The 30Cr3Ni2 alloy steel samples were prepared by direct laser deposition (DLD) technology with different scanning speeds. The microstructure and mechanical properties of the samples were studied by metallographic microscope, scanning electron microscopy, energy dispersive spectroscopy, microhardness tester and electronic universal material tester. The results show that when the laser power was 2500W and the scanning speed was 10mm/s, the fabricated sample mainly consisted of granular bainite(GB) with (Fe,Cr)7C3 carbide. The average hardness value was 341HV, the tensile strength was 875Mpa, the yield strength was 867Mpa, and the elongation was 3.9%. This study provides the basis for the further development of alloy steel produced by DLD.
Based on the fretting wear failure of key parts of short stress line rolling mill, selective laser melting was chosen to repair the failure parts. The effect of laser scanning rate on microstructure, hardness and wear resistance of cladding layer was studied. The results show that the microstructure of the cladding layer is mainly lamellar martensite with a little retained austenite and carbide. The hardness of the cladding layer increases with the increase of scanning rate and the decrease of energy density. The maximum hardness is about 950 HV0.2. The friction coefficient of the cladding layer varies little with different laser scanning rate. The wear rate of the cladding layer increases firstly and then decreases with the increase of laser scanning rate. The wear rate of the sample with scanning rate of 6 mm/s is the smallest, which is 2.0466•10-5 mm3/(N·m) .
Effect of different TA15 powder additions on high temperature oxidation kinetics of pre-laid laser melting 45CrNiMoY alloy steel was studied. Thermogravimetric method was used to determine the kinetics curve of constant temperature oxidation of alloy steel sample at 700℃. The results show that bainite and acicular ferrite are the main microstructures of alloy steel after adding TA15 powder. With the increase of TA15 powder, the microstructures showed a distinct trend of refinement. The oxidation kinetics curves of alloy steels follow the linear law. The alloy steels with 1.0 wt.% TA15 powder have the best resistance to high temperature oxidation, and the oxidation rate constant is 1.48×10-4 mg2·cm-4·h-1. Particle reinforcement phase formed in alloy steel can provide pinning effect for oxide film, while micro-cracks added in excess TA15 alloy steel sample are not conducive to the improvement of high temperature oxidation resistance.