US3479157A - Welded articles and alloys containing hafnium and nickel - Google Patents

Description

Filed June 22, 1966 Nov. 18, 1969 c ns ETAL 3,479,157

WELDED ARTICLES AND ALLOYS CONTAINING HAFNIUM AND NICKEL 5 Sheets-Sheet 1 Nov. 18, 1969 RICHARDS ETAL 3,479,157

v WELDED ARTICLES AND ALLOYS CONTAINING HAFNIUM AND NICKEL Filed June 22, 1966 3 Sheets-Sheet 2 1969 E. G. RICHARDS ET AL 3,479,157

WELDED ARTICLES AND ALLOYS CONTAINING HAFNIUM AND NICKEL Filed June 22, 1966 3 Sheets-Sheet 5 I A l l 0 v. 0005- 00/ 001.005 0-/ 02 United States Patent 3,479,157 WELDED ARTICLES AND ALLOYS CONTAINING HAFNIUM AND NICKEL Edward Gordon Richards, West Hagley, David Marshall Ward, Birmnigham, Keith John Hales, Brierly Hill, and Norman Stephenson, Haywards Heath, England, assignors to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware Filed June 22, 1966, Ser. No. 559,456 Claims priority, application Great Britain, June 25, 1965, 27,074/ 65 Int. Cl. B23k 35/30; 1532b 15/20; C22c 19/00 US. Cl. 29-194 9 Claims ABSTRACT OF THE DISCLOSURE Weldable age-hardenable nickel-containing alloys and welded articles made from such alloys are provided wherein the alloys have additions of boron and/or zirconium therein as strengtheners and also include a hafnium .001% to 0.5% addition to improve weldability.

This invention relates to nickel-base alloys and, more particularly, to hafnium-containing nickel-base alloys having improved weldability.

Various nickel-containing alloys are well known to have exceptional strength at high temperatures and are commonly used when creep resistance is essential. These alloys vary widely in composition, but all those with which this invention is concerned are age-hardened and have a face-centered cubic lattice structure and a base consisting, in addition to nickel, of one or more of iron, cobalt, and chromium, with or without one or more metals of high melting point such as tungsten, molybdenum, niobium and tantalum. In these alloys nickel may be the main constituent, and then normally amounts to 30% or more of the alloy, or only a minor constituent as, for example, in the age-hardenable stainless steels. In general, all the alloys in question contain at least 7.5% nickel.

The alloys with which this invention is concerned are of a composition such that a strengthening phase is precipitated upon heat treatment. In some, the strengthening phase is carbidic and in others, it contains titanium or aluminum or both. These alloys we refer to as age hardenable.

As the compositions of these alloys are adjusted to increase the strength at high temperature, the ductility at high temperature commonly falls. Some years ago, the striking discovery was made that small amounts of boron and zirconium substantially improve the ductility at high temperature without loss of, and in many cases with increase in, the strength. At the present time alloys in which the highest strength at high temperature, say 650 C. and above, is required commonly contain both boron and zirconium in amounts up to 0.03% boron and 0.3% zirconium.

Unfortunately boron and zirconium severely reduce the weldability of the alloys. Their presence increases the tendency for cracks to form in both the deposited weld metal and the heat-affected zones, and this leads to unsound welds. Even if the alloy is being welded to a readily welded metal or alloy, e.g. mild steel, cracks may form in the heat-affected zone of the alloy that contains boron or zirconium. Weldability depends not only on the composition of the alloys that are being welded but also on the conditions of welding, including particularly the heat input and the degree of restraint of relative movement between the surfaces that are being welded together. If the heat input is high the surfaces being welded are displaced by thermal expansion to a greater extent than if it is low, thus increasing the stress to which the hot weld metal and the heat-affected zones are subjected during contraction when the welded structure cools. If there is complete restraint of relative movement, the deposited metal and the heat-affected zones are subjected to much more stress as a result of the contraction on cooling than if the welded surfaces can move towards one another. In either case cracking may occur.

The degree of restraint in a joint of a given configuration. also depends on the section size of the component parts. Thicker sections are less able to yield on cooling and thereby relieve the stress on the joint. In a thick section, e.g. one greater than one-half inch, the effects of thermal expansion at right angles to the plate surface lead to additional stress in the joint, which increases as the thickness increases.

