A method for manufacturing a high-strength galvanized steel sheet. The method includes a first heating step of holding the steel sheet in a temperature range of 750 C. to 880 C. for 20 s to 600 s in an atmosphere having an H.sub.2 concentration of 0.05% to 25.0% by volume and a dew point of 45 C. to 10 C., a cooling step, a rolling step of rolling the steel sheet with a rolling reduction of 0.3% to 2.0%, a pickling step of pickling the steel sheet with a pickling weight loss of 0.02 gram/m.sup.2 to 5 gram/m.sup.2 in terms of Fe, a second heating step of holding the steel sheet in a temperature range of 720 C. to 860 C. for 20 sec. to 300 sec. in an atmosphere having an H.sub.2 concentration of 0.05% to 25.0% by volume and a dew point of 10 C. or lower, and a galvanizing step.

A method for manufacturing a high-strength galvanized steel sheet. The method includes a first heating step of holding the steel sheet in a temperature range of 750 C. to 880 C. for 20 s to 600 s in an atmosphere having an H.sub.2 concentration of 0.05% to 25.0% by volume and a dew point of 45 C. to 10 C., a cooling step, a rolling step of rolling the steel sheet with a rolling reduction of 0.3% to 2.0%, a pickling step of pickling the steel sheet with a pickling weight loss of 0.02 gram/m.sup.2 to 5 gram/m.sup.2 in terms of Fe, a second heating step of holding the steel sheet in a temperature range of 720 C. to 860 C. for 20 sec. to 300 sec. in an atmosphere having an H.sub.2 concentration of 0.05% to 25.0% by volume and a dew point of 10 C. or lower, and a galvanizing step.

To make ultrasonic waves can be propagated with better efficiency throughout the entirety of a treatment tank, and an object to be cleaned can be cleaned with better efficiency regardless of the type of the object to be cleaned.

An ultrasonic cleaning equipment (1) according to the present invention includes a treatment tank (10) that stores a cleaning liquid that cleans an object to be cleaned and in which the object to be cleaned is immersed; an ultrasonic application mechanism (20) that applies ultrasonic waves to the cleaning liquid retained in an interior of the treatment tank; and a curved surface member (30) that is located in a range prescribed by a prescribed angle of inclination from a normal direction in an end portion of a vibrating surface of the ultrasonic application mechanism to an outside with respect to the vibrating surface and that is held on a wall surface and/or a bottom surface of the treatment tank. The curved surface member has a convex curved surface (31) in which at least a convex curved part (33) having a surface shape of a spherical surface or an aspherical surface exists and the convex curved part is in a state of protruding more on a side of the vibrating surface than a portion other than the convex curved part does, and the convex curved surface is held in a state of facing the vibrating surface in such a manner that at least part of first sound waves that are sound waves that are applied from the ultrasonic application mechanism and that have not experienced reflection arrive at the convex curved part of the convex curved surface.

A high-strength steel sheet with excellent formability and high yield ratio that has TS of 980 MPa or more and YR of 68% or more is obtained by providing a predetermined chemical composition and a steel microstructure that contains, in area ratio, 15 to 55% of polygonal ferrite, 8% or more of non-recrystallized ferrite, and 15 to 30% of martensite, and that contains, in volume fraction, 12% or more of retained austenite, in which the polygonal ferrite has a mean grain size of 4 m or less, the martensite has a mean grain size of 2 m or less, the retained austenite has a mean grain size of 2 m or less, and a value obtained by dividing an Mn content in the retained austenite (in mass %) by an Mn content in the polygonal ferrite (in mass %) equals 2.0 or more.

A high-strength steel sheet with excellent formability and high yield ratio that has TS of 980 MPa or more and YR of 68% or more is obtained by providing a predetermined chemical composition and a steel microstructure that contains, in area ratio, 15 to 55% of polygonal ferrite, 8% or more of non-recrystallized ferrite, and 15 to 30% of martensite, and that contains, in volume fraction, 12% or more of retained austenite, in which the polygonal ferrite has a mean grain size of 4 m or less, the martensite has a mean grain size of 2 m or less, the retained austenite has a mean grain size of 2 m or less, and a value obtained by dividing an Mn content in the retained austenite (in mass %) by an Mn content in the polygonal ferrite (in mass %) equals 2.0 or more.

