【作者】 杨可；

【导师】 余圣甫；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2009， 博士

【摘要】 氮作为间隙原子，与其它合金元素相互作用，能改善钢的强度、韧性、蠕变抗力、耐磨性和耐腐蚀性能。在硬面合金材料中用氮代替碳进行合金化，能提高抗焊接热裂纹、耐磨蚀和高温稳定性能。以氮代替部分碳进行硬面合金的氮合金化，成为提高硬面合金综合使用性能的新途径。系统研究了堆焊马氏体不锈钢硬面合金中氮的行为及其影响因素，确定了硬面合金中的合理氮含量，并设计出了氮合金化硬面合金的合金系列。通过药芯中添加氮化铬进行埋弧堆焊获得硬面合金的方法，对硬面合金中氮的吸收与析出进行了研究，结果表明Cr13马氏体不锈钢硬面合金中最大氮含量约为0.10％左右，添加微量的固氮元素铌、钒和钛能使硬面合金的氮含量达到0.20％以上，而不产生气孔。铌、钒、钛提高氮在马氏体不锈钢硬面合金中的溶解度，主要作用表现为：一是降低N在熔池金属中的活性系数，增大N的固溶度；二是作为碳氮化物形成元素与N作用，在硬面合金中形成复杂的碳氮化物粒子，增大含N量。氮合金化硬面合金中氮含量控制在0.10～0.13％，碳的含量可降低到0.20％以下。成功研制了焊接工艺性能良好的氮合金化自保护和埋弧硬面药芯焊丝。通过对自保护焊接过程深入分析，实现了利用空气中的自然氮进行合金化。研究发现，在没有气孔发生的条件下，通过调整渣系和固氮元素，可使自保护硬面堆焊合金增氮0.08％，开发出一种低成本的氮合化自保护硬面药芯焊丝。通过在药芯中加入适量氮化物的方法研制出了氮合金化埋弧硬面药芯焊丝，并研制出了与之匹配的烧结焊剂，渣系为MgO—CaF₂—Al₂O₃—SiO₂，碱度为1.8～2.0。对氮合金化硬面合金中的碳氮化物析出行为进行了深入分析，并对氮合金化硬面合金的强化机理进行了深入研究。研究发现硬面合金中的碳氮析出物为弥散分布在晶界和晶内的M（C、N）复合物，碳氮析出物的尺寸、形状和成分与其形成过程有关。在焊态条件下，碳氮化物主要为在液态金属凝固过程中形成的（Nb、Ti、V）（C、N）复合物，其尺寸大小为1～3.5μm；在450～650℃回火条件下，大量尺寸大小为5～200nm的细小碳氮析出物Nb（C、N）以棒形、球形弥散析出，产生二次硬化作用。硬面合金中的碳氮化物起到了细化一次结晶组织、钉扎位错阻碍晶粒长大促进显微组织细化和沉淀强化作用。碳氮化物不易长大，具有良好的高温稳定性，抑制了富Cr相的形成，使得硬面合金具有良好的热稳定性和耐腐蚀性能。研究了碳氮化物在硬面合金中的耐磨粒磨损作用，结果表明硬面合金中的碳氮化物沉淀相能有效抵御磨粒的微切削，起到提高耐磨性的作用，在500～600℃温度回火，大量弥散细小的碳氮化物沉淀析出，能有效促进硬面合金耐磨性能的提高。对氮合金化硬面合金组织进行了深入分析，结果表明氮合金化硬面合金的组织结构为板条马氏体、碳氮化物以及少量残余奥氏体。研究发现回火温度对硬面合金的组织产生重要影响。碳氮化物的析出温度高于碳化物，在500～650℃能大量沉淀析出，并具有良好的高温稳定性能；而碳化物在低于500℃沉淀析出，在高于600℃时分解，导致基体的硬度显著下降。大量弥散分布细小碳氮化物沉淀析出能有效促进硬面合金硬度的提高，并使硬面合金具有良好的抗回火软化性能。建立了氮合金化硬面合金的Ms温度计算公式：Ms／℃=550-330（w_C+0.86w_N-0.05）-35w_Mn-17W_Ni-12W_Cr-21W_Mo-10 W_Si-35(W_Nb+W_V+W_Ti)。对氮合金化和碳合金化硬面合金进行了高温高载荷金属间磨损对比试验研究。研究发现硬面合金与42CrMo钢的高温金属间磨损，为42CrMo钢表面高温下形成的氧化皮，粘着于堆焊马氏体不锈钢硬面合金表面，导致硬面合金产生了磨粒磨损。磨损金属间的高应力造成硬面合金的沿晶界开裂，降低了硬面合金的耐金属间磨损。氮合金化硬面合金细小的显微组织、良好的强韧性和碳氮化物质点在高温磨损过程中大量沉淀析出，使其具有比碳合金化硬面合金更优的耐高温磨损性能。更多还原

