Flange heat treatment quality problems some solutions
1, low gear carburizing and quenching hardness
A batch of in (Japan) UNICASE drip type gas carburizing nitriding furnace carburizing and quenching in more than 800 pieces of gear, flange requirements after carburizing and quenching surface hardness HRC 58 to 63, while sampling parts of the surface hardness is 52 ~ 56 HRC. This is carburizing, or quenching; Quenching is heating, and cooling problems puzzled at the moment. Because this batch of emergency gear of the production tasks, the author take 3 pieces have detection gear with wire bundle, reheating in salt bath furnace, quenching in oil tank, after about 30 ~ 40 min, finally quenched hardness of 63-65 HRC. Put this batch of gear after reheating quenching, smoking waste hardness all qualified. This kind of way to cut the Gordian knot, although not necessarily can find out the real cause of the problem, but to solve the production right now.
2, rod quenching cracks
Have a batch of phi is 14 mm x 240 mm of 40 cr after conditioning place buried them material, after about a week time (use) to be found almost all of the crack, crack shape for longitudinal crack, most crack crack through two end face bar stock. Judge the crack for quenching crack, and the operating personnel on duty is not dead. Homework records, can only look up to the number of bar stock for class 2 class three, quenching, tempering, and parts materials, quenching temperature and cooling medium and process parameters are not recorded. The author take a bar with joint of 45 steel in the salt bath furnace heating, and then in the salt water quenching, about 20 ~ 30 min after cooling, the bar crack, and crack shape same as the shape of the crack. In front of the fact that, the operator didn't admit that is mistaking the batch of bar as quenching of 45 steel.
3, box-type resistance furnace annealing hardness is uneven
Process routes of the flanges as follows: annealing, band saw cutting to rough turning, quenched and tempered to finish turning, grinding and nitride. Band saw cutting, often found on a rod material hardness uneven, local high hardness, low cutting efficiency, quick wear of saw blade. Through the analysis, it is because when the furnace charging bar, or bar. The box-type resistance furnace front place neither heating resistance wire, heat loss is big, so for general box-type resistance furnace, the furnace charging parts should be from the front inside of 200 ~ 300 mm, in order to ensure uniform heating temperature in furnace parts.
4, cast iron hardening trace alloy elements should be controlled
Cast iron thermal conductivity. Poor, when the quenching cooling oil cold in general. The same cast iron substrate with steel, is composed of pearlite and ferrite. Cast iron high carbon content, carbon content increases although can increase the hardenability, but growth is not big, after all. Therefore, improve the hardenability of cast iron: depends on the role of trace alloy elements in cast iron, good control of alloy element content, to ensure the quality of heat treatment hardening.