surface hardening methods of steam turbine blades · 2017-10-18 · steam turbine blades are...
TRANSCRIPT
SURFACE HARDENING METHODS
OF STEAM TURBINE BLADES
Zoran Karastojković1, Momo Dereta2, Milesa Srećković3, Nikola Bajić4,
Zoran Janjušević5, Dragan Stojiljković6
Technical college, 11070 Novi Beograd, Blvd. Dr Zorana Đinđića 152a,
Vostok 7 –Ros-Sorab, 22400 Ruma, Karađorđeva 88,
Faculty of electrical engineering, 11000 Belgrade, blvd. kralja Aleksandra 73,
IHIS Technoexperts 11080 Belgrade, Batajnički put 23,
Institute for technology of nuclear and other mineral raw materials, 11000 Belgrade, Franchѐt d'Esperey 86,
SPIT, 16254 Bošnjace,
Every thermopower plant represents
a pretty complex system.
• It is evident that for safe working of the entire system many
elements/components are responsible.
• No dubt that one of the main machine component in every
thermopower plant are turbine blades, so they are often the
limiting component of a turbine and the entire power system.
• Their working life in a thermopower plant is over 100000h.
BLADES IN THERMOPOWER TURBINES
Some shapes&sizes of turbine blades
from thermopower plant
ABOUT BLADE/ELISE IMPORTANCE
According to some qualified opinions, the state of the art in producing of blade/elise has had the crucial effect on achieving the dominance of Great Britain in air during the II World war againt the Germans, and finaly for victory.
САМО НЕК СЕ ЗНА: НЕГДЕ КРАЈЕМ 70-ГОДИНА ПРОШЛОГ ВЕКА ЈЕДАН НАШ ИСТРАЖИВАЧ ИЗ ВИНЧЕ ЈЕ У ЕНГЛЕСКОЈ ДОКТОРИРАО НА ЛИВЕЊУ ОВАКВИХ ЛОПАТИЦА - АЛИ НАМА ЈЕ ТАДА, КАО ДРУШТВУ, БИО
ПРЕЧИ ЗАКОН О УДРУЖЕНОМ РАДУ...
НАСТАВАК СА ПРЕТХОДНОГ СЛАЈДА
...али зато ми за Икеју производимо
оклагије и кухињске даске!
MATERIALS USED FOR TURBINE BLADES
There is always a need for better materials, for achieving the
heavy servicing performances, so much researching in the field
of alloys and manufacturing techniques were done.
Here will be discussed next materials:
stainless steels, superalloys, titanium alloys and some ceramics
matrix composites.
Table 1. Stainless steels used for steam power
turbine blades in two standardsEN ГОСТ
Martensitic stainless steels
X12CrNiMoV12-3 1.4938; 1.4939 11ХН2В2Мф;
Х12Н2ВМф
X12Cr13 1.408 12X13;
X20Cr13 1.4021 20X13
X22CrMoV12-2 1.4922; 1.4293 20Х12ВНМф
X4CrNiMo16-5-1 1.4418 -
Precipitation hardening stainless steels
X5CrNiCuNb16-4 1.4542 -
X5CrNiCuNb14-5 1.4549 -
X5CrNiCuNb15-3 - -
SUPERALLOYS
Superalloys were developed in the 1940s.
Modern turbine blades often use nickel-based
superalloys that incorporate chromium, cobalt, and
rhenium, microalloyed with boron (<0,018mas%).
Another group of superalloys is on cobalt base.
The only one disadvantage of cobalt base alloys is in
high cost of this metal.
Turbine blades from superalloys are able
for directional solidification casting process
TITANIUM ALLOYS
EN ГОСТ
Titanium alpha near alpha alloy
Ti5Al2,5Sn 3.7114 -
Ti6Al2Sn4Zr2Mo 3.7155 ВТ3
Ti8Al1Mo1V - -
Titanium alpha-beta alloy
Ti6Al4V 3.7165 ВТ6
Ti6Al8V2Sn 3.7175 -
Ti6Al2Sn4Zr6Mo - -
Titanium beta-near beta alloy (not yet standardized)
Ti10V2Fe3Al - -
Ti13V11Cr3Al - -
Ti15V3Cr3Al3Sn - -
Scetch of some constitutional diagram
of titanium alloys
CERAMIC MATRIX COMPOSITES
In ceramic matrix composites (CMC) fibers are embedded
in a ceramic matrix, and such material are developed
mainly in use for gas turbine blades.
The main advantage of CMCs over conventional
superalloys is their light weight and high temperature
capability.
silicon base composites is consisting of silicon matrix
reinforced by silicon carbide fibers, which withstand
operating temperatures 100°-150°C higher than nickel
superalloys.
