Heat treatment process of bearing steel parts

The adjustment method of controlled atmosphere

When using box-type multi-purpose furnace, bottom loading multi-purpose furnace, mesh belt furnace, roller furnace is used in the automatic production line controlled atmosphere to ensure that the carbon potential on the surface of the bearing parts, and does not produce decarburization phenomenon, is currently in use morer nitrogen methanol atmosphere and propane gas, because of its lower cost, they are a very stable source, are widely used both at home and abroad, for the purity of raw materials used in the manufacture atmosphere requirements need to be: 97% propane or greater, methanol 99.9% or higher, nitrogen 99.999% or higher. For types of sealed multi-purpose furnace stove, must will discharge air in furnace, when using the oven fire sealing device is good, the oven door seal performance is reliable, in a material bearing parts within the basket to distribution is reasonable, easy is heated evenly heating and quenching cooling of quenching medium good liquidity, when bearing parts have a heated to 600 ℃ isothermal soaking stage, and then heated to the required heating temperature, make the bearing parts inside the material basket to achieve uniform heating, the quenching of bearing parts every hardness uniformity of furnace is < 1 HRC.

In the use of controlled atmosphere the sealing box multi-purpose furnace or continuous conveyer belt type furnace heat treatment equipment, new stove furnace water must be fully ruled out clean, bearing parts before entering the furnace exhaust work is very important, when the temperature rises to 500 ℃ needs in the rear of the furnace into the nitrogen, continuous heat preservation for a few hours, and then continue to heat up to 800 ℃ bubbled into methanol atmosphere, heat preservation time, and finally up to working temperature, ventilation with propane continues to heat preservation after some time, when observing the oven flame color rendering of orange, furnace atmosphere has been adjusted, The pre - exhaust work will directly affect the surface color of bearing parts.

Questions about the surface of bearing parts abroad requires only achieve uniform color, but the domestic high attention, some enterprises in order to reach the light is bright color, big money, increased after the completion of the heat treatment of bearing parts sandblasting polishing rust and other measures, but in the case of not completely clean, remaining at the end of the silicon carbide become wear in slot on dust source, when bearing in high speed and sometimes fall into the groove, lead to bearing damage in advance, influence the normal operation of the machine and failure. Bearing steel parts manufactured in controlled atmosphere furnace heating surface brightness, requirements for metal color is can't do, because chromium under controlled atmosphere and the reaction of carbon monoxide and generates the dark color, this can be achieved by reasonable adjustment of controlled atmosphere in the furnace and select high-quality oil quenching to achieve the ratio of bearing parts surface color is can be improved, for thin-walled parts can be light.

Our practice is: control the quality of the air source, especially methanol and propane water to be strictly controlled, nitrogen use liquid nitrogen gasification. There are two ways to crack methanol: one is to generate methanol gas by cracking machine with methanol high or low temperature. The nickel-based catalyst should be replaced regularly, and the cracking machine should be drained timely when working. The cracking gas can only enter the air inlet at the end of the furnace after steam separation before entering the furnace chamber.

Another is the method of methanol in furnace straight, but often leads to pipe blocked, because the temperature inside the pipe in the roof insulation layer is 500 ~ 700 ℃, no gasification methanol liquid caused by carbon black to gradually exhausted, pipeline through special pipe after transforming basic can do no more than half of dredge pipe, air is also very clear. The storage tank of propane after long-term use will make the residual liquid containing water stay in the tank bottom, resulting in the propane gas quantity into the furnace is insufficient and the water content exceeds the standard, the furnace atmosphere containing water causes the generation of decarburization atmosphere, make the bearing parts surface has troostite and color blue or black appear, so the storage tank to carry out regular slag removal. In 300kg above propane storage tank installation, the equipment itself has gasification and water removal device, so propane gasification purity is much better, it also has a regular slag removal requirements, but the cycle can be longer.

In addition, it is very important to completely eliminate the air and water work in the furnace and quenching oil groove, can be into nitrogen to remove the air in the furnace, oil circulation pump and oil curtain pump need to ensure that its sealing can not leak. In the use of nitrate quenching tank in martensite bainite isothermal quenching, quenching or next nitrate slot water shoulds not be too much, otherwise for sealing type quenching tank, in the doorway into nitrate tank furnace, has contained high salt water vapor will run into the decarbonization caused in the hearth furnace, the occurrence of sexual atmosphere, surface of bearing parts for austenite. For the conveyor belt type of furnace, the oil curtain adjustment in the hopper is very critical, the hopper must have a peep hole and oil curtain size adjustment ball valve, the oil flue gas under the oil curtain must be pumped through the gas and oil separator, and then sent to the furnace mouth as an auxiliary fire curtain.

About the adjustment of the carbon potential in furnace, the normal use of the oxygen probe can ensure smooth atmosphere in the furnace, the factors influencing carbon potential is the atmosphere in the furnace, after enters the furnace to qualified atmosphere also there are the following: the reason of higher carbon potential in furnace atmosphere not adjust good, artifacts, not clean dry clean out of oil, oil smoke too much, curtain, oxygen sensor failure, furnace temperature failure, quenching oil, etc., which to smoke too much oil as the main reason, when oil shade adjustment is not good, a lot of oil will run into the chamber of a stove or furnace flue gas cause the appearance of high carbon potential. The carbon potential of the oxygen probe can be corrected by fixed carbon sheet. The fixed carbon sheet is made of low carbon steel foil with carbon content in wC=0.06% ~ 0.09% and thickness of 0.05mm. The detection of fixed carbon sheet can be carried out by C230 sulfur nitrogen analyzer.

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