Search Results for salt bath heat treatment

This article provides information on the salt baths used for a variety of heat treatments, including heating, quenching, interrupted quenching (austempering and martempering), case hardening, and tempering. It describes two general types of salt bath systems for steel hardening: the first type uses atmosphere austenitizing followed by salt quench and the second type employs austenitizing salt baths with rapid transfer to the quench salt. The article provides a detailed account on the construction, advantages and disadvantages, and limitations of isothermal quenching furnaces, submerged-electrode furnaces, immersed-electrode furnaces, and externally heated furnaces. It discusses the important applications of various furnace designs, including the austempering of ductile iron, the hardening of tool steels, and the isothermal annealing of high-alloy steels.

High-potential high-alloy tool steels (HATS) containing martensitic microstructure with undissolved hard phases are achieved by a number of complex heat treating cycles, predominantly tempering. This article focuses on three tempering treatments, namely, salt bath heat treatment, austenitizing, and vacuum heat treatment. It explains the result of these tempering processes with HSS M2 grade of HATS.

This article describes the uses of the liquid carburizing process carried out in low and high temperature cyanide-containing baths, and details the noncyanide liquid carburizing process which can be accomplished in a bath containing a special grade of carbon. It presents a simple formula for estimating total case depth, and illustrates the influence of carburizing temperature, duration of carburizing, quenching temperature, and quenching medium with the aid of typical hardness gradients. The article provides information on controlling of cyaniding time and temperature, bath composition, and case depth, and presents examples that relate dimensional change to several shapes that vary in complexity. It also provides information on the quenchant removal and salt removal processes, lists the applications of liquid carburizing in cyanide baths, and discusses the process and importance of cyanide waste disposal in detail.

Molten salt baths are anhydrous, fused chemical baths used at elevated temperatures for a variety of industrial cleaning applications. This article discusses their applications in paint stripping, polymer removal, casting cleaning, glass removal, and plasma/flame spray removal. It provides an overview of the basic design and safety considerations of the salt bath equipment and describes the environmental impact of molten salt bath cleaning.

The thermoreactive deposition and diffusion process is a heat-treatment-based method to form coatings with compacted layers of carbides, nitrides, or carbonitrides, onto some carbon/nitrogen-containing materials, including steels. The amount of active carbide forming elements/nitride forming elements, coating temperatures and time, and thickness of substrates influence the growth rate of coatings. This article lists carbide and nitride coatings that are formed on carbon/nitrogen-containing metallic materials, and describes the coating process and mechanism of coating reagents. It details the growth process and nucleation process of carbide and nitride coatings formed on the metal surface. The article discusses the advantages, disadvantages, and characteristics of the various coating processes, including high-temperature salt bath carbide coating, high-temperature fluidized-bed carbide coating, and low-temperature salt bath nitride coating.

The liquid nitriding process has several proprietary modifications and is applied to a wide variety of carbon steels, low-alloy steels, tool steels, stainless steels, and cast irons. This article discusses the applications, subclassifications, operating procedures, and maintenance procedures, as well as the equipment used (salt bath furnaces) and safety precautions to be undertaken during the liquid nitriding process. It describes the different types of liquid nitriding process, namely, liquid pressure nitriding, aerated bath nitriding, and liquid nitrocarburizing. Environmental considerations and the increased cost of detoxification of cyanide-containing effluents have led to the development of low-cyanide salt bath nitrocarburizing treatments. The article reviews the wear and antiscuffing characteristics of the compound zone produced in salt baths with the help of Falex scuff test.

Martempering and austempering processes may eliminate the need for conventional oil quenching and tempering. This article presents the suitability of steels for martempering and austempering. It discusses the compositions of oils suitable for marquenching and modified marquenching and also presents safety precautions recommended for the use of martempering oils. Finally, the article explains the effect of agitation and water in a molten salt bath.

This article provides a detailed discussion on the heating equipment used for austenitizing, quenching, and tempering tool steels. These include salt bath furnaces, controlled atmosphere furnaces, fluidized-bed furnaces, and vacuum furnaces. The article discusses the types of nitriding and nitrocarburizing processes and the equipment required for heat treating tool steels to improve hardness, wear resistance, and thermal fatigue. The various nitriding and nitrocarburizing processes covered are salt bath nitrocarburizing, gas nitriding and nitrocarburizing, and plasma nitriding and nitrocarburizing.

Molten salt, including nitrite/nitrate salts, is the quenching medium most commonly used in austempering and marquenching of ferrous materials. This article describes the use of molten salts in the quenching of ferrous materials. It provides information on the processing and operation of salt quenching including considerations of time, temperature, environment, and safety, as well as critical characteristics such as the composition of the quenchant, agitation, and water additions.

This article describes the advantages of martempering and the use of oil and salt as quenchants in the martempering process. It also discusses safety precautions to be followed by an operator and reviews the steels that are suitable for martempering. The article provides information on the importance of controlling process variables in martempering, including austenitizing temperature, temperature of the martempering bath, time in the bath, salt contamination, water additions to salt, agitation, and the rate of cooling from the martempering bath. It also describes specific situations in which distortion problems have been encountered during martempering. The article contains tables that indicate typical applications of martempering in salt and oil by listing commonly treated steel parts and giving details of martempering procedures and hardness requirements. The article also lists equipment requirements for oil and salt martempering of steel.

