I am working in a valve manufacturing company. we plan to change the material used for gatevalves and plug valves.

Before my joining my collegues forged the 17-4 PH steel but it was cracked. they tired again and left that plan.
note: they are all basically from mechanical background.
since i am the metallurgist in the company, i am facing lot of problems.

please give the exact forging temperature and soaking time before forging and all details.

17-4PH is a precipitation hardening stainless steel that is usually supplied in the solution annealed condition, i.e. annealed at 1900 F and cooled to room temperature. This treatment produces a low-carbon martensite upon cooling to room temperature which results in a hardness of 30 to 35 HRC. Machining can be more easily performed on material supplied in this condition. Subsequent hardening is accomplished by holding at temperature between 925 F and 1150 F for one hour per inch of thickness (4 hours minimum) and cooling to room temperature.

Material for forging is typically supplied in the overaged condition. This is accomplished by holding solution annealed material at 1150 F. Material in this condition may be readily cold sawed (abrasive wheel cutting is not recommended due to the possibility of cracking). For cross sections less than 16 square inches the recommended forging temperature is 2150 F. For larger cross sections a lower forging temperature should be used. Charging thick sections into too hot of a furnace may result in internal cracking due to the relatively high internal stresses developed. If it is necessary to re-heat during forging, the steel should be charged into a furnace at 2150 F. Heating time should be 30 minutes per inch of thickness, with a minimum soak time of 15 minutes for thin sections. A uniform temperature distribution in the forging results in uniformity of mechanical properties, and so reduces the probability of cracking during forging. Make sure thsat the parts are heated uniformly.

Cooling after forging should also be controlled to some extent. Sections greater than 3 inches and small intricate sections should be returned to the heating furnace and equalized at the forging temperature prior to cooling. Temperature equalization reduces the chances of cracking during cooling. Sections under 6 inches in thickness may be air cooled, while thicker sections should be covered with a light gage steel sheet during cooling.  I hope that this helps.

MORE NEWS