Precipitation hardening stainless steel flux

Abstract

To provide a precipitation hardening stainless steel flux for solving a problem with poor aspect ratio of weld beads formed between two precipitation hardening stainless steel work-pieces.SOLUTION: A precipitation hardening stainless steel flux contains: silicon dioxide of 20 to 25%; molybdenum trioxide of 20 to 25%; chrome oxide of 20 to 25%; nickel trioxide of 15 to 20%; aluminum oxide of 4 to 8%; aluminum nitride of 4 to 8%; nickel oxide of 4 to 8%; and copper oxide of 4 to 6%.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a flux, and particularly to a flux for precipitation hardening stainless steel.

Background Art

[0002] Generally, iron-chromium-nickel stainless steel (Fe-Cr-Ni stainless steel) can form precipitation hardening (PH) stainless steel with excellent mechanical strength, wear resistance, and good atmospheric corrosion resistance when elements such as copper (Cu), aluminum (Al), titanium (Ti), niobium (Nb), and molybdenum (Mo) are separately added and further solution treated and aged. Precipitation hardening stainless steel is widely applied to golf club heads, gas turbine blades, valves for oil pipelines, and parts for nuclear power generation.

[0003] Tungsten inert gas welding (TIG welding) is a high-quality arc welding process and is often applied to welding operations of metal materials such as aluminum alloys, titanium alloys, stainless steels, and nickel-based alloys. Tungsten inert gas welding uses an inert gas (argon, helium, or an argon-helium mixed gas) for protection, generates an arc with a tungsten electrode as the welding heat source, melts a conventional welding rod at the contact point of two precipitation hardening stainless steel workpieces, and the melted conventional welding rod forms a molten pool at that point. After the molten pool cools and solidifies, a weld bead is formed to tightly bond the two precipitation hardening stainless steel workpieces. After welding, the two precipitation hardening stainless steel workpieces become a precipitation hardening stainless steel weldment, and the welding process is completed. However, due to the low energy density heat source characteristics of tungsten inert gas welding, the formed weld bead is wide and shallow. Therefore, when welding a thicker workpiece (for example, a workpiece with a thickness of 3 mm or more), there is a problem that the penetration depth is insufficient.

[0004] To solve the above problems, before welding, the operator can perform a conventional beveling process on the workpiece. As shown in FIG. 6, as a conventional beveling process, the side edge 92 of the precipitation hardening stainless steel workpiece 9 is milled with a milling cutter M to form a slope 91, and a slope 92' is similarly formed on the side edge 91' of another precipitation hardening stainless steel workpiece 9'. Subsequently, as shown in FIGS. 7 and 8, when welding, the operator makes the side edges 91, 91' of the two precipitation hardening stainless steel workpieces 9, 9' contact each other so that the slopes 92, 92' form an open structure with an angle. Furthermore, with a tungsten electrode E and a conventional welding rod S, multiple welding processes can be performed in this structure to form a weld bead 93. However, although the penetration depth of the weld bead 93 can be increased by the beveling process, there is a problem that the width of the weld bead 93 is too wide. In the process of welding, the welding heat source forms a heat-affected zone near the welding location. Since the above-mentioned conventional groove machining process and subsequent multiple welding processes excessively expand this heat-affected zone, it not only reduces the mechanical strength of the obtained precipitation-hardening stainless steel weldment, but also causes serious thermal deformation and residual stress in the precipitation-hardening stainless steel weldment. Furthermore, the corrosion resistance of the weld bead may be significantly deteriorated. In addition to the above, the conventional groove machining process and subsequent multiple welding processes increase the production time and manufacturing cost.

[0005] In view of the above, if a flux applicable to the welding of precipitation-hardening stainless steel can be provided, the conventional groove machining process and subsequent multiple welding processes can be omitted, and the above problems can be solved.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In order to solve the above problems, an object of the present invention is to provide a precipitation-hardening stainless steel flux that can form a deep and narrow weld bead and can further omit the conventional groove machining process and subsequent multiple welding processes.

