Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1996-12-26
1999-04-20
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148651, C21D 800
Patent
active
058955348
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of increasing the yield strength of cold formed steel sections during the course of in-line roll forming a steel strip to a desired structural shape.
BACKGROUND ART
The process of forming steel strip into desired structural shapes such as rectangular hollow section, circular tube, angles, channels and other open profile sections is well known and has been in use for many years. The feed material is normally so-called "black" steel which has typically been formed into steel strip by a hot rolling process in a manufacturing mill.
In the past one normally recognised method of obtaining increased yield strength of the finished product formed from a subsequent cold rolling process, is to alter the "chemistry" of the steel strip, i.e. by adding various alloying metals into the composition of the steel before hot rolling. Another method is the use of thermomechanical practice during hot rolling. These are expensive processes due to the cost of the metal alloy and the process for obtaining the desired mix of alloy, the technological cost of processing by thermomechanical practices, and also because of the necessity to keep inventory of different types of metal section in order to meet the demand for different performance characteristics at an economical price.
For these reasons, the vast majority of all cold rolled steel sections are formed from common black steel with the size and weight of the section simply being increased where desired to obtain the necessary load-bearing characteristics.
There are however many applications where it is desirable from both engineering and economic points of view to enhance the yield characteristics of the steel from which a structural section is formed in order to give increased performance compared with a similar section rolled from black steel in the conventional manner.
DISCLOSURE OF INVENTION
The present invention therefore provides a method of increasing the yield strength of cold rolled steel sections as part of an in-line manufacturing process, comprising the steps of passing a steel section which has been at least partially cold worked and thereby subjected to a predetermined amount of strain, through a heating stage wherein the temperature of the steel section is elevated to a range between 200.degree. C. and 500.degree. C., and holding the temperature of the steel section in that temperature range for a time range between two and thirty seconds, the temperature and time combination being selected within the said ranges to achieve a predetermined degree of strain ageing.
Preferably the method includes steps of cooling the steel section after heating and strain ageing and then performing subsequent cold working on the steel section.
Preferably the step of passing the steel section through a heating stage comprises heating the steel section to a temperature between 200 and 450.degree. C. over a time between two and thirty seconds and holding the temperature at at least 440.degree. C. for between one and fifteen seconds.
More preferably the step or passing the steel section through a heating stage comprises heating the steel section to a temperature between 350 and 400.degree. C. over a time between two and ten seconds and holding the temperature between 440 and 460.degree. C. for between two and six seconds.
The step of cooling the steel section reduces the temperature of the section to below 90.degree. C. and preferably to between 25 and 45.degree. C. before subsequent cold working.
In one form of the invention the steps of elevating the temperature and holding that elevated temperature are performed by the preheating and subsequent coating of the steel section in an in-line galvanising operation.
Preferably the steel section has a steel composition containing between 0.01 and 0.25% carbon and between 0.001 and 0.006% nitrogen.
BRIEF DESCRIPTION OF DRAWINGS
Notwithstanding any other forms that may fall within its scope, one preferred form of the invention will now be described by way of example only with refer
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Crossingham Brian Roy
Daley Leigh Brian
Height Trevor Maxwell
Styan Andrew Thomas
Tubemakers of Australia Limited
Yee Deborah
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