A process for manufacturing a cold-rolled steel sheet with a strength of at least 1200 MPa and an elongation at break greater than 10%. A steel is provided having a microstructure comprising 65 to 90% bainite. A semifinished product is cast from the steel and heated to a temperature greater than 1150 C. The semifinished product is hot rolled to obtain a hot-rolled sheet; the coiled and pickled. Cold-rolling occurs with a reduction ratio of between 30 and 80% so as to obtain a cold-rolled sheet; and then reheating occurs at a rate V.sub.c between 5 and 15 C./s up to a temperature T.sub.1 between Ac3 and Ac3+20 C. and held at said temperature T.sub.1 for a time t.sub.1 between 50 and 150 s. The sheet is cooled at a rate V.sub.R1 greater than 40 C./s but below 100 C./s down to a temperature T.sub.2 between (M.sub.s30 C. and M.sub.s+30 C.). The sheet is maintained at temperature T.sub.2 for a time t.sub.2 between 150 and 350 s, and then cooled at a rate V.sub.R2 of less than 30 C./s down to an ambient temperature.

A process for manufacturing a cold-rolled steel sheet with a strength of at least 1200 MPa and an elongation at break greater than 10%. A steel is provided having a microstructure comprising 65 to 90% bainite. A semifinished product is cast from the steel and heated to a temperature greater than 1150 C. The semifinished product is hot rolled to obtain a hot-rolled sheet; the coiled and pickled. Cold-rolling occurs with a reduction ratio of between 30 and 80% so as to obtain a cold-rolled sheet; and then reheating occurs at a rate V.sub.c between 5 and 15 C./s up to a temperature T.sub.1 between Ac3 and Ac3+20 C. and held at said temperature T.sub.1 for a time t.sub.1 between 50 and 150 s. The sheet is cooled at a rate V.sub.R1 greater than 40 C./s but below 100 C./s down to a temperature T.sub.2 between (M.sub.s30 C. and M.sub.s+30 C.). The sheet is maintained at temperature T.sub.2 for a time t.sub.2 between 150 and 350 s, and then cooled at a rate V.sub.R2 of less than 30 C./s down to an ambient temperature.

A treatment device for single-stage treatment of a metal object to be treated by at least the steps of pickling and phosphating. The treatment device comprises at least the following: a treatment container for receiving the object to be treated and for receiving a flowable treatment substance; and a pump device for exchanging at least a fraction of the treatment substance. The treatment substance is flowable around at least one part of the object to be treated. The treatment substance comprises a phosphor- or phosphate-containing solution, in particular phosphoric acid. The phosphor- or phosphate-containing solution consists partly of water and partly of a reaction substance, and the reaction substance consists of phosphor or a phosphate and an additional treatment effect-improving substance. The proportion of the phosphor or phosphate in the reaction substance is at least 95%, and the reaction substance does not have a salt acid or sulfuric acid content.

A treatment device for single-stage treatment of a metal object to be treated by at least the steps of pickling and phosphating. The treatment device comprises at least the following: a treatment container for receiving the object to be treated and for receiving a flowable treatment substance; and a pump device for exchanging at least a fraction of the treatment substance. The treatment substance is flowable around at least one part of the object to be treated. The treatment substance comprises a phosphor- or phosphate-containing solution, in particular phosphoric acid. The phosphor- or phosphate-containing solution consists partly of water and partly of a reaction substance, and the reaction substance consists of phosphor or a phosphate and an additional treatment effect-improving substance. The proportion of the phosphor or phosphate in the reaction substance is at least 95%, and the reaction substance does not have a salt acid or sulfuric acid content.

A treatment device is provided for single-stage treatment of a metal object, wherein the treatment comprises at least pickling and phosphating of the object. The treatment device comprises a treatment container for holding the object to be treated and for holding a flowable treatment substance, and a pumping apparatus for circulating at least a portion of the treatment substance. The treatment substance is flowable around at least part of the object to be treated, and the treatment substance is a phosphorus- or phosphate-containing solution. The phosphorus- or phosphate-containing solution consists of water and a reaction substance, and the reaction substance consists of phosphorus or of a phosphate and at least one additional substance that improves the treatment effect. The fraction of the phosphorous or the phosphate in the reaction substance is between 75 vol % to 94 vol %, and the reaction substance has no fractions of hydrochloric acid and sulfuric acid.