KR101784275B1

KR101784275B1 - Method for welding alloy steel and carbon steel

Info

Publication number: KR101784275B1
Application number: KR1020160015610A
Authority: KR
Inventors: 고진현; 신태우; 이안식; 한겨례; 박소영
Original assignee: 한국기술교육대학교 산학협력단
Priority date: 2016-02-11
Filing date: 2016-02-11
Publication date: 2017-10-11
Also published as: KR20170094625A

Abstract

According to the welding method of the disclosed alloy steel and carbon steel, the alloy steel and the carbon steel are performed by flux cored arc welding using a flux cored wire. Wherein said alloy steel comprises 0.06 to 0.15 weight percent carbon, 0.25 to 0.66 weight percent manganese, 0.02 to 0.03 weight percent phosphorus, 0.005 to 0.020 weight percent sulfur, 0.18 to 0.56 weight percent silicon, 0.8 to 1.1 weight percent molybdenum, 7.9 to 9.6 weight percent chromium, 0.3 to 0.6% by weight of nickel, 0.05 to 0.11% by weight of niobium, 0.16 to 0.27% by weight of vanadium, 0.025 to 0.08% by weight of nitrogen and excess iron, wherein said carbon steel contains 0.2 to 0.3% by weight of carbon, 1.30 wt.%, 0.03-0.04 wt.%, 0.03-0.04 wt.% Sulfur, 0.13-0.45 wt.% Silicon and extra iron.

Description

[0001] METHOD FOR WELDING ALLOY STEEL AND CARBON STEEL [0002]

The present invention relates to a welding method, and more particularly, to a welding method of an alloy steel and carbon steel.

As the demand for energy such as petroleum, natural gas and electricity continues to increase, the construction of petrochemical plants and power plants is increasing, and the development of high-performance pressure vessels for energy efficiency is actively underway. All of the pressure vessels used in petrochemical plants and power plant fields are very harsh to use environment such as high temperature and high pressure. In addition, the large size and high performance of the devices to which pressure vessels are applied can lead to enormous damages in the event of an accident, so that there is a growing demand for high functionality, durability and safety, and thus securing the reliability of the construction method is becoming an important issue.

At present, in the nuclear power plant, the main machine is mainly made of alloy steel, but for the technical and payment reasons, it is necessary to partially apply the dissimilar metal welding.

The most widely used arc welding is multi-layered welding, which requires repeated welding several times during the welding of the backing steel, because the depth of penetration is not deep. Therefore, the welding productivity is very low. However, There is a problem that the physical properties of the welded portion and the thermal deformation due to the welding heat are increased when the heat input amount is increased.

Flux cored arc welding (FCAW) is widely used because it has excellent low temperature impact toughness, high efficiency, productivity and reliability. However, the dissimilar metal welding is lacking in field applications and is used for some structures due to metallurgical defects. Among them, the use of improper filler causes defects in the welds, which cause large and small problems.

Accordingly, the technical problem of the present invention is to provide a method of welding an alloy steel and a carbon steel, which can improve the welding characteristics of different metals.

According to an embodiment of the present invention for achieving the object of the present invention, the alloy steel and the carbon steel are subjected to flux cored arc welding using a flux cored wire. Wherein said alloy steel comprises 0.06 to 0.15 weight percent carbon, 0.25 to 0.66 weight percent manganese, 0.02 to 0.03 weight percent phosphorus, 0.005 to 0.020 weight percent sulfur, 0.18 to 0.56 weight percent silicon, 0.8 to 1.1 weight percent molybdenum, 7.9 to 9.6 weight percent chromium, 0.3 to 0.6% by weight of nickel, 0.05 to 0.11% by weight of niobium, 0.16 to 0.27% by weight of vanadium, 0.025 to 0.08% by weight of nitrogen and excess iron, wherein said carbon steel contains 0.2 to 0.3% by weight of carbon, 1.30 wt.%, 0.03-0.04 wt.%, 0.03-0.04 wt.% Sulfur, 0.13-0.45 wt.% Silicon and extra iron.

