铬含量对Fe-Cr-B堆焊合金显微组织及耐磨性的影响

目的在Fe-x Cr-3.5B-0.1C药芯焊丝中加入不同含量的铬,了解铬含量对堆焊合金硼化物形貌以及耐磨性能的影响。方法采用CO_2气体保护堆焊的方法在Q235钢基板上制备Fe-Cr-B系耐磨合金,利用光学显微镜、XRD、SEM等方法观察堆焊合金层的显微组织结构,以及湿砂橡胶轮磨粒磨损试验机对堆焊层进行磨粒磨损试验。结果堆焊合金层主要由铁素体枝晶、马氏体、珠光体和硼化物组成,硼化物随着Cr含量的增加发生Fe_2B到M_2B(M=Fe,Cr)的转变,它主要分布在金属基体的连续网状和鱼骨状结构中。凝固过程中,当Cr质量分数大于9%时,首先形成初生M_2B颗粒,随后形成共晶的M_2B和BCC结构的Fe基固溶体,这种共晶的微观结构主要由基体和长条状的M_2B硼化物组成。从Cr与(Fe,Cr)的原子数分数比值可以看出,硼化物发生从Fe_2B→(Fe,Cr)_2B→(Cr,Fe)_2B的转变。铬含量对Fe-Cr-B系耐磨堆焊合金的组织、硼化物形貌有较大影响。由于硼化物空间结构的变化,硼化物的显微硬度会随着铬原子进入Fe_2B而逐渐提高。结论随Cr含量的增加,及共晶硼化物硬质相的析出,堆焊合金的硬度和耐磨性呈现持续提高的趋势。当Cr含量为20%时,合金中生成的长条状M_2B相作为耐磨骨架无序的分布且镶嵌于基体中,合金耐磨料的磨损性能比Cr含量为9%时的提高了约7.4倍。

Effects of Chromium Content on Microstructure and Wear Resistance of Fe-Cr-B Surfacing Alloys

The work aims to understand the effects of chromium content on morphology of boride and wear resistance of surfacing alloy by adding different content of chromium to Fe-xCr-3.5B-0.1C flux cored wires.Fe-Cr-B wear-resistant alloys were prepared on Q235 steel substrate by flux-cored wire arc welding. The microstructure and composition of sur-facing alloy layer were analyzed by optical microscopy (OM), X-ray diffractometer and scanning electron microscopy. Abrasive wear test of the surfacing layer was conducted by grain-abrasion testing machine with wet sand rubber wheel. Fe–3.5B–xCr (x=9, 12, 15, 20 wt. %) alloys were mainly composed of dendrite ferrite, martensite, pearlite and borides. With increase of Cr content, boride transformed from Fe2B to (Cr,Fe)2B and was mainly distributed in the net or fishbone structure in the metallic substrate. When the chromium concentration exceeded 9 wt.% during solidification process, pri-mary (Cr,Fe)2B particles formed, and then eutectic M2B and Fe-based BCC solid solution formed. The eutectic micro-structure mainly consisted of the substrate and long striped M2B boride. The atom fraction ratio indicated that the borides changed from Fe2B→(Fe, Cr)2B→(Cr, Fe)2B. Cr content had significance to structure and boride morphology of Fe-Cr-B wear-resisting surfacing alloy. Microhardness of boride improved gradually as Chromium atoms entered Fe2B due to spa-tial structure change of boride. With the increase of Cr content, hardness and wear resistance of surfacing alloys show a trend of continuous improvement. Provided with Cr content as 20 wt.%, M2B phase is randomly embedded in the matrix as the wear-resistant framework and the wear resistance increases by about 7.4 times compared with that containing 9 wt.% Cr.