One Minute Mentor: Variations in Cooling Rate

November 20, 2018
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Variations in cooling rate, from point to point, can exaggerate the production of residual stresses because, in some instances, it is possible for austenite transformation products to be different in sections with different cooling rates. For example, in rapidly cooled sections in moderately alloyed irons, it is possible for the austenite to transform to martensite, a very hard and brittle microconstituent that expands a different amount than the normal pearlitic or bainitic constituent when it forms from austenite.

This difference in expansion rates between differing transformation products adds to differences in contraction rates due to differences in section sizes. Typical cast shapes that could be expected to have different cooling rates from point to point are illustrated in the diagram.

The diagram shows four cast shapes and corresponding causes of residual stresses in castings.

(a) Differences in cooling rates due to shape.

(b) Nonuniform metal sections.

(c) Mechanical mold restraint.

(d) Surface peening during cleaning. Diagram courtesy of the American Foundry Society

Volume 4D, Heat Treating of Irons and Steels -> Heat Treatment of Cast Irons -> Introduction to Cast Iron Heat Treatment -> Heat Treatment Processes

Instron expands Calibration Laboratory services to North America, Europe, and Asia

November 17, 2018
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Instron, Norwood, Mass., announces that its Calibration Laboratory has expanded its global reach to include providing accredited calibration services to its customers in North America, Europe, and Asia under a single National Voluntary Laboratory Accreditation Program (NVLAP).

Instron's Calibration laboratory is accredited to ISO/IEC 17025 for the calibration of Force, Angularity, Length, Electromagnetics, Time & Frequency, Hardness, Temperature, and Pressure by NVLAP, a program administered by the National Institute of Standards and Technology.

“One of the main advantages is that the calibration services for our multi-national customers will all fall under the same accreditation, simplifying internal processes associated with the validation of quality systems and much more,” says Jim Ritchey of Instron Service.

The NVLAP coverage includes both in-house calibration services and field calibration services. The biggest change to Instron’s coverage is that the company’s Limited Calibration Laboratory in the United Kingdom is now part of the Instron Calibration Laboratory in Norwood, covered under the NVLAP certificate. The U.K. lab was previously accredited to ISO 17025 for Force, Extension and Hardness by the United Kingdom Accreditation Service, Laboratory Number 0019.

NIST maintains an online register of certificates that can be found here:

https://www-s.nist.gov/niws/index.cfm?event=directory.search#no-back.

www.Instron.com

One Minute Mentor: Critical Temperature Ranges

November 11, 2018
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The critical temperatures at which austenite changes to ferrite or pearlite, and vice versa, for iron differ from those for carbon steel, because silicon raises the transformation temperature range. In addition, silicon in iron decreases carbon solubility in austenite and tends to dissociate iron carbide. Thus, the carbon content of pearlite in iron can be appreciably lower than in the plain carbon and low-alloy steels. Depending on the silicon content and the cooling rate, the carbon content of pearlite varies and can be as low as 0.50 wt% C with 2.5% Si.

The dependence of critical temperatures on silicon content is shown in the graph, for cooling rates of 5 °C/h (9 °F/h). In this figure, the upper critical is shown as the temperature where ferrite first begins to form on cooling, and the lower critical temperature is the temperature where there is no remaining austenite.

Critical temperature values for heating at this same rate can be obtained by adding 33°C (60°F) to the critical temperatures on cooling. Note that neither the total carbon contents nor the combined carbon contents are significant.

Volume 4D, Heat Treating of Irons and Steels -> Introduction to Cast Iron Heat Treatment -> Critical Temperature Ranges

Seco Warwick custom vacuum furnace system heat treats precision tool steels

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Seco Warwick, Meadville, Pa., announces that its engineers have developed a precision vacuum furnace system to meet a Japanese customer’s expectations and standards for quality production of precision tool steel components. This specialized system reduces energy consumption through power optimization and cycle time reduction, customized to work within tight physical space limitations. Seco Warwick's loading systems will be integrated into the existing line, providing additional capacity within the same space, meeting requirements for equipment footprint as well as production.

“In terms of heat treatment processes, we already had the furnace that the client needed,” says Maciej Korecki, VP of Vacuum Heat Treatment Furnaces. “However, because the traditional solution was too big and did not fit the customer’s tight physical space limitations, our engineers customized the furnace and created one that fits the limited manufacturing space perfectly. Transforming a horizontal furnace door into the special system of vertical opening and lifting was the secret sauce, keeping outstanding thermal process performance, especially with regard to quenching control.”

www.secowarwick.com