Although stainless steel is naturally passivated by exposure to air and other oxidizers, additional surface treatments are needed to prevent corrosion. Passivation, pickling, electropolishing, and mechanical cleaning are important surface treatments for the successful performance of stainless steel. This article describes the surface treatment of stainless steels including abrasive blast cleaning, acid pickling, salt bath descaling, passivation treatments, electropolishing, and the necessary coating processes involved. It also describes the surface treatment of heat-resistant alloys including metallic contaminant removal, tarnish removal, oxide and scale removal, finishing, and coating processes.

Nitriding is a general term for all processes based on the addition of nitrogen to the surface of steel. When carbon is added along with the nitrogen, the process is called nitrocarburizing. This article provides a detailed discussion on the functional and structural properties of nitrided layers. It describes the structural changes on the surface of carbon steels, alloy steels, and austenitic stainless steels. The article explains the effects of the various nitriding processes, namely, gaseous nitriding, plasma nitriding, gaseous nitrocarburizing, and salt bath nitrocarburizing, on the structure and properties of nitrided layers.

Heating time and holding time refer, respectively, to the time required to bring a part to temperature and the time a part is held at the required heat-treatment temperature. This article provides information on heating times and holding times with different types of furnace systems during steel hardening and tempering.

Heat treatment of depleted uranium (DU) alloys with 4.0 wt% or more molybdenum or equivalent is similar to that of dilute alloys. This article discusses the metallurgical characteristics and processing considerations of DU and its alloys, and describes the control of grain size and orientation using beta treatment. It lists the typical mechanical properties of DU as functions of the amount of cold work and hardness data of uranium rod, and describes the annealing of cold-worked DU. The article also describes the heat treatment of dilute alloys of DU, focusing on the three basic furnace designs used for heating or heat treating of unalloyed uranium: molten salt baths, inert-atmosphere furnaces, and vacuum furnaces. Finally, it presents procedures that are examples of heat treatment used to meet certain specifications of ultimate tensile strength, yield strength, and elongation.

Cast irons, like steels, are iron-carbon alloys but with higher carbon levels than steels to take advantage of eutectic solidification in the binary iron-carbon system. This article introduces the solid-state heat treatment of iron castings and describes the various processes of heat treatment of cast iron. It provides information on stress relieving, annealing, normalizing, through hardening, and surface hardening of these castings. The article discusses general considerations for the heat treatment of cast iron. Cast irons are occasionally nitrided for various applications with the aim of enhancing surface hardness and corrosion resistance of the products. The article describes molten salt bath cyaniding and ion nitriding of cast iron.

This article discusses the important characteristics of fluidized beds. The total space occupied by a fluidized bed can be divided into three zones: grid zone, main zone, and above-bed zone. The article discusses the various types of atmospheres of fluidized beds, such as oxidizing and decarburizing atmosphere; nitrocarburizing and nitriding atmosphere; carburizing and carbonitriding atmosphere; and chemical vapor deposition atmosphere. External resistance heating, external combustion heating, internal resistance heating, direct resistance heating, submerged combustion heating, and internal combustion heating can be used to achieve the heat input for a fluidized bed. The article also describes the operations, design considerations, and applications of fluidized-bed furnaces in heat treating. Thermochemical surface treatments, such as carburizing, carbonitriding, nitriding, and nitrocarburizing, are also discussed. Finally, the article reviews the principles and applications of fluidized-bed heat treatment.

The use of gases or molten salts as the quenchant for steel parts is commonly limited to the quenching of high-alloy steel or the carbonizing quenching of low-alloy steel. This article reviews the quenching process of steels with molten metals (quenchant) such as molten lead, molten bismuth, and molten sodium. It also contains tables that list the physical properties of lead, bismuth, sodium, and molten sodium.

This article provides information on the Unified Numbering System designations and temper designations of copper and copper alloys. It discusses the basic types of heat treating processes of copper and copper alloys, namely, homogenizing, annealing, and stress relieving, and hardening treatments such as precipitation hardening, spinodal hardening, order hardening, and quench hardening and tempering. The article presents tables that list the compositions and mechanical properties of copper alloys. It also discusses two strengthening mechanisms of copper alloys, solid-solution strengthening and work hardening. Finally, the article provides information on the equipment used for the heat treating of copper and copper alloys, including batch-type atmosphere furnaces, continuous atmosphere furnaces, and salt baths.

This article describes the methods for removing metallic contaminants, tarnish, and scale resulting from hot-working or heat-treating operations on nickel-, cobalt-, and iron-base heat-resistant alloys. It provides a brief description of applicable finishing and coating processes, including polishing, electroplating, ceramic coatings, diffusion coatings, and shot-peening. The article presents numerous examples that identify cleaning and finishing problems and the procedures used to solve them.