JPH0454557B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a coated arc welding rod used for butt welding or overlay welding of rails for railways or cranes. (Prior art) In order to butt weld or overlay weld the rails, there is a method in which the end faces of the joined rails are grooved and sequentially multi-layered welded, or after they are butted together with an I-shaped groove and the rail foot is welded in multiple layers, An enclosure welding method is used in which the abdomen and head are surrounded by enclosure metal material and continuously welded. In addition, there are methods of overlay welding of rails, such as hard overlaying the rail head surface of a butt weld, and overlaying repair of local surface flaws or worn parts of the rail. Due to the intended use of the rail, the head surface is required to have high wear resistance against rolling contact with wheels and resistance to severe fatigue, that is, high fatigue damage resistance. On the other hand, the legs and abdomen must have sufficient static strength and fatigue strength to withstand the impact or bending load caused by passing wheels, and there are no or practically no weld defects such as weld cracks. It must be kept as low as possible. Currently, the chemical composition of ordinary railway rails in the world is the first in the world.
As shown in the table, C: 0.40-0.82%, Si:
Contains 0.05-0.35%, Mn: 0.60-1.25%, its metal structure is pearlite, and its tensile strength is
70Kg/mm2 or ^more .

[Table] Recently, there have been many studies on the performance of rails in use.Pearlite structure has the best wear resistance and fatigue damage resistance, martensite structure is harmful, and pearlite structure has the same hardness and high C content. has been shown to be better. (Problems to be Solved by the Invention) In order to further improve these performances, Si: 1.0% or less is added to the hard-headed rail whose head surface or the whole of the above-mentioned normal rail is heat-treated, or to the component of the above-mentioned normal rail.
Mn: increased to 1.50% or less, and further Cr, Mo, V,
Cr with one or more of Nb, Ni, and Cu:
1.3% or less, Mo or V: 0.3% or less, Nb: 0.1%
Below, alloy steel rails containing 0.3% or less of Cu and alloy steel heat-treated rails using a combination of both have been put into practical use. Covered arc welding rods conventionally used for butt welding or overlay welding of rails are JIS Z3213 coated arc welding rods for low-alloy high-strength steel, as shown in Table 2. These welding rods are usually used for thick steel plates, etc., so they contain Ni, Ni, and C: 0.25% or less and Mn: 0.65% or less as defined by JIS3503 coated arc welding rod core wire rods or JISG3505 mild steel wire rods.
It is coated with a flux containing one or more alloy components of Cr and Mo. Therefore, when such a welding rod is applied to a rail, the weld metal formed contains C: 0.3% or less, Si,
In addition to Mn, it contains 0.1% or more of one or more of Ni, Cr, and Mo. As a result, hot cracks occur near the melting boundary of the rail base material. This hot cracking is theoretically unavoidable because the melting point of rail steel is approximately 1470°C, whereas the melting point of weld metal is higher, approximately 1530°C. Furthermore, a large amount of martensitic structure is generated near this fusion boundary while welding, which significantly reduces fatigue strength.
Normally, after welding, it must be tempered or annealed at a temperature below 710℃. As a result, the structure of the weld metal produces bainite, which has low wear resistance, so when welding a rail using the above-mentioned welding rod, the weld metal layer locally forms prematurely even if the hardness is the same as that of the base metal rail. wear out. Such hot cracking and local wear become more pronounced as the base rail is made of alloyed steel with a higher C content, that is, the higher the strength is increased, and in fact, high strength rails have become unweldable.

