GB2424423A

GB2424423A - Component made from martensitic and precipation hardened steels

Info

Publication number: GB2424423A
Application number: GB0505999A
Authority: GB
Inventors: Stuart Richard Holdsworth; Ian John Chilton; Bruce Wynn Roberts; Herbert Bartsch
Original assignee: Alstom Technology AG
Current assignee: General Electric Technology GmbH
Priority date: 2005-03-23
Filing date: 2005-03-23
Publication date: 2006-09-27
Also published as: GB0505999D0

Abstract

An insert 3 made of an air hardenable martensitic steel is welded to a body 2 made of a precipitation hardenable steel using a filler metal which matches the steel of the body 2 to form a component. The body 2 is solution heat treated either before or after welding. The component is aged so that the body 2 and weld are precipitation hardened. After ageing at least a part of the insert 3 is transformed into martensite by rapid heating and air cooling followed by tempering. The component may be a forged steam turbine blade, with the martensitic insert 3 forming a part of the leading edge 4 of the blade.

Description

1 2424423 Local Enhancement of Erosion Resistance This invention relates

to the local enhancement of the erosion resistance of a component, in particular (but not solely) a steam turbine blade.

In a steam turbine, since the steam is very wet in the last stage region, water droplet erosion of the blades in this region can be a problem.

US-A-5 351 395 discloses a method in which a component constituting a steam turbine blade member consisting of a martensitic steel is cast, the component is subjected to solution annealing to make it suitable for welding, a metal alloy insert is tempered to a hardness less than that of the annealed component, the insert is welded to the leading edge of the blade member, the component and insert are subjected to ageing heat treatment, the component and insert are machined, and then the insert is hardened through substantially its entire thickness.

The present invention provides a method of locally enhancing the erosion resistance of a component having a body consisting of a precipitation hardening steel, the method comprising the steps of: (a) welding an insert consisting of an air hardenable martensitic steel to the body using a filler metal having a composition which matches the steel of the body; (b) applying solution heat treatment to the body, before or after step (a) ; (c) applying ageing heat treatment to the component, after steps (a) and (b) have been done, thereby providing both the body and the weld with a precipitation hardened microstructure, and (d) hardening the insert by a process comprising rapid heating and air cooling followed by tempering, after steps (a), (b), and (c) have been done, thereby providing the insert with a hard martensitic microstructure.

The invention also provides a component having a body consisting of a precipitation hardening steel and an insert consisting of an air hardenable martensitic steel, the insert being connected to the body by a weld having a composition which matches the steel of the body, and the insert having a hard martensitic microstructure.

Preferred and optional features of the invention are set forth in the subsidiary claims.

The invention will be described further, by way of example only, with reference to the accompanying drawing, in which the sole figure is a view of a steam turbine blade.

The blade 1 illustrated is to be mounted in the last stage of a steam turbine and has a body 2 containing an insert 3, in the leading edge portion 4 of the blade, adjacent to the end of the blade (tip 6) remote from the root 7.

The body 2 is forged from a low-carbon precipitation hardening (PH) steel. The region of the leading edge adjacent the tip 6 is the region most susceptible to erosion.

The body 2 consists of a low-carbon steel containing Cr and Ni, having the designation 1 5-5PH. In particular, this steel may have the following composition: up to 0.07 wt.% C, up to 1.0 wt% Si, up to 1.0 wt.% Mn, 13.0-15.5 wt% Cr, 3. 5-6.00 wt.% Ni, 1.4-4.5 wt.% total Cu and Mo, the Mo being optional, and 0.15-0.45 wt.% Nb, the balance being Fe and incidental impurities. Two examples of 15-5 PH steel are: (1) up to 0.07 wt.% C, up to 0.7 wt.% Si, up to 1.0 wt% Mn, 13.0-15.0 wt. % Cr, 5.0-6.0 wt.% Ni, 1.2-2.0 wt.% Mo, 1.4-2.1 wt.% Cu, and 0.15-0.30 wt. % Nb, the balance being Fe and incidental impurities; and (2) up to 0.07 wt.% C, up to 1.0 wt.% Si, up to 1.0 wt.% Mn, 14.0-15.5 wt. % Cr, 3.5-5.5 wt.% Ni, 2.5-4.5 wt.% Cu, and 0.15-0.45 wt.% Nb, the balance being Fe and incidental impurities.

The insert 3 consists of an air hardenable martensitic steel, i.e. a steel which is hardenable by a process comprising rapid heating and air cooling, this process producing a martensitic microstructure. Such a steel is suitable for hardening by a selective hardening process, such as induction hardening or flame hardening, which can produce a hardened surface layer. A suitable steel is one referred to as a high-carbon 12% Cr steel. In particular it may be a steel denominated as 12%CrMoV having the following composition: 0.18-0.24 wt.% C, 0.10-0.50 wt.% Si, 0.30-0.90 wt. % Mn, 11.0- 12.5 wt.% Cr, 0.30-0.80 wt.% Ni, 0.80-1.20 wt.% Mo, and 0.25-0.35 wt.% V, the balance being Fe and incidental impurities.

