KR20160026132A - method of making needle valve - Google Patents

Abstract

The present invention relates to a method to manufacture a material for a needle valve having an unground high-strength duplex stainless steel surface, which realizes a method for continuously heating and forming a material from a high-frequency induction heating process to a shape rolling process in line to form duplex stainless steel for a needle valve having 150,000 psi, and additionally provides a method for forming a steel bar having a length of 1 m, a height of 25 mm, and a width of 50 mm through a shape drawing process. The method to manufacture a material for a needle valve having an unground high-strength duplex stainless steel surface comprises an induction heating process, a rolling process, and a drawing process.

Description

[0001] METHOD FOR MANUFACTURING MATERIAL FOR NON-GRINDING NEEDLE VALVES [0002]

The present invention relates to a method for manufacturing a duplex stainless steel material for a 150,000 psi needle valve using a die-casting precision rolling process and a die-cut precision drawing, and more particularly, Energy consumption and pollutant generation can be significantly reduced. Also, since the vertical and horizontal type rolling passes of the inline precision rolling are arranged in a straight line, the initial material continuously passes through each rolling pass, To a method of manufacturing a material for a high strength duplex stainless steel surface non-abrasive needle valve.

As is well known, duplex stainless steels consist of a 50:50 microstructure of austenite and ferrite, with a ratio of 40:60 for commercial alloys. The duplex stainless steel has better durability than austenitic stainless steel and is more resistant to corrosion of formulations and crevices.

Such duplex stainless steels have a higher amount of chromium (preferably 19% to 28%) and molybdenum (5% or more) and a lower nickel content than the other austenitic alloys. The most commonly used duplex stainless steels are 2205 (22% chromium, 5% nickel) and 2507 (25% chromium, 7% nickel), and the 2507 is called super duplex with high corrosion resistance. The super duplex system has a superiority in price competitiveness because it has corrosion resistance comparable to super austenitic system even at a low price. The physical properties of the duplex stainless steel and the austenitic stainless steel are similar. Duplex stainless steel, on the other hand, has the advantage of low thermal expansion coefficient and low risk of thermal fatigue.

Duplex stainless steel or super duplex stainless steel is emerging as an indispensable material for energy fields and desalination facilities because strength is more than two times higher than general industrial equipment stainless steel and corrosion resistance is excellent. In recent years, demand for DSS, in which nickel is added less than austenitic stainless steel, is increasing due to a surge in nickel (Ni) price. As a result, the demand for DSS is increasing every year by 20% or more every year.

As such, the importance of duplex stainless steels has become more important, and there is a growing interest in high-pressure needle valves, and demand is exploding. High pressure needle valve has become an important core part of high pressure equipment and seawater equipments. It is used for various kinds of chemicals such as autoclave, hydrostatic press, pressure tester, various pumps, fatigue tester, industrial pressure vessel, The applications are diverse so that there is no unused place in the research field, the pressure control part of the gas industry. In particular, desulfurization equipment and seawater cooling system, which are installed mandatory in thermal power plants, are being replaced by needle valves made of duplex stainless steel, which are superior in corrosion resistance and strength and economical. They will also be applied to 7 nuclear power plants under construction to be.

On the other hand, the materials used in general valves in Korea are directly available in Korea, and thus have international competitiveness such as cost reduction, quality assurance and short delivery time. However, needle valves used for high pressure, high strength, and high corrosion resistance import a significant amount from the United States, which has a competitive advantage. In the manufacture of high-pressure needle valves, foreign companies are replacing duplex stainless steel in the STS 316L due to problems such as mechanical properties (ie, deepness and strength) and formulations (corrosion resistance). However, to be.

Despite the significant increase in demand and importance as a valve material for duplex stainless steel, most raw materials are imported from foreign countries. In terms of distribution, domestic duplexers are importing and exporting in the form of a round bar at 'Outokompu', a stainless steel manufacturer in the UK, because the supply of materials is not smooth.

However, since the above-mentioned imported round bar is manufactured by machining to make the needle valve material, problems such as excessive material loss, lowering of production speed, and deterioration of mechanical properties are occurring. Further, it is difficult to satisfy the mechanical properties due to the absence of plastic working. In addition, although the cross-sectional shape of the needle valve material is not complicated, plastic processing is difficult due to the high hardness, toughness and strength of the duplex material.

