Study On Simulation Of Atmosphere Corrosion Of 316L Steel Of Reduction Furnace

Nowadays, corrosion problems caused by corrosive gas in the inner surface of the reduction furnace have posed potential threat to safety during polysilicon production. This paper targets at the existing corrosion in the reduction furnace and involves system design considering research reduction furnace corrosion defects.Thermodynamic data is applied to analyze complex ternary system “Si-Cl-H” in reduction furnace; the specific parameters of the test are set according to the environment of the reduction furnace. 316 L stainless steel specimen with weld joint and 40% cold plastic deforming specimen is corroded at 200 ℃、350 ℃、 500 ℃ with 0.2%、15% HCl under 48h、96h respectively. The analysis of metallographic microscope and scanning electron microscope are used to observe the surface of specimen after corrosion. Moreover, XRD is used to analyze corrosion products; using EDS to test elemental composition in a certain area.The original base material is equiaxed austenite grain, of which the boundaries got thicken after corrosion. This shows that intercrystalline corrosion, pitting corrosion and crack are most likely to happen in the weld joint and heat affected zone. In the process of tensile, the organization of 40% cold plastic deforming specimen is subjected to martensitic phase transformation and as a result the lath martensite α’ takes place. The pitting corrosion has increased and deteriorated. Uniform corrosion, pitting corrosion and corrosion crack both happens in three kinds of organizations. The corrosion of 316 L austenitic stainless steel proves to be a pure chemical reaction during 200~500℃, and the corresponding chemical reaction can be: 2Fe+6HCl=2Fe Cl3+H2. The pitting corrosion is caused by the inclusions and loosening. Other factors which cause the corrosion can be non-austenite、cold plastic deforming defects in heat affected zone. The pittiong corrosion of heat affected zone and cold plastic deforming specimen is more serious compared to other factors. Furthermore, 316 L stainless steel stress corrosion may occur along with 500 ℃, high working stress(about half the yield strength) and HCl atmosphere. Carbide ferrite is precipitated in heat affected zone grain boundary, which is sensitive to stress corrosion. Cold plastic deformation will help to turn austenite partly into martensite. Surface float and defect will happen which become the source of pitting corrosion. Pitting corrosion can be become the source of crack and lead to stress corrosion cracking under the effect of stress.Comprehensive analysis of the test results and the corrosion of Reduction Furnace are made and prevention and improvement measures are put forward. Structure of polysilicon reduction furnace is improved on.