An Overview of the Use of Microalloys in HSLA Steels with

An Overview of the Use of Microalloys in HSLA Steels with Particular Reference to Vanadium and Titanium
A.M. Sage

High Strength Low Alloy Steels have been variously defined but for this paper they will be considered as those high strength steels which contain small additions, not usually in excess of 0.2%, of carbide and nitride forming alloys which directly or indirectly control the strength and other properties of the structural steels. The term was originally confined to sheet, plate and sections but now extends to rods and bars and engineering steels used for forgings.

The alloys, often referred to as microalloys, apart from influencing the microstructure and hence the properties of structural and engineering steels through precipitation of their carbides and nitrides also influence the microstructure by other means particularly through their presence in solid solution. The alloys usually considered as microalloys are niobium, vanadium and titanium. Aluminium however should be included because aluminium nitride was the first nitride to be used to control grain size in normalised and heat treated steels for which it is still employed and in steels which are heat treated it can influence the balance of nitrogen between the microalloys and hence their performance.

Other alloys such as cerium and the rare earths which are added in very small amounts and have a very large effect on sulphide inclusions and ductility but which do not affect the basic microstructure are not discussed here.

The HSLA steels are used as plate, sheet, pipes made from plate and sheet, sections, rods and bar and in forged products. The original HSLA steels were used as rolled or normalised. Today they include controlled rolled plate, accelerated cooled plate and sections rolled bar and rod, forgings and castings and fully heat treated plates. The function of the alloys varies from one product to another and in some products the same alloy can have more than one function. In fully heat treated steels they work with larger additions of hardening alloys including molybdenum, chromium and nickel.

Many oftheproducts are weldedandthe effects ofthemicro alloys on the properties of the welds is a major factor in selecting steel compositions for applications where welding is involved.

In many steels more than one alloy may be added and although the effects of the different alloys are largely additive there is also a degree of interaction between the microalloys which has to be taken into account when designing a steel.

The microalloys control the microstructure of HSLA steels by several mechanisms which vary with the alloy but their function is monitored by the properties required in the finalproduct and the plant available to produce the steels in the form required.

This paper was a plenary presentation at the 2nd International Conference on HSLA Steels held in 1990.

Publisher: TMS
Product Format: PDF
Pages: 51-60
Date Published: October 1, 1990
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