Fracture Mechanisms in Steel Castings

The investigations were inspired with the problem of cracking of steel castings during the production process. A single mechanism of decohesion - the intergranular one - occurs in the case of hot cracking, while a variety of structural factors is decisive for hot cracking initiation, depending on chemical composition of the cast steel. The low-carbon and low-alloyed steel castings crack due to the presence of the type II sulphides, the cause of cracking of the high-carbon tool cast steels is the net of secondary cementite and/or ledeburite precipitated along the boundaries of solidified grains. Also the brittle phosphor and carbide eutectics precipitated in the final stage solidification are responsible for cracking of castings made of Hadfield steel. The examination of mechanical properties at 1050°C revealed low or very low strength of high-carbon cast steels

The analysis of solidification process of ferritic-austenitic cast steel

Abstract One of the most common defects leading to the rejection of faulty castings made of duplex cast steel is hot cracking. Hot crackingdifferently from cold cracking which occur on cooling, when the material exhibits already distinct elastic properties -proceeds in the semi-solid state, particularly when the temperature of solidifying casting is close to the equilibrium solidus point. There exist a range of temperatures in the vicinity of the solidus point within which the solidifying metal shows very small deformation ability and small strength. Therefore even little stresses occurring at the solidification stage and caused by density difference between ferrite and austenite, or restricted shrinkage, or various temperature gradients, can be the reason of hot cracking. Copper addition, as it is used in cast steel grades implemented in Polish power industry applications, decreases the temperature of the end of solidification, thus affecting beneficially the surface reproduction quality, but on the other hand it can promote, along with several other elements contained in duplex cast steel, the peritectic transformation during the last stage of solidification. The presence of peritectic solidification, i.e. strictly speaking the structural stresses accompanying that process, is the well-known and significant reason of the increased steel defectiveness in the continuous steel casting (CSC) technology if the steel with carbon content promoting the peritectic transformation is processed. The authors have presented the examination results of the solidification phenomenon for two duplex cast steel grades -one without copper addition, and the other with addition of about 3.0% Cu

Optimization of Heat Treatment in Aspect of Production's Costs Reducing and Improving of Casting Quality from Duplex Cast Steel

Abstract The paper determines possibilities of cost optimisation in the production of GX2CrNiMoCu25-6-3-3 type duplex cast steel castings through selection of appropriate solution heat treatment temperature, which value depends on the content of alloying elements. Metallographic analysis was carried out for as-cast and heat treated cast steel. Hardness and impact strength of the cast steel were determined, which were correlated with the volume fraction of phases determined by means of ImagePro computer image analyser. It has been shown that increased carbon content creates a need to use higher treatment temperatures, thereby increasing the production cost. With increasing carbon content the cast steel hardness after solution heat treatment increases, however, crack resistance decrease

Influence of carbides morphology on fracture toughness of cast steel G200CrMoNi4-3-3

We analyze the influence of small modification of chemical composition of G200CrMoNi4-3-3 cast steel on the morphology of carbides and on material crack resistance. Using the Termo-Calc software the volume fraction of carbide phase was determined and the results correlated with microstructure observations. Crack resistance of cast steel was determined using SENB specimens and finding critical values of stress intensity factor KQ. Metallographic and fractographic observations of fracture surfaces allowed identifying the mechanism of cracking.Исследуется влияние незначительной моди­фикации химического состава литой стали G200СгМоNi4-3-3 на морфологию карбидов и трещиностойкость материала. С исполь­зованием расчетной программы Termo-Calc были выполнены оценка объемной доли карбидной фазы и сравнительный анализ полученных результатов с данными микрструктурных исследований. Трещиностой­кость литой стали исследовалась на образ­цах с краевой трещиной, для которых определялись критические значения коэффициента интенсивности напряжений KQ. Металлографические и фрактографические исследования поверхностей разрушения по­зволили определить механизм трещинообразования

Influence of carbides morphology on fracture toughness of cast steel G200CrMoNi4-3-3

We analyze the influence of small modification of chemical composition of G200CrMoNi4-3-3 cast steel on the morphology of carbides and on material crack resistance. Using the Termo-Calc software the volume fraction of carbide phase was determined and the results correlated with microstructure observations. Crack resistance of cast steel was determined using SENB specimens and finding critical values of stress intensity factor KQ. Metallographic and fractographic observations of fracture surfaces allowed identifying the mechanism of cracking.Исследуется влияние незначительной моди­фикации химического состава литой стали G200СгМоNi4-3-3 на морфологию карбидов и трещиностойкость материала. С исполь­зованием расчетной программы Termo-Calc были выполнены оценка объемной доли карбидной фазы и сравнительный анализ полученных результатов с данными микрструктурных исследований. Трещиностой­кость литой стали исследовалась на образ­цах с краевой трещиной, для которых определялись критические значения коэффициента интенсивности напряжений KQ. Металлографические и фрактографические исследования поверхностей разрушения по­зволили определить механизм трещинообразования

