通过焊接热影响区最高硬度试验、斜Y形坡口焊接裂纹试验、典型对接接头性能评价试验及典型对接接头疲劳性能试验,结合金相显微镜(optical microscope,OM)和扫描电子显微镜(scanning electron microscope,SEM)两种表征手段,深入研究了新...通过焊接热影响区最高硬度试验、斜Y形坡口焊接裂纹试验、典型对接接头性能评价试验及典型对接接头疲劳性能试验,结合金相显微镜(optical microscope,OM)和扫描电子显微镜(scanning electron microscope,SEM)两种表征手段,深入研究了新型低锰微铌钢(MnNb钢)与普通Q355钢(Q355钢)焊接性能差异及机理。结果表明,在不预热条件下,Q355钢表现出强烈的焊接淬硬倾向,而MnNb钢无淬硬倾向;MnNb钢和Q355钢均具备优良的防止焊接冷裂纹性能。相比于Q355钢接头,MnNb钢对接接头抗拉强度稍低,但其热影响区冲击吸收能量明显更优,这主要是由于Q355钢粗晶区中存在细小的晶内组织和侧板条铁素体组织,而MnNb钢粗晶区具有大量针状铁素体与较小的原始奥氏体晶粒。MnNb钢接头的条件疲劳极限强度比Q355钢接头高57 MPa,其扩展区疲劳辉纹间距更小,裂纹扩展速度更慢,MnNb钢对接接头的疲劳性能显著优于Q355钢对接接头。展开更多
阐述了EVI的概念、目的及意义,综述了热成形钢、淬火分配(Quenching and Partitioning,QP)钢及DH钢冷成形钢、和新能源汽车专用的高强度钢硅钢新材料方面的进展,以及可实现高精度碰撞模拟的材料断裂卡片和实现剪切边缘冲压模拟的材料成...阐述了EVI的概念、目的及意义,综述了热成形钢、淬火分配(Quenching and Partitioning,QP)钢及DH钢冷成形钢、和新能源汽车专用的高强度钢硅钢新材料方面的进展,以及可实现高精度碰撞模拟的材料断裂卡片和实现剪切边缘冲压模拟的材料成形卡片的开发进展,论述了在新材料开发和精准成形及碰撞模拟的基础上的乘用车车身正向选材,实现EVI的核心目标之一“合适的材料用在合适的地方”。探讨了热成形门环、一体化铝合金下车体、商用车热成形上装及车轮最新制造工艺技术。分析了“双碳”和“抗氢脆”两个共性需求,并提出了低碳排放汽车钢及铝合金零件的实施路径,以及抗氢脆热成形钢和冷成形钢的实现路径。对原材料企业和零部件企业当前和未来基于EVI技术和服务方向提出了建议。展开更多
This paper presents a microstructural characterization of standard ferroniobium(FeNb) and a study of its dissolution in steel.Interrupted dissolution trials at different temperatures were carried out in a laboratory i...This paper presents a microstructural characterization of standard ferroniobium(FeNb) and a study of its dissolution in steel.Interrupted dissolution trials at different temperatures were carried out in a laboratory induction furnace.The microstructure at the interface between solid FeNb and frozen steel was analyzed and compared with the original FeNb particles.The results allowed clarifying both the FeNb dissolution mechanism and its incorporation kinetics at steelmaking temperatures.Experimental results from the dissolution of standard FeNb in liquid steel proved that the dissolution rates of FeNb particles were higher than those reported in the pertinent literature,where models assume that FeNb dissolves only by the diffusion of solid particles due to its high melting temperatures(over 1 600℃).Most recent FeNb phase diagrams and DTA analyses have shown that standard FeNb begins to melt down below 1 600℃.The experimental evidences in this work have led to the adoption of a new description of the dissolution mechanism whereby standard FeNb dissolves predominantly by the melting of its eutectic zones at 1500℃to 1510℃and,later on,by the melting of the primary laths between 1530℃and 1575℃,i.e.,below the steelmaking temperatures of around 1 600℃.Based on these results and on previous melting-shop experience,this paper recommends the best practices for the addition of FeNb during the microalloyed steels secondary refining phase.展开更多
The potential for use of microalloy additions to suppress abnormal austenite grain growth and produce steels with enhanced bending fatigue resistance after high temperature vacuum carburizing was investigated in a ser...The potential for use of microalloy additions to suppress abnormal austenite grain growth and produce steels with enhanced bending fatigue resistance after high temperature vacuum carburizing was investigated in a series of Ti-modified SAE 8620 steels with w(niobium) additions up to 0.1%.Results are considered from a series of papers at the Advanced Steel Processing and Products Research Center on the effects of Nb content,heating rate, rolling history,and processing temperature on the evolution of austenite grain structures in carburizing steels. Emphasis is placed on understanding the effects of alloying and processing on each stage in the annealing process including the as received laboratory rolled conditions,during the onset of carburizing after annealing at different heating rates,and after annealing for various times at carburizing temperatures up to 1 100℃.Heating rate to the carburizing temperature was shown to be an influential variable and suppression of abnormal grain growth was dependent on the development of a critical distribution of fine NbC precipitates,stable at the austenitizing temperature.The importance to industrial carburizing practice of heating rate effects on precipitates and austenite grain size evolution are discussed and correlated to selected data on fatigue performance.展开更多
