GB1569552A - Method of producing steel sections of quality - Google Patents

Description

(54) METHOD OF PRODUCING STEEL SECTIONS OF IMPROVED QUALITY (71) We, CENTRE DE RECHERCEES METALLURGIQUES-CENTRUM VOOR RE SEARCH IN DE METALLURGIE, a Belgian Body Corporate, of 47 Rue Montoyer, Brussels, Belgium, and A R B E D, ACIERES REUNIES DE BURBACH-EICH-DUDELANGE, a Luxembourg Body Corporate, of Luxembourg (Grand Duchy of Luxembourg), do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the - following statement : - The present invention relates to a method of improving the quality of rolled steel products in the form of sections, the method being applicable to any kind of steel, whether killed, semi-killed, or rimming steel.

The main qualities required by users of steel sections are, among other things, as high as possible an elastic limit for the grade of steel used, as well as weldability, fatigue strength, and ductility satisfactory for the use to which the sections are to be put.

On the other hand, in order to improve weldability and ductility of a steel, it is necessary to decrease its carbon and manganese content, which concurrently results in a decrease of its tensile strength. To remedy this drawback, steel can be subjected to a suitable cooling treatment, preferably applied directly at the outlet of a rolling mill, which permits the elastic limit of the section to be raised.

When cooling is effected by convection or radiation, the cooling law of a rolled section depends to a large extent on its dimensions. Thus for a section having predetermined dimensions it is necessary, in order to modify its elastic limit, to adopt further procedures to complete the effect of the cooling as such. Among these procedures one should mention in particular increasing the content of alloying elements. This is certainly effective but has the drawback of being more costly the higher the elastic limit desired.

What is required is a method permitting the above-mentioned drawback to be eliminated without increasing the carbon and manganese content of the steel in a way which is inacceptable with regard to weld- ability.

The present invention provides a method of improving the quality of a steel section having a thickness of 6 to 40 mm, emerging from a hot rolling mill at a temperature of 1000 to 800 C, the method comprising subjecting the section to surface quenching for 2 to 6 seconds, wherein the cooling rate during the surface quenching is 1.5 to 5 MW/m2, and the equalization temperature of the section due to subsequent self-tempering is 500 to 70"C.

Self-teenpering is tempering of the quenched surface by heat conducted to that surface from the remainder of the section.

The eqi'alization temperature is the temperature towards which the quenched surface and the remainder of the section coverage during self-tempering.

The application of this method to steel containing 0.11 to 0.20% carbon, 0.5 to 1.1% manganese, 0.20 to 0.40% silicon, and 0.018 to 0.040% aluminium made it possible to classify this steel as St.52 with an elastic limit higher than 36 kg/mm2 and a Charpy V impact strength higher than 5 /g/cm2 at 20 C. The same method when applied to steel containing 0.11 to 0.20% carbon and 0.5 to 1.1% manganese but being of a semi filled kind made it possi'ole to obtain steel of the same class but whose Charpy V impact strength was higher than 3 kg/cm2 at -200C.

In a second test of the method according to the invention, applied this time to steel containing 0.05 to 0.20% carbon, 0.20 to 0.40% silicon, 1 to 2% manganese, and 0.018 to 0.040% aluminium, the steel being aluminium killed and optionally also containing 0.015 to 0.040% niobium, it was possible to obtain steel of class St.E47 whose elastic limit was at least 47 kg/mm2 and whose Charpy V impact strength was 5 kg/cm2 at -200C.

In a third test of the method according to the invention, applied to steel having the same composition as the preceding steel but containing up to 0.06% niobium and 0.04 to 0.20% vanadium, it was possible to obtain steel of class St.E 70 with an elastic limit of at least 70 kg/mm2 and a Charpy V impact strength higher than 5 kg/cm2 at -600C.

WHAT WE CLAIM IS: 1. A method of improving the quality of a steel section having a thickness of 6 to 40 mm, emerging from a hot rolling mill at a temperature of 1000 to 800"C, the method comprising subjecting the section to surface quenching for 2 to 6 seconds, wherein the cooling rate during the surface quenching is 1.5 to 5 MW/m2, and the equalization temperature of the section due to subsequent self-tempering is 500 to 7000C.

2. A method as claimed in claim 1, in which the steel contains 0.11 to 0.20% carbon, 0.5 to 1.1% manganese, 0.20 to 0.40% silicon, and 0.018 to 0.040% aluminium.

3. A method as claimed in claim 1 or 2, in which the steel is semi-killed steel containing 0.11 to 0.20% carbon, 0.5 to 1.1% manganese, 0.20 to 0.40% silicon, and 0.018 to 0.040% aluminium.

4. A method as claimed in claim 1, in which the steel is aluminium killed steel containing 0.05 to 0.20% carbon, 0.20 to 0.40% silicon, 1 to 2% manganese, and 0.018 to 0.040% aluminium.

5. A method as claimed in claim 4, in which the steel further contains 0.015 to 0.040% niobium.

6. A method as claimed in claim 1, in which the steel contains 0.05 to 0.20% carbon, 0.20 to 0.40% silicon, 1 to 2% manganese, 0.018 to 0.040% aluminium, max.

0.06% niobium, and 0.04 to 0.20% vanadium.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. 0.40% silicon, 1 to 2% manganese, and 0.018 to 0.040% aluminium, the steel being aluminium killed and optionally also containing 0.015 to 0.040% niobium, it was possible to obtain steel of class St.E47 whose elastic limit was at least 47 kg/mm2 and whose Charpy V impact strength was 5 kg/cm2 at -200C. In a third test of the method according to the invention, applied to steel having the same composition as the preceding steel but containing up to 0.06% niobium and 0.04 to 0.20% vanadium, it was possible to obtain steel of class St.E 70 with an elastic limit of at least 70 kg/mm2 and a Charpy V impact strength higher than 5 kg/cm2 at -600C. WHAT WE CLAIM IS:

1. A method of improving the quality of a steel section having a thickness of 6 to 40 mm, emerging from a hot rolling mill at a temperature of 1000 to 800"C, the method comprising subjecting the section to surface quenching for 2 to 6 seconds, wherein the cooling rate during the surface quenching is 1.5 to 5 MW/m2, and the equalization temperature of the section due to subsequent self-tempering is 500 to 7000C.

2. A method as claimed in claim 1, in which the steel contains 0.11 to 0.20% carbon, 0.5 to 1.1% manganese, 0.20 to 0.40% silicon, and 0.018 to 0.040% aluminium.

3. A method as claimed in claim 1 or 2, in which the steel is semi-killed steel containing 0.11 to 0.20% carbon, 0.5 to 1.1% manganese, 0.20 to 0.40% silicon, and 0.018 to 0.040% aluminium.

4. A method as claimed in claim 1, in which the steel is aluminium killed steel containing 0.05 to 0.20% carbon, 0.20 to 0.40% silicon, 1 to 2% manganese, and 0.018 to 0.040% aluminium.

5. A method as claimed in claim 4, in which the steel further contains 0.015 to 0.040% niobium.

6. A method as claimed in claim 1, in which the steel contains 0.05 to 0.20% carbon, 0.20 to 0.40% silicon, 1 to 2% manganese, 0.018 to 0.040% aluminium, max.

0.06% niobium, and 0.04 to 0.20% vanadium.