[Table] In addition, for the rail overlay welding method, JIS Z3251 hard overlay covered arc welding rods as shown in Table 2 are used.
A welding rod corresponding to DF2A or DF2B is used. Since the welding rod corresponding to DF2A is almost the same as the welding rod for low-alloy high strength steel, the above-mentioned problem still applies. The weld metal formed by DF2B will generate a martensitic structure if it is left unwelded, so it must be tempered after welding. For this reason, not only does the weld metal become a tempered martensitic structure and a pearlite structure cannot be obtained, but also when heat-treated rails are subjected to such post-heat treatment, the head surface of the base metal rail, which is affected by this heat, becomes soft and changes. A situation occurred in which wear became significant. The present invention essentially solves the problems in the prior art described above, and provides a rail or crane rail that can stably ensure good joint performance even for high-strength rails such as heat-treated or alloy steel rails. Provides a coated arc welding rod for use in the present invention. For this purpose, the inventors conducted extensive research and found that the deposited metal formed by the conventional coated arc welding rod has a composition significantly different from that of the base metal rail, as shown in Table 2. As a result, we discovered that the above-mentioned problems would occur, and invented a completely new coated arc welding rod for rails in which the weld metal has a high C-type pearlite structure similar to that of the base material rail, which was conventionally considered unsuitable for welding. did. (Means for solving the problems) The gist of the present invention is that C: 1.0% or less in weight %,
In an arc welding rod in which a welding core consisting of Si: 1.0% or less, Mn: 1.6% or less, and the balance consisting of Fe and unavoidable impurities is coated with a flux consisting of a slag forming agent or an alloying agent, the entire welding rod is The alloy components contained in the welding rod total weight%,
C: 0.4-3.0%, Si: 0.1-10.0%, Mn: 0.6-3.0
% C: 1.0% or less,
Si: 1.0% or less, Mn: 1.6% or less, and Cr: 1.3
% or less, Mo: 0.3% or less, V: 0.3% or less, Nb:
0.1% or less, Ni: 2.0% or less, Cu: 0.3% or less1
In an arc welding rod, the welding core is coated with a flux consisting of a slag forming agent or an alloying agent containing the slag forming agent or an alloying agent, and the remainder is Fe and unavoidable impurities. The alloy components are C:
0.4-3.0% or less, Si: 0.1-10.0% or less, Mn: 0.6
~3.0%, Cr: 1.3% or less, Mo: 0.3% or less,
V: 0.3% or less, Nb: 0.1% or less, Ni: 2.0% or less,
This is a coated arc welding rod for rails that is characterized by having a Cu content of 0.3% or less. (Function) The weld metal obtained with the welding rod of the present invention has a C: 0.4
~0.9% or less, Si: 0.1-1.0%, Mn: 0.6-1.5%,
Or further Cr: 1.3% or less, Mo: 0.3% or less,
V: 0.3% or less, Nb: 0.1% or less, Ni: 2.0% or less,
Cu: Contains one or more types at 0.3% or less, and the remainder is Fe and unavoidable impurities, so the composition is high C steel similar to the base rail, and hot cracking occurs in the molten boundary layer of the base rail. By performing appropriate post-heat treatment, joint performance such as pearlite structure, hardness, tensile strength, and corrosion resistance similar to that of the base rail can be obtained. The present invention will be explained in detail below. The alloying components in the deposited metal of coated arc welding can be added from the welding core, the alloying component of the flux, or both. Therefore, in the coated arc welding rod of the present invention, the alloying component of the welding core or flux and the amount of the alloying component added to the entire welding rod are determined in consideration of the yield of the welding rod to the deposited metal. According to the findings of the present inventors, the yield is highest when the alloying components of the weld metal are added from the weld core, with C, Si, and Mn at over 90%, and Cr, Mo, V, and
Almost 100% can be expected for Nb, Cu, and Ni. Therefore, the alloy composition of the weld core wire in the welding rod of the present invention corresponds to the upper limit of the deposited metal when the yield is minimum. That is, the weld core wire of the present invention has C: 1.0% or less,
Si: 1.0% or less, Mn: 1.6% or less, or further
Cr: 1.3% or less, Mo: 0.3% or less, V: 0.3% or less,
