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The sludge produced from the pickling of stainless bands settles to the bottom of the pickling tank and becomes an impediment to the operation. In The neutralized sludge is loaded into a lugger bag and can be used as a raw material for steei making.

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Iron oxides can be reduced in a scale by batch annealing treatment in a reducing atmosphere of 7 vol% H2+93 vol% N2 at 1123 K for hot-rolled coils of type430 stainless steel. The heating processes cause cracks, a Cr2O3 layer in the scale and a Cr depleted layer on the substrate. It is possible to produce a large number of cracks in the scale by employing a scale breaker. The ease of descaling is positively related to the amount of bending elongation. Similarly with shot blasting, descaling becomes easier as the projection energy of the shot blasting increases. The pickling solution penetrates the scale through cracks on the surface of the strip, and its acid dissolves the stainless steel coil and part of the scale. The scale peels from the stainless steel coil in island-like exfoliation until the scale has been removed from the entire surface of the stainless steel coil.

In the preliminary studies, the followings are verified:(1 ) As a method of analyzing hydrofluoric acid, the iron-acetylacetone complexdiscoloration absorbance method is adopted.(2) As a method of ana]yzing nitric acid, the method of subtracting the concentration of hydrofluoric acid from the total acid amounts obtained by neutralization titration is adopted. As a method of analyzing the iron content, the iron-salicylic acid complex absorbance method is adopted, By fu[ly automating the series of analytical processes described above, the following are achieved:(1 ) The work load of line operators can be reduced, making substantial labor saving possible.

The microstructural influence of martensitic carbon steel on torsional fatigue endurance was investigated, taking into consideration the application of high strength steel electric resistance welded (ERW) tubes to automotive structural parts. The chemical composition of the base steel alloy was 0.1-0.2%C-0.2-1.5%Si-1.3-1.9%Mn-0.01%P-0.001%S-(Cr,Mo,Ti,Nb,B). Laboratory vacuum-fused ingots were hot-rolled, heated to 1023 or 1223 K in a salt bath, and then waterquenched and tempered at 473 K. Consequently, three types of microstructure, martensite (M), martensite and ferrite (M+F), and ferrite and pearlite (F+P), were prepared. Fully reversed torsional fatigue testing was conducted with 6 mm diameter round bar specimens. Torsional fatigue endurance was found to monotonously increase with increases in the tensile strength of the specimen from 540 to 1380 MPa. The martensitic single structure and the M+F dual-phase structure showed a similar level of fatigue endurance at a tensile strength of approximately 950 MPa. However, fatigue micro-crack morphology varied slightly between them. At the surface of the M+F specimen, many small cracks were observed in addition to the main crack. Conversely, in the martensitic specimen, these small cracks were rarely observed. ∆K decreasing/increasing crack growth testing with compact tension (CT)-type specimens was also conducted. Based on these experimental results, the effect of microstructure and stress level on the initiation/propagation cycle ratio is discussed. In addition to fatigue properties, some practical properties, such as low-temperature toughness and hydrogen embrittlement resistance, were also evaluated in view of actual applications for automotive structural parts.