KR101657838B1 - Non-painting and high-corrosion-resistant welded joint and the method of manufacturing the same - Google Patents

Abstract

In one aspect of the present invention, there is provided a method of manufacturing a semiconductor device, which comprises 0.02 to 0.14% carbon, 0.4 to 1.3% silicon, 3.8 to 15% manganese, 0.02% (S): not more than 0.007% (excluding 0%), chromium (Cr): 22 to 32%, nickel (Ni): not more than 10% (excluding 0%), the balance iron (Fe) and other unavoidable impurities To provide a high corrosion resistance weld joint.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-coated high-corrosion welded joint,

The present invention relates to a welded joint manufactured by arc welding and a method of manufacturing the same.

The high corrosion-resistant alloy-coated steel sheet has been developed for the purpose of using unpainted coatings, which do not require painting for corrosion after construction. However, when welding a high corrosion-resistant alloy-plated steel sheet, there is a loss of the plating portion in the weld portion, thereby causing a decrease in corrosion resistance.

In order to solve the problem of lowering the corrosion resistance, there has been a problem in the process of manufacturing the structure by proceeding the partial coating separately from the welded portion.

An object of the present invention is to provide a welded joint having enhanced corrosion resistance so that a separate coating is not required in a high corrosion resistant alloy-plated steel sheet.

In order to achieve the above object, one aspect of the present invention is a welded joint of a high corrosion-resistant alloy-plated steel sheet, comprising 0.02 to 0.14% of carbon (C), 0.4 to 1.3% of silicon (Si) (P): 0.02% (excluding 0%), sulfur (S): 0.007% or less (excluding 0%), chromium (Cr): 22 to 32%, nickel Ni): not more than 10% (excluding 0%), the balance iron (Fe) and other unavoidable impurities.

In one embodiment of the present invention, the ferrite fraction of the weld joint can be at least 55%.

In one embodiment of the present invention, the weld joint may have an average step difference of less than 30 占 퐉 after the weld joint is immersed in an aqueous solution of pH 0.75, 10% sodium chloride (NaCl) for 168 hours.

Another aspect of the present invention is to provide a high alloy steel plate coated with a high corrosion resistant alloy coated steel sheet with a heat input of 3.0 kJ / cm or less to provide 0.02 to 0.14% of carbon (C), 0.4 to 1.3% of silicon (Si) (Except for 0%), sulfur (S): 0.007% or less (excluding 0%), chromium (Cr): 22 to 32%, nickel (Ni) : 10% or less (excluding 0%), the balance iron (Fe) and other unavoidable impurities.

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS The various features and advantages and effects of the present invention will become more fully understood with reference to the following specific embodiments.

The welded joint of the present invention has the effect of preventing the occurrence of liquid embrittlement phenomenon in the plating portion in the welded portion without a separate coating process, thereby preventing corrosion resistance from being lowered.

1A to 1C are photographs of weld joints manufactured according to an embodiment of the present invention with different heat input amounts.
FIGS. 2A to 2C are optical microscope photographs of weld joints manufactured according to an embodiment of the present invention with different heat input amounts.

The high corrosion-resistant alloy-plated steel sheet has been developed for the purpose of using unpainted steel sheets that do not require any painting work for corrosion after construction of the structure. Specifically, hot-dip galvanized steel sheets are often used.

The hot-dip galvanized steel sheet is a relatively inexpensive and sacrificial corrosion protection, and can be manufactured by galvanizing and then continuous processing with a desired shape of steel pipe.

However, in the process of galvanizing the steel pipe by a series of processes after galvanizing in this way, the welding operation must be performed, and the welded portion may be present. Zinc stagnation may occur due to the heat generated by the heat during the welding, and the liquid zinc may penetrate into the welded portion and break into the grain boundary of the welded metal during the cooling process. Therefore, in order to solve the problem of lowering corrosion resistance of the welded portion, a welded joint portion is required which requires no separate partial coating for the welded portion.

The inventors of the present invention have completed the present invention by confirming that a welded joint having improved corrosion resistance can be obtained by increasing the ferrite fraction while reducing the nickel content in an expensive manner.

