GB1571330A

GB1571330A - Production of closure members

Info

Publication number: GB1571330A
Application number: GB585177A
Authority: GB
Original assignee: Dervaux SA
Current assignee: Dervaux SA
Priority date: 1976-02-11
Filing date: 1977-02-11
Publication date: 1980-07-16
Also published as: JPS5298816A; DK56677A; JPS5943541B2; FI770405A; DK146376C; NL7701465A; FR2341039B1; NL174229C; IT1082462B; NL174229B; DK146376B; ES456217A1; SE422338B; SE7701511L; DE2705344C2; FR2341039A1; DE2705344A1; SU849986A3

Description

(54) IMPROVEMENTS IN OR RELATING TO THE PRODUCTION OF CLOSURE MEMBERS (71) We, ETABLISSEMENTS DERVAUX a Societe anonyme existing under the laws of France of 71 rue de Monceau, Paris (8e), Seine, France, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: The invention relates to a method of producing a closure member intended to cooperate with a seat in a hot and corrosive environment. It relates more particularly, though not exclusively, to the manufacture of valves for internal combustion engines.

In known manner, valves of this type comprises a head which, integral with a stem, cooperates with a seat to ensure the closure of a gas inlet or outlet conduit.

When an engine is supplied with heavy oil, it is known that the combustion products contain various salts, such as sodium vanadates and complex sulphur compounds. The effect of these various precipitates is to impair the good seal of the surfaces of the cylinder head seats and valve seating surfaces which are in contact. In addition and all the more when the temperature is high, they cause ocrrosion peculiar to themselves.

To prevent this corrosion, the solutions which have hitherto been used generally in the valve industry have proved ineffective.

The Applicant has directed its research firstly to fighting against the corrosion proper and then against the solid deposits which prevent a seal of the surfaces in contact.

According to the present invention there is provided a method of producing a closure member having a seating surface intended to cooperate with a seat in a hot and corrosive environment, the method comprising, (a) forming a part from a first corrosion resistant alloy composed of nonwferrous metals and including a predominent proportion of nickel and a smaller proportion of chromium, (b) providing a seating surface for said part by fusing thereto a second corrosion resistant alloy which includes a predominant proportion of cobalt and an amount of chromium substantially equal to the difference between the weight percentages of chromium and nickel in the first alloy, said fusion being carried out at a temperature which effects inter-diffusion of the constituents of the first and second alloys thereby leading to the formation of a seating surface comprised of a third alloy containing chromium and nickel in substantially equal proportions, (c) thermally treating the seating surface to effect homogenization of the composition of the third alloy, (d) subjecting the seating surface to working in order to obtain a reduction of its grain size and hardening of its structure, and (e) ageing the closure member.

A closure member prdduced in accordance with the method of the invention not only resists corrosion, but also has a hardness which makes its use possible on engines in which the combustion products form deposits.

Preferably the first corrosion resistant alloy contains the predominant proportion of nickel and at least 25%, more preferably at least 30% by weight of chromium. The most preferred first alloy is one containing 30% by weight of chromium and 62% by weight of nickel. The alloys specified above as the preferred first alloys are generally considered as being unsuitable for forming valves for an engine using heavy oil, owing to their low hardness. However, as a result of the working step in the method of the invention they may be used for forming valves and also provide a positive solution to the problem of high temperature corrosion.

The second corrosion resistant alloy comprising a predominant proportion of cobalt and weight percentage of chromium which is substantially equal to the difference between the weight percentages of nickel and chromium in the first alloy. Preferably, the second alloy includes, in addition to the cobalt and chromium, tungsten and/or molybdenum together with various hardening agents. The preferred second alloy is one which contains substantially 51% by weight cobalt, 32% by weight chromium, 140/0 by weight tungsten, 2% by weight niobium and 1% by weight carbon.

The third alloy, which is formed by interdiffusion of the components of the first and second alloys, preferably comprises of the order of 30% by weight of each of chromium and nickel.

