METHOD FOR MANUFACTURING A DOUBLE-LAYERED HEAT EXCHANGE WALL

Abstract

A method for manufacturing a double-layer heat-exchange wall including first and second metal layers includes the following successive steps: (i) providing a first metal sheet forming the first layer, a second metal sheet forming the second layer, and a leaf of iron Fe.sup.0 having a thickness of between 10 m and 100 m; (ii) assembling the first and second metal sheets and the leaf of iron Fe.sup.0, the leaf interposed between the first and second metal sheets; (iii) mechanical pressing of the assembly at a minimum pressure of 1 MPa; (iv) peripheral welding of the pressed assembly; and (v) heat treatment of the welded assembly, the heat treatment being implemented by hot isostatic pressing conducted at a temperature of between 800 C. and 1200 C., at a pressure of between 10.sup.8 Pa and 2.10.sup.8 Pa, for a period of between 1 hour and 3 hours.

Claims

1. A method for manufacturing a double-layer heat-exchange wall comprising a first layer and a second layer, the first and second layers being metallic, this manufacturing method comprising the following successive steps (i) to (v), and optionally (vi): (i) the provision: of a first metal sheet intended to form the first layer and having a thickness e.sub.1, of a second metal sheet intended to form the second layer and having a thickness e.sub.2, and of a leaf of iron Fe.sup.0 having a thickness e.sub.3 of between 10 m and 100 m and, advantageously, between 50 m and 100 m; (ii) the assembly of the first and second metal sheets and the leaf of iron Fe.sup.0, the leaf being interposed between the first and second metal sheets, (iii) the mechanical pressing of the assembly obtained at the end of the previous step at a minimum pressure of 1 MPa; (iv) the peripheral welding of the pressed assembly obtained at the end of step (iii); (v) the heat treatment of the welded assembly obtained at the end of step (iv), this heat treatment being implemented by hot isostatic pressing conducted at a temperature of between 800 C. and 1200 C., at a pressure of between 10.sup.8 Pa and 2.10.sup.8 Pa, for a period of between 1 hour and 3 hours; and, optionally, (vi) a supplementary treatment such as curving, bending, quenching, normalised ageing or annealing.

2. The method according to claim 1, wherein steps (i) and (ii) are respectively replaced by the following steps (i) and (ii): (i) the provision: of a first metal sheet intended to form the first layer and having a thickness e.sub.1, and of a second metal sheet intended to form the second layer and having a thickness e.sub.2, this second metal sheet comprising, on one of its surfaces, a coating of iron Fe.sup.0, this coating having a thickness e.sub.3 of between 10 m and 100 m and, advantageously, between 50 m and 100 m, the coated second metal sheet having a thickness e.sub.2 such that e.sub.2=e.sub.2+e.sub.3; and (ii) the assembly of the first metal sheet and of the coated second metal sheet, the coating of iron Fe.sup.0 being placed between the first and second metal sheets.

3. The method according to claim 2, wherein the coating of iron Fe.sup.0 is obtained by cold spraying of iron powder Fe.sup.0 on one of the surfaces of the second metal sheet.

4. The method according to claim 1, wherein the welding step (iv) is implemented by an arc welding method with a non-meltable electrode, where appropriate in the presence of a filler metal.

5. The method according to claim 1, further comprising a step of cleaning the surfaces of the first metal sheet and the surfaces of the coated second metal sheet, this cleaning step being implemented prior to the assembly step (ii).

6. The method according to claim 1, further comprising a step of grinding the first and second metal sheets, this grinding step being implemented prior to the assembly step (ii).

7. The method according to claim 1, further comprising at least one step of grinding the assembly, this or these grinding steps being implemented prior to the welding step (iv) and/or prior to the heat treatment step (v).

8. The method according to claim 1, which does not comprise a degassing step between the mechanical pressing step (iii) and the welding step (iv) and/or between the welding step (iv) and the heat treatment step (v).

9. The method according to claim 1, wherein the first and second metal sheets are produced from a material comprising iron, this material advantageously being selected from iron Fe.sup.0 and a steel.

10. The method according to claim 1, wherein the materials of the first and second metal sheets are identical.

11. The method according to claim 1, wherein the thicknesses e.sub.1 and e.sub.2 of the first and second metal sheets are between 1 mm and 30 mm, advantageously between 1 mm and 5 mm, and preferentially between 1 mm and 2 mm.

12. The method according to claim 2, further comprising a step of cleaning the surfaces of the first metal sheet and the surfaces of the coated second metal sheet, this cleaning step being implemented prior to the assembly step (ii).

13. The method according to claim 2, further comprising a step of grinding the first and second metal sheets, this grinding step being implemented prior to the assembly step (ii).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0085] FIG. 1 illustrates the evolution of the progression of a fatigue crack (denoted a and expressed in mm), at ambient temperature, as a function of the number of cycles (denoted N) of two double-layer walls in accordance with the invention (denoted RS and CS) and of a reference similar solid wall (denoted Massive).

