Instrumented oscillographic study on impact toughness of an axle steel DZ2 with different tempering temperatures

Compared with the conventional Charpy impact test method,the oscillographic impact test can help in the behavioral analysis of materials during the fracture process.In this study,the trade-off relationship between the strength and toughness of a DZ2 axle steel at various tempering temperatures and the cause of the improvement in impact toughness was evaluated.The tempering process dramatically influenced carbide precipitation behavior,which resulted in different aspect ratios of carbides.Impact toughness improved along with the rise in tempering temperature mainly due to the increase in energy required in impact crack propagation.The characteristics of the impact crack propagation process were studied through a comprehensive analysis of stress distribution,oscilloscopic impact statistics,fracture morphology,and carbide morphology.The poor impact toughness of low-tempering-temperature specimens was attributed to the increased number of stress concentration points caused by carbide morphology in the small plastic zone during the propagation process,which resulted in a mixed distribution of brittle and ductile fractures on the fracture surface.

Effect of nitrogen content on the microstructure and mechanical properties of titanium-bearing nonquenched and tempered steel after hot forging

The microstructure and mechanical properties of titanium(Ti)-bearing medium-carbon nonquenched and tempered steel with different nitrogen content before and after hot forging were investigated through smelting,forging,and laboratory tests.The results show that the grain size of nonquenched and tempered steel was gradually refined,and the ferrite content gradually increased with an increase in nitrogen content.The grain size of the material with low nitrogen content increased abnormally,and its impact properties significantly decreased after hot forging.The grain size of nonquenched and tempered steel with higher nitrogen content was slightly larger than that before forging,and the tensile and yield strength increased,but the impact toughness was not significantly reduced.The Ti-bearing nonquenched and tempered steel showed better strength and toughness after hot forging with the addition of 0.010%0.015%nitrogen.

Corrosion behavior of tempered dual-phase steel embedded in concrete

Dual-phase （DP） steels with different martensite contents were obtained by appropriate heat treatment of an SAE1010 structural carbon steel, which was cheap and widely used in the construction industry. The corrosion behavior of DP steels in concrete was investigated under various tempering conditions. Intercritical annealing heat treatment was applied to the reinforcing steel to obtain DP steels with different contents of martensite. These DP steels were tempered at 200, 300, and 400℃ for 45 min and then cooled to room temperature. Corrosion experiments were conducted in two stages. In the first stage, the corrosion potential of DP steels embedded in concrete was measured every day for a period of 30 d based on the ASTM C 876 standard. In the second stage, the anodic and cathodic polarization values of these steels were obtained and subsequently the corrosion currents were determined with the aid of cathodic polarization curves. It was observed that the amount of second phase had a definite effect on the corrosion behavior of the DP steel embedded in concrete. As a result of this study, it is found that the corrosion rate of the DP steel increases with an increase in the amount of martensite.

Effect of low-temperature tempering on the mechanical properties of cold-rolled martensitic steel

Cold-rolled martensitic steel is an important type of advanced high-strength steel for automobile production.With martensite as its primary microstructure constituent, martensitic steel possesses exceptional high strength despite its low alloy content.As the strength of cold-rolled martensitic steel increases, the martensite and carbon content also increases, leading to a decrease in bending properties and toughness.In this paper, the effect of various tempering parameters on the bending property and impact toughness of a quenched cold-rolled martensitic steel sheet was studied.It is found that after quenching, the ductility and impact toughness of the experimental steel are improved using low-temperature heat treatment.The optimal tempering conditions for ductility and toughness are analyzed.

Research into Grinding Hardening of Microalloyed Non-quenched and Tempered Steel

Grinding hardening is a new technology of hardening steel piece surfaces with grinding heat generated in the grinding process instead of with a high or medium frequency induction heating method,which can effectively integrate grinding and surface hardening. Experimental studies were carried out on grinding hardening of non-quenched and tempered steel. Through grinding experiments with variable depths of cut and feeding rate,the variation in the depth of the hardening layer was studied and the microstructure of the hardening zone of the test pieces was subsequently ana-lyzed. In the end,the hardening effect of non-quenched and tempered steel was compared with that of 40Cr steel,which revealed the superiority of non-quenched and tempered steel in grinding hardening technology.

