This study examines parameters of post-weld heat treatment on the test specimens made of cast steel GS30Mn5. The welding is performed with shielded metal arc welding (SMAW) process. The aim is to obtain the surface without illicit cracks, with hardness ranging from 320 up to 400 HB. After induction heating, the specimens are cooled alternately with air and water. Decreased speed of quenching results in avoiding the occurrence of illicit splashes, while the hardness is maintained within the prescribed limits

I. Opačak

I. Samardžić

L. Marušić

V. Marušić

English

Directory of Open Access Journals

Influence of induction hardening parameters on the GS30Mn5 weld properties

Hrčak - Portal of scientific journals of Croatia

730  METALURGIJA 55 (2016) 4, 730-732V. MARUŠIĆ, I. SAMARDŽIĆ, I. OPAČAK, L. MARUŠIĆINFLUENCE OF INDUCTION HARDENING PARAMETERS ON THE GS30Mn5 WELD PROPERTIESReceived – Primljeno: 2015-11-18Accepted – Prihvaćeno: 2016-03-10Preliminary Note – Prethodno priopćenjeV. Marušić, I. Samardžić, I. Opačak. Faculty of Mechanical Engineer-ing in Slavonski Brod, University of Osijek, Croatia.L. Marušić. Technical Department of the College of Slavonski Brod, Croatia.This study examines parameters of post-weld heat treatment on the test specimens made of cast steel GS30Mn5. The welding is performed with shielded metal arc welding (SMAW) process. The aim is to obtain the surface without illicit cracks, with hardness ranging from 320 up to 400 HB. After induction heating, the specimens are cooled alter-nately with air and water. Decreased speed of quenching results in avoiding the occurrence of illicit splashes, while the hardness is maintained within the prescribed limits.Key words: welding, GS30Mn5, post weld heat treatment, mechanical properties, structureINTRODUCTIONDamages on castings may occur due to dirt and re-sidual gases, or due to rapid cooling [1]. Welding can repair cracks, corrosion effects and errors in castings. In some cases, new layer can be welded on castings in or-der to extend the lifetime of a component or equipment [2]. Additional requirements are sometimes set on the welded layer in terms of achieving the appropriate structure and hardness. This paper elaborates welding parameters of specimens made of GS30Mn5 cast steel and effects that subsequent heat treatment has on the structure and hardness of the specimens.EXPERIMENTAL PARTThe GS30Mn5 cast steel is often used in manufac-ture of large and heavy castings [3], which are exposed to various wear mechanisms. The Table 1 overviews chemical composition of GS30Mn5, and plates used in our experiment were prepared. Table 1 Chemical composition of the GS30Mn5 / wt. %Element C Mn Si P S Cr Ni CuRequest DIN172050,27÷0,341,20÷1,50≤0,60≤0,020≤0,015- - -Test plate 0,31 1,41 0,40 0,014 0,005 0,19 0,25 0,14In delivered casting conditions, hardness of castings was below 200 HB. For a welder to be able to detect errors in a material, depths and types of cracks, and to ISSN 0543-5846METABK 55(4) 730-732 (2016)UDC – UDK 621.791.052:669.182:621.741.78:620.17:18=111determine quality of surface and thickness of welding layer of a material. According to [4], it is defined that surface cracks longer than 2 mm before the hardening and cracks in length up to 5 mm after hardening are ac-ceptable. It is also defined that the hardness after hard-ening shall range from 320 up to 400 HB. EXPERIMENT RESULTSSurface dimension and quality shall meet all re-quirements defined by the technical documentation. Therefore, the machine parts shall apply non-destruc-tive control methods, such as magnet, hardness measur-ing and fingerprinting of the structure [5]. The Figure 1 shows a characteristic test performed on prisoners dredgers. Control indication of surface cracks is per-formed with a magnetic method. Damages may occur in characteristic forms, e.g. as inclusions of dirt, inclusions of residual gases and cracks of different forms due to rapid cooling of cast-ings. If considering the fact that the base material GS30Mn5 has a Cekv = 0,61 %, there is a need for pre-heating before welding [6]. If multiple layers are weld-ed, then the temperature of the previous layer should be equal to the reheating temperature. If Cekv is greater than 0,6, then it is necessary to overheat the material to a temperature of 200 ÷ 300 °C. Shielded metal arc proce- a) b)Figure 1  The characteristic example of determining the formation of cracks indications; a) control indication of surface cracks with magnetic particles; b) the appearance of surface