KR102402940B1 - Welding method of high nitrogen steel - Google Patents

Abstract

The present invention relates to a welding method of high nitrogen steel. As the welding method of one-phase stainless steel containing equal to and more than 0.3 wt% of N, the welding method of the high-nitrogen steel of the present invention comprises equal to or more than 2 vol% of nitrogen gas respect to a total volume as protective gas. In addition, the welding method of the high nitrogen steel contains a remainder of inert gas. The present invention is to provide the welding method of the high-nitrogen steel, securing a high nitrogen content of a welded unit.

Description

Welding method of high nitrogen steel {WELDING METHOD OF HIGH NITROGEN STEEL}

The present invention relates to a welding method of high nitrogen steel. Specifically, the present invention relates to a welding method of high nitrogen steel for maintaining the strength of the weld.

In the case of conventional stainless steel, corrosion resistance of steel materials was improved by adding a large amount of alloying elements such as Cr to form a passivation film on the surface of the material. , and improved low-temperature toughness. However, in the case of austenitic stainless steel, despite its excellent corrosion resistance, strength, and formability, it contains a lot of relatively expensive elements such as Ni, so its cost is high, and the market volatility of raw material prices such as Ni has large disadvantages.

In order to solve this problem, many efforts have been made to replace Ni, and recently, by employing N, the development of high nitrogen steel having corrosion resistance and strength equivalent to or higher than that of existing stainless steel is being actively developed.

In the case of high nitrogen steel containing nitrogen, strength, corrosion resistance, and low temperature toughness are improved even when nitrogen is added in a small amount of less than 0.5%. It was also applied to hydrogen piping.

However, since nitrogen has a low solubility in steel, a large amount of nitrogen is released during the melting/resolidification process, and the nitrogen solid content in the re-solidification region is rapidly reduced, so there is a problem in that the strength and other properties of the base material are deteriorated.

Accordingly, there is a need to develop a high-nitrogen steel welding method that maintains the strength of the base material by securing a high nitrogen capacity of the welding portion by controlling the protective gas atmosphere in the welding portion.

An object of the present invention is to provide a high nitrogen steel welding method for securing a high nitrogen capacity of a welding part by controlling the composition of a protective gas.

A welding method according to an embodiment of the present invention is a welding method of one-phase stainless steel containing N: 0.3 wt% or more, and includes nitrogen gas in an amount of 2 vol% or more with respect to the total volume as a protective gas, and the remainder including inert gas use that

The one-phase stainless steel is made of only one phase of austenite.

The one-phase stainless steel is Cr: 21 to 23 wt%, Ni: 8 to 12 wt%, N: 0.3 to 0.4 wt%, C: 0.01 to 0.03 wt% Si: 0 to 0.5 wt%, and the balance Fe and unavoidable impurities.

The protective gas includes 2 to 10 vol% of nitrogen gas based on the total volume.

The inert gas included in the protective gas is Ar.

The welding method is tungsten inert-gas arc welding (TIG).

The tungsten inert gas welding method uses a welding rod, and the welding rod contains C: 0.01wt% or less.

The welding rod is C: 0.04 wt.% or less, Si: 0.30 to 0.90 wt.%, Cr: 22 to 25 wt%, Ni: 12 to 14 wt%, Mo: 2 to 3 wt%, Mn: 0.5 to 2.5 wt% %, and the balance contains Fe and unavoidable impurities.

According to the present invention, it is possible to provide a protective gas capable of securing a high nitrogen capacity of the welding portion.

According to the present invention, since the nitrogen content of the weld is not reduced, a welding method having excellent physical properties such as strength, toughness, and hydrogen embrittlement resistance can be provided.

The terms first, second and third etc. are used to describe, but are not limited to, various parts, components, regions, layers and/or sections. These terms are used only to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first part, component, region, layer or section described below may be referred to as a second part, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is for the purpose of referring to specific embodiments only, and is not intended to limit the present invention. As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite. As used herein, the meaning of "comprising" specifies a particular characteristic, region, integer, step, operation, element and/or component, and the presence or absence of another characteristic, region, integer, step, operation, element and/or component It does not exclude additions.

