The post weld heat treatment (PWHT) was used to reduce the level of the residual stresses and increase of the crack resistance of the material in the connection part. The article presents the results of the residual stress measurements immediately after welding and after the stress relaxation by the PWHT

I. Samardžić

Lj. Milović

M. Zrilić

T. Vuherer

V. Gliha

English

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243METALURGIJA 53 (2014) 2, 243-246T. VUHERER, M. ZRILIĆ, Lj. MILOVIĆ, I. SAMARDŽIĆ, V. GLIHA SUITABILITY OF HEAT TREATMENT FOR CRACK RESISTANCE OF MATERIAL IN THE CONNECTION PART OF HEAVY TRANSPORTER FOR LIQUID SLAG Received – Prispjelo: 2013-02-15Accepted – Prihvaćeno: 2013-08-28Preliminary Note – Prethodno priopćenjeISSN 0543-5846METABK 53(2) 243-246 (2014)UDC – UDK 621.791.057:621.78:620.16=111T. Vuherer, V. Gliha, University of Maribor, Faculty of Mechanical En-gineering, S lovenia, , M . Z rilić, L j. M ilović, Un iversity o f B elgrade, Faculty of Technology and Metallurgy, Serbia, I. Samardžić, Mechani-cal engineering faculty in Slavonski Brod, University of OsijekThe post weld heat treatment (PWHT) was used to reduce the level of the residual stresses and increase of the crack resistance of the material in the connection part. The article presents the results of the residual stress measurements immediately after welding and after the stress relaxation by the PWHT. Key words: weld, heat treatment, residual stress, stress relaxation, crack resistanceINTRODUCTIONResidual stresses (RSs) arise due to local plastic de-formation. The plastic deformations always occur dur -ing welding by melting. The fi rst such mechanism which generates RSs is hindering contraction resulting from local heating during welding process [1-3]. As a result, RSs arise due to hindering shrinkage. The second cause is the microstructural transformation, where suffi ciently heated part of materials are transformed during cooling, so the crystal lattice with surface centred cube changes into crystal lattice with body centred cube [2,4]. The weld metal and part of the heat affected zone areas have tendency to increase their volumes during transforma-tion, but the colder not transformed material in the sur -rounding area hinder their expansion. As a result, RSs arise due to microstructural transformation. The fi nal level of the RSs depends on interaction of the two mechanisms which generated RSs, temperature when the transformation occurs, heat input during the weld-ing and constraint of the construction during the weld-ing [2]. It is desirable that welded constructions after welding have low level of the RSs, because they can have a harmful infl uence. Tensile RSs are the most un-desirable, because they try to open small welding de-fects. This can lead to cracks initiation on the welding defects and their further propagation [5,6]. When the level of the RSs is high, various methods are used to reduce the RSs, for example post weld heat treatment (PWHT), vibration during welding, vibration after welding, local plastic deformation etc [2,4]. The PWHT is the one of the most ef fective methods for relaxation of the RSs, where hardness and yield stress of the mate-rial is also reduced and impact toughness is normally increased [2]. The method is appropriate for low alloy construction steels, but more problems occur with its use at micro-alloyed and HSLA steels due to precipita-tion of carbides. This article deals with RSs measure-ments on the connection part of the hinge joint of the mobile transporter’s construction for transport of liquid slag. It’s construction weights 120 tons and can carry 90 tons of liquid slag. During exploitation on the connec-tion part of the transporter crack initiated and propagate until transporter need to be serviced. Figure 1 shows the mobile transporter for liquid slag, the rear part of the transporter and location where crack appeared in ex-ploitation (detail A).It has been proved during the exploitation that the vital part is the connection part of the hinge joint, which has to be as small as possible