Plastic processing, also known as press processing, is a processing method in which a metal or alloy material is plastically deformed under the action of an external force to obtain a desired shape size and performance.
The plastic processing process is divided into primary deformation and secondary deformation, and the initial deformation is the blanking.
The tungsten, molybdenum and alloy strips for drawing are produced by powder metallurgy method, which is a fine-grained structure, which does not need to be stacked and forged, and can be directly subjected to selective section and hole type rolling. For arc smelting and electron beam melting ingots with coarse grain structure, it is necessary to first extrude or forge the blank to withstand the three-way compressive stress state to avoid the occurrence of grain boundary cracks for further processing.
The plasticity of a material is the degree of deformation of the material before fracture. The strength is the ability of the material to resist deformation and fracture. The toughness is the ability of the material to absorb energy from plastic deformation to fracture. Tungsten-molybdenum and its alloys tend to be high in strength, but have poor plastic deformation ability, or can hardly withstand plastic deformation under normal conditions, and exhibit poor toughness and brittleness.
1,plastic-brittle transition temperature
The brittleness and toughness behavior of the material change with temperature. It is pure in a plastic-brittle transition temperature range (DBTT), that is, it can be plastically deformed under high stress above this temperature range, showing good toughness. Different forms of brittle fracture are prone to occur during processing deformation below this temperature range. Different metals have different plastic-brittle transition temperatures, tungsten is generally around 400 ° C, and molybdenum is near room temperature. The high plastic-brittle transition temperature is an important characterization of material brittleness. The factors affecting DBTT are the factors that affect brittle fracture. Any factors that promote the brittleness of materials will increase DBTT. The measures to reduce DBTT are to overcome brittleness and increase. Resilience measures.
The factors affecting the plastic-brittle transition temperature of the material are the purity, grain size, degree of deformation, stress state and alloying elements of the material.
2, low temperature (or room temperature) recrystallization brittleness
The industrial tungsten and molybdenum materials in the recrystallized state exhibit completely different mechanical behaviors from the industrially pure face-centered cubic copper and aluminum materials at room temperature. The recrystallized and annealed copper and aluminum materials form an equiaxed recrystallized grain structure, which has excellent room temperature processing plasticity and can be arbitrarily processed into a material at room temperature, and tungsten and molybdenum exhibit severe brittleness at room temperature after recrystallization. Various forms of brittle fracture are easily generated during processing and use.