JP2010264510A - Welding alloy and articles for use in welding, welded product and method for producing welded product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nickel-chromium-iron-based welding alloy suitable for use in the assembling of a device used for nuclear power generation. <P>SOLUTION: The nickel-chromium-iron alloy for use in producing weld deposits comprises, by wt.%, about 27 to 31.5 chromium; about 7 to 11 iron; about 0.005 to 0.05 carbon; not more than about 1.0 manganese; about 0.60 to 0.95 niobium; less than 0.50 silicon; 0.01 to 0.35 titanium; 0.01 to 0.25 aluminum; less than 0.20 copper; less than 1.0 tungsten; less than 1.0 molybdenum; less than 0.12 cobalt; less than 0.10 tantalum; not more than about 0.10 zirconium; not more than about 0.01 sulfur; not more than about 0.01 boron; not more than about 0.02 phosphorous; and balance nickel and incidental impurities. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

FIELD OF THE INVENTION This invention relates to nickel chrome iron weld alloys, articles made from the alloys for use in the manufacture of weldments, and weldments and methods of making the weldments.

BRIEF DESCRIPTION OF THE PRIOR ART In various welding applications, including equipment used in nuclear power generation, the weldment is required to have resistance to various cracking phenomena. Such cracks include not only stress corrosion cracks but also hot cracks, cold cracks and root cracks.

  Commercial and military nuclear power emerged in the late 20th century. During this period, the industry has replaced the first generation NiCrFe alloys containing 14-15% Cr with alloys containing higher concentrations of Cr on the order of 30%. This change was based on the discovery that stress corrosion cracking in nuclear pure water could be avoided with this type of alloy containing the above amount of chromium. These alloys have been used for 20-25 years.

  A specific application in a nuclear power plant that requires the majority of welds and welded parts in a nuclear power plant is the manufacture of a nuclear steam generator. This steam generator is essentially a large tube / shell heat exchanger that generates water vapor from secondary water from the reactor primary coolant. An important component of this steam generator is the tubesheet. It is often 15-20 feet in diameter, more than 1 foot thick, and usually forged from high strength, low alloy steels, but with good formability and in pure nuclear water It is necessary to weld coat with NiCrFe alloy that can resist stress corrosion cracking. Due to the dimensions of the tubesheet, the weld is subjected to considerable residual stresses during coating. In addition, the weld metal overlay must be re-weldable after drilling in a location that accepts thousands of steam generating capillaries. In order to make a helium leak tight weld, these tubes must be seal welded to the overlay deposit. These welds must be of exceptionally high quality and provide a 30-50 year life with high predictive accuracy. In addition, both the overlay deposit and the weld steam generator tube must have excellent resistance to cracking. This requirement is met by most existing 30% Cr weldments with respect to resistance to hot and stress corrosion cracking, also called “solidification cracking”.

  In addition to hot crack resistance and stress corrosion crack resistance, root crack resistance is required for welding pipes and tube sheets. Tube-to-tube sheet welding melts the tube end with or without a weld overlay ring around the tube (with or without filler material) to seal the space between the tube wall and the tube plate hole. It is done by doing. There is a tendency for these welds to crack at the weld intersection of the joint between the tube and the tube sheet. This type of crack is referred to as a “root crack” because it is a crack that occurs at the root of the weld. Existing 30% Cr weld alloys are not resistant to root cracking.

  A third type of crack that may be encountered is cold cracking, also known as “ductility dip cracking”. This crack occurs only in the solidified state after the weld solidification is completed. After solidification, shrinkage stress begins to develop as a result of volume shrinkage of the weld alloy at low temperatures. At the same time, upon completion of solidification, the ductility rapidly recovers over a temperature period of several hundred degrees, followed by a temporary drop in ductility, and again slow ductility recovery continues until room temperature is reached. When the alloy exhibits this sharp reduction in ductility, cracking in the solid state can occur if the residual stress of cooling is sufficiently large. This results from the portion of the microstructure that does not have sufficient strength or ductility to resist the stress at commonly used temperatures. Currently available commercial 30% Cr weld alloys do not have sufficient resistance to cold cracking.

