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Printed Edition of the Special Issue Published in Metals

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Influence of quenching and the partitioning process on the transformation kinetics and hardness in a lean medium manganese TRIP steel. Influence of the quenching and splitting process on the transformation kinetics and hardness in a lean medium manganese TRIP steel. Metals.

Influence of the Quenching and Partitioning Process on the Transformation Kinetics and Hardness in a

  • Introduction
  • Materials and Methods
  • Results
  • Discussion
  • Conclusions

On the one hand, the IBT in the TBF regime was remarkably slower compared to the Q&P procedure. For comparison, the microstructure of the sample annealed in the TBF regime is shown in Fig. 6d.

Table 1 shows the chemical composition of the investigated steel grade in wt.%. The steel was melted in a medium frequency induction furnace and cast under laboratory conditions in an ingot of 80 kg
Table 1 shows the chemical composition of the investigated steel grade in wt.%. The steel was melted in a medium frequency induction furnace and cast under laboratory conditions in an ingot of 80 kg

Quantitative Analysis of Microstructure Evolution in Hot-Rolled Multiphase Steel Subjected to Interrupted

Material and Methods 1. Material

The amount of residual austenite detected for the sample deformed to 10% strain was estimated to be approximately 8%. The amount of residual austenite remaining in the microstructure of the fracture-deformed sample is approx.

Figure 1. Parameters of thermomechanical processing of investigated steel.
Figure 1. Parameters of thermomechanical processing of investigated steel.

Evolution of Microstructure and Hardness of High Carbon Steel under Different Compressive

Strain Rates

Experimental

A PANalytical Empyrean XRD instrument (Malvern Panalytical, Malvern, UK) was used with unfiltered co-irradiation at 45 kV and 40 mA current for quantitative X-ray diffraction (XRD) to measure the volume fraction of the phases from the 2θ spectrum obtained at a step size of 0.0260 over an angular range of 40°. up to 130◦. EBSD patterns were collected in 2 × 2 binning mode and a scan step size of 0.15 μm using AZTEC software.

Results and Discussion 1. Base Material

It is noteworthy that dislocation density in the microstructure was a little less in 2×10−4/s (Figure3(c2)) compared to 2×10−5/s (Figure3(b2)) strain rate induced sample. This is the reason behind the slightly reduced dislocation density at 2×10−4/s strain rate (Figure3(c2)) compared to the 2×10−5/s strain rate (Figure3(b2)).

Figure 2. (a) X-ray diffraction of high carbon steel compressed at different strain rates at room temperature show the martensitic phase transformation of RA; (b) Deformation-induced samples show decreasing RA fraction and increasing martensite with increa
Figure 2. (a) X-ray diffraction of high carbon steel compressed at different strain rates at room temperature show the martensitic phase transformation of RA; (b) Deformation-induced samples show decreasing RA fraction and increasing martensite with increa

Conclusions

Effect of a small addition of Cr on the stability of retained austenite in high carbon steel. Mater. Nano-indentation study on the mechanical stability of individual austenite in carbon steel.Mater.

Effect of Deformation Temperature on Mechanical Properties and Deformation Mechanisms of

Cold-Rolled Low C High Mn TRIP/TWIP Steel

However, a systematic study on the effect of deformation temperature on the deformation mechanism and mechanical properties of TRIP/TWIP steel has not been performed. 24] investigated the deformation mechanism in a high-alloy austenitic CrMnNi austenitic TRIP/TWIP steel in the temperature range of. In summary, a systematic study on the influence of deformation temperature (over a wide range of temperature) on the deformation mechanism and tensile properties of TRIP/TWIP steel is required at this time.

The experimental results have a certain practical significance in the TRIP/TWIP steel deformation technology in different temperature ranges. If we combine Figure 1 and Table 1, we can see that the deformation temperature has a significant effect on the mechanical behavior of the investigated steel. The moment hardening exponent (n) can further reveal the deformation behavior of the experimental steel during deformation.

Meanwhile, α-martensite (confirmed by electron diffraction pattern analysis) was transformed from austenite during deformation (shown in Figure 7b), which indicated that the deformation was induced.

Figure 1 shows engineering stress-strain curves of the experimental steel at different tensile test temperatures
Figure 1 shows engineering stress-strain curves of the experimental steel at different tensile test temperatures

Effect of Deformation Temperature on the Portevin-Le Chatelier Effect in Medium-Mn Steel

The consequence of the appearance of the PLC effect is the appearance of technological problems in plastic transformation. The different course of the curve in Figure 3b is related to the appearance of the PLC effect in the early stages of uniform deformation. Some of the differences may be due to the different intensity of the TRIP effect and the PLC effect at different temperatures.

An explanation of the PLC phenomenon in medium manganese steels appears to be a difficult problem due to the multiphase. This is related to the lower contribution of the TRIP effect, i.e. the mechanical stability of retained austenite increases [47,48]. Since the amount of retained austenite in the current steel is relatively low (~10%), the contribution of the TRIP effect to the PLC effect cannot be significant.

