APMR- Cold Heading

Valbruna Grade

APMR

Description of material

APMR is a low- carbon austenitic stainless steel with Molybdenum. It has good general and pitting corrosion resistance as well as good intergranular corrosion resistance after welding processes. This grade has been designed in order to offer a good cold deforming and cold head ability, thanks an exact chemical balance of elements such as Carbon, Nitrogen and Nickel.

Applications

APMR is suitable for the fabrication of many products such as flanges, valves, screws, bolting, pumps shafts, food /beverages industry equipment, storage tanks, many organic chemicals, and parts working in mild to medium corrosive environments.

Melting practices

Argon Oxygen Decarburization

Corrosion resistance

APMR is resistant to fresh water, many organic chemicals and inorganic compounds, atmospheric corrosion, marine environments, many products used in chemical processing, paper production equipment, rural applications and sterilizing solutions. In marine environments, this grade is more resistant to pitting and crevice corrosion than 304L type grades such as AISR . However, pitting and crevice corrosion may occur in environments if the chloride concentration, pH and temperature are at determinate levels. As with other standard austenitic grades, APMR 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

APMR is readily fabricated by cold working such as cold drawing and allows a good amount of cold heading thanks to its chemical balance. Its structure after cold deformation is less hard than AISR. If heavy cold heading performance were required, Valbruna produces an alternative grade for these purposes, such as APMRU, whose chemical balance provides higher cold deformability and lower CWHF. It has a good polish-ability or mirror finishing ability, but it’s should be pointed out that these properties improve with a fine grain structure, harder than a fully annealed one. APMR is usually supplied in wire and wire rods with different conditions such as: (1) annealed+ pickled (2) annealed + pickled and special mill coating (3) annealed + cold drawn with some kind of mill coating and ready to be entered in the header (4) annealed +cold drawn + protective atmosphere annealed + mill coated ready for cold heading with or without sizing operations, before entering in the header. It should be noted that, as with all hot rolled wire rod surfaces, conditions (1) and (2) offer a higher surface roughness compared to other ones.

Machinability

APMR has a poor machinability due to a low Sulfur content, and produces tough and stringy chips. The best performances are obtained when employing the correct machining parameters while using multi - spindle and automatic screw machines. However, 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 roughness of machined parts improves in the case of harder structure, rather than the fully annealed one. MVAPML could be used in cases where a good machinability was required but a higher strain hardening of cold worked parts needed to be considered. However, MVAPML must not be used for high polish-ability or mirror finishing processes.

Weldability

APMR has a special chemical composition which helps to avoid solidification cracks in the fused-zone of autogenous welds due to a suitable Ferrite balance. Neither preheating nor post welding heat treatment is required. Nevertheless, in the case of aggressive environments, a post welding heat treatment is suggested. If welded or cold headed parts have to be heat treated, an annealing at 1020-1050°C and fast cooling should be done.

Hot working

APMR is usually supplied in wire or wire rod for cold heading processes. This grade can be easily hot headed; no preheating is required and forging temperatures are the typical ones of austenitic stainless steel. Small forging can be rapid quenched in air or water cooled.

Designations