In this paper,CCT(continuous cooling transformation)diagrams are determined for Nb-containing reinforcing bars with different Nb,Mn additions,and initial austenite grain sizes by simulating industrial conditions via d...In this paper,CCT(continuous cooling transformation)diagrams are determined for Nb-containing reinforcing bars with different Nb,Mn additions,and initial austenite grain sizes by simulating industrial conditions via dilatometry tests.It was found that coarse austenite grain size,high Mn content and Nb remaining in solution all increase hardenability of Nb-containing rebars,namely lower Ar3 for acicular phase transformation products,which leads to continuous yielding during tensile deformation when the volume fraction of acicular ferrite or bainite microstructure reaches a certain volume fraction.By coupling with actual cooling rates for different size rebars,it can be explained why bainitic structure is prone to form in the center of rebars,especially for small size rebars.In order to achieve required ferrite-pearlite microstructure,cooling strategy is optimized for industrial production.展开更多
Controlling of the solution and precipitation for microalloying additions of Nb,V,Ti and their combination is the basic building block of microalloyed steels.Among three microalloying elements,Nb has been regarded the...Controlling of the solution and precipitation for microalloying additions of Nb,V,Ti and their combination is the basic building block of microalloyed steels.Among three microalloying elements,Nb has been regarded the most effective microalloying ingredient used for low carbon flat products due to marked strengthening effect of grain refinement and relatively weak precipitation strengthening effect by matching proper thermomechanical processing(TMP).However,Nb was not viewed as attractive as V for medium carbon long products in the past because of limited solubility during reheating process.What is more,hot working is usually carried out at high temperatures in the recrystallization regime,so it is difficult to exert conventional controlled rolling to obtain pancaked austenite,which has further affected the research and application of Nb in medium carbon long products.Because of these factors,studies of Nb in medium carbon long products were incomplete,and even some recognitions and conclusions are subjected to debate.In order to clarify the strengthening effects of Nb in medium carbon long products,the reinforcing bars have been chosen as experimental steels to clarify the role of Nb on microstructural changes along the whole hot working,cooling processes.In addition,qualitative and quantitative analyses of Nb’s state and distribution in reheating,rolling and cooling had been carried out to illustrate some singularities.展开更多
文摘通过焊接热影响区最高硬度试验、斜Y形坡口焊接裂纹试验、典型对接接头性能评价试验及典型对接接头疲劳性能试验,结合金相显微镜(optical microscope,OM)和扫描电子显微镜(scanning electron microscope,SEM)两种表征手段,深入研究了新型低锰微铌钢(MnNb钢)与普通Q355钢(Q355钢)焊接性能差异及机理。结果表明,在不预热条件下,Q355钢表现出强烈的焊接淬硬倾向,而MnNb钢无淬硬倾向;MnNb钢和Q355钢均具备优良的防止焊接冷裂纹性能。相比于Q355钢接头,MnNb钢对接接头抗拉强度稍低,但其热影响区冲击吸收能量明显更优,这主要是由于Q355钢粗晶区中存在细小的晶内组织和侧板条铁素体组织,而MnNb钢粗晶区具有大量针状铁素体与较小的原始奥氏体晶粒。MnNb钢接头的条件疲劳极限强度比Q355钢接头高57 MPa,其扩展区疲劳辉纹间距更小,裂纹扩展速度更慢,MnNb钢对接接头的疲劳性能显著优于Q355钢对接接头。
文摘阐述了EVI的概念、目的及意义,综述了热成形钢、淬火分配(Quenching and Partitioning,QP)钢及DH钢冷成形钢、和新能源汽车专用的高强度钢硅钢新材料方面的进展,以及可实现高精度碰撞模拟的材料断裂卡片和实现剪切边缘冲压模拟的材料成形卡片的开发进展,论述了在新材料开发和精准成形及碰撞模拟的基础上的乘用车车身正向选材,实现EVI的核心目标之一“合适的材料用在合适的地方”。探讨了热成形门环、一体化铝合金下车体、商用车热成形上装及车轮最新制造工艺技术。分析了“双碳”和“抗氢脆”两个共性需求,并提出了低碳排放汽车钢及铝合金零件的实施路径,以及抗氢脆热成形钢和冷成形钢的实现路径。对原材料企业和零部件企业当前和未来基于EVI技术和服务方向提出了建议。
文摘This paper presents a microstructural characterization of standard ferroniobium(FeNb) and a study of its dissolution in steel.Interrupted dissolution trials at different temperatures were carried out in a laboratory induction furnace.The microstructure at the interface between solid FeNb and frozen steel was analyzed and compared with the original FeNb particles.The results allowed clarifying both the FeNb dissolution mechanism and its incorporation kinetics at steelmaking temperatures.Experimental results from the dissolution of standard FeNb in liquid steel proved that the dissolution rates of FeNb particles were higher than those reported in the pertinent literature,where models assume that FeNb dissolves only by the diffusion of solid particles due to its high melting temperatures(over 1 600℃).Most recent FeNb phase diagrams and DTA analyses have shown that standard FeNb begins to melt down below 1 600℃.The experimental evidences in this work have led to the adoption of a new description of the dissolution mechanism whereby standard FeNb dissolves predominantly by the melting of its eutectic zones at 1500℃to 1510℃and,later on,by the melting of the primary laths between 1530℃and 1575℃,i.e.,below the steelmaking temperatures of around 1 600℃.Based on these results and on previous melting-shop experience,this paper recommends the best practices for the addition of FeNb during the microalloyed steels secondary refining phase.
