Title of Invention	METHOD OF FRICTION WELDING PROCEDURE FOR FERRITIC STAINLESS STEEL RODS
Abstract	This invention relates to a friction welding process by adapting ferritic stainless steel rods, comprising the steps of rotating the weldable components in a friction -welding machine; applying an upsetting force; and allowing the components to undergo a post-weld annealing treatment. The post-weld annealing treatment further comprises the steps of; keeping the weld sample in an annealing furnace; heating the weld sample to 800°C at the rate of 200°C per hour; maintaining the temperature of 800°C for 120 minutes; cooling the component to 500°C inside the furnace at the rate of 150°C per hour; and air cooling the component from 500°C to room temperature.

Title of Invention

METHOD OF FRICTION WELDING PROCEDURE FOR FERRITIC STAINLESS STEEL RODS

Abstract

This invention relates to a friction welding process by adapting ferritic stainless steel rods, comprising the steps of rotating the weldable components in a friction -welding machine; applying an upsetting force; and allowing the components to undergo a post-weld annealing treatment. The post-weld annealing treatment further comprises the steps of; keeping the weld sample in an annealing furnace; heating the weld sample to 800°C at the rate of 200°C per hour; maintaining the temperature of 800°C for 120 minutes; cooling the component to 500°C inside the furnace at the rate of 150°C per hour; and air cooling the component from 500°C to room temperature.