damage731V. MARUŠIĆ et al.: INFLUENCE OF INDUCTION HARDENING PARAMETERS ON THE GS30Mn5 WELD PROPERTIESMETALURGIJA 55 (2016) 4, 730-732dure is applied to repair illicit cracks. The reason for choosing this procedure is the fact that the cracks were only locally present. To check the possibility of improv-ing the damage, coated electrode in diameter ø 2,5 of composition: ≈ 0,06 % C; 1,4 % Mn; 0,3 % Si; 0,015 % P and 0,01 % S [7], is selected as an additional material. Those electrodes are chosen because of their chemical composition and mechanical properties. Declared me-chanical properties of the electrodes are shown in the Table 2. It is important to note that the declared content of carbon is very low and that the minimum declared ductility is 28 %. The low content of the carbon is a prerequirement for decreasing excretion of the mar-tensite and the too high hardness. Relatively high duc-tility should reduce the risk of cracking.Table 2  Declared mechanical properties of additional materials [7]Yield strength Rp0,2 / MPaTensile strength Rm / MPaDuctility A5/ %ToughnessKV (-20 ºC) / Jmin. 480 min. 580 min. 28 min. 200Plate in dimension of ~ 50 x 150 x 300 mm is pre-pared for this experiment. The temperature of preheat-ing plate is 230 °C. Control of target temperature is per-formed with corresponding digital portable device. Af-ter overheating of the plate, welding is performed at three points along the plate length. Welding voltage (U) amounted to 23 ÷ 26 V, current welding (I) amounted to 110 ÷ 140 A, voltage of idle was 60 V, and energy of efficiency for melting of 0,78 at the speed of welding of 1,5 mm/s. Welding is performed in one, two and in three layers, as of Figure 2. The aim is to cover different sizes (depth) of surface damages. The weld surface is leveled with the milling to the first pure measure. Samples are cut for control of hardness and metallographic analysis. Surface hardness is controlled by the Brinell method (HB2,5/1000/15) on three points along the welded layer length and on three points in the heat affected zone. The measured hardness values of the welded layer and of heat affected zones are given in the Figure 2.Control of the base material and the welded layer is performed in a non-etched condition. Evaluation of the metallurgical cleanliness is performed according to ASTME 45 [8]:-  the base material exhibited the presence of inclu-sions of type D and globular oxide type, heavy series No. 3; -  the weld showed inclusions of type D and oxides of globular type – easy series No. 5. Characteristic structures of the weld and of heat af-fected zone in etched condition are shown in the Figure 3. The weld structure is fine-grained, dendritic, with no anomalies in the form of micro - and/or macrocracks. Likewise, the structure of the heat affected zone is fine-grained without anomalies.After analysis of the structure, control of hardness is completed on metallographic samples. The Figure 4 shows the results of control hardness HV10 on the cross-section. Based on the results of hardness meas-urements, it is concluded that the measured values of the base material and of the welded layer are ranging from 180 to 195 HV and of the heat affected zone from 200 to 220 HV. Based on these results, it is concluded that the meas-ured values of the base material and weld were below the prescribed value. It is therefore necessary to carry out in-duction hardening. This procedure leads to overheating of the surface layer to the desired depth, to reduce occur-rence of macro deformation to a minimum. In order to continue this experiment, the test plate is cut transversely to the welding direction, and then divided into two equal parts, marked as test plate 1 and test plate 2. Induction hardening of samples On the test plate 1, heating of the surface is per-formed with flat inductor with cooling by water. The following parameters of the induction hardening are ob-tained: energy F, 54 %; feed S, 5 mm-1; frequency, 15,4 ÷ 15,5 kHz; generator F, 13 %. Appearance of the in-ductors is shown on Figure 5a.Figure 2  The test plates welded with SMAW process and the results of measurements of surface hardness HB2,5/1000/15 a) b)Figure 3  The characteristic structure of weld (a) and heat affected zone (b), magn. 400 x, etched nital 3 %Figure 4  Schedule of measurement places on the sample and the measured hardness HV10 on the cross – section of welds before the induction hardening732V. MARUŠIĆ et al.: INFLUENCE OF INDUCTION HARDENING PARAMETERS ON THE GS30Mn5 WELD PROPERTIES