Vacuum heat treatment of T10 steel turning tool

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T10 steel turning tools are tools with one cutting section for turning operations. Turning tools are one of the most widely used tools in machining. The working part of the turning tool is the part that generates and processes the chips, including the cutting edge, the structure to break or roll up the chips, the space for chip removal or storage, and the passage of the cutting fluid. During the cutting process, the cutting part of the tool is subjected to great pressure, friction, impact and high temperature. Therefore, the tool material must have high hardness, high wear resistance, sufficient strength, toughness and oxidation resistance, as well as high heat resistance (red hardness), that is, the performance of maintaining sufficient hardness at high temperatures.

Vacuum heat treatment 1

Spheroidizing Vacuum Annealing

For various tool steels, abrasive steels, bearing steels, eutectoid and hypereutectoid steel forgings, etc. with carbon content greater than 0.6%, in order to improve their various properties or improve the final vacuum heat treatment structure and properties, it is often used. Vacuum annealing or spheroidizing vacuum annealing process. Spheroidizing vacuum annealing is a pre-vacuum heat treatment process for high carbon steel. Vacuum annealing is generally slow cooling in the furnace to provide microstructure preparation for uniform austenitization in the vacuum quenching process.

There are four types of spheroidizing vacuum annealing methods:

1 Heat the steel to a temperature close to the critical temperature A1 for a long time.

2Heat the steel to a temperature slightly higher than the critical temperature A1 and heat the steel for a short time to form uneven austenite and some undissolved carbides, and then decompose isothermally by slow cooling or below the critical point, or cycle heating and cooling for several times up and down the A1 point. times to spheroidize the carbide.

3 Vacuum quenching and high temperature vacuum tempering after high temperature solid solution.

4 Deformation spheroidizing vacuum annealing.

T10 is a carbon tool steel with a carbon content of about 1%. The function of spheroidizing vacuum annealing is to eliminate the reticulated carbides in the steel, improve the metallographic structure, (because the grains are coarse and the hardness is high after forging.) Improve the plasticity, toughness, and reduce the hardness of the steel, so as to facilitate the cutting process and reduce the final Deformation and cracking tendency during vacuum heat treatment, and also prepares the structure for vacuum quenching. The vacuum annealing temperature is between Ac1~Acm, and the heating temperature of vacuum annealing must be strictly controlled. The microstructure after vacuum annealing is uniform and fine carbide particles distributed on the bulk matrix. The hardness should reach about 41HRC.

Microstructure of T10 steel after spheroidizing vacuum annealing:

Vacuum heat treatment 2

Vacuum quenching: refers to heating the steel to a temperature above Ac3 or Ac1 (the lower critical point temperature of steel) for a certain period of time, and then at an appropriate cooling rate to obtain a vacuum of martensite (or bainite) structure heat treatment process. Common vacuum quenching processes include vacuum salt bath quenching, vacuum martensite graded quenching, vacuum bainite isothermal quenching, surface vacuum quenching and partial vacuum quenching, etc. The purpose of vacuum quenching is to make supercooled austenite into martensite or martensite. Bainite transformation to obtain martensite or lower bainite structure, selection of vacuum quenching heating temperature: usually hypoeutectoid steel vacuum quenching heating temperature is Ac3+30~50C, eutectoid steel and hypereutectoid steel are Ac1+ 30~50C, for T10 steel (hypereutectoid steel), Ac1 is 730°C, and its heating temperature is Ac1+30~50°C, namely 770°C, 780°C, 790°C. In addition, the selection of vacuum quenching heating temperature should also consider the size and shape of the workpiece, heating equipment, alloy composition, etc. Determination of holding time: The heating time is related to the composition of the steel, the shape and size of the workpiece, the required heating medium and the heating method, and can generally be estimated according to the experience formula.

The experience formula of warm time is: t= a KD (minute), where: D is the effective thickness of the workpiece, the unit is mm; K is the heating coefficient, generally K=1.0~1.5 minutes/mm

Vacuum heat treatment 2.It is vacuum quenching + vacuum low temperature tempering, vacuum quenching obtains carbide + martensite, and the high hardness of the tool is obtained. The hardness after vacuum quenching is about 63HRC, which can be carried out several times of vacuum tempering to make the performance more stable. Vacuum tempering is to obtain vacuum tempered martensite.

vacuum tempering

The function is to make the T10 steel have a certain hardness, thereby improving the machining performance of the turning tool, and vacuum low-temperature tempering makes the supersaturated carbon atoms in the twin martensite precipitate and precipitate carbides dispersed in the martensite phase, improving the martensite. Stability, at the same time make vacuum quenching micro-crack welding, that is to improve the toughness of steel, but also maintain high hardness, strength and wear resistance, reduce the possibility of parts cracking, alleviate the serious internal stress state caused by vacuum quenching, vacuum tempering The hardness after vacuum tempering is generally 58-64HRC, and the hardness does not decrease after vacuum tempering.

Purpose of vacuum tempering:

1 Eliminate the residual stress of thermal stress and tissue stress generated during vacuum quenching

2 is the precipitation of carbides by vacuum quenching martensite aging, obtaining vacuum tempering martensite, vacuum tempering troostite or vacuum tempering sorbite, and improving the plasticity and toughness of the material without reducing the strength and hardness, Obtain excellent mechanical properties

3The unstable martensite and residual austenite during vacuum quenching can be transformed into a high-temperature structure to stabilize the size of the parts.

T10 steel after vacuum quenching + vacuum low temperature tempering:

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