Objects of the invention The object of the present invention is a nickel-chromium-iron welded alloy with desired strength and corrosion resistance in addition to resistance to hot cracking, cold cracking, root cracking and stress corrosion cracking, and made from the alloy It is to provide a weldment.

  It is a further object of the present invention to provide a nickel chromium iron type welding alloy that is particularly suitable for use in the assembly of equipment used in nuclear power generation.

SUMMARY OF THE INVENTION In accordance with the present invention, a nickel chrome iron alloy is provided for use in the manufacture of weld deposits. This alloy is, by weight, about 27-31.5 chromium, about 7-11 iron, about 0.005-0.05 carbon, about 1.0 manganese or less (preferably 0.30-0.95 manganese), about 0.60-0.95 niobium. , Less than 0.50 silicon (preferably 0.10 to 0.30 silicon), 0.01 to 0.35 titanium, 0.01 to 0.25 aluminum, less than 0.20 copper, less than 1.0 tungsten, less than 1.0 molybdenum, less than 0.12, cobalt, less than 0.10 Tantalum, less than about 0.10 zirconium (preferably 0.002 to 0.10 zirconium), less than 0.01 sulfur, less than about 0.01 boron (preferably 0.001 to 0.01 boron), less than about 0.02, phosphorus, residual nickel and incidental Consists of impurities.

  The alloy is considered to exhibit sufficient stress corrosion cracking resistance in view of the chromium content. The form of the alloy can be in the form of a weld, a welding electrode, a weld overlay, or a weld including an alloy substrate (eg, a steel having an overlay of the alloy of the present invention). This alloy may be used in a method of manufacturing a weld or weld in the form of a flux-coated electrode used to make a weld including welding performed by submerged arc welding or electroslag welding. Further, the alloy can be used as an article for producing a weldment, and the article can be in the form of a wire, strip, plate, rod, electrode, prealloy powder, or elemental powder.

DESCRIPTION OF PREFERRED EMBODIMENTS The NiCrFe weld alloy according to the present invention contains sufficient chromium to provide adequate corrosion resistance in addition to excellent resistance to stress corrosion cracking, as well as trace elements as well as secondary chemical constituents. There are fairly strict controls. In addition, the alloy must resist solidification cracking, root cracking, and cold cracking under reheat conditions.

  In order to provide resistance to solidification cracking, the alloy should be sufficiently soluble in its alloying elements and have a narrow liquidus and solidus temperature range. Similarly, low levels of sulfur, phosphorus, and other low melting elements should be included at low levels, and elements that form a low melting phase in the alloy should be included at a minimum level.

  Resistance to cold cracking is controlled by increasing the high temperature strength and ductility at the grain boundaries. To achieve this, niobium, zirconium and boron are carefully combined according to the scope of the present invention. Niobium is required to be limited to avoid the formation of secondary phases while contributing to the grain boundary strength in the solid state. Niobium is also required for resistance to stress corrosion cracking. Although boron contributes to grain boundary strength and improves hot ductility, it is detrimental to hot cracking resistance at levels higher than those according to the present invention. Zirconium improves the solid state strength and ductility at grain boundaries, and improves oxidation resistance at grain boundaries. At levels higher than those according to the present invention, zirconium causes hot cracking. When boron and zirconium are present at lower levels than in accordance with the present invention, a relatively low cold cracking resistance results. The addition of boron alone appears to have very little improvement in cold crack resistance, but boron in conjunction with the level of zirconium according to the present invention substantially eliminates cold cracking.

  Although resistance to root cracking can be achieved in accordance with the present invention, joining conditions such as clearance between articles to be welded, cleanliness, and relative motion during welding, which exceed the control of the weld manufacture designer, vary. There is no guarantee. The alloys of the present invention require low levels of aluminum and titanium in conjunction with controlled niobium, silicon, boron, zirconium and manganese to achieve the desired metallurgical properties. These requirements can be met while optimally maintaining resistance to hot cracking, cold cracking and stress corrosion cracking. Aluminum and titanium should be kept as low as possible for root crack resistance, but even small amounts of titanium are beneficial for stress corrosion crack resistance. Silicon is not particularly harmful to root crack resistance when maintained below 0.50%. This is an acceptable level because it is preferable to have silicon below 0.30% for other reasons. With the advent of AOD melting methods that produce very low levels of sulfur, large amounts of manganese addition are not necessary. In fact, manganese levels above 7% result in metallurgical instability when exposed to temperatures above 1000 ° F. In the past, it was thought that 1% to 5% manganese addition was necessary to resist both hot cracking and root cracking. In the present invention, it is necessary to maintain manganese at 1.0% or less, preferably about 0.80% for hot crack resistance. At the same time, however, manganese is sufficient to avoid root cracking at less than 1.0% for balance with other ingredients.

