A device based on a high pressure die-casting(HPDC) machine was constructed,with a capacity to produce thixo-casts from steel.After inductive heating to the required semi-solid temperature range,the samples were trans...A device based on a high pressure die-casting(HPDC) machine was constructed,with a capacity to produce thixo-casts from steel.After inductive heating to the required semi-solid temperature range,the samples were transported in a protective argon atmosphere to a cylinder of modified HPDC and injected into a pre-heated die.Bearing steel 100Cr6(after forging) was used as the feedstock material.The metallographic analysis of the steel showed a homogenous structure within a whole volume characterized by a grain size between 2 μm and 8 μm.Differential scanning calorimetry(DSC) analysis allowed to estimate the process temperature for thixoforming at 1 390 ?C which was attributed to about 45% of a liquid phase.With such technological parameters after the semi-solid processing the microstructure consisted of globular grains of size from 15 μm to 40 μm.The microstructure of globules indicated predominant presence of martensite(about 76% volume fraction) with residual austenite between plates.X-ray analysis confirmed that the thixo-cast samples contain mainly martensite and residual austenite.The hardness of the initial forged sample was HRC 27 and after the thixoforming process it was HRC 60,which confirms the presence of martensite and carbides.The thixo-casts were subjected to low tempering,at temperature of 150 °C for a period of 2 h,in order to remove stresses created during the process of thixoforming and to increase plasticity.The hardness after tempering was HRC 62.3.Additionally,in order to identify phases present in the thixo-casts,transmission electron microscopy(TEM) was carried out.展开更多
Center segregation is the main reason for cup fracture of high-carbon wire rod during drawing. Therefore, to continuously produce cast billets with very low center segregation is an important objective. The soft reduc...Center segregation is the main reason for cup fracture of high-carbon wire rod during drawing. Therefore, to continuously produce cast billets with very low center segregation is an important objective. The soft reduction technology is considered to be an effective method to minimize center segregation. To elucidate the effect of soft reduction on the internal quality of high-carbon steel billets, soft reduction was applied with different solid fractions in the core area of billets in a laboratory casting machine. A coupled temperature/displacement finite element model was developed to calculate the solid fraction using the commercial software ABAQUS. Center segregation, center porosity, homogeneity of elements, and equiaxed crystal zone were obviously improved by applying soft reduction, especially when the solid fraction was less than 1.0. The optimal results were obtained when the solid fraction was approximately 0.9.展开更多
利用热膨胀仪、热模拟试验机、金相显微镜、场发射扫描电镜等测定了100Cr6轴承钢的CCT曲线,试验研究了热压缩及控轧控冷对网状碳化物析出行为的影响。结果表明:第二道次压缩温度从850℃降低至700℃时,奥氏体再结晶细化向未再结晶转变,...利用热膨胀仪、热模拟试验机、金相显微镜、场发射扫描电镜等测定了100Cr6轴承钢的CCT曲线,试验研究了热压缩及控轧控冷对网状碳化物析出行为的影响。结果表明:第二道次压缩温度从850℃降低至700℃时,奥氏体再结晶细化向未再结晶转变,二次碳化物逐步由晶界封闭网状向半封闭条状、短杆状再向沿拉长的奥氏体晶界链状转变,750~800℃内变形碳化物细小、分散;Φ10 mm 100Cr6线材采用910℃降至770℃温度控轧+快速冷却工艺,其热轧态、球化退火及淬回火后碳化物分布均匀性逐步提升,奥氏体晶粒由8.0级细化至10.0级,晶界碳化物由封闭网状向断续条状转变,平均厚度从0.54μm降低至0.11μm,网状级别由3.0级占比33%降低至≤2.0级占比100%,可缩短球化退火时间及提高轴承的疲劳寿命。展开更多
文摘A device based on a high pressure die-casting(HPDC) machine was constructed,with a capacity to produce thixo-casts from steel.After inductive heating to the required semi-solid temperature range,the samples were transported in a protective argon atmosphere to a cylinder of modified HPDC and injected into a pre-heated die.Bearing steel 100Cr6(after forging) was used as the feedstock material.The metallographic analysis of the steel showed a homogenous structure within a whole volume characterized by a grain size between 2 μm and 8 μm.Differential scanning calorimetry(DSC) analysis allowed to estimate the process temperature for thixoforming at 1 390 ?C which was attributed to about 45% of a liquid phase.With such technological parameters after the semi-solid processing the microstructure consisted of globular grains of size from 15 μm to 40 μm.The microstructure of globules indicated predominant presence of martensite(about 76% volume fraction) with residual austenite between plates.X-ray analysis confirmed that the thixo-cast samples contain mainly martensite and residual austenite.The hardness of the initial forged sample was HRC 27 and after the thixoforming process it was HRC 60,which confirms the presence of martensite and carbides.The thixo-casts were subjected to low tempering,at temperature of 150 °C for a period of 2 h,in order to remove stresses created during the process of thixoforming and to increase plasticity.The hardness after tempering was HRC 62.3.Additionally,in order to identify phases present in the thixo-casts,transmission electron microscopy(TEM) was carried out.
文摘Center segregation is the main reason for cup fracture of high-carbon wire rod during drawing. Therefore, to continuously produce cast billets with very low center segregation is an important objective. The soft reduction technology is considered to be an effective method to minimize center segregation. To elucidate the effect of soft reduction on the internal quality of high-carbon steel billets, soft reduction was applied with different solid fractions in the core area of billets in a laboratory casting machine. A coupled temperature/displacement finite element model was developed to calculate the solid fraction using the commercial software ABAQUS. Center segregation, center porosity, homogeneity of elements, and equiaxed crystal zone were obviously improved by applying soft reduction, especially when the solid fraction was less than 1.0. The optimal results were obtained when the solid fraction was approximately 0.9.
文摘利用热膨胀仪、热模拟试验机、金相显微镜、场发射扫描电镜等测定了100Cr6轴承钢的CCT曲线,试验研究了热压缩及控轧控冷对网状碳化物析出行为的影响。结果表明:第二道次压缩温度从850℃降低至700℃时,奥氏体再结晶细化向未再结晶转变,二次碳化物逐步由晶界封闭网状向半封闭条状、短杆状再向沿拉长的奥氏体晶界链状转变,750~800℃内变形碳化物细小、分散;Φ10 mm 100Cr6线材采用910℃降至770℃温度控轧+快速冷却工艺,其热轧态、球化退火及淬回火后碳化物分布均匀性逐步提升,奥氏体晶粒由8.0级细化至10.0级,晶界碳化物由封闭网状向断续条状转变,平均厚度从0.54μm降低至0.11μm,网状级别由3.0级占比33%降低至≤2.0级占比100%,可缩短球化退火时间及提高轴承的疲劳寿命。
