Abstract
The 24CrNiMo alloy steel powder was used as experimental material. The microstructure and mechanical properties of as-deposited, quenched and tempered (QT) and stress-relief annealed (SR) specimens were analyzed. The X-ray diffraction (XRD) analysis showed that the specimens in the three states were mainly ferrite (α-Fe), in which the as-deposited samples had puny face-centered cubic (FCC) structure Fe (γ-Fe). The microstructure observation showed that the as-deposited specimens were made up of ferrite, granular bainite, a small amount of cementite and residual austenite. The tensile test results indicated that the tensile strength and yield strength of the as-deposited specimens were 1199 MPa and 1053 MPa respectively, and the elongation at break was 10.7%. The elongation of QT and SR specimens increased to 11.6% and 12.8%, respectively. The electron backscattered scattering detection (EBSD) analysis results showed that the small-angle grain boundary content of the as-deposited samples was 58%, and large-angle grain boundary content was 15%. After QT and SR, small-angle and large-angle grain boundaries were obtained than those in the as-deposited specimens. The high-temperature friction and wear properties and thermal fatigue performances of the QT and SR specimens were improved significantly. The QT specimens had the smallest wear and thermal fatigue crack lengths, excellent resistance to friction and wear performance and prevention of crack growth, with an ideal comprehensive properties.
Highlights
Cr-Ni low-alloy structural steels are widely used in the manufacture of critical internal parts of industrial equipment due to their dramatic advantages of remarkable machinability and mechanical properties, such as 12CrNi2 for camshafts of emergency diesel engines [1,2,3,4] and 34CrNiMo6 for ultra-high-strength fasteners [5]
The results show that 24CrNiMo alloy steel brake discs with superior performance prepared by Selective laser melting (SLM) have great potential application value
The peak value became higher after heat treatment, indicating that the crystallinity was improved
Summary
Cr-Ni low-alloy structural steels are widely used in the manufacture of critical internal parts of industrial equipment due to their dramatic advantages of remarkable machinability and mechanical properties, such as 12CrNi2 for camshafts of emergency diesel engines [1,2,3,4] and 34CrNiMo6 for ultra-high-strength fasteners [5]. The research on heat treatment processing of QT and SR are insufficient at present Against this background, 24CrNiMo alloy steel specimens were prepared by SLM technology under the optimized process parameters in this paper. The relationship between microstructure characteristics such as grain size, grain orientation, grain boundary quantity and high-temperature friction and wear properties and thermal fatigue properties of as-deposited QT and SR states were studied. This provides the test basis for the preparation of the metal parts of the brake discs of high-speed trains and the safe operation of high-speed rail vehicles
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