Mold growing in the modern manufacturing industry occupies an important place and, in particular the automotive and electrical industry more than 70% of the parts in the mold manufacturing process used. However, INDIA imported a large number of high-quality molds to analyze the main reason for our high quality steel is not steel-making level, but do not realize that improving the quality of the die steel is a system control process.
In addition to metallurgical quality, making the process of forging processing, preparation heat treatment, machining and final heat treatment will affect the internal organization of the mold and the stress state to determine the final performance of mold. According to all in the mold manufacturing process, the die life and made of precision, quality, surface properties, except with the mold design, manufacturing, machine tools and precision as well as other conditions of operation, but with the mold materials and heat treatment process are closely related.
According to the statistics show that the mold material selection due to early failure and internal defects caused by improper accounting for about 10%, caused by the improper heat treatment, about 50%, so the correct choice of mold steel with excellent quality and the correct treatment is of great significance.
The properties of die steel including the use of performance, process performance and the three aspects of metallurgical quality:-
A) tool steel performance requirements in the work
(1) hardness:-
Die at work is a complex stress state, such as hot die temperature is usually in exchange to withstand alternating stress, so it should have good resistance to softening or plastic deformation ability of the state, despite the long-term work environment to maintain the shape and size precision molds. Mold steel hardness is one of the students to the performance. The hardness of cold-working die generally choose to 58HRC more, hot die, especially for high resistance to thermal fatigue properties of the mold, usually of about the hardness of 45HRC. On the common use of plastic molds, usually around 35HRC hardness required.
(2) strength and toughness:-
Part in the forming of the die under enormous impact, distortion and other loads, especially in modern high-speed stamping, high precision forging and liquid molding techniques and the development of a forming mold to bear a bigger load, often due to the strength of steel and toughness is not enough, resulting in marginal or partial collapse of the cavity, chipping or breaking and early failure, so the mold heat treatment should have high hardness and toughness.
(3) wear:-
Parts forming the mold cavity surface materials and the relative motion, so that the wear surface of the cavity, which makes the dimensional accuracy of mold, shape and surface roughness change and failure. Wear is a complex process, affecting many factors, in addition to the role of the mold depends on external conditions, also depends largely on the uneven use of the chemical composition of steel, organizational status, mechanical properties.
(4)fatigue:-
Mold work suffer mechanical shock and thermal shock alternating stress, hot work die in the process, thermal alternating stress more clearly lead to mold thermal cracking. By the impact of stress and temperature gradient caused by cracks, often in small shallow cavity surface cracks, which led to the rapid spread and expansion of die failure. In addition, the steel chemical composition and organization of the uneven presence in steel metallurgical defects such as inclusions, pores, micro cracks can lead to reduced fatigue strength of steel, because the action of alternating stress, first These weak areas and the development of fatigue cracks as fatigue failure.
(5) adhesion:-
The surface of the mold parts Picks of the two metal atoms with each other or single-phase diffusion function, often there will be some adhesion of the metal to be processed, especially the cutting, cutting tools and stamping tools, or scarring of the surface will produce the phenomenon of adhesion This will affect the degree of edge sharpness and local organizations, the chemical composition changes to the edge part of the crack or scratch off adhesive metal mold, so that the surface rough. So good anti-adhesion is also very important.
(6)polishing and etching performance:-
With the mold, in particular the widespread use of plastic mold, low surface roughness values (sometimes even the extent of the mirror) has been very nature of the necessary, low surface roughness effects to mold the life and production efficiency and product quality. High surface quality can reduce corrosion (especially local pitting); reduce the risk of cracking, polished steel, chemical composition, structure, hardness and carbide distribution must be uniform. Large carbides and in particular their segregation into the strip, the polishing of the surface is extremely harmful. Particularly important that the steel can not contain no large deformation of oxide inclusions, or segregation, and thus must be strictly controlled, and oxygen smelting process. Vacuum arc remelting, electroslag remelting good effect, this process has become the main advanced plastic mold steel production. Even the simple vacuum degassing will also help eliminate a large oxide inclusions, the smelting process can not only reduce the oxide content, and oxides can be more fine, uniform, while controlling the process of smelting and oxygen, can also change the inclusions type, so that the plastic softening and has good toughness and improve the polishing performance.
