Carburizing furnaces

Small batch retorts, heated electrically or hy combustion, are widely used as carburizing furnaces and are applicable also to chemic processes involving the heat treating of particulate sohds. These are mounted on a structural-steel base, complete with cyhnder, furnace, drive motor, burner, etc. Units are commercially av able in diameters from 0.24 to 1.25 m and lengths of 1 to 2 m. Continuous retorts with helical internal spirals are employed for metal-heat-treating purposes. Precise retention control is maintained in these operations. Standard diameters are 0.33, 0.5, and 0.67 m with effec tive lengths up... 

Environments. Among the environmental factors that can shorten life under thermal fatigue conditions are surface decarburization, oxidation, and carburization. The last can be detrimental because it is likely to reduce both hot strength and ductility at the same time. The usual failure mechanism of heat-resistant alloy fixtures in carburizing furnaces is by thermal fatigue damage, evidenced by a prominent network of deep cracks. 

All this taken together illustrates that a carburization furnace will in any case, be a compromise in regard to lifetime. 

FIGURE 9.5. Push-type carburization furnaces used for conventional powder carburization (maximum temperature 1650 °C). By courtesy of Wolfram Bergbau und Hiittenges.m.b.H, Austria. 

FIGURE 9.6. High-temperature carburization furnace with graphite resistance heating system capable of 1500 to 2400 °C continuous operation automated introduction and discharge of the powdered product loaded in graphite carriers. By courtesy of Harper International, USA. 

Heat-treatment Gas carburizing Furnace components 870-1090X Carburization... 

Gas carburizing Furnace brick anchors. 540-820 X Metal dusting... 

Carburization was carried out in a fixed-b i stainlras strel reactor (ID = 6 mm). Typically about 0.5 g of metal sulphide was sandwiched between 2 layers of quartz wool placed centrally in a temperature-programmed furnace. iTie sample was heated at 10 Kmin" to the... 

The Primary Reformer is a steam-hydrocarbon reforming tubular furnace that is typically externally fired at 25 to 35 bar and 780°C to 820°C on the process side. The reformer tubes function under an external heat flux of 75,000 W/m2 and are subject to carburization, oxidation, over-heating, stress-corrosion cracking (SCC), sulfidation and thermal cycling. Previously SS 304, SS 310 and SS 347 were used as tube materials. However these materials developed cracks that very frequently led to premature tube failures (see Table 5.10)88. 

The feedstock in hydrodealkylation units is heated to 1,200° F (650°C) in a preheat furnace before entering the reactor. Above 1,100°F (590°C), metal dusting or catastrophic carburization occurs on ail alloys that are otherwise suitable for the temperature conditions. The attack is very rapid and takes the form of round bottom pits. The surface of the remaining metal is heavily carburized. A small quantity of sulfur (0.05 to 0.5 wt%) in the form of hydrogen sulfide or mercaptan added to the feed will prevent attack. Aluminizing has also been used to prevent attack. 

A steel part whose initial carbon content is 0.12 pet cent by mass is to be case-hardened in a furnace at 1150 K by exposing it to a carburizing gas. The diffusion coefficient of carbon in steel is strongly temperature dependent, and at the... 

The following furnace types are utilized for carburization reactions ... 

The Leeds Northrup Co. has developed a two-couple continuous curve recorder for automatically heating furnaces to definite temperatures. As applied in carburizing and tempering of steel one thermocouple is placed in the furnace chamber and the other in contact with the steel piece. The controller automatically maintains the furnace for instance at 1,000°C. until the steel has reached 900°C. and then it drops the furnace to 900 C. Such an arrangement for control can be applied to a great many processes. 

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