Hot rolling

Metal Cleaning. About 204 thousand metric tons of HCl (100% basis) was consumed in 1993 for steel pickling, wherein the hydrochloric acid readily dissolves all of the various oxides present in the scale formed during the hot rolling process. Using suitable inhibitors such as alkyl pyridines, HCl reacts very slowly with the base metal rendering the surface so clean that it must be passivated with a mild alkaline rinse. 

The development of a sharp COE texture in the finished strip requires complex control of numerous variables. The conventional commercial process (18) involves hot-rolling a cast ingot at ca 1370°C to a thickness of about 2 mm, annealing at 800—1000°C, and then cold-rolling to a final thickness of 0.27—0.35 mm in two steps of 70 and 50%, respectively, with a recrystallization (800—1000°C) aimeal in between. The cold-roUed strip is decarburized (800°C) to ca 0.003% C in mixtures of wet results in a primary recrystallized stmcture containing grains of the COE... 

Fig. 14. Hot rolling of steel slabs to plate. In the foreground is a steel plate mill behind the plate is the next slab to be roUed.

W. L. Roberts, Hot Rolling of Metals, Marcel Dekker, New York, 1983. 

Cathodes Hot rolled and cold rolled to produce strip and sheet... 

Heavily scaled and heavily rusted surfaces (hohrotled sheets) Heavily scaled, but mildly rusted-surfaces (hot-rolled sheets) Mildly scaled and mildly rusted surfaces (cold-rolled sheets) ... 

This is a process to remove heavy black scale and rust from the surface. Hot-rolled sheets that may have such scale formation need only be acid pickled. Cold-rolled sheets, which may carry no such scales, need not be acid pickled. Depending upon the type of surface, one of the following methods may be adopted. 

The torque required to drive the rolls increases with yield strength so hot-rolling (when CTy is low - see Chapter 17) takes less power than cold-rolling. It obviously increases with the reduction in section (t - t2). And it increases with roll diameter 2r this is one of the reasons why small-diameter rolls, often backed by two or more rolls of larger diameter (simply to stop them bending), are used. 

It is required to find the torque without slippage that can be transmitted by a hub that is assembled by an interference fit to a powered shaft. The hub outside diameter D = 070 mm, and the shaft diameter d = 050 mm, as shown in Figure 4.55. The length of the hub is 100 mm. Both hub and shaft are machined from hot rolled steel SAE 1035 with a yield strength Sy A(342,26) MPa (see Table 4.6). Given that the hub is stopped suddenly in service due to a malfunction, and considering only the torsional stresses, what is the probability that the shaft will yield ... 

A suitable material would be hot rolled mild steel 070M20, which has a minimum yield strength, S jVin = 215 MPa (BS 970, 1991). By considering that the minimum yield strength is —3 standard deviations from the mean and that the typical coefficient of variation = 0.08 for the yield strength of steel, the Normal distribution parameters for 070M20 can be approximated by ... 

The load carried comprises approximately half the mass of the conveyor unit (50 9 kg), and half the mass of the items being conveyed at any one time. The mass of the items being conveyed on half of each conveyor unit fluctuates from 0 to 72 kg, approximately following a Normal distribution. The material specified for the hanger is hot rolled Grade 43C structural steel, which has a minimum yield strength SjVin = 275 MPa for a thickness t < 16 mm (BS 4360, 1990). 

The above equations ean all be written in terms of the nominal dimensions, a, b and t, for the seetion. Solutions for the mean and standard deviation of eaeh property, for any seetion, ean be found using Monte Carlo simulation with knowledge of the likely dimensional variation for hot rolling of struetural steel seetions. The eoeffieient of variation for this proeess/material eombination is = 0.0083 (Haugen, 1980). 

A speeifie statistieal representation of the yield strength for Grade 43C hot rolled steel is not available however, the eoeffieient of variation, for the yield strength of British struetural steels is given as 0.05 for a thiekness t < 12.7 mm (Rao, 1992). For eonvenienee, the parameters of the Normal distribution will be ealeulated by assuming that the minimum value is —3 standard deviations from the expeeted... 

Shafts are made of material ranging from medium carbon to low alloy steel and are usually heat treated. Shafts were originally made of forgings for the compressors in process service. But because of the availability ot high quality material, hot rolled bar stock has been used for shafts up to S inches in diameter. Bar stock shafts are given the same heat treatment and quality control as forgings. Many of the process users prefer a low alloy, chrome-moly-nickel material for shafting, particularly for compressors in critical service. 

Lenard, J.G., Pietrzyk. M. and Cser, L. (1999) Mathematical and Physical Simulation of the Properties of Hot-Rolled Products (Elsevier, Amsterdam). 

The slabs, blooms, or billets are then transported to the hot rolling mill for rolling into steel products which can be used by the manufacturing industry. 

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