Increasing Tempering Temperature Research Articles

Characterization of Carbide Precipitation during Tempering for Quenched Dievar Steel

Carbide precipitation and coarsening are investigated for quenched Dievar steel during tempering. Lath/lenticular martensite, retained austenite, lower bainite, auto-tempered, and larger spherical carbides are all observed in the as-quenched condition. The carbide precipitation sequence on tempering is ascertained to be: M8C7 + cementite → M8C7 + M2C + M7C3 → M8C7 + M7C3 + M23C6 → M8C7 + M7C3 + M23C6 + M6C; carbides become coarser on tempering, and the sizes for inter-lath carbides increase noticeably with increasing tempering temperatures due to the faster grain boundary diffusion, whereas the sizes for intra-lath carbides remain nearly constant. The rate of coarsening for carbides by tempering at 650 °C is much higher than those by tempering at 550 °C and 600 °C, due to the faster diffusion of alloying elements at higher temperatures.

Effect of tempering on stability of retained austenite and tensile properties of nanostructured bainitic steel

In this investigation, the evolution of the mechanical stability of retained austenite (RA) and the strength-plasticity of nanostructured bainitic steel tempered at a temperature ranged from 250 °C to 510 °C were studied. Results show that the mechanical stability of RA decreased after tempering mainly due to the weakened shielding effect of the bainite ferrite (BF) on RA. The RA with high mechanical stability generated a little mechanically induced martensite when the tempering temperature was below 380 °C, leading to less contribution to elongation. In addition, the poor deformation ability of the bainitic matrix resulted in nanostructured bainitic steel with low elongation. With increasing tempering temperature to 380 °C and higher, the mechanical stability of RA decreased significantly and mechanically induced martensite transformation occurred easily. However, the contribution of RA to the elongation remained low due to the formation of a substantial quantity of mechanically induced martensite after 380 °C specimen yield. The elongation was improved remarkably with increasing tempering temperature to 450 °C and above. The main reason was the improvement of the coordinated deformation ability of bainite matrix with a large number of carbide particles precipitated in BF and RA. Finally, the specimen tempered at 450 °C presented the optimum tensile mechanical properties. The yield and ultimate tensile strength of nanostructured bainitic steel increased at first and then decreased with increasing tempering temperature, and both of them reached the maximum in the 250 °C specimen.

Effect of heat treatment process on Microstructure and properties of 4Cr13N corrosion resistant plastic die steel

The effect of heat treatment process on microstructure and mechanical properties of 4Cr13N corrosion-resistant plastic die steel were investigated. The experimental results indicate that, with the increase of quenching temperature of 4Cr13N steel, the undissolved second phase gradually decreased, the martensitic lath gradually coarsened, and the hardness first rise up and then move down. The hardness of 4Cr13N steel reaches the highest at 1020 °C, at this time, the quenching microstructure is martensite + undissolved carbide + retained austenite, and the type of undissolved carbide is M23C6. The tempering hardness curve has an obvious secondary hardening peak, the peak temperature is 500 °C, and the peak hardness is 55 HRC. Below 500 °C , with the increase of tempering temperature, granular nitride Cr2N dispersion precipitation from matrix, resulted in second phase strengthening, hardness increased, impact toughness decreased, and the fracture mode is quasi-cleavage fracture; Above 500 °C, the structure gradually transformed to sorbite, the hardness decreased, and the toughness increased. Over all, to achieve a better match of strength and toughness, 4Cr13N plastic die steel should be tempered between 200 ~ 480 °C, impact energy are above 15 J, hardness above 50 HRC.

Hydrogen permeation in a Cr–Mo–V medium-carbon steel: Effect of the quenching medium and tempering temperature

Hydrogen permeation tests are carried out to evaluate the effect of the quenching medium and tempering temperature on the permeation parameters and density of hydrogen traps, of a Cr–Mo–V low-alloy medium-carbon steel. Three types of steel membranes are tested: 1) in the as-quenched condition, 2) tempered at 235 °C and 3) tempered at 530 °C; each one quenched in two different media: oil or brine. From the as-quenched condition, the apparent concentration of hydrogen and hydrogen flux, tend to decrease as the tempering temperature increases. The membranes in the as-quenched condition and tempered at 530 °C, show lower hydrogen diffusivity and higher density of hydrogen traps than membranes tempered at 235 °C. It is concluded that tempering at 235 °C, promotes hydrogen induced cracking, which is contrary to what has been previously determined. The cracking is related to a higher hydrogen diffusivity and lower density of hydrogen traps.

