Influence of Tempering Process on Mechanical Properties of 00Cr13Ni4Mo Supermartensitic Stainless Steel

To investigate the influence of tempering process on microstructural evolutions and mechanical properties of 00Cr13Ni4Mo supermartensitic stainless steel(SMSS),specimens were tempered in the temperature range of 520-720 ℃ for 3 h followed by air cooling and an optimized tempering temperature was chosen to prolong holding time from 3 to 12 h.After heat treatments,microstructure examination was conducted by scanning electron microscope,X-ray diffraction examinations,hardness measurements and tensile tests.The results revealed that the superior mechanical properties were achieved by quenching at 1040 ℃ for 1 h+water cooling and tempering at 600 ℃ for 3 h+air cooling.Increasing isothermal tempering time could improve the toughness notably.It was believed that the property was correlated with the microstructure of tempered lath martensite and retained austenite.More retained austenite content is beneficial to the higher toughness of the SMSS.     

Microstructure Characterization and Mechanical Properties of TRIP-aided Steel under Rapid Heating for Different Holding Time

In order to develop a comprehensive understanding about the effect of different holding time under rapid heating on the microstructural evolution and mechanical properties of transformation-induced plasticity (TRIP)steel, continuous annealing process simulations were performed using a thermal system with resistance heating method. The morphology and distribution of all phases present in the microstructure and the mechanical properties of TRIP steel were revealed.It appeared that the final tensile strength of the TRIP steel increased and retained austenite car-bon content decreased with increasing holding time.An overlap between ferrite recrystallization and austenitization was observed during intercritical holding.In addition,the work hardening of the samples was evaluated by calculat-ing the instantaneous n value as a function of the true strain.The difference in work hardening behavior corresponds to the rate of the retained austenite transformation during straining,which can be attributed to the carbon content and the morphology of the retained austenite.     

Comparison of Microstructure and Mechanical Properties of a High-Carbon Bainitic Steel Treated by Long-Time Bainitic Austempering and Short-Time Austempering Plus Tempering Processes

Herein, the microstructure and mechanical properties of a high-carbon bainitic steel treated by long-time bainitic austempering and short-time austempering plus tempering processes are compared. The multiphase microstructures are characterized by dilatometry, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy to correlate with mechanical properties. Results show that although long-time austempering treatment can reduce the volume fraction of brittle martensite, no significant improvement is observed in fracture damage resistance. Besides, the cementite is prone to precipitation from the austenite at the later period of the long-time austempering process. The cementite precipitation in austenite decreases the carbon content in retained austenite (RA) and consequently reduces the mechanical stability of RA. In contrast, the cementite has not been able to precipitate from austenite after short-time austempering treatment, whereas the martensite is softened and the stability of RA is improved during subsequent tempering. Therefore, excellent mechanical properties are obtained in the samples treated by short-time austempering plus tempering process: ultimate tensile strength, 1489 MPa, yield strength, 1014 MPa, total elongation, 33.2%, and the product of strength and elongation (PSE) of 48.4 GPa%, where PSE is increased by 27% compared with the sample after long-time bainitic austempering.     

Effect of BainiticTreatment on Microstructure and Mechanical Properties of TRIP Cold-Rolled Steel Sheets

The effects of bainitic treatment on microstructure and mechanical properties of 0.10C-1.5Mn-l.5Al TRIP-aided cold-rolled steels have been investigated.The samples were heated by intercritical annealing at 820℃for 2 min and quenched in banitic temperature with different hoding time for 5 to 300s,two salt bath were used for the heat treatment.Experimental results show that the yield strength and elongation increase with the increasing of bainitic holding time,while the tensile strength decrease.The volume fraction of retained austenite rise at the beginning of bainitic holding and then reduce,the carbon content of retained austenite increase during the bainitic holding.The tensile strengthen multiply elongation reaches the highest value at 120s.The mechanical stability of retained austenite fits well with strain hardening during deformation.     

Effect of Multi-Step Tempering on Retained Austenite and Mechanical Properties of Low Alloy Steel

 The effect of multi-step tempering on retained austenite content and mechanical properties of low alloy steel used in the forged cold back-up roll was investigated. Microstructural evolutions were characterized by optical microscope, X-ray diffraction, scanning electron microscope and Feritscope, while the mechanical properties were determined by hardness and tensile tests. The results revealed that the content of retained austenite decreased by about 2% after multi-step tempering. However, the content of retained austenite increased from 36% to 51% by increasing multi-step tempering temperature. The hardness and tensile strength increased as the austenitization temperature changed from 800 to 920 ℃, while above 920 ℃, hardness and tensile strength decreased. In addition, the maximum values of hardness, ultimate and yield strength were obtained via triple tempering at 520 ℃, while beyond 520 ℃, the hardness, ultimate and yield strength decreased sharply.     

Microstructure and Mechanical Properties of High Manganese TRIP Steel

 Abstract： Microstructure evolution and mechanical properties of newly designed 01C-6Mn-05Si-1Al TRIP-aided steels under different annealing conditions and the effects of matrix microstructure before intercritical annealing on the final microstructure were studied by means of X-ray diffraction (XRD), scanning electron microcopy (SEM), dilatometric simulation, optical microstructure (OM) and tensile testing in this work. The experimental results indicate that the TRIP steel with Mn of 6% could form a considerable amount of retained austenite with good TRIP effect after a simple intercritical annealing treatment, and the matrix microstructure before intercritical annealing treatment can greatly affect the final microstructure. The original microstructure of the ferritic matrix steel was eliminated, while annealed martensite was remained from the martensite matrix steel under the same intercritical annealing conditions.     