  All the alloys in Table 1 show the strength and corrosion resistance required for welding applications, including the manufacture of equipment used in nuclear power generation. The results of the cracking test shown in Table 1 demonstrate that the NiCrFe weld alloy composition according to the present invention additionally provides improved crack resistance over this type of conventional alloy. This includes not only stress corrosion cracking resistance, but also hot cracking resistance, cold cracking resistance, and root cracking resistance in combination.

  As can be seen from Table 1, sample melt numbers 1124, 1125 and 1127 are free of all types of cracks and thus constitute alloys within the scope of the present invention. Each of these samples contains low silicon and the required amounts of boron and zirconium. Sample 1128 showed both cold cracking and root cracking due to the unacceptably high silicon content even though boron and zirconium were within the scope of the present invention.

  Other embodiments of the invention will be apparent to those skilled in the art from consideration of the detailed description and practice of the invention disclosed herein. The above description and examples are to be regarded as illustrative only, with the true scope and spirit of the invention being indicated by the following claims.

Claims (18)

  Nickel-chromium iron alloy for use in the manufacture of weld deposits, by weight, about 27-31.5 chromium, about 7-11 iron, about 0.005-0.05 carbon, about 1.0 or less manganese, about 0.60 ~ 0.95 niobium, less than 0.50 silicon, 0.01 to 0.35 titanium, 0.01 to 0.25 aluminum, less than 0.20 copper, less than 1.0 tungsten, less than 1.0 molybdenum, less than 0.12, cobalt less than 0.12, less than 0.10 tantalum, about 0.10 or less The above alloy composed of zirconium, less than 0.01 sulfur, less than 0.01 boron, less than 0.02 phosphorus, residual nickel and incidental impurities.   The alloy of claim 1 comprising 0.30 to 0.95 manganese, 0.002 to 0.10 zirconium, 0.001 to 0.01 boron, and 0.10 to 0.30 silicon.   Nickel-chromium iron deposit, by weight, about 27-31.5 chromium, about 7-11 iron, about 0.005-0.05 carbon, about 1.0 or less manganese, about 0.60-0.95 niobium, less than 0.50 Silicon, 0.01-0.35 titanium, 0.01-0.25 aluminum, less than 0.20 copper, less than 1.0 tungsten, less than 1.0 molybdenum, less than 0.12, cobalt less than 0.12, tantalum less than 0.10, zirconium less than about 0.10, sulfur less than 0.01, The above deposit consisting of less than about 0.01 boron, less than 0.02 phosphorus, residual nickel and incidental impurities.   The weld deposit of claim 3 comprising 0.30 to 0.95 manganese, 0.002 to 0.10 zirconium, 0.001 to 0.01 boron, and 0.10 to 0.30 silicon.   A welding electrode for producing a deposit, the weld comprising, by weight, about 27-31.5 chromium, about 7-11 iron, about 0.005-0.05 carbon, about 1.0 or less manganese, about 0.60 ~ 0.95 niobium, less than 0.50 silicon, 0.01 to 0.35 titanium, 0.01 to 0.25 aluminum, less than 0.20 copper, less than 1.0 tungsten, less than 1.0 molybdenum, less than 0.12, cobalt less than 0.12, less than 0.10 tantalum, about 0.10 or less Electrode for welding, comprising less than 0.01 sulfur, less than about 0.01 boron, less than about 0.02 phosphorus, residual nickel and incidental impurities.   The welding electrode according to claim 5, wherein a weld comprising 0.30 to 0.95 manganese, 0.002 to 0.10 zirconium, 0.001 to 0.01 boron, and 0.10 to 0.30 silicon is manufactured.   The welding electrode according to claim 5 or 6, comprising a nickel chrome wire having a flux cover.   