Stainless Steel Grade AISI 631 | EN 1.4568 | DIN X7CrNiAl17-7

AISI 631 | EN 1.4568 | DIN X7CrNiAl17-7 - stainless alloy which is a martensitic precipitation hardening stainless steel providing high strength and hardness, excellent fatigue properties, good corrosion resistance, good formability and minimal deformation during heat treatment.

The properties of this alloy are well suited for aerospace applications. AISI 631 is suitable for use in both fresh water and industrial oxidizing environments. Its forming characteristics are similar to AISI 301 stainless steel.

This grade of metal is mainly used where corrosion resistance, good strength and mechanical properties at operating temperatures up to 427 °C are required. It is also regularly used for the manufacture of complex parts due to its low deformation during heat treatment.

In the annealed state, the steel has an austenitic structure, after heat treatment of aging it turns into martensite, increasing its strength properties along with obtaining magnetic properties. This alloy has excellent fatigue strength and good corrosion resistance. It is mainly used on valve parts, tanks, springs, spring washers, knives, diaphragms, low and high temperature parts, heat exchangers, special valves and installations, structures and components of machines. The steel is intended for aerospace, oil, chemical and petrochemical industries, energy, food and cryogenic industries in the form of strips, wires, sheets and rods. Suitable for use in industrial atmospheres. Not recommended for use in salt water or reducing environments.

Welding

Conventional arc and resistance welding methods can be used. In order to reduce the oxidation of aluminum during the process, it is suggested to use inert gas shielding during fusion welding.

Formation

The processing characteristics are almost identical to those of AISI 301 stainless steel. For radical forming operations, intermediate annealing may be required.

Heat treatment

Heat treatment requires three important steps: conditioning of austenite, cooling to convert austenite to martensite, and precipitation hardening to the appropriate condition.

Annealing

Annealing is carried out at a temperature of 1066 °C for 3 min for every 2.5 mm of thickness, and then cooled in air.

Aging

The steel is solution annealed at 1177 °C for 4 hours and air cooled. The same step is performed at 1079 °C for 4 hours and air cooled, then at 843 °C for 24 hours and air cooled, and at 760 °C for 16 hours and air cooled. This completes the precipitation hardening process. To achieve excellent results and productivity, the material must be clean, free of scale and impurities.

Processing

The machinability of this stainless steel is rated as satisfactory. When machined, this alloy produces long, sticky chips. It is recommended that low speeds and constant feeds during machining provide excellent results.

Physical properties