When a part is referred to as being “on” or “on” another part, it may be directly on or on the other part, or the other part may be involved in between. In contrast, when a part is referred to as being "directly above" another part, the other part is not interposed therebetween.

In addition, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

In an embodiment of the present invention, the meaning of further including the additional element means that the remaining iron (Fe) is included by replacing the additional amount of the additional element.

Although not defined otherwise, all terms including technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Commonly used terms defined in the dictionary are additionally interpreted as having a meaning consistent with the related technical literature and the presently disclosed content, and unless defined, are not interpreted in an ideal or very formal meaning.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily implement them. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

Hereinafter, each step will be described in detail.

High nitrogen steel is manufactured by preparing molten metal in a nitrogen atmosphere under high pressure or by adding nitrogen to the solid solution.

At this time, when solidification is delayed due to a low cooling rate or solidification is performed after re-melting for reasons such as welding, dissolved nitrogen is released and the content of dissolved nitrogen is reduced.

When the nitrogen content is reduced, the physical performance required for the material, such as strength, toughness, and hydrogen embrittlement resistance, is insufficient, and thus the performance degradation of the final product is unavoidable. In particular, when a remelting/solidification process such as welding is involved, it is an important task to secure a high nitrogen capacity in the part where the remelting/solidification is performed, such as a welding part.

In order to secure a high nitrogen capacity in the weld, various process conditions must be controlled during welding, and the temperature, welding time, and solidification speed of the weld, as well as the presence or absence of a protective gas, are important factors.

On the other hand, it is difficult to precisely control the temperature, time, and cooling rate of the welding part in the actual welding process, and at the same time, a large difference occurs depending on the type of the base material and welding material. It is easy to use and has excellent reproducibility, so it can be said that it is the most suitable variable for actual field application.

In the case of general stainless steel or high nitrogen steel, welding by tungsten inert-gas arc welding (TIG) is the most common, and various welding rod materials are available depending on the content of major elements such as Cr, Ni, and Mo of the base material being welded. will be used

A shielding gas is used during TIG welding. In this case, it is common to use an inert gas, especially Ar gas.

One embodiment of the present invention is to provide a welding method of one-phase stainless steel containing, in particular, N: 0.3wt% or more of high nitrogen steel. Specifically, it is intended to provide a welding method of the one-phase stainless steel consisting of only one phase of austenite.

The specific composition of the one-phase stainless steel is Cr: 21 to 23 wt%, Ni: 8 to 12 wt%, N: 0.3 to 0.4 wt%, C: 0.01 to 0.03 wt% Si: 0 to 0.5 wt%, and It may contain Fe and unavoidable impurities as a part.

As the welding method, a tungsten inert gas welding method (TIG, Tungsten Inert-Gas arc welding) may be used.

At this time, it is possible to include nitrogen gas in an amount of 2 vol% or more with respect to the total volume as a protective gas used in the TIG welding method, and the remainder including inert gas. Specifically, the protective gas may include 2 to 10 vol% or 4 to 10 vol% or 4 to 6 vol% of nitrogen gas based on the total volume. If the volume fraction of nitrogen gas in the protective gas is too low, there is a disadvantage in that a high nitrogen capacity in the welding part is not secured. On the other hand, if the volume fraction of nitrogen gas in the protective gas is too high, there is an inefficiency problem because the high nitrogen capacity does not increase any more compared to the amount of nitrogen gas.

In addition, the inert gas included in the protective gas may be Ar gas.

The tungsten inert gas welding method uses a welding rod, and the welding rod may contain C: 0.01wt% or less. Specifically, the welding electrode is C: 0.04 wt.% or less, Si: 0.30 to 0.90 wt.%, Cr: 22 to 25 wt%, Ni: 12 to 14 wt%, Mo: 2 to 3 wt%, Mn: 0.5 to 2.5 wt%, and the balance may include Fe and unavoidable impurities. By controlling the carbon content, it is possible to minimize the effect of the weld on the carbon in the electrode.