The welding electrode according to claim 5 or 6, comprising a nickel chromium iron sheath having a flux core.   A weld composed of an alloy substrate and a deposit overlay thereon, the weld overlay comprising, by weight, about 27-31.5 chromium, about 7-11 iron, about 0.005-0.05 carbon; About 1.0 or less manganese, about 0.60 to 0.95 niobium, less than 0.50 silicon, 0.01 to 0.35 titanium, 0.01 to 0.25 aluminum, less than 0.20 copper, less than 1.0 tungsten, less than 1.0 molybdenum, less than 0.12 cobalt, The above weld comprising less than 0.10 tantalum, less than about 0.10 zirconium, less than 0.01 sulfur, less than about 0.01 boron, less than 0.02 phosphorus, residual nickel and incidental impurities.   The weldment of claim 9, comprising 0.30 to 0.95 manganese, 0.002 to 0.10 zirconium, 0.001 to 0.01 boron, and 0.10 to 0.30 silicon.   11. A weldment according to claim 9 or 10 which is in the form of a tube plate of a nuclear steam generator.   A method for producing a welded article, comprising producing a flux-coated electrode of nickel chrome wire or nickel chrome iron wire, and melting the electrode to produce a welded material, wherein the welded material has a weight percentage of about 27 to 31.5 chromium, about 7-11 iron, about 0.005-0.05 carbon, about 1.0 manganese or less, about 0.60-0.95 niobium, less than 0.50 silicon, 0.01-0.35 titanium, 0.01-0.25 aluminum, less than 0.20 Copper, less than 1.0 tungsten, less than 1.0 molybdenum, less than 0.12 cobalt, less than 0.10 tantalum, less than about 0.10 zirconium, less than 0.01 sulfur, less than about 0.01 boron, less than 0.02, phosphorus, residual nickel and incidental A method as described above consisting of typical impurities.   The method of claim 12 for producing a deposit comprising 0.30 to 0.95 manganese, 0.002 to 0.10 zirconium, 0.001 to 0.01 boron, and 0.10 to 0.30 silicon.   The method according to claim 12 or 13, wherein the melting of the electrode is performed by submerged arc welding or electroslag welding.   A method of making a weld comprising producing an electrode of a nickel chrome iron alloy, the alloy comprising, by weight, about 27-31.5 chromium, about 7-11 iron, about 0.005-0.05 carbon, About 1.0 or less manganese, about 0.60 to 0.95 niobium, less than 0.50 silicon, 0.01 to 0.35 titanium, 0.01 to 0.25 aluminum, less than 0.20 copper, less than 1.0 tungsten, less than 1.0 molybdenum, less than 0.12 cobalt, The above method consisting of less than 0.10 tantalum, less than about 0.10 zirconium, less than 0.01 sulfur, less than about 0.01 boron, less than 0.02 phosphorus, residual nickel and incidental impurities.   The method of manufacturing a welded article according to claim 15, comprising 0.30 to 0.95 manganese, 0.002 to 0.10 zirconium, 0.001 to 0.01 boron, and 0.10 to 0.30 silicon.   Articles for use in the manufacture of weldments, wherein the article is in the form of a wire, strip, sheath, rod, electrode, pre-alloyed powder, or elemental powder, the article having a weight %, About 27-31.5 chromium, about 7-11 iron, about 0.005-0.05 carbon, about 1.0 manganese or less, about 0.60-0.95 niobium, less than 0.50 silicon, 0.01-0.35 titanium, 0.01- 0.25 aluminum, less than 0.20 copper, less than 1.0 tungsten, less than 1.0 molybdenum, less than 0.12 cobalt, less than 0.12 tantalum, less than about 0.10 zirconium, less than 0.01 sulfur, less than about 0.01 boron, less than 0.02 phosphorus The article, composed of residual nickel and incidental impurities.   The article of claim 17, comprising 0.30 to 0.95 manganese, 0.002 to 0.10 zirconium, 0.001 to 0.01 boron, and 0.10 to 0.30 silicon.