Three heat treatment methods for Heat-resistant Steel Castings
Firstly, the solid heat treatment of heat resistant steel casting is discussed. The main purpose of the solution heat treatment, high manganese steel casting is eliminating intracrystalline and grain boundary carbides in the as-cast organization, get single-phase austenitic organization, improve the strength and toughness of high manganese steel, enlarge its application scope. 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 solution heat treatment is also called water toughness treatment.
It has a large amount of precipitated carbide in the cast structure of high manganese steel, so its toughness is low and its use is easily broken.
(1) the temperature of the water toughening treatment: water toughening temperature depends on the composition of high manganese steel, usually for 1050 ~ 1050 ℃ high carbon content or high alloy content should be water toughening temperature limit, high manganese steel such as ZGMnl3 GXl20Mnl7 steel and steel. But the high water temperature can cause the casting surface to be seriously decarbonized, and the grain of high manganese steel is rapidly brought up to affect the performance of high manganese steel.
(2) heating rate: the thermal conductivity of high manganese steel is worse than that of ordinary carbon steel. The stress of high manganese steel castings in heating is large and easy to crack, so the heating rate should be determined according to the thickness and shape of the castings. The simple casting of thin wall can be heated at a faster rate. Thick wall casting should be slowly heated. 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 thermal insulation time depends on the thickness of the casting wall to ensure that the carbide in the cast structure is completely dissolved and the austenitic homogenization. Usually the heat preservation time can be calculated according to the thickness of the casting wall.
(4) cooling: the cooling process has a great influence on the performance of the castings and the state of the organization.
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 shall not exceed 30s from the time of the release to A water; The water temperature is kept below 30 degrees. The water temperature shall not exceed 60 degrees after quenching. The mechanical properties of high manganese steel decreased significantly when the water temperature was higher. Water when the water toughening treatment must be casting and hanging bar weighs more than 8 times, if use the circulating water to add to the amount of water on a regular basis. Good heat using clean circulating water or water quality using compressed air agitating. The cooling of casting can be accelerated by swinging lifting basket.
High manganese steel water toughness treatment multi-purpose vehicle type. Heat treatment furnace. The casting person's water is often used for automatic tilting or hanging basket. The former is easy to cause deformation of large and complex thin wall parts, and it is difficult to get out the casting from the pool after quenching. The latter is easy to get out after quenching, but the hanging basket is used up.
Heat treatment of casting of Heat-resistant Steel Castings. In order to shorten the heat treatment cycle, the castable waste heat can be used for the treatment of high manganese steel. The following process: casting in 1100 ~ 1180 ℃ when removed from the mold, after deoxidization in addition to the core, casting allows cooled to a temperature of 900 ~ 1000 ℃, and then loaded into a furnace heated to l050-1080 ℃ heat insulating water after 3 ~ 5 h. The treatment process simplifies the heat treatment process, but the production operation is difficult.
The precipitation of Heat-resistant Steel Castings is strengthened by heat treatment. Resistance to blind precipitation strengthening heat treatment, the purpose of high manganese steel is in adding suitable amount of carbide forming elements (such as molybdenum, tungsten, vanadium, titanium, niobium and chromium), on the basis of a certain number is obtained by heat treatment method in the high manganese steel and the size of the dispersed distribution of second phase particle carbides, strengthened austenitic matrix, improve the antiwear properties of high manganese steel. This heat treatment method is expensive and the process is complicated.