Ann: CDP Completes Significant Milestone, page-44

At 900C steel becomes pretty soft, so I presume its reduced strength is an issue. I believe a refractory material is the usual alternative and because it has to be replaced periodically a high temperature alloy was chosen instead. Actually 900C is relatively low, easy to achieve and part of the efficiency of the Hazer process. (the higher the temperature the greater the heat loss). Variation of temperature and pressure results in different morphologies of the carbon product as well as proportion of hydrogen to carbon output.