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Article

Effects of Finish Rolling Temperature on the Critical Crack Tip Opening Displacement (CTOD) of Typical 500 MPa Grade Weathering Steel

by
Junping Wu
1,2,
Guangming Bai
3,
Liyang Zhao
3,
Zhongde Zhang
3,
Yan Peng
1,
Juefei Chu
2 and
Qingfeng Wang
3,*
1
School of Mechanical Engineering, Yanshan University, Qinhuangdao 066004, China
2
Nanjing Iron & Steel United Co., Ltd., Nanjing 210035, China
3
Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China
*
Author to whom correspondence should be addressed.
Metals 2023, 13(10), 1791; https://doi.org/10.3390/met13101791
Submission received: 19 September 2023 / Revised: 17 October 2023 / Accepted: 18 October 2023 / Published: 23 October 2023
(This article belongs to the Special Issue Advances in Weathering Bridge Steels)
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Versions Notes

Abstract

:
In this study, the effect of finish rolling temperature on the critical crack tip opening displacement (CTOD) of typical 500 MPa grade weathering steel was elucidated. The microstructures were observed via optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), and electron back-scattered diffraction (EBSD). The cryogenic fracture toughness and microstructures of steels were analyzed at different finish rolling temperatures (780–840 °C). The results show that a mixed microstructure, i.e., granular bainitic ferrite (GBF), polygonal ferrite (PF), and martensite/austenite (M/A), constituent was formed in each sample. With the decrease of the finish rolling temperature, the GBF content decreased, PF content increased, and the high angle grain boundary (HAGB) number fraction of the matrix increased. Furthermore, the fraction of M/A constituents was increased with reduced average size. The value of CTOD increased significantly from 0.28 to 1.12 mm as the finish rolling temperature decreased from 840 to 780 °C. Both the decrease of M/A constituents and the increase of HAGB increased the cryogenic (−40 °C) fracture toughness of the typical 500 MPa grade weathering steel.

1. Introduction

In recent years, high-strength weathering steel [1,2,3,4,5] has been widely preferred for bridges, buildings, wind power, and in other structural construction fields. It possesses excellent strength, toughness, weldability, and atmospheric corrosion. Considering facile process flow, controllability, and low cost, a thermomechanical control process (TMCP) allows for weathering steel with comprehensive features [1,2,6,7,8].
TMCP includes controlled rolling and cooling, and the key process parameters impact microstructure and properties like finish rolling temperature [7,9], cooling rate [10,11], and finish cooling temperature [4,6]. Extensive research has been carried out on mechanical properties, focusing on the coordination of microstructure and tensile or impact properties. For instance, low finish cooling temperature due to the increase of bainite, dislocation density, M/A constituent refinement, and large angle grain boundary reduces the strength and toughness of 460 MPa grade fire-resistant and weather-resistant building structure steel [4]. Fan et al. [11] reported that a fast cooling rate during the control cooling process can refine QPF + GBF grains, enhance dislocation density, and reduce M/A constituents, resulting in a significantly high tensile strength. Further, low finish rolling temperature (from 830 °C to 810 °C) can improve the content of bainite and M/A constitunts, while shrinking the size, which stimulates yield and tensile strength [7]. The refinement of M/A constituents also improves the impact toughness. Guo et al. [9] also found that the finish rolling temperature has a more significant effect on microstructure. These studies evaluated impact performance under instantaneous load in the process of fracture of the specimen, but steel structure under actual service conditions consists of instantaneous shock load, as well as slow fracture failure under a long-term heavy load. Several studies shed light on the significance of the fracture toughness of materials [12,13,14,15,16,17]; however, little research concentrates on the role of alloying elements in fracture toughness [14,15,16]. The doping of Ni (9% to 7%) in low-carbon martensitic steel can roughen M/A constituents and decrease the fracture toughness at low temperatures [14]. The dense and local distribution of M/A constituents causes brittle instability or fracture, which, in turn, deteriorates the toughness of low-temperature fractures. Seok et al. [16] showed that the doping of Mo, i.e., 0.002% to 0.35% in molybdenum-containing high-strength low-alloy (HSLA) steel, can boost the volume fraction of GB, BF, and MA, resulting in a significant decrease in CTOD value. A brittle and hard M/A constituent provides a nucleation site for the initiation of cleavage cracks, which leads to the deterioration of low-temperature fracture toughness. So far, the role of TMCP on fracture toughness has not been studied in depth.
The influence of the TMCP on the microstructure is no less than the regulatory effect of alloying elements. It strongly impacts fracture toughness. Considering the finish rolling temperature as an example, a typical 500 MPa grade high-strength weathering steel is the research object in this work. A systematic study was carried out on the relationship between microstructure evolution and fracture toughness of 500 MPa grade high-strength weathering steel at different finish rolling temperatures and revealed the mechanism of action. This work provides guidance for the TMCP design of high-strength weathering steel to achieve excellent fracture toughness.