The effect of boron and zirconium on weldability depends both on the composition of the alloys as a whole and on the content of boron or zirconium or both. Some of the alloys are not weldable even when they are free from boron and zirconium. In other alloys the presence of either boron or zirconium inhibits weldability, even under the most favorable welding conditions. Still other alloys can be welded when the contents of boron and zirconium are very small, but lose weldability when the contents of boron and zirconium are increased to desirable values.

Because of these facts it is not at present feasible to make use of the alloys having the highest high-temperatur'e properties if components are to be fabricated by methods that include welding, particularly when thick sections are concerned.

We have now discovered a way in which age-hardenable alloys containing boron and/or zirconium, in amounts sufficient to substantially increase strength and ductility, can be made weldable without adversely affecting strength or ductility.

An object of the present invention is to provide high temperature alloys having high strength, ductility and weldability.

Another object of this invention is to provide high temperature, age-hardenable. alloys containing boron and/or zirconium which can be welded without cracking.

A further object of this invention is to provide a welded, high temperature alloy free from cracks and other weld defects.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawings in which:

FIGURES 1 to 3 show the permissible levels of boron and/or zirconium as a function of hafnium content in alloys of three different base compositions, and

FIGURE 4 shows the effect of hafnium on the multiplying factor.

The invention is based on the surprising discovery that the weldability of alloys of the kind in question containing boron or zirconium or both is much improved if the alloys contain a small amount of hafniums, and generally speaking, the present invention contemplates weldable, e.g., arc-weldable or otherwise, age-hardenable, nickel base alloys containing boron and/or zirconium with small additions of hafnium. The improvement due to hafnium appears to be only a little affected by the base composi tion of the alloy, but to be dependent upon the boron and zirconium contents.

Extremely small additions of hafnium, that is to say as little as 0.005% or less, improve the weldability of the alloys, but the greatest improvement is obtained with amounts of hafnium in the range of 0.007% to 0.07%. The way in which hafnium acts is not understood. One possibility is that the hafnium increases the melting point of grain boundary constituents and thus reduces or eliminates liquid films around the grains which provide lines of Weakness in the alloy during cooling after welding. Alternatively the hafnium addition may change the way in which the zirconium and boron are distributed in the alloy, and thus counteract their adverse effect on weldability. Whatever the mechanism by which it acts, this advantageous effect of hafnium enables us to produce welded articles in which at least one of the surfaces that are welded together is of an alloy of the kind in question that contains boron or zirconium or both and also hafnium in an amount such as to render the alloy or alloys Weldable despite the presence of the boron or zirconium or both.

Weldable alloys in accordance with the invention have a face-centered cubic lattice structure and comprise up to about 35% chromium, up to about 30% or even 45% cobalt, up to about 80% iron, up to about 1.5% carbon, up to about 10% manganese, up to about 2% copper, up to about 10% molybdenum, up to about 15% or 20% or even 27% tungsten, up to about 10% niobium, up to about 10% tantalum, up to about 8% silicon, up to about 8% titanium, up to about 8% aluminium, up to about 2% vanadium, at least one metal selected from the group consisting of boron and zirconium, an amount of hafnium effective to prevent cracking of the alloy on welding, and the balance essentially nickel in amounts of at least 7 .5%. One group of such alloys in which the strengthening phase contains titanium and aluminium comprises about 12% to 22% chromium, up to about 23% cobalt, up to about 40% iron, up to about 0.2% carbon, up to about 1% manganese, up to about 0.5% copper, up to about 6% molybdenum, up to about 2% tungsten, up to about 2% niobium, up to about 2% tantalum, up to about 2% silicon, about 0.2% to 3.5% titanium, about 0.1% to aluminium, 0.005 to 0.2% hafnium, at least one metal selected from the group consisting of boron and Zirconium,

and the balance essentially nickel in amounts of at least about 7.5%. Generally speaking the amount of hafnium present will be from 0.001% to 0.5%, e.g. about 0.005% to 0.2% hafnium.

