m 45 � m 4 � Vol.45 No.4

2009 u 4 � m 428—433 [ ACTA METALLURGICA SINICA Apr. 2009 pp.428–433

Oqy^}℄v 54SiCr6 YSjdlT ∗

�� ��� �Æ� �� �� ���(0-)A��TK�e4T'L)A-i (E<) =QI, 4T 110016)~ { ~��ZN� 54SiCr6 3 4EKkut� (=?��, 85:4G) g|98r6J.K:�y. sy|9KUQ mCny:�S2j, 3 4EK8�~mg|9�yvyV2�. |.���h, 3 4|9U�Y�v!{g|.4^. x1db�mC| [, +ada!{8�|9�y#mgsH'�, M���%!{8�g!{KUg���|9�yp!^�.Z_R ��ZN�, EKk, |9�y, �mC| [�rVWf\ TG 142 twMoh A t�L\ 0412−1961(2009)04−0428−06

FATIGUE STRENGTHS OF THE 54SiCr6 STEEL UNDER

DIFFERENT CYCLIC LOADING CONDITIONS

CHEN Shuming, LI Yongde, LIU Yangbo, YANG Zhenguo, LI Shouxin, ZHANG ZhefengShenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences,

Shenyang 110016

Correspondent: CHEN Shuming, Tel: (024)83978023, E-mail: smchen@imr.ac.cnSupported by National Basic Research Program of China (No.G2004CB619100)Manuscript received 2008–09–19, in revised form 2008–12–22

ABSTRACT Since ultrasonic fatigue test has been used to study the very high cycle fatigue(107—109 cyc), the difference between ultrasonic and conventional fatigue test methods should beevaluated in order to ensure the validity of ultrasonic fatigue result. By comparing some results ofother researchers, it is found that the frequency effect is negligible, and the loading condition is themain reason for the difference. A comparison of the fatigue strengths of the 54SiCr6 high strengthspring steel under three kinds of cyclic loading conditions, rotating bending (RB), tension compression(TC) and ultrasonic (UL), was reported. The results reveal that the three kinds of fatigue specimensdisplay different fracture features, and the fatigue strength of RB is the highest, TC is the lowest,and UL is somewhere in between. The difference in the fatigue strengths is mainly attributed to thedistinctions of stress gradient and the size of specimens. By taking highly stressed cross–section area(HSCA) into consideration, a relationship of the fatigue strength and loading condition was proposed,and the two constants σlim,0 and αΞA in the equation of HSCA are mainly dependent on materialstrength and inclusion size, respectively. A relationship of fatigue strengths between RB and TC isalso discussed specifically.KEY WORDS high strength spring steel, cyclic loading, fatigue strength, highly stressed

cross–section area (HSCA)����h6+�8}: (� 107 cyc) `��7KWI?SM�,<W*rh�E>���?S (rotating

bending, p< RB) ba6+5H?S (tension com-

pression, p< TC). �w6, rz����rvuhq�, ;W��9�8}: (107—109 cyc) �7?SM�,<W*rh�E96}:?S� (ultrasonic, p<* .j6oWFL���dHB=(o G2004CB619100MaB�" : 2008–09–19, Ma:��" : 2008–12–22H�o� : ;Yk, p, 1983 v7, ^D7

UL), k� I�Yz� (15—30 kHz), sWW~:K}:?S<n;�r [1−7], k�#il�7J.96}6+ TC }:h<W��E�Y;l�Ah3�. Furuya j [8], Marines j [9] ; Wang j [10]y26+}: (10—100 Hz) ;96}: (20 kHz) h[� �, !��Yh�I�(Mh}:9so'"W.

