Gogaev and V. I. Ul'shin UDC 621.762Optimum temperatures for deforming powder tool steels are determined. It is established that the ductility limit during deformation of these steels in the dynamic recrystallization temperature region is higher than that at 1100-1150°C. Jet moulding technology followed by deformation in the temperature range established is shown to be promising.Tool steels are most in demand in enterprises of various branches of industry as a material for cutting tools and measuring instruments, and forging equipment. A considerable increase in the quality of tool steels due a sharp increase in the dispersion of carbides and their uniform distribution within the volume of the metal has been achieved due to the use of powder metallurgy technology.The main industrial process for preparing graded metal made from powder tool steels, in particular high-speed steels, is the ASIA-STORA process [1]. It includes the following operations: preparation of powder by atomizing molten metal with an inert gas, loading the powder into capsules, evacuating and sealing the powder, hydro-and gasostatic treatment of capsules with the powder, forging the capsules in forging presses, and rolling graded metal. For low-series production of tool steels made from high-speed steels the authors in [2] have developed technology for preparing powder billets without using capsules and binders. The main operations for this technology are preparing powder by atomizing molten metal with gas, vacuum annealing, cold powder compaction, vacuum sintering of the powder billet, and hot extrusion.Recently in the technologically developed countries of the world new production technology has been developed and introduced for preparing powder billets of a prescribed shape by jet moulding [3]. Jet moulding (OSPREY-process) combines gas atomizing of molten metal and deposition of liquid droplets on a substrate (solidifier) where a billet with a density of 96-98% is formed from the droplets in the liquid, solid-liquid, and solid states. This makes it possible to heat a billet for subsequent deformation in furnaces without a protective atmosphere. The high cooling rate (10 3 -10 5 deg/sec) during solidification provides formation of a highly dispersed structure with uniaxial grains and uniformly distributed carbides.Jet moulding of powder billets made from alloy steels is more economic than the traditional powder metallurgy technology. Compared with the processes described in [1, 2] jet moulding excludes a whole series energy-consuming operations such as vacuum annealing, cold compaction, and vacuum sintering. After jet moulding billets are compacted by means of hot plastic deformation (rolling, forging, extrusion).It is very important in metal forming to have a specific deformation temperature range. For powder tool steels the temperature range for deformation is normally 900-1200°C, i.e. it is the same as for steels of the traditional production method (melting, pouring into an ingot, and preparation of graded metal by forming). Due to the di...
The initial texture and anisotropy of alloyed tool steel specimens are studied by constructing pole figures and conducting compression tests. Scattered initial axial crystallographic growth texture and weak anisotropy of yield stress and ultimate strength are established. A relationship between deformability and texture is determined.Texture is believed [1][2][3][4][5] to affect the behavior of metals when rolled; in particular, their elongation and expansion, shape of a billet, and pressure on rolls. A review of the literature [6][7][8][9][10][11] shows that the texture of sprayformed billets of alloy tool steel has not been investigated on a systematic basis. An isotropic initial texture in sprayformed billets is mentioned in just a few studies [10,11]. Such conclusions are based solely on metallographic examination of equilibrium crystals.The objective of this paper is to investigate the initial texture and anisotropy of spray-formed alloy tool steels and to analyze the relationship between the rolling conditions and initial texture.Billets of alloy tool steels such as 95Kh18, R2AM5F3SB, R2AM5F2NYu, and Kh12MF were spray-formed using a URS-40 gas spraying apparatus; a billet weighed 6 to 8 kg and had a density of 96 to 98%. The 95Kh18, R2AM5F3SB, and R2AM5F2NYu steels were smelted in an induction furnace with regular lining based on a conventional technology at 1580 to 1620°C. The Kh12MF steel was smelted in temperature-time treatment of liquid metal; i.e., it was 300 to 350°C overheated above the liquidus temperature T l [12,13].The specimens for the Kh12MF steel texture analysis were cut from the top in the central part of a spray-formed billet after temperature-time treatment and also from bands and strips after templates were rolled. Figure 1 illustrates that the failure surface of the billet and fragment is slightly curved and inclined toward the substrate (crystallizer). An imaginary normal line can be drawn from each point of this surface in the direction of crystallization heat removal. This assumes, in principle, the presence of texture in the billet. At the same time, the Kh12MF initial crystallites are isotropic (Fig. 2a, b).To analyze the Kh12MF texture, pole figures were drawn using a DRON-3 diffractometer with a texture device by reflection for (110) interference in Fe-K α radiation. The survey was conducted by inclination in the direction the sprayed metal precipitated. The spray-formed and rolled specimens were surveyed in the direction perpendicular to the rolling plane [14,15]. Figure 3 shows equivalent equal-intensity lines of scattered x-rays. A spray-formed specimen (Fig. 3a) has an axial scattered texture. Relative to the cooling surface, the axes of equilibrium crystals and their crystallographic direction have (110) [001] orientation with a texture scattering angle 30 to 40%. This is evidence of a texture in the spray-formed specimen subjected to temperature-time treatment.After rolling (Fig. 3b), the specimen has a limited axial texture typical for bcc metals; it can be described by tw...
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