KR100711453B1 - Welding method of high carbon steel for endless hot rolling - Google Patents

Abstract

The present invention relates to a method of joining high carbon steel for continuous rolling that can stably provide weld quality by welding welding materials by reducing the hardened structure of the weld by joining the rolled materials by laser welding in continuous rolling of the high carbon steel.

In the present invention, by weight% C: 0.5% or more, Si: 0.1-0.5%, Mn: 0.3-0.6%, P: 0.05% or less, S: 0.05% or less, Cu: 0.5% or less, Ni: 3% or less, A step of mutually opposing the high carbon steel rolled material containing Cr: 0.05 to 0.5% and Al: 0.05% or less and other unavoidable impurities and the remaining Fe; Welding with the laser welder using a welding material containing C ≦ 0.1% and Cr ≦ 1.22% in Fe or Ni main components and other inevitable impurities in the welding step of the butt portion of the rolled material; And continuously rolling the rolled material; It provides a welding method of high carbon steel for continuous rolling comprising a.

High Carbon Steel, Continuous Rolling, Welding Material, Laser Welding, Weldment, Heat Treatment

Description

Welding method of high carbon steel for continuous rolling {WELDING METHOD OF HIGH CARBON STEEL FOR ENDLESS HOT ROLLING}

1 is a conceptual diagram showing a high carbon steel laser welding apparatus according to an embodiment of the present invention.

Figure 2 is a graph showing the heat cycle of the high carbon steel laser welding portion according to an embodiment of the present invention.

Figure 3 is a photograph showing the laser welding portion after the PCM continuous rolling for the rolled material of the SK85 steel in one embodiment of the present invention.

The present invention relates to a method for welding a rolled material that is continuously rolled by mutually bonding the rolled material in the rolling process, and more particularly, the rolled material is joined by laser welding in the continuous rolling of high carbon steel to form a hardened structure of the welded portion. The present invention relates to a method and apparatus for joining high carbon steel for continuous rolling, which can reduce and stably provide welding quality of a welded portion.

In the technical field of producing sheet metal, continuous demands for the improvement of productivity and quality, and the enlargement of the size that can be manufactured are made strong.

Such continuous rolling is extended to high grade steel such as electrical steel sheet and ferritic stainless steel sheet.

The cold rolled coil obtained from the hot rolled coil may be manufactured by a pickling and tandem cold rolling mill (PC) process and a pickling and tandem cold rolling mill (PCM) process in which pickling and continuous rolling are simultaneously performed. The PCM process has been widely applied in recent years because the productivity can be greatly improved compared to the process of pickling and TCM respectively.

An important point in this continuous rolling field is the joining technology of the rolled sheet material which joins the rear end of the preceding rolled sheet material and the subsequent rolled sheet material to each other.

As a technique for joining a rolled sheet material for continuous rolling, there are a solid state joining method and a joining method by welding.

In the joining method by welding, the rear end of the preceding rolled sheet material and the subsequent rolled sheet material are welded to each other to form a welded portion, and then pass through the subsequent rolling line at the inlet side of the continuous rolling line.

In this case, if the quality of the weld is poor, it causes a serious problem that the weld breaks and the production stops entirely during the subsequent rolling line.

Therefore, for continuous rolling, it is important to secure the quality characteristics of welded parts of hot rolled and cold rolled coils.

In particular, the PCM line requires more stringent welding quality than the existing line because the production line is longer than the pickling line and the TCM line and the number of loopers that hold the coil is higher.

Welding methods applied to continuous rolling lines include flash butt welding, in which short circuit and flashing occur repeatedly, and laser welding using a high density heat source.

Since the flash butt welding has a large heat input amount, there is a limit in the selection of the welded material. As an example, in the case of electrical steel sheet, ferritic stainless steel, high carbon steel, etc., bond strength may not be secured and plate breakage may occur during cold rolling. In particular, high carbon steels have high carbon (C) content and are evaluated as a material that is very difficult to flash butt welding. In addition, even when the welding schedule and the welding conditions are set to be constant, it has been pointed out that there is a problem in the reproducibility, such as a variation in the quality characteristics of individual welds.

