APMLN/DE- Austenitic Stainless Steel

Valbruna Grade

APMLN/DE

Description of material

APMLN is a low-Carbon, Nickel, Nitrogen and Molybdenum austenitic stainless steel with good general, pitting and intergranular corrosion resistance also after welding process. This grade offers a low temperature toughness and higher strength than the typical 316/316L grades.

Applications

APMLNDE is suitable for the fabrication of many products as flanges, valves, screws, bolting, pumps shafts, medical applications, pharmaceutical and paper industries, food /beverages industry equipment , storage tanks, many organic chemical, parts working in the mild medium corrosive environments and pressure vessels products. For Marine Propellers , see MARINOX 16.

Corrosion resistance

APMLNDE is resistant to fresh water, several organic chemical and inorganic compound , atmospheric corrosion, marine environments , many products used in chemical process, paper production equipment , rural applications and sterilizing solution . In marine environments, this grade is slightly more resistance to pitting and crevice than TP 316/316L . However, pitting and crevice corrosion may occur in environments if the chloride concentrations , pH and temperature are at determinate levels. As other standard austenitic grades, APMLNDE suffers from stress corrosion cracking about thirty /forty degrees ( C°) above room temperature and above certain levels of stress and halogen concentrations. Strain hardened structures increase the risk of stress corrosion cracking. It should be noted that this grade, as for every kind of stainless steel, surfaces should be free of contaminant and scale, heat tint , and passivated for optimum resistance to corrosion.

Cold working

APMLNDE is readily fabricated by cold working such as cold drawing and bending, but should only be used for a moderate amount of cold heading, because its chemical balance does not allow it to obtain a soft strain hardening structure after cold deformation due to a high CWHF (Cold Working Hardening Factor) mainly due to its high Nitrogen content . Even if its high Nickel content could reduce this hardening, when compared to APMLN, this could still result in a certain amount of die wear.

Machinability

Austenitic grades are different from Ferritic and Alloy steels and require more rigid and powerful machines in addition to the correct choice of tools, coatings and cutting fluids. The Austenite structure is prone to transform in to α’Martensite caused by strain hardening of the tool on the surface of the machined piece. The knowledge of this behavior must be correctly considered when a piece requires two or several cutting steps to be finished. The layer of α’Martensite is very hard and, if the subsequent turning or milling processes work on this hardened layer, a rapid tool wear could happen. The tool must work under this layer. Even if the structure of APMLNDE is micro - resulphured and offers a little advantage in chip breaking ability, the strain hardening effect due to Nitrogen strongly influence the some kind of operations.

Weldability

APMLNDE can be welded without PWHT due to its low carbon content which avoids the precipitation of Cr-Carbide on the grain boundaries. However, in the case of aggressive environments or of risk of stress corrosion, a PWHT should be considered. In the case of filler metal welding, a filler with a matching composition of APMLNDE or over-alloyed fillers are recommended to maintain weld steel properties. Neither preheating nor post welding heat treatment is required. Normally, APMLNDE has a special chemical composition which helps to avoid solidification cracks in the fused-zone of autogenous welds due to a suitable Ferrite balance. Nevertheless, the Cr/Ni equivalent balance of the supplied product should be well evaluated to avoid the risk of solidification cracks in the fused-zone of high energy autogenous welds.

Hot working

APMLNDE offers a very good hot workability and is usually supplied as billets, blooms, or ingots. No preheating is required. In Primary hot transformation processes, a high temperature homogenization of large ingots and dynamic recrystallization parameters should be rightly evaluated. In the case of open die forging of large ingots and shapes, AISH offers a good hot plasticity if a suitable soaking and a right temperature are applied. In Secondary hot transformation processes, such as extrusion, rolling or close die forging, temperatures, strain and strain rate should be well considered because they influence the properties of the austenitic structure. Suitable strain in terms of section reduction ( for instance: 15-30%) at a lower range of hot working temperature is recommended in order to obtain a fine grain austenitic structure which is very important for mechanical, fatigue and corrosions resistance properties and makes it easier for ultrasonic testing to detect small indications as required by several International Norms. Small forgings should be cooled rapidly in air or water.

Designations