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07/12/2018

Problems and Solutions in Heat Treatment of Large Rolled Flange

The problems often encountered in the heat treatment process of large rolled stainless steel flange are as follows: 1. Low hardness of carburized quenched gear 2. Quenching crack of bar material.

1. More than 800 large rolled carbon steel flanges carburized and quenched in UNICASE drip-type gas carburizing and nitriding furnace require surface hardness of 58-63HRC after carburizing and quenching, while the surface hardness of parts during spot inspection is 52-56HRC. Because it is not certain whether it is carburizing or quenching, heating or cooling, a simple method is adopted to help the product achieve the required surface hardness. The process of the method is to take three tested gears and tie them with wire, reheat them in a salt bath furnace and quench them in an oil tank. However, after about 30-40 MIN, the final quenching hardness was 63-65 HRC. After reheating and quenching these gears, the hardness of the spare gear is all qualified.

2. After being buried in the quenched and tempered part of the 40CR salary material of 14MM * 240MM, almost all cracks were found in about a week (when used). The crack shape was a single longitudinal crack, and most of the cracks penetrated both ends of the bar. According to the crack morphology, it can be judged as quenching crack. The batch of bars are quenched in two shifts and tempered in three shifts, while the process parameters such as parts material, quenching temperature and cooling medium are not recorded. After the following treatment: take a bar and 45 steel joints together in the salt bath furnace heating, then quenching and cooling in brine, cooling about 20-30 MIN, the bar cracked, and the crack shape is the same as the above crack shape. It has been proved that the bars were mistaken for 45 steel for quenching.