Importance of presence of alloys in stainless steel

Molybdenum is introduced as an alloying element in stainless steel to reduce susceptibility to these types of wear. The presence of molybdenum allows the formation of a more resistant passive layer in cases where the stainless steel 304 does not resist the action of some media. This leads it to corrosion by drilling or cracks; stainless steel 316 and 317 is an excellent solution. They are steel with great use in the chemical, alcohol, petrochemical, paper and cellulose industries, in the petroleum, textile and pharmaceutical industries.

When exposed for some time to temperatures between 450 and 850 ° C, austenitic stainless steels undergo precipitation of chromium carbide in the grain surroundings, making them sensitive. This loyal deposition of carbides and awareness leads to a decrease in the chromium content in the areas near the edges. These are the areas where their resistance to corrosion is highly exposed to ASTM A270 Sanitary Tubing, which make the material vulnerable to intergranular corrosion. The thermally affected areas of welding processes are especially sensitive to this form of corrosion. Because during the thermal welding cycle a portion of the materials are kept in the critical temperature range. Consideration of this phenomenon led to the development of additional low austenitic stainless steel, 304L, 316L and 317L. In this steel the carbon content is controlled with a maximum of 0.03%, which reduces the possibility of sensitization.

Use of stabilizers is also intended to avoid the allergy problem of ASTM A554 Square Tube. Titanium, added as an alloy element, prevents the formation of chromium carbide. Due to the fact that titanium has a greater affinity than the carbon that contains chromium. Thus, titanium carbide is deposited and the chromium remains in a solid solution. Niobium can be used for the same purpose.

Both titanium and niobium are carbon stabilizers, and then stainless steel is obtained, and 321 and 347 are known as stable stainless steels. 316 Ti stainless is the stable version of type 316. For applications in equipment operating between 400 and 900 ° C, stable stainless steel is the most recommended. It maintains better mechanical properties at those temperatures than additional low carbon steels; Known climbing resistance.

In 904-liter stainless steel (20Cr-25Ni-4, 5Mo-1,5Cu), the addition of alloy elements seeks to improve not only furrow resistance but also corrosion resistance in acid-reducing media. The high nickel content also improves stress wear resistance.

In cases where good mechanical resistance is intentional and there is no significant concern about intergranular corrosion. Stainless steel 304H and 316H is recommended, with carbon grades in the range of 0.04 / 0.10%. Precipitation of a fine mesh of chromium carbide, very harmful from the point of view of corrosion, becomes useful when mechanical properties are important.

Significant increases in chromium and nickel content allow an austenitic stainless steel scale forming temperature to increase. ASTM A269 Stainless Steel Tubeis recommended for outdoor use, at temperatures below 925 ° C in continuous services. Under the same conditions, 310 stainless steel, with 24/26% chrome and 19/22% nickel, resists temperatures up to 1150 ° C. It is a material classified as refractory stainless steel.