| In this paper, the316LN austenitic stainless steel was taken as the object in this study. The experimental or analytical equipments such as Metallographic microscope, SEM, Multifunctional mechnical testing machine, Gleeble-3500thermal simulated test machine and chamber electric furnace were used. The contents of this study are as fllows,(1)The metallographic microstrcture’s change rule, the grains growing up ways and laws, and the mechannical property’s change rules of solution-treated316LN stainless steel with different initial grain structural conditions.(2)The influence of different cool rates to the preciptated phasen, and the influence of different ageing time and temperature to the preciptated phase.(3), the change of grains microstructure after solution treatment with different cold deformative rate.In the solution experiment part, three kinds of316LN stainless steel samples with different initial organization condition named as samples Ⅰ, Ⅱ and Ⅲ were studied. Samples Ⅰ were inhomogeneous, samples Ⅱ were homogeneous while the grains size is not very fine, and samples Ⅲ were homogeneous and fine.When Samples Ⅰ are solutioned at1000℃, with the prolongation of holding time, the grains grow up in a abnormal way, a few oversize grains are surrounded by fine grains. After solution for720minutes, the average size of grains is90.8μm, the size and holding time have a approximate linear relation.When samples Ⅰ are solution treated at1050℃, with the prolongation of holding time, the grains grow up in a normal way, all the size of the grains are similar. While the holding time is less than120minutes, the grains grow up rapidly, and then become slower gradually. The average size of grains reached187.0μm after holding for720minutes. The growing law of grains is according to the Beck equation, the relationship between average grian size and holding time is D1050=12.90t0.2518.Solution treated the samples, Ⅱ and Ⅲ at1100℃, with the prolongation of holding time, all the grains grow up in a normal way. Samples I have the maximum growing rate, Ⅱ are in the middle, and Ⅲ have the minimum,which certified that the finer the initial grain, the harder it to grow up. While the holding time is less than180minutes, the grains grow up rapidly, and then become slower gradually, the average size of the samples respectively reached355.2μm,323.7μm and240.8μm after holding for720minutes. The growing laws of grains are all according to the Beck equation, the relationship between average grian size and holding time are D Ⅰ=22.36tt0’2569, DⅡ=26.73t0.2313and DⅢ=29.78t0.1901. While solution treated at this temperature, Besides, comparing with the growing rates of samples I at three solution temperature, it can be found that the higher the solution temperature is, the quicker the grains grow.The mechanical property test is taken for the three kinds of samples solution treated at1100℃for different time. The results show that, the tensile strength, yield strength, elongation and reduction of area of samples I are relatively steady within180minutes, and just fluctuate in a small range. While solution time is over180minutes, all the properties fall down rapidly, the properties become steady again after360minutes. The tensile strength and yield strength of Samples Ⅱ and Ⅲ decline gently in the mass, The elongation and reduction of area are all increase first, and then decrease, at180minutes reach the maximum. By morphology observation of the tensile fracture, all the samples have excellent plastic fracture, fibrous region and shear lips region are obvious in the fracture.The316LN stainless steel was cooled at different rate after solution-treatment. When the cooling rate is slower than12℃/min, corrosion pits appear in the grain boundary after etched by vilella reagent, and this implies the corrosion resistance of grain boundary becomes worse. When the cooling rate is slower than0.5℃/min, the second phase grains are observed obviously after etching, all the grains are rich in Cr and (or) Mo when tested by EDS.Aging at500℃、600℃、700℃and800℃separately, the results show that, with the rising of aging temperature, the precipitation time of316LN stainless steel shortened rapidly. The precipitates can not be obserbed after aging for50h at500℃, but at600℃aging for25h, or at700℃and800℃for4h, the precipitates can be observed, all the precipitates are rich in Cr and (or) Mo.Compressing the316LN stainless steel at room temperature, the results show that, with the increasing of deformation, the slip bands appear on the grain boundaries primarily, and then on the twin boundaries gradually. Keeping the deformed samples at1100℃for120seconds, and the result shows that, the critical deformative range of static recrystallization of316LN stainless steel is7.57%-12.43%. |
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