KR20150029462A

KR20150029462A - Method for welding high carbon steel using laser welding machine and welding apparatus using the same

Info

Publication number: KR20150029462A
Application number: KR20130108696A
Authority: KR
Inventors: 고재용; 임선규
Original assignee: 주식회사 포스코
Priority date: 2013-09-10
Filing date: 2013-09-10
Publication date: 2015-03-18

Abstract

The present invention relates to a method to weld high carbon steel using a laser welder capable of preventing pores and cracks from being generated in a welding part of high carbon steel. Moreover, the method to weld high carbon steel comprises: a preparing step of forming a welding part to be welded as high carbon steel is in contact with each other; and a welding step of welding the welding part in the welder output of 5.09 [kW] or more and less than 7.63 [kW], and at the welding speed of 1.52 [m/min] or more and less than 3.30 [m/min].

Description

TECHNICAL FIELD [0001] The present invention relates to a method of welding a high carbon steel using a laser welding machine and a welding apparatus using the same,

The present invention relates to a method for welding high carbon steel and a welding apparatus using the same, and more particularly, to an apparatus and a method for welding a high carbon steel by controlling the output of the welding machine and the welding speed to prolong the time for releasing carbon monoxide (CO) And a method of welding a high carbon steel using the laser welder.

Generally, the cold-rolled coils obtained from hot-rolled coils can be produced by pickling and tandem cold rolling mills, which are connected by pickling and continuous rolling, respectively. . In particular, the PCM process has been widely applied in recent years because it can greatly improve the productivity compared to the process of pickling and TCM.

An important point in such a continuous rolling field is a joining technique of a rolled plate material joining the rear end of a preceding rolled plate to a succeeding rolled plate material. Examples of techniques for joining the rolled plate material include a solid-phase joining method and a welding method .

Here, in the joining method by welding, the trailing edge of the preceding rolled plate and the trailing rolled plate are welded to each other at the inlet side of the continuous rolling line to form a welded portion, and then pass through the subsequent rolling line. In this case, if the quality of the welded portion is poor, it causes a serious problem that the welded portion breaks during the passage through the subsequent rolling line and the production is completely stopped. Therefore, it is important to secure the quality characteristics of hot-rolled and cold-rolled coil welds for continuous rolling. In particular, the PCM line requires a strict welding quality compared to conventional lines because the production line is longer and the number of looper holding coils is larger than the existing pickling line and TCM line.

Meanwhile, as a welding method applied to the continuous rolling line, there are flash butt welding in which short circuit and flashing are repeatedly generated, and laser welding using a high-density heat source.

Flash butt welding has a limited amount of welding re-selection due to its large heat input. As an example thereof, the joining strength is not ensured for an electric steel plate, a ferritic stainless steel, a high carbon steel, etc., and plate breakage may occur during cold rolling. Particularly, since high carbon steel has a high content of carbon (C), flash butt welding is regarded as a very difficult material. Further, even when the welding schedule and the welding conditions are set to be constant and the welding operation is repeated, it is pointed out that there is a problem in reproducibility such as showing a deviation in the quality characteristics of the individual welds.

It is known that laser welding has higher energy density and smaller amount of heat input than conventional flash butt welding. However, when continuous welding is performed by welding high carbon steel by laser welding, pores and pin pores of the weld metal are generated and cracks are generated in the weld metal and weld heat affected zone. Pore and fin pore are closely related to the carbon content in the material. It is known that the carbon in the molten metal reacts with oxygen in the atmosphere during the welding, and the gas which is not released to the outside as it forms carbon monoxide (CO) gas remains at the time of solidification and pores are generated.

Therefore, it is possible to apply to high carbon steel having a carbon content of 0.5% or more, and a technique for securing the quality characteristic of the welded joint to a degree suitable for continuous rolling of the high carbon steel sheet is required.

Korean Patent Publication No. 2000-0040974 (July 15, 2000)

SUMMARY OF THE INVENTION It is an object of the present invention to provide a welding method of a high carbon steel using a laser welder capable of preventing pores and cracks from occurring in welds of high carbon steel, and a welding apparatus using the same.

According to an aspect of the present invention, there is provided a method of welding a high carbon steel having a carbon content of 5% or more, comprising the steps of: preparing a welded portion of the high carbon steel to be welded to each other; And a welding step of welding the welded part with a welder output of 5.09 [㎾] or more to less than 7.63 [㎾] and a welding speed of 1.52 [m / min] to less than 3.30 [m / min] to provide.

