Under the working environment of high temperature and strong load impact,hot forging die is prone to failure which reduces the service life of die.Using arc additive manufacturing in the die cavity,a gradient material...Under the working environment of high temperature and strong load impact,hot forging die is prone to failure which reduces the service life of die.Using arc additive manufacturing in the die cavity,a gradient material hot forging die with high precision,superior per-formance,and conformal cooling channels is developed.This improves the toughness of the die cavity and reduces the working temperature,thereby forming an isothermal field,which is an effective method to enhance the lifespan of the hot forging die.Three kinds of gradient flux-cored wires are designed for the surface of 5CrNiMo steel,and the microstructure and mechanical properties between gradient interfaces were studied.Based on the spatial curved structure of shaped waterways in the hot forging die cavity,a study was conducted on the strategy of partitioned forming for the manufacturing of the die with shaped waterways.In order to avoid interference with the arc gun,the hot for-ging die is divided into four regions,namely the transition region,upper,middle,and lower region,based on a combination of cavity depth and internal U-shaped and quadrilateral structures.The results show that the developed flux-cored wires have good moldability with straight sides of deposited metal under different process parameters and flat surface without cracks,pores and other defects.Under the same working conditions,the life of hot forging die formed by the gradient materials is more than multiple times that of the single material hot forging die,and the temperature gradient field of the shaped waterway die is 7℃/cm smaller than that of traditional straight waterway.展开更多
通过研究不同工艺参数下激光调控电弧的行为,发现激光可以压缩电弧,使得电弧稳定,激光对电弧有调控作用;进而分析不同工艺参数下激光对堆积层稳定性的影响以及激光约束电弧熔丝增材制造构件的表面粗糙度。研究发现相较于熔化极活性气体...通过研究不同工艺参数下激光调控电弧的行为,发现激光可以压缩电弧,使得电弧稳定,激光对电弧有调控作用;进而分析不同工艺参数下激光对堆积层稳定性的影响以及激光约束电弧熔丝增材制造构件的表面粗糙度。研究发现相较于熔化极活性气体保护电弧焊(Metal Active Gas Arc Welding,MAG)作用而言,激光作用后,堆积层稳定性得到提高,并且小规范参数下,构件表面粗糙度Ra值由150.178μm降低到53.521μm;中等规范参数下,构件表面粗糙度Ra值由71.328μm降低到41.498μm;大规范参数下,构件表面粗糙度Ra值由110.163μm降低到82.352μm。展开更多
In this study,the welding thermal cycle curve exhibited two temperature peaks in high heat-input twin-wire separate-pool submerged-arc welding and coarse-grained heat affected zone existed in the welded joint. The inc...In this study,the welding thermal cycle curve exhibited two temperature peaks in high heat-input twin-wire separate-pool submerged-arc welding and coarse-grained heat affected zone existed in the welded joint. The inclusions of primary weld metal and coarse-grained heat affected zone of Ce-added SAW should be Al_2O_3,MnO,SiO_2,TiO,Ce_2S_3,CeS,Ce_2O_2S and Ce_2O_3. Under the effect of welding thermal cycle,oxy-sulfides inclusions of Ce,the diameter of which was less than 2. 0 μm,slightly grew larger,but the composition and type of the inclusions didn't change. The microstructure of the large heat input weld metal had acicular ferrite that Ce oxide sulphide particles induced nucleation and proeutectoid ferrite. In the coarse-grained heat affected zone of weld metal,home-position precipitation of acicular ferrite and sympathetic acicular ferrite were both observed. It was supposed that previous crystal cells of acicular ferrite in austenite grain promoted home-position precipitation of acicular ferrite. Meanwhile,sympathetic acicular ferrite tended to nucleate at the primary acicular ferrite grain boundaries,where high dislocation density was located,and grew inside the neighboring carbon-depleted austenitic regions. The granular bainite nucleated in the austenitic zone with high carbon content close to acicular ferrite and sympathetic acicular ferrite.展开更多