Means for Solving the Problems

[0008] Terms of direction or approximations thereof described throughout the specification of the present invention, such as "front", "rear", "left", "right", "top", "bottom", "inner", "outer", "side", etc., are based on the directions in the attached drawings, and each term of direction or approximations thereof is only for assisting in the description and understanding of each embodiment of the present invention and does not limit the present invention. Throughout the specification of the present invention, numeral words such as "one" or "a" used for parts or components are used for convenience and give the normal meaning to the scope included in the present invention. In the present invention, it should be interpreted as one or at least one, and unless clearly indicating another meaning, the concept of one also includes multiple cases.

[0009] The precipitation hardening stainless steel flux of the present invention can contain 20 - 25% silicon dioxide, 20 - 25% molybdenum trioxide, 20 - 25% chromium oxide, 15 - 20% nickel sesquioxide, 4 - 8% aluminum oxide, 4 - 8% aluminum nitride, 4 - 8% nickel oxide, and 4 - 6% copper oxide.

[0010] Thereby, when the precipitation hardening stainless steel flux of the present invention is used for welding a precipitation hardening stainless steel workpiece, the aspect ratio of the formed weld bead can be effectively improved by silicon dioxide, molybdenum trioxide, chromium(III) oxide, nickel sesquioxide, aluminum oxide, aluminum nitride, nickel(II) oxide, and copper oxide having specific composition ratios. It can not only reduce the thermal deformation and residual stress caused by welding, but also omit the groove machining process and subsequent multiple welding processes when welding a precipitation hardening stainless steel workpiece with a thickness of 3 mm or more. Furthermore, it can avoid the problems of the reduction in the strength of the precipitation hardening stainless steel weldment and the too wide heat affected zone caused by the groove machining process, and has the effect of reducing the working time and manufacturing cost increased in the groove machining process.

[0011] In addition, the precipitation hardening stainless steel flux of the present invention may have an average particle size of the powder of the precipitation hardening stainless steel flux of 50 to 90 μm. Thereby, the mixing uniformity of each powder particle of the precipitation hardening stainless steel flux can be improved, so that not only can the precipitation hardening stainless steel flux be easily and uniformly applied to the surfaces of two precipitation hardening stainless steel workpieces, but also during TIG welding operations, the precipitation hardening stainless steel flux can be completely melted by the welding heat source, so that it has the effect of effectively increasing the aspect ratio of the weld bead.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0013] To make it easier to understand the above objects, other objects, and advantages of the present invention, embodiments of the present invention are given as follows and will be described in detail with reference to the drawings. Also, in different drawings, those marked with the same reference numerals are regarded as the same and their descriptions are omitted.

[0014] The precipitation hardening stainless steel of the present invention may be of types of precipitation hardening stainless steel such as UNS S17400, UNS S17700, and UNS S66286, which are matters understandable by those skilled in the art, but are not limited thereto.

[0015] The precipitation hardening stainless steel according to one embodiment of the present invention can contain components such as silicon dioxide (SiO2), molybdenum trioxide (MoO3), chromium(III) oxide (Cr2O3), nickel(III) oxide (Ni2O3), aluminum oxide (Al2O3), aluminum nitride (AlN), nickel(II) oxide (NiO), and copper(II) oxide (CuO). Together with the TIG welding process, it can be used for welding precipitation hardening stainless steel workpieces with a thickness of 3 mm or more.

[0016] Specifically, the precipitation hardening stainless steel flux can contain 20 - 25% silicon dioxide, 20 - 25% molybdenum trioxide, 20 - 25% chromium oxide, 15 - 20% nickel sesquioxide, 4 - 8% aluminum oxide, 4 - 8% aluminum nitride, 4 - 8% nickel oxide, and 4 - 6% copper oxide. Thereby, when used in the TIG welding process, the weld bead formed between two precipitation hardening stainless steel workpieces can have an aspect ratio of 0.8 or more, the heat affected zone formed between the two precipitation hardening stainless steel workpieces can be reduced, and thus, the thermal deformation and residual stress of the precipitation hardening stainless steel weldment can be reduced.

