Claims:We Claim:

1. Impact resistant refractory bricks comprising metallic fibres incorporated reinforced refractory bricks.

2. Impact resistant refractory bricks as claimed in claim 1 comprising stainless steel fibre incorporated reinforced MgO-C brick composition for steel ladle.

3. Impact resistant refractory bricks as claimed in anyone of claims 1 or 2 comprising metallic fibres incorporated Magnesia carbon bricks composition comprising:
Items Wt%
SS fibre (SS304/310S) 2-3
MgO 91-93
Graphite 5-5.5

4. Impact resistant refractory bricks as claimed in anyone of claims 1 to 3 comprising steel fibre incorporated magnesia carbon brick suitable for impact area of steel ladles comprising selective grades and up to 5 mm particle size Magnesia, Graphite, SS fiber and Pitch/Resin as binder such as to achieve high Refractory Toughness (Cold crushing Strength (CCS), coked at 10000C/2hrs, 408 to 451 kg/cm2 and high Hot Modulus of Rupture property 44 to 56 kg/cm2 for bottom impact area of steel ladle.

5. Impact resistant refractory bricks as claimed in anyone of claims 1 to 4 comprising Magnesia carbon bricks wherein the Magnesia includes:
MgO, min. 97
CaO, max. 2
SiO2, max. 0.35
Fe2O3 , max. 0.20
Al2O3 , max. 0.12
B2O3 , max. 0.03
Bulk density (g/cm3), min 3.4
Avg. crystal size (micron), min 100

6. Impact resistant refractory bricks as claimed in anyone of claims 1 to 5 comprising Magnesia carbon bricks wherein Graphite includes:

Fixed Carbon 96 min
Ash 3 max
Volatile matter 0.5 max
Moisture 0.5 max
Size Range
+ 0.295 mm 20 max
- 0.295 + 0.211 mm 60 min
- 0.211mm 21 ax

7. Impact resistant refractory bricks claimed in anyone of claims 1 to 6 comprising Magnesia carbon bricks wherein Pitch/Resin as binder includes:
Pitch

Soft. point (R&B), (C) 90-95
Benzene insl, (%), min 28
Quinoline insoluble, (%), min 8
?-resin 20

Resin:
Non-volatile matter (%) 68-72
Fixed carbon (%) 35-40
Viscosity (cp), at 250C 250-300
Sp.Gravity at 200C 1.17-1.19
pH at 200C 6.5-7
Moisture Content (%) 8-10
Free Phenol (%) 14 (± 2)
Free Formaldehyde (%) 0.9 (± 0.2)

8. Impact resistant refractory bricks claimed in anyone of claims 1 to 7 comprising Magnesia carbon bricks wherein SS fibres include:

SS fibre of ASTM 304 grade
C Mn Si S P Ni Cr
0.08 2 1.0 0.03 0.045 8-11 18-20

And /or SS fibre of ASTM 310S grade
C Mn Si S P Ni Cr
0.08 2 1.5 0.030 0.045 19-22 24-26

9. A process of manufacturing impact resistant refractory bricks as claimed in anyone of claims 1 to 8 comprising :
mixing selective refractory ingredients;
adding binder ;
incorporating the metallic fibres ;
forming blocks and curing.

10. A process as claimed in claim 9 wherein said ingredients, binder and metallic fibre preferably SS fibre of selective specification are used to achieve high refractory Toughness (Cold crushing Strength (CCS) coked at 10000C/2hrs, 408 to 451 kg/cm2 and high Hot Modulus of Rupture property, 44 to 56 kg/cm2 for bottom impact area of steel ladle.

Dated this the 14th day of September, 2015
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

, Description:FIELD OF THE INVENTION

The present invention relates to high impact resistant refractory brick product for lining of impact area of steel ladle. More particularly, the present invention is directed to provide improved quality magnesia carbon bricks for impact area of steel ladles by addition of particular variety of stainless steel fibres along with other ingredients like flake graphite, and granular magnesite (MgO) so as to produce MgO-C bricks having high Refractory Toughness (Cold crushing Strength (CCS), coked at 10000C/2hrs) and thermal shock resistance with a high hot strength so as to eliminate additional repair in a full campaign and thereby enhancing steel ladle availability and improving productivity in steel melting units.

