Weldability and machinability are the main aspects to measure the technological performance of steel. All alloy elements that can improve the hardenability are unfavorable to the weldability of steel. Because hard and brittle structures such as martensite are easy to form when cooling at the side of weld heat affected zone near the fusion line, which may lead to cracking. On the other hand, the grains near the fusion line in the heat affected zone are easy to coarsen due to high heat. Therefore, it is beneficial to have elements such as titanium and vanadium in the alloy steel that can refine the grains.
The machinability of steel can be improved by adding some elements such as sulfur and lead (see free cutting steel). The alloy elements in alloy steel will generally increase the hardness of steel, thus increasing the cutting resistance and tool wear. The machinability of steel can be affected by changing the matrix structure, the type, quantity and shape of inclusions.