Laser welding has a high energy density and low heat input, and is known to obtain superior quality characteristics compared to conventional flash butt welding.

However, continuous welding of high carbon steel by laser welding causes pores and pinholes in the weld metal and cracks in the weld metal and the heat affected zone.

Pores and pinholes are closely related to the carbon content in the material. As the carbon in the molten metal reacts with oxygen in the atmosphere during welding and forms a CO gas, gas that has not been released to the outside remains at the time of solidification, causing porosity.

Therefore, it is important to reduce the carbon content of the molten metal portion, and by using an appropriate welding material, it is possible to reduce the generation of pores.

Weld cracks are related to hardened structure, and martensitic structure produced during rapid heating and quenching process is found to be the main cause in high carbon steel.

Since the hardened structure of the weld occurs at the same time as the weld metal and the weld heat direction, the improvement methods are also complicated and diverse.

As described above, the prior art for continuous rolling high carbon steel has the following technology.

First, Japanese Patent Laid-Open Publication No. H5-50276 relates to heat treatment of a welded portion, and discloses a method of maintaining a predetermined time at a specific heat treatment temperature according to the carbon content of the rolled material using a fixed heat source. However, this method has a problem in that the overall welding construction time increases with the heat treatment holding time.

Another prior art is Japanese Patent Application Laid-open No. Hei 5-132719, which relates to a method of heat-treating at a temperature range of 400 ° C. or higher and Ac 1 point or less within 1 minute after welding a weld by laser welding. However, this technique must be maintained for a very long time to completely remove the hardened structure at 400 ° C and below Ac1 point, and in the case of rapid cooling such as laser welding, the weld must be rapidly heated and heat treated within a few seconds after welding. There is a problem that the construction method is very complicated.

Another prior art is Japanese Patent Application Laid-open No. Hei 8-57502, which relates to a method of inserting and welding low carbon steel having excellent weldability between the joint portions of a high carbon steel sheet. This technique is more than twice the number of welding processes compared to other welding methods, and the problem of having to prepare a leader strip every time is not suitable for mass production.

Another prior art is Japanese Patent Application Laid-open No. Hei 8-215872, which relates to a method of heat treatment such that a laser weld is cooled while passing through a mixed region of ferrite and pearlite. This technique relates to laser welding, which is difficult to transform into a region in which ferrite and perlite are mixed because it is rapidly heated and quenched compared to arc welding. In particular, there is a problem that hardening phenomenon occurs remarkably when welding for high carbon steel.

Another prior art is Japanese Patent Laid-Open No. 2000-317642, which relates to a method of heat treatment of a rolled material after completion of laser welding on a joint. However, since this technique also applies laser welding, there is a problem in that the weld is quenched and the transformation is completed to the martensite structure immediately before the heat treatment is performed to generate microcracks. Therefore, this technology is difficult to apply in production lines requiring high quality such as PCM.

Another prior art is Japanese Patent Application Laid-Open No. 2001-353587, which uses a filler wire at different joints of high carbon steel and low carbon steel, does not perform heat treatment, and irradiates a laser beam on the low carbon steel side. The present invention relates to a method of preventing cracks in welds. However, this technique has a problem that it is not possible to remove the hardened structure generated in the weld heat affected zone on the high-carbon steel side that does not melt.

Another prior art is Japanese Patent Laid-Open No. 2000-317642, which relates to flash butt welding and relates to a method of performing heat treatment on a weld. Although the welding method is different, similar techniques to the above-mentioned heat treatment to the welded part include Japanese Patent Laid-Open Publication Nos. Hei 5-132719, No. 2000-317642 and No. 2004-76159, all of which have a carbon content of 0.5% or more. There is a problem that it is difficult to stably secure the quality of the weld portion of the high carbon steel included.

As mentioned above, there are many joining technologies of steel sheet for continuous rolling, but most of them are high carbon steels with relatively low carbon content or are applicable to production lines that do not require much welding quality.

Therefore, there is a demand for a technique for securing quality characteristics of a welded joint that can be applied to high carbon steel having a carbon content of 0.5% or more and suitable for continuous rolling of such high carbon steel sheet.

