The effect of a cooling rate on the S690Q quenched and tempered steel welded joint coarse grain heat affected zone microstructure was investigated using a dilatometer with controlled heating and cooling fixture. Steel samples were heated to a peak temperature of 1350 °C and cooled at the different cooling time Dt8/5. A dilatometric analysis and hardness measurements of the simulated thermal cycle coarse grain samples were done. Transformation start and finish temperature were determined using dilatation vs. temperature data analysis. The microstructure of the sample with a cooling time 5 s consists of martensite, whereas at cooling time 80 s a bainitic microstructure was observed. The investigated steel cooling cycle using simulation approach makes possible to determine the range of an optimum CG HAZ cooling time for the welding.

The number of carbide particles stringers at boundaries and subboundaries of martensite per unit of surface decreases with the third root of tempering time at 1073 K. The accelerated creep rate at 853 K depends on the number of stringers of carbide particles per unit of surface, and below an inflection point, the creep rate increases strongly. Equations relating for creep rate are discussed in terms of experimental creep rate, number of carbide particles stringers and average particles spacing.

The high-strength steel grade S690QL and a filler welding wire Mn3Ni1CrMo were the materials chosen for welding a V-shaped butt weld. In order to prevent the weld's cold cracking, a multi-pass welding technique was applied. A metallographic investigation revealed microstructure variations in different areas of the weld's heat-affected zone. A reverse-engineering approach was used to test a dilatometer's capabilities to simulate different HAZ microstructures. Hollow steel-cylinder specimens were subjected to several weld thermal cycles in order to generate similar microstructures as in the real weld's HAZ. The microstructures of the as-welded and simulated heat-affected zone specimens were investigated. Good agreement was found between the dilatometer-simulated HAZ microstructures and those in a real HAZ weld. Keywords: welded joint, microstructure, high-strength low-alloy steel, simulation, dilatometer, heat-affected zone Visokotrdno jeklo S690QL in varilna`ica Mn3Ni1CrMo kot dodatni material, sta bila uporabljena pri varjenju so~elnega V-spoja. Za prepre~itev pokanja v hladnem je bila uporabljena tehnika ve~varkovnega varjenja. Metalografska preiskava je odkrila razli~ne mikrostrukture v razli~nih predelih toplotno vplivanega podro~ja zvara. Za preizkus delovanja dilatometra je bil, za simulacijo mikrostruktur razli~nih podro~ij toplotno vplivanega podro~ja, uporabljen princip povratnega in`enirstva. Razli~na mikrostruktura toplotno vplivanega podro~ja je bila simulirana z izpostavitvijo votlih cilindri~nih vzorcev razli~nim toplotnim ciklom. Opravljena je bila metalografska preiskava realnega zvarjenega spoja in simuliranih vzorcev. Primerjava rezultatov je pokazala dobro ujemanje simuliranih in realnih mikrostruktur.

The impurities sulphur, phosphorus, lead, bismuth, tin and antimony affect the hot workability of stainless steels. In this study, the authors show that sulphur and lead segregate to phase and solidification grain boundaries, where cracks appear during hot deformation. The workability was tested by the hot rolling and hot bending of industrial and laboratory steels.

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Preiskovani so bili vzorci zvarov feritnega nerjavnega jekla X6Cr17 (W.Nr. 1.4016). Prikazane so metalografske zna~ilnosti pre~nega in kro`nega zvara. Dolo~ena je bila hitrost korozije v dveh korozijskih medijih in pri dveh temperaturah. Predstavljeni so rezultati osnovnega materiala, dveh zvarov in dveh primerjalnih materialov, jekla X2CrTi17 in malooglji~nega jekla DC01 EN10130. Rezultati preiskave so pokazali, da se v zvaru pove~a velikost zrn, po mejah zrn pa je izlo~ena martenzitna faza, oboje pa vpliva na korozijsko obstojnost. Nobeden od preiskovanih vzorcev ni pokazal izrazite pasivacije povr{ine pri elektrokemijskem korozijskem preizkusu. Klju~ne besede: feritno nerjavno jeklo, metalografija, zvar, korozijska odpornost Samples of welds made from the ferritic stainless steel X6Cr17 (W.Nr. 1.4016) were investigated. Here we present the results of the metallographic charaterisations of these welds. We determined the corrosion rate in two corrosion media at two temperatures. The results from the base material and two welds are presented and compared with the steel X2CrTi17 and the low-carbon steel DC01 EN10130. The results revealed enlarged grains in the weld and martensite at the grain boundaries, both have an influence on the corrosion resistance. None of the investigated samples showed distinctive passivation of the surfaces during the electrochemical corrosion tests. Keywords: ferritic stainless steel, metallography, weld, corrosion resistance UVODFeritna nerjavna jekla so poceni, cenovno stabilna in korozijsko odporna jekla. Uporaba teh nerjavnih jekel je pogosta v avtomobilski industriji, pri izdelavi kuhinjskih pripomo~kov in naprav ter tudi na drugih podro~jih. Feritna nerjavna jekla se zaradi njihove dobre toplotne prevodnosti in majhnega toplotnega raztezka uporabljajo tako za izdelavo dimnikov, glu{nikov, izpu{nih sistemov, pritrdilnih elementov, kot tudi za grelne elemente, ki se jih uporablja v kopelih staljene soli za toplotno obdelavo, v konstrukcijske namene in podobno. [1][2][3][4][5] Pri visokih temperaturah iz taline nastaja faza delta ferita (d), ki se potem ko kristalizira, pri ohlajanju ne spremeni. Te popolnoma feritne mikrostrukture se ne da toplotno obdelati. Neprisotnost fazne premene razlo`i, zakaj so pri ogrevanju ta jekla nagnjena k rasti zrn.Feritna faza v zvaru in toplotno vplivana cona sta ob~utljivi na intersticijske elemente, kot sta ogljik in du{ik, ki pri visokih temperaturah z difuzijo spremenita feritno fazo v avstenit. Ta avstenit pa se pri ohlajanju po mejah zrn pretvori v martenzit (krhek). Dodaten problem je tudi z rastjo zrn v toplotno vplivani coni in v zvaru. 6,7 Za zadr`anje duktilnosti feritne strukture, ki vsebuje tudi martenzit, je potrebno izvr{iti toplotno obdelavo~im prej po zaklju~nem varjenju. Ta obdelava za odpravo napetosti se izvede pri maksimalni temperaturi 750-800°C, kar je malo pod temperaturo nastanka avstenita v podro~jih bogatih z ogljikom. Namen te obdelave je popustiti martenzit, zmanj{ati zaostale napetosti v zvaru ter pove~ati`ilavost zvarn...

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Two creep resistant steels, P91 and X20, were tempered for 17520 h at 650 8C or 8760 h at 750 8C to study the growth and redistribution of carbide precipitates in martensite. On specimens annealed for a different time, yield stress at room temperature and accelerated creep rate at 580 8C were determined. With increasing yield stress in the range from 350 to 650 MPa the accelerated creep rate decreased continuously by about 2 orders of magnitude from 8Á10 À7 s À1 to 5Á10 À9 s À1 . For equal yield stress, the creep rate was slightly lower for the steel P91 than for the steel X20.