304 Stainless Steel - DIN 1.4301 - X5CrNi18-10 - ~SUS 304

Stainless steel 304 is an austenitic steel, also known as 18/8 due to its 18% chromium and 8% nickel composition and has good workability, weldability, heat resistance, strength and good mechanical properties at low temperatures, good hot workability such as stamping and bending. The combination of low yield strength and high elongation benefits manufacturing parts such as sinks and saucepans or hollow ware. 304 stainless steel is easily molded or rolled into a multitude of forms for industrial, architectural and transportation applications.

Corrosion resistance

General corrosion

304 has excellent corrosion resistance in many environments and when in contact with different corrosive media. The formation of chromium carbides on the grain boundaries and the resulting chromium depletion in the surrounding areas makes the 304 susceptible to intergranular corrosion. 304 exhibits good corrosion resistance in natural environmental media in the absence of chlorine and salt concentrations.

Pitting corrosion

When in contact with chloride solutions or oxidizing media, pitting resistance is important as those conditions may facilitate the penetration of the passive surface film in places. A single deep point of entry may cause more damage than many shallow ones. If pitting corrosion is expected, steels containing molybdenum such as 316L/316 should be considered.  

Intergranular corrosion

Intergranular corrosion is the result due to the precipitation of chromium carbides at the grain boundaries when cooled after welding at the sensitizing temperature range of 840-1560°F (450-850°C). Therefore, sensitized materials should not be exposed to corrosive environments as intergranular corrosion may occur at the welding point.

Atmospheric corrosion

304 performs well in urban and rural areas, however for maximum resistance to pitting and staining the addition of molybdenum as in 316L/316 should be used.

Stress corrosion cracking

Austenitic steels are prone to stress corrosion cracking, as can be encountered at temperatures above 140°F (60°C) when the steel is exposed to tensile stresses or comes into contact with solutions containing chlorides for example at the same time.

Heat Resistance

304 steel has good oxidation resistance in intermittent service to 1598°F (870°C) and in continuous service to 1697°F (925°C). Not recommended is continuous use in the range of 797-1580°F (425-860°C) if aqueous corrosion resistance is important later on.

Heat treatment

Unlike martensitc steel, 304 stainless steel cannot be hardened by heat treatment as no phase changes occur on heating and cooling.

Annealing

Heat the protected steel through to 1630°F (890°C), cool after in the furnace at 40°F (20°C) per hour down to 1560°F (850°C), then further down to 1290°F (700°C) at 20°F (10°C) per hour. This is followed up by air cooling.

Stress relieving

Heat the material through to 1112°F (600°C) after rough machining and hold for 2 hours. Cool slowly to 930°F (500°C), then it can be freely cooled further in air. Stress relieving above 1112°F (600°C) will cause a serious threat of grain boundary sensitization accompanied with loss of corrosion resistance.

Hardening

Preheating temperature: 1110-1560°F (600-850°C)

Austenitizing temperature: 1830-1920°F (1000-1050°C), should usually be done at 1870-1885°F (1020-1030°C)

Parts need to be protected against decarburization and oxidation during the hardening process.

Quenching media

• Fluidized bed or salt bath at 480-1020°F (250-550°C) followed by cooling in an air blast
• Vacuum with sufficient positive pressure
• High speed gas/circulating atmosphere

To obtain its greatest properties cool the parts as quickly as possible, but care should be taken to maintain acceptable distortion. 4-5 bar. The parts have to be tempered as soon as they reach the temperature of 120-160°F (50-70°C).

Tempering

Choose the tempering temperature that needs to be achieved, temper twice and cool between tempering to room temperature. Do not let the tempering temperature drop below 480°F (250°C) and hold at the chosen temperature for a minimum of 2 hours. At the tempering temperature of 480°F (250°C) the best combination of toughness, hardness and corrosion resistance can be achieved.

For our tempering diagram, please click here

Dimensional changes

Depending on temperature, equipment and cooling media used during heat treatment, dimensional changes of approx. 0.15% per side should be taken into account. Also important is the size and geometric shape of the tool and a stress relief should be done between rough and semi-finishing.

Welding

Good results can be achieved, when welding tool steel, if the proper precautions are taken during welding (increased working temperature, joint preparation, choice of filler metals and the welding procedure). For the best results after polishing and photo-etching a filler of the same composition as the base should be used.