2. Experimental Procedure

The test steel was melted in a 120 kg vacuum induction furnace, and its final chemical composition is listed in Table 1. It was rolled into a thickness of 20 mm using the TMCP. A schematic diagram of the TMCP is shown in Figure 1. The 140 mm thick ingot was heated to 1210 °C at a rate of 10 °C/s and kept hot for 3 h. Using a φ450 mm test rolling mill, the ingot was thinned to 60 mm through 5 rolling passes at 1020–1100 °C. The roughing process crushed and refined the coarse austenite grains. The steel plate was cooled naturally and then finished to 20 mm in 6 passes at 780–840 °C. The finishing process generated a large number of deformation bands and crystal defects in the test steel, forming nucleation sites for the subsequent microstructural transformation during the cooling process, which produced more refined ferrite grains. The air cooling of the steel plate started the accelerated cooling below 760 °C, and the average cooling rate was 10 °C/s, which was completed at 500 °C. Due to inside heat transfer, the surface temperature of the steel plate rose to 550 °C. The whole process temperature point was measured by a fixed-point thermometer. The TMCP parameters of the test steel were measured at different finish rolling temperatures (Table 2). The temperature parameters of the series of finishing rolling were 840 °C, 820 °C, 800 °C, and 780 °C, which were named zz840, zz820, zz800, and zz780, respectively.
According to BS 7448-2 (1997) [18], the crack tip opening displacement (CTOD) of the specimen was machined transversely along rolled sheets. A single-edge notched bending specimen with a width of 36 mm and a thickness of 18 mm was chosen for the test, as shown in Figure 2. The fatigue pre-cracking was performed at room temperature. A 3-point bending experiment was carried out at −40 °C with a fixed loading rate of 0.5 mm/min. For each case, 3 samples were examined, with the average value reported.
After testing, the fracture section of the specimen was machined to observe the specimen, as shown in Figure 3. Next, the ground and polished sample was subjected to corrosion in 4% nitric acid alcohol, and a metallographic observation was carried out. The basic tissue morphology was observed by an Axiover-200MAT metallographic microscope. Furthermore, scanning electron microscopy (SEM-Hitachi SU5000, Hitachi Limited, Tokyo, Japan) was used to observe the microstructure features, i.e., M/A constituents, and changes in the content and size of M/A constituents were quantitatively calculated by Image-pro Plus software. The statistical results were collected under no less than 10 fields of view. After a mechanical polish, the sample was electrolytically polished in a 90% methanol and 10% perchloric acid solution at 1.2 A of polishing current and 18 V of voltage for 25 s of polishing time. It was observed using SEM equipped with a TSL electron backscatter diffraction (EBSD) lens in a scanning step of 0.2.
A 5 × 5 × 0.2 mm3 sheet was cut from the metallographic sample, which was ground to a thickness of 50–70 μm by sandpaper. The sheet was electrolytically double-sprayed with a 10% HClO4 + 90% CH3COOH solution to prepare the sample for TEM testing at 25 V and a flow rate of 18 cm/s. The bainite ferrite matrix morphology, dislocation configuration, and M/A constituent morphology were observed in detail using a transmission electron microscope (FEI Talos F200X, Thermo Fisher Scientific, Hillsboro, OR, USA).
The thermal expansion curves of the TMCP were obtained by using a Gleeble 3500 thermal simulation testing machine with a thermal dilatometer, with a sample size of 6 mm in diameter and 80 mm in length. The experimental process parameters were consistent with the TMCP mentioned above. The continuous cooling transition process of samples with different finish rolling temperatures is shown in Figure 1.
The influence of different finish rolling temperatures on the fracture behavior of the test steel was studied through the main fracture morphology of the CTOD specimen by SEM. Furthermore, the propagation characteristics of secondary cracks were observed at the cross-section near the fracture by using SEM and EBSD.

3. Results

3.1. Microstructure

Figure 4 shows the microstructure and surface morphology of samples at different finish rolling temperatures. The microstructure consisted of granular bainite (GB), polygonal ferrite (PF), and martensite/austenitic (M/A) constituents. As the finish rolling temperature was reduced from 840 °C to 780 °C, the proportion of GB decreased, while PF content increased. Moreover, the SEM observation of M/A constituents showed that the area fraction of M/A constituents increased from 7.56 to 10.12%, but their average size significantly decreased from 2.16 to 1.22 μm (Figure 4 and Table 3).
Figure 5 shows the TEM results of the samples at different finish rolling temperatures and verifies the formation of PF, GBF, and M/A constituent microstructures at respective finish rolling temperatures. At 840 °C of finish rolling temperature (Figure 5a), a small number of sub-grain structures, i.e., dislocation entanglement, were distributed on the coarse GBF matrix in the sample. This was attributed to the deformation and phase transition process during the controlled rolling and cooling process [10,11,19]. M/A constituents were distributed at the interface between the GBF and PF slats, which were relatively large in size and appeared as long strips or blocks. As the finish rolling temperature decreased from 840 °C to 780 °C (Figure 5b), the proportion of PF increased and refined, GBF content decreased and refined, and the size of M/A constituents decreased, while the number of M/A constituents increased significantly. In addition, the content of sub-grain structures, i.e., dislocation tangles, inside GBF increased significantly and, overall, the sample showed high dislocation density. From Figure 5c,d, it can be observed that M/A internally possessed a high-density dislocation structure, and the selected area electron diffraction (SAED) results (Figure 5e) demonstrate a composition of martensite and austenite.
The inverse pole figure (IPF) obtained by EBSD analysis of the sample with different finish rolling temperatures is shown in Figure 6. The mean equivalent diameter (MED) corresponding to misorientation tolerance angles (MTA) is shown in Figure 7a. The grain boundary distribution defined by each orientation difference angle is shown in Figure 7b. The quantitative results are summarized in Table 3. As the finish rolling temperature decreased from 840 °C to 780 °C, the average grain size (MEDθ≥15°) of the specimen decreased significantly from 3.70 μm to 2.20 μm. The proportion of large angle grain boundary (MTAθ≥15°) gradually increased from 44.8% to 53.1%. The large-angle grain boundary had the effect of preventing crack growth because the crack growth through the large-angle grain boundary absorbed more crack propagation energy [20].

3.2. CTOD Test Results

The force-displacement (F-V) curves obtained by the CTOD test of samples with different finish rolling temperatures are shown in Figure 8. The fracture toughness of zz840 samples was 0.280 mm. With the finish rolling temperatures decreased to 780 °C, the CTOD value of fracture toughness increased significantly to 1.109 mm (Table 4). The CTOD value increased by nearly three times, indicating a significant improvement in fracture toughness.
Figure 9a–d show the macroscopic morphology of the fracture side of the test steel after CTOD testing, and the micromorphology of the fracture along the crack tip is shown in Figure 9e–h. From Figure 9a–d, it can be observed that the CTOD specimens with different finish rolling temperatures showed a certain degree of plastic deformation near the crack growth path (red circle in the figure). The degree of plastic deformation increased as the finish rolling temperature decreased, which is consistent with increasing fracture toughness [21]. From the topography of the fracture, the crack growth path of the ZZ840 specimen was long, showing a large crack growth area. At 780 °C (Figure 9h), the length of crack propagation of the specimen decreased, which, in turn, reduced the area of the crack propagation zone, i.e., having better fracture toughness [15,22].
Figure 10 shows the fracture morphology of the steel with different finish rolling temperatures. These include macroscopic fractures (a, d), local micromorphology of crack propagation zones (b, e), and brittle fracture zones (c, f). The micromorphology of the fracture of the specimens at different finish rolling temperatures consisted of three areas: a prefabricated crack area, crack growth zone, and brittle fracture zone. As the finish rolling temperature decreased from 840 °C to 780 °C, the crack growth zone of the specimen increased, the area of the brittle fracture zone decreased, and the fracture mode changed from brittle to ductile. The local micromorphology of the crack propagation area (Figure 10b,e) can be observed, i.e., the extension zone of the ZZ840 fracture specimen generated cleavage surface, while the extension area of the ZZ780 fracture specimen was mainly dominated by small and deep dimples. In addition, the local micromorphology of the brittle fracture zone (Figure 10c,f) shows that all ZZ840 fracture samples were large-size cleavage surfaces. Several secondary cracks that extended straight were characterized by brittle fractures [16,17], resulting in poor fracture toughness. As for the ZZ780 samples, the cleavage surface was the main morphological feature in the brittle fracture zone; however, the size of the cleavage surface was small. More tear edges could be observed in the cleavage surface, showing better low-temperature fracture toughness.

4. Discussion

4.1. Effect of Finish Rolling Temperature on the Multi-Phase Microstructure

After the test steel was rolled under a series of finish rolling temperature processes, a multiphase composite structure of PF + GBF + M/A constituents was formed (Figure 4). With the decrease in finish rolling temperature, the PF microstructure increased, the proportion of GBF decreased, and the ferrite grain was refined (Figure 7a and Table 3). In addition, the content of hard-phase M/A constituents increased, but the average size was significantly refined (Table 3). These significant changes in microstructure are closely related to the process of microstructure transformation [2,10,19].
The thermal expansion curves of the continuous cooling transition process of samples with different finish rolling temperatures are shown in Figure 11. As the finish rolling temperature was reduced from 840 °C to 780 °C, the austenite-to-ferrite (γ → α) transition temperature, Ar3, increased significantly from 317 °C to 365 °C. Bang et al. [22] showed that the transition temperature of γ → GB is lower than that of γ → PF, i.e., the decrease in Ar3 temperature inhibits the transition of γ → GB, resulting in a decline in GB content and enhanced γ → PF transition. This transformation ultimately increases the whole PF content in steel. Further, at a low finish rolling temperature, the accumulation of the deformation increases during rolling, forming a large number of shear bands and dislocation substructures (Figure 5a,b). Such deformation enables a high density of ferrite nucleation sites, which causes microstructure refinement (Table 3 and Figure 7a) [7,9,23].
M/A constituents are a vital and typical microstructure of high-strength weathering steel that are transformed from austenite to ferrite. Ferrite stimulates carbon into austenite, which improves the stability of unconverted austenite, and its retained content generates a metastable γ′, which is γ→α + γ′. As the cooling process continues to the range of martensite transition point temperature, a martensite transition occurs in part of the metastable γ′. Thus, martensite and residual γ′ of this part of the transition are finally retained at room temperature, forming M/A constituents. The process is dominated by carbon diffusion. As shown in Figure 11, with a decrease in the finish rolling temperature, the time of the phase transition in the two-phase (α + γ) region is prolonged. This enriches the degree of C in γ′ increments, resulting in increased γ′ stability, which leads to the formation of a high content of M/A constituents at room temperature [2,3,19,20]. M/A constituents are mainly distributed at the boundary of GBF and PF, and their size and morphology are affected by the ferrite matrix structure [3,19,24]. With decreasing finish rolling temperature, GBF and PF slats are refined (Figure 5 and Figure 7a), causing a significant reduction in the size of M/A constituents and generating more fine, island-like M/A constituents.

4.2. Effect of Finish Rolling Temperature on Cryogenic Fracture Toughness

The size, morphology, and proportion of hard-phase M/A constituents affect the mechanical properties of steel [6,10,13,17,19]. Due to the presence of austenite and martensite, the hardness of M/A constituents is usually much higher than that of the adjacent matrix [3,16,19]. This causes a non-synergistic deformation of both phases during the deformation process, i.e., a local strain concentration occurs, which compromises performance. Large massive M/A or slender M/A constituents lead to microcrack formation, while small island M/A constituents increase critical stress (according to Griffith’s law), as well as effectively hinder the generation and propagation of secondary cracks [3,25,26,27]. As for cryogenic fracture toughness, when the finish rolling temperature was higher (840 °C), the average size of M/A constituents was large (Figure 4e and Table 3), and micro-cracks initiated and expanded at the coarse M/A constituents (Figure 12a). However, a lower finish rolling temperature significantly refined the size of M/A constituents and enhanced the content. This increased the critical stress of fracture and reduced the tendency of microcrack initiation [12,17,26]. The crack passes through the island M/A constituents were blocked, deflected, or terminated (Figure 12b), showing a certain ability to inhibit crack propagation.
On the other hand, the presence of a high fraction of HAGB in the sample could improve the capacity of the material to inhibit crack propagation, thereby improving the fracture toughness at low temperatures [1,3,26]. In this study, with a decrease in finish rolling temperature, the grain was refined and the PF content increased (belonging to HAGB [3,24]), which, in turn, gradually increased the proportion of HAGB in the sample. As shown in Figure 13a, microcrack propagation was observed in the expansion area of the ZZ840 specimen, showing a poor ability to hinder crack propagation. However, as for the ZZ780 sample, a microcrack growth process was observed in the expansion zone with frequent bending and deflection by HAGB, which requires more crack propagation energy, i.e., it had an excellent ability to hinder crack propagation. Thus, the low-temperature fracture toughness significantly increased with the decrease in finish rolling temperature.
As for this type of high-strength weathering steel which requires high corrosion resistance, various alloying elements such as Si, Cr, Ni, and Mo [2,4,5,26,27,28] usually need to be added. Unfortunately, this also leads to the formation of more dense hard-phase M/A constituents. According to the results of this paper, an appropriate low finish rolling temperature can significantly refine the size of M/A constituents and reduce the tendency of M/A constituents to germinate microcracks, which improves the fracture toughness. This provides an idea for the further development of the TMCP.

5. Conclusions

The microstructure and critical CTOD of a typical 500 MPa grade weathering steel with a varying finish rolling temperature were investigated in this work. The conclusions are as follows.
  • In the finish rolling temperature range of 780 to 840 °C, a GBF + PF + M/A constituent multiphase microstructure was formed in the typical 500 MPa grade weathering steel. With a decrease in finish rolling temperature, Ar3 increased, resulting in the increase of PF at the expense of the GBF. The area fraction of M/A constituents also increased, but their average size decreased significantly.
  • When the finish rolling temperature was decreased from 840 °C to 780 °C, the CTOD value increased significantly from 0.280 mm to 1.109 mm, the width of the crack propagation zone increased, and the fracture behavior changed from brittle fracture to ductile fracture.
  • With a decrease in the final rolling temperature, the increase in the fraction of HAGB improved the crack-hindering ability, and the decrease in the size of M/A constituents significantly reduced the tendency toward micro-crack initiation. Both of these resulted in a significant increase in cryogenic fracture toughness.

Author Contributions

Q.W. and J.W. conceived and designed the experiments; G.B. and Z.Z. performed the experiments; L.Z. and J.C. analyzed the data; Y.P. prepared the experimental steel and supervised the paper; and Q.W. and J.W. wrote the paper. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the National Key Research and Development Program of China (grant nos. 2017YFB0304800 and 2017YFB0304802 for the second subproject) and the Key Research and Development Program between Nanjing Iron & Steel United Co., Ltd. and Yanshan University (grant no. IGAB19060007).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Schematic diagram of TMCP of test steel.
Figure 1. Schematic diagram of TMCP of test steel.
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Figure 2. CTOD specimen drawing (W—width and a0—prefabricated crack length).
Figure 2. CTOD specimen drawing (W—width and a0—prefabricated crack length).
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Figure 3. Sampling method for secondary crack characterization of fracture cross-section.
Figure 3. Sampling method for secondary crack characterization of fracture cross-section.
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Figure 4. Optical micrographs (a–d) and SEM observations (e–h) of samples under different finish rolling temperatures: (a,e) ZZ840, (b,f) ZZ820, (c,g) ZZ800, and (d,h) ZZ780.
Figure 4. Optical micrographs (a–d) and SEM observations (e–h) of samples under different finish rolling temperatures: (a,e) ZZ840, (b,f) ZZ820, (c,g) ZZ800, and (d,h) ZZ780.
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Metals 13 01791 g005
Figure 5. TEM images of typical finish rolling temperature sample: (a) zz840, (b) zz780, and (c) M/A constituent brightfield image; darkfield image (d) and selected area electron diffraction (SAED) of zz780 specimen (e).
Figure 5. TEM images of typical finish rolling temperature sample: (a) zz840, (b) zz780, and (c) M/A constituent brightfield image; darkfield image (d) and selected area electron diffraction (SAED) of zz780 specimen (e).
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Metals 13 01791 g006
Figure 6. IPF plot of samples at different finish rolling temperatures: (a) zz840, (b) zz820, (c) zz800, and (d) zz780.
Figure 6. IPF plot of samples at different finish rolling temperatures: (a) zz840, (b) zz820, (c) zz800, and (d) zz780.
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Metals 13 01791 g007
Figure 7. MED varied with MTA (a) and distribution of grain boundary misorientation (b) for each sample obtained by EBSD.
Figure 7. MED varied with MTA (a) and distribution of grain boundary misorientation (b) for each sample obtained by EBSD.
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Metals 13 01791 g008
Figure 8. F-V curves of CTOD test for samples with different finish rolling temperatures: (a) ZZ840, (b) ZZ820, (c) ZZ800, and (d) ZZ780.