The seating surface of the closure member, formed of the third alloy, provides effective resistance to corrosion coupled with the desired hardness.

Preferably also, the step of fusing the second alloy to the first alloy is effected at a temperature of 30000C and at a fairly high speed in order to be able to utilise the principle of additivity of the components, i.e. to favour the intimate mixing and fusion of the elements composing the first alloy and the second alloy at a temperature which is greater than that at which certain of its components burn. As a result of this fusion step, there is inter-diffusion of the components of the first and second alloys with the result that a seating surface is produced which is composed of a third alloy including substantially equal amounts of chromium and nickel, preferably of the order of 30% by weight of each of chromium and nickel.

The thermal treatment step, i.e. step (c), is carried out by heating at least the area of the seating surface to a very high temperature, preferably of the order of 3000 C, to obtain homogenization of the composition of the metal forming the seating surface. This thermal treatment further improves the resistance to corrosion of the seating surface.

The working step, i.e. step (d), may be either a cold working or a hot working. In the latter case it is preferred to effect the working at a temperature higher than the temperature to which the closure member will operate, but less than the temperature which causes dissolution of the third alloy.

It is apparent from the aforesaid that after hot or cold working, the alloys used for improving the life expectancy of the closure members, alloys which are chosen for their resistance to corrosion, also make it possible to obtain the desired hardness for the seating surface in order that the latter ensures crushing of solid combustion products, without any danger of deterioration.

The working is followed by an ageing process step (e), carried out at least on the area of the seating surface. Preferably, this ageing is carried out at a temperature very slightly greater than the intended operating temperature of the part.

The ageing process causes stabilisation of the structure of the seating surface and thus, at the operating temperature of the part, prevents this structure from being subject to internal movements promoting corrosion, as is normally the case with austenitic alloys. It thus guarantees the stability of this structure in the long term.

The following examples will make it easier to understand how the method of manufacture according to the invention is carried out.

In all these examples, the closure members which have been produced were all in the shape of a valve head having a diameter of 40 mm and a height of 23 mm. The seating surface formed an angle of 45O with respect to the flat upper side of the valve head which was integral with a section of stem having a diameter of 10 mm and a length of 9 mm. This seating surface was provided by incorporating the second alloy (described more fully below) in a groove of 5 mm having a diameter at the base of the groove of30 mm.

EXAMPLE 1 This relates to the manufacture of a series of six samples referred to by the numerals 1 to 6 all having the shapes and dimensions shown above.

The body of all these samples was produced from a metal alloy A, which was resistant to corrosion and essentially comprised 62% nickel, 30% chromium, of the order of 0.05% carbon and traces or components of various other metals or residual components. This alloy corresponds to that sold by the French company Aubert et Duval under the name "Nimonic 80EA3".

The "second" alloy for producing the seating surfaces of these samples was a metal alloy B which was resistant to corrosion and comprised: 51% cobalt, 32% chromium, 14% tungsten, 1% carbon and 2% niobium. This alloy is sold by the French company Aubert et Duval under the name 'Allacnte 52T".

For all the samples of this example, deposition of the second alloy was carried out in the groove by electrical arc fusion in a neutral atmosphere, at a temperature of the order of 30000 C. This deposition was carried out on a part which had been previously heated to a temperature of the order of 500"C.

In all cases, chemical analysis of the seating surface area obtained by transfer of the components of the two alloys showed that it was composed of 31% nickel, 31% chromium, 26% cobalt, 7% tungsten, 1% niobium, 0.5% carbon and traces of other metals or impurities.

These various samples can therefore only be differentiated by the stages of their manufacture: SAMPLE 1 (Comparative): A blank of the sample was produced by forging a cylindrical billet of the alloy A at 1050 C. This blank was subjected to semi-finishing forging at 1 0500C, then after cooling, was machined to produce the groove. Then, a single strand of the alloy B was manually placed in the groove to form a single annulus therein. After slow cooling, this deposition was subjected to a second homogenisation fusion at high temperature, of the order of 30000 C. The part thus produced was subjected to finishing forging at 7000 C, ensuring its working.