Influence of the strain rate on the PLC power and acoustic emission in single crystals of the CuZn30 alloy compressed at an elevated temperature. Mater.

Table 1. Chemical composition of the investigated medium-Mn steel in wt.%.
Table 1. Chemical composition of the investigated medium-Mn steel in wt.%.

Effect of Manganese on the Structure-Properties Relationship of Cold Rolled AHSS Treated by

Thus, to adjust a comparable amount of α'prim, the increase of the Mn content requires a lower TQ. Regarding the influence of the chemical composition, no significant effect of Mn on the microstructural development could be observed at low TQ, whereas for the higher TQ a larger volume fraction of a'final. Regardless of the chemical composition, an increasing TQ led to a remarkable decrease in the amount of α", whereas the volume fraction of αB simultaneously increased.

On the contrary, the further increase in Mn content from 3.5 to 4.0 wt.% hardly affected. However, for the samples containing even lower volume fractions of a'prim (<70 vol.%), a significant influence of the chemical composition on the phase transformation behavior and the resulting structure–property relationship was found. A significant influence of the Mn content on the phase transformation behavior could be observed, especially with increasing TQ and thus decreasing α'prime fraction.

Influence of the phase transformation behavior on the microstructure and mechanical properties of a 4.5 wt.% Mn Q&P steel. HTM J.

Table 1. Chemical composition of the investigated cold rolled steel grades.
Table 1. Chemical composition of the investigated cold rolled steel grades.

The Impact of Strain Heterogeneity and Transformation of Metastable Austenite on

Experimental Procedure

The study focused on 1300 MPa grade cold rolled QP steel and 1200 MPa grade DP steel. Cold rolled QP steels and dual phase (DP) steels, 1.2 mm thick, were provided by Hansteel. Bending test specimens were cut from QP and DP steel along the rolling direction with a length and width of 66 mm and 20 mm, respectively, in accordance with the VDA238-100 standard.

Based on the photographs of specimens before and after rebound, the rebound angles of DP and QP steel were calculated. The yellow rectangles represent the outer zone, middle zone and inner zone in the thickness direction; (c) Diagram of the bending specimens. After mechanical grinding, EBSD samples were polished and electropolished at room temperature using a solution containing 95 vol % C2H5OH and 5 vol % HClO4.

The TEM samples were mechanically ground to a thickness of 50μm and then electropolished with a two-jet electropolishing machine (Struers TenuPol-5, Copenhagen, Denmark) at -20◦C with a solution containing 85 vol % C2H5OH and 15 vol % HClO4.

Results and Discussion 1. Initial Microstructures

Figure3a illustrated that the stress of the DP steel and QP steel increased rapidly with the bending angle. The rebound angle of the DP steel increased with the increase in the bending angle. Nevertheless, the springback angle of the QP steel strained at 104◦ was lower than that strained at 74◦ .

Grain boundary maps (Figure 4a,c) from the EBSD measurements showed that the majority of the grain boundary angles had values ​​below 15◦ (low angle grain boundary; LAGB; black) in the outer zone and the inner zone of the bent specimen. Thus, the springback angle of the DP steel increased with the increase in the bending angle, which is in good agreement with the results in Figure 3b. As the sample was strained at a 104◦ bending angle, the retained austenite volume fraction of the outer zone and inner zone decreased significantly.

When the specimens were strained at a higher angle, the preserved austenite in the central region changed to martensite (Figure 11c).

Figure 2. Microstructure of DP and QP steel prior to deformation. (a,b) Distribution of ferrite (F) and martensite (M) in DP steel
Figure 2. Microstructure of DP and QP steel prior to deformation. (a,b) Distribution of ferrite (F) and martensite (M) in DP steel

Effects of Cr and Mo on Mechanical Properties of Hot-Forged Medium Carbon TRIP-Aided Bainitic

Results and Discussion

It has been found that the FA process significantly improves the sizes of previously austenitic grains, proeutectoid ferrite, bainitic ferrite and retained austenite in Steels A-C. The size of retained austenite is the largest in steels A to C. The FA process increases the fraction of the MA phase. g–i) are high-magnification orientation maps of the squares in (d–f), respectively. Figure 6a–d shows an initial volume fraction (fγ0), carbon concentration (Cγ0) and total carbon concentration (fγ0×Cγ0) of retained austenite and a ratio offγ0×Cγ0 to added C content (fγ0 .×Cγ0/C), as a function of carbon equivalent in Steels A to C.

It is worth noting that the equivalent carbon dependences of retained austenite characteristics in steels D to G are almost the same as those of steels A to C. The high dislocation density of acular bainitic ferrite and retained austenite (Figure 5) contributes to the higher yield and higher strength of the steel caused by the higher resistance of the steel. austenite than those of steels F and G (Figure 6), as well as the matrix structure of bainitic ferrite without carbides.

This may be due to the reduced carbon concentration (or low mechanical stability) of the retained austenite.