to ensure manoeuvrability of the mobile transporter . As a result, it is heavily dy-namically loaded, because it connects the front part of the mobile transporter and the rear loading part of the transporter’s construction where there is the pot for transport of the liquid slag. High tensile RSs in this part of the mobile transporter ’s construction are not desira-ble, because they can have a harmful infl  uence. The PWHT is used on the connection part to relax RSs gen-erated at welding process. The RSs were measured by using magnetic method in the ‘’as welded’ ’ condition and in the ‘’PWHT’’ condition..EXPERIMENTAL PROCEDUREThe 40 mm thick material S355 J2 was used for ex-perimental investigation as a base material. MAG weld-ing process was used for welding. The gas mixture of 82 % Ar and 18 % CO2 and welding fi ller material VAC 60 ∅1.2 mm were used at welding. Mechanical properties are shown in Table 1. The connection part during manufacturing by weld-ing is presented in Figure 2.244  METALURGIJA 53 (2014) 2, 243-246T. VUHERER et al.: SUITABILITY OF HEAT TREATMENT FOR CRACK RESISTANCE OF MATERIAL IN THE...Post weld heat treatment was performed in the fur -nace. The heating speed was 140 °C/h. The connection part was held for 2 h at temperature of 590 °C and then it was cool down in the furnace. The cooling speed was 100 °C/h. When the connection part reached 200 °C, it was cooled down in the air . Vickers Hardness HV10 were measured in the in the weld joint in the vicinity where crack initiate and propagate in exploitation in the connection part of the hinge joint. Hardness were meas-ured in “as welded” condition and post weld heat treated condition (“PWHT”) as well. Three different magnetic methods exist for measuring of RSs [1]. The fi rst is In-duced Magnetic Anisotropy Method, the second is Berkhausen Emissions Method and the last is Magnetic Acoustic Emission Method [7]. The Induced Magnetic Anisotropy Method is used for the experimental meas-urements. We have measured the dif ference between principal RSs and their direction. The calibration of the method was necessary to be performed on the same ma-terial before measurements. For this purpose the fl  at tensile specimen (40 × 20 mm) was machined from steel S355 J2. The calibration curve is shown in Figure 3.Firstly, the RSs were measured by the magnetic method on the connection part after manufacturing. They were measured immediately after welding, there-fore in ‘’as welding’ ’ condition. The locations of the measurements are shown in Figure 4 on the left side. Secondly, the connection part was PWHT and then RSs were measured again by using the magnetic method on the same locations to get the level of the RSs in ‘’PWHT’’ condition.  Figure 1  Mobile transporter for slag: a) transporter and detail A where is connection part of the hinge joint located, b) rear part of the transporter, c) connection part and the hinge joint, d) crack in the connection part of the hinge joint in exploitationTable 1  Mechanical properties of the base and fi ller materialsMaterial Rp0,2 / MPa Rm / MPa A5 / % KV / J (20 °C)Base mat. 459 551 25 146Filler mat. 410 550 22 47Figure 2  The connection part of the transporter’s construction during manufacturing, a) before welding, b) after welding245METALURGIJA 53 (2014) 2, 243-246T. VUHERER et al.: SUITABILITY OF HEAT TREATMENT FOR CRACK RESISTANCE OF MATERIAL IN THE...- at the position 2 in the corner of paths (I. – II.), -  at position 3 in corners of paths (I. – II. and IV . – I.), where the welds are cross each other and those parts  of material are heavily dynamically loaded in exploita-tion. In those regions cracks started to appear on the most heavily loaded mobile transporters in practice, which did not use PWHT for relaxation of the RSs in the connection part of hinge joint. Appropriate results in Figure 5 in  RESULTS AND DISCUSSIONResults of hardness measurement HV10 are shown in Figure 4. Hardness were measured in weld metal - WM, heat affected zone - HAZ and base material – BM. Figure 4a shows results in ‘’As welded’ ’ condition