For many years, we’ve been supplying high-temperature muffle tubes for furnaces dedicated to everything from wire drawing mills and bundy tube, to razor blades and tube annealing.
Some of the protective “shielding” gases used in the tubes are highly aggressive and, combined with high temperatures, can significantly shorten the service life of the tubes due to oxidation or loss of mechanical strength.
To avoid production losses due to unscheduled downtime, it is advisable to select a superior grade that can help extend the lifetime of the tube. For example, in aggressive environments with cracked ammonia, we often recommend Sanicro® 31HT. This helps protect against rapid nitriding of the material, which reduces mechanical strength.
Sanicro® 31HT is an optimal material if you are using pure nitrogen or a gas mixture of nitrogen and hydrogen. Nitrogen creates a less severe environment than cracked ammonia. Otherwise, endogas would tend to cause rapid carburization.
When hydrogen is being used, the most cost-effective material is Alleima® 253 MA, followed by Sanicro® 31HT. For the cost-effective annealing of carbon steel, we recommend Alleima® 4C54 since temperatures are in the lower range.