Full Text	FIELD OF INVENTION This invention relates to adapting ferritic stainless steel rods with Type 430 grade (17% Chromium), which are not generally weldable grades. More particularly, the invention relates to a friction welding procedure adapting ferritic stainless steel rods with post-weld annealing cycle. BACKGROUND OF THE INVENTION AND DIFFICULTIES OF PRIOR ARTS Welding of ferritic stainless steel (FSS) rods is very much required for automobile and general structural components. Brittleness of FSS welds was found in the existing procedure without post-weld annealing. Due to its poor weldability (grain coarsening and poor toughness, poor ductility in FSS weld and heat affected zone), FSS are not preferred but instead (three times costly) the austenitic stainless steel (ASS) rods are being used in industries. Not many research papers and patents are available in the field of welding of FSS 430 rods. One of the research papers by Ginn (1980) studied the non-fusion welding process such as friction welding of austenitic stainless steel components for its toughness behaviour. Friction welding is a popular process for joining of machine components, which are all in the cylindrical shapes. OBJECTS OF THE INVENTION It is therefore an object of the invention to propose a friction welding procedure for ferritic stainless steel rods. Another object of the invention is to propose a friction welding procedure for ferritic stainless steel rods, in which a post-weld annealing heat treatment cycle is implemented to improve the toughness and ductility of the FSS weld samples. A further object of the invention is to propose a friction welding procedure for ferritic stainless steel rods, which includes a bend test to confirm the reduction in weld zone hardness of FSS weld samples. These and other objects and advantages of the invention will be apparent from the ensuing description. SUMMARY OF THE INVENTION For industrial FSS applications friction welding process was established. Due to brittleness in FSS welds the use of FSS are not very common in industries. The proposed post-weld annealing was done at 800°C for two hour soaking time and it was found to improve the ductility of the FSS welds. Generally post-weld annealing is not carried out for solid-state welding process. But due to poor ductility in FSS rods, post-weld annealing was introduced in this invention. The heating rate was maintained at 200°C per hour in the furnace. The FSS weld samples were cooled in the furnace upto 500°C at the cooling rate of 150°C per hour. Afterwards air cooling was carried out from 500°C upto room temperature. This procedure achieved good toughness, ductility in FSS welds. Post-weld annealing parameters and friction welding procedures were optimized. During post-weld annealing cycle, FSS weld samples experience the redistribution of chromium in weld and heat affected zone, reduction in hardness, internal stresses are relieved and the improvement in weld ductility was achieved. Post-weld annealing of FSS friction joint results were found lower in weld zone hardness - 180 Hv compared to the 360 Hv hardness of as-welded samples. Friction welds exhibited good impact toughness value of 60 J/mm2, compared to the base metal impact toughness value of 78 J/mm2. Excellent bend ductility was observed in the bend test after post-weld annealing. With this new method of post-weld annealing for FSS rods was established using friction welding process. The problems of poor weldability, poor weld toughness and poor weld ductility were improved in this invention. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING Fig. 1 - schematically shows a friction welding process including the sequences of friction welding of round components with the application of external pressure for proper welding. Figure 2 graphically shows the post-weld annealing heat treatment cycle for FSS rods, including peak temperature : 800°C, soaking duration : 120 minutes, cooling upto 500°C in furnace. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION Friction welding is a solid phase welding process in which joining of metals is produced at a temperature lower than the melting temperature of the two parts being joined. This is a method of welding in which the "welding" heat is generated by sliding or rubbing together of two mating surfaces under pressure. The sequence of operations necessary to produce a friction weld of rods is shown in Figure 1. High quality, mass production, dissimilar metal joints are made and no weld consumables are used in this method. Automobile axle, engine exhaust valves, twist drills, pump shafts and valve flanges are the most common industrial components that are welded by friction welding process. A new method of welding procedure with post-weld annealing cycle and testing of weld details are given below : - In this invention friction welding process was selected for welding of FSS rods for structural and automobile components in industries. The benefit of friction welding process helps to achieve very tiny interface and fine grain size in the fusion zone with 5-10 microns compared to 400 microns in welds made by gas tungsten arc welding (GTAW) process. Metallurgically, the friction weld quality is superior since no fusion related defects are taking place. An interesting concept of friction welding was attempted to join FSS rods with 14 mm diameter. Continuous drive friction welding was done and the optimum set of friction weld parameters were selected based on the weld quality, tensile strength and the location of failure (at base metal region). The test results, microstructural features, post-weld annealing and fracture surface studies of weld samples are analysed. Friction welding does not involve melting, but the weld zone is mechanically worked ; therefore the bond region is made of finer- grained microstructure than that is found in the FSS base metal. Friction welding parameters with post-weld annealing, tensile test results are established. Using these as base parameters, further optimization of welding conditions was done using a statistical factorial design procedure. Optimised friction weld base parameters are completed. Hence it can be expected to achieve better weld metal properties in FSS through friction welding than that can be resulted by fusion welding processes. For confirming the friction weld parameters, it was ensured that during the examination of macrostructure, the cut section of the weld should have uniform flash at top and bottom of weld, parallel weld width in the cross section and complete bonding to be observed at the centre of the joint. After the initial set of welding trials, tensile tests were conducted to assess the quality of welds. It was found that many of the tensile test samples failed at weld zone and only few weld samples failed in the base metal region. Tensile strength, hardness and impact toughness of welds were evaluated. The weld joints were tested to get the tensile strength of the joints. The results of the tensile test of the joints in the as-received condition are established. To study the effect of ductility and toughness of the joints, post-weld annealing was carried out. Some of the weld joints, failed at the weld region during tensile test. Though the tensile strength of joint was higher than that of base metal, the failure at the joint was due to coarse grains and the weld defects such as very fine pores, resulting in cleavage brittle fracture. The tensile test, notch tensile test, static shear test, impact test, bend test, macro, micro-examinations and scanning electron microscope (SEM) fracture surface studies were carried out to assess the quality of the friction weld joints. With the optimum set of weld parameters, sufficient tensile strength of the welds was obtained. Failure occurred at the base metal region and not at the joint. WE CLAIM 1. A friction welding process by adapting ferritic stainless steel rods, comprising the steps of: - rotating the weldable components in a friction -welding machine; - applying an upsetting force; and - allowing the components to undergo a post-weld annealing treatment; characterized in that the post-weld annealing treatment further comprises the steps of: a) keeping the weld sample in an annealing furnace; b) heating the weld sample to 800°C at the rate of 200°C per hour; c) maintaining the temperature of 800°C for 120 minutes; d) cooling the component to 500°C inside the furnace at the rate of 150°C per hour; and e) air cooling the component from 500°C to room temperature. 2. A testing method to determine the ductility and toughness of ferritic stainless steel rods in a welding procedure as claimed in claim 1, comprising the steps of: - carrying out a tensile test of the FSS weld samples; - carrying out a notch tensile test of the weld samples; - carrying out a static shear test of the weld samples; - carrying out an impact test of the weld samples; - carrying out a bend test of the weld samples; - carrying out a macro and micro examination of the weld samples; and - effecting a fracture surface study of the weld samples using a scanning electron microscope. 3. The method as claimed in claim 2, further comprising a step of comparing as welded and post -weld annealed bend test results of the weld samples. 4. A friction welding procedure by adapting ferrictic stainless steel rods, as substantially described and illustrated herein with reference to the accompanying drawings. This invention relates to a friction welding process by adapting ferritic stainless steel rods, comprising the steps of rotating the weldable components in a friction -welding machine; applying an upsetting force; and allowing the components to undergo a post-weld annealing treatment. The post-weld annealing treatment further comprises the steps of; keeping the weld sample in an annealing furnace; heating the weld sample to 800°C at the rate of 200°C per hour; maintaining the temperature of 800°C for 120 minutes; cooling the component to 500°C inside the furnace at the rate of 150°C per hour; and air cooling the component from 500°C to room temperature.