[0017] Also, the average particle size of the powder of the precipitation hardening stainless steel flux may be 50 - 90 μm. Thereby, the mixing uniformity of the powder particles of the precipitation hardening stainless steel flux can be improved, so that not only can the precipitation hardening stainless steel flux be easily and uniformly applied to the surfaces of the two precipitation hardening stainless steel workpieces, but also during TIG welding, the precipitation hardening stainless steel flux can be completely melted by the welding heat source, and thus the aspect ratio of the weld bead can be effectively improved.

[0018] As shown in FIG. 1, before the operator performs the TIG welding process, the side edges 11, 11' of the two precipitation hardening stainless steel workpieces 1, 1' are abutted, and the precipitation hardening stainless steel flux 2 is applied to the abutting portion of the two precipitation hardening stainless steel workpieces with a wire brush B, and the subsequent welding operation can be performed after the application is completed. As shown in FIG. 2, using the welding heat source H and the tungsten electrode E together, the precipitation hardening stainless steel flux 2 is melted between the side edges 11, 11' of the two precipitation hardening stainless steel workpieces to form a molten pool, and after the molten pool cools and solidifies, a weld bead 12 is formed. At this time, due to the use of the precipitation hardening stainless steel flux 2, the formed weld bead 12 has a form with a deep penetration depth, a narrow width, and a large aspect ratio.

[0019] The above precipitation hardening stainless steel flux was used in the TIG welding process to prove that two precipitation hardening stainless steel workpieces can become welded objects together and improve the aspect ratio of the formed weld bead. The following tests were conducted.

[0020] (A) Preparation of precipitation hardening stainless steel flux

[0021] Powders such as 15% silicon dioxide, 30% molybdenum trioxide, 20% chromium oxide, 12% nickel sesquioxide, 6% aluminum oxide, 6% aluminum nitride, 6% nickel oxide, and 5% copper oxide were mixed, and then made into a slurry using methanol as a solvent to prepare the precipitation hardening stainless steel flux of Group A01. The preparation methods of the precipitation hardening stainless steel fluxes of Groups A02 to A12 are the same as above, but the composition ratios of the powders such as silicon dioxide, molybdenum trioxide, chromium(III) oxide, nickel sesquioxide, aluminum oxide, aluminum nitride, nickel(II) oxide, and copper oxide are as shown in Table 1.

[0022] Table 1. Composition ratios of the precipitation hardening stainless steel fluxes of Groups A01 to A12

Table 1

[0023] (B) Properties of precipitation hardening stainless steel weldments

[0024] In this test, two steel plates of precipitation hardening stainless steel (UNS S17400) with a thickness of 7 mm each were used as the precipitation hardening stainless steel workpieces 1 and 1'. After removing the dirt on the two precipitation hardening stainless steel workpieces 1 and 1' using silicon carbide paper emery with a particle size of #240, the two precipitation hardening stainless steel workpieces 1 and 1' were wiped with acetone.

[0025] Then, as shown in Fig. 1, the side edges 11, 11' of the two precipitation hardening stainless steel workpieces 1, 1' were abutted, and the slurry-like precipitation hardening stainless steel flux 2 of sets A01 - A12 was applied to the surfaces of the precipitation hardening stainless steel workpieces 1, 1' with a wire brush B. After the methanol was completely volatilized, TIG welding was performed.

[0026] As shown in Fig. 2, the welding heat source H and the tungsten electrode E were used together to melt the precipitation hardening stainless steel flux between the side edges 11, 11' of the two precipitation hardening stainless steel workpieces 1, 1' to generate a molten pool. After the molten pool cooled and solidified, a weld bead 12 was formed, and precipitation hardening stainless steel welds of sets B01 - B12 were obtained respectively. Note that the precipitation hardening stainless steel weld of set B00 is a precipitation hardening stainless steel weld formed by performing TIG welding on the two precipitation hardening stainless steel workpieces 1, 1' under the condition of not applying any flux.