Ebara[1] !�nD\�zk (}:^#��) <, �Yho'?+. ��z RB, EK.W�Y3��, MwnD $h"| [11]. M�96;6+}:h3�, s$w>z a��-}:?S�w�3&hK�, �96}:?

m 4 � :Xji : zDJ7� 54SiCr6 �f{8Æx 429�Seb�℄%h��}nr.�Æ?�Kq3h-r[O� 54SiCr6, *r&|h�H?;l , 1eD 3 5F="|}:LSZhV��7?S. }:?SC, N��O��,�7 �, *r)er��7}/)1. �L, �z"|?Svu�hS–N �%;}:�zh3�. GC, Br�95Ag�nhnDoz(�, �=�hÆ [�, �"|l�vu�}:�zh3��DKtI&e.

1 nzP��?S*rhE%�� 15 mm h�� 54SiCr6 �(, �IC= (/I [, %) �: C 0.57, Si 1.52, Cr

0.71, Mn 0.68, S≤0.01, P≤0.01, Al≤0.015, Fe {I.gwV��l =52LV; 3 5}:V�h℄z, �*r&|h�H? : 870 ��� 30 min �HsICuP; 430 ��� 45 min PT. ?SV�h�5}AT%� 1 gC, �K�V�h}O,�2, ?SV�w*r,V51e. �Kq/�d�"�}:9sho', _L*r 400, 600, 800, 1200 ; 2000 6+*� 3 5V�h�d�7Mn. RB, TC ; UL LV �Æ/4 PQ1–6I��}:LSZ, /4 PLG–100C rJ.�}:LSZ;^� USF–2000 96}:?SZ.�7/L. �FLl��Y �� 89 Hz, 110 Hz ; 20 kHz, �2 UL?Sh#�n�<n� 150 ms. �K�z�z, �9�R "� −1. tz?S<nh#., RB ; TC ?S/t107 cyc <}:�z, � UL ?S/t 107 } 109 cyc <}:�z. }:�z*r9x�/t. r LEO–SUPRA–

35)er� (SEM) �}:}/5_, �>s� (EDS)�tO��Hh��5<.

s 1 >Rq|9KUg�SFig.1 Dimensions of the samples used in fatigue tests of

rotating bending (RB) (a), ultrasonic (UL) (b) and

tension compression (TC) (c)

2 nz`[2.1 m|kexi��H?C, 52?SÆ Instron 8801 ?SZ.�7, n�aY� 10−3 s−1, �DC9s (�2: �Æ�zσs, '5�z σb, N2Y δ, Hpz HV ba}:�zσ−1) %� 1 gC. 3 5?SV�h S–N(}:nD (σa)

— }:Om (Nf)) �%%� 2 gC. N�,s, RB ;N 1 54SiCr6 ZN�gCB8rTable 1 Mechanical properties of commercial 54SiCr6 spring

steel

σs σb δ HV σ−1, MPa

MPa MPa % GPa RB UL TC

1628 1882 10.6 5.26 843 7411),766 663

Note: 1) 741 is the fatigue strength for 109cyc and the oth-

ers for107cyc

104 105 106 107 108

800

900

1000

Ran out

Surface of matrix Internal inclusion

a, MP

a

Nf, cyc

(a)

843 MPa

Origin of the fatigue crack

104 105 106 107 108 109600

700

800

900

Ran out

Internal inclusion Surface of matrix Subsurface inclusion

a, MP

a

Nf, cyc

(b)

741 MPa

Origin of the fatigue crack

104 105 106 107 108600

700

800

900

Ran out

Surface of matrix Internal inclusion

a, MP

a

Nf, cyc

(c)

663 MPa

Origin of the fatigue crack

s 2 3 4>RU�g S–N �$�Fig.2 S–N curves of the fatigue specimens tested in RB (a),

UL (b) and TC (c)

�430 ��S��� m 45 �TC h[� (9�zW, ��} UL "|hE, iah}:O�b8,<WÆ�d, � UL �Æ 107 cyc q�wz�hq&h���O. Æ}:�zh��., ,b%b RB G�, � UL L$, GkE TC. �nh}:�z[�eNz� 1, �-�0w�i?Sl�Ah"|�S–N �%a}:�zwzWo'.