In one embodiment, the flux cored wire comprises 0.08 to 0.13 weight percent carbon, 1.00 to 1.40 weight percent manganese, 0.01 to 0.03 weight percent phosphorus, 0.01 to 0.03 weight percent sulfur, 0.3 to 0.7 weight percent silicon, 0.85 weight percent molybdenum, And a flux core comprising 1.2 wt%, chromium 8.0 to 10.5 wt%, nickel 0.7 to 0.9 wt%, niobium 0.02 to 0.07 wt%, vanadium 0.15 to 0.25 wt%, nitrogen 0.02 to 0.07 wt%, and excess iron .

In one embodiment, the heat input of the flux cored arc welding is 10 to 40 kJ / cm.

In one embodiment, the shield gas of the flux cored arc welding includes a carbon dioxide gas or a mixed gas of a carbon dioxide gas and an inert gas.

In one embodiment, the weld obtained by the flux cored arc welding is subsequently heat treated at 700 ° C to 800 ° C.

In one embodiment, the microstructure of the weld of the weld obtained by flux cored arc welding comprises tempered martensite and lower bainite.

According to the embodiment of the present invention, the dissimilar alloys (carbon steel and alloy steel) can be welded, and the obtained welded material can have excellent physical properties.

1 is a perspective view showing a flux cored wire that can be used in a method of welding an alloy steel and carbon steel according to an embodiment of the present invention.
2 is a block diagram schematically illustrating a welding system that can be used in a welding method of alloy steel and carbon steel according to an embodiment of the present invention.
3 is a cross-sectional view showing the specimen and the welding method of Examples 1 to 3.
Fig. 4 is a graph showing the results of tensile tests according to the heat input amount in the welds of the weldments obtained in Examples 1 to 3. Fig.
Fig. 5 is a graph showing the results of an impact test according to the amount of heat input under the temperature change condition in the welds of the weldments obtained in Examples 1 to 3. Fig.
Fig. 6 is a graph showing hardness values measured in a horizontal direction at 2 mm directly under the surface in the welded portion of the welded product obtained in Examples 1 to 3. Fig.
7 is a graph showing vertical hardness values according to the heat input amount in the welds of the welds obtained in Examples 1 to 3.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. It is to be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but on the contrary, is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing. The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms.

The terms are used only for the purpose of distinguishing one component from another. The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise.

In the present application, the term "comprises" or "comprising ", etc. is intended to specify that there is a stated feature, figure, step, operation, component, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

According to one embodiment of the present invention, alloy steel and carbon steel are welded using flux cored arc welding.

The alloy steel may be at least one selected from the group consisting of carbon (C), manganese (Mn), phosphorus (P), sulfur (S), silicon (Si), molybdenum (Mo), chromium (Cr), nickel (Ni), niobium (V), nitrogen (N), and excess iron. For example, the alloy steel may include 0.06 to 0.15 wt% carbon, 0.25 to 0.66 wt% manganese, 0.02 to 0.03 wt% phosphorous, 0.005 to 0.020 wt% sulfur, 0.18 to 0.56 wt% silicon, 0.8 to 1.1 wt% molybdenum, (Including inevitable impurities) of 7.9 to 9.6 wt%, nickel 0.3 to 0.6 wt%, niobium 0.05 to 0.11 wt%, vanadium 0.16 to 0.27 wt%, nitrogen 0.025 to 0.08 wt%, and excess iron.

For example, the tensile strength of the alloy steel may be about 585 to 760 MPa. The alloy steel has excellent strength at high temperature.

The carbon steel includes carbon, manganese, phosphorus, sulfur, silicon and extra iron. For example, the carbon steel may comprise 0.2 to 0.3% by weight of carbon, 0.79 to 1.30% by weight of manganese, 0.03 to 0.04% by weight of phosphorus, 0.03 to 0.04% by weight of sulfur, 0.13 to 0.45% (Including inevitable impurities).

For example, the tensile strength of the carbon steel may be about 485 to 620 MPa. The carbon steel has high reliability at a low temperature and can have relatively high strength and notch toughness.

A welding wire may be used for the welding. For example, a flux cored wire may be used as the welding wire.