Svojstva spoja u dvokovinskim motkama Cu-Al i Cu-čeliku nakon platiranja eksplozivom i valjanja

In the paper the microhardness, the microstructure and the bond strength of interface of bimetallic joint on the cross sections of the test bar have been investigated. For the experimental analysis, a bimetallic bar was manufactured using an explosive technique method and the process of rolling. For tests, 23 sets of specimens were prepared each consisting of copper tubes (grade M1-E), rolled steel rods (grade St3S), drawn rods (grade 55) and aluminium rods (grade PA6). The copper tubes and the steel and aluminium rods had different diameters, owing to which different distances between the rods and the internal tube walls were obtained. The results of the research show a significant deviation in microhardness distribution in the both layers near the joining border.U radu su prikazani rezultati istraživanja mikrotvordoće, mikrostrukture i čvrstoće sljubljivanja dvokovinskog spoja na presijeku ispitne šipke. Za potrebe eksperimentalne analize dvokovinska šipka je izrađena metodom primjene eksploziva i naknadnog valjanja. Za ispitivanja su pripremljena 23 kompleta uzoraka od kojih se svaki sastoji iz kompleta cijevi (kvaliteta M1-E), valjanih čeličnih šipki (kvalitete St35), vučenih šipki (kvaliteta 55) i aluminijskih šipki (kvaliteta PA6). Bakarne cijevi i čelične i aluminijske šipke su imale su imale različite promjere zbog kojih su dobivene različite udaljenosti između šipki i unutrašnjih stijenki cijevi. Rezultat ispitivanja pokazuje u oba sloja značajnu odstupanja u raspodjeli mikrotvrdoće uz granicu spoja

Solidification structure of massive castings from duplex cast steel,

SUMMARY Problems related with duplex massive cast production are presented in this work. Macro and microstructure investigations of GX2CrNiMoCu25-6-3-3 cast steel after solidification were done. The influence of cooling rates and segregation on intermetallic phases formation, especially sigma phase, were shown. The segregation process and cooling rates during solidification have great influence on intermetallic phases formation. Sigma phase occurrence in the cast structure causes deterioration of technological and functional properties

Microstructural and fracture analysis of aged cast duplex steel

The effect of increased carbon content and heat treatment parameters on the microstructure and selected properties of ferritic-austenitic duplex cast steel is discussed. Test results show that the cast steel microstructure after the solution heat treatment changes substantially with increasing carbon content. Ageing after the solution heat treatment results in approx. 20% increase in hardness and a few-times decrease in impact strength. Fractographic examinations show thatfracture surfaces of specimens of steel with low carbon content are typically of transcrystalline ductile micromechanism. An increase in carbon content is accompanied by a decline in ductility areas, whilefracture of specimens is of mixed nature: ductile and brittle. After ageing, only cases of mixed fracture were observed.Исследовано влияние повышенного содержа­ния углерода и параметров термообработки на микроструктуру и некоторые свойства ферритоаустенитной литой двухфазной ста­ли. Из экспериментальных результатов сле­дует, что микроструктура литой стали после термической обработки на твердый раствор существенно изменяется при повышении содержания углерода. Процесс старения стали после термической обработки на твер­дый раствор приводит к примерно 20%- ному повышению твердости и снижению ударной прочности в несколько раз. Фрактографические исследования показывают, что для поверхностей разрушения образцов из стали с низким содержанием углерода ха­рактерным является транскристаллитный вязкий микромеханизм разрушения. Повы­шение содержания углерода сопровождается уменьшением удельной доли зон пластичес­кого разрушения и проявлением смешанного (хрупкого и вязкого) разрушения образцов. После старения стали наблюдался лишь смешанный характер разрушения

Technological Assessment of the Possibility of Making Light-section Castings of GX2CrNiMoN25-6-3 Cast Steel by the Centrifugal Casting Method

The paper presents the results of investigation into the technological possibility of making light-section castings of GX2CrNiMoN25-6-3 cast steel. For making castings with a wall thickness in the thinnest place as small as below 1 mm, the centrifugal casting technology was employed. The technology under consideration enables items with high surface quality to be obtained, while providing a reduced consumption of the charge materials and, as a result, a reduction in the costs of unit casting production