Full Text

FIELD OF INVENTION
This invention relates to adapting ferritic stainless steel rods with Type 430 grade
(17% Chromium), which are not generally weldable grades. More particularly,
the invention relates to a friction welding procedure adapting ferritic stainless
steel rods with post-weld annealing cycle.
BACKGROUND OF THE INVENTION AND DIFFICULTIES OF PRIOR ARTS
Welding of ferritic stainless steel (FSS) rods is very much required for automobile
and general structural components. Brittleness of FSS welds was found in the
existing procedure without post-weld annealing. Due to its poor weldability (grain
coarsening and poor toughness, poor ductility in FSS weld and heat affected
zone), FSS are not preferred but instead (three times costly) the austenitic
stainless steel (ASS) rods are being used in industries.
Not many research papers and patents are available in the field of welding of
FSS 430 rods. One of the research papers by Ginn (1980) studied the non-fusion
welding process such as friction welding of austenitic stainless steel components
for its toughness behaviour. Friction welding is a popular process for joining of
machine components, which are all in the cylindrical shapes.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a friction welding procedure
for ferritic stainless steel rods.

Another object of the invention is to propose a friction welding procedure for
ferritic stainless steel rods, in which a post-weld annealing heat treatment cycle
is implemented to improve the toughness and ductility of the FSS weld samples.
A further object of the invention is to propose a friction welding procedure for
ferritic stainless steel rods, which includes a bend test to confirm the reduction in
weld zone hardness of FSS weld samples.
These and other objects and advantages of the invention will be apparent
from the ensuing description.
SUMMARY OF THE INVENTION
For industrial FSS applications friction welding process was established. Due to
brittleness in FSS welds the use of FSS are not very common in industries. The
proposed post-weld annealing was done at 800°C for two hour soaking time and
it was found to improve the ductility of the FSS welds. Generally post-weld
annealing is not carried out for solid-state welding process. But due to poor
ductility in FSS rods, post-weld annealing was introduced in this invention. The
heating rate was maintained at 200°C per hour in the furnace. The FSS weld
samples were cooled in the furnace upto 500°C at the cooling rate of 150°C per
hour. Afterwards air cooling was carried out from 500°C upto room temperature.
This procedure achieved good toughness, ductility in FSS welds. Post-weld
annealing parameters and friction welding procedures were optimized. During
post-weld annealing cycle, FSS weld samples experience the redistribution of

chromium in weld and heat affected zone, reduction in hardness, internal
stresses are relieved and the improvement in weld ductility was achieved.
Post-weld annealing of FSS friction joint results were found lower in weld zone
hardness - 180 Hv compared to the 360 Hv hardness of as-welded samples.
Friction welds exhibited good impact toughness value of 60 J/mm2, compared to
the base metal impact toughness value of 78 J/mm2. Excellent bend ductility was
observed in the bend test after post-weld annealing. With this new method of
post-weld annealing for FSS rods was established using friction welding process.
The problems of poor weldability, poor weld toughness and poor weld ductility
were improved in this invention.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig. 1 - schematically shows a friction welding process including the sequences
of friction welding of round components with the application of external pressure
for proper welding.
Figure 2 graphically shows the post-weld annealing heat treatment cycle for FSS
rods, including peak temperature : 800°C, soaking duration : 120 minutes,
cooling upto 500°C in furnace.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Friction welding is a solid phase welding process in which joining of metals is
produced at a temperature lower than the melting temperature of the two parts
being joined. This is a method of welding in which the "welding" heat is
generated by sliding or rubbing together of two mating surfaces under pressure.
The sequence of operations necessary to produce a friction weld of rods is
shown in Figure 1. High quality, mass production, dissimilar metal joints are
made and no weld consumables are used in this method. Automobile axle,
engine exhaust valves, twist drills, pump shafts and valve flanges are the most
common industrial components that are welded by friction welding process.
A new method of welding procedure with post-weld annealing cycle and testing
of weld details are given below : -
In this invention friction welding process was selected for welding of FSS rods for
structural and automobile components in industries.
The benefit of friction welding process helps to achieve very tiny interface and
fine grain size in the fusion zone with 5-10 microns compared to 400 microns in
welds made by gas tungsten arc welding (GTAW) process. Metallurgically, the
friction weld quality is superior since no fusion related defects are taking place.
An interesting concept of friction welding was attempted to join FSS rods with 14
mm diameter. Continuous drive friction welding was done and the optimum set
of friction weld parameters were selected based on the weld quality, tensile

