JP2003501557A - Welding alloy and article used for welding, welded article, and method for producing welded article - Google Patents

Abstract

  (57) [Summary] Nickel-chromium iron alloy for use in the production of weldments. The alloy comprises, by weight, about 27-31.5 chromium, about 7-11 iron, about 0.005-0.05 carbon, about 1.0 or less manganese (preferably 0.30-0.95 manganese), about 0.60-0.95 niobium. Less than 0.50 silicon (preferably 0.10-0.30 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, about 0.10 or less zirconium (preferably 0.002-0.10 zirconium), about 0.01 or less sulfur, about 0.01 or less boron (preferably 0.001-0.01 boron), about 0.02 or less phosphorus, residual nickel and Composed of various impurities.

Description

Detailed Description of the Invention

FIELD OF THE INVENTION The present invention relates to nickel-chromium-iron welding alloys, articles made from such alloys for use in the manufacture of weldments, as well as weldments and methods of making the weldments.

[0002] including the apparatus used in the brief description nuclear power of the prior art, in various welding applications, weldments are required to include resistance to various cracking phenomenon. Such cracks include hot corrosion, cold cracking and root cracking as well as stress corrosion cracking.

[0003] Commercial and military nuclear power generation began to emerge in the second half of the 20th century. During this period, the industry has seen 30% of first-generation NiCrFe alloys containing 14-15% Cr.
Replaced with alloys containing higher concentrations of Cr. This change was based on the finding that stress corrosion cracking in nuclear pure water can be avoided with alloys of this type containing the above amounts of chromium. These alloys have been used for 20-25 years.

A particular application in nuclear power plants that require most welding and welded parts in nuclear power plants is the manufacture of nuclear steam generators. This steam generator is essentially a large tube / shell heat exchanger, and generates steam from secondary water from the reactor primary cooling medium. An important component of this steam generator is the tubesheet. It is often 15 to 20 feet in diameter, has a thickness of more than 1 foot, and is usually forged from high strength low alloy steels, but with good formability and in pure water. NiCrFe can resist stress corrosion cracking
Must be weld coated with alloy. Due to the size of the tubesheet, the weld deposit experiences significant residual stress during coating. In addition, the deposited metal overlay must be reweldable after drilling holes to receive thousands of steam generating capillaries. These tubes must be seal welded to the overlay weld to create a helium leak tight weld. These welds must be of exceptional quality and
It must provide a lifetime of 30 to 50 years with high prediction accuracy. In addition, both the overlay deposit and the weld steam generator tube must have good resistance to cracking. This requirement is met by most existing 30% Cr welds in terms of resistance to hot and stress corrosion cracking, also called "solidification cracking".

In addition to hot cracking resistance and stress corrosion cracking resistance, root cracking resistance is required in the welding of pipes and tube sheets. Tube-tube sheet welding fuses the tube end (with or without filler material) with a ring of weld overlay material around the tube to seal the space between the tube wall and the tube sheet hole. It is done by doing. At the weld intersection of the tube-to-tube sheet joint, these welds tend to crack. This type of crack is called a "root crack" because it is a crack that occurs at the root of the weld. The existing 30% Cr weld alloy is 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 welding solidification is completed. After solidification, shrinkage stress begins to develop as a result of the volumetric shrinkage of the weld alloy at low temperatures. At the same time, when the solidification is complete, the ductility rapidly recovers over a temperature range of hundreds of degrees, followed by a sudden temporary decrease in ductility, and then again a slow recovery of ductility 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 large enough. This results from portions of the microstructure that are not sufficiently strong or ductile to withstand the stresses at the temperatures commonly used.
Currently available commercial 30% Cr weld alloys do not have sufficient resistance to cold cracking.

OBJECTS OF THE INVENTION It is an object of the present invention to provide nickel chrome iron weld alloys having desired strength and corrosion resistance in addition to resistance to hot cracking, cold cracking, root cracking and stress corrosion cracking, as well as said alloys. Is to provide weldments made from. A further object of the invention is to provide a nickel-chromium-iron-type weld alloy, which is particularly suitable for use in the assembly of equipment used in nuclear power generation.

