Improvement of the Welding Joints and Components by Shot Peeing for IIW

Author:  I. HUTHER, E. DANIEL
Source:  Conf Proc 2014: ICSP-12 Goslar, Germany (pgs.162-167)
Doc ID:  2014069
Year of Publication:  2014
Abstract:  
The commission XIII of the International Institute of Welding published in 2007 a document call "recommendations for fatigue design of welded joints and components". It presents various processes to improve fatigue life after welding. Shot peening is well known to improve fatigue life of metallic materials, including welded joints and components, but it has never been properly qualified for the IIW recommendation. In order to include the benefits of shot peening in this paper, METAL IMPROVEMENT COMPANY together with CETIM Senlis, achieved fatigue test to qualify it. The samples are longitudinal non-load-carrying fillet welds, done in DOMEX 700, a hot rolled high strength steel from SSAB Tunnplat, 8 millimeters thick. 12 samples have been peened by METAL IMPROVEMENT COMPANY and 3 not. They have been fatigue tested at CETIM SENLIS with 3 load levels up to 2 000 000 cycles at R=-1 and R=0.1 to quantify the benefits of shot peening. Shot peening is introducing compressive residual stress and also improving the geometry of the weld toe. It is the projection of hard shots made in steel, stainless steel, ceramic or glass of various sizes (diameters from 50 μm to 3 mm). There is also the control of the intensity and of the coverage rate (minimum 100%) of the treatment in order to get a uniform compressed layer. It can be apply manually till fully automatic controlled machines. It is used for more than 60 years to treat fatigue, fretting, pitting (contact fatigue), stress corrosion cracking, intergranular corrosion or thermal fatigue. It is applied for single as well as serial parts in all industrial fields: aerospace, automotive, energy, power generation, medical or general industry. Fatigue test have been done with 3 loads levels up to 2 000 000 cycles at R=0.1 and R=-1 in order to quantify the effect of compressive load on the fatigue life. The results are good. At 2 X 10⁶ cycles, the average stress level is 126 MPa for the as-welded samples and 221 MPa for the shot peened samples. It is an improvement of 75% of the fatigue life. The residual stress level has also been measured at the surface of the part close to the welded area and gives also good results of -500 to -650 MPa.