Vacuum heat treatment of sintered Mn steels: influence of martensite content on impact properties

Abstract

The influence of the martensite content on the impact properties of three through hardened Mn steels was investigated. When the maximum amount of martensite is 50%, impact properties are influenced by the martensite content through its effect on microhardness, according to the typical behaviour of a porous material having a tough microstructure. For higher amounts of martensite (up to 100%) a transition towards a brittle behaviour is observed. In this case, carbon content has a prevailing effect over the martensite content in determining the brittleness of materials. Steels with a medium low carbon content must be used to obtain a hardened but still deformable microstructure by through hardening and, when allowed by the actual cooling conditions, by sinterhardening.

Study of Different Vacuum Heat Treatments on the Strength of a Low Alloyed Sintered Steel

“…Available chemical and microstructural homogeneity of chromium sintered steels can be produced by choosing accurate C-contents and cooling rates. Rapid cooling integrated with sintering may be sufficient to transform a significant portion of the matrix microstructure to martensite, resulting in a significant increase of mechanical properties are called as a sinter hardening [13][14][15][16]23]. At lower cooling rates (in the range of 0.1-0.8 K=s) the microstructure will transform to mainly ferrite, pearlite and/or upper bainite.…”

“…Impact energy Hardness has been observed to increase with carbon content only up to 0.5 % C [14]; over this limit, hardness does not increase significantly, but brittleness further rises. Therefore, within certain limits, the cooling rate may help in obtaining a hardened steel with a limited brittleness.…”

“…One of the most prospective methods is the vacuum heat treatment, especially in terms of low alloyed sintered steels using sinter hardening methods [14][15][16].…”

The Effects of Post-Sintering Treatments on Microstructure and Mechanical Properties of Mn-Mo Steel

“…Due to the above mentioned reasons, research on sinteraustempering has focused mainly on the use of vacuum furnaces [4] and the use of inert, high pressure blown gas [5,6]. Unfortunately, the use of vacuum furnaces results in an increase in production costs, which translates into the high price of the produced item.…”

Microstructural effects in wear of hardened sintered steels produced by diffusion bonded and prealloyed powders

“…(i) through hardening 1,2 needs for the addition of 0?5-0?8% graphite in the powder blend, which slightly reduces green density, and uses oil as quenching media, which infiltrates the interconnected porosity and has to be removed before tempering, for environmental reasons (ii) carburising 3,4 needs for a less amount of graphite in the powder blend (up to 0?2-0?3%), but the case depth depends on the local density, being sometimes difficult to be controlled in parts with complex shape (density gradients); again, oil is the quenching medium (iii) sinterhardening 5,6 is a single step process which uses the sintering atmosphere as quenching medium in alternative to oil. But, since cooling rate is lower than in oil quenching, the base powder has to contain a minimum amount of alloying elements to get the proper hardenability, and graphite has to be added to the powder mixture: both decrease compressibility.…”