1. No category

Fatigue2014,11th International Fatigue Congress
March5,2014,Melbourne Cricket Ground
Melbourne, Australia
Nitriding Effect on
Corrosion Fatigue Strength of
Low Alloy Steel in
1% HCl Aqueous Solution
R.Ebara1,Y.Fukushima2, S.Nakagawa2 and R.Ueji2
1Institute
of Materials Science and Technology,Fukuoka University
Fukuoka, Japan, [email protected]
2 Student,Hiroshima Institute of Technology, Hiroshima,Japan
3 Department of Advanced Materials Science,Kagawa University
Takamatsu,Japan
Background
・Plastics extrusion machine
Cl-, Low alloy Steel,
Fatigue, Fretting Fatigue,Corrosion
・Nitriding:Gas nitriding,Ion nitriding
can improve Wear
Fatigue strength
Corrosion resistance
Corrosion Fatigue Strength Improvement
・NaCl aqueous solution
・K.Tokaji,K ,S.Takahashi；
Corrosion Fatigue Behavior and Fracture Mechanisms in Nitrided Low Alloy
Steel,Fatigue Fract Engng Struct,26(2003),pp215-221
SCM435,Gas nitriding,3%NaCl aqueous solution, Rotating
bending, Corrosion pit underneath the compound layer
・ T. Makishi,H.Yara, C.Makabe;
Corrosion Fatigue Behavior of Alloy Steels after Ion Nitriding
Proc.of the JSME,Kyushu Branch,(1994),No948-2,pp1-4
SUS430,Ion nitriding,5%NaCl aqueous solution, Rotating
bending, Corrosion pits underneath the compound layer
・ K.Shiozawa,K.Mitsutani,K, S.Nishino,
The Effect of Gas Nitriding on Corrosion Fatigue Behavior of Hard Steels
Proc. of the JSME,Hokuriku Shinetsu Branch,(2003),No.007-1,pp387-388
SKD61,HAP10,Gas nitriding,3%NaCl aqueous solution
Rotating bending, Corrosion pit underneath white layer
・K.Shiozawa,A.Shibata,S.Nishino,
Effect of Plasma Nitriding on Corrosion Fatigue Behavior of SCM435 Steel,Proc.
of the JSME,Hokuriku Shinetsu Branch,(2004)No.047-1,pp7-8
SCM435,Plasma nitriding,3%NaCl aqueous solution
Rotating bending, Corrosion pit at surface
Axial fatigue strength? HCl aqueous
solution? What kind nitridings?
Screening test
・Low alloy steels
・Ultrasonic Corrosion Fatigue Tests
Table1 Chemical compositions of tested steels(mass%).
Table2 Mechanical properties of tested steels.
Ultrasonic Corrosion Fatigue Test
・Ultrasonic fatigue testing machine
Shimadzu USF2000
・Frequency 20kHz
・R(the ratio of the minimum to
maximum stress loading cycle)=-1
・1%HCl aqueous solution
・Prevention of specimen heating
Compressed air
Intermittent frequency:110ms duty,
550ms pause
Fig.1 Fatigue test specimen.
Surface treatments
Cr-Mo steel
・Gas nitriding 783Kx20hr,813Kx28hr
・Gas nitriding 803Kx30hr,833Kx40hr
・Shot peening Steel shot,100μm
・Shot peening SKH51, 55μm
・Ion nitriding 793Kx30hr
DIN1.4418
・Ion nitriding
793Kx30hr
1200
Air
Stress amplitude,MPa
1000
800
1%HCl
Cr−Mo
Cr−Mo Ion nitriding (793Kx30hr)
Cr−Mo Shot peening (Steel shot,100μm)
Cr−Mo Gas nitriding (783Kx20hr,813Kx28hr)
DIN1.4418
DIN1.4418 Ion nitriding (793Kx30hr)
SUS630
600
400
200
0 4
10
10
5
6
7
8
10
10
10
10
Number of cycles to failure
9
10
10
Fig.2 S-N curves of Cr-Mo steel,DIN1.4418,SUS630, various surface treatedCrMo steel and ion nitrided DIN 1.4418 in air and 1%HCl aqueous solution.
