Title of Invention

A PROCESS FOR PRODUCING FIRE RESISTANT STRUCTURAL STEEL

Abstract

A process for producing fire/heat resistant structural steel comprising the following steps in sequence : (a) preparing molten steel in BOF, TOHF and EAF from iron ore, spar, burnt dolo, sand, mill scale, steel scrap, aluminium and known ferro alloys in required quantities; (b) tapping the molten steel at 1630 ± 20°C in a preheated ladle and adding more known ferro alloys and aluminium in the ladle as required; (c) top pouring the molten steel to form ingots of 5-12 tonnes weight followed by soaking the ingots at 1300-1320°C for 3-5 hours and rolling the ingots into blooms or concasting the molten steel directly into blooms at a tundish temperature of 1540-1550°C and unbending point temperature of over 800°C; (d) soaking the blooms at 1250°C for a time of 1 minute per nm of bloom thickness; (e) finish rolling the blooms into structurals; and (f) cooling the structurals to ambient temperature in natural air; characterised in that (i) the chemical composition of the steel produced is (by weight %) % C-0.11 to 0.20, Mn-0,70 to 1.50, Si-0.20 to 0.50, S-≤0.04, P-≤.0v04, Mo-0.20 to 0.26, Cr-0.20 to 0.55, Nb, V, Ti (total)-0.12 max and Fe-balanoe; and (ii) the blooms are finish rolled into structurals at 900-950°C.

Full Text

The present invention relates to a process for producing fire/heat resistant structural steel. The invention relates more particularly to a process for producing structural steel capable of maintaining atr 600°C at least two-third of the yield strength thereof at room temperature. If a fire breaks out in a building constructed with a framework of conventional steel the yield strength of the framework reduces appreciably below the yield strength thereof at ambient temperature, with the risk of collapse of the building. Wrapping of the steel frame with fire resistant material like rock wool, sometimes followed to retard the rate of rise in temperature of the structure is found to increase the cost of construction appreciably. The object of the present invention is to provide a process for producing structureal steel of increased fire/heat resistance to prevent reduction in its yield strength at an elevated temperature so that at least two-third of its yield strength at room temperature is maintained at an elevated temperature up to 600°C. The other object is to provide a process for producing structural steel meant for use in the construction of high-rise buildings, multistorey car parking garages, shopping centres, indoor stadia, ware houses, airport terminals, petroleum refineries etc. The fire/heat resistant structural steel has been produced in the process by optimising the content of the microalloying elements Mo, Cr, Nb and V both from the consideration of cost of production and the heat resistance property of the steel produced, by carrying out extensive investigations in the laboratory and trial productions in steel plants followed by evaluation of the properties of the steel produced. The optimised chemical composition of the steel produced in the invented process is presented in Table I. The invention is described fully and particularly in an unrestricted manner with reference to the accompanying drawings in which Figure 1 is a flow diagram showing the main steps followed in the process; Figure '2 illustrates the fall in yield strength of the steel produced in the process as well as of mild steel heated up to 600° 6; and Figure 3 shows the rate of rise in temperature with time of the steel produced in the process and of mild steel exposed to a standard heating condition. Referring to Fig. 1, the invented process comprises the following steps in sequence :- (a) molten steel is produced in basic oxygen furnace (BOF), twin open hearth furnace (TOHF) and electric arc furnace (BAF) from iron ore, spar, burnt dolo, sand, mill scale, steel scrap, aluminium and known ferro alloys in required quantities; We Claim :- 1. A process for producing fire/heat resistant structural steel comprising the following steps in sequence : (a) preparing molten steel in BOF, TOHP and BAF from iron ore, spar, burnt dolo, sand, mill scale, steel scrap, aluminium and known ferro alloys in required quantities; (b) tapping the molten steel at 1630 ± 20°C in a preheated ladle and adding more known ferro alloys and aluminium in the ladle as required; (c) top pouring the molten steel to form ingots of 5-12 tonnes weight followed by soaking the ingots at 1300-1320°C for 3-5 hours and rolling the ingots into blooms or concasting the molten steel directly into blooms at a tundish temperature of 1540-1550°C and unbending point temperature of over 800°C; (d) soaking the blooms at 1250°C for a time of 1 minute per mm of bloom thickness; (e) finish rolling the blooms into structurals; and (f) cooling the structurals to ambient temperature in natural air; characterised in that (i) the chemical composition of the steel produced is (by weight %)'. C-0.11 to 0.20, Mn-0.70 to 1.50, Si-0.20 to 0.50, S-≤0.04, P-≤ 0.04, Mo-0.20 to 0.26, Cr-0.20 to 0.55, Nb, V, Tl (total)-0.12 max and Fe-balance; and (ii) the blooms are finish rolled into structurals at 900-950°C. 2. The orocess as claimed in claim 1, wherein the chemical composition of the steel produced is (by weight %) : C-0.11-0.20, Mn-0.70-1,50, Si-0.20-0.50, 3-≤0.04, P-≤0.04, Mo-0.20-0.26, Cr-0.20-0.55 and Fe-the balance.

Documents:

132-CAL-1999-(22-02-1999)ABSTRACT.pdf

132-CAL-1999-(22-02-1999)CLAIMS.pdf

132-CAL-1999-(22-02-1999)CORRESPONDENCE.pdf

132-CAL-1999-(22-02-1999)DESCRIPTION (COMPLETE).pdf

132-CAL-1999-(22-02-1999)DRAWINGS.pdf

132-CAL-1999-(22-02-1999)FER.pdf

132-CAL-1999-(22-02-1999)FORM-1.pdf

132-CAL-1999-(22-02-1999)FORM-13.pdf

132-CAL-1999-(22-02-1999)FORM-19.pdf

132-CAL-1999-(22-02-1999)FORM-2.pdf

132-CAL-1999-(22-02-1999)OTHERS.pdf

132-CAL-1999-(22-02-1999)PA.pdf

132-CAL-1999-(22-02-1999)SPECIFICATION.pdf