FIELD OF THE INVENTION
The present invention relates to a process for manufacturing high quality steel for
application in cycle rim having selective chemical composition of said steel providing
improved properties like high hardness, strength, stiffness and weldability, making the rim
resistant to buckling under sudden impact load. More particularly, the cycle rim grade steel
of the invention is obtained by selective starting compositon and following defined process
steps, specifically totally eliminating Aluminium addition in any stage of the heats for such
steel so as to restrict the Al content to 0.005 wt% in final product. The steel composition so
obtained thus ensures fine grained microstructure and eliminates thin and elongated
sulphide inclusions and thus ensuring achieving said desired strength and stiffness
properties in rim steel of the invention and a characteristic sound of said rim while struck
that is indicative of corresponding desired quality.
PRIOR ART AND ITS LIMITATION:
The existing variety of the cycle rims are generally manufactured from alloy steel having the
chemical composition on wt % basis comprising %C-0.12 max, %Mn-0.60 max, %S and %P
0.050max, %Si-0.08 max, & % Si-0.08max. The essential properties for such product is
directed to achieve good formability and weldability and ensure a hardness value of
65(max) HRB. Since the alloying compositions usually have very wide range, the cycle rim
manufacturers faced a number of problems which included
1) Wide variation in chemical composition resulted in variation in hardness, weldability
and strength, creating problems at manufacturing stage.
2) Aluminium addition was being allowed to some extent in earlier Specification/alloy
compositions. Presence of Aluminium adversely affected the morphology of inclusions
and thereby reduced the stiffness of steel and a characteristic sound indicative of the
desired quality, was absent in rim steels where 'Al' was present. Because of the
lower stiffness of these rims, they had a tendency to buckle under sudden load.
BACKGROUND OF THE INVENTION:
There has been thus a continuing need to take care of the above problems in use of existing
grades of steel for cycle rim and developing an alloy composition for steel selectively
decided based on experimental observations and tests, for manufacturing of cycle rims as
the end product directed to achieving the following:
1) Variation in chemical compositions to be restricted to get consistency in hardness,
strength and weldability.
2) Addition of 'Al' at any stage of heat making was eliminated, to avoid adverse influence
on the morphology of sulphide inclusions and particularly, the thin and elongated
sulphide inclusions reducing weldability and stiffness properties of steel.
3) A uniform fine grain size essential for improved stiffness property of steel, obtained by
selectively controlling Finishing temperature in the range of 860°C-880°C and Coiling
temperature in the range of 660°C-680°C, to optimize a fine grain size, preferably
conforming to ASTM 8/9.
4) The best properties are achieved if the steel is truly balanced as revealed through
investigations and to get optimum deoxidation, it is imperative that the ingot top is flat.
Based on the above considerations, three different alternative grades/alloy compositions
without Al addition were preferred for the requirements of the cycle rim manufacturers.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to achieve an improved chemical composition of
steel and a process for manufacturing high quality cycle rim steel therefrom to ascertain
desired strength and stiffness properties.
A further object of the present invention is directed to eliminate addition of Al at any stage
of the heats for making of said cycle rim grade steel so as to limit the Al content to
0.005wt% and thus avoiding the harmful effects of thin and elongated sulphide inclusions in
said steel leading to sacrificing the stiffness, hardness or other desired properties in said
steel grade.
It is another object of the invention to achieve such chemical compositions and process,
capable to meet the requirements of various grades to produce tailor made products, and
specifically the cycle rims.
A still further object of the present invention is directed to a process ensuring eliminating
defects like lamination, scabs, burning, embedded scabs, crack and pulls and the like
surface imperfections to ensure desired quality of end product.
A still further object of the present invention is to ensure that the rim produced from steel
made through following the process of the invention that ensure a characteristic sound for
said steel, because the tubes made out of this steel generate a sound when hit which is
most sought after by the buyers, indicative of corresponding desired quality of the cycle rim
steel.
SUMMARY OF THE INVENTION
The basic aspect of the present invention therefore is directed to a process for the
manufacture of steel for cycle rims comprising the steps of,
(i) providing selective alloy steel composition ;
(ii) steel making in LD converter with initial additions in the ladle during tapping,
Nitrogen purging through the ladle bottom -and achieving desired uniform
composition of ingot;
(iii) slab making in slabbing mills wherein the cast ingots having desired alloy
composition are soaked at 1310°C-1320°C and rolled into desired thickness of
slabs ;and
(iv) hot rolling of slabs comprising heating slabs preferably to a temperature of
1250°C before rolling in order to maintain a finishing temperature in the range of
860°C-880°C and coiling temperature in the range of 660°C to 680°C , to optimize
a fine grain size preferably conforming to ASTM 8/9 and also optimizing the roll
crowns to obtain a profile of 20-70 microns and flatness < 50 I Units, such as to
obtain a steel grade having Wt % of C in the range of 0.06-0.11%; Mn in the
range of 0.30-0.50%; P in the range of 0.03-0.04%; S in the range of 0.03-
0.04%; Si in the range of 0.04-0.08%; Al in the range of 0.005%(max).
