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首页> 外文期刊>Acta Polytechnica Scandinavica. Mechanical Engineering Series >Effect of nitrogen content on precipitation behaviour and properties of P/M high nitrogen austenitic stainless steels
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Effect of nitrogen content on precipitation behaviour and properties of P/M high nitrogen austenitic stainless steels

机译：氮含量对P / M高氮奥氏体不锈钢析出行为和性能的影响

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摘要

The effect of nitrogen content on the precipitation behaviour and properties of solution annealed and further isothermally at elevated temperatures (450 ℃ or 750 ℃) annealed powder metallurgically manufactured (P/M) austenitic stainless steels (24Cr-22Ni-7, 3Mo-3, 5Mn-0, 3...1, 15N) was studied. The studied steels were manufactured by hot isostatic pressing (HIP) from gas atomized powders. Nitrogen alloying was performed during atomizing, and by further solid state nitriding of the powders in a fluidized bed furnace. The steels were studied with optical microscopy, transmission electron microscopy, dilatometric analyses, tensile testing, Charpy-V impact testing, hardness measurements and localized corrosion testing (6 % FeCl{sub}3 solution; modified ASTM G48 and G76). The solution annealed steels were observed to be fully austenitic, and to have a unique combination of high strength, good ductility and toughness, as well as excellent localized corrosion resistance, when the nitrogen content of the steel was 0,5 - 0,9 wt-%N. At lower nitrogen contents, intermetallic phases were precipitated, and at higher nitrogen contents, Cr{sub}2N was precipitated. In both cases ductility, toughness and localized corrosion resistance of the steels was deteriorated. Isothermal annealing at elevated temperatures (450 ℃ or 750 ℃) resulted in either intermetallic phase (σ and Laves), or both chromium nitride (Cr{sub}2N) and intermetallic phase precipitation, depending on the nitrogen content of the steel and on the annealing temperature and time. Intermetallic phases precipitated in the steels with ≤0,5 wt-%N when isothermally annealed at 450 ℃ for up to 500 h, and ductility, toughness, and localized corrosion resistance of the steels were deteriorated. The hardness and strength properties of the steels increased due to intermetallic phase precipitation. In steels with >0.5 wt-%N, intermetallic phases were not precipitated at 450 ℃ and the properties of the steels remained unaffected. Annealing at 750 ℃ resulted in intermetallic phases precipitation in steels with ≤0,5 wt-%N, whereas in steels with >0,5 wt-%N, both intermetallic phases and Cr{sub}2N were precipitated. The amount of intermetallic phase precipitation decreased with increasing nitrogen content of the steel. Precipitation of σ phase was retarded and Laves phase was stabilized in steels with >0,5 wt-%N. The tensile strength of the studied steels isothermally annealed at 750 ℃ either increased, remained unaffected, or decreased as their nitrogen content increased. The tensile ductility, impact toughness and localized corrosion resistance of the steels annealed at 750 ℃ decreased with increasing annealing time. The decrease in tensile ductility was the smaller the higher the nitrogen content of the steel was. The effect of nitrogen content on the decrease of impact toughness and localized corrosion resistance was not as clear as in the case of tensile ductility. Precipitation of intermetallic phases was more detrimental to tensile ductility and localized corrosion resistance than Cr{sub}2N, whereas Cr{sub}2N precipitation was more detrimental to impact toughness than intermetallic phases. The hardness of the studied steels annealed at 750 ℃ increased with increasing annealing time, due to precipitation of intermetallic phases and Cr{sub}2N.
机译：氮含量对粉末冶金（P / M）奥氏体不锈钢（24Cr-22Ni-7，3Mo-3，高温）（450/750或750℃）高温退火后的溶液的析出行为和性能的影响研究了5Mn-0，3 ... 1，15N）。所研究的钢是通过热等静压（HIP）由气体雾化的粉末制成的。氮合金化是在雾化过程中进行的，并通过在流化床炉中进一步对粉末进行固态氮化来进行。用光学显微镜，透射电子显微镜，膨胀计分析，拉伸试验，夏比-V冲击试验，硬度测量和局部腐蚀试验（6％FeCl {sub} 3溶液;改良的ASTM G48和G76）对钢进行了研究。当钢的氮含量为0.5-0.9 wt％时，观察到固溶退火钢是完全奥氏体，具有高强度，良好的延展性和韧性以及出色的局部耐腐蚀性的独特组合。 -％N。在较低的氮含量下，金属间相沉淀，而在较高的氮含量下，Cr {sub} 2N沉淀。在这两种情况下，钢的延展性，韧性和局部耐腐蚀性均下降。高温（450℃或750℃）的等温退火会导致金属间相（σ和Laves）或氮化铬（Cr {sub} 2N）和金属间相沉淀，这取决于钢中的氮含量和退火温度和时间。当在450℃下等温退火500 h时，N含量≤0.5wt％的钢中析出金属间相，钢的延展性，韧性和局部耐蚀性下降。由于金属间相的析出，钢的硬度和强度性能有所提高。氮含量> 0.5 wt％的钢在450℃时不会析出金属间相，且钢的性能不受影响。在≤0.5wt％N的钢中，在750℃退火导致金属间相析出，而在> 0.5 wt％N的钢中，金属间相和Cr {sub} 2N均析出。随着钢中氮含量的增加，金属间相的析出量减少。在氮含量> 0.5 wt％的钢中，σ相的析出被延迟并且Laves相稳定。随着氮含量的增加，在750℃下等温退火的研究钢的拉伸强度要么增加，不受影响，要么降低。随着退火时间的延长，在750℃退火的钢的拉伸延展性，冲击韧性和局部耐蚀性降低。钢的氮含量越高，拉伸延展性的降低越小。氮含量对冲击韧性和局部耐腐蚀性下降的影响不如拉伸延展性那么明显。金属间相的沉淀比Cr {sub} 2N更不利于拉伸延展性和局部耐腐蚀性，而Cr {sub} 2N沉淀比金属间相更不利于冲击韧性。由于金属间相和Cr {sub} 2N的析出，在750℃退火的研究钢的硬度随退火时间的增加而增加。

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