BACKGROUND OF THE INVENTION

In the recent scenario of competitive market and driven by customer, manufacturing processes of steel has changed significantly due to the rising demand of quality steel in the market. Plants have been modernized with addition of secondary steel making facilities to meet the stringent quality requirement of newer grades of steel. While making these grades in steel ladles lined with refractory face lot of mechanical, thermal and chemical treatment.

Primarily, the liquid steel is made in basic oxygen furnace (BOF) at a temperature of more than 1650oC and is poured in steel ladle from a height of around 8-9 metre depending upon the shop design. The liquid steel directly strikes on the bottom of the steel ladle with a high impact. This leads to higher erosion of bottom refractory. In many steel units, this impact area is eroded faster than the other area and hence need repair job manually by cooling down the steel ladle. The steel ladle is taken out of circulation for 2-3 days for the repair activity and preheating of the lining to return to the production circuit in the shop.

Based on the operating environment of different areas, the ladle lining is divided in 3-4 zones. These are bottom, bottom impact area, slag zone and freeboard zone. In present practice, value added Alumina magnesia carbon bricks (AMC) are used in bottom impact area to achieve higher straight life in a campaign.

However, the life of bottom bricks could not match with the full campaign lining life due to faster erosion of bottom impact bricks. As such an additional repair job is required in a campaign to replace these bricks with a new set of bricks. There has been thus a persistent need to develop an improved quality of magnesia carbon bricks for bottom impact area which will eliminate the additional repair job of impact area and keep the ladle in operation till its full campaign.

Refractory bricks used in bottom impact area have to withstand the impact of stream of liquid steel tapped directly from BOF. This also creates severe thermal shock in bricks. The bricks should be able to resist corrosive attack of left over slag after casting of steel for some time before dumping of slag. Therefore, bottom impact bricks should be dense, highly resistant to thermal shock, resistant to slag corrosion and should have high hot strength as well as high refractory toughness.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide impact resistant refractory bricks comprising magnesia carbon bricks reinforced with metallic fibres of different quality having high impact resistance of such refractory bricks making it suitable for bottom impact area of steel ladles and a process for its production.

A further object of the present invention is directed to provide impact resistant refractory bricks comprising magnesia carbon bricks reinforced with stainless steel fibres of different quality suitable for bottom impact area of steel ladles wherein the content of stainless fibres of SS 304 and SS 310S quality in magnesia carbon matrix suitable is optimized to ensure high Refractory Toughness (Cold crushing Strength (CCS), coked at 10000C/2hrs) and high hot strength to achieve better properties than conventional magnesia carbon bricks.

Another object of the present invention is directed to provide impact resistant refractory bricks comprising magnesia carbon bricks reinforced with stainless steel fibres suitable for bottom impact area of steel ladles to ensure avoidance of additional repair to match with campaign life of steel ladle.

Yet another object of the present invention is directed to magnesia carbon bricks reinforced with stainless steel fibres suitable for bottom impact area of steel ladles wherein a specified amount of SS fibre and mixing sequence would be used for making these bricks for more controlled expansion of brick during operation in ladle.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to provide impact resistant refractory bricks comprising metallic fibres incorporated reinforced refractory bricks.

A further aspect of the present invention is directed to said impact resistant refractory bricks comprising stainless steel fibre incorporated reinforced MgO-C brick composition for steel ladle.

A still further aspect of the present invention is directed to said impact resistant refractory bricks comprising metallic fibres incorporated Magnesia carbon bricks composition comprising:
Items Wt%
SS fibre (SS304/310S) 2-3
MgO 91-93
Graphite 5-5.5

Another aspect of the present invention is directed to said impact resistant refractory bricks comprising steel fibre incorporated magnesia carbon brick suitable for impact area of steel ladles comprising selective grades and upto 5 mm particle size Magnesia, Graphite, SS fiber and Pitch/Resin as binder such as to achieve high Refractory Toughness (Cold crushing Strength (CCS), coked at 10000C/2hrs , 408 to 451 kg/cm2 and high Hot Modulus of Rupture property 44 to 56 kg/cm2 for bottom impact area of steel ladle.

