Contribution deals with experimental modeling of quick thermal cycles of metal specimens. In the introduction of
contribution will be presented measured graphs of thermal cycle of heat affected zone (HAZ) of weld. Next will be
presented experimental simulation of measured thermal cycle on the standard specimens, useable for material testing.
This approach makes possible to create material structures of heat affected zone of weld, big enough for standard
material testing.Web of Science55473673

Juránek, Martin

Klaus, Pavel

Kulhánek, Jiří

Tomčík, Petr

Trojan, Radim

Contribution deals with experimental modeling of quick thermal cycles of metal specimens. In the introduction of contribution will be presented measured graphs of thermal cycle of heat affected zone (HAZ) of weld. Next will be presented experimental simulation of measured thermal cycle on the standard specimens, useable for material testing. This approach makes possible to create material structures of heat affected zone of weld, big enough for standard material testing

Kulhánek, J.

Tomčík, P.

Trojan, R.

Juránek, M.

Klaus, P.

Hrčak - Portal of scientific journals of Croatia

733METALURGIJA 55 (2016) 4, 733-736J. KULHÁNEK, P. TOMČÍK, R. TROJAN, M. JURÁNEK, P. KLAUSEXPERIMENTAL MODELING OF WELD THERMAL CYCLE OF THE HEAT AFFECTED ZONE (HAZ)Received – Prispjelo: 2015-11-06Accepted – Prihvaćeno: 2016-03-30Preliminary Note – Prethodno priopćenjeJ. Kulhánek, P.Tomčík, R.Trojan, M.Juránek, P.Klaus, Faculty of Metal-lurgy and Materials Engineering, VŠB-Technical University of Ostra-va, Czech RepublicContribution deals with experimental modeling of quick thermal cycles of metal specimens. In the introduction of contribution will be presented measured graphs of thermal cycle of heat affected zone (HAZ) of weld. Next will be presented experimental simulation of measured thermal cycle on the standard specimens, useable for material test-ing. This approach makes possible to create material structures of heat affected zone of weld, big enough for stand-ard material testing.Keywords: weld, P92, thermal cycle modeling, HAZINTRODUCTIONThis paper is focused on the experimental tempera-ture cycle simulation of steels. Described process is mainly aimed at very quick and precise simulation of temperature cycles, which occurs during welding of metal materials. During such temperature cycles are created different material structures, with very small volumes. For such small volumes of heterogeneous ma-terial structures it is very complicated to perform stand-ard material testing (hardness, strength).Proposed process can create material structure for given temperature cycle in volume sufficient for stand-ard material tests (with use of metal samples of standard size of 10 mm x 10 mm x 100 mm). During temperature cycle can be created temperature affected zone of vol-ume about 10 mm x 10 mm x 20 mm (size of affected zone depends on the speed of cooling).Several experimental simulation of temperature cy-cles were done previously in [13] with use of tempera-ture cycles simulator (Smitweld TCS 1406 etc.). Here is presented unique experimental machine, which is able to achieve better values of heating and cooling gradi-ents, and which is more important, it is possible to use vacuum chamber for experiments.EXPERIMENTAL PROCEDUREFor identifying the temperature cycles and sizes of heat affected areas, we have to use precise and quick temperature measurement.Temperature measurement was done on the metal specimen made from the steel P92 [4] (see chemical composition in Table 1) with connected thermocouples.ISSN 0543-5846METABK 55(4) 733-736 (2016)UDC – UDK 621.791.057:669.14.018:621.78.086.5=111T able 1 Chemical composition of the P92 steel / wt.