Scaling Behaviour of Si-alloyed Steel Slabs under Reheating Conditions

Reheating of steel slabs for further processing such as hot rolling usually takes place in gas-fired pusher furnaces. Temperatures well above 1000°C, combined with an atmosphere containing H2O, CO2, and O2, lead to substantial oxidation of most steel grades. Newly developed advanced steels often contain significant amounts of Si. This element plays a dominant role in the scaling behaviour near the steel-scale-interface, since fayalite (Fe2SiO4) forms a eutectic with wuestite (Fe1–xO) that melts as low as 1177°C.To better understand the high temperature oxidation behaviour, lab-scale trials were performed with different steel grades containing up to 3 wt.% Si. Possible interactions of Si with other alloying elements present in the samples such as Cr, Mn and Al were also of interest. The atmosphere contained 20% H2O, 7% CO2, and 3% O2, resembling reheating conditions in pusher furnaces, and temperatures ranged from 1100 to 1240°C. For metallographic investigation, the oxidised samples were cold mounted under vacuum using taper section angles. After preparation, the sections were examined through light microscopy, SEM/EDS, XRD, and TEM. The local distribution of the alloying elements could be mapped efficiently, and phase identification was successful in most parts. Under the applied experimental conditions, the elements of interest were present in their oxidic form either as pure or as mixed oxides. Higher Si-contents led to an increased build-up of eutectic melting phase at the steel-scale-interface at temperatures above 1177°C, which in turn further accelerated the oxidation.

Reduction of Fuel Utilization Through Oxygen-Enriched Combustion in a Reheat Furnace Pusher-Type

Steelmaking is an energy-intensive process. Thus, energy efficiency is highly important. Several stages of steelmaking involve combustion processes. One of the most energy-consuming processes in steelmaking is the slab reheating process in a reheat furnace (RF). The energy released by fuel combustion is used to heat steel slabs to their proper hot-rolling temperature. The steel slabs move through the reheat furnace passing the three stages of heating called: Preheating Zone (PZ), Heating Zone (HZ), and Soaking Zone (SZ) to finally leave the discharge door at a rolling temperature of 2375 °F. One way to improve a reheat furnace’s fuel consumption is by implementing oxygen-enriched combustion. This study investigates the implementation of oxygen-enriched combustion in a pusher-type reheat furnace. The increment of oxygen in the combustion process allows for increasing the furnace gas temperature. Consequently, the oxygen enrichment approach allows for the reduction of fuel injection. The principal goal of this investigation is to model the combustion-based on oxygen-enrichment and develop parametric studies of fuel injection rates. The different simulations aim to match the slab heat flux profile of the industrial reheat furnace pusher-type. Computational fluid dynamics are used to generate the slab heat flux distribution. To reach more uniform slab heating, oxygen and fuel ports were alternated. Also, injection angles were modified to optimize slab heating and avoid the impact of hot spots. Thermocouple readings of the industrial reheat furnace are compared to simulation results. The results determined that 40–45% fuel reduction can be achieved.

Analisis Penyebab Kerusakan Unit Pompa Pendingin AC dan Kompresor menggunakan Metode FMEA

PT. XYZ is a company engaged in the steel industry which produces steel slabs, steel billets, steel plates and steel wires. One of the equipment that often gets damaged is the air conditioning pump and compressor unit in the fluid center service. The results of the availability of the AC and compressor refrigeration pump units show that the availability value is still below the company standards set so that an analysis of the root causes of the problem is needed and finding the best solution to fix existing problems by applying the failure mode and effect analysis (FMEA) method. FMEA is a method that systematically and structurally can analyze and identify the consequences of system and process failures and reduce or analyze the chances of failure. The purpose of this study is to identify and analyze the level of damage and its causes by applying the FMEA method. Based on the Pareto diagram of the damage to the air conditioning pump and compressor engine unit, it was found that the highest frequency of damage was the power supply with a down time percentage of 32.4%. The results of FMEA analysis produce two components that have a very high RPN value which is categorized as potential severity, namely fuse as the first component with an RPN value of 378 and the second is a fuse holder with an RPN value of 252. These two components are the main priority for improvement in the pump engine unit air conditioners and compressors especially for the machine and human aspects.

The effect of casting speed on slag-inclusion defects in 1050 × 200 mm ultra-low-carbon automobile steel slabs

The effect of casting speed on slag-inclusion defects in 1050 × 200 mm ultra-low-carbon automobile steel (UAS) slabs was studied by performing nail plate experiments and by monitoring the liquid level fluctuations during the continuous casting process. The number, location, length, and proportion of slag-inclusion defects in hot-rolled coils produced at different casting speeds were analyzed. The results showed that the defects in the hot-rolled coils were mainly owing to the mold protective slag. For the continuous casting speed of 1.6 m/min, the fraction of slag-inclusion defects was the lowest (at 5.3%), and the number of slag-inclusion defects was lower than for the other casting speeds. The length of slag inclusions was under 900 mm. Furthermore, the number of slag-inclusion defects on the upper and lower surfaces was smaller than those for the other casting speeds. At different casting speeds, slag-inclusion defects mainly existed within 100 mm of the edge on both surfaces of hot-rolled coil plates. The fluctuation within the 0–1 mm range was 98.1% for the casting speed of 1.6 m/min, indicating that the flow rate of molten steel on both sides of the nozzle was relatively stable, which helps to control slag-inclusion defects in hot-rolled coils.