HOT ROLLED STEEL AND A METHOD OF MANUFACTURING THEREOF

Abstract

A hot rolled steel having a composition including comprising of the following elements 0.01%≤Carbon≤0.1%, 0.2%≤Manganese≤2%, 0.2%≤Silicon≤1.5%, 0.01%≤Aluminum≤2%, 0.1%≤Tin≤1%, 0.1%≤Copper≤0.5%, 0.001%≤Niobium≤0.1%, 0.002%≤Phosphorus≤0.02%, 0%≤Sulfur≤0.005%, 0%≤Nitrogen≤0.01%, with 0.3%≤Sn+Cu≤1.2% and can contain one or more of the following optional elements 0%≤Titanium≤0.1%, 0%≤Vanadium≤0.1%, 0%≤Chromium≤1%, 0%≤Molybdenum≤0.5%, 0%≤Calcium≤0.01%, 0%≤Boron≤0.01%, 0%≤Magnesium≤0.05%, 0%≤Calcium≤0.01%, 0%≤Cerium≤0.1%, 0%≤Boron≤0.05%, 0%≤ Nickel≤0.01%, the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel sheet including in area fraction, 75% to 95% Ferrite, 1% to 15% Pearlite and optionally Bainite is between 0% and 25% wherein the average grain size of all the microstructural constituent is less than 15 microns.

Claims

1-19. (canceled)

20: A hot rolled steel having a composition expressed in percentage by weight comprising the following elements: 0.01%≤Carbon≤0.1% 0.2%≤Manganese≤2% 0.2%≤Silicon≤1.5% 0.01%≤Aluminum≤2% 0.1%≤Tin≤1% 0.1%≤Copper≤0.5% 0.001%≤Niobium≤0.1 0.002%≤Phosphorus≤0.02% 0%≤Sulfur≤0.005%. 0%≤Nitrogen≤0.01% with 0.3%≤Sn+Cu≤1.2% and optionally containing one or more of the following elements: 0%≤Titanium≤0.1% 0%≤Vanadium≤0.1% 0%≤Chromium≤1% 0%≤Molybdenum≤0.5% 0%≤Calcium≤0.01% 0%≤Boron≤0.01% 0%≤Magnesium≤0.05% 0%≤Calcium≤0.01% 0%≤Cerium≤0.1% 0%≤Boron≤0.05% 0%≤Nickel≤0.01% a remainder composition being composed of iron and unavoidable impurities caused by processing, a microstructure of the steel sheet comprising in area fraction, 75% to 95% Ferrite, 1% to 15% Pearlite and optionally Bainite between 0% and 25%, wherein an average grain size of all microstructural constituents is less than 15 microns.

21: The hot rolled steel as recited in claim 20 wherein the composition includes 0.1% to 0.8% of Tin.

22: The hot rolled steel as recited in claim 20 wherein the composition includes 0.01% to 0.09% of Carbon.

23: The hot rolled steel as recited in claim 22 wherein the composition includes 0.15% to 0.4% of Copper.

24: The hot rolled steel as recited in claim 20 wherein the composition includes 0.4% to 1.9% of Manganese.

25: The hot rolled steel as recited in claim 20 wherein the composition includes 0.2% to 1.4% of Silicon.

26: The hot rolled steel as recited in claim 20 wherein the composition includes 0.01% to 0.9% of Aluminum.

27: The hot rolled steel as recited in claim 20 wherein the average grain size is less than 12 microns and a cumulated amount of Ferrite and Pearlite is 90% or more.

28: The hot rolled steel as recited in claim 20 wherein the steel has tensile strength of 450 MPa or more, and a corrosion resistance of less than 0.55 grams/cm2 per 60 cycles.

29: The hot rolled steel as recited in claim 28 wherein the steel is a steel sheet having tensile strength of 470 MPa or more and a corrosion resistance of less 0.53 grams/cm2 per 60 cycles.

30: A method of production of a hot rolled steel comprising the following successive steps: providing a semi-finished product with a steel composition expressed in percentage by weight comprising the following elements: 0.01%≤Carbon≤0.1% 0.2%≤Manganese≤2% 0.2%≤Silicon≤1.5% 0.01%≤Aluminum≤2% 0.1%≤Tin≤1% 0.1%≤Copper≤0.5% 0.001%≤Niobium≤0.1 0.002%≤Phosphorus≤0.02% 0%≤Sulfur≤0.005%. 0%≤Nitrogen≤0.01% with 0.3%≤Sn+Cu≤1.2% and optionally containing one or more of the following elements: 0%≤Titanium≤0.1% 0%≤Vanadium≤0.1% 0%≤Chromium≤1% 0%≤Molybdenum≤0.5% 0%≤Calcium≤0.01% 0%≤Boron≤0.01% 0%≤Magnesium≤0.05% 0%≤Calcium≤0.01% 0%≤Cerium≤0.1% 0%≤Boron≤0.05% 0%≤Nickel≤0.01% a remainder composition being composed of iron and unavoidable impurities caused by processing; reheating the semi-finished product to a temperature between 1050° C. and 1250° C.; hot rolling the semi-finished product, a finishing temperature of the hot rolling being above Ar1, to obtain a hot rolled steel; then cooling the hot rolled steel at a cooling rate between 1° C./s and 20° C./s to cooling temperature below 500° C.; and cooling the hot rolled steel to room temperature to obtain the hot rolled steel plate.

31: The method as recited in claim 30 wherein the reheating temperature for semi-finished product is between 1100° C. and 1250° C.

