Laser shock peening of Cr5 steel

In the processing craft of steel, the roller is a critical component to roll steel. Cr5 steel is one of the most common roll steels used in the industry. In rolling process, rollers are exposed to both thermal and mechanical loads, which makes fatigue crack easier to generate and spread. Thus the working life of roller will be decreased and the cost will be improved. It is necessary to improve the surface strength of the roller. Laser shock peening (LSP) is an advanced surface treatment technique, which has been successfully applied to improve the fatigue, corrosion, and wearing resistance of metallic components, such as copper, aluminum and its alloys, nickle and its alloys and stainless steels, etc. Through the interaction of a pulsed high-intensity laser beam and an energy absorption layer on the metallic target surface, a high amplitude shock wave can be generated and propagates into the target. If the amplitude of the shock wave exceeds the Hugoniot elastic limit (HEL) of the target material, plastic deformation occurs as a result of dislocation motion and multiplication. Upon shock peening, residual compressive stresses are induced near the surface, which results in the enhancement of material performance.

1.The LSP affected depth

Vickers indentation tests on the cross-section of peened sample shows that the measured hardness increases in the surface layer, and then decreases to the value of untreated specimens at a depth about 600~700 μm.

 

2.The surface hardness enhancement after LSP

The surface hardness of untreated specimen is about 711±10 kg/mm2. The surface hardness of peened specimen is about 771±10, and 787±8kg/mm2 for laser power density 2.6, and 3.8GW/cm2respectively. It indicates that the surface hardness will increase with increasing the laser power density in the range of our study.

 

3.The surface roughness maintained after LSP

The sample with different roughness was peened with the same laser power density and the same number of shots. The surface roughness almost unchanged after LSP for when the initial surface roughness of the sample is lower than 1.0μm. Obvious fluctuations of the surface roughness after LSP can be observed when the initial surface roughness of the sample is around 3.0μm.