Use of liquid phase sintering in production of a new high alloy steel with good wear properties

Liquid phase sintering is a very suitable method for producing P/M (powder metallurgy)parts with very high density near theoretical density. This high alloy P/M steel in the sintered-heat treated condition, is a good material for wear applications. In this research, a high alloy steel with 7% molybdenum and 2% carbon was selected. Sintering of this high carbon-high molybdenum steel occurred at low temperature under liquid phase. Due to high content of carbon and molybdenum, a great amount of molybdenum carbides was formed in the microstructure. After compacting of metal powder mixtures with a pressure of 400 MPa, green compacts were sintered in a furnace with controlled atmosphere (N/sub 2/H/sub 2/) at 1210 deg. C for one hour. After sintering, densities beyond 98% of theoretical density were achieved. To improve mechanical properties, sintered specimens were heat treated. The heat treatment cycle was: austenitizing at 980 deg. c for 15 minutes and tempering at 500 deg. c for one hour. Tensile strength and hardness were 495 MPa and 491 HV30 respectively, which after heat treatment increased to 525 MPa and 560 HV30. Microstructure of above steel was stabilized by heat treating. A continuous ternary eutectic mixture with a laminar structure consisting of gamma-Fe, Fe/sub 2/MoC and Fe/sub 3/C phase formed between the grains. This high alloy P/M steel with a high hardness and good wear properties after nearly full densification, is a good material for severe wear conditions. Occurrence of liquid phase sintering at a relatively low temperature is a considerable advantage of this method. In this way, it is possible to sinter this steel in an ordinary production furnace (e.g., mesh belt type). Rocker arm tip would be a good candidate for this high alloy P/M steel. (author)