KR20020053272A - Laser welding method of ferritic stainless steels with filler wire - Google Patents

Abstract

PURPOSE: A laser welding method of ferritic stainless steel using a filler wire is provided to weld rolled ferritic stainless steel using the filler wire made of austenitic stainless steel containing Ni for continuous annealing and pickling operation. CONSTITUTION: In a laser welding method of ferritic stainless steel having a thickness of 3.5 to 4.5 mm containing 0.05 wt.% or less of C, 0.04 wt.% or less of N, 16 to 20 wt.% of Cr, 4 wt.% or less of Mo and a balance of Fe and inevitable impurities using a filler wire made of austenitic stainless material containing Ni, the laser welding method satisfies the following expressions under the working conditions of 0.5 to 2.0 mm of a filler wire diameter, 5 m/min of a filler wire feeding speed, 5 kW of a laser output, 0.5 to 3.0 m/min of a welding speed, and 0 to 1 mm of a gap:(1) WNi=BNix(1-D)+FNixD>0.02(2) D=SF/S=SF/(SB+SF)(3) SB=St-gxt, SF=πr2xf/s(4) St=7.3xs-0.74 where WNi, BNi and FNi respectively represent Ni contents of welding metal, base metal and a filler wire, S is the total area of the welding metal, SF is an area of the filler wire, St is an area except the female part, g is a gap between base metals, r is a radius of the filler wire, f is a feeding speed of the filler wire, and s is a welding speed.

Description

Laser welding method of ferritic stainless steels with filler wire}

The present invention relates to a laser welding method of ferritic stainless steel using a filler wire, and more particularly, continuous annealing and pickling of a ferritic stainless steel rolled using a filler wire made of austenitic stainless steel containing Ni. A method for welding for operation.

Since the laser welding is a deep penetration welding method using a beam of high energy density, the width of the welding bead is very narrow and the heat affected zone is small compared with the conventional thermally conductive arc welding, so that deterioration of the material due to the thermal history is suppressed. Moreover, the very small area concentrates the heat, so the welding speed can be set high. In order to improve productivity by utilizing such characteristics, the application of laser is increasing in welding between coils for continuous annealing and pickling operation after rolling in steel production process.

On the other hand, the weld metal of ferritic stainless steel is a structure in which the grains of coarse grains of ferrite single phase or martensite phase are precipitated at the grain boundary, and thus the toughness of the ferrous stainless steel is greatly reduced. In general, in the case of welding ferritic stainless steel for processing purposes, preheating before welding and postheating after welding are generally performed to secure toughness, but it is practically impossible in a continuous process. For this reason, in the continuous process, filler wire is used to impart toughness required for operation to the weld metal through a change in the microstructure and chemical composition of the weld metal.

In order to improve the toughness of the weld metal of ferritic stainless steel through filler wire supply, austenitic stainless steel filler wire having a high Ni equivalent weight is used. In the case of 18% Cr ferritic stainless steel, when the Ni content of the weld metal is used to the Ni content of the weld metal to 2% or more, the toughness of the weld metal is rapidly improved to prevent plate breakage. .

However, the welding conditions as described above are values that vary depending on the conditions of the process. Therefore, in the prior art, when welding the ferritic stainless steel while supplying the filler wire, the welding conditions for securing the toughness of the weld part are determined by trial and error through actual welding test. Set. However, this method is time consuming and economical and requires a faster approach.

The present invention has been made to solve the problems of the prior art as described above, when welding the coil-coil welding for continuous operation of annealing and pickling in the production of ferritic stainless steel hot-rolled steel sheet, various welding It is an object of the present invention to provide a laser welding method that can easily and quickly set a welding variable that does not cause plate breakage by a simple relational expression, rather than a method of trial and error regarding a condition between a variable and a component of a weld metal. Doing

1a and b are schematic diagrams of laser welding beads for explaining the parameters used in the present invention, respectively.

Figure 2 is a graph showing the relationship between the welding speed and S _t of the parameters used in the present invention.

In order to achieve the above object, the present invention is based on the weight% C: 0.05% or less, N: 0.04% or less, Cr: 16-20%, Mo: 4% or less, the balance is Fe and inevitable impurities In the method of laser welding a ferritic stainless steel containing a thickness of 3.5 to 4.5 mm using a filler wire made of austenitic stainless steel containing Ni, the filler wire diameter is 0.5 to 2.0 mm and a filler. The following relations are satisfied under the working conditions of wire supply speed: 5 m / min, laser output: 5 kW, welding speed: 0.5 to 3.0 m / min, and gap: 0 to 1 mm.

