CS259219B1 - Method of heating by the gate - Google Patents

Abstract

Method of gate heating in impingement furnaces in front of the director by rolling on hot wide strip lines for structural weldable steels with a chemical composition in weight percent: 0.01 to 0.25% carbon, 0.50 to 2.50% manganese, traces up to 1% silicon, total content of chromium, nickel, traces up to 1% molybdenum and total aluminum, titanium, niobium, vanadium and trace zirconium content up to 0.30% for the range of the final rake (h) of the sheet from 2 to 12 mm, while the slabs are heated to a temperature (Tj0 given by the relation T^ = 1 175 + + 50 . (% Al + % V) + 180 . (% Ti) + 250 . . (% Nb) + 10. (% Mn + % Cr + % Ni + % Mo) - - 2 . h 4 15 °C. The solution can be applied in the processing of technological procedures of controlled rolling of high-strength weldable smallest microalloyed steels. The advantage is the rationalization of energy use and the improvement of the structure and properties of rolled sheets

Description

The invention relates to a method of heating a door in a ram furnace prior to controlled rolling on warm broadband lines.

Temperatures between 1,250 to 1,280 ° C are generally used to heat the slabs in the impact furnaces prior to controlled rolling on hot broadband steel structural steels. Such a heating temperature ensures low deformation resistances during rolling, dissolution of carbonitrides and transition of microlegures to solid solution. However, during high austenitization temperatures, the austenite grain becomes excessive and heterogeneous. This unfavorable structural state in the rolling stage cannot be completely eliminated and even in the resulting structure is manifested in structural inhomogeneities having a degrading effect on the utility properties of rolled sheets and strips, in particular on the transition temperature of notched toughness.

This deficiency is addressed by the method of heating the slabs in the pusher furnaces prior to controlled rolling on warm broadband tracks for weldable structural steels with a chemical composition of 0.01% to 0.25% by weight carbon, from 0.50% to 2.50% manganese, traces up to 1% of silicon, total chromium, nickel and molybdenum content from trace to 1% and total aluminum, titanium, vanadium, niobium, trace zirconium content up to 0.30%, for final depth ranges (h). according to the invention, the principle of which is that the gates are heated to a temperature given by:

T _ft = 1175 + 50. (»A1 +» V) + 180. (% Ti) + 250. (% Nb) + 10. (% Mn +% Cr + +% Ni +% Mo) -2. h = 15 ° C, where (h) is the final thickness of the rolled product in mm, (% Me) - weight percent of additive or alloying element.

The advantages of the method of heating the gates according to the invention in addition to the economic benefits resulting from the reduced heating temperature of the billets consist in improving the structure of the final product mainly in terms of homogeneity and ferrite grain size. It can be used in the design of controlled rolling technology of various types of microalloyed high-strength weldable structural steels, for the dimensioning of heating capacities in the design of warm broadband lines, etc.

Example

Steel with a chemical composition of 0.11% carbon, 1.24% manganese, 0.33% silicon, 0.012 t-phosphorus, 0.07% sulfur, 0.04% aluminum, 0.042% niobium, 0.051% vanadium, 0.05 % of chromium and 0.10% of nickel are heated in impact furnaces according to the invention to a temperature of 1 180 ° C. The mean austenite grain size after heating is 185 µm. After rolling on a hot broadband mill to a sheet thickness of 8 mm and rolling at a temperature of 620 ° C, the mean ferrite grain size is 4.1 µm. The steel has a yield strength of 505 MPa and a transition temperature of notched toughness - 65 ° C.

The same steel is conventionally heated to a temperature of 1260 ° C.

The austenite grain size after heating is 390 μια. After rolling with unchanged mill calibration and keeping the rolling temperature of 620 ° C, the mean ferrite grain size is 6.2 µm. The steel has a yield strength of 490 MPa and a transition temperature of notched toughness - 35 ° Ó.

Claims (1)

SUBJECT MATERIALS A method of heating by beacons in ramming strips prior to controlled rolling on warm broadband lines for structural weldable steels with a chemical composition in weight percent of 0.01 to 0.25% carbon, 0.50 to 2.50% manganese, traces up to 1% silicon , the sum of chromium, nickel, molybdenum, trace up to 1%, and the sum total of aluminum, titanium, niobium, vanadium and zirconium trace up to 0.30% for the final ridge (h) of sheet metal from 2 to 12 mm characterized by the slabs being heated to the temperature (Tft) given by the relation TA = 1,175 + 50. (% Al +% V) + 180. (% Ti) + 250. (»Nb) + 10. (% Mn + 1 Cr +% Ni +% Mo) - 2. h ± 15 ° C.