Study on Evaluation of Residual Phase Stress of the Dual Phase Stainless Steel

In this study , we measured residual stress in ground layer of ( CY+ r )dual phase stainless steel by X-ray diffraction. In addition, the influence of changing depth of cut on residual stress was investigated. It was found that residual stress in the a! phase was dependent on depth of cut, while the stress in Y phase was not affected by depth of cut. As a results of stress measurement under applied stress, deformation behavior of ground layer which had large tensile residual stress was related to plastic deformation. INTRODUCTION ( o+ 7 )dual phase stainless steel is composite material consisting of a ferrite phase ( a phase) and a autenite phase ( 7 phase), and have high strength compared with single-phase stainless steel (I). Grinding is used for a manufacturing process, and residual stress and plastic strain occurs in the materials during grinding process. Especially, residual stress influences strength of materials. Evaluation of residual stress is important when strength of a material is evaluated (‘). X-ray stress measurement method is effective for the stress measurement of composite material (3). In this study, residual phase stress in ground layer of the dual phase stainless steel measured by X-ray diffraction, and influence of depth on the cut for residual stress was discussed. In addition, deformation behavior of the each phase during bending test was discussed. EXPERIMENTAL PROCEDURE Materials and specimens ( o + r )dual phase stainless steel(JIS-SUS329J4L), which was manufactured by a continuous casting, was used in this experiment. Microstructure of this material was shown in Fig.1. The 7 phase(inclusion) distributed in a phase(matrix). Chemical component and mechanical properties are shown in Table1 and Table2. Specimens were fabricated to a configuration having a length of 50mm, a thickness of 6mm and a width of IOmm by cutting, milling and grinding from a rolled plate of thickness of 6mm. Then, it was ground under the condition shown in Table3. The longitudinal direction and grinding direction of the specimen coincided with the rolling direction. Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol.44 222 Fig. 1 Microstructure of SUS329J4L. Table1 Chemical compositions of specimen (wt. %). Mn Cr Ni MO Fe 0.91 24.67 7.37 3.01 Bal. Table2 Mechanical properties. Yield strength 0.2% offset Tensile strength Elongation Reduction of area Hardness test 598 MPa 778 MPa 39% 71% 255 Hv Table3 Grinding conditions. Grinding wheel 180~13UW60KV.58 Grinding width ,mm/pass 13 Grinding direction Down-cut Number of pass 1 Nominal depth of cut , fl m 0,20,40,60,80 Table speed ,mm/sec. 170 Spindle speed ,r.p.m 3460 Theory of X-ray triaxial stress measurement Residual stress of composite material could be triaxial stress (4). In this study Ddlle-Hauk method (‘) was used as stress analysis. We write Xi for the specimen coordinate system, and Li for the laboratory coordinate system as shown in fig.2. When a lattice strain measured by a X-ray diffraction experiment and phase stress are expressed with E m I$k, gif, relation of both are expressed as eq( 1). ‘( k E’ PV = 2 a:, cos* 0 + a:, sin 2@ + ai, sin’ @)sin* v + S$ co? w + SF 2 ( 0:, + 0& +“:I)+$(~~~cos)+~~~sin~~in2y (1) sIk, szk I2 are X-ray elastic constants and the symbol k indicates each constitution phase. We defined a, k, azk as eq(2). ka, = ~c:,>o +&J )? 4 =;(&>” -E:,<“) (2) Substituting eq(2) to eq( l), we obtain eqs(3),(4). u: = $(0:, cod $ + a:, sin 24 + c$, sin* ) o&))sin* y + $o& + s: (OF, + 0& + 0:;) (3) u; = $ o,, cosq3 +c7:, sin @)sin 2v 7 1 (4) Using eqs(3),(4) and measured strain of @=O” ,45 o ,90” direction, we can calculate stress component( CJ II(7 33, o Z(3 33, iJ 31, 0 23, 0 12). u ,, and u 22 is able to calculate from the value of u ,Iu 33, U 22u 33 and U 33 calculated from intercept of aI k-sin2 ti diagrams. Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol.44 223