Influence of the heat treatment on the quantitative features of the fracture surfaces and the mechanical properties of AISI 4340 steel sheets

ABSTRACT The effects of austenitizing and tempering temperatures on the mechanical properties and fracture surface characteristics of AISI 4340 steel were investigated. The microstructure was also examined by scanning and transmission electron microscopy. The results indicated that with increasing the austenitizing temperature from 850°C to 1200°C, the yield strength, ultimate tensile strength, and impact energy were decreased by 23%, 24%, and 35%, respectively. Moreover, the increase of tempering temperature from 200 to 350°C decreased these mechanical properties by 15%, 7.5%, and 35%, respectively. The optimal combination of strength and ductility was obtained at austenitizing temperature of 900°C and tempering temperature of 200°C. The variation of total elongation and strength-elongation balance with the austenitizing and tempering temperatures were similar to that of the average dimple area. Likewise, the variation of the yeild strength with the tempering temperatures was similar to that of the average dimple area and opposite to that of the dimple area density.

The effect of vanadium content on hierarchical martensite structure and yield strength of petroleum casing steels

In the present study, the influence of V content and tempering temperature on the precipitation behavior of hierarchical martensite and yield strength of petroleum casing steels has been systematically studied. Moreover, the relationship between the precipitation behavior and strengthening mechanisms has been analyzed. It was found that yield strength increased with increase of V content. Especially, the steel with 0.10% V has the most efficient strengthening effect, and its yield strength increased nearly 370 MPa compared with that of steel without V. With increase of tempering temperature, the yield strength of steels with 0.10% V decreased in three stages because of the various precipitation behavior on hierarchical martensite structure. The results of nano-indentation tests showed more precipitates were aggregated preferentially in martensite blocks (MBs) of the high V steels (V10 and V15 steels), while the precipitates of V0 and V5 steels were uniformly distributed in martensite packets (MPs), leading to larger nano-hardness of MBs. Moreover, the precipitates on MBs decreased sharply with increase in tempering temperature, and the residual precipitates aggregated on the boundaries of MBs, leading to a dramatic decrease in the nano-hardness of MBs. Considering the size effect and precipitation behavior on the hierarchical martensite structure under different V content and tempering temperature, the traditional yield strength model was modified. Moreover, it was confirmed that the main strengthening mechanisms of V microalloyed petroleum casing steels were grain refinement strengthening and precipitation strengthening.

Effect of heat treatment on microstructure and mechanical properties of 34CrNiMo6 steel by laser solid forming

34CrNiMo6 steel was fabricated by laser solid forming technology. The effect of quenching and tempering treatment on the microstructure and mechanical properties was studied. The results showed that the microstructure of as-deposited samples consisted of martensite and bainite and tempered martensite. After quenching and tempering, the microstructure of the deposited layer was finer and became uniform, which was mainly tempered sorbite. When the sample was quenched at 830 °C and tempered at 460 °C, the microstructure was the tempered martensite. With the increase of tempering temperature, the content of carbide precipitated in martensite gradually increased. With the increase of quenching temperature, hardness of the samples increased firstly and then decreased. The hardness of the deposited layer gradually decreased with increasing the tempering temperature. The best quenching and tempering process for the laser solid forming 34CrNiMo6 steel was 830 °C quenching +540 °C tempering, which differed from the tempering treatment process for forged parts. The tensile strength increased from 980 MPa under the standard quenching and tempering conditions to 1230 MPa (increased by 25.5%) and the yield strength increased from 916 MPa under the standard quenching and tempering conditions to 1123 MPa (increased by 22.6%). But the elongation and percentage reduction of area obtained by the two quenching and tempering conditions were basically the same. The mechanical properties of LSFed 34CrNiMo6 steel after the optimal tempering treatment process had reaches the forging standard. The fracture mode of heat-treated LSFed sample was ductile fracture.

High-Cycle Fatigue Behavior and Fatigue Strength Prediction of Differently Heat-Treated 35CrMo Steels

In order to obtain the optimum fatigue performance, 35CrMo steel was processed by different heat treatment procedures. The microstructure, tensile properties, fatigue properties, and fatigue cracking mechanisms were compared and analyzed. The results show that fatigue strength and yield strength slowly increase at first and then rapidly decrease with the increase of tempering temperature, and both reach the maximum values at a tempering temperature of 200 °C. The yield strength affects the ratio of crack initiation site, fatigue strength coefficient, and fatigue strength exponent to a certain extent. Based on Basquin equation and fatigue crack initiation mechanism, a fatigue strength prediction method for 35CrMo steel was established.