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING
EXAMPLE:
The present invention therefore relates to a grade of steel for manufacturing cycle rim
having selective composition providing desired properties of enhanced strength, hardness,
stiffness, free of any thin and elongated sulphide inclusions. The invention is also directed to
control on process parameters such as the heating, soaking, finishing and coiling
temperatures at the different stages of the process according to the invention, as already
stated in the preceding paragraph also having desired fine grained macrostructure required
for attaining said properties. It has also been experimentally established that said alloy
composition for the rim steel for rim manufacturing essentially require eliminating
aluminium addition in the heats during steel making. This is purely semi-killed heats and
aluminium addition is totally prohibited. Customers prefer this steel because the tubes made
out of this steel generate a characteristic sound when hit which is most sought after by the
buyers, that is indicative of desired quality and properties. Such steels are impossible to
make through continuous casting route and conventional ladle teeming to ingot casting
route is followed. The inherent surface defects of the products cast through ingot casting
route is taken care of through use of standard operating practices (SDP) of ladle
preparations and ingot teeming. The ingots are charged in soaking pits of slabbing mill
where special care is taken in order to avoid any burning of ingots. Further, surface
refinements of rolled slabs are done through extreme hot and cold scarfing. The slabs after
inspection are charged in re-heating furnaces in hot strip mill where it is rolled into HR coils.
The finishing temperature and coiling temperature are kept at 880°C and 670°C
respectively. The product is supplied as HR coils, to the customers as desired by them
through out the country.
The process of manufacturing the steel grade for use in cycle rims and its sequential steps
along with the different process parameters are illustrated with the help of following
example:
EXAMPLE:
To carry out the process of manufacturing steel for cycle rims, according to the present
invention following sequential steps are being followed:
i) providing selective alloy steel composition preferably having Wt % of C in
the range of 0.06-0.11%; Mn in the range of 0.30-0.50%; P in the range
of 0.03-0.04%; S in the range of 0.03-0.04%; Si in the range of 0.04-
0.08%; Al in the range of 0.005%(max).
ii) the steel making is carried out in LD converter wherein the initial additions
are made in the ladle during tapping. Sample is taken and based on the
analysis, final additions are made to obtain the desired composition.
Nitrogen is purged through the ladle bottom to get a uniform composition.
To obtain proper ingot top water addition is made on ingot top after
teeming.
iii) slab making from cast in got is carried out in slabbing mills wherein the
cast ingots having desired alloy composition are soaked at 1310°C-1320°C
and rolled into desired thickness of slabs , preferably to 200mm thickness.
The slabs are subjected to hot scarfing to remove scabs. Extensive cold
scarfing is done in the yard to remove burning, embedded scabs and crack
and pulls.
iv) hot rolling of slabs comprising heating slabs preferably to a temperature
of 1250°C before rolling in order to maintain a finishing temperature in the
range of 860°C-880°C and coiling temperature in the range of 660°C to
680°C, to optimize a fine grain size preferably conforming to ASTM 8/9, to
achieve desired mechanical properties in said steel; such as to obtain a
steel grade having Wt % of C in the range of 0.06-0.11%; Mn in the range
of 0.30-0.50%; P in the range of 0.03-0.04%; S in the range of 0.03-
0.04%; Si in the range of 0.04-0.08%; Al in the range of 0.005%(max).
v) Descalers are operated to remove rolled-in scales and roll crowns are
optimized to obtain a profile of 20-70 microns and flatness < 50 I Units;
vi) The process is capable to develop three alternative grades, having
moderate variations in the composition range for identical application for
cycle rims as follows:
ADVANTAGES OF THE INVENTION;
1. Uniformity in steel composition, hardness, stiffness and grain size have ensured a
smooth manufacturing of cycle rims.
2. Optimum level of oxygen in steel, absence of elongated type II sulphide inclusions
and absence of Aluminium have imparted typical microstructure to the steel, which
has provided stiffness and characteristic sound to the rim.
3. Reduction in Phosphorous & Sulphur levels have helped in improving the weldability
and formability of steel.
We claim:
1. A process for the manufacture of steel for cycle rims comprising the steps of,
(i) providing selective alloy steel composition ;
(ii) steel making in LD converter with initial additions in the ladle during
tapping, Nitrogen purging through the ladle bottom and achieving desired
uniform composition of ingot;
(iii) slab making in slabbing mills wherein the cast ingots having desired alloy
composition are soaked at 1310°C-1320°C and rolled into desired
thickness of slabs ;and
(iv) hot rolling of slabs comprising heating slabs preferably to a temperature
of 1250°C before rolling such as to maintain a finishing temperature in the
range of 860°C-880°C and coiling temperature in the range of 660°C to
680°C and optimizing the roll crowns obtained such as provide a profile of
20-70 microns and flatness < 50 I Units, such as to obtain a steel grade
having Wt % of C in the range of 0.06-0.11%; Mn in the range of 0.30-
0.50%; P in the range of 0.03-0.04%; S in the range of 0.03-0.04%; Si
in the range of 0.04-0.08%; Al in the range of 0.005%(max).
2. A process for the manufacture of steel for cycle rims substantially^ as
hereindescribed and illustrated with reference to the accompanying examples.

A process for the manufacture of steel for cycle rims having selective alloy
composition providing fine grained structure with properties of high hardness,
strength, stiffness and improved weldability and formability. The process comprises
the steps of steel making, slab making and hot rolling using selective parameters.
Importantly, the cycle rim grade steel is obtained following defined process
parameters, eliminating Aluminium addition in any stage of the heats for such steel
so as to restrict the Al content to 0.005 wt% in final grades, having composition
comprising Wt % of C in the range of 0.06-0.11%; Mn in the range of 0.30-0.50%; P
in the range of 0.03-0.04%; S in the range of 0.03-0.04%; Si in the range of 0.04-
0.08%; Al in the range of 0.005%(max). Resulting rim steel is having fine grained
microstructure free of thin and elongated sulphide inclusions and surface defects,
ensuring improved strength and stiffness and a characteristic sound indicative of
corresponding desired quality.