%C 0,0930 Mn 0,5000 Si 0,3200P 0,0200 S 0,0030 Cu 0,1000Ni 0,2060 Cr 8,6200 Mo 0,5170V 0,1960 Ti <0,004 W 1,5600Al-c 0,0120 Nb 0,0640 Co 0,0230B 0,0021 As 0,0090 Sn 0,0070Pb 0,0030 Sb 0,0180 N 0,0330O2 0,0040 H /ppm 0,7000 Bi <0,003Figure 1 Testing plate with welded thermocouplesThermocouples were welded into holes in testing plate, isolated by ceramic (see Figure 1).The distance between thermocouple sensors was 16 mm in line of weld and distance (depth) of the thermo-couple sensors from the weld varies from 2 - 3 mm (see Figure 2).On the Figure 3 are measured temperature cycles for thermocouples T1 to T8. From these measured tempera-ture peaks can be identified type of heat affected zone (HAZ).For mechanical and material testing of these meas-ured temperature cycles and their zones, is necessary to have standard and homogenous specimens, which can be evaluated by standard tests. For such purposes, was developed unique testing machine, the Temperature cy-cle simulator with vacuum chamber (TCSV).734J. KULHÁNEK et al.: EXPERIMENTAL MODELING OF WELD THERMAL CYCLE OF THE HEAT AFFECTED ZONE METALURGIJA 55 (2016) 4, 733-736For temperature simulation was developed unique testing machine, with excellent power and quick control system with large number of measurement channels. (see Figure 4).ues. This problem is important, because measured tem-perature is the main goal of the temperature cycle simu-lator and should be very precise. The problem of false temperatures can be solved by different approaches:•  Change the temperature measurement method to infrared method. Disadvantage of this method is the necessary emissivity calibration and sensitivity to coolant gas.•  Solve the false temperature by subtracting the para-sitic voltage from the measurement, for such process we have to calibrate each connected thermocouple sensor before simulation by automated process.For quick and precise temperature measurement on the specimen have to be used thin thermocouple wires (0,5 mm and thinner). The thermocouple wires have to be welded to the surface of the specimen, and the joint should be very small. Good joint with specimen is nec-essary due to good heat transport. Also very important property of sensor joint with specimen is low resistance, because of risk of parasitic temperature.COMPENSATION OF TEMPERATURE MEASUREMENTPrinciple of temperature measurement with thermo-couple is based on measurement of voltage in millivolts. During resistive heating is on specimen surface gradient of voltage in millivolts also, which can create false, parasitic temperatures on thermocouples.For automatic detection of parasitic temperature is used short current pulse of 3000 A. During this pulse, the specimen is heated by electric work, visible on the Figure 5 from time 15 s to 18 s (linear progression). At the end of current pulse, the temperature rises slowly for several seconds due to the inertia of system (to the time 26 s). On the Figure 5 thermocouple responds to the current (the dashed curve). This sensitivity makes it impossible to control temperature.For compensation of temperature jump was created compensation formula: Tcomp.= T · (1 + Uclamps· k) /°CTcomp. ... compensated temperature /°CT … measured temperature /°CFigure 3 Measured temperature cyclesFigure 4  Temperature cycle simulator with vacuum chamber (TCSV)Figure 2 Thermocouples position on testing plateTable 2 Main parameters of TCSVMaximal heating current 6 000 /AMaximum voltage on specimen 7 /VMaximum temperature heating gradient1 200 /°K/sMaximum temperature cooling gradient1 50 /°K/sMaximal temperature of specimen 1 250 /°CMinimal temperature of specimen 15 /°CSize of specimen plane 10 x 10 /mmLength of specimen 70 – 200 /mmMinimal vacuum pressure 0,15 /mBarNumber of thermocouple inputs 8 pcs1Depends on material of specimenThe main parameters of the temperature simulator are in Table 2.For heating of specimen was used the DC current. The advantage of the DC current for heating is more homogenous temperature distribution in the specimen plane, next advantage are smaller EMC interferences. The disadvantage of using DC current for heating is the persistent voltage gradient on the surface of specimen. This voltage gradient in millivolts / mm can affect welded thermocouples and create false temperature val-735J. KULHÁNEK et al.: EXPERIMENTAL MODELING OF WELD THERMAL CYCLE OF THE HEAT AFFECTED ZONEMETALURGIJA 55 (2016) 4, 733-736Uclamps  ... measured voltage on clamps /Vk ... compensation constant /V-1From the current pulse and measured voltage on clamps (Figure 5) is computed compensation constant k. For higher values of k is better to create new thermo-couple sensor.COOLING OF SPECIMENThe temperature simulator (TCSV) has excellent pa-rameters