SAMPLE 2: The latter was produced exactly in the same way as the preceding sample, but after working, was subjected to an ageing process at 7000C for 16 hours.

SAMPLE 3 (Comparative): Forging of the blank from a cylindrical billet of the alloy A at 10500C was immediately followed by finishing forging at 1050 C. The groove was machined and the alloy B deposited in this groove in the same way as for Sample I. Slow cooling followed. In other words, this sample was subjected neither to homogenisation, nor to working of its seating surface.

SAMPLE 4 (Comparative): This sample was produced exactly as in the case of Sample 3 but, was also subjected to ageing at 700 C for 16 hours.

SAMPLE 5 (Comparative): After forging of the blank from a cylindrical billet of the alloy A at 10500C, semi-finishing forging at 10500C and machining of the groove, a single strand of the alloy B was manually placed in the latter to form a single annulus therein. Immediately afterwards and without further homogenisation of the deposit, the blank was subjected to finishing forging at 7000 C, ensuring its working.

SAMPLE 6 (Comparative): This sample was manufactured in an identical manner to Example 5, but was subjected to ageing at 700 C for 16 hours.

After manufacture, these various samples were subjected to rough machining of their seating surfaces.

It should be noted that in these particular examples, the research was carried out in order to resolve roblem of a valve operating at 6500C. bue to this, the working and ageing operations were carried out at a temperature of 7000 C, which is thus 50 higher than the operating temperature of the valve in question.

It is obvious that for any other operating temperature of the valve, the temperatures of the working and ageing operations are modified accordingly.

The samples of the Example were subjected to corrosion tests, during which each of them was placed in a vessel containing a powdery mixture composed of sodium sulphate and sodium metavanadate, whose molar proportions were respectively 14% and 86%. The vessel containing the sample covered by the eutectic mixture was placed in an oven in order to be heated for a period of 2 hours, to a constant temperature of 650"C, corresponding to the operating temperature of an internal combustion engine valve.

Since all the samples withstood the synthetic corrosive medium for the period of the tests, one then proceeded with another series of tests in a more corrosive medium.

To this end, the initial mixture was replaced by pure vanadium pentoxide.

Under the same test conditions as above, both as regards duration and temperature, the various samples showed no visible corro simon. The tests were then continued by increasing the oven temperature in stages of 50 C. Thus, in order to achieve a selective test, it was necessary to increase the temperature to 9000 C.

The results of these tests are given in the accompanying table showing the method of manufacture of each sample and its hardness measured when cold, after manufacture.

This table shows that the samples resist corrosion better when their seating surface has undergone homogenisation of its structure and when they have been worked.

On the other hand, these tests have not been able to show the advantage of ageing, since they were carried out over too short a period.

In fact, ageing is desirable for stabilising the structure and in the long term and during use of the part, firstly preventing the intergranular corrosion and secondly preventing the part from being subjected to dimensional variations which may cause poor closure of the seat by the valve and local destruction of this valve.

This table also shows that homogenisation and working of the seating surface area for SAMPLES 1 2 3 4 5 6 Manufacture Rough forging at 10500C x x x x x x Semi-finishing forging at 10500C x x o o x x Finishing forging at 10500C o o x o o o Cooling x x x x o o Machining the groove x x x x x x Deposition of alloy B x x x x x x Slow cooling x x x x o o Homogenisation x x o o o o Finishing forging at 7000C x x o o x x (working) Ageing at 7000C o x o x o x Mean Hardness When cold in Hv measured 525 560 320 345 510 570 at the seat Corrosion Tests 2 hours in pure V2 05 at 9000 no cor- no cor- very very average average rosion rosion corroded corroded cor- cor rosion rosion the samples of the Example make it possible to obtain very satisfactory hardness when cold and, in all cases, much greater than that of approximately 300 Hv obtained by conventional methods of manufacture not using these two stages of manufacture during processing of similar alloys.