Hereinafter, the non-coated high corrosion resistant welded joint of the present invention and its manufacturing method will be described in detail.

The welded joint according to the present invention is composed of 0.02 to 0.14% of carbon (C), 0.4 to 1.3% of silicon (Si), 3.8 to 15% of manganese (Mn), 0.02% (Excluding 0%), sulfur (S): not more than 0.007% (excluding 0%), chromium (Cr): 22 to 32%, nickel (Ni): not more than 10% It may contain unavoidable impurities.

Hereinafter, the reason for restricting the components as described above will be described in detail.

Carbon (C): 0.02 to 0.14% by weight,

Carbon can improve the strength of weld joints. In order to exhibit such effects in the present invention, the carbon content may be 0.02 wt% or more. On the other hand, when the content of carbon is more than 0.14 wt%, low-temperature cracks tend to occur at welded joints during welding, and impact toughness of welded joints may be greatly deteriorated. Therefore, the carbon content may be limited to 0.02 to 0.14% by weight.

Silicon (Si): 0.4 to 1.3 wt%

Silicon is an element added to improve the corrosion resistance and strength of welded joints. In order to exhibit such an effect in the present invention, the silicon content may be 0.4 wt% or more. On the other hand, if the silicon content is more than 1.3 wt%, the toughness of the welded joint may be deteriorated due to formation of a coarse oxide in the weld joint. Therefore, the content of silicon may be limited to 0.4 to 1.3% by weight.

Manganese (Mn): 3.8-15.0 wt%

The manganese is an element to be added to improve the strength of the welded joint. In order to exhibit such an effect in the present invention, the content of manganese may be 3.8 wt% or more. On the other hand, when the content of manganese exceeds 15.0% by weight, the toughness of the welded joint may be deteriorated due to formation of coarse oxide in the welded joint. Therefore, the content of manganese may be limited to 3.8-15.0 wt%.

Chromium (Cr): 22.0 to 32.0 wt%

Chromium is a strong anti-oxidation element as a ferrite stabilizing element, and it can increase the degree of secondary oxidation corresponding to an external oxidation atmosphere. In order to secure the fraction of ferrite and the corrosion resistance, chromium can be limited to 22.0 ~ 32.0 wt%.

Nickel (Ni): not more than 10% by weight

Nickel is an element added to improve the corrosion resistance of the welded joint itself. In order to exhibit such an effect in the present invention, the nickel content may be 10 wt% or less. At this time, nickel should not be added at all, and it is necessary to add at least a minimum amount, but it can be added relatively little because it is an expensive element.

Phosphorus (P): not more than 0.02% by weight

If the content of phosphorus exceeds 0.02% by weight, there is a fear of causing brittleness and a problem that the impact toughness is rapidly lowered. Therefore, in the present invention, the content of phosphorus can be controlled to 0.02% by weight or less. At this time, phosphorus should not be present at all and it should add more than minimum amount.

Sulfur (S): 0.007% by weight or less

Sulfur can be managed as low as possible because it is an impurity element that promotes high temperature cracking during welding. In particular, when the content exceeds 0.007% by weight, a low melting point compound such as iron (FeS) can be formed to cause a high temperature crack. At this time, sulfur should not be present at all and it should add more than minimum amount.

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.

The ferrite fraction of the weld joint according to an embodiment of the present invention may be 55% or more. Therefore, the welded portion can be solidified into a ferrite single phase after cooling, and thereafter, it can form an unclear crystal due to the formation of austenite at the time of transformation, thereby preventing the penetration of zinc. Since the penetration of the liquid zinc is prevented, the corrosion resistance of the welded joint does not deteriorate even if there is no separate coating.

The welded joint according to an embodiment of the present invention may be 30 μm or less when the mean level difference of the surface is measured after immersing in a 10% sodium chloride (NaCl) aqueous solution having a pH of 0.75 and a temperature of 30 ° C for 168 hours. When the average step difference of the surface exceeds 30 탆, it can be said that the welding part is corroded and peeling phenomenon appears.

