cast irons.Changing silicon content in the range of from 2.8%up to 3,4%,the effectiv enes of precipitation ferrile phases in small thicknesses of castings scction (Fig.4,section 7mm and 12mm)is more higher than that in the larges ones (30,45, 60mm).Intensification of ferrilic structure formation for section 30,45,60 mm of cast iron with 0.5%Mn is almost the same within 2.8~3.2%Si (Fig.4). This phenomenon may be explained by thei weak action of low manganese content on the graphitization processes. 100 100 90 80 70 059%Mn 0.1%Mn 50 40 40L 2.83.03.23.43.6 2.83.03.23.43.6 Si,94 Si, Fig.4 Effect of silicon on formation Fig.5 Effect of silicon on formation of ferritic structure:(0.5%Mn) of ferritic structure;(0.1%Mn) (1)7mm,(2)12mm,(3)30mm, (1)7mm,(2)12mm,(3)30mm, (4)45mm,(5)60mm (4)45mm,(5)60mm, 2.2 Mechanical Properties In each case of producing step-shape casting tests of different compositions for determination of structural changes,test bars of 25 mm wall-thicknesses were made simultancously.These wedge-shape were intended for a further machining standard specimens for definition of mechanical properties. The effect of silicon content on mechanical properties of nodular cast irons with 0.5%Mn and 0.1%6 Mn is illustrated in Fig.6 and Fig.7 respectively. The results obtained show that an increase in silicon content which giving rise to different variation in the matrix structure leads to a change of mechanical propertics of nodular cast irons.Increasing ratio ferrite to pearlite in nodular cast irons with 0.5%Mn by addition of silicon from 2.8%up to 3.4%leads first to an increasc,followed by a decrease in elongation,tensile strength and impact toughness,while the hardness changes in the opposite direction (Fig.6). Tensile strength and elongation of this series nodular cast iron with 3.2%Si are maximum of about 524.6N/mm and 19.8%respectively.In the second series nodular cast irons with 0.1%Mn,the silicon addition first increases after the decreases in elongation,impact strength and hardness,while tensile strength changes 548· ， ， 、 · · 少‘ ， 。 、 、 〔 ， ， ， 一 ， ， 、 云 主 盯 ， ， ” · 飞 一 · 三 、、 一 、 · · 产 二一 州丢 ‘ 口气尸 氏试 午一’少’ 产 一 丈 ， · 洲 刁 示 密黔 二 朽 入 ︸ 冰 角﹃祠。翻﹂叭 ﹃刹。闪﹄‘。 。 。 ， ， 几 。 ， 阮门咬内月 六八 。 乡石 「 一 万 。 ， ， ， ， ， ， ， ， 功 ， 尸 一 ， 从 · 一 ， · 矶 · 一 卜 全 · 一 爪 。 一 梦百 一 石 入丁 · · · 〔 一 、、 · 、 一 几 · 《。 二 · ，石 ， 叭 ， ， 一 ， 、 、 。 、 、 ， 艺 百 。 二 。 早石 ， 。 。 ，