The high carbon steel welding method may further include a preheating step of preheating the welded portion with a preheater before the welding step, wherein the output of the preheater may be 1.67 [㎾] or more and 6.66 [㎾] or less.

The high carbon steel welding method may further include a post heat step of post-heat treating the welded portion after the welding step, wherein the heat output of the high heat carbon steel may be 3.33 [㎾] or more and 6.66 [㎾] or less.

In addition, the welding method of the high carbon steel may include a preheating step of preheating the welded portion with the preheater before the welding step; Wherein the preheating treatment temperature is 600 to 899 [deg.] C, the post-heat treatment temperature is 700 [deg.] C to 1135 [deg.] C, and the post- Lt; 0 > C].

In addition, the welding step may weld the weld using a welding material containing 0.07% or more carbon.

Further, the speed at which the welding material is supplied to the welding machine may be 1.80 [m / min] or less.

According to another aspect of the present invention, there is provided an apparatus for welding high carbon steel having a carbon content of 5% or more, comprising: a welder for welding the welded portion to be welded to the high carbon steel; A pre-heater installed in front of the welder in a traveling direction of the welder and preheating the weld; A post-heater installed at a rear side of the welder in a traveling direction of the welder, for post-heating the weld; And a filler feeder connected to the welder and supplying a welding material to the welder, wherein the output of the welder is less than 7.63 [kW] from 5.09 [kW] and the welding speed of the welder is 1.52 [m / min] to less than 3.30 [m / min].

Here, the welding material may contain 0.07% or more of carbon.

The welding method of the high carbon steel using the laser welder according to the present invention and the effect of the welding apparatus using the method are described as follows.

First, there is an advantage that pores and cracks can be prevented from occurring in the welded portion of the high carbon steel.

Second, there is an advantage of not only improving the productivity by shortening the working time but also preventing the safety accident of the worker.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a typical PCM (Pickling & Tandem cold rolling mill) process.
2 is a schematic view of a welding machine according to an embodiment of the present invention;
Fig. 3 (a) is a view showing a scale layer of a general steel, Fig. 3 (b) is a view showing a scale layer of high carbon steel
4 is a view showing a state where pores are formed in a welded portion.
Fig. 5 (a) is a photograph of a welded structure, and Fig. 5 (b) is a photograph showing a state of a welded portion after cold rolling.
6 is a flowchart of a welding method of high carbon steel using a laser welding machine according to an embodiment of the present invention.

Referring to FIG. 1, the pickling and tandem cold rolling mill (PCM) is a process of pickling and side trimming using ordinary carbon steel, electrical steel sheet and STS as a material, through FH (full hard), CR EG (Electric Galvanize), NO (Non-oriented) and STS (Stainless Steel). Of these, high carbon steel FH products are mainly sold to customers in Southeast Asia, Central and South America, and Japan, and demand for high carbon steel FH ash is steadily increasing. In order to cope with the increasing demand, it is necessary to supply the low-cost and high-efficiency steel process technology development using the tandem mill in the interrupted multi-process production method through the existing reverse mill.

In addition, high carbon steel is a high-margin product with a higher sales price than general FH. In order to improve the profitability of 2PCM and differentiate it as a specialized product, it is necessary to increase the share of high-grade steel such as high carbon steel.

In spite of the demand for continuous expansion of supply by customers, however, there is a difficulty in expanding supply due to the problem of manufacturing technology. In other words, the PCM process is difficult to smoothly continue because of the uncertainty of welding and manufacturing technology of high carbon steel. In particular, there is a safety risk for workers by adding manual re-welding after automatic welding at the mouth. In addition, there is a problem of productivity decrease due to long working time due to passive flash welding, so it is necessary to develop technology for this problem. Major problems are as follows.

First, referring to FIG. 3, the scale layer of the general steel is 7.9 mu m, the scale layer of the high carbon steel is about 10.6 mu m, and the scale layer is thicker than the ordinary steel in the case of high carbon steel. Accordingly, there is a problem in that, when the laser welding is performed, the energy calorie flowing into the base material from the surface layer is absorbed in the surface layer, and the base material is not uniformly penetrated. The welding quality is poor due to this metallurgical obstacle, and as a result, the problem of plate breaking occurs in the mill. If a plate break occurs, the line is shut down for a long time, resulting in a lot of problems due to burdens of the worker and abnormal operation.