for heating of specimen, for precise simulation of temperature cycle of welding it is also necessary to have good cooling gradient.The cooling gradient is dependent on [5]:• Heat transfer to water cooled clamps• Heat radiation• Heat transfer to air (gas)In vacuum chamber is the most important factor the heat transfer to the water cooled clamps (see Figure 6). Figure 5 Temperature compensationFigure 6 Heating and cooling of specimen in the clampsFor higher cooling gradient it is necessary to move clamps closer to each other. For even higher cooling rate can be used also cooling with inert gas nozzle.MECHANICAL AND MATERIAL TESTS OF SPECIMENFor validation of temperature simulation accuracy were done several tests of material structures and me-chanical parameters. On the Figure 7 there is one of tested temperature cycle corresponding to the T3 tem-perature from Figure 3. The dashed curve is desired temperature cycle measured from welding, the solid curve is measured temperature from TCSV. The differ-ence between desired and measured temperature is min-imal and acceptable.In the microstructure of simulated specimen are vis-ible dissolved particles of precipitate (see Figure 8) with full austenitization. It is identical with microstruc-ture of real welded material.On the Figure 9 there is measurement of the hard-ness in longitudinal axis, the distance is measured from the center of specimen. On the hardness curve is visible significant border between heat affected zone (HAZ) and basic material (BM) in the distance of 5 mm. It cor-responds to with the size of heat affected volume 10 x 10 x 10 mm.Figure 7 Simulation of temperature cycleFigure 8  Microstructure of simulated specimen with precipitationFigure 9 Hardness in longitudinal axis of specimen736J. KULHÁNEK et al.: EXPERIMENTAL MODELING OF WELD THERMAL CYCLE OF THE HEAT AFFECTED ZONE METALURGIJA 55 (2016) 4, 733-736CONCLUSIONMain goal of this work is to verify ability of TCSV machine to accurate simulate temperature cycles of welding.On the TCSV machine was simulated specimen with identical temperature cycle, and this specimen was compared with parameters of heat affected zone from testing plate.Compared microstructures and hardness parameters were identical, it proved accuracy of temperature cycle simulation. This test was done for several different tem-perature cycles with good results.Next it is necessary to test different materials and different types of heat treatment to create methodology for experimental simulation of temperature cycles. It is necessary to consider, that gradient of cooling rate is dependent on material and his microstructure [6].AcknowledgementThis paper has been elaborated thanks to project No: SP 2016/69 - “Development tests and studies of select-ed car parts” supported by the Ministry of Education, Youth and SportsREFERENCES[1] Z. Boumerzoug, E. Raouache, F. Delaunois, Thermal cycle simulation of welding process in low carbon steel, Mate-rials Science and Engineering: A 530 (2011) 191-195.[2] N.E. Glover, C.L. Davis, Thermal cycle simulation of a Ni-base superalloy, Scripta Materialia 34 (1996) 675-684.[3] I. Samardžić, A. Stoić, D. Kozak, I. Kladaric, M. Dunđer, Application of Weld Thermal Cycle Simulator in Manu-facturing Engineering, Journal of Manufacturing and Indu-strial Engineering 1-2 (2013) 7-11.[4] P. Mohyla, J. Zapletal, Investigations of Microstructure and Creep Properties of a Homogenous P92 Weld, Proceedings, METAL 2011 Conference, Brno, 2011, Tanger Ltd., pp. 63.[5] K. Poorhaydari, B. M. Patchett, D. G. Ivey, Estimation of cooling rate in the welding of plates with intermediate thickness, Welding Journal 84 (2005) 10 149-155.[6] M.J. Attarha, I. Sattari-Far, Study on welding temperature distribution in thin welded plates through experimental measurements and finite element simulation, Journal of Materials Processing Technology 211 (2011) 688-694.Note:  The responsible for English language is J. Taussik (State Exam in English)

Experimental modeling of weld thermal cycle of the heat affected zone (HAZ)

Abstract

Similar works

Full text

Available Versions

Hrčak - Portal of scientific journals of Croatia

DSpace at VSB Technical University of Ostrava

Directory of Open Access Journals