The amount of hafnium required to provide weldability in an alloy of given base composition may readily be determined without the need to produce test plates of large numbers of alloys of different composition by a simple test in which weld deposits of the alloy under test is made between plates of an alloy of the base compositionfree from boron, zirconium and hafnium, the deposits being formed from cast filler rods containing varying amounts of these elements; such filler rods can be made quite easily.

In carrying out such tests, a vertical and horizontal plate of an alloy of the base composition under test were arranged in the form of an inverted T, the vertical plate being held A3" away from the horizontal plate by a spacer. The plates were joined and held in position by a' weld along one lower edge of the vertical plate and by metal supports welded to both plates and arranged at right angles to both of them, on the side on which the holding weld between the plates was made. The plates forming the T were free from boron, zirconium and hafnium.

The test weld was made between the other lower edge of the vertical plate and the adjacent surface of the horizontal plate, using the inert-gas-shielded tungsten-arc process, using a A" diameter filler rod of the alloy of which the weldability was being tested. This had the same base composition as the plates of the T, but also contained one or more of boron, zirconium and hafnium. A single pass was made, and the resulting weld deposit was inspected with the naked eye, the absence of any visible cracks being taken as the criterion of weldability of the alloy of the composition of the deposit. The results of such tests on alloys of three different base composition were used to construction FIGURES 1 to 3 of the accompanying drawings, each of which is a graph in which the boron contents are plotted as abscissae and the zirconium contents as ordinates.

FIGURE 1 relates to alloys all nominally containing 20% chromium, 16% cobalt, 2.4% titanium and 1.2% aluminium, the balance being substantially all nickel, except for varying amounts of boron, zirconium and hafnium. Each of the lines in FIGURE 1 indicates the approximate boundary zone for weldability in accordance with the hafnium content, those alloys with compositions such as to fall below the line being Weldable. Thus it will be seen that in the absence of hafnium only alloys containing up to either 0.004% boron or 0.04% zirconium, or lesser amounts of both, can be welded, and these contents are not enough to give the desired high-temperature strength. When the hafnium content is 0.03%, alloys containing up to 0.02% boron and up to 0.13% zirconium can be Welded.

It will readily be appreciated that FIGURE 1 can be used to determine the amount of hafnium required in an alloy of any given boron and zirconium content. Thus an alloy containing 0.005% boron and 0.02% zirconium is indicated by the point X in FIGURE 1, which is just above the 0.005% hafnium line, and so should contain more than 0.005 hafnium to be Weldable. However, it is also above the 0.1% hafnium line, so 0.1% hafnium is too much.

FIGURE 1 also shows that the beneficial effect of hafnium decreases as the hafnium content increases above 0.03%, but the upper limit of the hafnium content that brings about improvement depends not only on the total content of boron and zirconium but also upon their relative contents. Thus in the boron-free alloy the presence of 0.1% hafnium actually decreases the weldability, and the upper limit of the hafnium content in such an alloy is 0.08%. In a zirconium-free alloy, however, hafnium contents of 0.2% or more improve the weldability.

The facts graphically shown in FIGURE 1 can be mathematically expressed as follows:

FIGURE 2 relates to the welding of alloys nominally containing 42% nickel, 16% chromium, 3.3% molybdenum, 1.2% titanium and 1.2% aluminium, the balance being substantially all iron, except for varying quantities of boron, zirconium and hafnium. It will be seen that in an alloy (Y) containing 0.005% boron and 0.02% zirconium, 0.01% hafnium will confer weldability. Again 0.1% hafnium is too much.

FIGURE 3 relates to alloys all nominally containing 15% chromium, 20% cobalt, 5% molybdenum, 1.2% titanium and 4.6% aluminium, the balance being nickel except for varying quantities of boron, zirconium and hafnium. Alloys of this base composition are unweldable in the absence of boron and zirconium, as is shown by FIGURE 3. The invention enables these alloys to be welded even when they contain boron and zirconium. It will be seen, for example that in an alloy (Z) again containing 0.005% boron and 0.02% zirconium, 0.01% hafnium is not enough, but only a little more is required. On the other hand 0.1% hafnium is too much.

