Microstructural Tailoring And Evolution Mechanisms Of Stainless Steel And Carbon Steel With Micro/nano-crystalline Structure By Annealing And Rolling

The 304, 316 L stainless steel and 20, 45 carbon steel with nano/micro-crystalline structure were prepared by an aluminothermic reaction casting method. The material was about 200 mm in diameter and 10 mm in thickness, and studied the microstructural revolution of the stainless steel after annealed with different time and temperature, rolled with different thickness reduction and temperature, first cogged and followed rolled with different thickness reduction and temperature. Study the microstructural revolution of the carbon steel after annealed with different time and temperature, rolled with different thickness reduction at 600°C. By analysis the grain size of nanocrystalline austenite, submicrocrystalline austenite and ferrite, and thier volume fraction in stainless steel; the volume fraction and lamellar spacing of the pearlite, the shape of the cementite in pearlite in carbon steel. We raised the mechanism of microstructure revolution according to research results.1. The 304 and 316 L stainless steel was annealed with different time at 800°C and 1000°C, after annealed at 800°C, the ferrite grain size increased with the annealing time; after annealed at 1000°C, the ferrite grain size did not change with the annealing time, and separated out Fe Ni Cr Al phase from stainless steel. The grain size of nanocrystalline austenite increased with the annealing time or the annealing temperature, but the volume fraction decreased, the higher of the tempera ture or the longer of the annealing time, this variation trend more obvious.2. After the 304 and 316 L stainless steel were rolled at 800°C less than or equal to 60% thickness reduction, the grain size of ferrite increased with the thickness reduction. After rolled more than 60% thickness reduction, the grain size of ferrite decreased; After the 304 stainless steel was rolled at 1000°C, the grain size of ferrite almost did not change with the thickness reduction. When the thickness reduction less than or equal to 40%, the grain size of nanocrystalline austenite increased with the thickness reduction, volume fraction decreased; when the thickness reduction more than or equal to 60%, nanocrystalline austenite grain vanished and turned into submicrocrystalline in 304 stainless steel, nanocrystalline austenite grain of 316 L stainless steel in itself was vanished, and produced nanocrystalline austenite grain which broke up from submicron austenite grain; after the 304 stainless steel was rolled less than or equal to 40% thickness reduction at 800°C and 1000°C, the volume fraction of submicron austenite increased with the thickness reduction; when rolled at 800°C more than 40%, the volume fraction of submicron austenite decreased with the thickness reduction; when rolled at 1000°C more than or equal to 60%, the submicron austenite grain vanished; when the 316 L was rolled at 800℃, the grain size and volume fraction of submicron austenite grain decreased with the thickness reduction.3. After the cogged 304 stainless steel was rolled at 700 and 600°C less than or equal to 50% thickness reduction, the grain size of ferrite increased with the thickness reduction, when the thickness reduction was 70%, the grain size of ferrite almost did not change. The grain size of nanocrystalline austenite increased with the thickness reduction, grain size of submicrocystalline austenite decreased. After rolled at 700°C, the volume fraction of nanocrystalline and submicro crystalline austenite decreased with the thickness reduction. After rolled with 50% thickness reduction at 600°C, the volume fraction of nanocrystalline austenite decreased, the vol ume fraction of submicrocrystalline austenite increased; after rolled with 70% thickness reduction, the volume fraction of nanocrystalline austenite increased, the volume fraction of submicrocrystalline austenite decreased.4. When the cogged 316 L stainless steel was rolled at 700°C less than or equal to 50% thickness reduction, the nanocrystalline austenite grain vanished,the grain size of ferrite and volume fraction of submicrocrystalline austenite almost did not change with the thickness reduction; when the thickness reduction was 70%, the submicrocrystalline broke up to nanocrystalline austenite grain, the grain size of ferrite increased and the volume fraction of submicrocrystalline austen ite decreased. After rolled at 600°C, the grain size of ferrite decreased with the thickness reduction; when thickness reduction more than or equal to 50%, submicron austenite grain broke up and appeared nanocrystalline austenite grain, the grain size of nanocrystalline austenite decreased and its volume fraction increased with the thickness reduction; grain size of submicron austenite decreased and distributed more uniformly, and the volume fraction also decreased.5. The 20 and 45 carbon steel was annealed at 600°C with different time, the volume fraction of the pearlite almost did not change with the annealing time, the lamellar spacing of the pearlite increased. After the 20 carbon steel was annealed at 800°C with 2h, the pearlite globularization almost completely; after annealed with 16 h, the pealite disappeared and separated out Fe3 C from surface of the steel. The 45 carbon steel was annealed at 600°C less than or equal to 4h, the structure of the pearlite was lamellar structure. When the annealing time was more than or equal to 6h, the pearlite began globularization, the globularization of pearlite more and more significant with the annealing time. After the steel was annealed at 800°C with 2h, the pearlite was still kept in lamellar structure, after annealed with 16 h, the majority of pearlite globularization.6. The 20 and 45 carbon steel was rolled at 600°C with different thickness reduction, the volume fraction of the pearlite almost did not change. When the thickness reduction was 20%, the cementite in pearlite began to break up; when the thickness reduction increased to 40%, the lamellar cementite broke up to rod cementite; when the thickness reduction increased to 60%, some rod cementite broke up to globular cementite; when the thickness reduction rose to 80%, the globular cementite broke up to submicron cementite particles; when the thickness reduction increased to 90%, the submicron cementite particles of the 20 carbon steel broke up to nano cementite particles, while the size of the globular cementite particle of the 45 carbon steel increased.