Microstructure Of Steel Aermet100 Ultra High Strength Steel By Laser Phase Transformation Hardening

AerMet100 steel is a new type of ultra-high strength steel with excellent strength and toughness. It may be used as main steel for load-bearing structure of plane. Therefore, in the use of the process, in addition to the requirements of overall performance, the surface and local part of AerMet100 is likely to have higher performance requirements.In this study, Laser Transformation Hardening (LTH) treatment were used to strengthen the surface of ultra-high strength steel AerMet100. The influence of primitive conditions, laser power, and deep freezing to microstructures and the distribution of hardness were studied. The content of reverted austenite and the distribution of residual stress were analysised by using X-ray diffraction, the mechanism of reverse of austenite and secondary hardening phenomenon were studied.The results showed that the hardness of the surface was improved after laser transformation hardening, and the depth of harden layer increase and the hardness increase while laser power increase; original state affects the hardness, The hardness of harden layer of quenched state is harder than that of annealed state after LTH; the deep freezing process refinemented the size of grain, retained austenite to martensite transformation, further improved the hardness of harden layer; The tempering process impact inverse austenite content. The content of reverted austenite in laser hardened samples increases with the increase of the tempering time and tempering tempreture and this leads to the hardness decrease in hardened layer. Comprehenssive stress were detected on the surface of harden layer after LTH, and it increasing while laser power increase; Secondary hardening phenomenon exists in the tempering process of harden layer after LTH, which caused surface residual stress reached it's top while tempered after 3 hours at 482℃.This paper also studied the mechanical properties of AerMet100 steel after LTH by using multi-impact fatigue test. The fracture was observed by SEM, the a-N diagram and da/dN- △K diagram were drawed. The result shows that LTH increase the fatigue life of AerMet100, and while the laser power increase, the crack growth rate of the material decrease.