Second, as mentioned above, when the steel is rolled in a mill without manual welding, a problem of plate fracture occurs. Manual welding is performed to prevent plate breakage, which causes additional problems such as gap open. There is a problem of lowering of the error rate due to the occurrence of scrap during the mill gap opening and lowering of the workability of increasing the quality defect occurrence rate. Normally, when the gap is opened, the scrap rate is 1 ton / s, and the rate of failure is reduced. In addition, there is a problem in that when a gap open (Gap Open) is transmitted, the risk of occurrence of quality defects such as off gauge and shape defect due to abnormal operation is increased.

Third, when manual welding is performed, the productivity of the steel is lowered due to an excessive time required for the cold rolling work. After automatic welding, when the welding part breaks through the Erickson test, it is judged that it can not be threaded. In this case, manual override welding is performed. If the sample is sampled after laser welding and the Ericsson test is performed and manual welding is performed, the production may be delayed for 10 minutes to 30 minutes or less.

In the existing work methods, the welding was tried by increasing the power of the preheater and the post heat to increase the weldability. In addition, we used the method to increase the output of the welder as much as possible and to work by lowering the welding speed. The reason for this is that when the output of the welder is raised, it is considered to have an effect of suppressing the bubble formation by the inclusions, and it is judged that the weldability can be secured by increasing the heat quantity due to lowering of the welding speed.

However, in the present technology development, the welding parameters were changed by reversing the existing welding theory. In other words, to minimize the dissolved and scattered fume gas, welder output and welding speed were lowered, and preheater and postheater output were lowered. The welding operation conditions were changed to reduce the amount of heat input. In addition, the planishing pressure was lowered to change the working conditions so that no bubbles were generated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a laser welding machine according to the present invention and a method of welding high carbon steel using such a laser welding machine will be described with reference to the accompanying drawings.

Referring to FIG. 2, a laser welder according to an embodiment of the present invention will be described. The laser welder according to the present embodiment includes a welding machine 100 and a heat treatment machine 200.

The welding machine 100 is for joining the preceding material 10 and the succeeding material 20 by welding the trailing end of the preceding material 10 and the leading end of the trailing material 20 in the width direction and comprises a laser oscillator (120) and a filler feeder (160) for supplying a welding material. At this time, the welding material is supplied from the filler feeder 160 to the welding portion 30, and basically both carbon steel and Ni alloy which is a tough material are applicable, but carbon steel series is preferable because it can secure the welding quality more stably.

The heat treatment apparatus 200 is a heat source for heating the rolled material and includes a preheater 220 and a welder 100 which are installed in front of the welder 100 in the traveling direction of the welder 100 and heat the rolled material before welding, (240) installed at the rear of the welding machine (100) in the traveling direction of the welding machine and heating the rolled material after welding. That is, when the preceding material 10 and the following material 20 are welded by using the laser welding machine according to the present invention, the front end of the following material 20 and the rear end of the preceding material 10 are brought into contact with each other, The welded portion 30 is welded to the welder 100 and the welded portions 30 are welded to each other. At this time, when the rolled material is welded using the laser welder according to the present invention, the welder 100 moves, but it is also possible that the rolled material moves. At this time, the moving direction of the rolled material and the moving direction of the welder 100 may be the same or opposite.

Hereinafter, referring to FIG. 6, a method of welding high carbon steel using a laser welder according to an embodiment of the present invention will be described.

First, a step of forming a welded portion 30, which is a portion to be welded by the welding machine 100, is performed in such a manner that high carbon steel having a carbon content of 0.48% or more is stitched against each other (S10). At this time, since the high carbon steels are in contact with each other in the longitudinal direction, the welded portion 30 is formed in the width direction of the high carbon steel.

Next, the preheater 220 preheats the weld 30 (S20). At this time, the output of the preheater 220 is preferably 1.67 [㎾] or more and 6.66 [㎾] or less.

Next, a step of welding the welded portion 30 by the welder 100 is performed (S30). At this time, the welding machine output is preferably 5.09 [㎾] or more and less than 7.63 [㎾], and the welding speed is preferably 1.52 [m / min] or more and less than 3.30 [m / min]. Here, it is preferable that the welding material used for welding contains 0.07% or more of carbon, and the speed at which the welding material is supplied to the welding machine 100 is preferably 1.80 [m / min] or less.