32: The method as recited in claim 30 wherein the hot rolling finishing temperature is between Ar1 and Ar3 +200° C.

33: The method as recited in claim 30 wherein the hot rolling finishing temperature is between Ar1 and Ar3 +150° C.

34: The method as recited in claim 30 wherein the cooling temperature for hot rolled steel is below 475° C.

35: The method as recited in claim 30 wherein the cooling rate after hot rolling is between 1° C./s and 15° C./s.

36: The method as recited in claim 30 wherein the cooling rate after hot rolling is between 1° C./s and 12° C./s.

37: The method as recited in claim 30 wherein a final thickness of the hot rolled steel plate after hot rolling is between 2 mm and 80 mm.

38: A method of manufacturing a structural member for onshore or offshore equipment comprising: providing the steel as recited in claim 20 in the structural member.

39: A method of manufacturing a structural member for onshore or offshore equipment comprising: producing the hot rolled steel as recited in claim 30 and providing the hot rolled steel in the structural member.

Description

EXAMPLES

[0042] The following tests and examples presented herein are non-restricting in nature and must be considered for purposes of illustration only, and they will display the advantageous features of the present invention and expound the significance of the parameters chosen by inventors after extensive experiments and further establish the properties that can be achieved by the steel according to the invention.

[0043] Samples of the steel sheets according to the invention and to some comparative grades were prepared with the compositions gathered in table 1 and the processing parameters gathered in table 2. The corresponding microstructures of those steel sheets were gathered in table 3 and the properties in table 4.

[0044] Table 1 depicts the steels with the compositions expressed in percentages by weight.

TABLE-US-00001 Steel Sn + Samples C Mn Si Al Sn Cu Nb P S N Ti V Cr Mo Ni Cu 1 0.051  1.477 0.305 0.013 0.144 0.174 0.026 0.0035 0.0011 0.005  0.013  0.003 0.015 0.002  0     0.318 2 0.051  1.477 0.305 0.013 0.144 0.174 0.026 0.0035 0.0011 0.005  0.013  0.003 0.015 0.002  0     0.318 3 0.071  0.510 1.05  0.293 0.143 0.215 0.026 0.0032 0.0004 0.0035 0.0144 0     0     0.358 4 0.0500 1.500 0.320 0.052 0     0.175 0.027 0.0046 0.0012 0.0025 0.014  0.003 0.017 0.002  0.288 0.175 5 0.15   1.418 0.350 0.028 0.137 0.024 0.036 0.0034 0.0011 0.0029 0.014  0.017 0.425 0.161 6 0.05   1.48  0.301 0.023 0.146 0.010 0.026 0.0026 0.0011 0.0043 0.013  0.003 0.015 0.0023 0.297 0.156 underlined values: not according to the invention.

[0045] Table 2 gathers the process parameters implemented on steels of Table 1 and Table 2 also shows Ar1 and Ar3 temperatures for all the steel Samples.

TABLE-US-00002 TABLE 2 process parameters of the trials: Rolling average reduction Cooling Cooling Final Steel Reheating in HR Finish speed stop Thickness Ar1 Ar3 Sample Trials (° C.) finishing (° C.) (° C./s) (° C.) (mm) (°C.) (° C.) 1 I1 1200 2.5 838 2 Room 20 677 750 Temperature 2 I2 1200 2.5 778 11 450* 20 677 750 3 I3 1200 2.5 981 2 Room 20 844 892 Temperature 4 R1 1200 2.5 799 2 Room 20 581 714 Temperature 5 R2 1200 2.5 798 2 Room 20 484 737 Temperature 6 R3 1200 2.5 777 2 Room 20 597 772 Temperature *Denotes that the steel of trial I2 is fist cooled to a temperature below 500° C. and then to room temperature. I = according to the invention; R = reference; underlined values: not according to the invention. underlined values: not according to the invention.

[0046] Table 3 gathers the results of test conducted in accordance of standards on different microscopes such as Scanning Electron Microscope for determining microstructural composition of both the inventive steel and reference trials.

TABLE-US-00003 TABLE 3 microstructures of the trials Average Grain Steel Sample Trials Ferrite Pearlite Bainite size 1 I1 92 8 0 11.4 2 I2 90 2 8 12 3 I3 95 5 0 9.9 4 R1 95 5 0 11.9 5 R2 81 19 0 11.8 6 R3 93 7 0 11.4 underlined values: not according to the invention.

[0047] Table 4 gathers the mechanical properties of both the inventive steel and reference steel. The tensile strength test is conducted in accordance with JIS Z2241 standards. For the saline weather corrosion resistance the test is conducted according to the modified version of the SAE J2334 standard test with modified spray salt composition: 6 h at 100% RH, 50° C.; 15 min spray with 5% NaCl+0.1% CaCl.sub.2); 17.75 h at 50% RH, at 60° C.

TABLE-US-00004 TABLE 4 mechanical properties of the trials Steel Tensile Strength Corrosion resistance @ Sample Trials (in MPa) 60 cycles (in g/cm2) 1 I1 474.5 0.52 2 I2 524.5 0.52 3 I3 487 0.41 4 R1 479.5 0.63 5 R2 596.5 0.67 6 R3 490 0.70 I = according to the invention; R = reference; underlined values: not according to the invention. underlined values: not according to the invention.

[0048] The examples show that the steel sheets according to the invention are the only one to show all the targeted properties thanks to their specific composition and microstructures.