Two experts from Baosteel – the largest steel producer in China - recently presented a technical paper which addressed a tough problem they had struggled with in the past at the company’s hot rolling plant in Shanghai. The first part of the problem was to identify the primary causes. As the researchers described, hot rolling defects are easily formed due to the poor hot workability of duplex stainless steels, and at Baosteel this presented as edge cracking.
Lei Bao, Hong Mei Song, and Yan Bin Yang carried out research to identify the main influencing factors for edge cracking during the manufacture of duplex. These included the rolling temperature, phase proportion, ơ phase, and micro-alloying elements. The sulfur and oxygen content also proved important.
The researchers went on to explain that the starting and finishing rolling temperature, cooling rate, and precipitation of ơ phase needed to be strictly controlled during the rolling process, and that the proper phase proportion should be ensured to avoid hot brittleness cracks.
The good news was that their research uncovered several effective methods to solve problems in hot rolling. The technical paper explains these in greater details, but the three core points of their conclusions were that in order to control edge cracking the manufacturer must:
- Try to maintain the nitrogen and sulfur content in duplex stainless steel at a suitable level.
- Use every available method to ensure a rolling temperature of above 1000º.
- Design a reasonable compression ratio according to the strip thickness.
As you can see in the photos at the top of this blog, the company was successful in significantly improved edge cracking in its duplex stainless steel production following implementation of the methods described in the technical paper.