Title of Invention

AN IMPROVED PROCESS FOR MANUFACTURING WHEELS OF RAILWAY WAGONS AND COACHES

Abstract

An improved process for manufacturing wheels of railways wagons and coaches, having higher wear resistance, fracture toughness and strength, comprising the steps: (a) producing molten steel of composition, such as herein described, in an electric arc furnace of 10 tonne capacity by charging ingredients, such as herein described, in the furnace and additional ingredients, such as herein described, in ladles; (b) casting the molten steel into pencil ingots of weight 2 torne each in moulds, such as herein described; (c) cutting the ingots into blocks; (d) forging and rolling the blocks into wheels in a known manner; and (e) subjecting the wheels to a heat treatment, such as herein described; characterised in that (i) the ingredients charged into the furnace comprise wheel punch, ferro-alloys Fe-Si, Fe-Mn, Fe-Mo and aluminium bars, and the ingredients charged into ladle comprise ferro-alloy Fe-V and a slag containing lime-60%, Al shots - 25% and CaF2- 15% by weight, in proportion required to make the composition of the steel produced different from that of the existing composition by weight (C-0.52% max, Mn - 0.60/0.80% Si - 0.15/0.40%, Cr - 0.25% max, Ni - 0.25% max, Mo - 0.06% max, Cu - 0.28% max, V - 0.05% max, P - 0.03% max, S - 0.03% max and H - 3ppm) only in respect of the contents of micro alloying elements Mo, Al, V and Nb which are respectively, 0.20% max, 0.03% max, 0.20% max and 0.05% max by weight; (ii) the moulds used are pre-coated with graphite and pre-dried; and (iii) the heat treatment applied to the wheels comprises heating the wheels in a furnace to a temperature of 920-950°C, soaking the wheels at 920-950°C for one hour, and allowing the wheels to cool in natural air for 4-5 hours as against the existing heat treatment comprising heated and soaked quenching the rim of the similarly heated and sooked wheel for 5 minutes followed by tempering at 500° C temperature in furnace for 1.5 hours under hot charged condition and for 2.5 hours under cold charged condition and finally cooling in natural air.