It is thus proved that the method of manufacture according to the invention makes it possible to obtain mechanical parts, in particular valves, whose resistance in the long term, both from the structural, struct ural, chemical as well as mechanical point of view, is much greater than that of tradi tional valves, which makes it possible to increase the period of time between in spections and even to increase this period to the value corresponding to the interval between inspections of a marine engine.

This advantage is very important, since it reduces the time for which ships are station ary and consequently provides a substantial increase in their profitability and the cost of transportation.

It is obvious that this method of manu facture, which was described in the case of its application to valves, may be used for manufacturing any other mechanical part operating in a corrosive medium such as: flap valves, valve parts etc.

Naturally, the alloys A and B, mentioned in these examples, may be replaced by any other alloys which resist corrosion and in particular, by alloys having nickel and chromium contents each having a value of at least 25% and preferably more than 30%.

WHAT WOE CLAIM IS: 1. A method of producing a closure mem ber having a seating surface intended to co operate with a seat in a hot and corrosive environment, the method comprising, (a) forming a part from a first corrosion resistant alloy composed on non-ferrous metals and including a predominant proportion of nickel and a smaller proportion of chromium, (b) providing a seating surface for said part by fusing thereto a second corrosion resistant alloy which includes a predominant proportion of cobalt and an amount of chromium sub stantially equal to the different between the weight percentages of chromium and nickel in the first alloy, said fusion being carried out at a temperature which effects inter-diffusion of the constituents of the first and second alloys thereby leading to the formation of a seating surface comprised of a third alloy containing chromium and nickel in substantially equal proportions, (c) thermally treating the seating surface to effect homogenization of the composition of the third alloy, (d) subjecting the seating surface to working in order to obtain a reduction of its grain size and hardening of its structure, and (e) ageing the closure member.

2. Method according to claim 1 wherein the third alloy includes of the order of 30% by weight of each of chromium and nickel.

3. Method according to claim 1 or 2 wherein the fusion of the second alloy to the first alloy is effected at a temperature of the order of 30000 C.

4. Method according to any one of claims 1 to 3, wherein said first alloy contains substantially 30% by weight chromium and 62% by weight nickel and said second alloy contains

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SAMPLES

1 2 3 4 5 6 Manufacture Rough forging at 10500C x x x x x x Semi-finishing forging at 10500C x x o o x x Finishing forging at 10500C o o x o o o Cooling x x x x o o Machining the groove x x x x x x Deposition of alloy B x x x x x x Slow cooling x x x x o o Homogenisation x x o o o o Finishing forging at 7000C x x o o x x (working) Ageing at 7000C o x o x o x Mean Hardness When cold in Hv measured 525 560 320 345 510 570 at the seat Corrosion Tests 2 hours in pure V2 05 at 9000 no cor- no cor- very very average average rosion rosion corroded corroded cor- cor rosion rosion the samples of the Example make it possible to obtain very satisfactory hardness when cold and, in all cases, much greater than that of approximately 300 Hv obtained by conventional methods of manufacture not using these two stages of manufacture during processing of similar alloys.

substantially 51% by weight cobalt, 32% by weight chromium, 14% by weight tungsten, 2% by weight niobium and 1% by weight carbon.

5. Method according to any one of claims 1 to 4, wherein the homogenization comprises heating the seating surface to a temperature of 30000C to obtain homogenisation of the composition of the third alloy.

6. Method according to any one of claims 1 to 5, wherein working is effected at a temperature higher than the temperature at which the member is intended to operate, but less than the temperature at which the third alloy dissolves.

7. Method according to any one of claims 1 to 6, wherein ageing is carried out at a tempera.

ture which is very slightly higher than that at which the member is intended to operate.

8. Method as claimed in claim 1 of produced ing a closure member substantially as wherein.

before described.

9. A closure member when produced by the method of any one of the claims 1 to 8.