2.2 UbXuy2� 3 5V�h}/)1, %� 3—5 gC, ,b%b�D�w℄tmQh5_. �2 UL ; TC LVh}/5_�z&�, ,b%bO����w�A��jh3��, �C�&la3��, GC�&52℄}�,

s 3 UL KUg|. SEM ��Fig.3 Fractographs of the specimens in UL fatigue test

(a) macro graph, 775 MPa, 8.825×105 cyc, crack ini-

tiated at the surface of specimen

(b) crack initiated at internal CaO·(MgO)x inclu-

sion, 775 MPa, 1.027×107 cyc

(c) crack initiated at internal Al2O3·(MgO)x inclu-

sion, 750 MPa, 6.469×108 cyc

s 4 TC KUg|. SEM ��Fig.4 Macro (a) and micro (b) fractographs of the spec-

imen in TC fatigue test under 675 MPa and 4.5×

106 cyc, crack initiated at the surface of specimen

s 5 RB KUg|9|. SEM ��Fig.5 Macro (a) and micro (b) fractographs of the spec-

imen in RB fatigue test under 825 MPa and 4.2×

106 cyc, crack initiated at the surface of specimen

m 4 � :Xji : zDJ7� 54SiCr6 �f{8Æx 431�}/z��!. RB LV} UL, TC LV}/h��<WEO��;℄}�h $: %0NO��;LV22G℄v%%, UL ; TC LV}/%%G�h5_X�℄+,� RB LVh℄}�~z℄-. T�, RB h}/z UL; TC h}/O,.N�O,(X, ULLVh�O,<WÆh��,�;LVh}:Om7{w(. Es6%, �nz�nDhk8� (107 cyc b�), b�d�"�O�� (� 3a),t�dl ℄>;I�dh��l�$O; ��nzknDh�8� (107 cyc b.) Ebh���< (� 3b, 3c),|<D�y6g<h GBF � (granular bright facet, p< GBF)[12], V� ODA � (optically dark area, p<ODA)[13], }9�8}:hm &�=. y2 EDS �,", h��h5<� Al2O3, MgO ; CaO, VEiah�=h�, w<Zw TiN; GWh�� 31 µm, G+�12 µm, �"h�AT� 16.7 µm.�z TC ; RB ?S, tzk8� (107 cyc b�)h}:�z�l_7z�dl /I, gb W�[ME�d�O (� 4—5). T�, RB LVhnD $E�0W, 2&+, ���d�$d=�}:O��, �s�1wSÆl\& �7 �. RB LV�d}:�O�d*G-h3�azz0, �2}>�*&�h℄-, O�3��0, `+K}:E%48~�. �Etz}:���v** >�<, }:� dh& �bnDz+h,, $dPb�=o', �}:�CdhR�p{�GWnDh,<, PO��=o'z+, O�ÆKf<3�,�V���=* >�hO��*C3��0, N�48K}:O��;GC℄}�h"�< $ (� 5a), �ERB LV}/h℄�m . K�, tzO�O�d3�0,3�ChE%*}:�*~�, }}:���hhE%~�*&�, �E RB LV}/hn��m [14].

3 pg� 1 ;� 2 �i, '5�9�h}:�zRÆ�zWh3�. UL ; TC LVg?PhwE�<5H�9,Æ�}d.`wnDoz $, wEY*nD; g"|h)E�Y;}d\h"|. &(M� [1,8−10] �i, �Y,nho',bDZ. tzLSZvuh#., g/V�h}d\"|, ,!� TC ; UL h}:�z3�Etz}d\h"|�=h (AT,n). � RB Æ?S2>2EKAT,n, MRÆAnDozho', %� 6 gC.�E RB }:�z�Wz TC ; UL }:�zh<W�k, ZE�N�d�Oh7W�k.dAV�s\h�l, V�2D��O�, �", �Vh�ba-�jh Y�l, N��lK}:}Oh Y, `+}:�z�x. (zAT,nhM� [15−19] `w?�, �2 Carpinteri j [19] *rh�E Weibull

s 6 RB KUmC�#:�mCr[Bf� [11]

