MARTEMPERING/MARQUENCHING: MARTEMPERING/MARQUENCHING In this the steel is cooled rapidly by a rate more than the CCR to temp between the nose and Ms, soaked at this temp for sufficient time for equilisation of temp but not long enough tom permit the formation of bainite.then cooled up to room temp in air or in oil Applicable to high c steel and low alloy steel The martensite formed by this process has the following advantages Results in less distortaion and warping since martensite formation starts at the same time throught the material Less possibility of quenching cracks in the component. MARAGING: MARAGING These steels can be air hardened by martensitic transformation and subsequently precipitation hardened by aging hence called maraging These steels low C steels PROCESS: Heated upto austenitic temp.to make austenitic structure from surface to core then held there for 1 hr per 25mm thickness or dia Then it is cooled in air up to room temp. The martensite is soft and tough rather than hard and brittle It can be cold worked to a high degree Steels are then aged at about 500c During aging strain induced precipitation hardening occurs due to precipitation of Ni3TiAl and Ni3Mo phases The structure is very fine precipitates in the martensite matrix Fig. MECHANISM OF HEAT REMOVAL DURING QUENCHING: MECHANISM OF HEAT REMOVAL DURING QUENCHING The mechanism of heat removal during cooling is in 3 stages Vapour blanket cooling stage: the outer surface cools faster than the core The temp of the metal is so high that quenching medium gets vapourised at the surface of the metal and a thin stable film of vapour surrounds the hot metal. Cooling rate is relatively slow in this stage. Vapour transport cooling stage:starts when metal is cooled to a temp where the vapour film is no longer stable When temp falls away the vapour film breakes and liquid comes in contact with the hot metal Due to this violent boiling occurs and metal cools rapidly Fastest stage of cooling and martensite formation occurs in this stage 3.
Establishing Service Connection for Hearing Loss and Tinnitus. The VA will take the auditory test results and, use a numerical formula, to determine the actual rating that will be assigned. This formula can be found in Section 4.85 of the Code of Federal Regulations. Typical ratings for hearing loss are 0% or 10%. How Your Two Tests Are Used to Calculate Your VA Hearing Loss Disability Rating. Your puretone threshold score will be the average decibel loss from the frequencies of 1000 Hertz, 2000 Hertz, 3000 Hertz, and 4000 Hertz. Staying on the chart’s row you had based on the speech discrimination score, move to the right based on the average decibel loss in the puretone threshold test. Do this for each ear. Hearing loss claims and the valencia.
Liquid cooling stage:This starts when the temp of the metal reaches the boiling point of liquid Cooling is by conduction and convection through the liquid The cooling rate is slowest in this stage It is desirable to have martensite formation during this stage so that distortion and cracking will be least Fig. QUENCHING MEDIUMS: QUENCHING MEDIUMS Ideal cooling medium should have fast initial cooling to avoid nose of TTT dia Followed by slow cooling to avoid distorsion and quench cracks No liquid satisfies these conditions like water is having fast initial as well as final cooling rate while conventional oils show slow rate of cooling In order of decreasing cooling rates the liquids are Fig. 4.24 Water solution of 10% NaCl Tap water Fused liquid salt Soluble oil and water solutions Oil Air With Brine quenching hardness up to 60 HRC Oil quenching gives about 28HRC. VARIABLES AFFECTING HARDENING OF STEEL: VARIABLES AFFECTING HARDENING OF STEEL Hardness of steel is affected by Austenetising temperature: Steel heated to optimum austenetising temperature If lower temp. Lower hardness If higher temp lower hardness due to coarse grain structure having more retained austenite 2. Holding time: For complete transformation of austenite proper holding time holding time increases with thickness or diameter 3. Delay in quenching: results in reduction in hardness of steel due to partial transformation of austenite to other phases like pearlite,ferrite etc 4.
Martempering is similar to austempering, in that the steel is quenched in a bath of molten metal or salts to quickly cool it past the pearlite-forming range. However, in martempering, the goal is to create martensite rather than bainite. Salt Bath and Bath-Type Annealing, Tempering and Austempering. Martempering Furnaces using Neutral Salt. There are manual and automatic. Automatic gas feed panel with pressure reducer, two adjustable flow meters and two.