製鋼工場に於ける品質管理の一例

抄録

Quality control has been recently adopted in various fields of industry and now the authors gave a glance at it in their steel-making plant. Steel-making operations are divided into four parts; namely material preparation, meltng, refining and teeming, so some examples in each operation were shown.
1. Material preparation:
Pig iron and scrap steel were classified and the ratio of pig iron to scrap steel used was determined according to the quality of steel to be produced, in order to make succeeding operations easier.
2. Melting operation:
In the melting period, the most suitable carbon content at melt-down was aimed at to get the shortest heat time, which proved to be 0.55% C and 0.65% C for sheet and plate steel respetively in the 35t O.H.F. and 0.45% C (sheet steel only) in the 70t O.H.F.
In the acceleration of combustion by using oxygen through furnace-end burners, most advantageous method or "6-5-4 method" is being adopted. According to this method, oxygen flows into the furnace in the rate of 6m³/min, 5m³/min. and 4m³/min. for the three periods of onehour from the start of charging, 2 hours, therefrom and the remaining time till melt-down after that, respectively.
3. Refining:
To improve the weldability of the hull plate, a chart was prepared which showed the suitable weight of ferro-manganese to be thrown into ladle to make Mn/C in steel over 2.5.
4. Teeming:
In pouring, standard operations were as follows:
a) To decrease the brick and clay marks of ingots, silica mortar was used and newly lined ladle was avoided.
b) A wooden plate was floated over the molten steel in each of six molds around the central pouring well in the bottom pouring, in order to reduce violent metal splashes, which might cause scabs of ingots.