Experimental Study On Edge-cracking In Low-Nickel Austenitic Stainless Steel During Hot Rolling

Austenitic stainless steel is prone to suffer from edge cracking, edge damagingand other defects in hot deformation. A large number of experiences have been accumulatedfor influencing factors in edge cracking, but these factors have not been uniformunderstanding. Utilizing cheaper nitrogen and manganese substituting some or all nickel, thelow-nickel austenitic stainless steel is developed. This steel is easily prone to suffer from edgecracking, edge damaging and other defects in hot deformation.On the basis of stress state and deformation feature of slab during hot rolling and basedon Thermorestor-W thermal simulator existing function, an experimental hot rolling device isdesigned and made. This device c ould b e us e d c oop er at e with t h erm al simula tor,and t he a ctu al hot-rollin g pr odu ction pro ces s c ould be si mulat ed th rou ghthe d evi ce. Then, hot rolling tests conducted on this device are performed on the samplesfrom Cr₁₅Mn₉Cu₂NiN and Cr₁₇Mn₆Ni₄Cu₂N slab shell to investigate formationmechanism of edge cracks. Press quantity is10⁶0%. Deformation temperature is in the rangeof950¹250℃, and temperature interval is50℃. Side morphology of rolled samples isobserved and analyzed, especially production situation of edge cracks.As for Cr₁₅Mn₉Cu₂NiN slab, when press quantity is large enough, samples will crackon edge at all test temperatures. All the edge cracks propagate along austenitic grainboundaries. In the range of975-1150℃, cracking tendency of samples is severe. Thecharacteristic of microstructures in hot rolled specimens is deformation substructures andtwins boundaries in coarse grains in this temperature range. But at1200℃, the grain size ofspecimens is smaller, and all substructures and twins boundaries disappear in the grains.During small press quantity and multiple passes hot rolling, cracking tendency of samples isrelatively smaller. Twins boundaries and the refined recrystallization grains are observed inmicrostructure of samples, but deformation substructures are not observed in grains. The grainsize is more uniform with increasing the quantity of rolling passes.As for C r17Mn6Ni4C u2N slab, in the range of1100¹150℃, cracking tendency ofsamples is severe. The certain quantitative of ferrite is observed in rolled samples. As thetemperature increases, the ferrite size on grain boundaries or in austenitic grains increases.Ferrite is continuous vermicular on austenitic grain boundaries, or p arti c le in aust eniti cgrai ns t hat w as t he same a s C r15Mn9Cu2NiN. After deformation, dendrite t runksof Cr₁₇Mn₆Ni₄Cu₂N suffer from dislocation and distortion, meanwhile, the originalsecondary grains are distributed in particle. The grain size is smaller in Cr₁₇Mn₆Ni₄Cu₂N rolled samples.