Effects of various impurity elements on the stainless steel

According tometal powder supplier, cobalt as an alloying element is rarely used in steel, this is because of the high price of cobalt and it has more important purposes in other respects (such as high-speed steel, carbide, cobalt-based heat resistant alloy, magnetic steel or hard magnetic alloy, etc.). Cobalt is not commonly used as alloy elements in stainless steel, common stainless steel such as 9Crl7MoVCo steel (containing 1.2-1.8 % cobalt) plus cobalt was not meant to improve corrosion resistance but to improve the hardness, because the main purpose of this stainless steel is manufacturing sliced mechanical cutting tools, scissors and scalpel blades.

Boron: in high chromium ferritic stainless steel Crl7Mo2Ti add 0.005% boron powder, can improve the corrosion resistance of boiling 65% acetic acid. Plus trace amounts of boron powder (0.0006~0.0007%) can improve the thermal state ductility of the austenitic stainless steel. A small amount of boron powder because of forming low-melting crystals, make the tendency of austenitic steel produce hot cracking increased while welding, but when it contains a lot of boron powder (0.5% to 0.6%), it can prevent the generation of thermal cracks instead. Because when containing 0.5% to 0.6 % boron, it formed of austenite-borides two-phase structure, so that lower the melting point of the weld. When the molten bath’s solidification temperature is less than half-melted zone, the tensile stress of base material generated in the cooling is withstood by the liquid state, solid state weld metal, it would not cause cracks at this time, even near the seam zone is formed of cracks, it can also be filled by the liquid-solid metal. Chrome-nickel austenitic stainless steel containing boron has a special purpose in the atomic energy industry.

Phosphorus: in general stainless steel are impurity elements, but its harmfulness in austenitic stainless steels is not significant like in the general steel, so the content allows high, some data show that it can be up to 0.06%, to facilitate smelting control. Individual manganese-containing austenitic steels can contain phosphorus up to 0.06% (such as 2Crl3NiMn9 steel) to 0.08% (such as Cr14Mnl4Ni steel). Use the strengthening effect of phosphorus on steel, also can add phosphorus as age-hardening stainless steel alloying elements, the PH17-10P steel (containing 0.25% phosphorus ),  PH - HNM steel (containing 0.30 phosphorus).

Sulfur and selenium: In general stainless steel is also the common impurity elements. But add 0.2% to 0.4 % sulfur in stainless steel, the stainless steel can be improved cutting performance, the selenium also has the same effect. Sulfur and selenium improve the cutting performance of the stainless steel is because they reduce the toughness of the stainless steel, for example, the impact value of general 18-8 chrome-nickel stainless steel can be up to 30 kg/cm2. Both sulfur and selenium can reduce the corrosion resistance of stainless steel, so that actual apply them as alloying elements of stainless steel is rarely.

Rare earth elements: rare earth element used in stainless steel, is mainly used to improve process performance at present. Such as add a small amount of rare earth elements to the Crl7Ti steel and Cr17Mo2Ti steel, can eliminate the bubbles caused by hydrogen and reduce the cracks in the ingot. Add 0.02% to 0.5% of the rare earth elements (lanthanum cerium alloy) in austenitic and austenitic-ferritic stainless steel, can significantly improve the forging performance. There have been a austenitic steel containing 19.5% chromium, 23% nickel and molybdenum - copper - manganese, the thermal processing performance can only produce castings in the past, adding the rare earth elements can be rolled into a variety of profiles.

Source:http://www.mhcmp.com