[0008] According to the Summary of the Invention invention, the nickel-chromium-iron alloys used in the manufacture of a weld deposit is provided. This alloy, by weight percent, is about 27-31.5 chromium, about 7-11 iron, about 0.005-0.05.
Carbon, about 1.0 or less manganese (preferably 0.30 to 0.95 manganese), about 0.60 to 0
0.95 niobium, less than 0.50 silicon (preferably 0.10 to 0.30 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, about 0
Less than .10 zirconium (preferably 0.002-0.10 zirconium), less than 0.01 sulfur, less than about 0.01 boron (preferably 0.001-0.01 boron), less than about 0.02 phosphorus, residual nickel and incidental impurities. Composed.

The alloy is considered to exhibit sufficient stress corrosion cracking resistance in consideration of the chromium content. The alloy morphology can be in the form of a weldment, welding electrode, weld overlay, or weldment containing an alloy substrate (eg, steel having an overlay of the alloy of the invention). This alloy may be used in a method of making a deposit or weldment in the form of a flux coated electrode used in the manufacture of a deposit, including welding performed by submerged arc welding or electroslag welding. Further, the alloy can be used as an article for producing a weldment, the article comprising wire, strip, plate, bar,
It can be in the form of electrodes, prealloyed powder, or elemental powder.

Description of the Preferred Embodiments A 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 secondary elements as well as secondary elements. There is fairly strict control of the chemical composition. Further, the alloy has solidification cracks,
It must resist root cracking and cold cracking under reheat conditions. To impart resistance to solidification cracking, the alloy should be sufficiently soluble in its alloying constituent elements and have a narrow temperature range between the liquidus and solidus. Similarly, it should contain low levels of sulfur, phosphorus, and other low melting elements, and minimal levels of elements that form low melting phases in the alloy.

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

Although resistance to root cracking may be achieved in accordance with the present invention, joining conditions such as gaps between articles to be welded, cleanliness, and relative motion during welding are beyond the control of the weldment manufacturing designer. As such, we cannot guarantee it. The alloys of the present invention include controlled niobium, silicon, boron, in order to achieve the desired metallurgical properties.
Low levels of aluminum and titanium associated with zirconium and manganese are required. These requirements can be met while optimally maintaining resistance to hot, cold 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 detrimental to root crack resistance if it is maintained below 0.50%. 0.30% silicon for other reasons
This is an acceptable level as lower is preferred. With the advent of AOD melting processes that produce very low levels of sulfur, large additions of manganese are not necessary. In fact, manganese levels above 7% lead to 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 and root cracking. The present invention requires maintaining manganese at 1.0% or less, preferably about 0.80%, for hot cracking resistance. But at the same time, due to the balance with other components, manganese less than 1.0% is sufficient to avoid root cracking.

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

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

Other embodiments of this invention will be apparent to those of skill in the art upon consideration of the detailed description and practice of the invention disclosed herein. The above description and examples are considered merely exemplary, and the true scope and spirit of the invention is set forth in the following claims.

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Claims (18)

