Today we will talk about the annealing heat treatment of W3M02Cr4VSi (301) steel machine taps

301 steel is a new steel type developed in my country in the early 1980s. Its main features are low W equivalent (W+2Mo) and the use of Si for supplementary alloying. It can replace general high-speed steel (HSS) to manufacture tools with low cutting speeds. The following is an introduction to the annealing heat treatment process of 301 steel taps.

1) Annealing process. There are two commonly used annealing processes, namely low temperature annealing and spheroidizing annealing.

① Low temperature annealing. The blank punched by the punch is subjected to low-temperature annealing treatment in order to eliminate internal stress and work hardening. The process is 770-790℃x 3 ~ 4h, the furnace is cooled to 50wC and then air-cooled out of the furnace. The hardness after annealing is ≤255HBW.

② Spheroidizing annealing. The process is 880 -900gC x2 -3h, furnace cooling to 720 -74WC x3 -4h, furnace cooling to 50WC and air cooling out of the furnace. Structure after spheroidizing annealing: sorbite + granular carbide, carbide unevenness ≤2 levels, hardness 210-255HBW, with good cutting performance.

2)Quenching and tempering. At present, there are two main types: salt bath and vacuum quenching. The salt bath heating method is introduced below.

① Preheat. The two preheating steps are air furnace preheating at about 500℃ and salt bath preheating at about 85WC. The preheating time is twice the heating time, the heating coefficient is 30s/mm, and the tap is fully immersed in the salt bath.

② Heating. 1170 -1180gC x 15s/mm. Lift the handle out of the salt bath liquid level. The high-temperature furnace should fully deoxidize and remove slag, and control the slag below 0.30Pa (mass fraction).

③ Cool down. In order to ensure quality, two classifications or isothermal quenching are generally used, and the grain size is controlled at 11 to 10 levels. Because 301 steel is a low-alloy high-speed steel with high toughness, the grains should not be too fine.

④ Tempering. 540-56WCxlh x3 times (isothermal quenching 4 times), hardness ≥63HRC, fully tempered.

3) Surface strengthening. By performing surface strengthening such as steam treatment, the tap life will be further improved.