| 摘要 |
A steel composition consists of 0.08-0.25% by weight of carbon, 0.3-2.0% by weight of silicon, 0.6-1.8% by weight of manganese, 0.04-0.20% by weight of phosphorus, less than 0.10% by weight of aluminum, less than 0.01% by weight of boron if necessary, unavoidable impurities and balance iron. The composition is subjected to hot rolling under the condition that the coiling temperature is less than 600 deg C. and cold rolling. The cold rolled steel is heated for 1-10 min at a temperature (Acl +10) deg C. to Ac3-10) deg C., then cooled at a rate greater than 50 deg C./sec up to a temperature 350-500 deg C. with a holding period of 1-10 min at that temperature before final air cooling. The microstructure of the cold rolled annealed steel has ferrite, martensite and retained austenite, the percentage of the retained austenite being more than 8%, and the steel has a tensile strength of 70kgf/sq.mm and the value of the product of the elongation and the tensile strength is greater than 2400kgf/sq.mm %.
|
