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

Transcription

1 Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol Study on Evaluation of Residual Phase Stress of the Dual Phase Stainless Steel Hajime Hirose*, Hideaki Hashi** and Toshihiko Sasaki** *Kinjo College, KasBma, Matto, , Japan **Kanazawa University, Kakuma-machi, Kanazawa, 920-l 192, Japan ABSTRACT 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. Fig. 1 Microstructure of SUS329J4L.

2 This document was presented at the Denver X-ray Conference (DXC) on Applications of X-ray Analysis. Sponsored by the International Centre for Diffraction Data (ICDD). This document is provided by ICDD in cooperation with the authors and presenters of the DXC for the express purpose of educating the scientific community. All copyrights for the document are retained by ICDD. Usage is restricted for the purposes of education and scientific research. DXC Website ICDD Website -

3 Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol Table1 Chemical compositions of specimen (wt. %). Mn Cr Ni MO Fe 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$k, gif, relation of both are expressed as eq( 1). k E PV = ( 2 a:, cos* 0 + a:, sin 2@ + ai, v + S$ 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). a, k- = ~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; = $ 7 o,, 1 cosq3 +c7:, 2v Using eqs(3),(4) and measured strain o,90 direction, we can calculate stress component( CJ II- (733, o Z- (333, ij 31, 0 23, 0 12). u,, and u 22 is able to calculate from the value of u,i- u 33, U 22- u 33 and U 33 calculated from intercept of ai k-sin2 ti diagrams. (4)

4 Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol Fig.2 Definition of coordinate system and angles 6 and ti. A method for determining plastic strain For dual phase composites, which consist of both isotropic spherical inclusions and isotropic matrix, the following equations are obtained from the EshelbyIMori-Tanaka model (We). ~,-a;l,=3b (~-~)-3B,(l-fX~-~) (6) A E ij is a difference of the plastic strain between the matrix and the inclusion. Other parameters in eqs(5),(6) can be obtained from Young s modulus of the matrix(e), and the inclusion(e*), Poisson s ratio of the matrix( u ) and the inclusion( v *) respectively using using the following equations. 3R 2(4-5~) p= (1-v),p= J =$,B, = 2(p;)pp R=P-[P-.W-WP-P*) The symbolfindicates volume fraction of inclusion. From eqs(5),(6) we have following equation. A&:; -A&:; = + (a;, - o;, )- 5 (CT;; - 0;; ) (7) (8) From eq(8) the plastic strain A E pii - A E q3 can be obtained using phase stresses( u /? constants(e, E*, u and v *) and the volume fraction of the inclusions(f) are known. u lj!> when material Conditions for X-ray stress measurement Each residual phase stresses in a phase and ~Phase were measured using the X-ray stress measurement method. The conditions used for the X-ray diffraction experiment are summarized in table 4. Table4 Conditions of X-ray diffraction. o -phase 7 -phase Characteristic X-ray Cr-K (I! V-K cr Diffraction plane, hkz K /LI-Filter V Ti Tube voltage, kv 30 Tube current, ma 10 Fixed time, sec. 2 5 Number of 11, tilt angle 7 Irradiated area, mm* 8X8 Diffraction angle in stress free, deg X-ray elastic constant (2/s2),GPa

5 Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol Peak determination Scanning method Half value breadth method Z!J constant method Iso-inclination method Conditions for loading experiment The evaluation method of deformation behavior of ground layer is as follows. Changes of stress measurement under applied stress was measured by means of a two point bending jig shown in Fig.3. The applied ranged from to +1000X IO with an interval of 250X 10M6. The applied strain was monitored by means of strain gauge bounded to the specimen on the surface opposite to the X-ray irradiated one. It was converted into applied stress from applied strain by using experiment value of mechanical Young s modulus( 194GPa). Fig.3 Two points bending jig. RESULTS AND DISCUSSION Debye-Scherrer ring Fig.4 shows examples of the Debye-Scherrer ring obtained from ground layer of the specimen(down-cut80,v m). The distribution of the intensity for the rings from the specimen is continuous and almost uniform. The measurement results means there is enough number of grains to carry out the X-ray stress measurement successfully and extreme texture is not formed in this specimen..- Fig.4 a-211 I Debye-Scherrer rings obtained from Down-cut80 ti m specimen using image plate Sin 11, diagrams Fig.5 shows E -sin2 II, diagram of 6 =0,45,90 obtained from specimen(down-cut 80 LL m). The 11, -splitting ( O) is hardly observed in a graph of 6 =O and 90. It means the value of u 31, u 23 is very small. In addition, (3 t2 was calculated from a measurement result =45, and it was also small value. It appeared that the value of CJ r, is larger than it of u 22 because slope of al-sin2 ti diagrams becomes gentle with increase of 6 angle.