【Abstract】 As a gap-atom element, nitrogen can improve many properties of steels throughcombining with other alloy elements, including hardness, toughness, creep resistance,wearing resistance and corrosion resistance. Using the nitrogen instead of the carbon, thewelding hot-crack resistance, wear resistance, corrosion resistance and high temperaturestability of hardfacing materials can be greatly improved. The hardfacing materials arealloyed through nitrogen replacing part of carbon, which has been used as a new way toimprove the comprehensive properties of hardfacing alloy.The behavior of nitrogen and the factors affecting nitrogen content in the martensitestainless hardfacing alloy had been studied systematically. The reasonable nitrogen contentof hardfacing alloy was obtained, and the alloying composition of the nitrogen-alloyhardfacing alloy was designed. The dissolution and release of nitrogen during welding ofhardfacing alloy was studied by submerged-arc welding using nitrogen-alloyinghardfacing flux-cored wire with addition of CrN. The maximal nitrogen content in Crl3steel is approximately 0.10%, which can up to 0.20% and has no porosity in it throughadding extremely a little quantities of Nb, V and Ti elements. Additions of Nb, V and Tican increase nitrogen solubility in the hardfacing alloy, which has two means: Firstly, theycan reduce activity coefficient of nitrogen in molten metal and then increase its solidsolubility. Secondly, these alloying elements as the most effective carbonitride formingelements added in harfacing alloy to enlarge nitrogen content. When the nitrogen contentof nitrogen-alloying hardfacing alloy is controlled within reasonable range from 0.10% to0.13%, the carbon content can be reduced to less than 0.20%.The self-shielded and submerged-arc nitrogen-alloying hardfacing flux-cored wireswith good welding performance had been developed successfully. The welding process ofself-shield hardfacing flux-cored wire was gone deep into analysis, and a new preparingapproach of nitrogen-alloying harfacing alloy had been created by making full use ofnatural nitrogen in air. The hardfacing alloy of self-shielded hardfacing flux-cored wirecould get 0.08% nitrogen content through adjusting slag system and effectivenitride-forming elements, which had no porosity in it. And a low cost of nitrogen-alloying self-shielded nitrogen-alloying hardfacing flux-cored wire was developed. Thenitrogen-alloying submerged-arc hardfacing flux-cored wire was made by addition ofnitride, and a kind of sintered flux which is adaptive to the hardfacing flux-cored wire wasalso developed. It has the slag series for MgO-CaF₂-Al₂O₃-SiO₂, and the alkalinity is1.8～2.0.The precipitation behavior of carbonitride in hardfacing alloy was systematicallyanalyzed, and the strengthening mechanism of it was also studied. It was revealed thatcarbonitride particles in the hardfacing alloy are complex M（C、N） distributing on thegrain boundary or matrix of the hardfacing alloy. These carbonitrides have dissimilar size,morphology and composition in different formation process of it. In as-welded condition,most of carbonitride are （Nb、V、Ti）（C、N） precipitate with characteristic cuboidal shape,which can readily precipitate from the hardfacing alloy with large size（1～3.5μm） as theywere formed already during solidification. At the temper temperature of 450～650℃, alarge number of carbonitride Nb（C、N） can be precipitated out with the size range from 5to 200nm. These fine carbonitride has two forms of bar and globular, which have a greatsecondary hardening effect on the matrix. The carbonitride in hardfaced alloy caneffectively refine the microstructure during welding and hinder the crystal boundarymigration by fixing the crystal boundary, which had a grain refinement and precipitationstrengthening effect on the hardfacing alloy. The carbonitride precipitates prevented theformation of chromium-rich phase at grain boundaries and intergranular chromiumdepletion, so the hardfacing alloy had good stability and corrosion resistance. The effect ofcarbonitride precipitates on the abrasive wear behaviour of hardfacing alloy was studied.The results showed that the carbonitride had an effectively protecting effect on thehardfacing alloy to keep the hardfacing alloy from wearing by the abrasion particles. Thehomogeneous distribution of very fine carbonitride could precipitate out during the tempertemperature of 500～600℃and improve markedly the wear resistance of hardfacing alloy.The microstructure of nitrogen-alloying hardfacing alloy was deeply analyzed. Theresult shows that the hardfacing alloy has three main phases of lath martensite,carbonitride and the residual austenite. It is found that the temper temperature has asignificant effect on the microstructure of hardfacing alloy, and the temperature of carbonitride precipitation was above that of the carbide precipitation. The carbonitride canprecipitate out during the temperature of 500～650℃and has a good stability at the hightemperature. Meanwhile, the carbide precipitated out below the temper temperature of 500℃and decompounded above 600℃. The hardness of hardfacing alloy decreased sharplywhen the carbide decompounded. The homogeneous distribution of very fine carbonitridecould improve markedly the hardness of hardfacing alloy, so the nitrogen-alloyinghardfacing alloy had a good softening resistance at high temperature tempering. The Ms ofnitrogen-alloying hardfacing alloy was established, and the calculation formula is listed:Ms/℃=550-330（w_C+0.86w_N-0.05）-35w_Mn-17w_Ni-12w_Cr-21w_Mo-10 w_Si-35(w_Nb+w_V+w_Ti).The high temperature wear resistance of nitrogen-alloying hardfacing alloy wastested under a high load, and compared with those of conventional carbon-alloyinghardfacing alloy. It is found that the high temperature wear mechanism of hardfacing alloyand 42CrMo steel was abrasive wear due to the effect of scale formation on the surface of42CrMo steel. The scale was sticking on the surface of hardfacing alloys and increasingthe abrasive wear damage. And the crack occured on the grain-boundary because of thehigh stress effect on the wear surface of metals, which decreased the metal-metal wearresistance of hardfacing alloy. The results showed that the nitrogen-alloying hardfacingalloy had more excellent high temperature wear property than that of carbon-alloyinghardfacing alloy due to the fine microstructure, good tenacious property and the effect of alarge number carbonitride homogeneously precipitated out during high temperaturewearing.更多还原