CA1112549A

CA1112549A - Method of producing steel sections of improved quality

Info

Publication number: CA1112549A
Application number: CA303,251A
Authority: CA
Inventors: Stephan H. Wilmotte; Marios Economopoulos; Emile Blondelot
Original assignee: A R B E D ACIERIES REUNIES DE BURBACH-EICH-DUDELANGE; Centre de Recherches Metallurgiques CRM ASBL
Current assignee: A R B E D ACIERIES REUNIES DE BURBACH-EICH-DUDELANGE; Centre de Recherches Metallurgiques CRM ASBL
Priority date: 1977-05-13
Filing date: 1978-05-12
Publication date: 1981-11-17
Also published as: GB1569552A; DE2820323A1

Abstract

ABSTRACT

A steel section 6 to 40 mm thick, emerging from a hot rolling mill at 1000 to 800°C is surface quenched for 2 to 6 seconds at a cooling rate of the order of 1.5 to 5 MW(megawatts)/m2. During subsequent self-tempering of the quenched surface by heat from the remainder, the section tends to an equalization temperature of 500 to 700°C.

Description

:
The present inven-tion relates to a method of improving the qlali-ty of rolled steel products in the form of sections, the method being applicable to any ~ind 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 elas-tic 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.
` 10 On the other hand, in order to improve weldability .~ and ductility of a steel, it is necessary to decrease its carbon and manganese conten-t, which concurrently resul-ts in a decrease of its tensile strength. To remedy this draw-back, steel can be subjected to a sui-table cooling treatment, 15 preferably applied directly at -the outlet of a rolling mill, which permits the elastic limit of the sec-tion to be raised.
When cooling is effected by convection or radiation, the coolinæ law of a rolled section depends to a large extent on its dimensions. Thus for a sec-tion having 20 predetermined dimensions it is necessary, in order to modify its elastic limit, to adopt further procedures to complete ; -the effect of the coolinæ as such. ~ong these procedures one should men-tion in particular increasing the content of alloying elements. This is certainly effective but has the .
25 drawback of beirg more costly the higher the elastic limit desired.
~nat is required is a me-thod permitting the above-, ;- mentioned drawback to be elimina-ted wi-thou-t increasing -the carbon and manganese content of the s-teel in a way which is inacceptable wi-th regard to weldability.
:
The present inven-tion provides a me-thod in whic~l, at the ou-tlet of a hot rolling mil], the said section while being at a -temperature of 1000 -to ~00C is subjected to surface ~lenching for 2 to 6 seconds, the sec-tion whose thickness is of 6 to 40 ~n being subjected during quenc~hing ~ J~SQ~V~
`~ ~ to a cooling rate of the order of 1.5 to 5 ~w~m', -the equaliza-tion -temperature of the section due to selL-tempering being be-tween 500 and 700C.
Self-temperin~ is tempering of the q-uenched surface b~y heat conduc-ted -to -that surface froin the remainder of the section.
The equalization temperature is the tempera-ture -towards which the quenched ~;urface and -the renainder of the sec-tion converge during self-tempering.
~he application of -this me-thod -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 0.040~0 aluminium made i-t 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 kg/cm2 at -20 C. ~he same method when applied -to steel con-taining 0.11 to 0.20% carbon and 0.5 -to 1.1% manganese but being of a semi-killed kind made it possible -to ob-tain steel of the same class but whose Charpy V impac-t strength was higher than 3 kg/cm2 at -20C.
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 s-teel being al~uminium killed and optionally also con-taining 0.015 -to 0.040% niobium, it was possible to obtain steel of class St.E47 whose elastic limit was a-t least 47 kg/m.n2 and whose Charpy V impact strength was 5 kg/cm2 at -20C.
: In a third test of the method according to the inven-tion, applied to steel having the same composi-tion as the preceding s-teel but con-taining up -to 0.06% niobium and 0.04 to 0.20% vanadium, it was possible to obtain s-teel of class St.E 70 with an elastic limit of at leas-t 70 kg/mm2 and a Charpy V impact strength higher -than 5 kg/cm2 at -60Co

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

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 5 seconds, wherein the cooling rate during the surface quenching is of the order of 1.5 to 5 MW(megawatts)/m2, and the equalization temperature of the section due to subsequent self-tempering is 500 to 700°C.

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