Fig.6 Stress distribution and schematic of highly stressed

volume for cylindrical specimen in RB fatigue test}e�x;[C 5�. �Ær�nDs\h�x [20], �tnDoz;s\�I#|48h�}:9sho'. �>���LV, nD σ h $ (� 6) 4[�σ =

x

rσ0 (1)A2, x ��LV9%h�=, r �LV��, σ0 �GWh�dlhnD. �z>���, *r Kuguel[20] h�nDs\�x, th�nDs\ VΞ �LVl�<�z Ξ �GWnD& hs\, y6� Ξ � 0.90 V 0.95, s\�

V0.90 V V0.95, !�)w VΞ & )S�}:�z48o', �nh VΞ �W, �}:�z�k. �nh}:�ze "A�σlim,χ1

σlim,χ2

=(VΞ1

VΞ2

)αΞV

(2)A2, σlim,χ1; σlim,χ2

�|5(MG5nDoz�hV�}:�z (χ1, χ2 �X�G5V�hnDoz\�),

αΞV �t(M9sg�th6[. Sonsino[21,22] (D:RÆ℄�Q�s\ (��W�Æ 30—60 mm3), 92��s\}:�zw"��x. �z�?S, tz*rK,V51e, }:}O�#Æ℄�G+h}d��, `w92Q�s\. �Kp�, *r}d\Xts\h�, ,beb�A:σlim,χ1

σlim,χ2

=(AΞ1

AΞ2

)αΞA

(3)A2, αΞA �t(M9sg�th6[, A �}d\. %0� AΞ2=1, �nh σlim,χ2= σlim,0, �.A�/�

σlim,χ = σlim,0AαΞA

Ξ(4a)��[Ce:

lgσlim,χ = lgσlim,0 + αΞAlgAΞ (4b)�z RB, %0(XnD�zGWnD σ0 h Ξ �, |<(XnDoz, bnD}��h%9(� (A (1)), w:

AΞ = πr2(1 − Ξ 2) (5)�Æ� Ξ=0.95, wLV�� r=3.75 mm X&, �nhAΞ = 1.37π mm2. �z TC ; UL LV, k�LV}d.`wnDoz, gw}dw�GWhlhnD, kKA

�432 ��S��� m 45 �(5) ,�/�

AΞ = πr2 (6)X& TC ; UL LVh�� �� 2 ; 1.5 mm, ebAΞ �� 4π mm2 ; 2.25π mm2.� 7 E σ

−1 } AΞ h(��. �[��7t=eblgσlim,0 = 3.07, αΞA = −0.23, �G)E}(M�nh6[. � 7 MCDKÆ [23] ; [24] 2 3 5 60Si2CrVA�LVh σ

−1 } AΞ h(�, K 3 5LVh�H?.zaDC9ss� 2. t=C�nh D60, H60, A60 3 5LVh lgσlim,0 & �� 2.96, 3.01, 3.05, αΞA & �� −0.22, −0.21, −0.19, �-w}�?S 54SiCr6 �h[��z{�.

σlim,0 E�nz AΞ=1π mm2 < 107 cyc h}:�z, ,b!�(Mh}d\6+, q&�)�" (%,h��, �O�, -�j) hIr�z+, kK σlim,0 EÆ8L℄th�1�, t(M= ;�zg�nh6[. y2�z D60, H60, A60 '5�z} σlim,0 h(�(� 8), ,b%bdA'5�zhq�, σlim,0 Z:vq�. αΞA X�V�}:�zdA}d\h�W�"}q+hsD, �}q&�)�"w(. � 9 �zK αΞA }�"h��ATh(�, ,b%b, dAh��ATh�l, −αΞA &"}�l, (Mh σ