Effect of Tempering Temperature on Microstructure and Properties of a New Type of Nitrogen‐Containing Hot‐Work Die Steel 3Cr7Mo2NiSiVN

Herein, the effect of tempering temperature on the microstructure evolution and mechanical properties of a new nitrogen‐containing hot‐work die steel 3Cr7Mo2NiSiVN is investigated. The new type of hot‐work die steel is quenched at 1080 °C and then conducts a double tempering from 200 to 700 °C. The quenching microstructure contains martensite, film‐retained austenite, and undissolved precipitates, and these precipitates play a Zener pinning effect role in prior austenite grains growing. Based on the Thermo‐Calc thermodynamic calculation and experimental results, the die steel contains V‐rich M2N nitride, Cr‐rich M23C6 carbide, Mo‐rich M6C carbide, and (Nb,V)‐rich M(C,N) precipitates. A secondary hardening phenomenon occurs and the brittle fracture turns to ductile fracture under the scanning electron microscope (SEM) field when the tempering temperature is 500 °C. Room strength decreases and the plasticity improves with the continual increase of tempering temperature. Many nano‐size spherical M2N nitride and strip‐like M(C,N) carbonitride precipitate when the tempered temperature exceeds 550 °C with transmission electron microscope (TEM) observation. Finely dispersed M2N nitride and M(C,N) carbonitride are beneficial for stabilizing microstructure at high temperatures and improving high‐temperature strength. Therefore, the high‐temperature strength of the new type of hot‐work die steel is much higher than that of the traditional hot‐work die steel.

Effect of tempering on the microstructure and properties of a new multi-functional 460 MPa Grade construction structural steel

A new generation of multi-functional construction structural steel with high yield strength of ∼545 MPa, excellent toughness of ∼170 J/cm2 at −20 °C, lower yield ratio smaller than 0.83, good fire resistance, and good corrosion resistance was successfully developed by thermo-mechanical controlled processing plus tempering. The effects of tempering on the microstructure and mechanical properties were investigated. The results show that although the bainite lath slightly coarsens and the dislocation density slightly decreases as the tempering temperature increases, the yield strength of the steel increases mainly due to the precipitation strengthening. The samples tempered at 300 °C show the best combination of strength, toughness, and yield ratio. In addition, the high-temperature strength of the newly developed Q460 steel is obviously higher than the conventional one, which is mainly attributed to the bainitic strengthening and precipitation strengthening. Moreover, a denser rust layer forms on the surface of new Q460 steel during corrosion because of the addition of Cr and Cu, which increases the corrosion resistance of the steel.

Effect of tempering temperature and hydrogen on deformation during tensile tests in a V-added high strength low alloy steel

Tensile behavior and hydrogen embrittlement have been investigated in a V-added high strength low alloy steel tempered at three different temperatures through slow strain-rate tensile tests and simultaneously hydrogen charging at different current densities. In the meantime, the in-situ strain field was quantitatively supervised using digital image correlation (DIC) technique. With increasing hydrogen content, the strain to fracture and work hardening exponent are greatly reduced regardless of the tempering temperature, which can indeed affect the susceptibility to hydrogen-induced embrittlement (HIE). However, in the absence of hydrogen, the steel per se displays decrement in strength, increment in ductility and slight increase in work hardening exponent with raising tempering temperature. These changes were elaborated by microstructure and a model of interaction between dislocation and hydrogen. With increasing tempering temperature, the tangled dislocation gets incompact. The hydrogen can pin the separated dislocation, but facilitate movement of the multiple dislocation. Hence the assistant force stemmed from hydrogen always increases with continuous deformation, reduces strain hardening ability, accelerates local deformation which can result in the very closely spaced dislocations being absorbed by grain boundary, then gives rise to the steel premature fracture.