and Figure 4b shows results in ‘’’PWHT’’ condition. Meas-urements were performed in weld joint in the vicinity where crack appeared in exploitation. The infl uences of macro and micro RSs (I., II. and III. order) together are possible to be measured by the magnetic method, but only the differences of the princi-pal RSs and their directions can be obtained. Figure 5 shows the results of RSs measurements on the connec-tion part of the hinge joint at in the ˝as welded˝ and the ˝PWHT˝ conditions. The roman numbers in Figure 5 on the right side corresponds to the measurement paths, which are shown on the left side. The important is the fact that relaxed RSs are as small as possible in ˝PWHT˝ condition in some special regions:-  at the position 1 in corners of paths (I. – II and II. – III.),Figure 3 The calibration curve Figure 4  Results of hardness measurements; a) ‘’As welded’’ condition, b) ‘’PWHT’’ conditionsFigure 5  The results of RSs measurements In ˝as welded˝ and ˝PWHT˝ conditions; for position 1(a), for position 2(b) and for  position 3(c)246  METALURGIJA 53 (2014) 2, 243-246T. VUHERER et al.: SUITABILITY OF HEAT TREATMENT FOR CRACK RESISTANCE OF MATERIAL IN THE...those regions show that the RSs relaxed more than 50 % in dif ferences between principal RSs after the PWHT . Hardness in those regions is also reduced by PWHT what infl uence on decreasing of impact toughness and increas-ing of the crack resistance of the material. The regime of the PWHT for relaxation of RSs is adequate and enables  safe operations of the mobile transporter for liquid slag in future. In particular mobile transporter where crack ap-peared in exploitation, the connection part of the hinge  joint was cut and replaced by new one which had been  PWHT before. Another safety step which was performed in this mobile transporter are additional ribs which were  welded in the positions where cracks appeared before in  order to reduce the load and increase the safety and crack resistance of the material of the mobile transporter . Mo-bile transporter still works in exploitation without any  problems. CONCLUSIONSThe post weld heat treatment (PWHT) was used for RSs relaxation on the connection part of 120 tone mo-bile transporter for transport of the liquid slag. RSs were measured by magnetic method in the ˝as welded˝ condi-tion immediately after welding and in ˝PWHT˝ condi-tion after the heat treatment. The differences of the prin-cipal RSs were lowered for more than 50 % in regions where cracks appear in exploitation of the heavily load-ed mobile transporter which used connection part in ˝as welded˝ conditions so the PWHT  regime (590 °C/2h) was appropriate. Another safety measure in company is that additional ribs were welded in the positions where cracks appeared before in practice during fabrication of the connection part before PWHT in order to reduce the load and increase crack resistance of the material and safety of the mobile transporter. Particular mobile trans-porter where crack appeared in exploitation, after two years, still works in practice since it has been serviced and connection part of hinge joint was replaced by new one which had been post weld heat treated before.REFERENCES[1] D. M. Finch, Rewiew of Non Destructive Residual Stress Measurement Techniques; ERA Internal Report 94/0101R, 1994, pp. 1-35.[2] T. Vuherer, L. Milović, , I. Samardžić, M. Zrilić, Strojarst-vo, 51(2009)4, 323-331.[3] F. Trebunja, F. Šimčák, J. Bocko, P. Šarga, P. Trebunja, M. Pástor, J. Mihok, Metalurgija 47(2008)2, 133-137.[4] A. Ghosh, S. Chattopadhyaya, S. Hloch, Tehnički vjesnik 19(2012)3, 617-620.[5]  R. Chaari, M. Abdennadher, J. Louati, M. Haddar, Interna-tiona Journal of Simulation Modelling, 10(2011)2, 66-77.[6] M. Burzić, R. Prokić-Cvetković, M. Manjgo, Lj. Milović, M. Arsić, O. Popovićl, Structural Integrity and Life, 12(2012)3, 215-220.[7] L. Lipus C., B. Acko, A. Hamler, International Journal of Simulation Modelling, 11(2012)3, 141-149.Note:  Responsible person for English translation: M. Šuto, M.A., J.J. Strossmayer University of Osijek, Croatia