Next, the post-heater 240 heats the weld 30 (S40). At this time, the output of the post-heater 240 is preferably 3.33 [㎾] or more and 6.66 [㎾] or less.

Meanwhile, in the present invention, the method for heat-treating the welded portion 30 includes a preheating treatment performed before welding to prevent cracking of the weld joint and a post-heat treatment performed to mitigate the hardening phenomenon of the welded joint after welding. Here, when the high carbon steel having a carbon content of 0.48% or more is subjected to laser welding and only the post-heat treatment is applied to the welded joint, the welded portion 30 after the welding is quenched before the post- And cracks are generated. Therefore, it is preferable to preheat the high carbon steel having a high carbon content in order to alleviate the quenching thermal cycle caused by the laser welding.

As described above, in the case of preheating the welded portion of the high carbon steel, the preheating treatment temperature is preferably in the range of 600 캜 to 899 캜. If the preheating treatment is performed at a temperature of 600 ° C or lower, sufficient time can not be secured for preheating the rolled material, and sufficient quality characteristics can not be ensured for the welded part. If the preheat temperature exceeds 899 ° C, The welded portion 30 is deformed and a secure welded portion 30 can not be secured.

When preheating the welded portion of the high carbon steel, the post-heat treatment temperature of the welded portion 30 is preferably in the range of 700 to 1135 ° C. This is because when the post-heat treatment temperature of the weld portion is 700 ° C or less, the amount of heat input is insufficient and the martensite structure is formed in the structure of the welded portion after cooling, so there is no effect of reducing the hardness. The structure of the welded part is coarsened and partly because the martensitic structure, which is a hardened structure, is regenerated again upon cooling, which deteriorates the physical properties of the welded part.

Hereinafter, an embodiment of a welding method of high carbon steel using the laser welder according to the present invention will be described.

In this embodiment, a high carbon steel having a carbon content of 0.5% or more was used, and the thickness of the rolled material was 2.1 [T]. These rolled materials were welded to each other under the conditions shown in [Table 1] using a laser welder with a maximum output of 12 KW.

division Setting value Welding speed (m / min) 2.12 Welding machine output (Kw) 6.36 Laser beam frequency (Khz) 50 Distance between welder beam and strip (mm) -1.0 Welder head pressure (bar) 10.10 Strip Inlet, Outlet Gap (mm) 0.14 Plating Roll Pressure (bar) 20 Preheater output (kW) 3.33 Post heat output (kW) 6.67

The welding conditions in Table 1 above were set to 6.35 [kW] and 2.12 [m / min] for the laser welder output. Tests under these conditions showed that the welding quality was good and that it was also good through the Erichsen Test. Therefore, it was judged that there would be no problems even if the work could be carried out normally without manually re-welding, and it was possible to obtain good quality by automatic welding without producing a gap open operation in the rolling mill. In other words, as a result of extending the time for releasing carbon monoxide (CO) gas in the welded part by lowering the output and the speed of the laser welder, holes and cracks were not generated in the welded part.

As a result of Erichsen test after changing the thickness of the rolled material to 1.9 [T] under the conditions shown in [Table 1] above, the welding was broken and the normal operation It was judged impossible. As a result of the analysis of welding part, the shape defect caused by excessive penetration occurred, and the pore in the weld part was excessive, resulting in welding failure. This is because the output of the laser welding machine is higher than that of the thin rolled material, and the shape of the welded part is distorted. Therefore, when the thickness of the rolled material is small, the output of the laser welder, the preheater, and the post heat is set to be lower than that of [Example 1] as shown in the following Table 2 for adjusting the heat input amount.

division Setting value Welding speed (m / min) 2.88 Welding machine output (kW) 5.73 Laser beam frequency (Khz) 50 Distance between welder beam and strip (mm) -1.5 Welder head pressure (bar) 5.05 Strip Inlet, Outlet Gap (mm) 0.12 Plating Roll Pressure (bar) 10.10 Preheater output (kW) 1.67 Post heat output (kW) 3.33

The welding conditions in Table 2 above were set to 5.73 [kW] and 2.88 [m / min] for the laser welder output. As a result of checking workability, the welded part condition was good as shown in Fig. 5 (a), and the welded part condition after cold rolling was good as shown in Fig. 5 (b). The results show that, in the case of high carbon steel having a carbon content of 5% or more, when the heat input is excessive due to the high output of the laser, it is necessary to minimize the metal fume gas which is dissolved and scattered, We concluded that the planishing roll pressure should be kept low.