No. 10-1999-0044433 (entitled "Valve Needle and Method for Manufacturing the Same", Published Date: June 25, 1999) Registered Utility Model Registration No. 20-0348821 (Name of Design: Needle Valve. Date of Notification: April 30, 2004) Patent Publication No. 10-2012-0066622 (entitled "Electric Needle Valve", Published Date: June 22, 2012) Patent Publication No. 10-2009-0005458 (entitled: Magnetic Needle Valve, Published Date: Jan. 14, 2009)

The present invention provides a method of manufacturing a material for a high strength duplex stainless steel surface non-abrasive needle valve which can reduce the processing time with energy saving effect by realizing the dimensional precision, the bending phenomenon of the material, and the mechanical property improvement. It has its purpose.

It is another object of the present invention to provide a method for manufacturing a high strength duplex stainless steel surface non-abrasive needle valve material capable of exerting a great effect on prevention of global warming by reducing greenhouse gases and noxious gas emissions.

The method for manufacturing a material for a high strength duplex stainless steel surface grinding needle valve according to the present invention is characterized in that it is performed in the order of an induction heating process, a rolling process, a heat treatment process, and a drawing process.

The method of manufacturing a material for a nibble valve of a high strength duplex stainless steel according to the present invention can achieve the following many effects.

First, the present invention can reduce the production cost by about 60% by reducing the material cost by 56% compared to the conventional machining and by improving the productivity by 50%, and it is possible to reduce the production cost by eliminating the warping phenomenon of the material, It is possible to reduce the process time and the cost competitiveness, and also to reduce the emission of greenhouse gas and harmful gas, and thus it is possible to exert a great effect on prevention of global warming.

Secondly, according to the present invention, by changing the heating method of the initial material from the heating furnace method using the conventional LNG to the high frequency induction heating method, it is possible to heat the material in a short time, There is an advantage that the generation can be remarkably reduced.

Third, the present invention is characterized in that the inline precision rolling vertical / horizontal type rolling passes are arranged in a straight line so that the initial material continuously passes through each rolling pass and the production speed is very fast. In addition, It is possible to apply it to the production of high precision parts.

Fourth, the present invention is used as a basic data for control of the precipitation of the sigma phase, which is a concern during the hot rolling and stress relief hot treatment of a high Cr-N-Mo alloy material such as a duplex related material. And a technique for preventing defects in super-tuplex stainless steel can be obtained.

1 to 4 show a method of manufacturing a material for a high strength duplex stainless steel surface grinding needle valve according to a preferred embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following detailed description, exemplary embodiments of the present invention will be described in order to accomplish the above-mentioned technical problems. And other embodiments which may be presented by the present invention are replaced by descriptions in the constitution of the present invention.

The present invention proposes a method of manufacturing a material for a nibble valve of a high strength duplex stainless steel. Specifically, for the formation of a stainless steel tube for a 150,000 psi needle valve, the material is heated in inline from high frequency induction heating to shape rolling, And a method of forming a steel bar having a precise dimension of 1 mm in length, 25 mm in height, and 50 mm in width through the shape drawing process is implemented.

For this, a specific manufacturing method from the high-frequency induction heating to the final product, such as the needle valve, is to be proposed. In addition, the design of precision die rolling should include setting the appropriate number of passes, setting the reduction rate for each pass, setting the rolling speed, and setting the ball shape for each pass.

A method for manufacturing a material for a high strength duplex stainless steel surface non-abrasive needle valve according to a preferred embodiment of the present invention will be described in detail with reference to Figs. 1 to 4. Fig. The manufacturing method of the material for high strength duplex stainless steel surface grinding needle valve according to the present invention is performed in the order of induction heating → rolling → heat treatment → drawing process (shot, coating, drawing).

1. Induction heating process

As shown in Figs. 1 and 2, nine individual induction heating apparatuses are constituted by one set, and a method of replacing them in accordance with the diameter of the raw material is adopted. When passing from 1 to 6 at a speed of 0.322 m / min, the temperature rises to 1,050 ° C, and surface oxidation does not occur due to rapid heating time. In addition, it is possible to heat up to the inside of the material by using the low frequency of 1 KHz and the forward and reverse rotation of the feed roll. When the induction heating time was 55 seconds due to the heating time, the internal temperature of the material reached 940 ° C, and the external temperature reached 1050 ° C, where no sigma phase occurred. However, considering the temperature drop due to the transfer distance to the rolling roll after heating and the temperature drop during the rolling pass, it is necessary to further heat the material, so that the material is heated for 60 seconds before the rolling process is performed. Therefore, it is easy to roll shaped products that have almost no temperature gradient inside and outside the material.