The facts graphically shown in FIGURES 2 and 3 can be mathematically expressed as follows:

The increased tolerance for boron and zirconium with changes in hafnium content is shown by the reduction in the value of the multiplying factor for these elements in the equations. In FIGURE 4 of the accompanying drawings the multiplying factors for both boron and zircopium are plotted against hafnium content, the curves in full lines relating to the alloys of FIGURE 1, those in broken lines to the alloys of FIGURE 2, and those in chain lines to the alloys of FIGURE 3. FIGURE 4 clearly shows the desirablity of working in the range of 0.007% to 0.07% hafnium.

The equations given above relate to the composition of both the weld deposit and the heat-affected zones when the weld has been made.

In determining the hafnium content of an alloy of the kind in question regard must, of course, be paid to the possible effect of dilution of the alloy by a weld metal of composition different from that of the alloy.

Use is made of these facts in the invention by including hafnium in high temperature age-hardenable alloys that contain boron or zirconium or both and producing articles or components from them by welding with or without a filler.

A welded article according to the invention may consist of a single piece of an alloy having two surfaces Welded together to form, for example, a tube; of two components of the same alloy welded together; of two components of different alloys each of the kind in question welded together; or of a component of an alloy of the kind in question welded to a weldable metal or alloy. In the last-mentioned case, the beneficial effect is to prevent cracking in the heat affected zone of the alloy of the kind in question.

The welding may be effected with or without a filler. If the filler is used it may conveniently be of an alloy of the kind in question, which preferably but not necessarily also contains boron or zirconium or both. If it does contain boron or zirconium or both it should contain hafnium as well. The use of a filler of an alloy of the kind in question which is free from boron and zirconium leads to loss of strength at the weld. Therefore these elements are preferably present in such a filler, and it is desirable also to offset their effect by the inclusion of hafnium in the filler. The most uniform properties throughout a welded structure are generally obtained when the surfaces that are welded together and the filler used in the welding are all of the same alloy.

When, however, the design of the (welded article is such that high strength is not required in the weld, though of course cracking must be avoided, a filler that is less susceptible to cracking may advantageously be used. Again, when the parts to be welded are of dissimilar alloys, it is advantageous to use a filler different in composition from, but compatible with both the alloys.

The nickel base alloys which are weldable in accordance with this invention and the alloys for use as filler material may be prepared in the usual manner of preparing high temperature alloys. In this regard, preparation by vacuum melting is satisfactory but is not essential.

Hafnium and zirconium commonly occur together in nature, and it may be convenient to introduce the desired amounts of hafnium and zirconium by means of an addition agent containing both of these metals, e.g. a nickelzirconium-hafnium alloy.

For the purpose of giving those skilled in the art a better understanding of the invention, the following illustrative examples are given:

EXAMPLE I An alloy, prepared in the usual manner, contained 20% chromium, 16% cobalt, 2.4% titanium, 1.2% aluminium, 0.003% boron, 0.02% zirconium, 0.08% hafnium, balance essentially nickel. A second alloy, prepared in the same manner, contained 0.11% hafnium, but otherwise had a composition identical to the first. A third alloy,

prepared in the same manner, was free from hafnium but otherwise had a composition identical to the first two alloys. Butt welds were made between pairs of inch thick plates of the alloys by the fine wire process under highly restrained conditions, using a filler of the same composition as the plates being welded. The weld cracked when the alloy was hafnium free but was sound when the hafnium content was 0.08% and again when it was 0.11%.

EXAMPLE II An alloy, prepared in the usual manner, contained 42% nickel, 16% chromium, 3.3% molybdenum, 1.2%titaniurn, 1.2% aluminium, 0.004% boron, 0.02% zirconium, 0.1% hafnium, balance substantially iron. Another alloy, prepared in the same manner, had an identical composition to the first except that it did not contain hafnium. Butt welds were made between pairs of A3 inch thick plates of the alloys by the metal-inert gas short are proc ess under highly restrained conditions, using a filler of the same composition as the plates being welded. The heat affected zone of the hafnium free alloy showed cracks while the weld made with the hafnium containing alloy was sound.

