Texture and anisotropy of mechanical properties of spray-formed alloy tool steels

Abstract

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...