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Effect of Zr on undissolved phases and carbide precipitation in Ti microalloyed low-carbon steel

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Journal of Iron and Steel Research International 2019年第7期26卷 720-732页

作者： Peng-cheng Liu Jian-chun Cao Shu-biao Yin Yin-hui Yang Peng Gao Faculty of Materials Science and Engineering Kunming University of Science and Technology Kunming 650093 Yunnan China Faculty of Metallurgical and Energy Engineering Kunming University of Science and Technology Kunming 650093 Yunnan China

The undissolved phases and carbide precipitation in Ti and Ti-Zr microalloyed low-carbon steels were investigated by scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectrometry. At 1225℃, the replacement of Ti by Zr formed Zr2CS and (Zr, Ti)N (the Ti/Zr atomic ratio is 0.11) and reduced the consumption of Ti. At 925℃, it was identified that TiC phases were precipitated at first and Zr was incorporated into the TiC lattice in the subsequent precipitation process, which promoted the precipitation of titanium carbide. The calculation of the interaction coefficient between Ti, C, N and Zr showed that Zr reduced the activity of Ti and C and increased the activity of N in the iron matrix. Therefore, with the addition of Zr, the solubility of Ti was increased, and the consumption of Ti was reduced at high temperature in Ti microalloyed low-carbon steel. The thermodynamic calculation of carbide precipitation transformation showed that the replacement of Ti by Zr increased the nucleation driving force and the nucleation rate of titanium carbide, while the critical core size and the critical nuclear energy were reduced. As the holding time was extended, the Zr/ Ti atomic ratio increased and the size of the precipitates also increased. When the Zr/Ti atomic ratio reached a certain level, the size of the precipitates did not increase with further increase in atomic ratio. When the Zr/Ti atomic ratio in (Ti, Zr)C was 0.05-0.17,(Ti, Zr)C was the most stable carbide and the easiest to nucleate at 925℃. There was more of the (Ti, Zr)C phase than TiC at 925 ℃ after 50 and 100 s, and the time to complete the coarsening behavior of (Ti, Zr)C was shorter than that of TiC.

关键词： Ti-Zr microalloyed steel Undissolved phase Carbide precipitation Zirconium Thermodynamics

Thermodynamic model for precipitation of carbonitrides in microalloyed steels and its application in Ti-V-C-N system

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Rare Metals 2016年第10期35卷 735-741页

作者： Yan-Lin Wang Long-Chao Zhuo Ming-Wen Chen Zi-Dong Wang School of Materials Science and Engineering Tsinghua University School of Materials Science and Engineering University of Science and Technology Beijing School of Materials Science and Engineering Xi'an University of Technology School of Mathematical and Physical Sciences University of Science and Technology Beijing

Based on mass balance and solubility product equations, a thermodynamic model enabling the calcula- tion of equilibrium carbonitride composition and relative amounts as a function of steel composition and tem- perature was developed, which provides a method to es- timate the carbonitride complete dissolution temperature for different steel compositions. Actual carbonitride pre- cipitation behavior was further verified in Ti-V-C-N microalloyed steel system. The model suggests that for higher IV] and [Ti] dissolved in steels, it is available to decrease the addition of C and N during alloy composi- tion design. The resultant longer fatigue life of the modified steel could be attributed to the more [V] and [Ti] dissolved in the matrix, inducing finer dispersion of carbonitrides. Therefore, this model is proved to be effective in determining better chemical composition for high-performance steels, leading to possible reductions in the cost of production and improvements in the combined mechanical properties of the steels.

关键词： microalloyed Carbonitrides Thermodynamic model Dissolution

Microstructure-mechanical property relationship in Ti-Mo microalloyed steel with random and interphase precipitates

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Journal of Iron and Steel Research International 2019年第8期26卷 838-845页

作者： Hai-long Yi Lu-ran Zhang Rui-hai Duan Xin-zeng Liang State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110819 Liaoning China

The relationship between microstructure and mechanical properties of Ti-Mo microalloyed steels composed of ferrite and bainite with nanometer-sized carbides and isothermally transformed at different temperatures and time was systematically investigated by tensile test, hardness test, and transmission electron microscopy. Ferrite formed at high temperatures exhibited both planar/curved sheet-like dispersions of interphase precipitates and random dispersion precipitates, with the interphase precipitates being the dominant morphology. In contrast, bainite formed at low temperatures exhibited only random dispersion precipitates. Furthermore, random dispersion precipitates and interphase precipitates were observed within the same ferrite grains. The mechanical properties of the ferrite specimen were superior to those of the bainite specimen. The stress-strain curves of both specimens indicated continuous yielding, high strength, and sufficient tensile elongation. The strengthening of the ferrite specimen was attributed to grain size strengthening, dislocation strengthening, and precipitation hardening, and the degree of precipitation strengthening was approximately 300 MPa.

