Sanicro® 31HT is an austenitic, nickel-iron-chromium stainless steel combining good resistance to high-temperature corrosion with high mechanical strength. Developed for severe, high-temperature environments, Sanicro® 31HT can be used at temperatures up to 1100°C (2010°F) in oxidizing atmospheres.
The grade performs exceptionally well in different combustion and synthesis gases and also has good resistance to carburization and isothermal and cyclic oxidation. Typical applications for Sanicro® 31HT include muffle tubes for wire annealing furnaces, furnace tubes and heat exchangers.
Excellent nitridation resistance
One of the most distinguishing characteristics of Sanicro® 31HT is its excellent resistance to nitrogen absorption at high temperatures. This is due to the relatively high chromium and nickel contents and makes this grade a recommended material for use in cracked ammonia (NH3) and hydrogen (H2). The nickel content also contributes to very good structural stability, including very good ductility and high creep strength.
Main characteristics of Sanicro® 31HT
- High creep strength
- Very good resistance to oxidation
- Good resistance to combustion gases
- Very good resistance to carburization
- Excellent resistance to nitrogen absorption
- Good structural stability at high temperatures
- Good weldability
Case in brief
A Belgian steel wire manufacturer experienced problems with nitridation attack and oxidation with their existing muffle tubes made from a high-temperature steel grade of type 21Cr11Ni. They wanted to prolong the service life of the muffle tubes to reduce costs for downtime, re-tubing and loss of production. Using cracked ammonia and hydrogen as the protective gas and a relatively high operating temperature, 1100°C (2010°F), there was a need for an alloy with improved high-temperature corrosion properties.
After discussions with Alleima engineers, the company decided to upgrade to muffle tubes in Sanicro® 31HT. The decision was based mainly on the excellent nitridation resistance of Sanicro® 31HT, but also on our documented references for similar applications and environments. Tubes in Sanicro® 31HT were installed in two furnaces and as a result, the overall service life of the muffle tubes has been increased by over 50 percent.