Investigation of a Mechanism of Structural Transformations in High-Strength Steel

Mechanical, technological and operational properties of metal materials are largely influenced by changes of concentrations, morphology, dimensions, localization, elemental and phase composition of dispersed precipitates. This paper is devoted to a study of dispersed carbides of submicron size at tempering of high-strength medium-carbon steel. The main emphasis is on comparing the data obtained by small-angle neutron scattering and transmission electron microscopy. As a result of the analysis, it was found that carbide growth begins in the investigated steel immediately after quenching when the tempering temperature increases. First, it is fixed by a transmission electron microscopy and a small-angle neutron scattering and then above ~ 300 ° C carbide growth is fixed by neutron diffraction. The residual austenite is also completely dissolved by the time the temperature reaches ~ 300 °C. A good matching has been reached for the methods used. It has been shown that a complex use of integral and local methods allows to obtain fully information about the structure and properties of the investigated material.

Achievement of ultra-high strength in 45Si2MnCr2Mo steel via efficient and low-energy tempering

In this study, 45Si2MnCr2Mo steel was fabricated by casting, hot rolling, and normalizing, followed by tempering at different temperatures from 180 to 520 °C for 2 h. Special attention was paid to the effects of tempering on the microstructure and mechanical properties of the steel. The results indicate that microstructure of tempered steel consists of bainite, martensite, and retained austenite (RA), and it is not sensitive to tempering at temperatures below 320 °C. However, after tempering at temperatures of 420 and 520 °C, bainitic ferrite plates merged and their lath boundaries became vague. In turn, RA decomposed, whereas carbide particles appeared and then coarsened. With increasing tempering temperature, the volume fraction of RA achieved its peak value at 320 °C and carbon concentration within RA attained its peak value at 420 °C. The optimal balance of ultimate tensile strength of 2306 MPa and total elongation of 8.24% in the steel were achieved after being normalized at 950 °C for 0.5 h and subsequent tempering at 220 °C for 2 h. These values are found to exceed those of air-cooled and isothermal bainitic steels. Finally, the correlation between microstructure and mechanical properties of the steel under consideration was discussed.

Effect of heat treatment on microstructure and properties of modified hypereutectic high chromium cast iron

Abstract The effect of heat treatment on the microstructure, hardness and wear resistance of modified hypereutectic high chromium cast iron (HCCI) was investigated. The results show that the quenching treatment partially dissolves the edges of the primary carbides, and the sharp corners become rounded and blunt. As the quenching temperature increases, the carbide re-dissolves into the matrix, and the hardness and wear resistance first increase and then decrease. The hardness and wear resistance are the best when quenched at 1000 °C. After tempering, the martensite is transformed into tempered martensite, and the precipitation of secondary carbides increases. As the tempering temperature increases, the secondary carbides gradually become coarser. When the tempering temperature is 500 °C, the hypereutectic HCCI shows the highest hardness and the best wear resistance. When tempered at 400 °C, hypereutectic HCCI shows the best erosion and wear resistance.

Effect of Tempering Treatment on Microstructural Evolution and Mechanical Behavior of Heavy-Wall Heat Induction Seamless Bend Pipe.

In this paper, the microstructure and mechanical properties of heavy-wall seamless bend pipe after quenching at different tempering temperatures, including 550 °C, 600 °C, 650 °C, and 700 °C, were studied. Microstructure and dislocations observations were characterized by means of an optical microscope, a scanning electron microscope, a transmission electron microscope, and X-ray diffraction. As the tempering temperature increases, the dislocation density in the test steel gradually decreases, and the precipitation behavior of (Nb, V)(C, N) increases. The sample tempered at 650 °C exhibits a granular bainite structure with a dislocation cell structure and a large number of smaller precipitates. The yield platforms of tempered samples at 650 °C and 700 °C are attributed to the pinning effect of the Cottrell atmosphere on dislocations. The sample tempered at 650 °C not only presents the highest strength, but also the highest uniform elongation, which is attributed to the higher strain-hardening rate and instantaneous work-hardening index. This is closely related to the multiplication of dislocations, the interaction between dislocations and dislocations, and the interaction between dislocations and precipitates during plastic deformation of the 650 °C-tempered samples with low dislocation density, which delays the occurrence of necking.

Effect of tempering temperature on microstructure and mechanical properties of nanostructured bainitic steel

The previous research on tempered nanostructured bainite has been mainly focused on the carbide precipitation at high temperatures with few details on nanostructured bainite tempered at lower temperatures. In this research, the microstructure evolution and the corresponding mechanical properties of the nanostructured bainite tempered at a temperature ranged from 180 °C to 400 °C were studied via X-ray diffraction, transmission electron microscope and high-resolution thermal dilatometer. Results show that retained austenite occurred bainitic transformation when the tempering temperature ranged from 210 °C to 320 °C. The amount of newly formed bainite increased at first and then decreased slightly with increasing tempering temperature. When the tempering temperature reached 380 °C and higher, the cementite precipitated from retained austenite and reduced the stability of over-stable retained austenite. As a result, it can be concluded that stress-induced martensitic transformation would occur easily in retained austenite during deformation process, leading to the optimum increase of retained austenite contribution to toughness.