WHAT ARE REASONS FOR SURFACE HARDENING
OF BLADES
USABLE HARDENING METHODS FOR
TURBINE BLADES
Different methods for hardening of steam turbine blade
surface were developed&applied.
Some of them may be done at „new“ blades or partially
damaged.
The most known groups of usable methods for blade
hardening are: surface quenching, coating deposition by
chemical or electrochemical methods, brazing, hard-
surfacing (cladding) and shot peening („bombardment“).
Surface quenching
The outcomming part of a turbine blade some
producers treated by induction quenching.
If the parrent metal (with pearlitic-carbide
structure) shows hardness in range 260±20HV;
After induction hardnening (with tempered
martensitic structure) the hardness values usually
are in range 440±20HV.
(Electro)chemical depositionThere are two principal groups of deposition:
electrochemical (galvanic) and chemical (electroless)
method. As could be seen the uniformity of coat
thickness is superior at chemical deposition.
In chemical method is possible to
deposit not only metals but alloys.
One example of using chemical coating from Ni-P-B
alloy for protection a steam turbine blade
(martensitic steel ≈270HV) is provided in
termopower plant „Kolubara“, Serbia, by this autor.
The thickness of such uniform coatings in this
example was in range 20-25µm, with hardness
values about 500-540HV.
TIG cladding
The relatively large amount of heat input during
TIG welding/cladding is needed for melting of hard
(and heavy melted) materials,
Such great heating is undesirable when strong
tolerances of treated machine component must
remain.
This method is rare applicable for large surfaces.
Electrospark cladding
Electrospark deposition (ESD) is a pulsed micro-
welding process.
Electrospark deposition is used for small scale and
precision repair of high value worn or misfabricated
components.
For this method one could find terms as "spark
hardening", "electrospark toughening" or "electrospark
alloying".
Partially damaged blade may be repaired by deposition of
hard and tough coating by using a electrospark method, in
Fig. 6. is shown result when tungstencarbide (WC) is used
only at the turbine edge.
Brazing
Brazing as a production method, generally, is
disregarded.
But, brazing technology offers some specifics which
may be successfully applied for joining of a thin film
(layer) over a blade surface. Such film is made of a
corrosion resistant material, which also posses
antiwearing property.
Handling during brazing of such film needs pretty
skilled workers.
Laser cladding
Laser remelting in last decade became widely accepted
method for welding or cladding.
Cladding overlays b) and microstructure of laser
cladded and parent material c)
Plasma cladding
Plasma cladding is an able method for (re)melting
of material to be deposited, but this material
rather should be in a wire shape because the
powder is easily blown up.
Heating up of a parent metal in this method is
significant.
Shot peening
Shot peening is pretty simple cold working process,
similar to sandblasting: each (hard) particle
functions as a ball-peen hammer, producing
compressive residual stress layer, after that
mechanical properties of metals are modified.
The shot is used as round metallic, glass, wood, or
ceramic particles, with force sufficient to create
plastic deformation and then strengthening.
For shot peening of turbine-jet blades the most
valuable material are almond shells.
Shot peening in action is shown in Figs.
8a, b) and treated blades in Fig. 8c).
CONCLUSION
Steam turbine blades are exposed to heavy mechanical
loads at the moisture atmosphere.
So, their surfaces undergo to wearing and corrosion or
cavitation atack.
For satisfying such demands the steam turbine blades
should be manufactured from a qualitative material,
but some areas of blades need further hardening or
strengthening.
Here are shown contemporary methods for hardening
of steam turbine blades, which are applicable in
industrial circumstances.
ПОУКА (ИЛИ ЗАКЉУЧАК) НА СПРСКОМ:
Замена турбинских лопатица у једној
термоелектрани, у доба санкција, коштала је од
3-5 000000 марака.
Због блокаде земље оформљена је екипа људи
из: једне наше термоелектране, Машинског
факултета у Београду, Института за испитивање
материјала из Београда и Војно-техничког
института из Жаркова, да се такве лопатице (од
мартензитног челика) направе код нас.
Када је направљена прва лопатица, само по
геометрији, поносни професор је исту однео
неком из врха ЕПС-а.
Одговор је био: Ко вам је то рекао да радите?
ПИТАЊЕ ЗА ЖИКИНУ ШАРЕНИЦУ:
ДА ЛИ ЈЕ БОЉЕ ПРОИЗВОДИТИ
- ЈАКО СКУПЕ ЛОПАТИЦЕ ТУРБИНЕ ИЛИ
- ОКЛАГИЈЕ?