Mild steel, hard steel, or special steel wire containing one or more of Nb: 0.1% or less and Ni: 2.0% or less can be used. On the other hand, the amount of alloying agent added to the flux coated on the weld core is adjusted depending on the amount of the alloy component in the weld core and the yield of the alloy supply substance relative to the deposited metal. Since this yield differs depending on each alloying element, the type of alloy supply material, and welding conditions, the limiting value of the alloying components contained in the entire welding rod is the maximum value of this yield for each alloying element, that is, 100%. Determine from % and minimum value. The reason for adding each alloy component in the coated arc welding rod for rails of the present invention and its limiting values will be explained below. C is an essential component for producing a pearlite structure in the weld metal similar to that of rail steel, and at the same time,
By adjusting the weld metal to high C steel, that is, C: 0.4 to 0.9%, and making the solidification temperature almost the same as that of rail steel, the high temperature in the molten boundary layer of the base rail that occurs in the conventional technology can be reduced. This prevents liquefaction cracking and is the most distinctive feature of the present invention. Furthermore, as the C content of the weld metal increases, the joint tensile strength and hardness increase, so the wear resistance and fatigue damage resistance of the weld metal can be improved. The amount of C in the weld metal is added to the C component contained in the weld core or the alloying component of flux from a C supply material such as graphite, C alloy iron, cast iron, C compound, or both. Therefore, the upper limit of the amount of C in the entire welding rod is determined from the case where the yield of the C supply material to the deposited metal is minimized. In other words, using a mild steel core wire containing almost no C component,
If only 30% of graphite powder with the lowest yield to weld metal is added to the flux alloying agent, in order to obtain the above-mentioned weld metal, the C in the entire welding rod must be
The content will be up to 3.0%. On the other hand, the lower limit of the C content in the entire welding rod corresponds to the case where the yield of the alloy component of the weld core or flux to the deposited metal is maximum, that is, 100%, and the minimum value is 0.4
%. Therefore, the amount of C contained in the entire welding rod in the present invention was set to 0.4 to 3.0% by total weight of the welding rod. If the C content of the welding rod is less than 0.4%, the C content of the weld metal may be less than 0.4, causing hot cracks to occur in the molten boundary layer of the base metal rail and reducing the pearlite structure of the weld metal, resulting in joint tensile stress. A strength of 70Kg/mm ² or more cannot be obtained. If the C content of the welding rod exceeds 3.0%, the C content of the weld metal will exceed 0.9%,
Pro-eutectoid cementite precipitates on the weld metal, making the weld metal extremely brittle. Si is normally included as a deoxidizing agent for the deposited metal in the alloy component of the flux of coated arc welding rods, and is added to the ferroalloy. The Si content of rail steel is usually 0.1% or more, and Si strengthens ferrite in the pearlite structure, increasing strength and improving fatigue damage resistance. Furthermore, it has an effect on the onset time and temperature of pearlite transformation. Because it is small, even if the weld metal contains more Si than the rail steel, it will not be harmful as long as it is 1.0% or less. However, if the content exceeds 1.1%, when rails are butt-welded in multiple layers, as the composition of the weld metal becomes high in Si, the weld metal becomes susceptible to solidification cracking and solidification cracking occurs, significantly shortening the service life of the rail. There is a problem of shortening the lifespan. The yield of Si contained in the ferroalloy of flux varies depending on the deoxidation state of the weld core or the welding conditions, and according to the findings of the present inventors, the yield of Si contained in the weld core is low when the Si content is low. The retention rate will be low, reaching a minimum of 10%. Therefore, in order to obtain the Si content of the weld metal, the amount of Si contained in the entire welding rod should be 0.1 to 10.0% in terms of the total weight of the welding rod. If the amount of Si in the welding rod is less than 0.1%, the weld metal will not be sufficiently deoxidized, and oxidized inclusions will increase in the weld metal. If the amount of Si in the welding rod exceeds 10.0%, not only will high-temperature solidification cracks occur in the weld metal, but the fluidity of the slag will decrease, making welding difficult. Like Si, Mn is contained in the alloy component in the flux of a coated arc welding rod as a deoxidizing agent for the deposited metal, and is added from the ferroalloy or metal Mn. The Mn content of the rail steel is 0.6% or more,