In this embodiment, a high carbon steel having a carbon content of 0.5% or more was used, and the thickness of the rolled material was 2.1 [T]. These rolled welds were welded to each other while changing the welding parameters (welding machine output, welding speed, preheater output, post heat output, etc.) as shown in [Table 3] below using a laser welder with a maximum output of 12 kW.

Welding machine output (㎾) Welding speed (m / min ) Preheater output (㎾) Post Opening Output (㎾) Remarks 6.36 2.12 3.33 6.66 Very good 6.36 2.12 1.67 3.33 Very good 5.09 2.12 3.33 6.66 Good 5.72 2.12 6.66 6.66 Good 6.11 1.52 6.66 3.33 Good 7.63 3.03 3.33 6.66 Bad 8.27 3.03 6.66 9.99 Bad 8.90 6.06 3.33 6.66 Bad 8.90 7.58 3.33 6.66 Bad 8.90 8.33 6.66 9.99 Bad 10.18 8.33 6.66 9.99 Very bad 10.81 8.33 6.66 10.29 Very bad 11.45 8.33 9.99 13.32 Very bad 10.18 8.33 6.66 6.66 Very bad 10.18 8.33 9.99 13.32 Very bad

As can be seen from Table 3, when the welding machine output is less than 5.09 [㎾] and less than 7.63 [㎾], and the welding speed is more than 1.52 [m / min] and less than 3.30 [m / min] . In addition, stable welding quality is shown when the output of the preheater is 1.67 [㎾] or more and 6.66 [㎾] or less and the output of post heat is 3.33 [㎾] or more and 6.66 [㎾] or less.

As a result, the high carbon steel welding method using the laser welder according to the present embodiment adjusts the output and welding speed of the welder 100 as described above, thereby prolonging the time for releasing carbon monoxide (CO) from the welding portion 30 , It is possible to prevent pores and cracks from being generated in the welded portion (30).

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims and their equivalents. Of course, such modifications are within the scope of the claims.

10: preceding material 20:
30: welding part 100: welding machine
120: laser oscillator 140: laser
160: filler feeder 200: heat treatment machine
220: preheater 240: after opening

Claims

A method of welding high carbon steel having a carbon content of 5% or more,
A preparation step of forming a welded portion which is a portion to be welded to the high carbon steel against each other;
And a welding step of welding the welded part with a welder output of 5.09 [㎾] or more to less than 7.63 [㎾] and a welding speed of 1.52 [m / min] to less than 3.30 [m / min].

The method according to claim 1,
The welding method of the high carbon steel
And a preheating step of preheating the welded portion with a preheater before the welding step,
Wherein an output of the preheater is 1.67 [㎾] or more and 6.66 [㎾] or less.

The method according to claim 1,
The welding method of the high carbon steel
And a post-heating step of post-heat-treating the welded portion after the welding step,
Wherein the output of the post heat is not less than 3.33 [kW] and not more than 6.66 [kW].

The method according to claim 1,
The welding method of the high carbon steel
A preheating step of preheating the welded part with a preheater before the welding step;
And a post-heating step of post-heat-treating the welded portion after the welding step,
Wherein the preheating treatment temperature ranges from 600 [deg.] C to 899 [deg.] C, and the post-heat treatment temperature ranges from 700 [deg.] C to 1135 [deg.] C.

The method according to claim 1,
Wherein said welding step comprises welding said welded portion using a welding material containing 0.07% or more carbon.

The method of claim 5,
Wherein a speed at which the welding material is supplied to the welding machine is not more than 1.80 [m / min].

An apparatus for welding high carbon steel having a carbon content of 5% or more,
A welder for welding the welded portion of the high carbon steel to be welded to each other;
A preheater installed in front of the welder in a traveling direction of the welder, the preheater preheating the weld;
A post-heating furnace disposed behind the welding machine in a traveling direction of the welding machine, for post-heating the welding section;
And a filler feeder connected to the welder and supplying a welding material to the welder,
Wherein the welding machine has an output of 5.09 [㎾] or more and less than 7.63 [㎾], and a welding speed of the welder is less than 3.30 [m / min].

The method of claim 7,
Wherein the welding material contains 0.07% or more carbon.