Effect of inclusions on the formation of acicular ferrite in Ti-bearing non quenched-and-tempered steel

Nucleation of acicular ferrite and its influence factors in non quenched-and-tempered steel was studied by using TEM and thermodynamic calculation. The results show that the complex particles with a center made of Ti oxide, Al2O3, and silicate and an outside made of a small quantity of mixture of TiN and MnS are able to act as ferrite nucleation nuclei. The acicular ferrite percentage changes little with Ti. When the oxygen content was 80 ppm, the volume percentage of acicular ferrite decreased due to an increase in allotriomorphic ferrite. The larger the cooling rate and the shorter the incubation time, the finer the titanium oxide and the higher the nucleation ratio of acicular ferrite.

The Research and Application of Non-quenched and Tempered Steel 12Mn2VBS

In this paper, the study group has researched the comprehensive performance and application of the content of sulfur properly.Based on the research such a conclusion can be d non-quenched and tempered steel 12Mn2VBS made of 12Mn2VB by increasing the rawn: 12Mn2VBS the non-quenched and tempered steel has superior comprehensive performance to traditional quenched and tempered steel such as 45 and 40Cr,and it is the best material to manufacture automobile parts.

Effect of Rare Earths on Tempered Martensite Embrittlement of Steel

The mechanical properties of SiMnCr and SiMnMo steels tempered in lowtemperature range were studied. The results show that there is no notable effect of RE on material strength during lowtemperature tempering. There are toughness troughs of tempered martensite embrittlement(TME) at 350 ℃ and 400 ℃ for steel SiMnCr and SiMnMo respectively. RE raises the toughness of TME troughs to some extent by refining grains and restraining embrittlment of austenite grain boundary, although it does not change TME temperature.

Rotating arc horizontal narrow gap welding of high strength quenched and tempered steel

Rotating arc borizontal narrow gap welding of quenched ＆ tempered （Q＆T） steel was innovatively performed for solving the bottleneck that the molten pool sagged due to the gravity. The shapely multilayer single pass horizontal joint could be obtairzed by using the rotating are welding process. The cold crack was not observed in the joint without controlling the heat input and selecting the consumables intentionally. Microstructure of the joint could be divided into three zones： base metal zone （BMZ） , heat-affected zone （ HAZ） and weld zone （WZ）. Because of the characteristic of the rotating arc horizontal welding process, the defects in the joints were slag inclztsion formed at the interlayer of lower side wall. Tbe tensile strength and hardness of HAZ and WZ were larger than those of BMZ. The impact toughness in WZ, HAZ and BM at 0 % is equal to 11.5, 212 and 236 J, respectively.

Development of non-quenched and tempered bolt steel

The 8.8 grade non-quenched and tempered bolt steel was studied according to the process conditions of wire rod plant and customer requirments.Three types of experimental steel grades were selected.10MnSiTi Nb and 20Mn2VTi(N) were chosen as the formal steel after several experimemts.

Effect of cooling rate on microstructure and mechanical properties of CB2 tempered martensitic steel

The cooling rate of casting has a significant effect on microstructure and mechanical properties of castings.The 9Cr-1.5Mo-1Co cast steel,referred to as CB2,is one of the most promising alloys for various cast components to be used under ultrasupercritical conditions.In this study,HRTEM,SEM,and XRD methods were used for qualitative and quantitative analyses of contents,phases,and sizes of the inclusions and precipitates,as well as microstructure observation of the tempered martensitic steel at different cooling rates.Traditional tensile tests were conducted to characterize the material mechanical properties.Results show that the size of the boron nitride and precipitate,the width of the martensite lath and the content of theδ-ferrite are reduced as the cooling rate increases from 5-8℃·min^-1(CB2-S steel)to 50-60℃·min^-1(CB2-F steel).The precipitates are mainly composed of M23C6 and a small amount of M3C.The average diameters of the M23C6 precipitates in CB2-F and CB2-S are 202 nm and 209 nm,respectively.The inclusions are mainly composed of BN,Al2O3 and MnO2,and the inclusion ratios are 0.1969%for the CB2-F and 0.06556%for CB2-S steel.The average martensite lath widths of CB2-F and CB2-S steels are 289 nm and 301 nm,respectively.Furthermore,the M3C having a diameter of about 150 nm and a thickness of 20 nm is observed in theδ-ferrite of the tempered CB2-S steel.The presence of theδ-ferrite reduces the precipitation strengthening and dislocation density in CB2-S steel.In addition,the lower cooling rate stabilizes theδ-ferrite structure at room temperature.

