% By mass
C: 0.60 to 0.95%,
Si: 0.10 to 1.20%,
Mn: 0.20 to 1.50% is contained,
Ceq represented by the formula of Ceq = C + Si / 10 + Mn / 6 satisfies 0.6 to 1.0, and the balance consists of iron and inevitable impurities, and after product rolling, 1 to 2.5 between 800 and 500 ° C. A method for producing a highly weldable rail, which is subjected to accelerated cooling at a temperature of ° C / s and has a hardness of HB220 to 300. % By mass
C: 0.60 to 0.95%,
Si: 0.10 to 1.20%,
Mn: 0.20 to 1.50%
In addition,
Cr: 0.01 to 0.50%,
Mo: 0.01-0.20%,
Co: 0.1 to 2.0%
Containing one or more of
Ceq represented by the formula Ceq = C + Si / 10 + Mn / 6 + Cr / 5 + Mo / 4 + Co / 5 satisfies 0.6 to 1.0, the balance is made of iron and inevitable impurities, and after product rolling, 800 to 500 ° C. A method for producing a high-weldability rail, characterized by receiving accelerated cooling of 1 to 2.5 ° C./s between and a hardness of HB220 to 300. % By mass, further Cu: 0.05-1.00%,
Ni: 0.05-1.00%
1 or 2 types of these are contained, The manufacturing method of the highly weldable rail of Claim 1 or 2 characterized by the above-mentioned. % By mass, further V: 0.005 to 0.20%,
Nb: 0.005 to 0.05%,
Ti: 0.005 to 0.05%
One type or two types or more of these are contained, The manufacturing method of the high weldability rail of any one of Claim 1 thru | or 3 characterized by the above-mentioned.