The hot deformation behaviors of two medium carbon ultra-high strength steels with different niobium contents were investigated by using Zener-Hollmom parameter and processing map,and the effect of niobium addition on...The hot deformation behaviors of two medium carbon ultra-high strength steels with different niobium contents were investigated by using Zener-Hollmom parameter and processing map,and the effect of niobium addition on the hot deformation behavior of medium carbon steel was determined.The hot compression tests were conducted on a Gleeble-3500 thermo-mechanical simulator deformed at temperatures from 850 to 1 200 ℃ and strain rates from 0.001 to 1 s^-1.The processing maps of two test steels were built at a true strain of 0.7 based on dynamic materials model（DMM）.There are two peak efficiency domains and two flow instability regions in both test steels.However,the peak efficiency domains of Nb-bearing steel move to higher temperature due to the inhibition of dynamic recrystaUization（DRX）,and the instability domains of Nb-bearing steel are enlarged due to the precipitation of Nb-containing particles during hot deformation.The optimum process parameters of Nb-bearing and Nb-free steels for industrial production were determined according to the processing map and the microstructural observation.展开更多
The high strength bridge steel was processed with the simulated coarse grain heat affected zone（CGHAZ） thermal cycle with heat input varying from 30 to 60 kJ/cm, the microstructures were investigated by means of opt...The high strength bridge steel was processed with the simulated coarse grain heat affected zone（CGHAZ） thermal cycle with heat input varying from 30 to 60 kJ/cm, the microstructures were investigated by means of optical microscope（OM）, scanning electron microscope（SEM）, electron backscattering diffraction（EBSD） and transmission electron microscope（TEM）, and the impact properties were evaluated from the welding thermal cycle treated samples. The results indicate that the microstructure is primarily composed of lath bainite. With decreasing heat input, both bainite packet and block are significantly refined, and the toughness has an increasing tendency due to the grain refinement. The fracture surfaces all present cleavage or fracture for the samples with different heat inputs. Moreover, the average cleavage facet size for the CGHAZ is nearly equal to the average bainite packet size and the bainitic packet boundary can strongly impede the crack propagation, indicating that the bainitic packet is the most effective unit in control of impact toughness in the simulated CGHAZ of high strength bridge steel.展开更多
基金supported by the National Key R&D Program of China(No.2017YFB1103200).
文摘Under the working environment of high temperature and strong load impact,hot forging die is prone to failure which reduces the service life of die.Using arc additive manufacturing in the die cavity,a gradient material hot forging die with high precision,superior per-formance,and conformal cooling channels is developed.This improves the toughness of the die cavity and reduces the working temperature,thereby forming an isothermal field,which is an effective method to enhance the lifespan of the hot forging die.Three kinds of gradient flux-cored wires are designed for the surface of 5CrNiMo steel,and the microstructure and mechanical properties between gradient interfaces were studied.Based on the spatial curved structure of shaped waterways in the hot forging die cavity,a study was conducted on the strategy of partitioned forming for the manufacturing of the die with shaped waterways.In order to avoid interference with the arc gun,the hot for-ging die is divided into four regions,namely the transition region,upper,middle,and lower region,based on a combination of cavity depth and internal U-shaped and quadrilateral structures.The results show that the developed flux-cored wires have good moldability with straight sides of deposited metal under different process parameters and flat surface without cracks,pores and other defects.Under the same working conditions,the life of hot forging die formed by the gradient materials is more than multiple times that of the single material hot forging die,and the temperature gradient field of the shaped waterway die is 7℃/cm smaller than that of traditional straight waterway.