[0086] FIG. 2 illustrates the evolution of the equivalent thermal conductivity (denoted and expressed in W/m.Math.K) as a function of temperature (denoted T and expressed in K) of two double-layer walls in accordance with the invention (denoted RS and CS) and of a reference similar solid wall (denoted Massive).

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

1. Manufacture of double-layer walls by the method according to the invention and of a reference wall

[0087] 1.1. A first double-layer wall, denoted RS, was manufactured by the method according to the invention.

[0088] Rolling of two metal sheets made from Eurofer-97 was implemented so as to confer thereon a thickness of 6.00 mm (+0.0/0.1 mm) for the first metal sheet and a thickness of 4 mm (+0.0/0.1 mm) for the second metal sheet.

[0089] Rolling of a sheet of metallic iron Fe.sup.0 was implemented until a leaf having a thickness of 100 m was obtained.

[0090] After grinding and then cleaning of the surfaces of the two metal sheets, the two metal sheets and the leaf were assembled in a sandwich by interposing this leaf of metallic iron between the first and second metal sheets.

[0091] The mechanical pressing of the assembly was then implemented by exerting a pressure of 1 MPa by means of a press and then peripheral welding by TIG was implemented over the entire periphery of the assembly.

[0092] The assembly thus welded was then subjected to heat treatment by implementing a hot isostatic pressing (HIP) cycle conducted at a temperature of 1100 C. and at a pressure of 1200 bar (1.210.sup.8 Pa) for 1 hour, and then to supplementary heat treatments of quenching after maintaining a temperature of 980 C. for 30 minutes and of ageing at 760 C. for 90 minutes.

[0093] At the end of these heat treatments, the double-layer wall RS is obtained.

[0094] 1.2. A second double-layer wall, denoted CS, was manufactured by the method according to the invention.

[0095] Rolling of two metal sheets made from Eurofer-97 was implemented so as to confer thereon a thickness of 6.00 mm (+0.0/0.1 mm) for the first metal sheet and a thickness of 4 mm (+0.0/0.1 mm) for the second metal sheet.

[0096] A deposition by cold spraying of a metallic iron powder was then implemented on one of the surfaces of the second metal sheet so as to form a coating of iron with a thickness of more than 100 m.

[0097] After grinding of the deposit to a thickness of 100 m and then cleaning of the surfaces of the two metal sheets, assembly of the first metal sheet and of the coated second metal sheet was implemented, the coating of metallic iron being positioned between the first and second metal sheets.

[0098] The assembly thus obtained was next subjected to the steps of mechanical pressing, welding, heat treatment by HIC and supplementary heat treatments described in part 1.1. above.

[0099] At the end of these heat treatments, the double-layer wall CS is obtained.

[0100] 1.3. A reference wall, denoted Massive, was also produced.

[0101] Rolling of a metal sheet made from Eurofer-97 was implemented so as to confer thereon a thickness of 10.00 mm (+0.0/0.1 mm).

[0102] The metal sheet was next subjected to the steps of heat treatment by HIC and supplementary heat treatments described in part 1.1. above.

[0103] At the end of these heat treatments, the reference wall Massive is obtained.

2. Characterisation of the Double-Layer Walls RS and CS and of the Reference Wall Massive

[0104] 2.1. Bending test pieces of 101055 mm were taken from each of the walls RS, CS and Massive. A notch of 2 mm, marked by the point A on FIG. 1, was formed in each of the test pieces, respectively denoted RS, CS and Massive, to allow the initiation of a fatigue crack during fatigue loading.

[0105] The propagation of this notch was next examined by subjecting the test pieces to cycles of three-point bending stresses at constant maximum force of 60% of the yield strength of the material of the metal sheets. A minimum force of 150 N is maintained in order not to detach the tool from the test piece. The path of the crack is followed in situ by image correlation.

[0106] With reference to the zone marked B in FIG. 1, it is observed that the test pieces RS and CS according to the invention are characterised by a delayed propagation of the crack compared with that of the reference test pieces Massive.

[0107] With reference to the zone marked C in FIG. 1, it is also noted that the test pieces RS and CS according to the invention exhibit a stagnation of the length of the crack at the interphase (propagation distance of 6 mm). This leads to an increase in the service life of the double-layer walls RS and CS compared with that of the reference wall Massive.

[0108] These results clearly show that selecting a ductile interphase of Fe.sup.0 makes it possible to significantly modify the crack propagation speed and to significantly increase the service life under fatigue at ambient temperature of the undamaged layer.

[0109] 2.2. The thermal conductivity of each of the test pieces RS, CS and Massive was measured.

[0110] Referring to the results illustrated on FIG. 2, it is observed that the test pieces RS and CS manufactured by the method according to the invention have a thermal conductivity A very close to the reference test piece Massive and that this coefficient of thermal conductivity represents at least 80% of the thermal conductivity of the reference wall Massive for the double-layer wall CS and close to 95% for the double-layer wall RS.

BIBLIOGRAPHY

[0111] [1] US 2013/0205861 A1 [0112] [2] CN 203928838 U [0113] [3] US 2013/070889 A1 [0114] [4] GB 2 241 339 A