Effect of deep cryogenic treatment on microstructure and properties of M35 high speed steel

The effects of cryogenic treatment on microstructure, hardness, red hardness and wear resistance of M35 high speed steel(HSS) were studied by means of scanning electron microscope, X-ray diffractograph, friction and wear tester and Rockwell hardness tester. The results show that with the increase of tempering temperature, the residual austenite in M35 HSS decreases and the grain size increases gradually. After deep cryogenic treatment (DCT), the grain size of M35 HSS is refined and the wear volume is reduced. DCT at 525°C has the best wear resistance. With the increase of tempering temperature, the hardness of M35 HSS decreases first and then increases, and finally decreases sharply. The Rockwell hardness of M35 HSS at 525 °C is the highest, which is 67.1 HRC. The peak hardness of Rockwell increased by 0.7 HRC and the tempering temperature decreased from 550 °C to 525 °C, which showed good stability of red hardness.

Effects of quenching and tempering heat treatment on microstructure, mechanical properties, and fatigue crack growth behavior of 51CrV4 spring steel

Herein, the microstructure, mechanical properties, and fatigue crack growth (FCG) behavior of 51CrV4 spring steels under different quenching and tempering heat treatment were studied. Results show that tempering temperature would not affect the prior austenite grain (PAG) size, while quenching temperature has a great influence on it; the volume fraction of carbide precipitates decreased with increasing quenching temperature. The width of martensite lath has little relationship with the prior austenite grain size. The mechanical properties of the investigated steels decreased with an increasing tempering temperature. Tempering temperature had a greater influence on the fatigue crack growth behavior compared with quenching temperature. The FCG of all the investigated steels were well interpreted by Paris model. When the quenching temperature was 840 °C, the stable expanding stage of the fatigue fracture was representative fatigue striations, fatigue steps and secondary cracks; multiple failure mechanisms coexisted in the rapid expanding stage; the fracture morphology of unstable failure stage was mainly dimples. When the quenching temperature increased to 880 °C and 920 °C, quasi-cleavage was observed in all the stages compared with the samples quenched at 840 °C. Secondary cracks, fatigue steps and crack closure could retard the FCG rate by consuming the driving force near the tip of fatigue crack.

Effect of tempering temperature on monotonic and low-cycle fatigue properties of a new low-carbon martensitic steel

The relationship between tempering temperature and low cycle fatigue (LCF) is not clear. New low-carbon martensitic steels under different tempering temperatures (320 °C, 350 °C, 380 °C) are tested for tensile mechanical properties, LCF, and microstructure. The results show that the monotone mechanical properties of martensite steels decrease with the increase of tempering temperature. The microstructure shows that the width of the laths increases, the residual austenite is decomposed, and the dislocation density decreases. A damage hysteresis fatigue life prediction model considering tempering temperature is proposed and the fatigue performance is evaluated. The fatigue performance parameters show that the fatigue damage capacity (W0) decreases and the damage transition index (β) increased. The established fatigue life model can predict the fatigue life at different tempering temperatures.

Effects of Tempering Temperature on the Microstructure and Mechanical Properties of Low Alloy Ultra-High Strength 45CrNiSiMnMoVA Steel

The effects of different tempering temperatures on the microstructure evolution and mechanical properties of the new low-alloy ultra-high-strength 45CrNiSiMnMoVA steel after quenching were investigated by mechanical property tests, SEM and TEM. The results show that a complex phase organization consisting of martensite/ lower bainite of the tested steel after treated at 920°C×1h+(320~380)°C×4h was obtained, and the partition interface of the lath martensite bundle became blurred from clear with the increase of tempering temperature; In the proposed tempering temperature range, the toughness of the alloy has become better while maintain the strength without decreasing basically, and when the tempering temperature is 350°C, the alloy has the optimal comprehensive mechanical properties of strength, plasticity and toughness together. The analysis concluded that the strong toughening of the tested steel was mainly attributed to the coupling effect of the alloying elements in the steel and the composite toughening of the nano-precipitated phases, among other aspects.