An embodiment of the present invention is a method of manufacturing a semiconductor device, comprising: 0.02 to 0.14% carbon; 0.4 to 1.3% silicon; 3.8 to 15% manganese; 0.02% Sulfur (S): not more than 0.007% (excluding 0%), chromium (Cr): 22 to 32%, nickel (Ni): not more than 10% As a method of manufacturing a welded joint, a method of adjusting the heat input to 3.0 kJ / cm or less can be provided. When the heat input exceeds 3.0 kJ / cm 2, the ferrite fraction of the weld joint may be less than 55%, which may weaken the corrosion resistance of the welded joint.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

< Example >

The hot-dip galvanized steel sheets were subjected to submerged arc welding at an input heat quantity of 2.2 kJ / cm to form weld joints having the compositions of Examples 1 to 3 and Comparative Examples 1 to 3 shown in Table 1 below.

Composition of weld joint (% by weight) Ferrite fraction (%) C Si Mn P S Cr Ni Example 1 0.033 0.42 4.14 0.02 0.002 31 7.1 68 Example 2 0.108 1.20 8.09 0.01 0.002 27 3.1 81 Example 3 0.051 1.24 12.4 0.01 0.002 24 2.1 83 Comparative Example 1 0.018 0.21 2.4 0.02 0.002 20.4 5.1 34 Comparative Example 2 0.128 0.51 15.3 0.01 0.002 21.1 1.0 18 Comparative Example 3 0.135 1.23 17.1 0.02 0.002 29 3.1 39

In Table 1, the weld joints of Examples 1 to 3 having the compositions proposed by the present invention were obtained by immersing in a 10% sodium chloride (NaCl) aqueous solution having a ferrite fraction of 55% or more and a pH of 0.75 at a temperature of 30 캜 for 168 hours When the mean level difference of the posterior surface was measured, it was confirmed to be 30 탆 or less, which indicates excellent corrosion resistance.

On the other hand, it was confirmed that the welded joint portions of Comparative Examples 1 to 3 having no composition proposed by the present invention had a ferrite fraction of less than 55% and a poor corrosion resistance.

Figs. 1A to 1C are photographs of welds produced by using welding materials having the same composition and having heat input amounts of 2.2 kJ / cm, 3.3 kJ / cm and 4.3 kJ / cm, respectively.

Referring to FIGS. 1A to 1C, it can be seen that no corrosion occurs when the heat input is 2.2 kJ / cm, which is 3.0 kJ / cm or less.

Figs. 2A to 2C are optical microscope photographs of welded joints produced by using welding materials having the same composition and having heat input amounts of 2.2 kJ / cm, 3.3 kJ / cm and 4.3 kJ / cm, respectively.

Referring to FIGS. 2A to 2C, it can be seen that, even if welding is performed using a welding material having the same composition, the ferrite fraction changes when the heat input amount is varied.

Claims (4)

(C): 0.02 to 0.14%, silicon (Si): 0.4 to 1.3%, manganese (Mn): 3.8 to 15%, phosphorus (P) 0.02% (excluding 0%), sulfur (S): not more than 0.007% (excluding 0%), chromium (Cr): 22 to 32%, nickel (Ni): not more than 10% ) And other unavoidable impurities.
The method according to claim 1,
Wherein the weld portion has a ferrite fraction of 55% or more.
The method according to claim 1,
Wherein the welded joint is an untreated high corrosion resistant welded joint having an average step difference of not more than 30 占 퐉 after the welded joint is immersed in an aqueous solution of 10% sodium chloride (NaCl) at a pH of 0.75 for 168 hours.
The ingot heat amount of 3.0 kJ / cm or less was supplied to the high corrosion resistant alloy-plated steel sheet,
(C): 0.02 to 0.14%, silicon (Si): 0.4 to 1.3%, manganese (Mn): 3.8 to 15%, phosphorus (P): 0.02% ): Not more than 0.007% (excluding 0%), chromium (Cr): 22 to 32%, nickel (Ni): not more than 10% (excluding 0%), Wherein said method comprises the steps of:

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