Mon, 30 Jul 2018 01:46:41 +0000
Wear – resistant high manganese steel casting heat treatment
First of all, the solid solution heat treatment of wear – resistant high manganese steel castings. The main purpose of solid solution heat treatment for high manganese steel castings is to eliminate the carbide in and around the grain boundary in the cast structure, obtain the microstructure of single phase austenite, improve the strength and toughness of high manganese steel, and expand its application range. To eliminate the as-cast organization of carbide, should be the steel is heated to above 1040 ℃, and heat preservation time, appropriate to make it solid carbide completely dissolved in single-phase austenitic, then rapid cooling austenite interstitial tissue. This solid-solution heat treatment is also called water toughness treatment.
There are a lot of precipitated carbides in the cast structure of high manganese steel treated with water toughness.
(1) the temperature of the water toughening treatment: water toughening temperature depends on the composition of high manganese steel, usually for 1050 ~ 1100 ℃ high carbon content or high alloy content should be water toughening temperature limit, high manganese steel such as ZGMnl3 GXl20Mnl7 steel and steel. However, high water toughness temperature will lead to serious decarbonization of casting surface, and promote the rapid growth of grain size of high manganese steel, which will affect the service performance of high manganese steel.
(2) heating rate: the heat conductivity of high manganese steel is worse than that of general carbon steel, and the high manganese steel casting is easy to crack due to the greater stress during heating, so its heating rate should be determined according to the thickness and shape of the casting wall. Generally simple thin – walled castings can be heated at a fast rate. Thick – walled castings should be heated slowly. In order to reduce the casting deformation or cracking in the heating process, the production in advance at about 650 ℃ is often used to heat preservation, reduce thick-walled casting temperature difference between inside and outside, furnace temperature uniformity, and then quickly rise to the temperature of the water toughening treatment process.
(3) heat preservation time: the heat preservation time mainly depends on the thickness of the casting wall, so as to ensure the complete dissolution of carbide in the cast structure and the homogenization of austenite. Generally, the insulation time can be calculated according to the casting wall thickness of 25mm lh.
(4) cooling: the cooling process has a great influence on the performance and structure of the casting.
When the water toughening treatment before casting into the water temperature at 950 ℃ will, in order to avoid carbide precipitation. For this reason, the casting time from furnace to A water should not exceed 30s; The water is kept below 30 degrees. The maximum water temperature after quenching shall not exceed 60 degrees. The mechanical properties of high manganese steel decreased significantly when the water temperature was high. During water toughness treatment, the amount of water should be more than 8 times of the weight of casting and hanging bars. If non-circulating water is used, the amount of water should be increased regularly. Use clean circulating water or use compressed air to stir the pool. When quenching by hanging basket, the cooling of casting can be accelerated by means of swinging basket.