关键词： Mechanical property Interphase precipitate Dispersion precipitate Precipitation strengthening Ti-Mo microalloyed stee

Microstructural features and precipitation behavior of Ti,Nb and V microalloyed steel during isothermal processing

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Journal of Iron and Steel Research International 2019年第1期26卷 102-111页

作者： Qi Zhou Zhuang Li Zhan-shan Wei Di Wu Jin-yu Li Zhen-yao Shao School of Environment and Chenlical Engineering Shenyang Ligong UniversityShenyang 110159LiaoningChina College of Materials Science and Engineering Shenyang Aerospace UniversityShenyang 110136LiaoningChina State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110004LiaoningChina

Thermal simulations of Ti,Nb and V microalloyed steel were conducled using a thermomechanical simulator,and the microstructural evolution and the precipitation behavior during isothermal processing were *** results show that with increasing holding time,the microstructural constituents change from the martensite and bainitic ferrites to granular bainite and polygonal *** maximum hardness is obtained for the specimen after isothermal holding for 5s due to the martensite strengthening *** hardness of the specimen decreases after isothermal holding for 10s,because the strengthening contribution of fine dispersed precipitates becomes *** hardness values of the specimens increase and then remain high after isothermal holding for 60 and *** is attributed to the contribution of the interphase precipitation hardening to the hardness of the studied *** precipitates in the specimen are coarsened after isothermal holding for 3600s,even though the coarsening is not *** precipitates are fee(***)(N.C)particles and belong to the MX-type *** beneficial effects of precipitation strengthening are *** hardness decreases to a minimum hardness value due to the presence of large amounts of polygonal ferrite after isothermal holding for *** coarse precipitates are the primary origin of the hardness decrease.

关键词： microalloyed steel Isothermal holding time Microstructural constituent Precipitation Hardness

The Effects of Cooling Mode on the Properties of Ti–Nb microalloyed High-strength Hot-rolled Steels

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Journal of Wuhan University of Technology(Materials Science) 2019年第3期34卷 692-697页

作者： ZHU Min XU Guang The State Key Laboratory of Refractories and Metallurgy Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of EducationWuhan University of Science and TechnologyWuhan430081China Research and Development Center of Wuhan Iron and Steel(Group)Corp Wuhan430080China

The industrial trials of two cooling modes, i e, water cooling in forepart + air cooling in later part (WAC) and air cooling in forepart + water cooling in later part (AWC), were carried out for a Ti- Nb microalloyed steel. The average cooling rates and coiling temperature were the same for two modes. The continuous cooling transformation (CCT) curve of the tested steel was drawn. The effects of the cooling mode on the microstructure, precipitates, and properties of the steels were investigated. Results show that the strength of the steel in the WAC mode is significantly larger than that in the AWC mode, mainly because the smaller the grain size, the more and finer the grain precipitates. Therefore, when the average cooling rate is constant, the fast cooling in the forepart is an effective method to increase the strength of steels. However, the increase in the strength is accompanied by the decrease in toughness, so that the toughness of the steel should be considered when changing the cooling mode.

关键词： cooling mode strength toughness microalloyed steel fracture

Study on a new type nitriding steel microalloyed with niobium

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Baosteel Technical Research 2010年第S1期4卷 60-页

作者： MIN Yongan~(1)),LIAO Jianxiong~(1)),HUANG Zemin~(2)),HUA Wenjie~(2)) and LI Yang~(2)) 1) School of Materials Science and Engineering,Shanghai University,Shanghai 200072,China 2) Special Steel Division,Baoshan Iron & Steel Co.,Ltd.,Shanghai 200941,China

A niobium microalloyed nitriding steel has been introduced to meet the high demand in modern engine applications,based on compositions of traditional nitriding steels,and on phase calculation and prediction with JmatPro *** new nitriding steel BTHJ-1 shows a better nitriding tendency,as well as a good combination of strength and toughness,while compared with 38CrMoAl and H13 ***-1 steel also shows a better thermal stability when being held at 620℃.Investigations with OM,TEM,XRD have been made so as to get a better understand on the characteristics of BTHJ-1 *** quantities optimization of alloy elements and the grain refinement of niobium seem to be reasons for the improved properties of the nitriding steel.