Mn is an element that retards pearlite transformation, and the start of pearlite transformation changes depending on the amount added, and the strength also changes, so the Mn content of the weld metal must roughly correspond to that of the rail steel. The yield of Mn changes depending on the amount of C and Si in the welding rod, and when the amount of C and Si is low, the yield of Mn decreases and reaches a minimum.
It will be 50%. Therefore, the amount of Mn contained in the entire welding rod to obtain the amount of Mn in the weld metal is 0.6 to 3.0% in terms of the total weight of the welding rod. The amount of Mn in the welding rod is
If it is less than 0.6%, the amount of Mn in the weld metal becomes low, and the tensile strength or elongation, that is, ductility, of the weld metal decreases. If the Mn content of the weld metal exceeds 3.0%, the weld metal
As the amount of Mn increases, post-heat treatment to transform martensite precipitated in the weld metal into pearlite becomes extremely difficult. In addition to the above-mentioned C, Si, and Mn, the base material rail is Cr, Mo,
When one or more of V, Nb, Ni, and Cu are contained, the weld metal may also have to contain these alloy components in an amount equal to or less than that of the base metal rail. i.e. Cr,
Like Mn, Mo and V are elements that retard pearlite transformation, and depending on the amount added, the start of pearlite transformation changes and the strength also changes, so when the base rail is alloy steel containing these alloy components, If the welding rod used for the top surface of the rail does not contain these alloy components, metallographic hardness and joint tensile strength similar to those of the base rail cannot be obtained as welded or by heat treatment after welding. . Therefore, the Cr, Mo, and V contents of the weld metal are Cr:
1.3% or less, Mo, V: 0.3% or less. Nb is an element that significantly shortens the completion time of pearlite transformation, so it has the effect of preventing harmful martensite generated during cooling after welding.
However, if the Nb content of the weld metal exceeds 0.1%, huge carbon and nitrides will be formed, reducing toughness and fatigue strength, so the Nb content of the weld metal should be 0.1% or less. Cu is an alloy component that is effective in improving the corrosion resistance of rail steel, and is contained in corrosion-resistant rails at 0.3% or less. Therefore, when welding corrosion-resistant rails, the same corrosion resistance as the base metal rail cannot be obtained unless the weld metal also contains 0.3% or less of Cu. However, if the Cu content of the weld metal exceeds 0.3%, hot embrittlement will occur and surface flaws will occur, so the Cu content of the weld metal should be 0.3 or less. Ni is an alloy component that improves the ductility or toughness of rail steel, but since rail steel is originally a steel material with low ductility or toughness, it is rarely added to rails. However, if the weld metal contains 2% or less of Ni, the ductility or toughness will improve, so it may be necessary to add Ni to the weld metal. However, if the weld metal contains more than 2.0% Ni, high-temperature solidification cracking is likely to occur in the weld metal.
Ni content shall be 2.0% or less. One or more of Cr, Mo, V, Nb, Ni, and Cu in the weld metal, Cr: 1.3% or less, Mo: 0.3% or less, V: 0.3% or less, Nb: 0.1% or less, Ni: 2.0%
Below, if Cu: 0.3% or less is contained, the yield can be expected to be almost 100% even if these alloying components are added from the flux, so the amount of the alloying components contained in the entire welding rod is Cr in weight%: 1.3
% or less, Mo: 0.3% or less, V: 0.3% or less, Nb:
0.1% or less, Ni: 2.0% or less, Cu: 0.3% or less. The coated arc welding rod for rails according to the present invention can crack hot cracks even when welded to rails under normal welding conditions by appropriately selecting the wire diameter of the welding core, flux coverage, and composition of flux constituent materials. By combining appropriate post-welding heat treatment after welding, it is possible to obtain a welded joint that is free of harmful structures and has the same hardness and pearlite structure as the base metal rail. The effects of the present invention will be explained in more detail below using Examples. (Examples) Example 1 Multilayer butt welding Using an arc welding rod in which the weld core wires in Table 3 were coated with the flux adjusted as shown in Table 4, butt welding was performed on the ordinary rails shown in Table 5. For welding, a specially shaped bevel is applied to the end surface of the rail joint.
After preheating to 400-500℃, multi-layer welding is performed with the feet facing downward, the abdomen facing upright, and the head facing downward. After welding, we use a multi-hole nozzle burner to evenly heat the entire rail cross section to 900-1000℃. It was heated and allowed to cool. Table 6 shows the chemical composition and hardness of the weld metal and the results of the tensile test of the welded joint. The weld metal had a pearlite structure, and no hot cracks were observed.