On the other hand, as shown in Figs. 1 and 3, the electric power for heating to 1,050 占 폚 is maintained at 1,000 kW for # 1, 2, 3 / # 4,5,6 / # 7,8,9. After heating from # 1 to # 8 and reheating from # 8 to # 1, final heating is performed from # 1 to # 9, followed by rolling. The temperature for each step is shown in Table 1 below.

#One #2 # 3 #4 # 5 # 6 # 7 #8 # 9 200 ℃ 350 ℃ 500 ℃ 600 ℃ 700 ℃ 800 ° C 900 ℃ 1000 ℃ 1050 ° C

Particularly, in the present invention, the chemical state of duplex stainless steel (UNS S31803) is inputted by using Thermo-calc program, and the state of the material is predicted through analysis. As a result, the temperature range in which the σ phase did not occur was 940 ~ 1300 ℃ when the molybdenum content was 3.0% and 900 ~ 1180 ℃ when the chromium content was 22%. Based on these results, in the present invention, the target temperature during high-frequency induction heating is set at 950 to 1150 ° C.

As described above, in the present invention, the target temperature is set for the high-frequency induction heating. This is to solve the problem caused by the high-frequency induction heating. That is, the heating process required for the initial material is required to manufacture the hot rolled products, and in the conventional shape rolling process, fossil fuels such as Bunker C oil and LNG are used for heating the material. However, It is in very poor condition from the side. Therefore, it is effective to use a high-frequency induction heating in which heating time is fast and heating temperature control is effective. However, since the quantitative evaluation of the heating temperature of the material by induction heating is not performed in the field, many problems arise due to nonuniform local heating of the material. Accordingly, in the present invention, the heating temperature of the material is evaluated for the induction heating process in order to prevent the above problems and reduce the generation of defects.

2. Rolling process

According to the present invention, the material for the needle valve is duplex stainless steel, the size of the material is Ø65 mm, and the initial material length is 2.5 m. Before the shape rolling, the material was chamfered at the front part of the material so that the material could be well adhered to the shape rolling roll through the guide, and then the shape was rolled by high frequency induction heating. The temperature of the high frequency induction heated material was measured at 1050 ° C. The heated material is entrained in the form roll at a feed rate of 300 mm / s. In this case, the roll rotation speed of each pass is set so that the material is not subjected to compression or tensile force between the stands. The material of the roll is DCI (Ductile Casting Iron), and the cooling of the roll is performed using distilled water.

On the other hand, there is a risk that loops and tension may occur in each stand-rolling material in the in-line precision rolling process with a short distance as in the present invention. In this case, the quality and reliability of the rolled product can be greatly influenced. Therefore, according to the present invention, an HMD (Hot Metal Detect) system which measures the progress and speed of a hot material traveling between rolling stands and compares it with a standard speed of 0.322 m / min and corrects the error is applied. In addition, the error measured by this HMD system is maintained by the minimum tension between roll stands so that the MTC (Minimum Tension Control) system, which controls the return to the standard speed, is applied to maintain the optimum roll speed for a specific product .

For example, as shown in FIG. 4, after the material enters the R1 having the speed of V1, the cross-section of the work is deformed into A2, and then enters the R2 having the speed of V2, Tension T1 or loop occurs due to the speed difference between the rolls. To solve this problem, the applied MTC adjusts the speed of V1 or V2 to maintain the prescribed tension.

3. The solution treatment process

The solid solution heat treatment according to the present invention is a basic heat treatment of stainless steel, which removes internal stress caused by molding or the like and recrystallizes the processed structure to recover ductility, and intermetallic compounds and σ phase precipitated by hot working are treated with austenite It is a heat treatment to increase the corrosion resistance by being hardened in the tissue. The heating temperature for the duplex stainless steel is set at 1,050 to 1,200 ° C, which does not cause a sigma phase. However, as the heating temperature is high, the carbide solidifies and softens sufficiently when the temperature is too high. However, if the temperature is too high, And the surface of the material became worse. Therefore, the temperature was kept at 1,050 ° C for 75 minutes and then quenched to prevent the deposition of carbide.

Claims (2)

A method of manufacturing a material for a high strength duplex stainless steel surface grinding needle valve,
Wherein the heating step is performed in the order of an induction heating step, a rolling step, a heat treatment step, and a drawing step.
The method according to claim 1,
Wherein the induction heating process is performed at a temperature of from 950 to 1150 ° C.

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