关键词： nitriding steel microalloyed thermal stability phase calculation

Effect of increased nitrogen content on continuous cooling transition of γ→α in hot-deformed low-C Mo-V-Ti steels

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Journal of Iron and Steel Research International 2019年第7期26卷 733-742页

作者： Xin-ping Xiao Gen-hao Shi Shu-ming Zhang Yu-wei Gao Qing-feng Wang Fu-cheng Zhang State Key Laboratory of Metastable Materials Science and Technology Yanshan University Qinhuangdao 066004 Hebei China Qinhuangdao Vocational and Technical College Qinhuangdao 066100 Hebei China National Engineering Research Center for Equipment and Technology of Cold Strip Rolling Yanshan University Qinhuangdao 066004 Hebei China

The two-stage controlled rolling and cooling at 0.5-50℃/s of low-carbon Mo-V-Ti steels with the increasing nitrogen content from 0.0032 to 0.0081 and 0.0123 wt.% were simulated through a Gleeble 3500 system. The continuous cooling transition (CCT) of γ→α in each steel was estimated via microstructure characterization and CCT diagram. The results indicated that CCT diagram for each steel was divided into three regions of γ→ferrite,γ→pearlite and γ→ bainite, and the increasing N content elevated all the starting temperatures for γ→α. Consequently, the polygonal ferrite (PF) and pearlite formed in each steel cooled at 1℃/s and, however, the increasing N content led to slightly coarser ferrite grain and pearlite colony. With the increased cooling rate to 10 and 30℃/s, a mixed microstructure of acicular ferrite (AF), granular bainite (GB) and lath bainite (LB) formed in 32N steel and in contrast, the mixture of PF+AF+GB in 8IN and 123N steels. The increasing N content promoted (Ti,V)(C,N) precipitation, enhanced the intragranular PF/AF nucleation, increased martensite/austenite constituent and depressed LB. In addition, the mechanisms dominating the effect of increasing N on this CCT of γ→α were discussed.

关键词： V-N microalloyed steel Continuous cooling transition Microstructure Precipitation Intragranular ferrite

Effects of Austenitising Conditions on the Microstructures and Mechanical Properties of Martensitic Steel with Dual Matrix Structure

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Journal of Minerals and Materials Characterization and Engineering 2012年第1期11卷 69-83页

作者： K.A. Bello S.B. Hassan O. Aponbiede Department of Metallurgical and Materials Engineering Ahmadu Bello University Zaria Nigeria

A new high strength steel with dual matrix structure and exceptionally high toughness plus ductility have been produced by intermediate quenching of 0.22_wt% C microalloyed steel. The treatment consisted of initial austenitization and rapid quenching of the steel samples to achieve a fully martensitic state followed by annealing in the intercritical (α+γ) region of 730℃-810℃ for the period of 30, 60 and 90_minutes. These samples were subsequently quenched to obtain dual phase microstructure containing varying proportions of ferrite and martensite constituents. The mechanical properties of the samples were measured according to ASTM standard and their microstructures were analyzed by optical microscopy. The experimental results show that martensitic dual phase (MDP) steel samples developed within the intercritical temperature range of 770–790℃ revealed finer martensite and precipitate-free ferrite microstructure. The tensile and impact properties of the developed HMDP steels increased with intercritical annealing (ICA) temperatures, with an optimum properties obtained at 790℃ mainly due to finer microstructure of the constituent phases and absence of carbide precipitate that permit ease of dislocation flow. A further increase in the intercritical annealing temperature beyond 790℃ led to general decrease in the mechanical properties. This is attributed to the formation of coarse structure in this region. The results further show that with increasing intercritical treatment time from 30 to 90 minutes, the general mechanical properties of the MDP steels were found to increase except at the higher temperature of 810℃ which showed decreasing values. In general, the tensile strengths and ductility as well as the impact properties of the developed dual phase steel samples are greatly improved with the intercritical heat treatment investigated.

关键词： Intercritical temperature dual phase steels microstructure microalloyed steel dual matrix