Suitability of heat treatment for crack resistance of material in the connection part of heavy transporter for liquid slag

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243 METALURGIJA 53 (2014) 2, 243-246T. VUHERER, M. ZRILIĆ, Lj. MILOVIĆ, I. SAMARDŽIĆ, V. GLIHA SUITABILITY OF HEAT TREATMENT FOR CRACK RESISTANCE OF MATERIAL IN THE CONNECTION PART OF HEAVY TRANSPORTER FOR LIQUID SLAG Received – Prispjelo: 2013-02-15Accepted – Prihvaćeno: 2013-08-28Preliminary Note – Prethodno priopćenjeISSN 0543-5846METABK 53(2) 243-246 (2014)UDC – UDK 621.791.057:621.78:620.16=111T. Vuherer, V. Gliha, University of Maribor, Faculty of Mechanical En-gineering, Slovenia, , M . Zrilić, Lj. Milović, University of Belgrade, Faculty of Technology and Metallurgy, Serbia, I. Samardžić, Mechani-cal engineering faculty in Slavonski Brod, University of OsijekThe post weld heat treatment (PWHT) was used to reduce the level of the residual stresses and increase of the crack resistance of the material in the connection part. The article presents the results of the residual stress measurements immediately after welding and after the stress relaxation by the PWHT. Key words: weld, heat treatment, residual stress, stress relaxation, crack resistanceINTRODUCTIONResidual stresses (RSs) arise due to local plastic de-formation. The plastic deformations always occur dur -ing welding by melting.  The ﬁ  rst such mechanism which generates RSs is hindering contraction resulting from local heating during welding process [1-3]. As a result, RSs arise due to hindering shrinkage. The second cause is the microstructural transformation, where sufﬁ  ciently heated part of materials are transformed during cooling, so the crystal lattice with surface centred cube changes into crystal lattice with body centred cube [2,4].  The weld metal and part of the heat af fected zone areas have tendency to increase their volumes during transforma-tion, but the colder not transformed material in the sur-rounding area hinder their expansion.  As a result, RSs arise due to microstructural transformation.  The ﬁ nal level of the RSs depends on interaction of the two mechanisms which generated RSs, temperature when the transformation occurs, heat input during the weld-ing and constraint of the construction during the weld-ing [2]. It is desirable that welded constructions after welding have low level of the RSs, because they can have a harmful inﬂ uence. Tensile RSs are the most un-desirable, because they try to open small welding de-fects. This can lead to cracks initiation on the welding defects and their further propagation [5,6].  When the level of the RSs is high, various methods are used to reduce the RSs, for example post weld heat treatment (PWHT), vibration during welding, vibration after welding, local plastic deformation etc [2,4]. The PWHT is the one of the most ef fective methods for relaxation of the RSs, where hardness and yield stress of the mate-rial is also reduced and impact toughness is normally increased [2]. The method is appropriate for low alloy construction steels, but more problems occur with its use at micro-alloyed and HSLA steels due to precipita-tion of carbides.  This article deals with RSs measure-ments on the connection part of the hinge joint of the mobile transporter’s construction for transport of liquid slag. It’s construction weights 120 tons and can carry 90 tons of liquid slag. During exploitation on the connec-tion part of the transporter crack initiated and propagate until transporter need to be serviced. Figure 1 shows the mobile transporter for liquid slag, the rear part of the transporter and location where crack appeared in ex-ploitation (detail A).It has been proved during the exploitation that the vital part is the connection part of the hinge joint, which has to be as small as possible to ensure manoeuvrability of the mobile transporter. As a result, it is heavily dy-namically loaded, because it connects the front part of the mobile transporter and the rear loading part of the transporter’s construction where there is the pot for transport of the liquid slag. High tensile RSs in this part of the mobile transporter’s construction are not desira-ble, because they can have a harmful inﬂ  uence. The PWHT is used on the connection part to relax RSs gen-erated at welding process.  