A ferritic stainless steel for an exhaust system heat exchanger having excellent sound absorption properties and a method for manufacturing the same are disclosed. The ferritic stainless steel for an exhaust system heat exchanger having excellent sound absorption properties includes, by weight percent, 0.001 to 0.01% of C, 0.001 to 0.01% of N, 0.2 to 1% of Si, 0.1 to 2% of Mn, 10 to 30% of Cr, 0.001 to 0.1% of Ti, 0.001 to 0.015% of Al, 0.3 to 0.6% of Nb, 0.01 to 2.5% of Mo, and the balance of Fe and other unavoidable impurities, wherein the number of inclusions existing in a ferrite matrix and satisfying the following Formula 1 is 5 ea/mm.sup.2 or more.

A method for producing an austenitic stainless steel slab by continuous casting of an austenitic stainless steel, including applying electric power to the molten steel in a depth region providing a solidification shell thickness of from 5 to 10 mm at least at a center position in the long edge direction, so as to cause flows in directions inverse to each other in the long edge direction on both long edge sides, thereby performing electro-magnetic stirring (EMS) to control a continuous casting condition satisfying 10<T<50F.sub.EMS+10. Herein, T represents a difference between an average molten steel temperature ( C.) and a solidification starting temperature ( C.) of the molten steel, and F.sub.EMS represents a stirring intensity index shown by a function of a molten steel flow velocity in the long edge direction imparted by the electro-magnetic stirring and a casting velocity.

The present invention provides a high-aluminum austenitic alloy and a high-aluminum austenitic centrifugal casting pipe. The high-aluminum austenitic alloy and the high-aluminum austenitic centrifugal casting pipe have excellent anti-corrosion capabilities and creep resistance at a temperature of 900 C. or above, while having required mechanical properties. In weight percentage, the high-aluminum austenitic alloy or the high-aluminum austenitic centrifugal casting pipe of the present invention is composed of the elements of: C, 0.3-0.7%; Mn, 0-0.5%; Si, 0-0.5%; Cr, 20-26%; Ni, 40-50%; Al, 3.5-5%; Ti, 0.01-0.3%; Zr, 0.01-0.3%; Nb, 0.1-1%; Ta, 0.01-2%; Mo, 0.01-1%; W, 0.01-1.9%; N, 0.001-0.04%; Re, 0.03-0.3%; the remainder being Fe and inevitable impurities. The present invention also relates to a method for manufacturing the high-aluminum austenitic alloy and the high-aluminum austenitic centrifugal casting pipe of the present invention.

This disclosure is directed at methods for mechanical property improvement in a metallic alloy that has undergone one or more mechanical property losses as a consequence of forming an edge, such as in the formation of an internal hole or an external edge. Methods are disclosed that provide the ability to improve mechanical properties of metallic alloys that have been formed with one or more edges placed in the metallic alloy by a variety of methods which may otherwise serve as a limiting factor for industrial applications.

A high-strength and high-toughness tube for perforating gun, having a formulation of chemical elements in percentage by mass as follows: C: 0.15%-0.22%, Si: 0.1%-0.4%, Mn: 0.5%-1%, Cr: 0.3%-0.7%, Mo: 0.3%-0.7%, Nb: 0.01%-0.04%, V: 0.1%-0.2%, Ti: 0.02%-0.05%, B: 0.0015%-0.005%, Al: 0.01%-0.05%, Ca: 0.001%-0.004%, N0.008%, and the balance of Fe and other inevitable impurities. Accordingly, further disclosed is a method for manufacturing a high-strength and high-toughness tube for perforating gun. The high-strength and high-toughness tube for perforating gun of the present invention has high strength, good toughness and uniform circumferential strength, and is suitable for application in the field of petroleum exploration and exploitation.

An austenitic stainless steel having excellent orange peel resistance and a method for producing the same are disclosed. In the austenitic stainless steel having excellent orange peel resistance, according to an embodiment of the present disclosure, a ratio Gs/Gi of an average crystal grain size Gs of surface crystal grains included in a first area corresponding to a depth of 10% or less of a total thickness of the austenitic stainless steel from the surface of the austenitic stainless steel with respect to an average crystal grain size Gi of internal crystal grains included in a second area corresponding to a depth that is deeper than 10% of the total thickness of the austenitic stainless steel from the surface of the austenitic stainless steel may be 0.5 or smaller. Therefore, it is possible to prevent deterioration of surface roughness due to orange peel of the steel surface even after post-processing of the austenitic stainless steel while increasing the sizes of crystal grains in order to reduce strength of the austenitic stainless steel, and also to reduce cost by replacing copper pipes

[PROBLEM] The invention provides a roll for hot rolling process having various types of more excellent durability performances than conventional rolls, and provides also a method for manufacturing the same.

[SOLUTION] A cladding layer 4 is formed on an outer circumference portion of a roll for hot rolling process 1, where the cladding layer 4 comprises: 0.5 to 0.7% by mass of C, 2.8 to 4.0% by mass of Si, 0.9 to 1.1% by mass of Cu, 1.4 to 1.6% by mass of Mn, 2.7 to 3.3% by mass of Ni, 13.5 to 14.5% by mass of Cr, 0.8 to 1.1% by mass of Mo, 0.9 to 1.1% by mass of Co, and 0.2 to 0.4% by mass of Nb, with a balance being Fe and inevitable impurities, and has a thickness of 5 mm or more.

A method of manufacturing a high-strength stainless steel pipe includes forming a steel pipe having a predetermined size, the steel having a composition comprising by mass % 0.005 to 0.05% C, 0.05 to 1.0% Si, 0.2 to 1.8% Mn, 0.03% or less P, 0.005% or less S, 14 to 20% Cr, 1.5 to 10% Ni, 1 to 5% Mo, 0.5% or less V, 0.15% or less N, 0.01% or less O, 0.002 to 0.1% Al, and Fe and unavoidable impurities as a balance; applying a quenching treatment two times or more to the steel pipe where the steel pipe is quenched by reheating to a temperature of 750 C. or above and cooling to a temperature of 100 C. or below at a cooling rate equal to or higher than an air-cooling rate; and applying a tempering treatment where the steel pipe is tempered at a temperature of 700 C. or below.

A method for improving smooth running of casting of rare earth stainless steel using pulse current includes the following steps: setting corresponding initial pulse voltage, pulse current, and pulse frequency in accordance with difference of rare earth element content in molten steel; and adjusting the pulse voltage, pulse current, and pulse frequency according to position change of stopper rod until the end of continuous casting. The method can stably improve the clogging of immersion nozzle during continuous casting, the smooth running of continuous casting and production efficiency, and decrease production cost.

Provided are a duplex stainless steel sheet having high surface quality and high corrosion resistance manufactured through a twin roll strip casting process, and a method for manufacturing the duplex stainless steel sheet.