Full Text

The present invention relates to an improved process for manufacturing wheels of railway wagons and coaches. The invention relates more particularly to a process in which wheels are manufactured to meet the revised specification No. R-19/93 laid down for same in replacement of the earlier specification No. R-19, by producing microalloyed steel of increased wear resistance, and subjecting the wheels, forged and rolled thereof; to' normalising' heat treatment in place of 'rim quenching and tempering' heat treatment as followed in the conventional process. The existing process for manufacturing wheels of earlier specification No. R-19 comprises the following main steps in sequence :- (a) producing steel of chemical composition as given in Table I herein in a 120 tonne. Basic Oxygen Furnace in the conventional way by blowing carbon to the extent of 0.07 - 0.0896 by weight of the steel, followed by partial carburisation thereof, addition of the necessary ferro alloys and petroleum carbon to molten steel in ladle, and casting the molten steel into ingots of required-size and cutting into blocks; (b) forging and rolling the blocks into wheels in the conventional process followed in a wheel making plant; (c) subjecting the forged and rolled wheels to the heat treatment involving rim quenching and tempering by pre-heating the wheels to a temperature of 920-950°C, soaking at 920-950°C for about 1 hour to attain temperature homogenisation, quenching - 2 - the wheel rims by spraying a water jet of high pressure i.e. 3-4 bar in about 5 min to a temperature of about 200°C and tempering the hot/cold charge at 500°C followed by air cooling, as illustrated hereinafter. The main drawbacks of the existing process are :- 1. The steel produced is of inadequate wear resistance to meet the revised specification No. R-19/93. 2. The heat treatment by rim quenching and tempering generates localised stress concentration in the wheel hubs owing to droplets of the quenching water falling on the hub thereof. 3. The unbalanced residual stress is built up in the wheel rim because of unavoidable fluctuation in the water jet pressure. 4. Variation in the hardness profile from surface to interior of wheel rim is produced by the non-uniformity in quenching thereof. 5. A sizeable proportion of the wheels is required to be subjected to reheat treatment for improving the mechanical properties thereof at an additional cost. The object of the present invention is to provide an improved process for manufacturing wheels according to revised specification No. R-19/93. The other object is to reduce the variation in the hardness profile from surface to interior of the wheel rim and prevent localised stress building in the wheel hub and eliminate thereby the need for reheat treatment of the wheels produced. - 3 - The invention is described fully and particularly in an unrestricted manner with reference to the accompanying drawings, in which Figure 1 illustrates schematically the change in shape of an ingot/block in different stages of forging and rolling followed in a wheel making plant; and Figure 2 illustrates the cycle followed in heat treatment by quenching and tempering of wheel rim. The invented process for manufacturing the wheels according to revised specification No. R-19/93 comprises the following steps in sequence :- (a) producing steel of chemical composition as given in Table 1 hereinafter in a 10 tonne Electric Arc Furnace in the known method with modifications, such as, (i) preparing the entire charge for the furnace from wheel punch for lowering the sulphur and phosphorus content and achieving high carbon opening to ensure active carbon boil in the steel, (ii) using preheated ladle for tapping the molten steel, (iii) forming a synthetic slag containing lime - 6096, Al shots - 25% and CaF2 - 15% (by weight) at a temperature of 1650°C just before tapping during the refining period of steel, for lowering the sulphur content, (iv) adding ferror-alloys Fe-Si, Fe-Mn, Fe-Mo, and Aluminium bar in the furnace and ferroalloy Fe-V in ladle just before tapping for de-oxidation and microalloying of the steel to the required level; (b) casting the molten steel by tapping into moulds which are pre-coated with graphite and pre-dried to produce pencil - 4 - ingots of weight 2 tonne each and cutting into blocks (c) forging and rolling the blocks into wheels in the steps in sequence as illustrated in Fig. 1, namely, (1) feeding blocks into forging machines, (2) producing rough-forged wheel blanks, (3) producing finished wheel blanks with punched holes therein, (4) rolling to produce rolled wheels, and (5) producing dished wheels; and (d) subjecting the forged and rolled wheels to the 'normalising' heat treatment comprising heating the wheels to a temperature of 920 - 950 C in a furnace, soaking for 1 hour in the furnace for temperature homogenisation in the wheels, removing the soaked wheels from the furnace and allowing the wheels to cool in natural air in about 4-5 hours,instead of the heat treatment by rim quenching and tempering as followed in the existing process and illustrated in Fig. 2 in which the wheels are soaked for 1 hour at 920 - 950°C, wheel rims are quenched by spraying a water jet at 3.0 - 3.5 bar pressure for 5 minutes and tempered at 500°C for 1.5 hour under hot charge condition (shown by dotted line) and for 2.5 hours under cold charge condition shown by full line, and finally cooled in natural air. As already stated the chemical compositions of steel used in the wheels manufactured in the existing and invented processesare presented in Table 1 from which it is noted that the composition of steel in the invented process is different from that in the existing process in respect of the content of micro alloys Molybdenum (Mo), Vanadium (V) and Niobium (Nb) which are upto 0.20, 0.20 and 0.05% respectively by weight in the invented - 5 - process against upto 0.06, 0.05 and 0 % respectively by weight in the existing process. The comparative mechanical properties of the wheels produced in the existing and invented processes are given in Table 2 from which it is noted that the wheels produced in the invented process have higher values in respect of ultimate tensile strength (UTS), elongation at break (Eln %), hardness (BHN) and impact strength each compared with the wheels produced in the existing process. The micrographic studies conducted reveal that the grain structure of steel in wheels produced in the invented process is fine ferrito pearlitic leading to increased wear resistance thereof. The wheels produced in the invented process are found to be generally free from defects in the form of cracks as often found in the wheels produced in the existing process. - 6 - Table 1 Chemical composition (weight %) by ladle Analysis. Elements Existing process Invented process C 0.52 max 0.52 max Mn 0.60-0.80 0.60-0.80 Si 0.15-0.40 0.15-0.40 Cr 0.25 max 0.25 max Ni 0.25 max 0.25 max Mo 0.06 max 0.12-0.20 AL - 0.015-0.03 Cu 0.28 max 0.28 V 0.05 max 0.10-0.20 Nb - 0.02-0.05 P =0.03 =0.03 a =0.03 =0.03 on = 3 ppm =3 ppm (liquid steel) Fe balance balance - 7 - Table 2 Mechanical Properties of Steel produced in the Existing and Invented Process, properties Existing Process Invented Process UTS( MPa) 820 - 940 860 - 960 Eln (%) 14 17 Min. Hardness (BHN) 241 - 277 248 - 288 Impact strength at + 20°C (J/cm2) 15 18 Min. Grain size (ASTM No 0 - 7-9 - 8 - We Claim :- 1. An improved process for manufacturing wheels of railways wagons and coaches, having higher wear resistance, fracture toughness and strength, comprising the steps : (a) producing molten steel of composition such as herein described, in an electric arc furnace of 10 tonne capacity by charging ingredients, such as herein described, in the furnace and additional ingredients, such as herein described, in ladles; (b) casting the molten steel into pencil ingots of weight 2 tonne each in moulds, such as herein described; (c) cutting the ingots into blocks; (d) forging and rolling the blocks into wheels in a known manner; and (e) subjecting the wheels to a heat treatment, such as herein described; characterised in that (i) the ingredients charged into the furnace comprise wheel punch, ferro-alloys Fe-Si, Fe-Mn, Fe-Mo and aluminium bars, and the ingredients charged into ladle comprise ferro-alloy Fe-V and a slag containing lime 6096, Al shots - 25% and CaF2- 15% by weight, in proportion required to make the composition of the steel produced different from that of the existing composition (C-0.5296 max, Mn - 0.60/0.8096, Si - 0.15/0. 4096, Cr - 0.2596 max, Ni - 0.2596 max, Mo - 0.0696 max, Cu - 0.2896 max, V - 0.0596 max, P -=0.0396, S -= 0.0396 and H -= 3ppm) only in respect of the contents of micro alloys elements Mo, Al, V and Nb which are respectively 0.12-0.2096, 0.015-0.0396, 0.10-0.20% and 0.02-0.0596 by weight; (ii) the moulds used are pre-coated with graphite and pre-dried; and (iii) the heat treatment applied to the wheels comprises heating the wheels in a furnace to a temperature of 920-950°C, soaking the wheels at 920-950°C for - 9 - one hour and allowing the wheels to cool in natural air for 4-5 hours whereas the wheels of existing composition are heated and soaked at similar temperatures and for similar duration, and after being taking out from furnace are rim quenched for 5 minutes and thereafter tempered at 500°C temperature in furnace for 1.5 hours under hot charged condition and for 2.5 hours under cold charged condition and finally cooled in natural air. (B. L. BANERJEE) of DePENNING & DePENNING Agent for the Applicants. - 10 - Dated this 27th day of March 1998. An improved process for manufacturing wheels of railways wagons and coaches, having higher wear resistance, fracture toughness and strength, comprising the steps: (a) producing molten steel of composition, such as herein described, in an electric arc furnace of 10 tonne capacity by charging ingredients, such as herein described, in the furnace and additional ingredients, such as herein described, in ladles; (b) casting the molten steel into pencil ingots of weight 2 torne each in moulds, such as herein described; (c) cutting the ingots into blocks; (d) forging and rolling the blocks into wheels in a known manner; and (e) subjecting the wheels to a heat treatment, such as herein described; characterised in that (i) the ingredients charged into the furnace comprise wheel punch, ferro-alloys Fe-Si, Fe-Mn, Fe-Mo and aluminium bars, and the ingredients charged into ladle comprise ferro-alloy Fe-V and a slag containing lime-60%, Al shots - 25% and CaF2- 15% by weight, in proportion required to make the composition of the steel produced different from that of the existing composition by weight (C-0.52% max, Mn - 0.60/0.80% Si - 0.15/0.40%, Cr - 0.25% max, Ni - 0.25% max, Mo - 0.06% max, Cu - 0.28% max, V - 0.05% max, P - 0.03% max, S - 0.03% max and H - 3ppm) only in respect of the contents of micro alloying elements Mo, Al, V and Nb which are respectively, 0.20% max, 0.03% max, 0.20% max and 0.05% max by weight; (ii) the moulds used are pre-coated with graphite and pre-dried; and (iii) the heat treatment applied to the wheels comprises heating the wheels in a furnace to a temperature of 920-950°C, soaking the wheels at 920-950°C for one hour, and allowing the wheels to cool in natural air for 4-5 hours as against the existing heat treatment comprising heated and soaked quenching the rim of the similarly heated and sooked wheel for 5 minutes followed by tempering at 500° C temperature in furnace for 1.5 hours under hot charged condition and for 2.5 hours under cold charged condition and finally cooling in natural air.

Documents:

00524-cal-1998 abstract.pdf

00524-cal-1998 assignment.pdf

00524-cal-1998 claims.pdf

00524-cal-1998 correspondence.pdf

00524-cal-1998 description(complete).pdf

00524-cal-1998 drawings.pdf

00524-cal-1998 form-1.pdf

00524-cal-1998 form-2.pdf

00524-cal-1998 form-3.pdf

00524-cal-1998 form-5.pdf

00524-cal-1998 gpa.pdf

524-cal-1998-granted-abstract.pdf

524-cal-1998-granted-assignment.pdf

524-cal-1998-granted-claims.pdf

524-cal-1998-granted-correspondence.pdf

524-cal-1998-granted-description (complete).pdf

524-cal-1998-granted-drawings.pdf

524-cal-1998-granted-examination report.pdf

524-cal-1998-granted-form 1.pdf

524-cal-1998-granted-form 2.pdf

524-cal-1998-granted-form 3.pdf

524-cal-1998-granted-form 6.pdf

524-cal-1998-granted-letter patent.pdf

524-cal-1998-granted-pa.pdf

524-cal-1998-granted-reply to examination report.pdf

524-cal-1998-granted-specification.pdf