Melting Temperature Of Steel Research Articles

Increase in the Slag Resistance of Refractories Based on the Al<sub>2</sub>O<sub>3</sub>-SiC-SiO<sub>2</sub> System

The technology for manufacturing corundum-carbide-silicon refractories with increased slag resistance has been developed. It is shown that one of the directions for improving the quality of carbon-containing products is the creation of protective antioxidant coating on the surface of particles. A dense protective film is formed during the processing on the surface of carbon-containing particles. The coating does not break down when heated to the melting temperature of steel. Therefore, the number of heat-conducting particles in the bond can be increased without the risk of loss of strength. An increase of the number of high-heat-conducting particles reduces the value of the temperature gradient inside the refractory and reduces the zone impregnated with the melt. A technique has been developed that makes it possible to determine the degree of interaction of a refractory with metal (slag) in ground samples under the binocular microscope MBS-9. The proof of high slag resistance is the depth of penetration of metal and slag into the structure of the sample by not more than 1 to 2 mm without changing the lateral surface of the conical hole.

Long-pulse quasi-CW laser cutting of metals

Long-pulse quasi-CW laser cutting of metals is well suited to small-scale manufacturing settings where process flexibility is of high value and investment capacity is limited. This process refers to cutting operations performed with millisecond laser pulses obtained through modulation of the pump source to achieve continuous-wave (CW) operation over limited time intervals. The ability to minimize heat conduction losses, comprising the vast majority of absorbed laser power at low velocity, allows processing of relatively thick sections compared to what would be possible at the same average power with a CW laser source. The present study quantifies the reduction in heat conduction losses with pulsed exposure by employing a simple power-balance representation of the heat flow problem. Laser-cutting experiments are performed with inert and active assist gases on 1- and 4-mm thick steel samples, varying peak power (0.3–3 k W), pulse energy (0.3–12 J), repetition rate (25–1000 H z), and velocity (1–40 m m/s). The lowest minimum laser cutting power and highest cutting efficiency are achieved with maximum peak power and lowest permissible pulse overlap for a continuous cut. Under these conditions, heat conduction losses are reduced by more than 60% with nitrogen assist gas compared to CW exposure and more than 50% with oxygen. The calculated average cutting front temperatures are 450–630 ∘C and 620–900 ∘C, respectively, well below the melting temperature of steel. Lowest dross adhesion and cut edge surface roughness are obtained with oxygen assist gas, leading to both the lowest minimum average cutting power and highest cut quality. These results demonstrate an efficient process that improves the feasibility of low velocity laser cutting and therefore the range of industrial applications in which laser technology can employed.

GTA-GMA 하이브리드공정에 따른 자동차용 아연도금강판의 용접부 기공감소 (I) - 선행 GTA의 영향

The Zn coating on automotive galvanized steel sheets can improve corrosion resistance. However, the boiling temperature of Zn is lower than the melting temperature of steel and it causes well-known spatter and porosity problem. One of most prominent solutions is a pretreatment of Zn coating by an additional welding arc prior to the main welding process. In this research, GTA and GMA are selected as heat sources for pretreatment and main welding processes, respectively. The authors suggested three possible mechanisms to reduce weld defects by the GTA pretreatment: (1) Formation of gap between the sheets; (2) Evaporation of Zn layer; (3) Oxidation of Zn layer. Among them, Zn Oxidation is the most important mechanism to reduce weld defects in the GTA-GMA hybrid process.

X-선 투과검사를 이용한 저항 점용접부 품질평가기법

For the resistance spot welds of CR1180 and GA1180 TRIP steels, the weld quality evaluation method using the digitalized X-ray transmission imaging apparatus was investigated in comparison with the crosssectional examination method. In the case of the resistance spot welding of CR1180, three circular regions, such as WZ(white zone), GZ(grey zone) and DZ(dark zone), appeared on X-ray image and they corresponded to the diameters of indentation mark, nugget and corona bond, respectively. The variation of X-ray transmission thickness due to the thickness variation of the weld seemed to be mainly responsible for the formation of those contrasts. The X-ray image contrast formed from the variation of transmission thickness at the outer border line of DZ could also enable the inspections of the notch shape, nonuniformity of the welding pressure and spatter from its sharpness, concentricity and the normal straight line, respectively. The X-ray image of the resistance spot weld of galvannealed GA1180 TRIP steel was very similar to that of CR1180 TRIP steel except the crown shaped outer border line of DZ which was considered to be due to the melting behavior of zinc having the boiling temperature even lower than the melting temperature of steel.

Laser welding of zinc coated steels in an edge lap configuration

Ever increasing amounts of zinc coated sheet steel are being applied in the automotive industry. At present, the main joining method used for this application is resistance spot welding. In many automotive applications there are opportunities for replacing this technique by laser welding. During the assembly of these sheets major problems arise when welding in overlap configuration as result of the low boiling temperature of zinc in comparison to the melting temperature of steel. This results in pores and/or blowholes in the weld due to instabilities during welding. In this article research is presented which shows the possibilities of welding these zinc coated steel sheets in an edge lap configuration without present gap. In this configuration the zinc vapor between the sheets has an alternative escape route other than through the weld pool and it is shown that the amount of spatter can be controlled when using such a joint configuration.

Effect of Outside Cooling on the Thermal Behavior of a Pressurized Water Reactor Vessel Lower Head

Flooding of the reactor vessel cavity is one of many accident management strategies being proposed to manage severe accidents in light water reactors. The effect of external cooling on the thermal behavior of the vessel lower head containing molten core material is numerically investigated using a two-dimensional implicit finite difference scheme. Results are obtained for the vessel shell temperature, pool temperature, and crust thicknesses for both unsteady and steady-state conditions. For both cases, the thermal behavior of the vessel lower head is investigated by parametrically changing the emissivity of the pool surface, the vessel wall, and the upper structure and by changing the temperature of the upper structure. For a certain set of parameters, nucleate boiling on the outer surface of the vessel wall is effective in lowering the temperature of the inner wall of the vessel below the melting temperature of steel. Steady-state results are obtained by using two different heat transfer correlations for the natural convection in the molten pool, which helps in understanding how uncertainties in the modeling of physical processes can influence the evaluation of accident management strategies.