Therefore, the present invention is to solve such a conventional problem, the object of the present invention is to reduce the hardened structure of the high-carbon steel laser welding portion to ensure the quality of the weld stably can significantly improve the productivity for continuous rolling The present invention provides a welding method of high carbon steel by laser welding.

In order to achieve the above object, the present invention, by weight% C: 0.5% or more, Si: 0.1-0.5%, Mn: 0.3-0.6%, P: 0.05% or less, S: 0.05% or less, Cu: 0.5% Or less, Ni: 3% or less, Cr: 0.05 to 0.5%, Al: 0.05% or less, and the step of mutually facing the high carbon steel rolled material made of other unavoidable impurities and the remaining Fe; Welding with the laser welder using a welding material containing C ≦ 0.1% and Cr ≦ 1.22% in Fe or Ni main components and other inevitable impurities in the welding step of the butt portion of the rolled material; And continuously rolling the rolled material; It provides a welding method of high carbon steel for continuous rolling comprising a.

In the present invention, the welding material is preferably used in the form of wire, powder or thin film.

In addition, in the welding method of a high carbon steel sheet according to an embodiment of the present invention, it is preferable to preheat the opposed portion of the rolled material in the range of 600 ° C. to 899 ° C. before the welding step.

In addition, in the welding method of a high carbon steel sheet according to an embodiment of the present invention, it is preferable to heat the welded part in a range of 700 to 1135 ° C. after the welding step, and to perform post-heat treatment.

In the present invention, it is preferable that the preheating treatment and the postheating treatment proceed simultaneously.

And the welding method of high carbon steel according to an embodiment of the present invention is preferably made in any one of a continuous rolling line of PCM (Pickling & Tandem Cold Rolling Mill), APL (Annealing & Pickling Line) or POL (Pickling & Oiling Line) Do.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

In the present invention, the high carbon steel is% by weight (hereinafter,% in the present invention means% by weight unless otherwise specified). C: 0.5% or more, Si: 0.1-0.5%, Mn: 0.3-0.6%, P: It is basically a high-carbon steel containing 0.05% or less, S: 0.05% or less, Cu: 0.5% or less, Ni: 3% or less, Cr: 0.05 to 0.5%, Al: 0.05% or less, and other unavoidable impurities and the remaining Fe. In terms of carbon content, high carbon steels containing 0.5% or more of C, regardless of whether elements such as Mo, V, Ti, W, B, Nb, and Sb are added in order to impart special functions. All should be interpreted as being included in the high carbon steel means in the present invention.

In addition, in the present invention, the "welding part" refers to a joint part formed by welding a subsequent end of the preceding rolled sheet material and the subsequent rolled sheet material with a laser welding machine for continuous rolling, and the molten metal part melted and then solidified by a laser. It is not meant to include a heat affected zone (HAZ) that is heat affected by the heat source of the laser.

First, in order to achieve the object of the present invention, the cause of the hardening phenomenon in the welded portion identified through the histological examination and the Ericsson test of the high carbon steel laser welded portion is examined.

According to the results confirmed by the inventors of the present invention, the hardening phenomenon of the weld portion occurred in the weld metal and the weld heat affected zone, respectively, and it was confirmed that martensite and carbide act as a major cause.

Such embrittlement structure can be controlled to a certain level by chemical composition and heat treatment of the weld. To this end, by using a welding material having a carbon content lower than that of the rolled material, the carbon content of the weld metal part may be reduced, and the hardness of the whole weld part may be reduced by heat treatment.

In addition, the quality characteristics of the high carbon steel welded portion are affected by the hardness of the welded portion as described above, but also by the hardness distribution of the entire welded portion.

Therefore, the present invention provides a technique for heat-treating the welded portion, while reducing the hardness of the welded portion, thereby relieving the hardness distribution of the entire welded portion, thereby making it possible to stably ensure the quality of the laser welded portion even in high carbon steel having a carbon content of 0.85% or more.

In addition, in a continuous line such as PCM, if the welding and heat treatment are performed separately, the welding construction time increases, and thus the overall production speed may be reduced. And as the carbon content of the rolled material increases, the heat treatment time also increases.