METALURGIJA 55 (2016) 4, 730-732After induction hardening of the test plate, hardness of surface layer and of base material was measured by the Brinell method. Measured values are ranging from a minimum of 528 HB to a maximum of 560 HB. Based on a comparison with the prescribed or permitted values of groove hardness (320 ÷ 400 HB), it is concluded that the cooling parameters should be changed. Because of the high speed of heat removal, partial elimination of martensite occurred in the surface layer. Probably, re-gardless of the very low content of carbon contained in the electrodes (C ≤ 0,06 %), as a consequence the ad-ditional material is mixing with the base material. The sample surface layer structure is characterized as fine-grained, dendrite without microcracks, as of Figure 6a. Similar structure is observed in the heat affected zone, as of Figure 6b.Induction hardening of samples In order to avoid too high hardness (limits are 320 ÷ 400 HB), it is necessary to choose a slightly slower speed of cooling. Therefore, inductors with two systems for cooling the heated surfaces are developed: the first system cooled the surface by air, and the second system cooled the same surface by water. The systems operated in a very short periods of time, alternately one after an-other. The appearance of this inductor is shown on Fig-ure 5b. Selected parameters of the induction hardening are the same as for hardening and quenching by only water. After hardening, surface hardness control is per-formed. Final control shows that the selected parameter of hardening and quenching by combined air and water could achieve satisfactory values of surface hardness, as presented in the Table 3.The structure is examined after the induction hard-ening. The Figure 7a presents the structure of the base material. It is characterized by a relatively coarse grain, however, it is evident that the material was subjected to heat treatment. Anomalies in the form of microcracks are not observed in the structure. The structure of heat affected zone is extremely fine-grained, without micro-cracks, Figure 7b. The structure of the weld is similar to that, as shown in Figure 6a.CONCLUSIONHardness in prescribed limits of minimum 320 up to maximum 400 HB is achieved by a cooling with alter-nation of air and water after induction heating. At the same time, there were illicit cracks and macro deforma-tion avoided. It is necessary to apply scientific methods in the analysis of tribosystem elements and in selection of parameters for welding and heat treatment. The de-scribed experiment proves that it was possible to achieve satisfactory structure and hardness without the presence of illicit anomalies that could affect the unac-ceptability of criteria given by the relevant norms.REFERENCES[1] Z. Glavaš, Osnove lijevanja metala, Metalurški fakultet Sisak, Sisak, 2014, 289 str.[2] F. Javor, Reparatura – primjena tehnologije zavarivanja i srodnih postupaka, Zavarivanje 56 (2013) 3/4, 113-115.[3] E. Fraś, M. Górny, Inoculation Effects of Cast Iron, Archi-ves of Foundry Engineering 12 (2012) 4, 39-46.[4] ASME VIII Division 1 Appendix 6 Methods for Magnetic Particle Examination A17.2.2, 1994.[5] J. Hola, K. Schabowicz, State of the art non-destructive methods for diagnostic testing of building structures–anti-cipated development trends, Archives of Civil and Mecha-nical Engineering 10 (2010) 3, 5-18.[6] Određivanje optimalnih parametara zavarivanja://www.sfsb.unios.hr/kth/zavar1/files/IP%202005%20-%20PDF/7.pdf, accessed on: 2nd November 2015.[7] EN 499-94: E 46 4 B 32 H5, Elektroda Conarc 49 C, 2009.[8] ASTME 45: Standard Test Methods for Determining the Inclusion Content of Steel, 2011.Note:  prof. Martina Šuto is responsible person for the translation into English language a) b)Figure 5 Inductors for hardening of welded samples a) b)Figure 6  The characteristic structure of weld (a) and heat affected zone (b) induction hardened samples cooled with water, magn. 400 x, etched nital 3 %Table 3  The results of hardness control after induction hardening and quenched air/waterTest place Hardness HB2,5/1000/15Basic material 373 ÷ 384Heat aff ected zone 377 ÷ 379Welded layers 287 ÷ 312 a) b)Figure 7  The characteristic structure of the base material (a) and heat affected zone (b), magn. 400 x, etched nital 3 %

Influence of induction hardening parameters on the GS30Mn5 weld properties

Abstract

Similar works

Full text

Available Versions

Directory of Open Access Journals

Hrčak - Portal of scientific journals of Croatia