−1 �x.%0*r&|%�h RB ; TC LV, �tA (3),

1 10400

600

800

1000

1200

Fatig

ue s

treng

th

-1, M

Pa

A0.95, mm2

54SiCr6 D60[23,24] H60[23,24] A60[23,24]

: RB: TC: UL

s 7 |9�y|�mC| A0.95 g'��$Fig.7 Dependences of the fatigue strength on the highly

stressed cross–section area A0.95 for the four steels

(5) ; (6) eb:

σlim,RB

σlim,TC= (1 − Ξ 2)αΞA (7)A (7) �i, RB ; TC }:�zh�<W��z Ξ }

αΞA &, tz.W?S�0eD αΞA �z&�, �z����_� αΞA &� −0.2. %0� Ξ &� 0.95, �nh}:�z�&� 1.59, %0 Ξ &� 0.90, ��nh}:�z�&� 1.39, kK Ξ &h?��}:�zw7Who'. (X�nDs\ (}d\) h�x, !� Ξ &Ph��AT}(M�zho'zW. %0h��ATz

1920 1935 1950 19652.9

3.0

3.1

lg(

lim,0, M

Pa)

b, MPas 8 5Z lgσlim,0 |&4�y σb g'�Fig.8 Relationship between parameter lgσlim,0 and tension

strength σb

10 20 30 40 500.15

0.20

0.25

-

din, ms 9 +Z −αΞA |�!g���Sg'� [23]

Fig.9 Relationship between parameter −αΞA and average

inclusion size, the average inclusion sizes of D60,

H60, A60 are 44, 28.6 and 15.4 µm, respectively[23]

N 2 60Si2CrVA ���g�G>-y`~mgCB8rTable 2 Heat treatment procedure and the corresponding mechanical properties of 60Si2CrVA high strength steel[23,24]

Specimen Heat treatment procedure σb, MPa σ−1, MPa

RB UL

D60 850 �/30 min+O.Q.+410 �/90 min+A.C. 1930 735 598

H60 925 �/30 min+O.Q.+410 �/90 min+A.C. 1955 835 688

A60 900 �/30 min+O.Q.+410 �/90 min+A.C. 1960 915 763

m 4 � :Xji : zDJ7� 54SiCr6 �f{8Æx 433�W, ���zz�, �(M�h��g�>zz�, K<RB LV2�30hh��Zww,s=�}:O��,,bw Ξ �� 0.90. ��zh��+���zzkh(M, RB h��}d\wWWq/, N�,� Ξ � 0.95.%� 10 gC, Æ [8] ; [25] grh(M� SNCM439[O�, *r&_h�H? , ebhDC9s&\,

RB } UL LVh%�w� 3 mm, GCeb 107 cych}:�z$�� 1.36. k� SNCM439 h'5�z�1955 MPa, ��h��hAT�� 9—82 µm, gb� Ξ&� 0.90, tA (7) �nh}:�z�� 1.39, }?S&�z�=.

104 105 106 107 108 109 1010600

800

1000

1200

Ran out

Internal inclusion Surface matrix

a, MP

a

Nf, cyc

809 MPa

(a) Origin of the fatigue crack

104 105 106 107 108 109 1010600

800

1000

1200

1400

1600

Ran out

Nf, cyc

Surface matrix Internal inclusion Internal matrix

a, MP

a

(b)

1100 MPa

Origin of the fatigue crack

s 10 SNCM439 g>R S-N �$� [8,25]

Fig.10 S–N curves of the spring steel SNCM439 under TC

(a) and RB (b) experiments[8,25]

3 `g|℄5���*r&|h�H?.z<, Æ>����5H;96 3 5?Svu�/th 107 cyc }:�zwzWh3�. BrAT,n}�nDs\�x, y2}d\Xts\, eDh}:�z(��UA�?S[�t=z5, �i.W�x� 3 5?SUeh}:�zh3�IK=?h�G, |<, Zw>z�5���dl�&���h}:�z.�11.*B��UL�f�*g;;g'_|=.

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