Study On Microstructure And Properties Of Spray Formed Cpm9V High Speed Steel

The high speed steel has been widely used in tools, dies, rolls, and other industries. With the development of industry, the content of carbon and alloyed elements is increasing continuously. The morphology of the carbide in tissue evolves from the mesh to the spherical. But the high-speed steel which was produced by the traditional process has problems like coarse microstructure, carbide severe segregation, unstable performance, serious failure etc. In this paper, CPM9V high-speed billet body was prepared by the Spray Forming (referred to as SF) technology, and then its body was densified by the Hot Isostatic Pressing (referred to as HIP) technology. CPM9V high speed steel over-spray powder (referred to as P), and its formed billet was prepared by the HIP technology. The improvement of high-speed steel billet microstructure was to improve the mechanical properties of the materials.In this thesis, using optical microscopy(OM), X-ray diffraction(XRD), scanning electron microscopy(SEM), and energy dispersive spectroscopy(EDS) mainly, Pore distribution states of as-deposited spray formed CPM9V high speed steel billet before-and-after HIP were analyzed. And the microstructures of as-deposited, and heat treated spray formed CPM9V high speed steel billet (referred to as SF body) before-and-after the HIP, else including heat treated state of the CPM9V high speed steel over-spray powder shaped body (referred to as P+HIP body) were analyzed, their mechanical properties were studied. It drawed the following main conclusions:Spray formed body microstructure was uniform, and had no segregation, grain size was about20μm. Spheroidal carbide particles were distributed uniformly in the matrix, the size of particles was less than1μm, the average porosity was0.9%. After HIP treatment, carbide particles were further spheroidized, and distrbuted uniformly, the average porosity was0.7%. Holes exsited in the form of near-spherical, multilateral angular edge shape, groove with different size etc.CPM9V high speed steel over-spray powder morphologies were basical spheroidal, and their sizes ranged from30μm to80μm mainly. After HIP treatment, microstructure of the material was uniform, and had no segregation, the sizes of pherical carbide particles were about1μm, and its average porosity was0.2%. The carbide quantity in the SF body and SF+HIP body reduced with the rising of quenching temperature, carbides gradually distributed along with grain boundaries. Using the same heat treatment, the amount increasing of carbides and tempered martensite in the SF+HIP body was more than that in the SF body. The quality in the first deposited carbide of P+HIP body reduced significantly with the increasing of quenching temperature, a large number secondary carbides were deposited simultaneously and mainly was VC. Their microstructures were composed of tempered martensite, carbide (MC) and a small amount of residual austenite.The quenching hardness increased with the increasing of the quenching temperature.The SF body and SF+HIP body showed a better impact resistance at1160℃, impact resistance of the SF body was enhanced after HIP, microstructural defect and the shape and distribution of carbide (MC) particles had great impact on it,impact fracture belonged to dimples-quasi-cleavage type mixed fracture. the wear mechanism was abrasive wear.