The insert 3 is welded to the body using a filler metal having a composition which matches the composition of the precipitation hardening steel of the body 2. The filler metal does not have to have precisely the same composition as the body. The filler metal is compatible with the steel of the body and fuses with it to produce a weld (weld metal) which is itself a precipitation hardening alloy steel. If the body is made of a 15-5PH steel, the filler metal is preferably also a 15-5PH steel. The filler metal preferably has the composition of the above-mentioned steel 15-5PH (1), whether the body is of 15-5PH (1) or 15-5PH (2).

For a steam turbine blade made of 15-5 PH steel, without the insert, a typical heat treatment procedure following blade forging would, for example, consist of the following sequence of treatments (the times and temperatures being approximate): solution treatment: hold for lh at 1000 C, then air cool; ageing treatment: hold for 4h at 530 C.

In accordance with the present invention the insert 3 may be welded to the body 2 either before or after the solution treatment.

Afler the ageing treatment, the insert can now be subjected to induction hardening or another selective hardening technique as mentioned above, without affecting the microstructure of the weld and body. The insert is provided with a martensitic structure that is harder than the body.

EXAMPLE

1) A blade body as described above is forged. The body consists of a steel having the composition I 5-5PH (1) mentioned above.

2) An insert as described above, consisting of the 12%CrMoV steel mentioned above, is welded to the body using a filler metal having the composition 1 5-5PH (1).

3) The blade (body and insert) is subjected to: solution treatment: lh, 1000 C, air cool, then ageing treatment: 4h, 530 C.

4) Final machining of the blade profile is carried out.

5) The leading edge portion of the insert is hardened and then tempered.

Thus the provision of the insert becomes an integral part of the blade forging production cycle, without having to modify the heat treatment applied to the body of the blade.

Welding an air hardenable martensitic steel to a precipitation hardening base steel, using a filler electrode that matches the base steel, enables established induction hardening heating processes to be applied to the hardenable material. The hardened material provides resistance to erosion. The heat treatment carried out after welding can fully stress relieve the welded joint while generating the required properties in the base steel.

Claims

CLAIMS: 1. A method of locally enhancing the erosion resistance of a

component having a body consisting of a precipitation hardening steel, the method comprising the steps of: (a) welding an insert consisting of an air hardenable martensitic steel to the body using a filler metal having a composition which matches the steel of the body; (b) applying solution heat treatment to the body; (c) applying ageing heat treatment to the component, after steps (a) and (b) have been done, thereby providing both the body and the weld with a precipitation hardened microstructure, and (d) hardening the insert by a process comprising rapid heating and air cooling followed by tempering, after stepr (a), (b), and (c) have been done, thereby providing the insert with a hard martensitic microstructure.
2. A method as claimed in claim 1, in which step (b) is done before step (a).
3. A method as claimed in claim 1 or 2, in which step (d) comprises induction hardening.
4. A method as claimed in any of claims ito 3, in which the air hardenable steel of the insert contains at least 0.1 wt.% C.
5. A method as claimed in claim 4, in which the said steel contains Cr, Mo, and V.
6. A method as claimed in claim 5, in which the said steel has the following composition: 0.18-0.24wt.% C, 0.l0-0.5Owt.% Si, 0.30-0.90 wt.% Mn, 11.0-12.5 wt.% Cr, 0.30-0.80 wt.% Ni, 0.80-1.20 wt.% Mo, and 0.25-0. 35 wt.% V, the balance being Fe and incidental impurities.
7. A method as claimed in any of claims 1 to 6, in which the precipitation hardening steel has the following composition: up to 0.07 wt% C, up to 1.0 wt% Si, up to 1.0 wt.% Mn, 13.0-15.5 wt% Cr, 3.5-6.00 wt. % Ni, 1.4-4.5 wt.% total Cu and Mo, the Mo being optional, and 0.15-0.45 wt.% Nb, the balance being Fe and incidental impurities.
8. A method as claimed in claim 7, in which the precipitation hardening steel has the following composition: up to 0.07 wt.% C, up to 0.7 wt.% Si, up to 1.0 wt% Mn, 13.0-15.0 wt.% Cr, 5.0-6.0 wt.% Ni, 1.2-2.0 wt.% Mo, 1.4-2.1 wt.% Cu, and 0.15-0.30 wt.% Nb, the balance being Fe and incidental impurities.
9. A method as claimed in claim 7, in which the precipitation hardening steel has the following composition: up to 0.07 wt.% C, up to 1.0 wt.% Si, up to 1.0 wt.% Mn, 14.0-15.5 wt.% Cr, 3.5-5.5 wt.%Ni, 2.5-4.5 wt.% Cu, and 0.15-0.45 wt.%Nb, the balance being Fe and incidental impurities.
10. A method as claimed in any of claims 1 to 9, in which the body is formed by forging.
11. A method as claimed in any of claims 1 to 10, in which the component is a steam turbine blade.
12. A method as claimed in claim 11, in which the insert is located in the leading edge portion of the blade.
13. A method as claimed in claim 11 or 12, in which the insert is located adjacent the end of the blade remote from the root of the blade.
14. A component having a body consisting of a precipitation hardening steel and an insert consisting of an air hardenable martensitic steel, the insert being connected to the body by a weld having a composition which matches the steel of the body, and the insert having a hard martensitic microstructure.
15. A steam turbine including a component according to claim 14.
16. A steam turbine as claimed in claim 15, in which the component is in the last stage of the turbine.
17. A method of locally enhancing the erosion resistance of a component, substantially as described in the Example.
18. A component substantially as described with reference to, and as shown in, the accompanying drawing.