[Claims] 1. A nickel-chromium-iron alloy for use in the manufacture of deposits, in weight percent, about 27-31.5 chromium, about 7-11 iron, about 0.005-0.05 carbon, about 1.
Manganese 0 or less, about 0.60 to 0.95 niobium, less than 0.50 silicon, 0.01 to 0.35
Titanium, 0.01 to 0.25 aluminum, copper less than 0.20, tungsten less than 1.0, molybdenum less than 1.0, cobalt less than 0.12, tantalum less than 0.10, zirconium less than about 0.10, sulfur less than 0.01, boron less than 0.01, The above alloy consisting of less than 0.02 phosphorus, residual nickel and incidental impurities. 2. Manganese of 0.30 to 0.95, zirconium of 0.002 to 0.10, 0.001
The alloy of claim 1 comprising .about.0.01 boron and 0.10 to 0.30 silicon. 3. A nickel chromium iron deposit, in weight percent, about 27 to 31.5 chromium, about 7 to 11 iron, about 0.005 to 0.05 carbon, about 1.0 or less manganese, about 0.60 to 0.
Niobium of .95, silicon of less than 0.50, titanium of 0.01 to 0.35, aluminum of 0.01 to 0.25, copper of less than 0.20, tungsten of less than 1.0, molybdenum of less than 1.0, 0.12
The above deposit comprising less than 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 impurities. 4. Manganese of 0.30 to 0.95, zirconium of 0.002 to 0.10, 0.001
4. The deposit of claim 3 comprising .about.0.01 boron and 0.10 to 0.30 silicon. 5. A welding electrode for producing a weld deposit, wherein the weld deposit is% 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 0.10 tantalum, less than about 0.10 zirconium, less than 0.01 sulfur, less than about 0.01 boron, less than 0.02. The welding electrode as described above, which is composed of phosphorus, residual nickel and incidental impurities. 6. Manganese of 0.30 to 0.95, zirconium of 0.002 to 0.10, 0.001
6. A weld deposit is produced that contains .about.0.01 boron and 0.10 to 0.30 silicon.
The welding electrode described. 7. The welding electrode according to claim 5, which is composed of a nickel chromium wire having a flux cover. 8. The welding electrode according to claim 5, comprising a nickel-chromium-iron sheath having a flux core. 9. A weldment comprising an alloy substrate and a deposit overlay thereon, wherein the deposit overlay is about 27-31.5 chromium by weight, about 7-1.
1 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, 0.20
Copper less than 1.0, tungsten less than 1.0, molybdenum less than 1.0, cobalt less than 0.12, tantalum less than 0.10, zirconium less than about 0.10, sulfur less than 0.01, boron less than 0.01, phosphorus less than 0.02, residual nickel and The above-mentioned weldment composed of incidental impurities. 10. Manganese of 0.30 to 0.95, zirconium of 0.002 to 0.10, 0.0
The weldment of claim 9 comprising 01-0.01 boron and 0.10-0.30 silicon. 11. A nuclear steam generator in the form of a tube plate.
The weldment described. 12. A method for producing a weld deposit, which comprises producing a flux-coated electrode of a nickel-chromium wire or a nickel-chromium iron wire, and melting the electrode to produce a weld deposit, wherein the weld deposit is% by weight. And about 27-31.5 chrome, about 7-11 iron, about 0
.005 to 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,
Tungsten less than 1.0, molybdenum less than 1.0, cobalt less than 0.12, tantalum less than 0.10, zirconium less than about 0.10, sulfur less than 0.01, boron less than 0.01, boron less than 0.02, residual nickel and incidental impurities. The method as described above, which comprises: 13. Manganese of 0.30 to 0.95, zirconium of 0.002 to 0.10, 0.0
For producing a deposit comprising 01-0.01 boron, and 0.10-0.30 silicon,
The method according to claim 12. 14. The method according to claim 12, wherein the melting of the electrode is performed by submerged arc welding or electroslag welding. 15. A method of making a weldment comprising producing electrodes of a nickel chromium iron alloy, the alloy comprising, by weight percent, 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, 0.
Silicon less than 50, 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, 0.10
Less than about 0.10 zirconium, less than about 0.01 sulfur, less than about 0.01 boron, less than 0.02 phosphorus, balance nickel and incidental impurities. 16. Manganese of 0.30 to 0.95, zirconium of 0.002 to 0.10, 0.0
The method for producing a welded product according to claim 15, comprising 01 to 0.01 boron and 0.10 to 0.30 silicon. 17. An article for use in the manufacture of a weldment, the article being in the form of a wire, strip, sheath, bar, electrode, pre-alloyed powder or elemental powder, The article, by weight percent, is about 27-31.5 chromium, about 7-11 iron, about 0.005-0.
Carbon of 05, manganese of about 1.0 or less, niobium of about 0.60 to 0.95, silicon of less than 0.50, titanium of 0.01 to 0.35, aluminum of 0.01 to 0.25, copper of less than 0.20, tungsten of less than 1.0, molybdenum of less than 1.0, 0.12 Less than cobalt, less than 0.10 tantalum, less than about 0.10 zirconium, less than 0.01 sulfur, less than about 0.01 boron, 0.02
Such an article, comprising less than phosphorus, residual nickel and incidental impurities. 18. Manganese of 0.30 to 0.95, zirconium of 0.002 to 0.10, 0.0
18. An article according to claim 17 comprising 01-0.01 boron and 0.10-0.30 silicon.