6 Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol ^ sin G sin 11 (a) a! Phase =O, middle: 6 =45, =90 ) sin* ti ^ sin?i> sin * - ai -3Oa sin2 ti (b) 7 Phase (Left: & =O, middle: & =45, right: & =90 ) Fig.5 E -sin* Q diagrams. Influence of depth of the cut for residual stress Fig.6 shows distribution of residual stress in ground layer measured from specimen. (T 1 r and (T22 in the (Y phase increased as depth of cut increased. On the other hand, the stress in r phase was not affected by changes of depth of cut. It is supposed that energy by grinding process was spent not for increase of residual stress, but for martensitic transformation. The value of (~~3 showed very small value in both phase. It was considered that the value of triaxial stress element( ~33) was relaxed by effect of free surface because particle spacing of inclusion was larger than X-ray penetrating depth Nominal depth ofcut, n m Nominal depth of cut, n m Fig.6 Result of residual stress measurement. Deformation behavior against elasticity loading Fig.7 shows the changes of phase stress from residual stress under the applied stress. The plots in the figure indicate measured value and the lines indicate theoretical value calculated using eqs(5),(6). It was assumed (7 ss= A E pr I= A E p33=0 in the calculation of the theoretical value. The left figure shows data obtained from specimen(0 ti m), and the right figure shows the one obtained from specimen(down-cut80 /J m). As a result, it was found that measured stress obtained from 0 fi m specimen agreed well with theoretical one. The measurement value of Down-cutSOym specimen also agreed with theory under the compressive loading. On the other hand, under the tensile applied stress, they have smaller value the volume fraction exceeds this value. The difference between the experimental and the theoretical results increases when the applied stress becomes larger.

7 Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol OOL I!s a! Phase / OiLIT m l(m)- (ak=131mpa) 3,./ n 2 o- b a -loo-,/ &',9-2()().,,,,, I,, Applied stress (7 All, MPa (a),*/ 0,U m ( o Phase) 2oot y Phase #/ 1 cd loo- O/m (o,=475mpa) n z o- b a -1oo I I a Phase A cd loo Dovmcut80lr m cd f, 0 c- a -100 (u,=1367mpa) t,a, Applied stress (7*t t, MPa (b) Down-cut80 LL m ( Q! Phase),,,i * NO Applied stress u ll,mpa Applied stress (7*t t, MPa (c) 0,U m (7 Phase) (d) Down-cut80 LL m ( Y Phase) Fig.7 Changes of phase stress. Fig.8 shows distributions of A E ij. The A E ij was calculated by eq(8) using measured phase stress of each loading. The A E ij of 0,U m specimen was almost constant. On the other hand, case of Down-cut80 /-L m the A E increased with tensile applied stress increase. In the ground layer which had large tensile residual stress over the yield stress, plastic deformation occurred by tensile loading. It is considered that plastic deformation in the layer play important roll in decreasing of changes of phase stress. -12 I 3 I I 1 I I I - OlLm 22 - Down-cutSO!L m t t 0 _ z-14- ^ x I P $15 F---- ; 19 I---- a I I, I, I I I I, Applied stress CJ t t*, MPa Applied stress u IIA, MPa 200 Fig.8 Changes of A E p in ground surface. CONCLUSIONS As a result of residual stress measurement in ground surface of ( (Y + ) ) dual phase stainless steel, it was found that u 11 and cr22 in the a phase was dependent on changes of depth of cut, while the stress in Y phase was not affected by changes of depth of cut. The value of crj3 was close to 0 in both phase. Deformation behavior of ground layer which had large tensile residual stress was related to plastic deformation. REFERENCE 1) Oyama,T., Morita,S., Yoshitake,S., A story about stainless steel, 147( 1990), Japan standard association 2) Kometani,S., Occurrence of residual stress and the measures, 163 (1975), Yokendo

8 Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol ) Japan Society of Materials Science, X-ray Stress Measurement Method, l( 1981),Yokendo 4) Tanaka,K., Matsui,M., Yomo,R., Nishikawa,T., Japan Society of Materials Science, 41,593 (1992) 5) Diille, H., Hauk, V., Haerterei-techn.Mitt.3 1,165-l 68., 12,489 (1979) 6) Eshelby, J. D., Proc. R. Sot. London, A241,376(1957) 7) Mori, T., Tanaka, K.,ActaMet., 21, 571(1973) 8) Sasaki, T., Rin, J., Hirose, Y., Japan Society of Mechanical Engineers, A-63, 370 (1997) 9) Sasaki, T., Rin, J., Hirose, Y., Japan Society of Mechanical Engineers, A-62,274 1 (1996) 10) Hanabusa, T., Fujiwara,H., Japan Society of Materials Science, 30, 1095 (198 1)