The Deoxidation Process of GCr15 Steel

D0I:10.13374/j.issn1001-053x.1989.06.026 第11卷第G期 北京科技大学学报 Vol.11 No.6 1989年11月 Journal of University of Science and Technology Beijing Nov,1989 Some Factors Affecting on the Structure- formation and Mechanical Properties of As-Cast High Toughness Nodular Cast Iron' Enoukidze Nodar A**,Lian Jinjiang(连金江)， Zhong Weizhen(钟作珍)，Rong Yu(戎獠)* ABSTRACT:Using sand moulds for step-shape casting tests and different silicon percentage of nodular cast iron it was possible to separate structural variations produced during freezing from those occurring at Ac:transformation temperature.The results show that an increasc in silicon content leading to di- fferent variation in the matrix structure,leads to a changing mechanical prope- rties of nodular cast irons.Tensile strength and elongation of obtained as-cast nodular cast iron with the composition of 3.9%C,3.2%Si,0.5%Mn are ma- ximum of about 524.5N/mm2 and 19.8%accordingly.In the same nodular cast iron,but only with 0.1%Mn the silicon addition first increases after decreases elongation,impact toughness and hardness.But tensile strength changes to the opposite side. KEY WORDS:cast iron,ferritic structure,thin-wall casting By varying the compesilion within the deformation limits,the wide variation in the microstructure and in mechanical propertics of nodular cast irons can be obtained.Further structural changes for a fixed iron composition can be readily brought about by heat treatment.But this technology becomes more expensive. Relating the compsition of these alloys to their mechanical properties is there- fore arbitrarily selected melt and solidification treatment,as well as for the cooling conditions during freezing(1.But there is the problem about selecting the chemical composition of as-cast nodular cast iron for production of thin-walled castings with ferritic structure and high elongation [2). Manuscript Received March 1,1989 ..Doctor,Ass.Prof.of Foundary Dept.of Gcorgian Polytechnic Institute, Tbilisi USSR ···Dcpt.of Metallurgy 544

第 卷第 期 年 刀 匕 写可 科 。 、 一 少 技 大 学 学 报 了 产 一 ’ 侧 月 一 夕 才 ’ 乍中伟珍 连 金 江 ， 夕 戎 像 一 “ · ， · ℃ 一 、、 一 ， ， 写 皿石 · 。 ， 、 、 ， ，· 二 ， ， 一 叭 · 尸 、 ， 手 ， 。 · 一 、 〕 · ‘ · 。 ， 川 · 一 一 一 ， 从 一 、 护 ， 二 ， ， … DOI ：10．13374／j ．issn1001－053x．1989．06．026

It was our task to select suitable composition of as-cast nodular cast iron for production thin-walled castings of ferritic struclure (more than 80%ferrite) with high mechanica!properties,especially high elongation. 1 Experimental Methods The alloy compositions were selected to examine the effects of silicon on the structure formation and mechanical properties of as-cast nodular cast iron with ordinary manganese content (0.5%).Master alloys were melted in acid lined induction furnace of the capacity 20kg.Silicon and magnesium alloy were added in a ladle,stirred,and the alloy poured in sand moulds for making of wedge-shape and step-shape castings with different thicknesses of 7,12,30,45, 60mm.All alloys were bypereutectic.The alloy compositions are given in Table 1. Table 1 Chemical Compositien of As-cast nocular cast iron Chemical composition, No. C Si Mn s P Mg C.E 1 3.9 2.8 0.5 0.010 0.058 0.062 4.83 2 3.9 3.2 0.5 0.010 0.058 0.055 4.97 3 3.9 3.4 0.5 0.011 0.045 0.051 5.03 3.9 2.8 0.1 0.011 0.045 0.054 4.83 5 3.9 3.0 0.1 0.012 0.045 0.056 4.90 6 3.9 3.2 0.1 0.010 0.045 0.053 4.97 2 Experimental Results and Discussion 2.1 Structure Photographs of the microstructures of step-shape castings sections of 12mm and 7 mm with different composition of silicon and manganese are shown in Fig.1.The graphite structure of the nodular cast iron in all cases was entirely spherulitic. Castings section of 12mm with the ordinary composition of manganese (0.5%) and silicon of about 2.8%solidifies as ferrite-pearlitic structure (60%ferrite, Fig.1,a).In spite of high cooling rate,due to low percentage of manganese (0.1%)the graphitization rate of similar to cast iron for castings section of 7mm is almost the same (65%ferrite).In both case,with the increasing of silicon content the process of ferritic structure formation is highly developed. 545