Yet another aspect of the present invention is directed to said impact resistant refractory bricks comprising Magnesia carbon bricks wherein the Magnesia includes:
MgO, min. 97 wt%
CaO, max. 2 wt%
SiO2, max. 0.35 wt%
Fe2O3 , max. 0.20 wt%
Al2O3 , max. 0.12 wt%
B2O3 , max. 0.03 wt%
Bulk density (g/cm3), min 3.4
Avg. crystal size (micron), min 100

A further aspect of the present invention is directed to said impact resistant refractory bricks comprising Magnesia carbon bricks wherein Graphite includes:

Fixed Carbon 96 min
Ash 3 max
Volatile matter 0.5 max
Moisture 0.5 max
Size Range
+ 0.295 mm 20 max
- 0.295 + 0.211 mm 60 min
- 0.211mm 20 ax

A still further aspect of the present invention is directed to said impact resistant refractory bricks comprising Magnesia carbon bricks wherein Pitch/Resin as binder includes:
Pitch

Soft. point (R&B), (C) 90-95
Benzene insl, (%), min 28
Quinoline insoluble, (%), min 8
?-resin 20

Resin:
Non-volatile matter (%) 68-72
Fixed carbon (%) 35-40
Viscosity (cp), at 250C 250-300
Sp.Gravity at 200C 1.17-1.19
pH at 200C 6.5-7
Moisture Content (%) 8-10
Free Phenol (%) 14 (± 2)
Free Formaldehyde (%) 0.8 (± 0.2)

A still further aspect of the present invention is directed to said impact resistant refractory bricks comprising Magnesia carbon bricks wherein SS fibres include:
SS fibre of ASTM 304 grade
C Mn Si S P Ni Cr
0.08 2 1.0 0.03 0.045 8-11 18-20

and/or SS fibre of ASTM 310S grade
C Mn Si S P Ni Cr
0.08 2 1.5 0.030 0.045 19-22 24-26

Another aspect of the present invention is directed to a process of manufacturing impact resistant refractory bricks as described above comprising :
mixing selective refractory ingredients;
adding binder ;
incorporating the metallic fibres ;
forming blocks and curing.

Yet another aspect of the present invention is directed to said process wherein said ingredients, binder and metallic fibre preferably SS fibre of selective specification are used to achieve high Refractory Toughness (Cold crushing Strength (CCS), coked at 10000C/2hrs, 408 to 451 kg/cm2 and high Hot Modulus of Rupture property 44 to 56 kg/cm2 for bottom impact area of steel ladle.

The above and other objects and advantages are described hereunder in greater details with reference to following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1: is the schematic sectional view of the steel ladle showing Lining design of 150T steel ladle at RSP with improved quality magnesia carbon (MC) bricks reinforced with SS fibre according to the present invention for bottom striking (impact pad) area.

Figure 2: Schematic view of liquid steel pouring from BOF into steel ladle bottom impact area.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

The present invention is directed to provide impact resistant refractory bricks comprising metallic fibres incorporated reinforced refractory bricks and in particular, magnesia carbon bricks reinforced with stainless steel fibres suitable for bottom impact area of steel ladles and a process for its production which would provide magnesia carbon bricks which is dense, and should have high hot strength as well as impact strength resulting in higher straight life as well as total campaign life. This is achieved by way of the present invention by using particular variety of SS fibre added along with graphite content, and granulometry wherein a specified amount of SS fibre and mixing sequence was used for making these bricks for controlled expansion of brick during operation in ladle and a specified grain size distribution is used.

Thus to improve the performance of impact area of steel ladles a special quality of MgO-C bricks have been developed by addition of a particular variety of SS fibre along with graphite content and granulometry.
These bricks were manufactured along with existing quantities of MgO-C bricks for other areas of steel ladles. Bricks were manufactured at captive brick plant at the applicants’ brick making unit at Rourkela Steel Plant, Rourkela.
Thus according to the present invention a process of manufacturing SS fibre added magnesia carbon bricks in which input materials of specified quality/chemical composition was used.

SS fibre is incorporated in magnesia carbon bricks for use in impact area of ladle. SS fibre of different varities (ASTM 304 grade and ASTM 310S grade) and sizes are available. A specific variety of SS fibre and of specified size was used for proper incorporation in magnesia carbon bricks. A specified amount of SS fibre and mixing sequence was used for making these bricks for controlled expansion of brick during operation in ladle. A specified grain size distribution was used for achieving high density and low porosity. Magnesia used for magnesia carbon bricks can be of different varieties (Fused, Sintered, dead burnt). A specific type of magnesia and chemical purity has been used to achieve high spalling resistance and slag corrosion resistance property required for bottom impact area. Combination of all these ingredients as per a specified proportion and grain size distribution have resulted development of special quality of magnesia carbon brick which has given superior performance in bottom impact area of steel ladle.

