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Title - Development of micro-alloyed High Strength welded Steel tubes for two and three wheelers.
The present invention relates to a development of Microalloyed High Strength weldable sleds applicable in automobile Industiy. More particularly, the present invention relates to a development of micro alloyed steel having high-strength and weldable properties adaptable to manufacture of tubes applicable to automobile pacts for two or three wheelers.
Background of The Present Invention
In modem days, the main problem for the autosnobite industry is the fuel efficiency of vehicles, in order to preserve the environment, Fbur wheelers industries have already taken step to solve this problem by weight reduction of automobiles by using high strength steels tubes for chassis and body parts. An emphasise h tried on two and three wheelers industries for reduction of weight, so that a huge saving in fuel can be envisaged

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Presently the two wheeler industry is using some ordinary grades of steel tubes with higher thickness in order to achieve the sectional strength and stability of the motor bikes. Once high strength with reduced thickness is used, the amount of weight reduction can be achieved as high as 15% -20%.
Objects of The Present Invention
It is therefore an object of the present invention to propose a development of Microalloyed steel having high-strength and weldable properties adaptable to manufacture of tubes applicable to automobile parts which enables for reduction of weight of vehicles up to 15% - 20% imparting superior dent and crash resistance.
Another object of the present invention is to propose a development of micro-alloyed sled having high-strength and weldable properties adaptable to manufacture of tubes applicable to automobile parts, which increases the fuel efficiency.

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A still another object of the present invention is to propose a development of Microalloyed steel having high-strength and weldable properties adaptable to manufacture of tubes applicable to automobile parts, which reduces the environmental pollution.
A further object of the present invention is to propose a development of Microalloyed steel having high-strength and weldable properties adaptable to manufacture of tubes applicable to automobile parts which does not affect the load bearing capacity.
A still further object of the present invention is to propose a development of Microalloyed steel having high-strength and weldable properties adaptable to manufacture of tubes applicable to automobile parts which possess 50% higher yield strength and 35% Tensile Strength.
An yet further object of the present invention is to propose a development of Microalloyed steel having high-strength and weldable properties

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adaptable to manufacture of tubes applicable to automobile parts which takes care of passenger safety by using thinner gauge high strength strip as input for tube making.
Summary of The Invention
A series of high strength precision welded tabes have been developed using Microalloyed steel possessing high strength and good weldability compared to conventional steels adaptable to automobile parts for two and three wheelers. An addition of small amount of alloying element hike. Ti, Nb and Vanadiun in low carbon steel shows a significant result in grain refining and precipitation hardening of low carbon steel Table-l shows the chemical composition of steel for present invention.


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The steel are then thermo mechanically processed and the micro alloying
are very effective in producing high strength steel.
Table: 2 Mechanical Properties and microstructures of Steel strip studied
(HR)

In Table 1, the 2 both law carbon micro alloyed steel are newly developed for manufacturing of tubes applicable to automobile parts. Sted 1 was hot rolled, odd rolled (70% - 80%) and then batch anneded Where as steel 2 was hot rolled in to thickness (2 mm - 3.5 mm) and used for tube making (34.0 to 57.15 mm diameters) directly by electric resistance welding.
The mechanical properties of steel strips used fir tube forming are shown in table-2. The yield strength values of the steel 1 and steel 2 were 330 MPa and 367 MPa respectively.which is more than 30% and

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45% respectively than that of existing steel 11M steels ate used for making strips whkh after further processing by electric resistance welding are used for production of tubes. The mechanical properties of the tubes of steel l and steel 2 are shown in Table 3;
The steel 1 with micro alloying clement after tube rolling showed the
Table: 3 Comparative Statement of Mechanical Properties of Rolled ERW tubes manufactured from the developed Microalloyed steel as compare to existing steel.


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yield strength increases from 330 MPa to 390-445 MPa. The % Elongation of the tubes reduces marginally due to cold tubes forming (Table 2 and Table 3). The yield strength of toe steel 1 tube after normalizing was found to 395 MPa which is also 58% higher than the initial strip. The basic strength of the strip was higher because fee fine gram microstracture produced after hot rolling and also due to cartadc/or carbonMde precipitation. After cold rolling and annealing the strength was farther enhanced due to refinement of the irricrostructures and precipitation hardening. As the cooling rate is higher in normalizing than annealing, the microstructure produced after normalizing became finer, hence the tensile properties are further increased.
The mechanical properties of all the steels before tube making and in the tube and normalize tube conditions were measured AD as welded tube made from both steel grades of different diameters are shown in Table 3. The tubes were tested as per IS:3074 for fall flattering keeping the weld at 0° and 90° and for drift expansion was found 40%

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which is satisfoctay result Micro hardness traverses were taken across tfao wold zone was also found satisfactory as shown in fig -1. There is a maiginaL increase in hardness at weldment
A comparative statement of improvement in mechanical properties and weight reduction over the convontional grade is shown in Table 4
Table; 4 Shows the percentage of increase in mechanical properties and the percentage of Microalloyed tubes over conventional tubes.