On microstructure and performance of tempered high-boron high-speed steel roll

Influences of the tempering temperature on the microstructure, mechanical property and wear resistance of High-Boron High Speed Steel （HBHSS） roll materials were investigated by means of optical microscopy, scanning electron microscopy （SEM）, X-ray diffraction, hardness measurement, impact tester, tensile tester and pin abrasion tester. The results show that the as-cast structure of HBHSS consists of a great amount of martensite and M2（B,C） and a few retained austenites and M23（B,C）6. After solution treated at 1,050℃ and followed by oil cooling, the amount of M23（B,C）6 carbo-borides in quenched HBHSS increases obviously and the macrohardness of the quenched HBHSS is 66 HRC, which is very close to the 65.8 HRC of as-cast HBHSS. On the whole, the hardness of HBHSS alloy shows a trend of slight decrease with increasing tempering temperature when tempered below 500 ℃. While when above 500 ℃, the hardness increases slightly as the tempering temperature increases and reaches a peak at 525 ℃ and then decreases obviously. The impact toughness of HBHSS has a tendency to increase as the tempering temperature increases. Tempering can improve the tensile strength and elongation of HBHSS, but a higher tempering temperature causes a slight decrease in both tensile strength and elongation. Excellent wear resistance can be obtained by tempering at 500 to 550 ℃.

Laser Beam Welding of 600 MPa Quenched and Tempered High-Strength Steel

Conventional fusion arc welding of high-strength quenched and tempered steel can be improved through the use of non-conventional laser beam welding. This article presents the investigations of autogenous bead on plate and butt CO2 Laser Welding (LW) of 7 mm thick high-strength quenched and tempered low alloy SM570 (JIS) steel plates. The influence of laser welding parameters, mainly welding speed, defocusing distance and shielding gas flow rate on the weld profile, i.e., weld zone penetration depth and width, microstructure and mechanical properties of welded joints was determined. All welded joints showed smooth and uniform weld beads free from superficial porosity and undercuts. The selected best welding conditions were a laser power of 5.0 kW, welding speed of 500 mm/min, argon gas shielding flow rate of 30 L/min and a defocusing distance of -0.5 mm. It was observed that these conditions gave complete penetration and minimized the width of the weld bead. The microstructure of the welded joints was evaluated by light optical microscopy. The weld metal (WM) and heat-affected zone (HAZ) near weld metal achieved maximum hardness (355 HV). The tensile fractured samples showed the ductile mode of failure and ultimate tensile strength of 580 MPa.

Plastic Deformation in Quench-and 650℃ Tempered Steel

The variations of the dislocation structures in the quench and 650℃ tempered steel with increase of elongations have been investigated by using transmission electron microscopy. In the small elongation stage, the boundaries between ferrite and carbide in this steel can release dislocations. As the elongations increase, the moving dislocations in the ferrite slip onto the carbides. Then, the interaction between moving dislocations and dislocations released from this boundaries, and the interaction between the dislocations moving to the carbides in every slip plane occurs. Thereby, the dislocation tangles around the carbides can be formed. In the large elongation stage, the dislocation tangles with high dislocation density and the developed dislocation cells are formed.

Review on regulation of MnS in non-qquenched and tempered steel

An overview of the current research status and control methods of MnS in non-quenched and tempered steel was provided.As a low-melting plastic inclusion,the morphology and distribution of MnS were influenced by various production processes.Therefore,control of MnS is a systematic problem that must be integrated into the entire production process.Based on the production process,the factors affecting the morphology and distribution of MnS in steel were introduced.The effects of oxygen activity,manganese,sulfur,and some alloys on MnS inclusion precipitation were summarized,mainly including MnS modification treatment and oxygen-sulfide composite precipitation control.It is believed that MnS precipitates during the solidification process of steel,and controlling the solidification cooling rate could effectively regulate the size and morphology of MnS,avoiding the precipitation of II-MnS.Additionally,by changing the deformation rate,deformation amount,deformation temperature during the hot deformation process,and heating time and temperature during heat treatment,the distribution and morphology of MnS could be improved.Through the fine control of the above process parameters,the number of II-MnS in steel could be effectively reduced,and their morphology could be improved,thereby enhancing the performance of non-quenched and tempered steel and promoting its wider application.Furthermore,applying laboratory research results to industrial production is an important direction for future research efforts in this field.