The input materials of specified quality/chemical composition used to produce the SS fibre added magnesia carbon bricks are as follows:

Table – 1: Specification of Magnesia used for brick making:
Properties Wt%
Chemical Analysis
MgO, min. 97
CaO, max. 2
SiO2, max. 0.35
Fe2O3 , max. 0.20
Al2O3 , max. 0.12
B2O3 , max. 0.03
Bulk density (g/cm3), min 3.4
Avg. crystal size (micron), min 100
Size Range
+ 25 mm (%) Nil
+ 12 mm (%), max 35
+ 6 mm (%), min 80
- 0.5 mm (%), max 2

Table – 2: Specification of Graphite used for brick making
Properties %
Fixed Carbon 96 min
Ash 3 max
Volatile matter 0.5 max
Moisture 0.5 max
Size Range
+ 0.295 mm 20 max
- 0.295 + 0.211 mm 60 min
- 0.211mm 20 max

Table – 3: Specification of Pitch/Resin used as binder for brick making
Properties of pitch
Properties Value
Soft. point (R&B), (C) 90-95
Benzene insl, (%), min 28
Quinoline 8
?-resin 20

Properties of Resin :
Non-volatile matter (%) 68-72
Fixed carbon (%) 35-40
Viscosity (cp), at 250C 250-300
Sp.Gravity at 200C 1.17-1.19
pH at 200C 6.5-7
Moisture Content (%) 8-10
Free Phenol (%) 14 (± 2)
Free Formaldehyde (%) 0.8 (± 0.2)

The SS fibres of following specifications have been used in the magnesia Carbon bricks produced according to the present invention:

Table 4: SS fibre of ASTM 304 grade:
C Mn Si S P Ni Cr
0.08 2 1.0 0.03 0.045 8-11 18-20

Table 5: SS fibre of ASTM 310S grade:
C Mn Si S P Ni Cr
0.08 2 1.5 0.030 0.045 19-22 24-26

The composition of the impact resistant Magnesia carbon bricks produced according to the present invention comprises the following:
Constituents Wt%
SS fibre (SS304/310S) 2-3
MgO 91-93
Graphite 5-5.5

The experimental procedure followed in laboratory scale to produce the magnesia carbon bricks reinforced with stainless steel fibre suitable for impact area of steel ladle according to the present invention is as follows:
(i) providing different grades of material as per the selected specification for sample bricks (0 to 5mm);
(ii) mixing of materials in a small 10kg mixer machine;
(iii) adding measured quantity of pitch/resin as binder slowly during mixing;
(iv) adding 1%, 2%, 3% fibre in the mixer;
(v) preparing sample blocks of 50x50mm (cylindrical) from the mixed ingredients in pilot 100T hydraulic press;
(vi) curing the sample blocks/bricks in muffle furnace at 240 0C/24 hours.
Standard testing were performed with the sample bricks produced according to the invention to determine the comparative improvement in properties evaluated against bricks without any fibre. The results are presented in the following table.

Table 6: Comparative Properties of MgO-C bricks with and without SS fibre

Properties
Fibre %
0 1 2 3
CCS (after coking at 10000C/2hrs
(kg/cm2)
SS-304
SS-310

408
408

387
396

430
451

476
370
HMOR (at 14000C/0.5hrs)
(kg/cm2)
SS-304
SS-310

44
44

55
56

Plant Trial

(i) In one trial, the bricks added with SS 304 fibre were applied in bottom striker zone (1.5mx 1.3 m area) of steel ladle and the impact pad lining so obtained could achieve full campaign life of 103 heats. Accompanying Figure 1 shows schematically the lining configuration and position of MgO-C bricks according to the invention lined in impact area of ladle. Accompanying Figure 2 is the schematic view showing the liquid steel pouring from BOF into steel ladle bottom impact area.

(ii) In another trial with impact bricks made with SS 310S fibre was used to line impart area of steel ladle with encouraging results in which Ladle completed 80 heats and further heats were under progress without any damage to bottom impact pad area.

It is thus possible by way of the present invention to provide magnesia carbon refractory bricks reinforced with SS fibre alongwith graphite content and selective granulometry so as to ensure refractory bricks with substantially higher refractory toughness and hot strength to ensure reliable application in lining of impact area of steel ladle with improved campaign life.