The Effect Of Heat Treatment On The Microstructure، Impact Toughness And Hardness Of Hadfield Steels With Molybdenum And Chromium Additions

Abstract

The crushing hammers and teeth of drill are very important industrial tools in industrial applications، and it is important that the material from which these hammers and teeth are made of is good to resist wear and shock. One of the most important materials is Hadfield high manganese steel، which contains a percentage of carbon that leads to the formation of carbides at the boundaries of the crystalline grains، and thus to rapid breakage as it is characterized by strain hardening. A solution must therefore be found، whether by heat treatment، or alloying elements. Chromium and molybdenum metals were added in two melts in different proportions and then the heat treatment was conducted for Hadfield class D steel with added molybdenum and chromium (a new class different from ASTM A128 classifications) according to two different heat treatment programs 1 and 2 (1 – heating to 1150°C with a holding time of 30 minutes، then rapid cooling in ice water (tempering). Then reheating to 600 degrees Celsius and keeping for 30 minutes، then cooling slowly in air (return)، 2- Heating to 650 degrees Celsius and keeping for 90 minutes، then heating to 1150 degrees Celsius and keeping for 45 minutes and cooling with plain water، and comparing the mechanical properties، such as wear resistance، impact durability، and hardness after heat treatment 1، 2. The results showed images of the resulting microstructures and an increase in hardness and thus an increase in wear resistance. Impact toughness also increased as a result of the heat treatment after the addition of molybdenum and chromium، as the heat treatment led to a relative separation of carbides in the austenitic ground (incubator material). And the growth of granules due to the dissolution of chromium and molybdenum. After heat treatment، the roughness of the austenite grains increases with the decrease in the size of the carbides، and thus we obtain a reduction in the economic cost because the resulting steel becomes more resistant to difficult working conditions. Treatment 2 achieved the best values for hardness، wear resistance، and impact durability in the two melts. The gradual application of the Heat Treatment 2 program also led to a saving in the time and temperature of heating in the heat treatment (due to progressive heating and one-time cooling compared to treatment 1، which was as follows: heating، holding and cooling، and then reheating، holding and cooling) and thus a saving in the economic costs because we did not have to open the furnace door and take out the piece، in addition to the scientific aspect.