strength and the location of failure (at base metal region). The test results,
microstructural features, post-weld annealing and fracture surface studies of
weld samples are analysed. Friction welding does not involve melting, but the
weld zone is mechanically worked ; therefore the bond region is made of finer-
grained microstructure than that is found in the FSS base metal.
Friction welding parameters with post-weld annealing, tensile test results are
established. Using these as base parameters, further optimization of welding
conditions was done using a statistical factorial design procedure. Optimised
friction weld base parameters are completed. Hence it can be expected to
achieve better weld metal properties in FSS through friction welding than that
can be resulted by fusion welding processes. For confirming the friction weld
parameters, it was ensured that during the examination of macrostructure, the
cut section of the weld should have uniform flash at top and bottom of weld,
parallel weld width in the cross section and complete bonding to be observed at
the centre of the joint. After the initial set of welding trials, tensile tests were
conducted to assess the quality of welds. It was found that many of the tensile
test samples failed at weld zone and only few weld samples failed in the base
metal region. Tensile strength, hardness and impact toughness of welds were
evaluated.
The weld joints were tested to get the tensile strength of the joints. The results
of the tensile test of the joints in the as-received condition are established. To
study the effect of ductility and toughness of the joints, post-weld annealing was
carried out. Some of the weld joints, failed at the weld region during tensile test.
Though the tensile strength of joint was higher than that of base metal, the

failure at the joint was due to coarse grains and the weld defects such as very
fine pores, resulting in cleavage brittle fracture. The tensile test, notch tensile
test, static shear test, impact test, bend test, macro, micro-examinations and
scanning electron microscope (SEM) fracture surface studies were carried out to
assess the quality of the friction weld joints. With the optimum set of weld
parameters, sufficient tensile strength of the welds was obtained. Failure
occurred at the base metal region and not at the joint.

WE CLAIM
1. A friction welding process by adapting ferritic stainless steel rods,
comprising the steps of:
- rotating the weldable components in a friction -welding machine;
- applying an upsetting force; and
- allowing the components to undergo a post-weld annealing
treatment;
characterized in that the post-weld annealing treatment further
comprises the steps of:
a) keeping the weld sample in an annealing furnace;
b) heating the weld sample to 800°C at the rate of 200°C per
hour;
c) maintaining the temperature of 800°C for 120 minutes;
d) cooling the component to 500°C inside the furnace at the
rate of 150°C per hour; and

e) air cooling the component from 500°C to room
temperature.
2. A testing method to determine the ductility and toughness of ferritic
stainless steel rods in a welding procedure as claimed in claim 1,
comprising the steps of:
- carrying out a tensile test of the FSS weld samples;
- carrying out a notch tensile test of the weld samples;
- carrying out a static shear test of the weld samples;
- carrying out an impact test of the weld samples;
- carrying out a bend test of the weld samples;
- carrying out a macro and micro examination of the weld samples;
and
- effecting a fracture surface study of the weld samples using a
scanning electron microscope.

3. The method as claimed in claim 2, further comprising a step of comparing
as welded and post -weld annealed bend test results of the weld samples.
4. A friction welding procedure by adapting ferrictic stainless steel rods, as
substantially described and illustrated herein with reference to the
accompanying drawings.

This invention relates to a friction welding process by adapting ferritic stainless
steel rods, comprising the steps of rotating the weldable components in a friction
-welding machine; applying an upsetting force; and allowing the components to
undergo a post-weld annealing treatment. The post-weld annealing treatment
further comprises the steps of; keeping the weld sample in an annealing furnace;
heating the weld sample to 800°C at the rate of 200°C per hour; maintaining the
temperature of 800°C for 120 minutes; cooling the component to 500°C inside
the furnace at the rate of 150°C per hour; and air cooling the component from
500°C to room temperature.

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Patent Number

268359

Indian Patent Application Number

859/KOL/2008

PG Journal Number

35/2015

Publication Date

28-Aug-2015

Grant Date

27-Aug-2015

Date of Filing

08-May-2008

Name of Patentee

BHARAT HEAVY ELECTRICALS LIMITED

Applicant Address

REGIONAL OPERATIONS DIVISION (ROD), PLOT NO. 9/1, DJBLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA

Inventors:

#	Inventor's Name	Inventor's Address
1	DR. VARADHAN ANBAZHAGAN	WELDING RESEARCH INSTITUTE BHARAT HEAVY ELECTRICALS LIMITED, TIRUCHIRAPPALLI - 620 014
2	DR. KALIDASS ASOKKUMAR	WELDING RESEARCH INSTITUTE BHARAT HEAVY ELECTRICALS LIMITED TIRUCHIRAPPALLI - 620 014
3	DR. ARASAN RAJA	WELDING RESEARCH INSTITUTE BHARAT HEAVY ELECTRICALS LIMITED TIRUCHIRAPPALLI - 620 014

PCT International Classification Number

B29C 27/08

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA