Structural Aspects of Execution and Thermal Treatment of Welded Joints of Hardox Extreme Steel
Abstract
:1. Introduction
2. Material and Methodology
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- weld type: BW (butt weld),
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- welding position: PA (flat),
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- electrode diameter: 3.0 mm,
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- arc voltage (weld layer: 1, 2): 34/35 V,
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- amperage (weld layer: 1, 2): 520/640 A,
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- polarity: DC(+),
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- welding rate (weld layer: 1, 2): 61/63 cm/min,
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- electrode wire: OK Autrod 13.43 (S3Ni2.5CrMo acc. to EN ISO 26304),
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- flux: OK Flux 10.62,
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- preheating: no,
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- interpass temperature: ≤100 °C,
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- preparation of sheet edges (chamfering): no.
3. Results
3.1. Mechanical Properties
3.2. Results of Microscopic Examinations and Hardness Measurements
3.3. Results of Fractographic Analysis
4. Summary
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- After welding, a highly morphologically diversified microstructure occurs in the entire area of the welded joint that shows, in comparison to the base material, lower hardness levels, tensile strength and impact energy. The obtained and relatively low mechanical properties of the welded joint make it possible to state that welding operations result in lowering the abrasive-wear resistance of the steel Hardox Extreme. The expected drop can occur in both the weld material and the area of base material directly adjacent to the very wide heat-affected zone.
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- The additional thermal treatments carried-out after welding make it possible to favorably modify the structure in the entire welded joint and wide heat-affected zone, to obtain the structures similar to those of Hardox Extreme steel in the as-delivered condition from the manufacturer’s plant.
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- The obtained average hardness level of the welded joint after welding, amounting to only 17 J/cm2 at +20 °C, clearly indicates susceptibility of this steel to brittle cracking. From practical point of view, it excludes application of welding techniques for joining Hardox Extreme sheets (irrespective of the relatively very high average tensile strength Rm = 1278 MPa obtained) with no additional heat treatment operations. The above statement is additionally confirmed by the performed fractographic analysis.
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- Examination results of heat-treated welded joints of Hardox Extreme steel indicate a possibility of restoring structural, mechanical, and impact properties “degraded” as a result of welding to the level corresponding to the base material. In the case of tensile strength, the obtained result Rm = 1831 MPa makes a good reason for undertaking the problems of welding and heat treatment of the considered steel. An additional justification of this question is also obtained through heat treatment of other mechanical properties that are much better than those existing in the as-welded condition. In spite of a significant increase of the Rm value (and also of the yield point, not cited in the reference), a nearly 12% increase percentage reduction of area reaching Z = 29.1% (Table 5) was noted, as well as an increase of impact strength at ambient temperature to KCV = 27 J/cm2. It is worth noting that the brittleness threshold of constructional materials is accepted as impact strength of 35 J/cm2 [30], which results from maintaining at least 50% share of ductile fracture. Therefore, the obtained impact strength value after heat treatment and results of fractographic analysis make it possible to conclude that there was an occurrence of a favorable “shift” of plastic properties of the welded joint beyond the accepted brittleness threshold.
Funding
Acknowledgments
Conflicts of Interest
References
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Grade of Steel | Rp0.2 | Rm | A5 | KCV−40 | HBW |
---|---|---|---|---|---|
[MPa] | [MPa] | [%] | [J/cm2] | ||
Hardox 400 | 1100 | 1250 | 10 | 56 | 370–430 |
Hardox 450 | 1200 | 1400 | 10 | 50 | 425–475 |
Hardox 500 | 1400 | 1550 | 10 | 46 | 470–530 |
Hardox 600 | 1650 | 2000 | 7 | 25 | 570–640 |
Hardox Extreme | NA | NA | NA | NA | 650–700 |
Brinar 400 | 900 | 1200 | 12 | 25 (−20 °C) | 340–440 |
Brinar 500 | 1350 | 1500 | 8 | 25 (−20 °C) | 480 |
XAR 600 | 1700 | 2000 | 8 | 25 (−20 °C) | >550 |
Element | Hardox | Brinar | XAR 600 | |||||
---|---|---|---|---|---|---|---|---|
400 | 450 | 500 | 600 | Extreme | 400 | 500 | ||
Selected Element [wt%] | ||||||||
C | 0.32 | 0.26 | 0.30 | 0.45 | 0.47 | 0.18 | 0.28 | 0.40 |
Mn | 1.60 | 1.60 | 1.60 | 1.40 | 1.40 | 2.00 | 1.50 | 1.50 |
Si | 0.70 | 0.70 | 0.70 | 0.70 | 0.50 | 0.50 | 0.80 | 0.80 |
P | 0.025 | 0.025 | 0.020 | 0.015 | 0.015 | 0.015 | 0.020 | 0.025 |
S | 0.010 | 0.010 | 0.010 | 0.010 | 0.010 | 0.005 | 0.005 | 0.010 |
Cr | 2.40 | 1.40 | 1.50 | 1.20 | 1.20 | 1.55 | 1.50 | 1.50 |
Ni | 1.50 | 1.50 | 1.50 | 2.50 | 2.50 | NA | NA | 1.50 |
Mo | 0.60 | 0.60 | 0.60 | 0.70 | 0.80 | 0.60 | 0.40 | 0.50 |
B | 0.004 | 0.005 | 0.005 | 0.005 | 0.005 | 0.005 | NA | 0.005 |
# [mm] | 8–20 | 10–19.9 | 4–13 | 6–35 | 8–19 | ≤80 | ≤60 | 15 |
CEVT | 0.44 | 0.48 | 0.51 | 0.66 | 0.66 | NA | NA | 0.79 |
CETT | 0.28 | 0.36 | 0.37 | 0.55 | 0.55 | NA | NA | 0.53 |
Element | Hardox Steels | Brinar Steels | XAR 600 | |||||
---|---|---|---|---|---|---|---|---|
400 | 450 | 500 | 600 | Extreme | 400 | 500 | ||
Selected Element [wt%] | ||||||||
C | 0.17 | 0.17 | 0.28 | 0.45 | 0.48 | 0.17 | 0.28 | 0.37 |
Mn | 1.00 | 1.00 | 0.69 | 0.51 | 0.52 | 1.14 | 0.95 | 0.85 |
Si | 0.37 | 0.32 | 0.26 | 0.16 | 0.16 | 0.22 | 0.66 | 0.19 |
P | 0.010 | 0.010 | 0.011 | 0.012 | 0.010 | 0.008 | 0.012 | 0.014 |
S | 0.002 | 0.000 | 0.001 | 0.002 | 0.001 | 0.000 | 0.000 | 0.001 |
Cr | 0.22 | 0.45 | 0.66 | 0.33 | 0.89 | 0.60 | 0.84 | 0.83 |
Ni | 0.05 | 0.05 | 0.08 | 1.98 | 1.96 | 0.38 | 0.01 | 1.21 |
Mo | 0.01 | 0.08 | 0.03 | 0.14 | 0.13 | 0.30 | 0.20 | 0.15 |
V | 0.004 | 0.005 | 0.010 | 0.009 | 0.008 | 0.039 | 0.006 | 0.002 |
Cu | 0.006 | 0.018 | 0.016 | 0.016 | 0.021 | 0.010 | 0.008 | 0.030 |
Al | 0.035 | 0.032 | 0.050 | 0.031 | 0.034 | 0.073 | 0.039 | 0.097 |
Ti | 0.020 | 0.016 | 0.005 | 0.006 | 0.006 | 0.009 | 0.012 | 0.003 |
Nb | 0.010 | 0.000 | 0.000 | 0.005 | 0.001 | 0.043 | 0.023 | 0.009 |
Co | 0.010 | 0.016 | 0.017 | 0.026 | 0.022 | 0.001 | 0.005 | 0.005 |
B | 0.0016 | 0.0014 | 0.0016 | 0.0026 | 0.0025 | 0.0023 | 0.0008 | 0.0021 |
# [mm] | 8 | 10 | 10 | 10 | 10 | 12 | 12 | 15 |
CEV | 0.38 | 0.44 | 0.54 | 0.76 | 0.90 | 0.58 | 0.65 | 0.79 |
CET | 0.28 | 0.30 | 0.39 | 0.58 | 0.64 | 0.36 | 0.43 | 0.54 |
Weld Metal | C | Mn | Si | Cr | Ni | Mo | Rp0.2 | Rm | A4 | KCV−40 |
---|---|---|---|---|---|---|---|---|---|---|
Chemical Composition [%] | [MPa] | [%] | [J/cm2] | |||||||
OK Autrod 13.43 + OK Flux 10.62 | 0.11 | 1.50 | 0.25 | 0.60 | 2.20 | 0.50 | 700 | 800 | 21 | 94 |
Specimen | Heat Treatment Parameters | Rm | Z | KCV+20 | KCV−40 | ||||
---|---|---|---|---|---|---|---|---|---|
[MPa] | [%] | [J/cm2] | |||||||
UTS-1 | No treatment | 1329 | 1278 | 26.0 | 17.4 | --- | |||
UTS-2 | 1263 | 16.3 | |||||||
UTS-3 | 1242 | 10.1 | |||||||
KCV-1 | --- | 18.7 | 17 | --- | |||||
KCV-2 | 16.4 | ||||||||
KCV-3 | 16.6 | ||||||||
KCV-4 | --- | 14.3 | 18 | ||||||
KCV-5 | 12.7 | ||||||||
KCV-6 | 26.1 | ||||||||
UTS-25 | Normalization: 800 °C/1h/Air + Quenching: 850 °C/20′/Oil + Tempering: 100 °C/20h/Air | 1831 | 1831 | 30.6 | 29.1 | --- | |||
UTS-26 | 1823 | 31.6 | |||||||
UTS-28 | 1839 | 25.2 | |||||||
KCV-7 | --- | 27.1 | 27 | --- | |||||
KCV-8 | 27.9 | ||||||||
KCV-9 | 25.9 | ||||||||
KCV-10 | --- | 21.6 | 19 | ||||||
KCV-11 | 17.1 | ||||||||
KCV-12 | 19.0 |
Element | X | Y | Z | OK 13.43 + OK Flux 10.62 | Hardox Extreme |
---|---|---|---|---|---|
Chemical Composition [wt%] | |||||
C | 0.31 | 0.32 | 0.31 | 0.10 | 0.48 |
Mn | 0.81 | 0.82 | 0.81 | 1.22 | 0.52 |
Si | 0.23 | 0.23 | 0.23 | 0.30 | 0.16 |
P | 0.013 | 0.013 | 0.014 | 0.020 | 0.010 |
S | 0.002 | 0.002 | 0.002 | 0.002 | 0.001 |
Cr | 0.81 | 0.82 | 0.81 | 0.50 | 0.89 |
Ni | 2.06 | 2.08 | 2.07 | 1.65 | 1.96 |
Mo | 0.23 | 0.23 | 0.22 | 0.31 | 0.13 |
V | 0.009 | 0.009 | 0.010 | 0.009 | 0.008 |
Cu | 0.040 | 0.038 | 0.041 | 0.105 | 0.021 |
Al | 0.020 | 0.021 | 0.020 | 0.013 | 0.034 |
Ti | 0.004 | 0.004 | 0.005 | 0.003 | 0.006 |
Nb | 0.000 | 0.000 | 0.000 | 0.000 | 0.001 |
Co | 0.017 | 0.016 | 0.018 | 0.006 | 0.022 |
B | 0.0021 | 0.0021 | 0.0021 | 0.0014 | 0.0025 |
CEV | 0.79 | 0.80 | 0.80 | 0.59 | 0.90 |
CET | 0.51 | 0.51 | 0.51 | 0.33 | 0.64 |
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Konat, Ł. Structural Aspects of Execution and Thermal Treatment of Welded Joints of Hardox Extreme Steel. Metals 2019, 9, 915. https://doi.org/10.3390/met9090915
Konat Ł. Structural Aspects of Execution and Thermal Treatment of Welded Joints of Hardox Extreme Steel. Metals. 2019; 9(9):915. https://doi.org/10.3390/met9090915
Chicago/Turabian StyleKonat, Łukasz. 2019. "Structural Aspects of Execution and Thermal Treatment of Welded Joints of Hardox Extreme Steel" Metals 9, no. 9: 915. https://doi.org/10.3390/met9090915