Design And Microstructure And Properties Of New Type High Expansion Duplex Stainless Steel

In the modern industrial machining fixture,the use of the difference between the thermal expansion coefficient of the tool holder(special stainless steel)and the tool(carbide)to greatly and accurately clamp the clamping of the tool greatly simplifies the complexity of the clamping system(17×10-6·K-1),and the higher strength(close to 40 HRC),the higher the thermal expansion coefficient(about 17×10-6·K-1)and the higher strength(close to 40 HRC).The use of low-cost industrial hair dryer simple hot air heating device,can be achieved at 300 ℃ low temperature to achieve hot operation.The high expansion coefficient alloy does not have a specific alloy system or material classification,which is mainly determined by the alloy crystal structure,alloying element type.In the general large-scale industrial applications,steel materials occupy an absolute dominant position.The austenitic stainless steel,represented by 304 stainless steel,has the highest coefficient of thermal expansion(greater than 18× 10-6·K-1)in the same material and has good corrosion resistance.But the use of the state of hardness is only about 16 HRC,tensile strength of only about 500 MPa,yield strength is only about 205 MPa.This study attempts to design a new alloy,the thermal expansion coefficient does not reduce too many cases,compared to 304 austenitic stainless steel,greatly enhance the strength.We first use JMat Pro thermodynamic simulation to simulate the effects of alloy elements on steel thermal expansion and mechanical properties.In order to selecte the suitable alloying elements.Then,through the thermodynamic simulation of the equilibrium phase diagram,two alloy components were designed starting from the 304 stainless steel composition,and one of them was selected by experimental verification.The heat treatment process of this component is explored and four processes are selected to test some performances.After the alloy was treated at 1200℃×0.5h,the average expansion coefficient of the alloy was 18.06×10-6·K-1 and the hardness was 21.75 HRC.After aging treatment,the matrix has been transformed into martensite.The average expansion coefficient is 16.66 × 10-6·K-1 aging at 650℃ for 2h,the hardness is 32.6HRC,the tensile strength is 1018.01 MPa,the yield strength is 355.03 MPa,the mechanical properties are the best aging at 700℃ for 6h,the hardness is 48.3HRC,tensile strength of 1235.92 MPa,yield strength is 460.73 MPa,the average expansion coefficient is 14.41×10-6·K-1.Compared to 304 stainless steel its mechanical properties have greatly improved.The oxidation resistance test of the alloy showed totally oxidation resistance grade at 600℃,650℃ aging 2h and 6h.The electro chemical polarization curves show that this four kinds of aging process at 650℃×2h,650℃×6h,700℃×2h and 700℃×6h corrosion resistance has no obvious difference.Chemical corrosion results show that the corrosion resistance of the alloy level is 5,corrosion level.