The RSs were measured by using magnetic method in the ‘’as welded’ ’ condition and in the ‘’PWHT’’ condition..EXPERIMENTAL PROCEDUREThe 40 mm thick material S355 J2 was used for ex-perimental investigation as a base material. MAG weld-ing process was used for welding.  The gas mixture of 82 % Ar and 18 % CO2 and welding ﬁ  ller material VAC 60 ∅1.2 mm were used at welding. Mechanical properties are shown in Table 1. The connection part during manufacturing by weld-ing is presented in Figure 2.244   METALURGIJA 53 (2014) 2, 243-246T. VUHERER et al.: SUITABILITY OF HEAT TREATMENT FOR CRACK RESISTANCE OF MATERIAL IN THE...Post weld heat treatment was performed in the fur -nace. The heating speed was 140 °C/h. The connection part was held for 2 h at temperature of 590 °C and then it was cool down in the furnace. The cooling speed was 100 °C/h. When the connection part reached 200 °C, it was cooled down in the air . Vickers Hardness HV10 were measured in the in the weld joint in the vicinity where crack initiate and propagate in exploitation in the connection part of the hinge joint. Hardness were meas-ured in “as welded” condition and post weld heat treated condition (“PWHT”) as well. Three different magnetic methods exist for measuring of RSs [1]. The ﬁ  rst is In-duced Magnetic  Anisotropy Method, the second is Berkhausen Emissions Method and the last is Magnetic Acoustic Emission Method [7]. The Induced Magnetic Anisotropy Method is used for the experimental meas-urements. We have measured the dif ference between principal RSs and their direction. The calibration of the method was necessary to be performed on the same ma-terial before measurements. For this purpose the ﬂ  at tensile specimen (40 × 20 mm) was machined from steel S355 J2. The calibration curve is shown in Figure 3.Firstly, the RSs were measured by the magnetic method on the connection part after manufacturing. They were measured immediately after welding, there-fore in ‘’as welding’ ’ condition.  The locations of the measurements are shown in Figure 4 on the left side. Secondly, the connection part was PWHT and then RSs were measured again by using the magnetic method on the same locations to get the level of the RSs in ‘’PWHT’ ’ condition.  Figure 1   Mobile transporter for slag: a) transporter and detail A where is connection part of the hinge joint located, b) rear part of the transporter, c) connection part and the hinge joint, d) crack in the connection part of the hinge joint in exploitationTable 1   Mechanical properties of the base and fi  ller materialsMaterial Rp0,2 / MPa Rm / MPa A5 / % KV / J (20 °C)Base mat. 459 551 25 146Filler mat. 410 550 22 47Figure 2   The connection part of the transporter’s construction during manufacturing, a) before welding, b) after welding245 METALURGIJA 53 (2014) 2, 243-246T. VUHERER et al.: SUITABILITY OF HEAT TREATMENT FOR CRACK RESISTANCE OF MATERIAL IN THE...- at the position 2 in the corner of paths (I. – II.), -   at position 3 in corners of paths (I. – II. and IV . – I.), where the welds are cross each other and those parts  of material are heavily dynamically loaded in exploita-tion. In those regions cracks started to appear on the most  heavily loaded mobile transporters in practice, which did not use PWHT for relaxation of the RSs in the connection  part of hinge joint.  Appropriate results in Figure 5 in  RESULTS AND DISCUSSIONResults of hardness measurement HV10 are shown in Figure 4. Hardness were measured in weld metal - WM, heat affected zone - HAZ and base material – BM. Figure 4a shows results in ‘’As welded’’ condition and Figure 4b shows results in ‘’’PWHT’’ condition. Meas-urements were performed in weld joint in the vicinity where crack appeared in exploitation. The inﬂ  uences of macro and micro RSs (I., II. and III. order) together are possible to be measured by the magnetic method, but only the differences of the princi-pal RSs and their directions can be obtained. Figure 5 shows the results of RSs measurements on the