Figure 4. EBSP phase maps of Steels A (a,d,g), B (b,e,h) and C (c,f,i) subjected to CA and FA process
Figure 4. EBSP phase maps of Steels A (a,d,g), B (b,e,h) and C (c,f,i) subjected to CA and FA process

Summary

From the above theory and the results of Figures 4 and 6e, high CIAV and combinations YS×CIAV and TS×CIAV of hot forged steel C can be mainly caused by a refined uniform acicular bainitic ferrite matrix and a large amount of metastable retained austenite. forging refined the mixed structure and increased the volume fraction and mechanical stability of preserved austenite. The excellent impact resistance was mainly due to a uniform fine-needle bainitic ferrite matrix structure and a large amount of metastable retained austenite.

Formability of Al-Nb bearing ultra-high strength TRIP supported plate steels with bainitic ferrite and/or martensite matrix.ISIJ Int. Effects of addition of Cr, Mo and Ni on the microstructure and retained austenite characteristics of 0.2% C–Si–Mn–Nb ultrahigh strength TRIP supported bainitic ferritic steels.ISIJ Int. Effects of microalloying on the impact strength of ultrahigh strength TRIP supported martensitic steel. Metal.

Development of TRIP assisted ultra high strength low alloy steel for hot forging parts. Steel Res.

An Overview of Fatigue Strength of Case-Hardening TRIP-Aided Martensitic Steels

The compressive residual stress of the TM steel is greater than that of the SNCM420 steel. It is worth noting that the Vickers hardness of the TM steel increases even inside the surface-hardened layer after fatigue deformation. Heat-treated TM steel subjected to fine particles under arc height of 0.104 mm (N) reaches higher fatigue limits than SNCM420 steel, especially for the notched specimen (Figure 14).

A white layer [69], which plays an important role in fatigue strength and wear resistance, is formed on the surface of the vacuum carburized TM steel subjected to fine particle hardening under arc heights higher than 0.41 mm (N). By comparing the fatigue limits with those [62] of heat-treated TM steels subjected to fine particles below an arc height of 0.104 mm (N), the fatigue limit increase (Δσw= 440 MPa) is greater than that (Δσw= 244 MPa) of . Consequently, the small drops in Vickers hardness and residual compressive stress during fatigue deformation are believed to significantly increase the fatigue limit.

Vacuum carburizing and subsequent fine particle peening further increased the fatigue strength of the steel, except for the notch fatigue limit.

Figure 1. Multi-step heat-treatment diagram (austenitizing and subsequent isothermal transforming, followed by partitioning) of TM steel [16]
Figure 1. Multi-step heat-treatment diagram (austenitizing and subsequent isothermal transforming, followed by partitioning) of TM steel [16]

Effects of Alloying Elements Addition on Delayed Fracture Properties of Ultra High-Strength

TRIP-Aided Martensitic Steels

The martensite lath matrix of the TM steel became fine and uniform due to the addition of alloying elements compared to that of steel A (Figures 2 and 3). Table 2 shows the retained austenite properties, area fraction of the M–A phase, tensile properties and previous austenite grain size of the TM steel. Typical applied stress-failure-time plots of the TM steel are shown in Figures 4 and 5 showing the relationship between delayed fracture strength (DFS), which is the maximum bending stress that does not cause failure of the specimen for 5 hours, and tensile strength (TS).

The TM steels (steels B–E) in this study showed a small size of the pre-austenitic grain, packet, block and martensitic lath due to the addition of the alloy (Figure 2). In addition, the improved hardenability of microalloyed TM steels inhibited cementite precipitation in martensitic laths. The mechanism of such a microstructural change of TM steels due to the addition of alloying elements has been described in previous reports [12, 20, 21].

Thus, it was suggested that the chromium-added TM steel showed excellent hydrogen embrittlement resistance due to the suppression of martensite transformation during hydrogen embrittlement tests due to the high stability of retained austenite.

Table 1. Chemical compositions (mass%), martensite transformation start temperature (M S ) and hardenability (Πfi) of transformation induced plasticity (TRIP)-aided steels with a martensite matrix (TM steels).
Table 1. Chemical compositions (mass%), martensite transformation start temperature (M S ) and hardenability (Πfi) of transformation induced plasticity (TRIP)-aided steels with a martensite matrix (TM steels).

MDPI

Hình ảnh

Table 1. Chemical composition of the investigated steel Fe-C-Mn-Al in wt.%.
Figure 3. Dilatometric curves at different T P (T B ) of (a) Q&amp;P heat-treatment (T Q = 310 ◦ C) and (b) TBF heat-treatment.
Figure 4. Dilatation due to α B formation as a function of isothermal holding time at different T P (T B ) for (a) Q&amp;P steel (T Q = 310 ◦ C) and (b) TBF steel.
Figure 5. (a) Dilatometric curves at different T Q (T P = 400 ◦ C) and (b) dilatation due to α B formation as a function of isothermal holding time at different T Q (T P = 400 ◦ C).
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