PSI - Issue 2_B

Andrzej Kubit et al. / Procedia Structural Integrity 2 (2016) 3330–3336 A. Kubit et al./ Structural Integrity Procedia 00 (2016) 000 – 000

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2. Experimental procedure The specimens used in the experiment were 110 x 38.4 and 1 mm thick and made of 51CrV4 spring steel. The chemical composition of the steel is presented in Table 1. Two series of specimens were strengthened. One series was heat treated by quenching (heated to the temperature of 860 o C and kept at that temperature for 2.15 min) in oil, then they were tempered at 480 o C for 15 min (Q&T). A CT 125 EKM furnace was used to heat treat the specimens. The second series was only shot peened (SP). The specimens were SP from both sides with 2 mm bearing balls for 10 min under the pressure of 0.6 MPa. The nozzle was located 95 mm from the workpiece. The operation was done using the device presented in Fig. 1. The baseline (reference) adopted specimens cut from sheet metal rolled across the direction of rolling with the surface that was not mechanically worked (WT). The uniaxial tensile test was conducted on a Zwick/Roell Z030 testing machine. The surface roughness of specimens was measured using a Surtronic 25 Taylor Hobson profilometer on a 8 mm segment with three repetitions. While, the microhardness was tested using Vicker's hardness test with a Reicherter C. Stiefelmayer microhardness tester with a load equal to F=1.96 N applied for 15 s. The degree of surface layer hardening was determined using Eq. 1. The test was conducted with 5 repetitions.

(1)

The fatigue tests were conducted on special test stand (ETS Solution L Series MPA 102 - L620M) that enabled to accelerate fatigue tests at a frequency of 300 cycles/s. During testing, the specimen was mounted in a hydraulic handle with a constant strength of interlocking and can lead to the resonance vibrations, which appeared with a sudden increase in vibration amplitude of the unfixed end. The tests were conducted at three different loads for every sample variant. The specimen was held at resonance vibrations until cracking or gaining final number of cycles. For the experiment, 2x10 6 cycles was used as the upper limit.

Table 1. Chemical compositions of the 51CrV4 spring steel.

Chemical composition % wt.

Material

C

Mn

Si

S

P

Cr

Ni

V

51CrV4

0.46-0.54

0.5-0.8

0.15- 0.40

0.03 max

0.03 max

0.8-1.1

0.4 max

0.1-0.2

Fig. 1. Device used for pneumatic shot peening: 1 – work chamber, 2 – specimen, 3 – shots, 4 – ejector nozzle, 5 – chuck, 6 – compressed air line, 7 – control panel.