Figure 8. F-V curves of CTOD test for samples with different finish rolling temperatures: (a) ZZ840, (b) ZZ820, (c) ZZ800, and (d) ZZ780.
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Metals 13 01791 g009
Figure 9. Macroscopic fracture images of CTOD-tested specimen (a,e) ZZ840, (b,f) ZZ820, (c,g) ZZ800, and (d,h) ZZ780.
Figure 9. Macroscopic fracture images of CTOD-tested specimen (a,e) ZZ840, (b,f) ZZ820, (c,g) ZZ800, and (d,h) ZZ780.
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Metals 13 01791 g010
Figure 10. SEM observation of the fractures at different finish rolling temperatures: (a–c) zz840 and (d–f) zz780.
Figure 10. SEM observation of the fractures at different finish rolling temperatures: (a–c) zz840 and (d–f) zz780.
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Metals 13 01791 g011
Figure 11. Transition curves of Ar3 and Ar1 at different finish rolling temperatures.
Figure 11. Transition curves of Ar3 and Ar1 at different finish rolling temperatures.
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Metals 13 01791 g012
Figure 12. Observation of secondary crack in CTOD specimen fracture sections: (a) zz840 and (b) zz780.
Figure 12. Observation of secondary crack in CTOD specimen fracture sections: (a) zz840 and (b) zz780.
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Metals 13 01791 g013
Figure 13. Observation of secondary crack in the extension zone of the fracture section of CTOD specimens: (a) zz840 and (b) zz780.
Figure 13. Observation of secondary crack in the extension zone of the fracture section of CTOD specimens: (a) zz840 and (b) zz780.
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Table 1. Chemical composition of 500 MPa weathering bridge steel (wt.%).
Table 1. Chemical composition of 500 MPa weathering bridge steel (wt.%).
IngredientCSiMnPSCu + Cr + Ni + MoNb + V + TiAlFe
Content0.050.301.480.0130.001.370.0600.029Bal.
Table 2. Measured TMCP parameters at different finish rolling temperatures.
Table 2. Measured TMCP parameters at different finish rolling temperatures.
SampleRRFT/°CFRST/°CFRFT/°CSCT/°CFCT/°CCooling Rate/°C/s
zz840102586084177049510
zz820103486282076349010
zz800104285779577349210.5
zz78010438657867715019.5
RRFT—rough rolling finish temperature; FRST—finish rolling start temperature; FRFT—finish rolling finish temperature; SCT—start cooling temperature; FCT—finish cooling temperature.
Table 3. Summary of the microstructure observations and quantifications.
Table 3. Summary of the microstructure observations and quantifications.
SamplefM/A
/%		dM/A
/μm		MED(θ≥15°)
/μm		f(θ ≥ 15)
/%
zz8407.56 ± 0.152.16 ± 0.153.7044.8
zz8208.32 ± 0.351.82 ± 0.082.9648.7
zz8009.7 ± 0.31.42 ± 0.082.5849.5
zz78010.12 ± 0.411.22 ± 0.052.2053.1
Table 4. Characteristic values corresponding to different finish rolling temperatures.
Table 4. Characteristic values corresponding to different finish rolling temperatures.
Samplezz840zz820zz800zz780
CTOD value (mm)0.280 ± 0.050.393 ± 0.040.933 ± 0.061.109 ± 0.04
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MDPI and ACS Style

Wu, J.; Bai, G.; Zhao, L.; Zhang, Z.; Peng, Y.; Chu, J.; Wang, Q. Effects of Finish Rolling Temperature on the Critical Crack Tip Opening Displacement (CTOD) of Typical 500 MPa Grade Weathering Steel. Metals 2023, 13, 1791. https://doi.org/10.3390/met13101791

AMA Style

Wu J, Bai G, Zhao L, Zhang Z, Peng Y, Chu J, Wang Q. Effects of Finish Rolling Temperature on the Critical Crack Tip Opening Displacement (CTOD) of Typical 500 MPa Grade Weathering Steel. Metals. 2023; 13(10):1791. https://doi.org/10.3390/met13101791

Chicago/Turabian Style

Wu, Junping, Guangming Bai, Liyang Zhao, Zhongde Zhang, Yan Peng, Juefei Chu, and Qingfeng Wang. 2023. "Effects of Finish Rolling Temperature on the Critical Crack Tip Opening Displacement (CTOD) of Typical 500 MPa Grade Weathering Steel" Metals 13, no. 10: 1791. https://doi.org/10.3390/met13101791

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