W _Ni = B _Ni × (1-D) + F _Ni × D〉 0.02 (1)

D = S _F / S = S _F / (S _B + S _F ) (2)

S _B = S _t -g × t, S _F = πr ² × f / s (3)

S _t = 7.3 × s ^-0.74 (4)

Where W _Ni , B _Ni , and F _Ni represent the Ni content of the weld metal, the base metal and the filler wire, respectively, S is the total area of the weld metal, S _F is the area of the filler wire, S _t is the area excluding the female part, g Is the gap between the base materials, t is the thickness of the base material, r is the radius of the filler wire, f is the feed rate of the filler wire, and s is the welding speed.

In the above formula (2) represents the definition of D as shown in Figure 1 D is defined as the ratio of the area (S _F ) of the filler wire supplied to the total area (S) of the weld metal, S is S _F and It is the sum of the area S _B of the molten base material. And as in the formula (3), S _B is the same as excluding the area (gap g * thickness t) formed by the gap from the area S _t excluding the female part. S _F is determined by the cross-sectional area of the filler wire, the filler wire feed rate f, and the welding speed s as shown in (3).

From the above relation, the item that is not directly determined from the welding variable is St. In laser welding, St is determined by material thickness, physical properties such as thermal conductivity, and heat input. Therefore, assuming that the laser power is constant at 5 kW in ferritic stainless steel having the same physical properties and there is no interference effect by the filler wire, S _t is determined by the thickness of the material and the welding speed. It is generally known that the area of the weld metal in laser welding is inversely proportional to s ^b . Therefore, S _t can be expressed by Equation (4) under the heat input condition that is a complete penetration.

Where a is a constant determined by the material thickness. FIG. 2 is a graph of measuring the actual welding speed and S _t in the case of STS 430 having a thickness of 4.2 m, and a and b are 7.3 and 0.74, respectively.

EXAMPLE

STS 430 (Ni: 0.35%) with a thickness of 4.2mm was supplied with 309L (Ni: 13.5%) with a diameter of 0.9mm, and the mechanical properties of the weld metal were evaluated by repeated bending test after laser welding under various welding conditions. As a result, Table 1 shows that when the value of W _Ni calculated by the above formulas (1) to (4) is less than 0.02, the fracture occurred at one or two times, whereas W _Ni was larger than 0.02. It showed very good weld toughness more than 10 times. The latter case is sufficient to prevent plate breakage in the stainless steel production process.

s (m / min) f (m / min) g (mm) S _F S _t S _B D W _Ni (%) Iterations Remarks One 1.2 0.1 0.76 7.30 6.88 0.10 1.66 One Wire diameter: 0.9mm One 1.8 0.1 1.14 7.30 6.88 0.14 2.23 13 1.5 1.2 0.1 0.51 5.41 4.99 0.09 1.57 One 1.5 1.8 0.1 0.76 5.41 4.99 0.13 2.09 10 2 1.2 0.1 0.38 4.37 3.95 0.09 1.51 2 2 1.8 0.1 0.57 4.37 3.95 0.13 2.01 10 2.5 1.2 0.1 0.31 3.71 3.29 0.08 1.47 One 2.5 1.8 0.1 0.46 3.71 3.71 0.11 1.80 2

Through the above-described configuration, the present invention can easily derive welding conditions through simple measurement and calculation in setting welding conditions, thereby improving product quality by deriving more accurate welding conditions. It can also be used to improve productivity.

Claims (1)

C-0.05% or less by weight, N: 0.04% or less, Cr: 16-20%, Mo: 4% or less as a main component, and the remainder is 3.5-4.5 mm thick perike system containing Fe and unavoidable impurities In the method of laser welding stainless steel using a filler wire made of austenitic stainless steel containing Ni, Filler wire diameter: 0.5 to 2.0 mm, filler wire supply speed: 5 m / min, laser output: 5 kW, welding speed: 0.5 to 3.0 m / min, gap: 0 to 1 mm Laser welding method. W _Ni = B _Ni × (1-D) + F _Ni × D〉 0.02 (1) D = S _F / S = S _F / (S _B + S _F ) (2) S _B = S _t -g × t, S _F = πr ² × f / s (3) S _t = 7.3 × s ^-0.74 (4) Where W _Ni , B _Ni , and F _Ni represent the Ni content of the weld metal, the base metal and the filler wire, respectively, S is the total area of the weld metal, S _F is the area of the filler wire, S _t is the area excluding the female part, g Is the gap between the base materials, t is the thickness of the base material, r is the radius of the filler wire, f is the feed rate of the filler wire, and s is the welding speed.