Fatigue strength at 109cycles in air(MPa)
550
・Cr-Mo
・DIN1.4418 525
513
・SUS630
Reduction of corrosion fatigue strength at 107
cycles(%)
60
・Cr-Mo
・DIN1.4418 50
58
・SUS630
Corrosion fatigue strength improvement,Cr-Mo
steel(%)
・Ion nitriding 70
・Shot peenimg 40
0
・Gas nitriding
1000
Stress amplitude,MPa
800
Air
1%HCl
Cr−Mo
Gas nitriding (783Kx20hr,813Kx28hr)
Gas nitriding (803Kx30hr,833Kx40hr)
Shot peening (Steel shot,100μm)
Shot peening (SKH59,55μm)
Ion nitriding (793Kx30hr)
600
400
200
0 4
10
10
5
6
7
8
10
10
10
10
Number of cycles to failure
9
Fig.3 S-N curves of Cr-Mo steel and various surface treated
Cr-Mo steel in air and 1%HCl aqueous solution.
10
10
Corrosion fatigue strength of Cr-Mo steel can be
improved.
・Gas nitriding(803Kx30hr,823Kx40hr) 232%
70%
・ Ion nitriding
40%
・ Shot peening
Experimental
Fatigue test
・Electrohydraulic fatigue testing machine
（Shimadzu,EHF-LB9.8kN）
・Environment Air, 1%HCl aqueous solution
・Frequency 20Hz
・R value(the ratio of minimum to maximum stress
in the loading cycle) 0.05
Surface and Fracture surface ovserbation
・Optical microscope(Keyence,VHX-100)
・Scanning electron microscope(JEOL,JSM5500S)
Fig.4 Fatigue test specimen.
Fig.5 S-N curves of various nitrided Cr-Mo steel in air.
Fig.6 S-N diagrams of various nitrided Cr-Mo steels in 1%HCl aqueous solution.
Corrosion fatigue strength improvement at 107
cycles
・Ion nitriding(793Kx30hr) 55%
・Gas nitriding (773Kx18,7p3Kx38hr)
Lower than 250MPa Improved
Higher than 250MPa Not improved
Fig.7 Residual compressive stress distribution in surface layer.
Fig.8 Vickers hardness distribution in surface layer of
various nitrided Cr-Mo steel.
Fig.9 Corrosion pit observed at corrosion fatigue crack initiation
area.1%HCl,200MPa、
a) Ion nitriding(823Kx30hr),5.04x106 cycles
b)NV nitriding,4.64x106 cycles
Fig.9 Surface cracks of gas nitrided(803Kx30hr,833Kx40hr) CrMo steel.
650MPa
a) air,1.234x108 cycles
b) 1% HCl ,5.952x106 cycles
Fig 10 Fatigue fracture surface of gas nitrided(803Kx30hr,833Kx40hr)
Cr-Mo steel.
700MPa
a) Air,2.269x106cycles
b) 1% HCl,4.846x106cycles
Arrow shows corrosion pit
Fig.11 Crack propagation area of gas nitrided(803Kx30hr,833Kx40hr)
Cr-Mo steel. 1mm from initiation
a) Air,625MPa,4.5x107 cycles
b) 1% HCl,700MPa,4.8x106 cycles
Concluding remarks
・It can be concluded that corrosion fatigue
strength of Cr-Mo steel in 1%HCl aqueous
solution can be improved by ion nitriding
and gas nitriding.
・The major cause of improvement can be
attributed to residual compressive stress at
the surface layer.
・Further study is recommended to conduct
on the effect of microstructure in the
hardened layer on corrosion fatigue strength
of ion and gas nitrided Cr-Mo steel.
結論
主たる結論は下記のとうりである。
・イオン窒化 (793Kx30hr)処理鋼の1%HCl水溶液
中10⁷回の疲労強度は母材と比較し55%向上した。
・ガス窒化（773Kx18h,793Kx38h)処理鋼において
250MPa以下では腐食疲労強度の改善効果が見ら
れた。しかし、250MPa以上ではガス窒化の影響は
見られなかった。
・イオン窒化処理鋼の腐食疲労強度改善の主因は、
イオン窒化の際に表面に発生する圧縮残留応力で
ある。
・1%HCl水溶液中では、全ての窒化処理鋼の疲労き
裂発生部に腐食ピットが観察された。