Therefore, in the present invention, in order to solve this problem, as shown in FIG. 1, the heat treatment apparatus is integrally formed with the welder, so that the welding apparatus of the rolled material is configured to be heat treated simultaneously with the welding.

Referring to Figure 1, the welding apparatus according to the present invention, the welding apparatus according to the present invention is largely composed of a welder 10 and the heat treatment machine 20, these devices are all formed integrally. In Fig. 1, the welding apparatus according to the present invention is schematically illustrated, and thus the configuration in which these apparatuses are integrally shown is not shown. Thus, the technique for constructing these apparatuses integrally can be implemented by conventional installation techniques. Detailed description of the technical configuration for integrally configuring the device will be omitted.

The welder 10 according to the present invention comprises a laser generator 12 for oscillating the laser 14 and a filler feeder 16 for supplying a welding material. In addition, the heat treatment machine 20 can be applied to any means that can be quickly heated as a heat source for heating the moving rolling material, it is preferable to use a high frequency induction coil. The heat treatment unit 20 is composed of a preheater 22 for heating the rolled material 40 before being welded and installed before the weld, and a post-heater 24 for heating the rolled material 50 after welding.

When welding the moving rolling material using the welding device according to the invention mutually first to the front end of the following rolling material 40 and the rear end of the preceding rolling material 50 and then welded in the state of heating with the preheater 22 ( The welds 60 welded to each other and joined to each other are post-heated by the post-heater 24.

In FIG. 1, reference numeral 30 denotes a guide roll.

When welding the rolling material to move using the welding device according to the present invention, the rolling material also moves, but also the welding device moves with it. At this time, the moving direction of the rolled material and the moving direction of the welding apparatus may be the same or vice versa. When the moving direction of the rolled material and the moving direction of the welding device are the same, it is preferable that the moving speed of the rolling material moves faster than or equal to the moving speed of the welding device.

FIG. 2 schematically illustrates a heat cycle history and a tissue state according to a mobile welding device and a welded portion of a rolled material when welding using the same in an embodiment of the present invention.

The present invention provides a method of controlling the chemical composition of the welded portion and a heat treatment method of the welded portion as a method for controlling the hardening phenomenon of the welded portion for continuous rolling of high carbon steel.

Hereinafter, these methods will be described in turn.

First, the method of controlling the chemical composition of a welded part is demonstrated.

This method is to control the welding material which forms most of the molten metal of the welding part. The welding material is supplied from the filler feeder 16 to the welding part 60, and both carbon steel and Ni alloy, which is a high toughness material, are basically applicable. Carbon steel series is preferable because it can ensure the welding quality more stably.

The welding material made of stainless steel and Ni alloy is intermittently embrittled because the wettability with the high carbon steel, which is the base material, does not fully dilute due to melting point difference when the optimum welding parameter is not derived. Occurs.

In the present invention, the composition of the weld metal portion is preferably controlled so that the carbon content is 0.4% or less. This is because in the case of laser welding, since a very small amount of welding material is melted and filled in the welding portion, the dilution ratio of the base material is much higher than that of ordinary arc welding.

For example, in the case of a high carbon steel rolled material having a carbon content in the rolled material of 0.85% or more, the carbon content of the welded material is about 0.1 wt% to set the dilution rate to 30% at the maximum and maintain the carbon content of the weld metal at 0.4% or less. It should be

In addition, since chromium (Cr) reacts with carbon in the rolled material to form chromium carbide in the vicinity of the weld metal and the weld heat affected zone, the content of chromium (Cr) is preferably controlled to 1.22% or less.

Therefore, in the present invention, the welding material supplied from the welding machine is preferably used a welding material containing C ≤ 0.1%, Cr ≤ 1.22% in the main component of Fe or Ni, and other unavoidable impurities. Thin film type welding materials can also be used.

Next, the heat treatment method of the welded portion will be described.

In the present invention, the weld heat treatment includes a preheat treatment performed before welding to prevent cracking of the weld joint and a post heat treatment performed to alleviate the hardening phenomenon of the weld joint after welding.