Precipitation behavior and martensite lath coarsening during tempering of T/P92 ferritic heat-resistant steel

Tempering is an important process for T/P92 ferritic heat-resistant steel from the viewpoint of microstructure control, as it facili- tates the formation of final tempered martensite under serving conditions. In this study, we have gained deeper insights on the mechanism underlying the microstructural evolution during tempering treatment, including the precipitation of carbides and the coarsening of martensite laths, as systematically analyzed by optical microscopy, transmission electron microscopy, and high-resolution transmission electron mi- croscopy. The chemical composition of the precipitates was analyzed using energy dispersive X-ray spectroscopy. Results indicate the for- mation of M3C （cementite） precipitates under normalized conditions. However, they tend to dissolve within a short time of tempering, owing to their low thermal stability. This phenomenon was substantiated by X-ray diffraction analysis. Besides, we could observe the precipitation of fine carbonitrides （MX） along the dislocations. The mechanism of carbon diffusion controlled growth of M23C6 can be expressed by the Zener＇s equation. The movement of Y-junctions was determined to be the fundamental mechanism underlying the martensite lath coarsening process. Vickers hardness was estimated to determine their mechanical properties. Based on the comprehensive analysis of both the micro- structural evolution and hardness variation, the process of tempering can be separated into three steps.

Effects of Si on the stability of retained austenite and temper embrittlement of ultrahigh strength steels

Effects of silicon （Si） content on the stability of retained austenite and temper embrittlement of ultrahigh strength steels were investigated using X-ray diffraction （XRD）,transmission electron microscopy （TEM）,and other experimental methods.The results show that Si can suppress temper embrittlement,improve temper resistance,and hinder the decomposition of retained austenite.Reversed austenite appears gradually with the increase of Si content during tempering.Si has a significant effect on enhancing carbon （C） partitioning and improving the stability of retained austenite.Si and C atoms are mutually exclusive in lath bainite,while they attract each other in austenite.ε-carbides are found in 1.8wt% Si steel tempered at 250℃,and they get coarsened obviously when tempered at 400℃,leading to temper embrittlement.Not ε-carbides but acicular or lath carbides lead to temper embrittlement in 0.4wt% Si steel,which can be inferred as cementites and composite compounds.Temper embrittlement is closely related to the decomposition of retained austenite and the formation of reversed austenite.

Tempering microstructure and mechanical properties of pipeline steel X80

The tempering microstructure and mechanical properties of X80 steel used for heating-bent pipe were analyzed. The results show that the microstructure of X80 steel tempered at 550 ℃ and 600 ℃ is bainitic ferrite (BF)+granular bainite (GB), and partial ferrite laths in BF merge and broaden. The interior sub-lath boundary of some GB begins to disappear due to merging, the M/A constituent (a mixture of martensite plus retained austenite) in GB is orbicular. At the two tempering temperatures the tested X80 steel shows a certain degree of tempering stability. After being tempered at 650 ℃, the microstructure of X80 steel is GB+quasi-polygonal ferrite(QF), and the original BF laths have merged to form smaller GB crystal grains. The reason is that the steel shows better match of strength and toughness. After being tempered at 700 ℃ , the microstructure of X80 steel is composed mainly of QF, which can improve the plasticity but decline severely the yield strength of X80, and the M/A constituent assembles and grows up at the grain boundary of QF, resulting in excellent lower low-temperature toughness of X80.

TEM observation of precipitation phase produced during tempering of steel AerMet100 and first principles calculations of phase evolution

The microstructure evolution law and the structure of precipitates produced during the tempering of steel AerMet100 based on TEM observation and the calibration of diffraction spot were revealed.The electronic structure and the stability of the MoxCr2-xC phase were calculated using the plane-wave pseudo-potential method on basis of density functional theory.TEM observations show that the precipitation phases Fe3C and Fe2-xCx(x=0.05～0.14) between martensite lath are produced at 425 and 480 ℃,respectively.The increase of tempering temperature or time can lead to the redissolution of both phases Fe3C and Fe2-xCx,and also lead to the precipitation of the phase Cr2C in martensite lath.The calculation results of formation energies and the density of state(DOS) demonstrate that in point of MoxCr2-xC structures formed during tempering,the early precipitation phase is Cr2C and finally later evolves into Mo2C phase with diffusing of incorporation of Mo atom into the Cr2C crystal cell,lattice,which can results in a energy decreases of the structure MoxCr2-xC phase with the increase of x.

Tempering stability of Fe–Cr–Mo–W–V hot forging die steels

The tempering stability of three Fe–Cr–Mo–W–V hot forging die steels(DM, H21, and H13) was investigated through hardness measurements and transmission electron microscopy(TEM) observations. Both dilatometer tests and TEM observations revealed that DM steel has a higher tempering stability than H21 and H13 steels because of its substantial amount of M_2C(M represents metallic element) carbide precipitations. The activation energies of the M_2C carbide precipitation processes in DM, H21, and H13 steels are 236.4, 212.0, and 228.9 kJ/mol, respectively. Furthermore, the results indicated that vanadium atoms both increase the activation energy and affect the evolution of M_2C carbides, resulting in gradual dissolution rather than over-aging during tempering.