A high-strength plated steel sheet has a plated layer on the surface of a base steel sheet and contains predetermined steel components. The steel sheet includes, in the order from the interface of the base steel sheet and the plated layer towards the base steel sheet: a soft layer having a Vickers hardness that is 90% or less of the Vickers hardness at a portion t/4 of the base steel sheet, where t is a sheet thickness of the base steel sheet; and a hard layer containing martensite and bainite, and ferrite in predetermined ranges. The average depth D of the soft layer is 20 μm or greater, and the average depth d of an internal oxide layer is 4 μm or greater and smaller than D.

A Si/Mn ratio of steel material components of a base material is not less than 0.27 nor more than 0.90 in mass ratio, an internal oxide layer having a thickness of not less than 1 μm nor more than 30 μm is provided right below an oxide scale of a steel sheet surface layer portion, and regarding the internal oxide layer, an internal oxide in a crystal grain of the internal oxide layer is an oxide containing Si and having a thickness of not less than 10 nm nor more than 200 nm in a crystal grain in a range of greater than 0% and 30% or less of a thickness of the internal oxide layer from an interface between the internal oxide layer and base iron toward a direction of the surface layer oxide scale, one or more branches of the internal oxide exist in a cross section of 1 μm×1 μm square, and in any crystal grain boundary having a length of 1 μm, one or more of the internal oxides in the crystal grain are connected to an internal oxide of the crystal grain boundary to form a net-like structure.

A Si/Mn ratio of steel material components of a base material is not less than 0.27 nor more than 0.90 in mass ratio, an internal oxide layer having a thickness of not less than 1 μm nor more than 30 μm is provided right below an oxide scale of a steel sheet surface layer portion, and regarding the internal oxide layer, an internal oxide in a crystal grain of the internal oxide layer is an oxide containing Si and having a thickness of not less than 10 nm nor more than 200 nm in a crystal grain in a range of greater than 0% and 30% or less of a thickness of the internal oxide layer from an interface between the internal oxide layer and base iron toward a direction of the surface layer oxide scale, one or more branches of the internal oxide exist in a cross section of 1 μm×1 μm square, and in any crystal grain boundary having a length of 1 μm, one or more of the internal oxides in the crystal grain are connected to an internal oxide of the crystal grain boundary to form a net-like structure.

A novel method of blackening surgical needles is disclosed. Surgical needles having outer surfaces are first placed into a first pretreatment bath having a novel composition. The needles are then placed into a second blackening bath having a novel composition for a sufficient period of time to effectively blacken the surfaces of the needles. The novel methods for blackening the surfaces of a stainless steel alloy surgical needle provide a chromium (VI)-free alternative to current needle manufacturing processes. Another unique feature of this novel method is its short processing time. The blackening processes of the present invention can be utilized for in-line treatment processes which can be easily incorporated into high speed needle manufacturing processes, such as strip mounted processes. In addition, the processes of the present invention are readily adaptable to batch processes. Also disclosed are novel systems for blackening surgical needles and novel blackening baths for surgical needles.

An aqueous synthetic acid composition for use in oil industry activities comprises lysine and hydrogen chloride in a molar ratio ranging from 1:3 to 1:12.5, preferably from more than 1:5 to 1:8.5. The composition can also further comprise a metal iodide or iodate; an alcohol or derivative thereof. The composition demonstrates advantageous properties over known synthetic acids at temperatures above 90° C. The composition is useful in various oil and gas industry operations. Preferred embodiments of the composition provide substantial advantages in matrix acidizing by increasing the effectiveness of wormholing as compared to conventional mineral acids such as HC1.

A composition for inhibiting corrosion and/or removing hydrocarbonaceous deposits in oil and gas applications is provided. The composition comprises an iron sulfide dissolver, an organic solvent, and a corrosion inhibitor.

Provided is a steel sheet having a predetermined chemical composition, wherein precipitates having a diameter of less than 0.1 μm are present in a number density of 10 to 200/μm.sup.2 in a depth region of 1 to 10 μm from a surface, an amount of dissolved C in a depth region of 10 to 60 μm from the surface is less than 0.20 mass %, and a tensile strength is 1200 MPa or more. Further, provided is a method for producing a steel sheet comprising a step of hot rolling a steel slab having a predetermined chemical composition, then coiling it at 580° C. or less, a step of pickling the hot rolled steel sheet to remove oxide scale and remove the surface layer of the hot rolled steel sheet down to at least 5 μm, and a step of cold rolling the hot rolled steel sheet, then holding it in an atmosphere of a dew point of −20 to 20° C. at a temperature region of 200 to 400° C. for 20 to 180 seconds and holding it at a temperature region of 740 to 900° C. for 40 to 300 seconds.

Provided is a steel sheet having a predetermined chemical composition, wherein precipitates having a diameter of less than 0.1 μm are present in a number density of 10 to 200/μm.sup.2 in a depth region of 1 to 10 μm from a surface, an amount of dissolved C in a depth region of 10 to 60 μm from the surface is less than 0.20 mass %, and a tensile strength is 1200 MPa or more. Further, provided is a method for producing a steel sheet comprising a step of hot rolling a steel slab having a predetermined chemical composition, then coiling it at 580° C. or less, a step of pickling the hot rolled steel sheet to remove oxide scale and remove the surface layer of the hot rolled steel sheet down to at least 5 μm, and a step of cold rolling the hot rolled steel sheet, then holding it in an atmosphere of a dew point of −20 to 20° C. at a temperature region of 200 to 400° C. for 20 to 180 seconds and holding it at a temperature region of 740 to 900° C. for 40 to 300 seconds.

Provided is a steel sheet having a predetermined chemical composition and microstructure, wherein a block size in a first depth region of 1 to 10 μm from the surface is 5.0 μm or less, a block size in a second depth region of 10 to 60 μm from the surface is 6.0 to 20.0 μm, and a block size in a third depth region of 60 μm to 1/4 thickness from the surface is less than 6.0 μm. Further, provided is a method for producing a steel sheet comprising a step of hot rolling a steel slab having a predetermined chemical composition, then coiling it at 500° C. or more, a step of pickling the hot rolled steel sheet to remove oxide scale, wherein an amount of removal of the surface layer of the hot rolled steel sheet is less than 5.00 μm, a step of cold rolling by a rolling reduction of 30 to 90%, and an annealing step of holding in an atmosphere of a dew point of −20 to 20° C. at a temperature region of 740 to 900° C. for 40 to 300 seconds.

Provided is a steel sheet having a predetermined chemical composition and microstructure, wherein a block size in a first depth region of 1 to 10 μm from the surface is 5.0 μm or less, a block size in a second depth region of 10 to 60 μm from the surface is 6.0 to 20.0 μm, and a block size in a third depth region of 60 μm to 1/4 thickness from the surface is less than 6.0 μm. Further, provided is a method for producing a steel sheet comprising a step of hot rolling a steel slab having a predetermined chemical composition, then coiling it at 500° C. or more, a step of pickling the hot rolled steel sheet to remove oxide scale, wherein an amount of removal of the surface layer of the hot rolled steel sheet is less than 5.00 μm, a step of cold rolling by a rolling reduction of 30 to 90%, and an annealing step of holding in an atmosphere of a dew point of −20 to 20° C. at a temperature region of 740 to 900° C. for 40 to 300 seconds.