Various welding rods such as 308N, 309Mo, 309MoL, and 3017LN which are mainly used for welding austenitic stainless steel can be applied.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily implement them. However, the present invention may be embodied in various different forms, and is not limited to the embodiments described herein.

stainless steel and welding rods

In this experimental example, stainless steel is Cr: 21 to 23 wt%, Ni: 8 to 12 wt%, N: 0.3 to 0.4 wt%, C: 0.01 to 0.03 wt% Si: 0 to 0.5 wt%, and the balance Those containing Fe and unavoidable impurities were used.

In addition, the composition of the welding rod is C: 0.04 wt.% or less, Si: 0.30 to 0.90 wt.%, Cr: 22 to 25 wt%, Ni: 12 to 14 wt%, Mo: 2 to 3 wt%, Mn: 0.5 to 2.5 wt %, and a 309 MoL electrode containing Fe and unavoidable impurities as the balance was used.

welding process

The ingot was manufactured through a vacuum induction melting process, and then it was manufactured into a 13mm thick plate through forging and rolling processes. After that, a plate material with a thickness of 3 mm was finally manufactured through hot rolling and cold rolling, and used as a base material.

For the manufactured plate, the welding part was processed into a v shape for welding to facilitate joining with a welding rod. Considering the thickness of the welded plate, a welding experiment was conducted using a welding rod with a diameter of 2.5 mm.

The protective gas used in the experiment was a mixed gas in which Ar and nitrogen were mixed in advance, and the ratio of nitrogen in each mixed gas was varied from 1 to 10 vol% in volume ratio, respectively (Table 1).

Confirmation of nitrogen content

division Nitrogen ratio in mixed gas (vol.%) welding rod type Welding part nitrogen content (wt.%) HAZ part nitrogen content (wt.%) Comparative Example 1 0 309 MoL 0.08 0.16 Comparative Example 2 One 0.12 0.19 Invention Example 1 2 0.18 0.22 Invention example 2 3 0.17 0.28 Invention example 3 4 0.22 0.29 Invention Example 4 5 0.25 0.30 Invention Example 5 6 0.24 0.29 Invention example 6 7 0.26 0.29 Invention Example 7 8 0.26 0.28 invention example 8 9 0.25 0.30 Invention Example 9 10 0.25 0.31

As the nitrogen ratio of the mixed gas increased, the nitrogen content of the welding part and the HAZ part also showed a tendency to increase.

In the case of the nitrogen content of the welding part, it increases linearly according to the nitrogen ratio of the mixed gas, but when the nitrogen ratio in the mixed gas becomes 5 vol% or more, the tendency to be saturated at 0.25 wt% level was confirmed.

In the case of the HAZ part, it did not dissolve directly, but the nitrogen solid content decreased to less than 0.2% due to exposure to high temperature.

The present invention is not limited to the embodiments, but can be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains can use other specific forms without changing the technical spirit or essential features of the present invention. It will be appreciated that this may be practiced. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (8)

N: As a welding method of one-phase stainless steel containing 0.3 wt% to 0.4 wt%,
As the protective gas, nitrogen gas is used in an amount of 2 vol% or more with respect to the total volume, and the remaining inert gas is used,
The composition of the one-phase stainless steel is Cr: 21 to 23 wt%, Ni: 8 to 12 wt%, N: 0.3 to 0.4 wt%, C: 0.01 to 0.03 wt% Si: 0 to 0.5 wt%, and the balance A welding method comprising Fe and unavoidable impurities. According to claim 1,
The one-phase stainless steel will consist of only one phase of austenite, a welding method. delete According to claim 1,
The protective gas includes 4 to 10 vol% of nitrogen gas based on the total volume, welding method. According to claim 1,
The inert gas contained in the protective gas is Ar, the welding method. According to claim 1,
The welding method is a tungsten inert-gas arc welding (TIG, Tungsten inert-gas arc welding), a welding method. 7. The method of claim 6,
The tungsten inert gas welding method uses a welding rod,
The welding rod is C: The welding method comprising 0.01wt% or less. 8. The method of claim 7,
The welding electrode is C: 0.04 wt.% or less, Si: 0.30 to 0.90 wt.%, Cr: 22 to 25 wt%, Ni: 12 to 14 wt%, Mo: 2 to 3 wt%, Mn: 0.5 to 2.5 wt% % and, the balance containing Fe and unavoidable impurities, the welding method.