【table】

【table】

【table】

[Table] Example 2 Enclosed arc welding Using an arc welding rod coated with the flux adjusted as shown in Table 8 to the weld core wire shown in Table 7, we enclosed the high C steel and low alloy steel rails shown in Table 9. I did arc welding. The welding process is performed by preheating to 400-500℃ using an I-shaped groove, then welding the legs in multiple layers facing downwards, and continuous welding from the abdomen to the head with an enclosure backing metal.After welding, weld the entire rail cross section evenly. The mixture was heated to 800-1000°C using a multi-hole nozzle burner and allowed to cool. Table 10 shows the chemical composition and hardness of the weld metal and the results of the tensile test of the welded joint. The weld metal had a pearlite structure and no high-temperature cracks were observed.

【table】

【table】

【table】

[Table] Example 3 Overlay Welding A V-shaped horizontal groove with a bottom angle of 60° and a depth of 20 mm is made on the head of the typical alloy steel rail shown in Table 11, and then a V-shaped horizontal groove with a depth of 20 mm is made from the rail steel as shown in Table 12. The fabricated weld core wire is
Overlay welding was carried out using an arc welding rod coated with a flux as shown in Table 13 and adjusted as shown in Table 14. In the welding process, the base material rail was preheated to 400-500℃, then multi-layer welding was performed, and after welding, it was heated to 800-1000℃ and allowed to cool. Table 15 shows the chemical composition and hardness of the weld metal and the results of the tensile test of the welded joint. The weld metal had a pearlite structure and no high-temperature cracks were observed.

【table】

【table】

【table】

【table】

[Table] (Effects of the invention) If rails are butt welded or built-up welded using the coated arc welding rod of the present invention, the welded part will suffer from hot cracking that could not be avoided with the conventional welding rods as described above. Not only can you prevent the occurrence of
The weld metal can be as welded or subjected to post-heat treatment such as air hardening after welding to obtain a pearlite structure, hardness, and joint strength similar to that of the base metal rail. That is, the present invention eliminates the fatal drawbacks of conventional welding rods by obtaining a weld metal with a high C-type pearlite structure similar to that of the base rail as described above and a tensile strength of 70 kg/mm ² or more. This is a coated arc welding rod for rails that can also be applied to high-strength rails.

Claims (1)

[Claims] 1% by weight, C: 1.0% or less, Si: 1.0% or less, Mn: 1.6% or less, the balance being Fe and unavoidable impurities. In an arc welding rod coated with a flux consisting of component agents, the alloy components contained in the entire welding rod in terms of the total weight of the welding rod are: C: 0.4 to 3.0%, Si: 0.1 to 10.0%, Mn: 0.6 to 3.0 A coated arc welding rod for rails, which is characterized by being adjusted to %. 2% by weight: C: 1.0% or less, Si: 1.0% or less, Mn: 1.6% or less, Cr: 1.3% or less, Mo: 0.3% or less, V: 0.3% or less, Nb: 0.1% or less, Ni: An arc in which a welding core containing one or more of Cu: 0.3% or less and the remainder consisting of Fe and unavoidable impurities is coated with a slag forming agent or a flux consisting of this and an alloy component. In the welding rod, the alloy components contained in the entire welding rod are as follows: C: 0.4 to 3.0%, Si: 0.1 to 10.0%, Mn: 0.6 to 3.0%, Cr: 1.3% or less, A coated arc welding rod for rails, characterized in that Mo: 0.3% or less, V: 0.3% or less, Nb: 0.1% or less, Ni: 2.0% or less, and Cu: 0.3% or less.