The influence of Si and V on the kinetics of phase transformation and microstructure of rapidly solidified Al-Fe-Zr alloys

The influence of Si and V on the precipitation kinetics of the rapidly solidified (RS) Al-Fe-Zr alloys is presented. Precipitation kinetics and microstructural development of RS Al-Fe-Zr alloys with Si or V addition have been investigated by the combination of four point electrical resistance measurement, optical microscopy, transmition electron microscopy (TEM) and scanning electron microscopy (SEM). For verification of the electrical resistivity measurement results differential scanning calorimetry (DSC) and differential thermal analysis (DTA) was also applied. Rapidly solidified samples, in the form of thin ribbons, were prepared with the single roll melt spun technique. For determination of the distinctive temperatures at which microstructural transformations occur in-situ electrical resistivity measurement during heating of the ribbons with various constant heating rates has been used. It was found that microstructure decomposition depends on heating rate and shifts to higher temperatures with increasing heating rate. After heating above the distinctive transition temperatures, heating was stopped and microstructure of the samples examined by electron microscopy

Fracture of drilling head pipe connection due to quenching of heat affected zone (HAZ)

The drilling head pipe connection is made of quenched and tempered steel 34CrNiMo6. The steel characteristic is high hardenability. Due to unsuitable and untested welding technology the heat affected zone (HAZ) cooling rate after welding surpassed the upper critical cooling rate. During horizontal drilling of the rock, the resulting brittle martensite could not bear the dynamic loads which led to a brittle fracture of the pipe connection

The analysis of particles emission during the process of grinding of steel EN 90MNV8

Metal grinding is a one of the manufacturing technologies that is greatly connected to particles emission. Particles generated during the grinding process are dangerous in terms of its potential penetration deeply into the lungs of an operator. The level of risk for human respiratory system is related to nature, shape and size of the particles, and for this reason it is important to have a quality characterization of emitted particles. This paper focuses on particles characterization on the bases of image analysis from scanning electron microscopy (SEM). The research was conducted during the process of grinding of steel EN 90MnV8, using personal sampler. Results of image analysis, consisted of Feret’s diameter and circularity, showed quite a wide range of sizes and significant deviation of particles from regular shape

Učinkovitost i kvaliteta indukcijskog zagrijavanja i kaljenja osovina startera dizel motora

Presented work discusses a complex process of inductive heating and quenching of carbon steel planetary shafts for diesel engine starters. On the measurements base of temperature fields on the surface of the planetary shafts by thermographic camera and theoretical knowledge, a mathematical model for temperature conditions determination in the shaft during the entire process of heating and quenching was carried out. On the basis of developed mathematical model a computer program was developed, and used for analyses and induction hardening process optimization of planetary shafts.U ovom se radu raspravlja o složenom procesu indukcijskog zagrijavanja i kaljenja osovina iz ugljičnog čelika za pokretanje dizelskih motora. Na temelju rezultata mjerenja temperaturnih polja na površini osovina termografskom kamerom i teorijskih spoznaja, razvijen je matematički model temperaturnih uvjeta tijekom procesa zagrijavanja i kaljenja osovina. Na temelju postavljenog matematičkog modela razvijen je računalni program koji je korišten za analizu i optimizaciju procesa zagrijavanja osovina

Effect of nonmetallic inclusions on steel welds metal hot cracking

Intercrystally distributed nonmetallic inclusions greatly increase weld susceptibility to hot cracking. Oxide and sulphide inclusions are the result of contaminated base material or its highly oxidised surfaces and they can be a consequence of metallurgical reactions between welding slag and remelted base material, while carbide inclusions can occur due to the mixing of high-carbon base and low-carbon filler material. All welding surfaces must thus be cleaned before welding and the least possible mixture of base with filler material must be enusured during welding

Structural and thermodynamic analysis of whiskers on the surface of grey cast iron

The paper focuses, first, on the characterization of the whiskers on the surface of grey cast iron and second, it gives an explanation of whiskers growth based on thermodynamic calculations. The whiskers were observed on the surface of hot plates for the electric stove after black-oxide-coating (blackening) performed the furnace at 650°C in order to produce a protective layer mainly of magnetite (Fe3O4). However, the whiskers caused brown spots on dark grey surface and thus, the surface was aesthetically damaged. The investigations confirmed that whiskers are of hematite (Fe2O3); however, the thermodynamic calculations present that hematite may be formed as a result of the oxidation of magnetite if the partial pressure of oxygen is increased during the blackening

Microstructure evolution and thermal stability of rapidly solidified Al-Ni-Co-RE alloy

In the frame of this work, Al-5Ni-1Co-3RE (RE-Rare Earth (Mischmetal)) rapidly solidified ribbons were manufactured and analyzed. The morphology of the as-cast structure, as well as the microstructural features were analyzed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Thermal stability has been investigated by combination of four point scanning electrical resistivity measurement (ER), differential scanning calorimetry (DSC) and microhardness measurement. From the results we can conclude, that Al-5Ni-1Co-3RE rapidly solidified alloys have good thermal stability due to very slow coarsening kinetics of precipitated particles

Structural and thermodynamic analysis of whiskers on the surface of grey cast iron

The paper focuses, first, on the characterization of the whiskers on the surface of grey cast iron and second, it gives an explanation of whiskers growth based on thermodynamic calculations. The whiskers were observed on the surface of hot plates for the electric stove after black-oxide-coating (blackening) performed the furnace at 650°C in order to produce a protective layer mainly of magnetite (Fe3O4). However, the whiskers caused brown spots on dark grey surface and thus, the surface was aesthetically damaged. The investigations confirmed that whiskers are of hematite (Fe2O3); however, the thermodynamic calculations present that hematite may be formed as a result of the oxidation of magnetite if the partial pressure of oxygen is increased during the blackening