connec-tion part of the hinge joint at in the ˝as welded˝ and the ˝PWHT˝ conditions. The roman numbers in Figure 5 on the right side corresponds to the measurement paths, which are shown on the left side. The important is the fact that relaxed RSs are as small as possible in ˝PWHT˝ condition in some special regions:-   at the position 1 in corners of paths (I. – II and II. – III.),Figure 3 The calibration curve Figure 4   Results of hardness measurements; a) ‘’As welded’’ condition, b) ‘’PWHT’’ conditionsFigure 5  The results of RSs measurements In ˝as welded˝ and ˝PWHT˝ conditions; for position 1(a), for position 2(b) and for  position 3(c)246   METALURGIJA 53 (2014) 2, 243-246T. VUHERER et al.: SUITABILITY OF HEAT TREATMENT FOR CRACK RESISTANCE OF MATERIAL IN THE...those regions show that the RSs relaxed more than 50 % in differences between principal RSs after the PWHT . Hardness in those regions is also reduced by PWHT  what inﬂ  uence on decreasing of impact toughness and increas-ing of the crack resistance of the material. The regime of the PWHT for relaxation of RSs is adequate and enables safe operations of the mobile transporter for liquid slag in  future. In particular mobile transporter where crack ap-peared in exploitation, the connection part of the hinge  joint was cut and replaced by new one which had been  PWHT before. Another safety step which was performed in this mobile transporter are additional ribs which were  welded in the positions where cracks appeared before in  order to reduce the load and increase the safety and crack  resistance of the material of the mobile transporter . Mo-bile transporter still works in exploitation without any  problems. CONCLUSIONSThe post weld heat treatment (PWHT) was used for RSs relaxation on the connection part of 120 tone mo-bile transporter for transport of the liquid slag. RSs were measured by magnetic method in the ˝as welded˝ condi-tion immediately after welding and in ˝PWHT˝ condi-tion after the heat treatment.  The differences of the prin-cipal RSs were lowered for more than 50 % in regions where cracks appear in exploitation of the heavily load-ed mobile transporter which used connection part in ˝as welded˝ conditions so the PWHT  regime (590 °C/2h) was appropriate. Another safety measure in company is that additional ribs were welded in the positions where cracks appeared before in practice during fabrication of the connection part before PWHT in order to reduce the load and increase crack resistance of the material and safety of the mobile transporter . Particular mobile trans-porter where crack appeared in exploitation, after two years, still works in practice since it has been serviced and connection part of hinge joint was replaced by new one which had been post weld heat treated before.REFERENCES[1]  D. M. Finch, Rewiew of Non Destructive Residual Stress Measurement Techniques; ERA Internal Report 94/0101R, 1994, pp. 1-35.[2]  T. Vuherer, L. Milović, , I. Samardžić, M. Zrilić, Strojarst-vo, 51(2009)4, 323-331.[3]  F. Trebunja, F. Šimčák, J. Bocko, P. Šarga, P. Trebunja, M. Pástor, J. Mihok, Metalurgija 47(2008)2, 133-137.[4]  A. Ghosh, S. Chattopadhyaya, S. Hloch,  Tehnički vjesnik 19(2012)3, 617-620.[5]   R. Chaari, M. Abdennadher, J. Louati, M. Haddar, Interna-tiona Journal of Simulation Modelling, 10(2011)2, 66-77.[6]  M. Burzić, R. Prokić-Cvetković, M. Manjgo, Lj. Milović, M.  Arsić, O. Popovićl, Structural Integrity and Life, 12(2012)3, 215-220.[7]  L. Lipus C., B. Acko, A. Hamler, International Journal of Simulation Modelling, 11(2012)3, 141-149.Note:   Responsible person for English translation: M. Šuto, M.A., J.J. Strossmayer University of Osijek, Croatia

The post weld heat treatment (PWHT) was used to reduce the level of the residual stresses and increase of the crack resistance of the material in the connection part.The article presents the results of the residual stress measurements immediately after welding and after the stress relaxation by the PWHT

Suitability of heat treatment for crack resistance of material in the connection part of heavy transporter for liquid slag

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