EXAMPLE III This is an example of welding with a non-matching filler material. An alloy, prepared in the usual manner, contained 42% nickel, 16% chromium, 3.3% molybdenum, 1.2% titanium, 1.2% aluminium, 0.003% boron, 0.02% zirconium, 0.07% hafnium, balance essentially iron. Another alloy, prepared in the same manner, had an identical composition to the first except that it did not contain hafnium. Butt joints were made between pairs of inch thick plates of the alloys, under highly re strained conditions, using the metal-inert gas spray transfer welding process. The filler material employed was a nickel-base alloy containing 16% chromium, 10% iron, 2% manganese and 3% titanium, the balance being nickel. The plates of hafnium-free alloy cracked in the heat-affected zone, but sound welds were obtained between those of the hafnium-containing alloy.

The presence of hafnium in the amounts required by the invention in alloys of the kind in question that contain boron or zirconium or both has not been found to impair the stress-rupture properties of the alloys.

The good welding characteristics displayed by the alloys of this invention, despite the presence of appreciable amounts of boron and/or zirconium, greatly enhance their potential for high temperature applications such as, for example, use in aircraft gas turbines as jet pipes, flame tubes and jet silencers.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A crack-free welded article having at least one metal body with a fused joint therein with at least one of the surfaces at the fused joint being made of an age-hardenable nickel-containing alloy having a face-centered cubic lattice structure and being composed of at least one metal from the group consisting of iron, cobalt and chromium; iron, when present, being present in an amount up to cobalt, when present, being present in an amount up to 45%; chromium when present, being present in an amount up to 35%, up to about 1.5% carbon, up to about 10% manganese, up to about 2% copper, up to about 10% molybdenum, up to 27% tungsten, up to about 10% niobium, up to about 10% tantalum, up to about 8% silicon, up to about 8% titanium, up to about 8% aluminum, up to about 2% vanadium, at least one element selected from the group consisting of boron in an amount up to 0.03% and zirconium in an amount up to 0.3% to strengthen and improve the ductility of the alloy, hafnium in an amount from 0.001% to 0.5% effective to prevent cracking of the welded article, and the balance essentially nickel in an amount of at least 7.5%.

2. A Welded article according to claim 1 in which all the welded surfaces are of an alloy of the same kind.

3. A welded article according to claim 1 in which the hafnium content of the alloy is from 0.007% to about 0.07%.

4. A Welded article according to claim 1 in which the hafnium is present in the amount of about 0.03%.

5. A welded article in accordance with claim 1 wherein the alloy is composed of about 42% nickel, about 16% chromium, about 3.3% molybdenum, about 1.2% titanium, about 1.2% aluminium, about 0.004% boron, about 0.02% zirconium, about 0.1% hafnium, and the balance substantially iron with normal amounts of impurities.

6. A welded article in accordance with claim 1 wherein the alloy is nickel-base and is composed of about 20% chromium, about 16% cobalt, about 2.4% titanium, about 1.2% aluminium, at least about 0.001% boron, at least about 0.02% zirconium and about 0.08% to 0.11% hafmum.

7. A weldable age-hardenable nickel-containing alloy composed of about 12% to 22% chromium, up to about 23% cobalt, up to about 40% iron, up to about 0.2% carbon, up to about 1% manganese, up to about 0.5% copper, up to about 6% molybdenum, up to about 2% tungsten, up to about 2% niobium, up to about 2% tantalum, up to about 2% silicon, about 0.2% to 3.5% titanium, about 0.1% to 5% aluminium, about 0.005% to 0.2% hafnium, at least one metal selected from the group consisting of boron in an amount up to 0.03% and zirconium in an amount up to 0.3% and the balance essentially nickel in an amount of at least 7.5%.

8. A filler material in accordance with claim 7 wherein the hafnium is present in amounts of about 0.007% to 0.07%.

9. A filler material in accordance with claim 7 wherein the hafnium is present in the amount of about 0.03%.

References Cited UNITED STATES PATENTS 2,428,033 9/1947 Nachtman 29196.6 3,024,109 3/1962 Hoppin.

3,184,577 5/1965 Witherell 128.8 3,201,233 8/1965 Hull 75-128.8 3,262,777 7/1966 Sadowski 75 12s.s 3,303,023 2/1967 Dulis 75- 12s.s 3,342,974 9/1967 Wallner 75 123 FOREIGN PATENTS 912,814 12/1962 Great Britain.

HYLAND BIZOT, Primary Examiner US. Cl. X.R.

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