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The microstructures and mechanical properties of eight kinds of Fe‐Cr‐B‐Al alloys containing X wt.%Al‐0.35 wt.%C‐10.0 wt.%Cr‐1.4 wt.%B‐0.6 wt.%Si‐0.8 wt.%Mn (X = 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0) were studied by means of optical microscopy (OM), scanning electron microscopy (SEM), X‐ray diffraction (XRD), Rockwell hardness and Vickers micro‐hardness testers. The results indicate that the as‐cast microstructure of aluminium‐free sample consists of the martensite, austenite and eutectic borocarbides, and the eutectic borocarbides are the mixture of (Fe, Cr)2B and (Cr, Fe)7(C, B)3, and its hardness reaches 65 HRC. When a small amount of aluminium element (Al ⪇ 1.0 wt.%) is added, the phase composition has no significant change, and the hardness excels 65 HRC. When the concentration of aluminium reaches 1.5 wt.%, the matrix of Fe‐Cr‐B‐Al alloy becomes pearlite and δ‐ferrite, leading to a sharply decrease of the hardness. The proportion of ferrite goes up along with increasing aluminium concentration, and the hardness of Fe‐Cr‐B‐Al alloy has slight decrease.

The circular-patch welding test was used to study the liquation and liquation cracking of AZseries Mg alloys. A heat treatment was carried out on the as-received AZ91 alloy to dissolve the γ (Mg 17 Al 12 ) particles before welding. The circular-patch welding test was then conducted on the heat-treated, as-received AZ91 alloy using AZ61 and AZ91 filler wires. The results showed that the susceptibility of AZ91 alloy to liquation and liquation cracking was significantly reduced by the dissolution of massive γ (Mg 17 Al 12 ) particles via a heat treatment before welding as the liquation mechanism was changed. Both constitutional liquation and incipient melting occurred in the partially melted zone of the as-received AZ91 welds, while only incipient melting occurred in the heat-treated AZ91 welds.

In this article, the effect of heat treatment in different quenching temperature on microstructure and hardness of Fe-Cr-B alloy was studied, by contrast with boron-free Fe-Cr alloy. The results indicated that microstructure of boron-free Fe-Cr alloy consisted of the martensite and a few (Cr, Fe) 7 C 3 type carbide. The microstructures had no obvious change with the increase of quenching temperature, but its hardness increased from 51.5 HRC to 60.8 HRC. When boron element was added into the Fe-Cr alloy, the netlike eutectic structure began to break and spheroidizing after quenching, in which the borocarbide turned into spherical groups and network Fe 2 B phase was broken. Moreover, the portion of martensite increased, and the amount of secondary carbide decreased, and the size of secondary carbide began to largen after quenching. When the quenching temperature reached 1100 8C, secondary carbide particles dissolved in the matrix wholly. The hardness of Fe-Cr-B alloy increased with the increase of quenching temperature below 1050 8C. The hardness of sample containing 2.0% B and quenching at 1050 8C reached 66.7 HRC. The hardness of Fe-Cr-B alloy had no obvious change when quenching temperature continued to increase. After tempered at 200 8C, the microstructure of Fe-Cr-B alloy had no significant change and its hardness had slight decrease. The hardness of sample containing 2.0% B tempered at 200 8C reached 63.9 HRC.