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Abstract In this work, the effect of solidification rate on the microstructure and impact toughness of high boron high speed steel is systematically investigated. The theoretical and experimental results indicate that the as-cast microstructure of high boron high speed steel consists of α-Fe matrix and eutectic borocarbide. Without Ca-Ti addition, borocarbide presents a continuous and reticular structure. After Ca-Ti modification, borocarbide possesses an isolated, fine structure. Besides, cooling rate obviously affects the extent of spheroidization. In modified high boron high speed steel, calcium possesses surface activity, which restrains the growth of eutectic borocarbide during solidification. Titanium exists in the form of dispersedly distributed TiC particles which act as heterogeneous nuclei for eutectic borocarbide. The impact toughness of high boron high speed steel is remarkably improved by Ca-Ti modification, which can be further improved by cooling rate. The effect of cooling rate on improving of the toughness can provide a scientific basis for the foundry process designing. [ABSTRACT FROM AUTHOR]

The effects of aluminum content on the morphology of eutectic borocarbide and temper softening resistance of high-boron high-speed steel with 2.0 wt pct B-0.4 wt pct C-6.0 wt pct Cr-4.0 wt pct Mo-x wt pct Al-1.0 wt pct Si-1.0 wt pct V-0.5 wt pct Mn (x = 0.0, 1.0, 1.5, 2.0) have been investigated in the present work. The experimental results indicate that aluminum not only promotes the refining and nodulizing of borocarbide, but also improves the red-hardness of the alloy. The as-cast microstructure of high-boron high-speed steel (with different aluminum contents) consists of matrix α-Fe, eutectic borocarbide M2(B,C), and boron-cementite M3(B,C) (M = Fe, Cr, Mo, V, Mn). Borocarbide presents a continuous network structure in the microstructure of alloy without aluminum addition. With increasing aluminum content, borocarbide is spheroidized, and its size decreases. Furthermore, the variation in aluminum content barely affects the phase type. The hardness testing results of heat-treated samples at 1050 °C, 1100 °C, and 1150 °C reveal that the quenching temperature for obtaining the martensite matrix rises with an increase of aluminum content. However, the alloy matrix with 2.0 wt pct aluminum cannot transform to a martensite matrix through quenching, even at 1150 °C. The red-hardness is defined as the alloy hardness after four rounds of tempering at 600 °C for 1 hour. The hardness of alloy without aluminum addition reduces significantly after tempering, while the hardness of alloy with 1.0 wt pct aluminum exhibited the highest value. Moreover, no apparent change in borocarbide morphology occurred after tempering, indicating that the alloy microstructure renders good tempering stability. [ABSTRACT FROM AUTHOR]

This study investigates the effect of cerium on the microstructures, mechanical properties of medium carbon Fe-B cast alloy. The as-cast microstructure of Fe-B cast alloy consists of the eutectic boride, pearlite, and ferrite. Compared with the coarse eutectic borides in the unmodified alloy, the eutectic boride structures in the modified alloy are greatly refined. Cerium promotes the formation of CeO phase. CeO can act as effective heterogeneous nuclei of primary austenite, and refine austenite and boride. After heat treatment, the impact toughness of the modified alloy is higher than that of the unmodified alloy because there are more broken borides in the modified alloy. Meanwhile, the fracture mechanism of medium carbon Fe-B alloy is depicted and analyzed by using fractography. [ABSTRACT FROM AUTHOR]

Abstract Based on cold metal transfer (CMT) welding, wire-arc additive manufacturing (WAAM) technology was adopted to manufacture 2Cr13 part. The spatial periodicity of the microstructural evolution and the anti-indentation properties was explored. The results show that the as-deposited part was featured by periodic martensite laths within the block-shaped ferrite matrix in the inner layers, followed by epitaxial ferrite grains containing ultra-fine acicular martensite in the top layer only. A slightly decreased Fe intensity was caused by local elemental segregation during the re-melting process; the homogeneity of Fe and Cr was attributed to similar cooling conditions in the top layer. The martensite size gradually coarsened from the fine grain zone to the coarse grain zone and the shape transformed correspondingly from irregularly short bar-like to orderly long rod-like due to the location-related thermal history. Elongated ferrite grains exhibited a slight fiber texture in the top layer and a random crystallographic orientation in the middle region. The anti-indentation properties evolved periodically due to the periodic microstructural characteristics. The obtained experimental results confirmed higher anti-indentation properties of the as-deposited part following comparison with the as-annealed base metal, while the elastic moduli of samples were not significantly different. Graphical abstract Unlabelled Image Highlights • 2Cr13 thin-wall part with defect-free was additively manufactured by robot-assisted CMT technology. • Martensite coarsened gradually from FZ to CZ while only ultra-fine acicular martensite in the top layer. • A random crystallographic orientation in the middle region while a slightly fiber texture in the top layer • Mechanical properties were evolved periodically due to the periodic microstructural evolution. [ABSTRACT FROM AUTHOR]

Abstract The crack-free H13 block was deposited through additive manufacturing with the cold metal transfer technology. The internal 3D pore distribution, the microstructural evolution, and the mechanical performances were explored. A negligible porosity with dispersive-distribution and spherical-shape below 0.001% guaranteed a sound metallurgical bonding within the as-deposited part. The martensite laths growth direction varied dramatically with a very short position variation, as well as the block-like size-inconsistent δ-ferrite presence in the overlap zone, which were mainly generated by the thermal flux direction from the center to margin within a single arc track. Massive second-phase particles with morphology-diversity and size-nonuniformity were precipitated, indicating a strong dependency with the intrinsic heating treatment. The enhanced microhardness in the body zone was attributed to the martensite strengthening mechanism, while slightly low hardness was produced due to the soft δ-ferrite formation. When compared with the other zones, the enhanced ultimate tensile strength was obtained in the body zone at the expense of tensile ductility, revealing a positive relationship with the rise of hard martensite percentage. This work demonstrated that a crack-free H13 block with limited porosity and desirable mechanical properties was deposited using the present technology, despite the nonhomogeneous microstructures. Highlights • A crack-free H13 block part innovatively and firstly deposited using the robotic CMT technology. • A negligible porosity even below 0.001% guaranteed a sound metallurgical bonding behavior. • Varied microstructural evolution with a very short position variation within a single arc track. • Desirable mechanical performances due to martensite strengthening and precipitation strengthening. [ABSTRACT FROM AUTHOR]

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]