[0027] In the TIG welding process, the welding current was 140 A, the welding speed was 50 mm / min, the shielding gas flow rate was 10 L / min, the tungsten electrode E was EWLa - 2 (φ3.2 mm), the working angle of the tungsten electrode E was 60°, and the distance from the tip of the tungsten electrode E to the surfaces of the two precipitation hardening stainless steel workpieces 1, 1' (i.e., the arc length) was 1 mm.

[0028] After TIG welding, cross-sections of the beads 12 of the precipitation hardening stainless steel welds in sets B00 - B12 were taken, and the depth D and width W of each weld bead 12 were recorded. Furthermore, the aspect ratio of each weld bead of the precipitation hardening stainless steel weld was calculated. The depth D, width W of the weld beads 12, and the calculated aspect ratios of the weld beads 12 of the precipitation hardening stainless steel welds in sets B00 - B12 are as shown in Table 2.

[0029] Table 2. Depth, width, and aspect ratio of the weld bead of the precipitation hardening stainless steel weldment of the B00 to B12 groups [Table 2]

[0030] Figures 3 to 5 show the cross-sectional morphologies of the precipitation hardening stainless steel weld bead 12 in the weldments of groups B00, B04, and B07, respectively, and it was found that the weld bead 12 completely penetrated only in the weldment of group B07. Furthermore, as shown in Table 2, compared with the weld bead 12 of the precipitation hardening stainless steel weldment of groups B01 to B05 and B10 to B12, the weld bead of the precipitation hardening stainless steel weldment of groups B06 to B09 is deeper and narrower. In terms of conversion, the aspect ratio of the weld bead of the weldment of groups B06 to B09 is at least 0.8 or more, and may reach 0.94 (group B07). Therefore, a narrower heat-affected zone can be formed, and thus, the thermal deformation and residual stress of the weldment can be reduced.

[0031] As described above, according to the precipitation hardening stainless steel flux of the present invention, when used for welding a precipitation hardening stainless steel workpiece, the aspect ratio of the formed weld bead can be effectively improved by silicon dioxide, molybdenum trioxide, chromium(III) oxide, nickel sesquioxide, aluminum oxide, aluminum nitride, nickel(II) oxide, and copper oxide having specific composition ratios. It can not only reduce the thermal deformation and residual stress caused by welding, but also omit the groove machining process and subsequent multiple welding processes when welding a precipitation hardening stainless steel workpiece with a thickness of 3 mm or more. Furthermore, it can avoid the problems of a decrease in the strength of the precipitation hardening stainless steel weldment and an overly wide heat-affected zone caused by the groove machining process, and has the effect of reducing the working time and manufacturing cost increased in the groove machining process.

[0032] The present invention has been disclosed with the above embodiments, but they do not limit the present invention. Those skilled in the art will fall within the scope protected by the present invention as long as various modifications are made to the above embodiments without departing from the spirit and scope of the present invention. Therefore, the scope protected by the present invention includes all modifications within the scope of the language described in the claims hereinafter and all equivalent scopes.

Explanation of Reference Numerals

[0033] 1, 1' ··· Precipitation hardening stainless steel workpieces 11, 11' ··· Side edges 12 ··· Weld bead 2 ··· Precipitation hardening stainless steel flux 9, 9' ··· Workpieces 91, 91' ··· Inclined surfaces 92, 92' ··· Side edges 93 ··· Weld bead B ··· Wire brush D ··· Depth of weld bead E ··· Tungsten electrode H ··· Welding heat source M ··· Milling cutter S ··· Welding rod W ··· Width of weld bead

Claims

1. A precipitation hardening stainless steel flux comprising 20-25% silicon dioxide, 20-25% molybdenum trioxide, 20-25% chromium oxide, 15-20% dinickel trioxide, 4-8% aluminum oxide, 4-8% aluminum nitride, 4-8% nickel oxide, and 4-6% copper oxide.

2. 2. The precipitation hardening stainless steel flux according to claim 1, wherein the powder of the precipitation hardening stainless steel flux has an average particle size of 50 to 90 μm.

Images