权 一 ， 一 · 。 。 一 荃 ， · 一 · 几 ， 性月 ， ， 从 ， 一 一 ， ， ， 。 · 卜 一 己 ， 。 只︸八“口 八口一了时八曰了 … 任寸户月任月往‘ 一 、 、 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 ﹂八 一刁 口匕月 ‘ 。 卜 一 牛 生 从 二 ， 。 一 盯 ， ， 。 。 ， 一 · 旦 · 百 · ， 、 产

Castings sections of 12mm and 7 mm with the composition of 3.2%Si,0.5%Mn and 3.0%Si,0.1%Mn accordingly represent the ferritic structure of about 80% or more (Fig.1,b).The results obtained in further investigation show that mechanical properties (especially elongation)of these compositions of as-cast nodular cast irons are maximums. The amount of ferritic structure according to the wall-thicknesses in different sections of castings is tabulated in Table 2.The effect of cooling rate on the formation of ferritic structure is illustrated in Fig.2. In nodular cast iron with 0.5%Mn (Fig.2),by the increase of silicon content and thicknesses of castings the amount of ferritic structure is increased also. But for the cast iron with 3.4%Si a slight decreasing ferritic structure within 30-60 mm of casting thicknesses is observed.When silicon contents are 2.8% and 3.2%and thicknesses of castings section is more than 30mm such a reduction of the amount of ferritic structure is observed also for nodular cast iron with low manganese content (Fig.3).This phenomenon is probably connected with reverse segregation of chemical elements present in nodular cast iron. Fig.1 MIcrostructure of step-shape castings section of 12mm a,2.8%Si;b.3.2%Si,c,3.4%Si(Mn=0.5%) 100 90 70 0,5%Mn 50 40 121824303642485460 Thickness of casting,mm Fig.2 Effect of cooling rate on formation of ferritic structure(0.5%Mn) (1)2.8%Si,(2)3.2%Si,(3)3.4%Si 546

· ， · ， · ， · 一 一 · · · · ， · 。 。 写 一 · · · 主 · 声 一 ， 尸 承 洲二 口 户口叫 叫 尸 二 二二二翻 一 ， 口甲已碑口‘ 二二石 砂己竺尸尸一夕尸 口，甲卜 叫 口 兰一一 声 厂 叹 ﹃俩白翻 ， 。 ， 呈， ， ， 笼

100 90 80 70 60 50 0.1%Mn 40h 6 12182430364245460 Thickness of casting,mm Fig.3 Effect of cooling rate on formation of ferritic structure (0.1%Mn) (1)2.8%Si, (2)3,0%Si, (3)3.2%Si Table 2 Microstructural results Nodular cast iron with Nodular cast iron with manganese content of 0.5% manganese content of 0.1% Speci- Silicon Thick- Fer- Speci- Silicon Thick- Fer- ness of rite. ness of rite men conlen casting men conten casting % mm % % mm % 2.8 7 45 16 2.8 7 65 2 2.8 12 60 17 2.8 12 85 3 2.8 30 85 18 2.8 30 78 4 2.8 45 90 19 2.8 45 82 5 2.8 60 95 2) 2.8 60 95 6 3.2 7 65 21 3.0 7 80 7 3.2 12 85 22 3.0 12 90 8 3.2 30 85 23 3.0 30 98 9 3.2 45 90 24 3.0 45 95 10 3.2 60 97 25 3.0 60 95 11 3.4 90 26 3.2 7 95 12 3.4 12 95 27 3.2 12 98 13 3.4 30 99 28 3.2 30 98 14 3.4 45 98 29 3.2 45 99 15 3.4 60 98 30 3.2 60 100 Comment:metallographic examinations carried out according to Chinese JB 1802-76 Fig.4 and Fig.5 show how the ferritic structure is changed in difference thicknesses of step-shape castings with the increasing of silicon content in nodular 547

爷‘ － 尸户户口 匕二二泊二二二目 三 曰沪尸 尸一 一， 刁卜 、 、 广，浏洲卜 产尸户 一产尸 母 孟 一二 ，， 上 。 呀 一卜乡冰‘ ， 一 一 。 ， 写 ， 写 。 自八工﹁山八勺︼﹄们工︸︸ 斤件，，竹匕八才生任八性︸内了︸浦 。 。 。 。 。 。 。 。 。 。 。 。 。 。 几月了、︺，八了 曰︸八任一‘ 口匕︺八口性刀合拭︵八口尸八︺一。︶比八，︺一口一 自山‘曰夕，，口上，只口︸ 巧 升只一乙任︸月生庄︼︶︸刀雌廿月止刀 … 斤只‘八乃八任尸才，，工月 八八口‘门 几 斗口乙八阳乃 曰土︸月 、 、 人 、 一 。 · 。 一 元 与

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 ， 。 。 ，