回火温度对Q960级高强结构钢组织及力学性能的影响

 以屈服强度960MPa级高强调质结构钢板开发为目标,研究了在相同轧制及淬火条件下,回火温度对试验钢显微结构及力学性能的影响。结果表明：随回火温度的升高,试验钢强度下降,韧塑性总体上呈现升高趋势,其中在300~450℃范围内出现一个韧塑性能的恶化区。当回火温度为600℃时,试验钢呈回火索氏体组织,屈服强度为1030MPa,抗拉强度为1080MPa,伸长率为15.9%,-40℃冲击功达144J,各项指标均满足国标GB/T 16270—2009要求。并对试验钢的拉伸力学性能进行了探讨。     

回火温度对热轧双相钢组织和力学性能影响研究

研究了100~300℃回火对0.054C-1.18Si-1.16Mn-0.49Cr成分热轧双相钢DP600的显微组织和力学性能的影响。结果表明:回火温度主要影响热轧双相钢中铁素体位错密度和马氏体微观结构;随着回火温度的增加,热轧双相钢中铁素体可动位错密度降低,马氏体部分发生分解,析出碳化物;回火温度对抗拉强度影响不大,对屈服强度和屈强比的影响显著,175℃以上回火,热轧双相钢屈服强度显著提高,并出现屈服平台,150℃以下回火热轧双相钢屈服强度增加不明显,不出现屈服现象。     

H13改进型热作模具钢的组织与性能

 研究了高锰型马氏体热作模具钢SDH3-Mod的室温冲击韧性、回火稳定性和热疲劳性能,并结合透射电镜(TEM)分析了锰对其微观组织的影响。结果表明：SDH3-Mod钢回火组织中残余奥氏体以薄膜状存在于马氏体板条间,提高冲击韧性,延缓裂纹扩展;同时,锰在高温时阻碍碳化物粗化长大和延迟基体的回复再结晶,提高抗回火软化能力和热疲劳性能,使SDH3-Mod性能优于H13。     

Effect of Intercritical Annealing Time on the Microstructure and Mechanical Properties of Dual-Phase Steel Processed by Large-Strain Asymmetric Cold-Rolling

Herein, the effect of intercritical annealing time on the microstructure and mechanical properties of dual-phase steel processed by large-strain asymmetric cold-rolling is studied. It is observed that the martensite islands are uniformly distributed in the ferrite phase in the microstructures of dual-phase steels due to performing the asymmetric cold-rolling before intercritical annealing treatment. As the intercritical annealing time increases up to 10 min, the fraction of martensite increases. By increasing the holding time and fraction of martensite, the carbon content of the martensite phase is decreased. The short-term intercritical annealing eliminates the yield point phenomenon. However, intercritical annealing at 860 °C for 20 min leads to the reoccurrence of a yield point phenomenon. Increasing the intercritical annealing time to 10 min improves the yield strength to 505 MPa and ultimate tensile strength to 834 MPa. However, the strength decreases sharply after the holding time of 20 min. There is a perfect linear relationship between the mechanical properties and the fraction of martensite. Ductile failure is observed at the center of the fracture surfaces of dual-phase steels while shear failure occurs at the edges of the fracture surfaces.     

Effect of Tempering Temperature on Microstructure and Mechanical Properties of Steel Containing Ni of 9 %

  Mechanical properties of quenching, intercritical quenching and tempering (QLT) treated steel containing Ni of 9% were evaluated from specimens subject to various tempering temperatures. The detailed microstructures of steel containing Ni of 9% at different tempering temperatures were observed by optical microscope (OM) and transmission electron microscope (TEM). The volume fraction of austenite was estimated by XRD. The results show that high strength and cryogenic toughness of steel containing Ni of 9% are obtained when the tempering temperature are between 540 and 580 ℃. The microstructure keeps the dual phase lamellar structure after the intercritical quenching and there is cementite created in the Ni rich constituents when tempering temperature is 540 ℃. When tempering temperatures are between 560 and 580 ℃, the reversed austenites (γ′) grow up and the dual phase lamellar structure is not clear. The γ′ becomes instable at 600 ℃. When tempered at temperature ranging from 500 to 520 ℃, the increase of dislocation density in the lamellar matrix makes both tensile strength and yield strength decrease. When tempered at 540 ℃ and higher temperature, the yield strength decreases continuously because the C and alloying elements in the matrix are absorbed by the cementite and the γ′, so the yield ratio is decreased by the γ′. There are two toughness mechanisms at different tempering temperatures. One is that the precipitation of cementite absorbs the carbon in the steel which plays a major role in improving cryogenic toughness at lower temperature. Another is that the γ′ and the purified matrix become major role at higher tempering temperature. When the tempering temperature is 600 ℃, the stability of γ′ is decreased quickly, even the transformation takes place at room temperature, which results in a sharp decrease of Charpy V impact energy at 77 K. The tempering temperature range is enlarged by the special distribution of cementite and the lamellar structure.     

两相区保温时间对冷轧双相钢组织性能的影响

对Q345冷轧钢板两相区退火进行了研究,通过对不同保温时间试验钢板的金相组织以及拉伸试验结果对比,得出如下结论：保温时间对试验钢微观组织和力学性能有影响,790℃下60～120 s退火,可以有效消除冷轧过程中产生的带状组织,并能避免因过长保温造成的组织粗化。