Insulating Method Improves Superalloy Forging

April 23, 2012
Researchers simplify a technique for preserving heat, maintaining surface and structural integrity, and increasing yield

Metal forming techniques continue to evolve according to the demands of downstream markets and the capabilities of materials, and a new approach to thermal management will offer insights to operations working to supply critical superalloy components in markets like power generation and aerospace. Recently, four researchers with Baoshan Iron & Steel's Special Steel business and Special Steel Technology Center (Wang Zixing, Chen Guosheng, Zhou Dianhua, and Wany Qingzeng) detailed the results of their study, "Application of a 'soft canning' heat preservation technique in the superalloy forging process." Their report concludes that decrease in surface temperature drops on heated ingots or billets can be achieved with an adhesive insulating material. With the surface temperature under better control, the finished products exhibit better surface quality and structural uniformity.

"Hard canning" is an insulation technique that involves wrapping cotton insulation around a heated ingot or billet during heating and forging, followed by another layer of alloy sheets. It's a complex procedure, and it inhibits the operators' ability to see forging defects or other issues during the process.

The "soft canning" process that Baosteel researchers developed uses a flexible adhesive insulating material with good lubricating and adhesive properties. It sticks to the material surface (hot or cold), and can reduce the temperature drop of the ingot or billet during transfer or hot working. Also, the insulating material can deform with the billet or ingot without temperature loss.

The Baosteel researchers noted the technique is suitable for cogging or forming for some hard wrought alloys with hot working temperature lower than 50 °C. It's a simpler method than the hard canning approach, is effective as an insulating method, and brings various benefits according to the forging process and material. "Compared with the traditional, multiple small-deformations forging process, this technique can increase the degree of a single fire deformation, uniformity of macrostructure or microstructure, and reduce the energy consumption," the authors indicated.

In detail, they applied the new method for cogging hard-wrought superalloy materials (i.e., materials with nickel, cobalt, or nickel-iron base alloys), and achieved a "relatively uniform" microstructure in the VIM/VAR ingots. The standard approach often leads to cracking on the ingot surface, and the average finished production rate is low, but the new method results in good surface quality for cogging production and finished forging. They also found that the ingot or billet dimensions can be increased, and the production rate will increase by %10 or more.

The researchers stated that their new technique significantly reduces the cold deformation zone on the surface of the cogging after forging, because there is significantly less decrease in surface temperature.

Other good results were by applying the insulating method for forging superalloy rods )enhancing the degree of deformation at lower temperatures, reducing the surface cold deformation zone, more uniform edge and center of the finished product); and superalloy hot-die forgings (reduced working temperature for the hot die arrangement, and making it possible to manufacture different superalloy hot die forgings.)

The report is presented in the quarterly publication, Baosteel Technical Research, vol. 5, no. 4.