1 is a perspective view showing a flux cored wire that can be used in a method of welding an alloy steel and carbon steel according to an embodiment of the present invention. Referring to FIG. 1, the flux cored wire may be formed by filling a flux core 120 inside a shell 110 made of a steel material formed in a cylindrical shape. For example, the flux cores may include carbon, manganese, phosphorous, sulfur, silicon, molybdenum, chromium, nickel, niobium, vanadium, nitrogen and excess iron. More specifically, the flux cores may comprise at least one selected from the group consisting of 0.08 to 0.13 weight percent carbon, 1.00 to 1.40 weight percent manganese, 0.01 to 0.03 weight percent phosphorus, 0.01 to 0.03 weight percent sulfur, 0.3 to 0.7 weight percent silicon, 0.85 to 1.2 weight percent molybdenum, (Including inevitable impurities), 8.0 to 10.5% by weight of chromium, 0.7 to 0.9% by weight of nickel, 0.02 to 0.07% by weight of niobium, 0.15 to 0.25% by weight of vanadium, 0.02 to 0.07% by weight of nitrogen and extra iron.

The flux cored arc welding is provided with a shielding gas. For example, the shielding gas may include carbon dioxide gas, or a mixed gas of carbon dioxide gas and an inert gas (e.g., argon gas).

In one embodiment, the flux cored arc weld may have an inlet calorific value between 10 and 40 kJ / cm.

According to one embodiment of the present invention, after welding of the alloy steel and the carbon steel, a post-weld heat treatment may be performed.

In one embodiment, the subsequent heat treatment may proceed at about 700 ° C to 800 ° C.

After the subsequent heat treatment, the welded composite is cooled through a method such as cooled in furnace.

The welding of the carbon steel and the alloy steel may be performed as a system for conventional flux cored arc welding.

For example, the welding system shown in Fig. 2 can be used. Referring to FIG. 2, the welding system 10 includes a welding power unit 12, a welding wire feeder 14, a gas supply system 16, and a welding torch 18. The welding power unit 12 generally supplies power to the welding system 10 and is also coupled to the workpiece 22 using a lead cable 24 having a clamp 26 as well as a cable bundle 20, To the welding wire feeder (14). In the illustrated embodiment, the welding wire feeder 14 is used to supply a consumable tubular welding wire (i.e., a welding electrode) and to supply power to the welding torch 18 during operation of the welding system 10, Is coupled to the welding torch (18) through a cable bundle (28). In another embodiment, the welding power unit 12 may couple with and directly supply power to the welding torch 18. [

According to the embodiments of the present invention, it is possible to weld different kinds of alloys (carbon steel and alloy steel), and the obtained welded product can have excellent physical properties.

Hereinafter, the effects of the present invention will be described with reference to specific examples and experimental examples.

Example 1-3

As alloy steel, A516 Gr. 91, as carbon steel, A387 Gr. (Sample size: 300 (L) x 300 (W) x 16 (T)) as shown in FIG. 3, the groove angle between the two steels was 60 °, the root surface was 2 mm, Pass FCA (Flux Cored Arc) welding. The protective gas used was 100% CO ₂ , and the flux cored wire used E91T1-B9C.

In proceeding with the welding, as shown in the following Table 1, welding was carried out at a heat input of 15.0, 22.5, and 30.0 kJ / cm by changing the current value (A) And then cooled.

Table 1

In order to observe the texture of each specimen, the alloy steel and the welded part after precision polishing were subjected to hydrothermal treatment using a water solution (nitric acid + hydrochloric acid) and carbon steel 5% (ethanol + nitric acid) And the pass sections of the deposited metal were observed.

Mechanical properties of each specimen were analyzed by impact, tensile and hardness tests, and chemical characteristics were analyzed by corrosion test and chemical composition analysis. The impact test was carried out using a Charpy impact tester with a load of 30 kg-m after four specimens of KS B 0809 No. 4 were prepared. The tensile test was carried out using a 14 A test piece of KS B 0801 and a universal tensile tester Experiments were performed. The hardness test was carried out with a micro-Vickers hardness machine under a load of 10 kgf and near the surface 2 mm and the welds.

Tempered martensite (TM) is observed in the 1st layer structure at the welded part (boundary between alloy steel and carbon steel, welded part) at the heat input of 15.0 kJ / cm. As the heat input increases, And the fraction of Lower Bainite (LB) increased.

In the heat affected zone (HAZ) for the alloy steel A516, grain bound ferrite (GBF), Widmannstatten ferrite (WF), acicular ferrite (AF) ) Were observed. In this section, as shown in Table 2 below, as the heat input increased, the GBF fraction increased and the WF fraction decreased.