文摘通过研究不同工艺参数下激光调控电弧的行为,发现激光可以压缩电弧,使得电弧稳定,激光对电弧有调控作用;进而分析不同工艺参数下激光对堆积层稳定性的影响以及激光约束电弧熔丝增材制造构件的表面粗糙度。研究发现相较于熔化极活性气体保护电弧焊(Metal Active Gas Arc Welding,MAG)作用而言,激光作用后,堆积层稳定性得到提高,并且小规范参数下,构件表面粗糙度Ra值由150.178μm降低到53.521μm;中等规范参数下,构件表面粗糙度Ra值由71.328μm降低到41.498μm;大规范参数下,构件表面粗糙度Ra值由110.163μm降低到82.352μm。
基金supported by the National Natural Science Foundation of China,the Baoshan Iron&Steel Co.,Ltd(No.U1260103)
文摘In this study,the welding thermal cycle curve exhibited two temperature peaks in high heat-input twin-wire separate-pool submerged-arc welding and coarse-grained heat affected zone existed in the welded joint. The inclusions of primary weld metal and coarse-grained heat affected zone of Ce-added SAW should be Al_2O_3,MnO,SiO_2,TiO,Ce_2S_3,CeS,Ce_2O_2S and Ce_2O_3. Under the effect of welding thermal cycle,oxy-sulfides inclusions of Ce,the diameter of which was less than 2. 0 μm,slightly grew larger,but the composition and type of the inclusions didn't change. The microstructure of the large heat input weld metal had acicular ferrite that Ce oxide sulphide particles induced nucleation and proeutectoid ferrite. In the coarse-grained heat affected zone of weld metal,home-position precipitation of acicular ferrite and sympathetic acicular ferrite were both observed. It was supposed that previous crystal cells of acicular ferrite in austenite grain promoted home-position precipitation of acicular ferrite. Meanwhile,sympathetic acicular ferrite tended to nucleate at the primary acicular ferrite grain boundaries,where high dislocation density was located,and grew inside the neighboring carbon-depleted austenitic regions. The granular bainite nucleated in the austenitic zone with high carbon content close to acicular ferrite and sympathetic acicular ferrite.
基金Supported by the National 863 Program of China(No.2015AA042505)Hubei Department of Education Youth Program(No.Q20123001)+1 种基金Hubei Province Natural Science Foundation(No.2014 cfb177)Wuhan Huaxia Fine Blanking Technology Co.,LTD Program(No.YYYY2014-015)
文摘The hot deformation behaviors of two medium carbon ultra-high strength steels with different niobium contents were investigated by using Zener-Hollmom parameter and processing map,and the effect of niobium addition on the hot deformation behavior of medium carbon steel was determined.The hot compression tests were conducted on a Gleeble-3500 thermo-mechanical simulator deformed at temperatures from 850 to 1 200 ℃ and strain rates from 0.001 to 1 s^-1.The processing maps of two test steels were built at a true strain of 0.7 based on dynamic materials model（DMM）.There are two peak efficiency domains and two flow instability regions in both test steels.However,the peak efficiency domains of Nb-bearing steel move to higher temperature due to the inhibition of dynamic recrystaUization（DRX）,and the instability domains of Nb-bearing steel are enlarged due to the precipitation of Nb-containing particles during hot deformation.The optimum process parameters of Nb-bearing and Nb-free steels for industrial production were determined according to the processing map and the microstructural observation.
基金Supported by the National 863 Program of China(No.2015AA042505)State Key Laboratory of Materials Processing and Die&Mould Technology of Huazhong University of Science and Technology(No.P2018-014)Major Science and Technology Project in Guangdong Province(No.2014B010130001)
文摘The high strength bridge steel was processed with the simulated coarse grain heat affected zone（CGHAZ） thermal cycle with heat input varying from 30 to 60 kJ/cm, the microstructures were investigated by means of optical microscope（OM）, scanning electron microscope（SEM）, electron backscattering diffraction（EBSD） and transmission electron microscope（TEM）, and the impact properties were evaluated from the welding thermal cycle treated samples. The results indicate that the microstructure is primarily composed of lath bainite. With decreasing heat input, both bainite packet and block are significantly refined, and the toughness has an increasing tendency due to the grain refinement. The fracture surfaces all present cleavage or fracture for the samples with different heat inputs. Moreover, the average cleavage facet size for the CGHAZ is nearly equal to the average bainite packet size and the bainitic packet boundary can strongly impede the crack propagation, indicating that the bainitic packet is the most effective unit in control of impact toughness in the simulated CGHAZ of high strength bridge steel.
