Complex and conflicting requirements imposed on materials used in modem vehicles impose that the steel industry respond to those requirements in order to maintain steels as the basic material of our cars. Over the last 20 years a series of development in the steel industry assisted the automotive industry to reach its goals. In the aftermath of the first oil crisis, in 1973, higher strength was important to allow weight reduction for fuel economy. Increased safety was also obtained. At present, however, the materials requirements for vehicles are much more demanding. To meet the expectations of comfort from end-users, of safety and of environment regulations a car is expected to have the following characteristics: Larger size, with air conditioning, air bag, ABS and side impact protection. Good looking. Low fuel consumption and limited atmosphere contamination. Guaranteed resistance against corrosion. Increased safety. Low cost. As a consequence, modern automotive steel products must exhibit, at high level, a combination of properties like formability, strength, fatigue, corrosion resistance and weldability, at low cost. The microalloyed steels have been meeting the desired requirements in different product forms, hot rolled strip, cold rolled sheet and forged and drawn steel grades. There are hot strip products produced direct from the hot strip mill with strength levels that could only be achieved in the past with the application of heat treating. These steels find application in chassis parts, wheels and industrial machinery. The interstitial Free, IF, steels were revamped in the early 80's , with extremely low carbon levels. With excellent formability, these steels are finding accelerated application in modern cars. The world production of IF steels has reached the level of 15 million ton per year. Similarly significant changes have occurred in the long products sector. Currently, there is large application of forged parts with the required properties obtained directly from the forging press, thus eliminating the usual and costly quenching and tempering treatments. Heat treatment is also being eliminated in high strength fasteners. Modern spring steels allow significant weight reduction in the final part. All these achievements have been possible through developments in microalloying technology and by practical application of every strengthening mechanisms available to the metallurgist. This paper presents an overview of the modern microalloyed steels - properties and alloy design - currently used in the automobile industry. Covering flat and long products.
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