Effect of alloying Elements in Steels

 In general, alloying elements are added to steel in small percentages-usually less than 5 percent-to improve strength or hardenability.

EFFECT OF ALLOYING ELEMENTS IN STEELS

✓ In general, alloying elements are added to steel in small percentages-usually less than 5 percent-to improve strength or hardenability. Otherwise, alloying elements are added to steel in much larger amounts-usually upto 20 percent - to produce special properties such as corrosion resistance or stability at high or low temperatures.

✓ The properties of all steels (or all alloys) are determined by the kinds and amounts of phases of which they are composed, by the properties of the phases, and by the way in which these phases are distributed among one another.

✓ Steels consist of two or more phases known as ferrite, austenite, carbides, and graphite.

✓ The alloying elements in steels affect the stability of these phases, the relative amounts of the phases, and how the phases are distributed or dispersed throughout one another. Thus, the alloying elements affect and control the properties of steels.

■ The alloying elements such as Ni, Mn, Cu, and Co tend to stabilize austenite.

■ The alloying elements such as Cr, W, Mo, V and Si tend to stabilize ferrite.

■ Some alloying elements such as Cr, W, Ti, Mo, Nb, V, and Mn tend to form carbides. Other elements such as Si, Co, Al, and Ni tend to destabilize carbides and form graphite.

The more important effects of the main alloying elements added to steels can be summarized in Table 3.5.

1. Some Important Alloy Steels

Though there are number of alloy steels available, the study of the following four alloy steels are very important from our subject point of view.

1. Stainless steels.

2. Tool steels,

3. HSLA steels, and

4. Maraging steels.