叙述并討論了合金元素对鉻錳碳氮奥氏体耐热鋼时效变脆的影响的初步实驗結果。結果指出钼釩促使这种类型鋼的变脆,硼能改善其时效脆性,适合于設計的要求。微量混合稀土元素对改善时效脆性的作用不明显。 金相和电子显微镜及X射线研究的結果指出,晶界和沿晶界边緣組織結构的变化是影响脆性的主要因素。时效后的主要沉淀为M_(23)C_6和(Cr,Fe)_2N;含钼較高的鋼种(>1％Mo),在更长时間的时效以后,有x相及σ相的出現,当其量較多时,也可增加鋼的脆性。硼不但減緩某些相的析出,而且也可以改变它們的分布状态,使晶界发生不連續沉淀,从而对韌性的降低較少。
It was known that the Cr-Mn-C-N austenitic steels become brittle (a_k<5) after long ageing at the service temperatures. The aim of the present investigation is to examine the effect of the various alloying elements on the age brittleness in a steel with the basic composition of 14% Cr, 17% Mn, 0.3% N and 0.1% C. From the impact tests after ageing up to 2000 hours at 650 and 700℃, it may be concluded that the carbide forming elements as Mo, V, or W deteriorate the toughness of the steel, while B has a beneficial effect.By a combination of electrolytic extraction, X-ray identification, optical and electron microscopic examination, it was found that the ageing embrittlement is caused mainly by the precipitate of carbide and nitride films along the grain boundaries. If the steel contains more than 1% Mo, x and σ phases will appear after ageing for longer periods; whether these intermetallic phases will cause brittleness or not, it depends upon the quantity and distribution of the brittle phases. The addition of boron to this steel will not only retard the precipitation processes but also make the grain boundary precipitate discontinuous, thus improving the toughness after long ageing.
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