If laser welding is performed on high carbon steel with a carbon content of 0.85% and only post-heat treatment is performed on the welded joint, the weld after welding is rapidly cooled before post-heat treatment, and cracks are generated at the weld. .

Therefore, in order to alleviate the rapid cooling heat cycle caused by laser welding for high carbon steel having a high carbon content, it is preferable to perform preheating treatment before welding.

Such a preheating temperature is preferably preheated to a higher temperature than the martensite transformation temperature (Ms) when a mobile heat treatment device is applied as in the embodiment of the present invention, since a sufficient preheating effect cannot be obtained.

Therefore, according to an embodiment of the present invention, when preheating the welded portion of high carbon steel, the heat treatment temperature is preferably performed in the range of 600 ° C to 899 ° C. When preheating is performed at the preheating temperature of 600 ℃ or less, sufficient time for preheating cannot be obtained for the moving rolled material, and sufficient quality characteristics cannot be secured at the welded part. When the preheating temperature is higher than 899 ℃, excessive Deformation occurs in the weld due to heat input, so a safe weld cannot be secured.

And the post-heat treatment of the weld in the present invention is largely carried out in two concepts.

The first concept is a tempering treatment method that maintains a relatively long time under Ac1 to change the martensite structure of the weld to tempered martensite to secure ductility.

The second concept is to actively control cooling heat cycles during laser welding to transform into ferrite and pearlite tissues.

Here, the tempering treatment method is advantageous in that sufficient ductility can be secured according to the heat treatment for a relatively long time. However, in a coil production line having a high production speed, productivity may be reduced if it takes a long time for the post-heat treatment. Therefore, in the laser welding system using a mobile heat source, it is more preferable to relax the cooling cycle after the latter laser welding.

It is preferable to heat the post-heat treatment temperature of a weld part in the range of 700-1135 degreeC, More preferably, it is the range of 950-1135 degreeC. In addition, it is preferable that the post-heat treatment of the weld part is naturally cooled without a holding time after heating.

If the post-heating temperature of the weld is less than 700 ℃, the amount of heat input is insufficient, and martensite structure is formed on the structure of the welded part after cooling, and there is no hardness reduction effect. If the post-heating temperature is 1135 ° C or higher, the heat input is excessive. The structure of coarsened, and part of the martensite structure, which is a hardened structure, is regenerated upon cooling, thereby deteriorating the physical properties of the weld.

In the rolling material bonding method for continuous rolling of high carbon steel according to the present invention described above, the coiled rolling material is connected to a continuous rolling line such as PCM (Pickling & Tandem Cold Rolling Mill) or APL (Annealing & Pickling Line) or POL (Pickling & Oiling Line). It is desirable to apply.

Hereinafter, a preferred embodiment according to the present invention will be described.

EXAMPLE

In this embodiment, a co-carbon steel hot rolled material having a composition as shown in Table 1 was used, and the thickness of the rolled material was 2.0 mm. These rolls were welded to each other using a CO2 laser welder with a maximum output of 12KW.

division C Si Mn P S S-Al Ni Cr N SK85 0.8572 0.193 0.410 0.013 0.003 0.010 0.01 0.16 0.0049 S50C 0.5043 0.192 0.704 0.020 0.003 0.016 0.01 0.09 0.0026

The welding material used in this embodiment was a filler of wire state (Φ 0.9 mm), and its chemical composition was as shown in Table 2 below. Nickel alloy-based ERNiCrMo03, ERNi, and the like were used.

Category (AWS) Mark C Si Mn P S Al Ti Ni Cr Mo Etc ER70S-G F1 0.07 0.50 1.05 0.012 0.016 - - - - - - ER80S-G F2 0.06 0.50 0.99 0.007 0.005 - - - 1.22 0.54 - ER308 F2 0.05 0.45 2.02 0.026 0.003 - - 9.76 19.86 - - ERNiCr Mo-3 F4 0.02 0.22 0.20 0.004 0.002 0.22 0.21 61.80 21.17 8.60 Nb + Ta 3.84 ERNi F5 0.025 0.70 0.50 0.015 0.007 0.24 2.6 97.3 - - Cu 0.12

When welding the rolled material with the laser welding machine, the laser welding condition was a condition that no welding defects such as the underfill of the weld were generated. The laser output was 8.4kW and the welding speed was 4.5m / min. The space | interval was 0.15 mm.