文摘The potential for use of microalloy additions to suppress abnormal austenite grain growth and produce steels with enhanced bending fatigue resistance after high temperature vacuum carburizing was investigated in a series of Ti-modified SAE 8620 steels with w(niobium) additions up to 0.1%.Results are considered from a series of papers at the Advanced Steel Processing and Products Research Center on the effects of Nb content,heating rate, rolling history,and processing temperature on the evolution of austenite grain structures in carburizing steels. Emphasis is placed on understanding the effects of alloying and processing on each stage in the annealing process including the as received laboratory rolled conditions,during the onset of carburizing after annealing at different heating rates,and after annealing for various times at carburizing temperatures up to 1 100℃.Heating rate to the carburizing temperature was shown to be an influential variable and suppression of abnormal grain growth was dependent on the development of a critical distribution of fine NbC precipitates,stable at the austenitizing temperature.The importance to industrial carburizing practice of heating rate effects on precipitates and austenite grain size evolution are discussed and correlated to selected data on fatigue performance.
文摘In this paper,CCT(continuous cooling transformation)diagrams are determined for Nb-containing reinforcing bars with different Nb,Mn additions,and initial austenite grain sizes by simulating industrial conditions via dilatometry tests.It was found that coarse austenite grain size,high Mn content and Nb remaining in solution all increase hardenability of Nb-containing rebars,namely lower Ar3 for acicular phase transformation products,which leads to continuous yielding during tensile deformation when the volume fraction of acicular ferrite or bainite microstructure reaches a certain volume fraction.By coupling with actual cooling rates for different size rebars,it can be explained why bainitic structure is prone to form in the center of rebars,especially for small size rebars.In order to achieve required ferrite-pearlite microstructure,cooling strategy is optimized for industrial production.
文摘Controlling of the solution and precipitation for microalloying additions of Nb,V,Ti and their combination is the basic building block of microalloyed steels.Among three microalloying elements,Nb has been regarded the most effective microalloying ingredient used for low carbon flat products due to marked strengthening effect of grain refinement and relatively weak precipitation strengthening effect by matching proper thermomechanical processing(TMP).However,Nb was not viewed as attractive as V for medium carbon long products in the past because of limited solubility during reheating process.What is more,hot working is usually carried out at high temperatures in the recrystallization regime,so it is difficult to exert conventional controlled rolling to obtain pancaked austenite,which has further affected the research and application of Nb in medium carbon long products.Because of these factors,studies of Nb in medium carbon long products were incomplete,and even some recognitions and conclusions are subjected to debate.In order to clarify the strengthening effects of Nb in medium carbon long products,the reinforcing bars have been chosen as experimental steels to clarify the role of Nb on microstructural changes along the whole hot working,cooling processes.In addition,qualitative and quantitative analyses of Nb’s state and distribution in reheating,rolling and cooling had been carried out to illustrate some singularities.