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BRIEF DESCRIPTION OF THE ACCOMPANYING
DRAWING
fig - 1. Shows the micro hardness across the welded zone (a) 34 mm x 2.50 mm strip (b) 37.15 mm x 3.0 mm strips.
Pig - 2, Shows a micro - structure across the weld region of high tensile welded tube of two section of steel 2.
(A) For Base metal
(B) Weldment
(C) HAZ.
Fig - 3 A - Steering tube after end flaring and end attaching
Fig- 3B-Steering Housing
fig - 4A & 4B - Shows testing rig for torture trade test simulation with
actual three wheeler Assembly.
DETAIL DESCRIPTION OF A PREFERRED EMBODIMENT
OF THE INVENTION:
Rg 1& 2 Shows ttie micro hardness traverses across flic weld zones of

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two wdded tubes (1,2) in Fig 1 of steel 2. It also shows that there is a marginal increase in hardness at the weldment The basic strength of this steel is higher because the microstructure (4) in Fig 2 produced after thermo mechanical processipg is very fine and also contains acicular fernite. After welding the microstructure (5) in Fig 2 become finer due to fester cooling rate during cooling after welding giving rise to hardness at this location where as the microetructures at HAZ (6) in Fig 2 contains acicular fcirite like structure. The microstructure of the base (4) in Fig 2 and wddment (5) in Fig 2 and HAZ (6) in Fig 2 are shown in fig-2.
Kg - 3A & 3B - Shows the steering tube (7) in Rg 3A after flaring and machining and housing (8) Fig 3B assembly. A chassis with micro -alley steering housing tube (7) Fig 3A of 5.4 mm x 3 mm size replaced 54 mm x 3.2S mm size and middle, rear cross tubes of 41.283d.2S size were tested on simulated conditions in laboratory and obtained satisfactory result
Fig - 4 A & 4B - Shows a testing rig for torture track test simulation with

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actual Ihreo-whcieler assembly. The test chassis assembled with dummy engine and loaded with 1-ton pay load was mounted on 3 poster rig comprising of servo hydraulic linear actuators and each wheel being in a fixture mounted on each poster. Vertical movement of
vehicle is restrained in such a way that only desired degrees of freedom were possible drive file for giving input to actuators was generated by recording acceleration, front suspension displacement and strain data by naming vehicle loaded with payload as per text condition on torture track. This data was converted into drive file using road load simulation software. AH the tubes successfully with stood the accelerated torture test conditions confirming their suitability for use in vehicle.

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1. Micro-alloyed ated having high strength and weldable properties
comprising
• a chemical composition in wt % C - 0.05 to 0.10. Mn - 1.0 to 1.5, Si ~ 0.06 max, P-0.02 max, S - 0,04 max, Al - 0.02 - 0,06 (V+Nb+Ti)-0,02 to 0.05,
2. A process of preparing Microaflqycd steel as claimed in daim 1
comprise Mowing steps
• Taktag liquid hot metal from blast furnace in a ladle;
• Pouring the Kquid metal into a basic oxygen furnace (L D) for
sted making wiA alloying addition;
• Castffigmadeintheformofslab;

3. The micaroa&oy sled as claimed in daim 1 which on further
processing in hot rolling converted to steel stips.
4. The Microalloyed steel as claimed in claim 1 which on further
processing in odd rolling converted to steel strips Mowed by

5. The Microalloyed steel strips produced in claim 3 which are
converted into tubes by electric resistance welding followed by
annealing at 700° C
6. The Microalloyed steel strips produced as claimed in claim 4 winch
on farther processing converted to tubes by electric resistance
welding followed by normalising at 90°.
7. The tubes are manufactured in claims 5 & 6 which shows an
increase of yield strength of about 50% and 30% respectively over
the conventional grade without sacrificing formability.
• »»
& The tubes are manufactured in claim 5 & 6 wherein a reduction of component weight by 16 to 23% depending upon tube size ami tioo.
9. The Microalloyed steel as claimed in claim 1 which possess
characteristic of yield strength 390 - 430 MPa and percentage of
dongpticn30-38.
10. The Microalloyed sled as claimed in claim 1 which is characterized
by a micro texture (<110>)//RD)and (<111>//ND) fibre

when measured through EBSD, The prosenco of fibre, particulariy the texture components like {323} <131> and {554} <225> in boih steel were responsible for good amount of fermabiltiy,
11, The Microalloyed sled as claimed in ckrim 1 which is characterized
by high strength due to presence of the fine grains of caibide or
carbonitride precipitation (ASTM No. 8) after thermo-mechanical
treatment
12, The Microalloyed steel tubes as claimed in proceeding claims
wherein the microstnicture across the weld zone of high strength
ERW tubes revealed wry fine polygonal ferrite structure of base,
fine acicular fernite of weld and coarse acicular fenitemHAZ.

13. The Microalloyed steel tubes as claims in the preceding claims
wherein the tubes manufactured conforms the technical parameter
as specified in IS: 3074 standard
14. Automobile components produced by the Microalloyed steel as
claimed in any of the preceding cliams,

15.The Microalloyed steel having high strength and weldable propertim as substantially described and illustrated herein with reference to accompanying drawings.