The heat treatment for the weld was used a high frequency induction furnace, and the heat treatment while moving along the welding line to a size of 20w × 200lmm while changing the output.

The heat treatment conditions were a heating rate of about 100 ℃ / s, and the heat treatment while changing the temperature of the preheating treatment and the post-heat treatment, and then naturally cooled (air cooling) after the heat treatment.

The temperature of the weld heated by the high frequency induction furnace was spot welded by the R-type thermocouple on the melting boundary and the temperature history of the weld was measured. The maximum temperature was obtained from the temperature history curve.

The welded parts welded under the above conditions were mailed according to the PCM line's plate standard (Ericsson height of 4mm or more), and the quality characteristics were evaluated using an Ericsson tester (Erichsen). The evaluation method of the quality characteristics of the weld was evaluated by measuring the plastically deformed height up to the time of crack formation at the weld.

First, the quality evaluation results according to the welding material and heat treatment conditions for the SK85 steel having a carbon content of 0.85% are shown in Table 2 below.

Welding material Heat treatment method Preheating temperature (℃) Post heat treatment temperature (℃) Erichsen height (mm) Remarks radish radish radish radish 0 Failed (breaking, pore, underfill occurs immediately after welding) ER70S-G radish radish radish 0 Failure (breaks immediately after welding) Preheat 723 radish 1.75 fail After heat radish 960 2.63 fail After heat radish 1005 2.83 fail Preheat + After Heat 899 radish 1.57 fail Preheat + After Heat 610 795 3.01 fail Preheat + After Heat 610 1021 4.13 pass Preheat + After Heat 723 1135 4.17 pass Preheat + After Heat 899 1090 4.25 pass Preheat + After Heat 480 940 3.67 fail Preheat + After Heat 899 843 3.53 fail Preheat + After Heat 723 1005 4.43 pass ER80S-G Preheat + After Heat 723 1005 4.15 pass ER308 Preheat + After Heat 723 1005 3.48 fail ERNiCrMo-3 Preheat + After Heat 723 1005 3.47 fail ERNi Preheat + After Heat 723 1005 4.35 pass

As shown in Table 3, when no welding material was used or no heat treatment was performed on the welded portion of the SK85 steel, a weld crack was generated in the welded portion immediately after welding, and thus a weldable joint was not obtained.

In addition, even when only the preheating treatment or the post-heating treatment alone was performed, the welded part quality characteristics such that the plate could be obtained could not be secured.

On the other hand, when both the preheating treatment and the post-heating treatment are performed as in the present invention, it can be seen that the quality of the welded part is improved as compared with the other embodiments.

In addition, as shown in Table 3, when the preheating temperature is set to 600 to 899 ° C and the post-heating temperature is heated to the range of 950 to 1135 ° C, the stability exceeding the Ericsson height of 4.0 mm, the limit criterion of PCM continuous rolling plate, is stable. Welding quality characteristics are shown.

In the case of ER70S-G, ER80S-G, and ERNi, the welding materials exceeded the limit of Ericsson height of 4.0 mm, but ER308, containing 19.86% and 21.17% of chromium (Cr), respectively. In the case of ERNiCrMo-3, even if the same heat treatment technique was applied, satisfactory welding quality was not obtained.

This is because the chromium (Cr) component contained in the welding material and the carbon component of the rolled material react during the welding to form chromium-carbide at the grain boundaries to embrittle the grain boundaries of the weld portion.

Next, the evaluation results of welding materials and heat treatment conditions for S50C steel with 0.5% carbon content are shown in Table 4 below.

The example shown in Table 4 was carried out at the heat treatment temperature conditions that indicate the highest Ericsson value identified in Table 3, that is, preheating temperature 723 ℃ and post-heat treatment temperature 1005 ℃.

Welding material Heat treatment method Preheating temperature (℃) Post heat treatment temperature (℃) Erichsen height (mm) Remarks radish radish radish radish 0 Failure (Some cracks, pores and underfill occur after welding) ER70S-G radish radish radish 0.94 fail Preheat 723 (30) radish 1.97 fail After heat radish 899 (40) 4.18 Partial Pass Preheat + After Heat 723 (30) 1005 (40) 7.28 pass ERNiCrMo-3 Preheat + After Heat 723 (30) 1005 (40) 3.88 fail ERNi Preheat + After Heat 723 (30) 1005 (40) 5.78 pass

As can be seen from Table 4, the quality characteristics of the laser welded portion of S50C steel are generally superior to the SK85 steel laser welded irrespective of the industrial material and the heat treatment method.

In addition, it can be seen that the quality characteristics of the laser welded portion of S50C steel exceeded the Ericsson height of 4.0 mm, which is the limit criterion even when the heat treatment alone was performed.

This result seems to be due to the reduction of hardening phenomenon with the reduction of carbon content in the steel.

In addition, referring to Table 4, when the preheating treatment and the post-heat treatment are applied simultaneously, it can be seen that the quality characteristics of the welded part are further improved.

Although a preferred embodiment of the present invention has been described so far, the present invention is not specific to welding conditions in welding during continuous rolling of high carbon steel shown in the above embodiments, but continuous of high carbon steel to which the idea of the present invention is applied. It is possible to apply to various welding conditions required for rolling.

Therefore, the present invention can be modified and implemented in various ways within the scope of the claims and the detailed description of the invention, and this also belongs to the scope of the invention.

As described above, the welding method of continuous rolling of high carbon steel according to the present invention provides a welding condition for continuous rolling of high carbon steel, which has not been applied so far, such as PCM (Pickling & Tandem Cold Rolling Mill) or APL (Annealing & Pickling Line) or POL ( It has the technical effect to apply high carbon steel in pickling & oiling line) and continuous rolling line.

In addition, the present invention can obtain a healthy laser welded joint without welding defect when welding the rolled material in order to continuously roll high carbon steel of 0.5% or more, and as shown in FIG. Provide the technical effects that make the work possible.

In addition, the present invention has a technical effect of significantly improving the steel productivity in continuous rolling by shortening the welding construction time to a range of 25 seconds, which is a general steel level irrespective of the carbon content of the steel.

As described above, if the welding conditions of the present invention are applied, even in the case of high carbon steel, it can withstand the strong compressive load applied to the continuous rolling line and the tensile load applied between the stand, so that continuous rolling without breaking the weld part can be performed even during continuous rolling. To be.

Claims (6)

By weight% C: 0.5% or more, Si: 0.1-0.5%, Mn: 0.3-0.6%, P: 0.05% or less, S: 0.05% or less, Cu: 0.5% or less, Ni: 3% or less, Cr: 0.05 Facing each other with a high carbon steel rolled material containing 0.5% or less of Al: 0.05% and consisting of other unavoidable impurities and the remaining Fe; Welding with the laser welder using a welding material containing C ≦ 0.1% and Cr ≦ 1.22% in Fe or Ni main components and other inevitable impurities in the welding step of the butt portion of the rolled material; And Continuously rolling the rolled material; Welding method of high carbon steel for continuous rolling including In claim 1 The welding material is a welding method of a high carbon steel sheet for continuous rolling in the form of wire or powder or thin film. In claim 1 The welding method of a high carbon steel sheet for continuous rolling to preheat the butt portion of the rolled material in the range of 600 ℃ to 899 ℃ before the welding step. In claim 1 After the welding step is a welding method of a high carbon steel sheet for continuous rolling to heat the welding portion in the range of 700 to 1135 ℃ after heat treatment. In paragraph 3 After the welding step is a welding method of a high carbon steel sheet for continuous rolling to heat the welding portion in the range of 700 to 1135 ℃ after heat treatment. In claim 1 The continuous rolling is a welding method of high carbon steel sheet for continuous rolling made of any one of a continuous rolling line of PCM (Pickling & Tandem Cold Rolling Mill) or APL (Annealing & Pickling Line) or POL (Pickling & Oiling Line).

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