How to perform heat treatment of high manganese steel?

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The purpose of solution heat treatment of wear-resistant high manganese steel castings:

Eliminate the carbides within the grains and grain boundaries in the as-cast structure to obtain a single-phase austenite structure, improve the strength and toughness of high manganese steel, and expand its application scope. To eliminate the carbides in its as-cast structure, the steel must be heated to above 1040°C and held for an appropriate time so that the carbides are completely dissolved in single-phase austenite, and then rapidly cooled to obtain an austenite solid solution structure. This solution heat treatment is also called water toughening treatment.

 

There are a large number of precipitated carbides in the as-cast structure of water-toughened wear-resistant high manganese steel, so its toughness is low and it is easy to break during use.

 

  1. Temperature of water toughening treatment:

The water toughening temperature depends on the composition of high manganese steel, usually 1050~1100℃. High manganese steel with high carbon content or high alloy content should have the upper limit of water toughening temperature, such as ZGMn13 steel and GXl20Mn17 steel. However, excessively high water toughening temperature will cause severe decarburization of the casting surface and cause the grains of high manganese steel to grow rapidly, affecting the performance of high manganese steel.

 

  1. Heating rate:
    High manganese steel has poorer thermal conductivity than ordinary carbon steel. High manganese steel castings have greater stress and are prone to cracking when heated. Therefore, the heating rate should be determined according to the wall thickness and shape of the casting. Generally, thin-walled simple castings can be heated at a faster rate; thick-walled castings should be heated slowly. To reduce the deformation or cracking of castings during the heating process, a process of preheating at around 650°C is often used in production to reduce the temperature difference between the inside and outside of thick-walled castings, make the temperature in the furnace uniform, and then quickly raise it to the water toughening temperature.

 

  1. Keeping time:

The holding time mainly depends on the wall thickness of the casting to ensure the complete dissolution of carbides in the cast structure and the homogenization of austenite. Usually, the heat preservation time can be calculated based on the casting wall thickness of 25mm for 1 hour of heat preservation.

 

  1. Cooling:

The cooling process has a great impact on the performance indicators and organizational state of castings.
During water toughening treatment, the temperature of the casting before entering the water must be above 950°C to prevent carbides from re-precipitating.

 

Multipurpose trolley-type heat treatment furnace for toughening treatment of high manganese molten steel. When castings enter water, automatic tipping or hanging basket lifting quenching methods are commonly used. The former can easily cause deformation of large parts and thin-walled parts with complex shapes, and it is also difficult to take out the castings from the pool after quenching; the latter is easy to take out the castings after quenching, but the hanging basket consumes a lot of money.

 

As-cast waste heat treatment of wear-resistant high manganese steel castings:

To shorten the heat treatment cycle, the waste heat of casting can be used to toughen high manganese steel. The process is as follows: the casting is taken out from the mold at 1100~1180℃, after core removal and sand cleaning, the casting temperature is allowed to cool to 900~1000℃, and then put into a furnace heated to 1050~1080℃ for 3~5 hours. After water cooling. This treatment process simplifies the heat treatment process, but there are certain difficulties in production operations.

 

Precipitation strengthening heat treatment of wear-resistant high manganese steel castings:

The purpose of precipitation-strengthening heat treatment of wear-resistant high manganese steel is to obtain a certain amount and size of high manganese steel through heat treatment based on adding an appropriate amount of carbide-forming elements (such as molybdenum, tungsten, vanadium, titanium, niobium, and chromium). The dispersed distribution of carbide second-phase particles strengthens the austenite matrix and improves the wear resistance of high manganese steel. This heat treatment method is more expensive and the process is more complicated.

 

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