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The microstructure and properties of Fe-1.50 wt%B-0.40 wt%C high-speed steel (i.e. High boron high-speed steel, HBHSS) containing various Al contents have been investigated. The results show that the microstructure of HBHSS is composed of martensite, a little M 6 (C,B) and a large number of eutectic M 2 B borides. With the increase of aluminum, the martensite can reduce and lots of ferrite and pearlite occur, while M 2 B boride is gradually refined and isolated. Meanwhile, most of aluminum is mainly segregated within the ferrite grains. The room tensile strength of the steel begins to decrease when Al content exceeds 0.6 wt%, whereas the fracture and impact toughness are remarkably enhanced. A little aluminum can maintain high-temperature tensile stress of the steel at 500 °C and simultaneously improve its elongation. The high-density dislocations can be formed within Al-segregated ferrite zone to exhibit the strengthening and toughening roles, and a possible orientation relationship between (Fe,Cr) 2 B and multi-component M 2 B is (110) (Fe,Cr)2B ∕∕ (110) M2B in the steels. [ABSTRACT FROM AUTHOR]

The effects of orientation and lamellar spacing on the interface microstructure and corrosion behavior of a directionally solidified (DS) Fe-B alloy in a hot-dip galvanization bath were investigated. The results indicated that the microstructure of the DS Fe-B alloy consisted of oriented α -Fe and Fe 2 B grains. The oriented Fe 2 B with [002] preferred growth orientation displayed low-angle grain boundaries on the Fe 2 B (001) basal plane. The DS Fe-B alloy with Fe 2 B vertical to the corrosion interface possessed the best corrosion resistance to liquid zinc owing to the formation of an interface-pinning multilayer induced by the Fe 2 B orientation. The epitaxially grown columnar ζ-FeZn 13 products were controlled by the geometric constraint of Fe 2 B grain orientation and size, and a mechanism model that explains the interfacial orientation-pinning behavior is discussed in detail. Transmission electron microscopy (TEM) results revealed that the possible orientation relationships of the oriented Fe 2 B and columnar ζ-FeZn 13 products are (001) Fe2B //(−402) ζ-FeZn13 and [002] Fe2B //[110] ζ-FeZn13 . The corrosion damage of the DS Fe-B alloy with Fe 2 B [002] orientation vertical to the corrosion interface in liquid zinc was governed by the competitive mechanisms of Fe 2 B/FeB transformation and microcrack-spallation resistance, which is proposed as being the result of a multiphase synergistic effect in the micro-structures. [ABSTRACT FROM AUTHOR]

Abstract: The cast low carbon Fe–3.5B alloys containing various chromium concentrations were prepared in a 10kg medium frequency induction furnace and the effects of chromium concentration on microstructure and properties of Fe–3.5B alloys have been examined by means of optical microscope (OM), scanning electron microscope (SEM), back-scattered electron microscope (BSE), electron probe microanalyzer (EPMA), energy dispersive spectrum (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and Vickers hardness. As a result, the as-cast structures of Fe–3.5B–XCr (X =0, 2, 5, 8, 12, 18, mass fraction) alloys are mainly composed of dendrite ferrite, martensite, pearlite and boride. The boride in the alloy without chromium addition comprises the eutectic Fe2B, which is continuous netlike or fish-bone structure distributed over the metallic matrix. With the increase of chromium concentration in Fe–3.5B alloy, matrix structure turns into the supersaturated α-Fe solid solution while the morphology of boride becomes dispersed due to the transformation of boride from simple Fe2B to (Fe,Cr)2B when the chromium concentration in Fe–3.5B alloy exceeds 8wt.%. Meanwhile, some primary M2B-type borides may precipitate under this condition. The bulk hardness of the as-cast alloy ranges from 41.8 to 46.8 HRC. However, the bulk hardness of the heat treated alloy rises first and falls later mainly because of the morphology variation of structure. Fracture toughness of boride is improved gradually owing to the entrance of chromium into Fe2B, which may be attributed to the change of spatial structure of boride. [Copyright &y& Elsevier]