Sigma-Phase Embrittlement
Many stainless steels and other iron-chromium alloys are susceptible to a grain boundary phenomenon known as sigma-phase embrittlement. This type of embrittlement has been shown to cause severe loss of ductility, toughness, and corrosion resistance resulting in cracking (Fig. 1) and failure of components, especially those subjected to impact loads or excessive stress. As heat treaters we need to know more about what sigma-phase embrittlement is and how to avoid its occurrence. Let’s learn more.
Prolonged exposure in the temperature range of 565-925°C (1050-1700°F) results in chromium depletion from the grain boundaries, making them susceptible to intergranular corrosion. The most rapid sigma-phase formation occurs in the range of 700-900°C (1290-1650°F). Alloy elements such as molybdenum, titanium and silicon promote the formation of sigma phase, while nitrogen and carbon reduce its tendency to form. By Daniel Herring
Effect of Quench Media on Steel Parts
This article reports the findings of an investigation into the effect of different media (oil and polymer) on the properties of different-grade steel parts.
Steel parts after manufacture will not have desired properties like wear resistance, tensile strength and surface and core hardness. To attain these, heat-treatment processes like case hardening (CH) or through hardening (TH) were carried out in a sealed-quench furnace and a rotary furnace. By By Veenarani A. R. and S. C. Maidargi
Does Quality Assurance Improve Quality?
While any kind of focus on quality is positive, don’t lose sight of the fact that quality assurance and quality improvement are not the same thing. Companies who confuse quality assurance and quality improvement may find that they do not achieve the results they were expecting.
Quality assurance (QA) describes the process by which organizations manage and account for the quality of their products and/or services to their stakeholders. For companies operating in highly regulated industries, this is the minimum quality expectation. Quality improvement (QI) is the way companies identify and act on opportunities to enhance the quality of their products and/or services to improve the value they offer to their stakeholders. By Joanna Leigh
Effect of Cryogenic Treatment on Properties of Tool Steels
The effect of cryogenic treatment (CT) on the properties of ledeburitic tool steels was investigated. CT is also used in conventional heat treatment to improve mechanical properties and wear resistance and decrease the amount of retained austenite.
The technology of CT was developed in the 1960s and still elicits contrary scientific opinions today. Some studies report that CT improves hardness, wear resistance, bending strength, toughness, fatigue strength, etc., but some scientists do not agree. Also, experts do not agree as to the main factor influencing results when CT is applied – austenitizing temperature, cooling rate, quench temperature, holding time, heating rate or tempering temperature. By Peter Jurci, Otakar Prikner, Petra Salabova, and Jana Sobotova
Consultants of the Roundtable
If you’ve ever visited Industrial Heating’s website, you’ve surely noticed “The Experts Speak,” which showcases blogs written by some of the industry’s leading authorities. What better way to highlight this feature than by gathering our featured experts together for a roundtable discussion? We asked our pros – all consultants in their respective areas of expertise – a variety of questions about their experiences in the field.
Spent Refractory - Recycle or Landfill?
Refractory is a vital component in industrial heating furnaces. Regardless of whether its primary purpose is containment of material or heat, time and use eventually take their toll, and replacement becomes necessary. The cause could be any combination of mechanical damage, abrasion, erosion, corrosion, chemical degradation, thermal cycling, thermal shock and other forms of wear and tear.
Recycling of used refractory materials is currently more popular in Europe (where landfill space is scarce), but it is becoming more common in the U.S., especially at aluminum and steel processing facilities. There are three primary questions a furnace user must answer when deciding the fate of the spent refractory solids: (1) Is the material hazardous? (2) Does the refractory installer offer a recycling option? (3) Is recycling or landfilling the lowest-cost option?. By By Richard J. Martin
Tool-Steel Carbides
Today, tool-steel heat treatment is based on a simple premise. To obtain the optimum performance from any given grade, every step of the heat-treating process must be precisely controlled — from stress relief and preheating to austenitizing temperature and time, quenching, deep freeze and tempering. Process and/or equipment variability cannot be tolerated, which is why vacuum processing is a popular choice for tool-steel heat treatment.
The selection of any tool steel depends on a combination of factors including component design, application end-use and performance expectation. For any given application, the goal of heat treating is to develop an optimized microstructure (Fig. 2) to help achieve the proper balance of desired properties (Table 1), namely hot (red) hardness, wear resistance, deep hardening and/or toughness. By Daniel Herring
Heat Treatment of Titanium Alloys
”I know the Greek alphabet well,” exclaimed the heat treater. “Alpha, beta, alpha-beta, gamma and so on.” “Oh, you must process titanium alloys,” surmised the scholar. How did he know? Let’s learn more.
Titanium has many attributes that are useful in today’s modern society. It is a relatively lightweight, corrosion-resistant structural material that can be strengthened dramatically through alloying and, in some cases, by heat treatment. Among its many advantages for aerospace, military and commercial: good strength-to-weight ratio, low density, low coefficient of thermal expansion, good corrosion resistance, good oxidation resistance at intermediate temperatures, good toughness and (relatively) low heat-treatment temperatures. By Daniel Herring
