Almost all components in technical applications experience alternating mechanical stress during their use. This can cause damage to the material, which increases with each load cycle and can ultimately lead to a fracture of the component. With regard to harsh, corrosive environments, austenitic stainless alloys are the material of choice. However, this highly favorable property is often opposed to relatively modest mechanical properties, particularly low fatigue and wear resistance.
Interstitial hardening accompanying low temperature carburizing prolongs the fatigue resistance, while maintaining the superb corrosion properties of this material class. This effect is due to the generation of large compressive residual stresses within the outermost surface of the component, which increases the surface hardness and prevents the surface nucleation of cracks.
Rotating bending fatigue tests acc. ISO 1143 on non-hardened and surface hardened AISI 316L (1.4404) were performed to generate a fatigue-life curve. The tests indicated that low temperature carburizing enhances the fatigue strength by more than 40 % (521 MPa) versus untreated material (366 MPa). Additional testing at a fixed stress level of 400 MPa conducted in a corrosive environment resulted in an at least 10 times longer fatigue life with surface hardening, compared to the untreated material, which failed after 1 million cycles. The untreated sample parts even show signs of corrosion due to crevice conditions at cracks, while the surface hardened samples remained free from corrosive attack.
Based on these test results, application examples for different industrial sectors are presented (e.g. drive shafts in pump technology or springs in injection systems for automotive applications).
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