Table 2

Tempered martensite (TM) was observed in the structure at the heat input of 15.0 kJ / cm in the heat affected zone on the carbon steel (A387). As the heat input increased, the TM fraction decreased and the LB fraction increased .

4 is a graph showing a tensile test result according to an amount of heat input in a welded portion.

Referring to FIG. 4, it can be seen that as the heat input increases, the tensile strength decreases. As the heat input increases, it may be that the fraction of TM, which is a light organization in the weld, decreases and the fraction of LB increases.

5 is a graph showing an impact test result according to an amount of heat input under a temperature change condition in a welded portion.

Referring to FIG. 5, the impact energy of the weld portion was significantly reduced in the range of -25 ° C to -35 ° C. As a result of the analysis of the fracture surface, it was found that a dimple as a soft fracture occurred at -25 ° C or higher, C, it was confirmed that cleavage fracture, which is a brittle fracture, occurs.

6 is a graph showing the hardness value measured in the horizontal direction at 2 mm directly below the surface of the welded portion.

Referring to FIG. 6, the hardness of the weld metal is higher than that of the carbon steel (A387) and the alloy steel (A516), but is lower than the thermal influence zone (HAZ) of the carbon steel. In general, the lower the heat input, the higher the hardness in most sections, because the cooling rate slows down as the heat input increases. A softening zone, which is lower in hardness than the carbon steel base material, is observed in the narrow region passing from the weld metal to the carbon steel heat affected zone (HAZ). This is due to the fact that during the subsequent heat treatment, This is because HAZ softening occurs due to destabilization of microstructure due to heat input. The hardness in the heat affected zone of alloy steel decreases as the heat input increases, because the carbon diffusion from the alloy steel to the deposited metal increases as the heat input increases.

7 is a graph showing vertical hardness values at the welded portions according to the amount of heat input.

Referring to FIG. 7, the hardness of the first pass decreases as the heat input increases. As the path increases, the overall average hardness value decreases as the heat input increases. It can be confirmed that the hardness value between the pass sections is low for each inlet heat, which may be due to the reheated zone which is a systematically changed section due to post-weld reheating applied to each pass section in multi-layer welding.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims. It can be understood that it is possible.

The present invention can be used for welding different alloys.

Claims

In a welding method of an alloy steel and a carbon steel,
Wherein said alloy steel comprises 0.06 to 0.15 weight percent carbon, 0.25 to 0.66 weight percent manganese, 0.02 to 0.03 weight percent phosphorus, 0.005 to 0.020 weight percent sulfur, 0.18 to 0.56 weight percent silicon, 0.8 to 1.1 weight percent molybdenum, 7.9 to 9.6 weight percent chromium, 0.3 to 0.6% by weight of nickel, 0.05 to 0.11% by weight of niobium, 0.16 to 0.27% by weight of vanadium, 0.025 to 0.08% by weight of nitrogen and excess iron,
Wherein the carbon steel comprises 0.2 to 0.3% by weight of carbon, 0.79 to 1.30% by weight of manganese, 0.03 to 0.04% by weight of phosphorus, 0.03 to 0.04% by weight of sulfur, 0.13 to 0.45%
The welding is performed by flux cored arc welding using a flux cored wire,
Wherein the flux cored wire comprises 0.08 to 0.13 weight percent carbon, 1.00 to 1.40 weight percent manganese, 0.01 to 0.03 weight percent phosphorus, 0.01 to 0.03 weight percent sulfur, 0.3 to 0.7 weight percent silicon, 0.85 to 1.2 weight percent molybdenum, Characterized in that it comprises a flux core comprising 8.0 to 10.5% by weight of nickel, 0.7 to 0.9% by weight of nickel, 0.02 to 0.07% by weight of niobium, 0.15 to 0.25% by weight of vanadium, 0.02 to 0.07% And carbon steel welding method.

delete

The welding method according to claim 1, wherein the heat input amount of the flux cored arc welding is 10 to 40 kJ / cm.

The method according to claim 1, wherein the shield gas of the flux cored arc welding comprises carbon dioxide gas or a mixed gas of carbon dioxide gas and inert gas.

The method according to claim 1, wherein the welded material obtained by the flux cored arc welding is subjected to a subsequent heat treatment at 700 ° C to 800 ° C.

The method according to claim 1, wherein the microstructure of the welded portion of the weld obtained by the flux cored arc welding comprises tempered martensite and lower bainite.