Steel, the hole is not closed for any would affect the polishing performance, so hot lamination process in the metallurgical defects such as loose and tight to keep the organization is necessary, which can be formed by the modern processing technologies. For example, repeatedly upsetting and stretching techniques, rotating forging technology, high temperature static and repression can be refined the original cast, dendrites in the gap. Remelting, vacuum arc remelting refining process, the uniformity of the steel is also very beneficial. Hardened by the heat treatment or surface defects caused should avoid decarburization causes uneven hardness. Composition of these measures with a reasonable design and control, we can produce steel mirror finish are excellent.
In addition, the mold should be based on differences in working conditions and environment, consider the use of tool steel should have good thermal conductivity, corrosion resistance, oxidation resistance and permeability and so on.
In addition to metallurgical quality, making the process of forging processing, preparation heat treatment, machining and final heat treatment will affect the internal organization of the mold and the stress state to determine the final performance of mold. According to all in the mold manufacturing process, the die life and made of precision, quality, surface properties, except with the mold design, manufacturing, machine tools and precision as well as other conditions of operation, but with the mold materials and heat treatment process are closely related.
According to the statistics show that the mold material selection due to early failure and internal defects caused by improper accounting for about 10%, caused by the improper heat treatment, about 50%, so the correct choice of mold steel with excellent quality and the correct treatment is of great significance.
The properties of die steel including the use of performance, process performance and the three aspects of metallurgical quality:-
A) tool steel performance requirements in the work
(1) hardness:-
Die at work is a complex stress state, such as hot die temperature is usually in exchange to withstand alternating stress, so it should have good resistance to softening or plastic deformation ability of the state, despite the long-term work environment to maintain the shape and size precision molds. Mold steel hardness is one of the students to the performance. The hardness of cold-working die generally choose to 58HRC more, hot die, especially for high resistance to thermal fatigue properties of the mold, usually of about the hardness of 45HRC. On the common use of plastic molds, usually around 35HRC hardness required.
(2) strength and toughness:-
Part in the forming of the die under enormous impact, distortion and other loads, especially in modern high-speed stamping, high precision forging and liquid molding techniques and the development of a forming mold to bear a bigger load, often due to the strength of steel and toughness is not enough, resulting in marginal or partial collapse of the cavity, chipping or breaking and early failure, so the mold heat treatment should have high hardness and toughness.
(3) wear:-
Parts forming the mold cavity surface materials and the relative motion, so that the wear surface of the cavity, which makes the dimensional accuracy of mold, shape and surface roughness change and failure. Wear is a complex process, affecting many factors, in addition to the role of the mold depends on external conditions, also depends largely on the uneven use of the chemical composition of steel, organizational status, mechanical properties.
(4)fatigue:-
Mold work suffer mechanical shock and thermal shock alternating stress, hot work die in the process, thermal alternating stress more clearly lead to mold thermal cracking. By the impact of stress and temperature gradient caused by cracks, often in small shallow cavity surface cracks, which led to the rapid spread and expansion of die failure. In addition, the steel chemical composition and organization of the uneven presence in steel metallurgical defects such as inclusions, pores, micro cracks can lead to reduced fatigue strength of steel, because the action of alternating stress, first These weak areas and the development of fatigue cracks as fatigue failure.
(5) adhesion:-
The surface of the mold parts Picks of the two metal atoms with each other or single-phase diffusion function, often there will be some adhesion of the metal to be processed, especially the cutting, cutting tools and stamping tools, or scarring of the surface will produce the phenomenon of adhesion This will affect the degree of edge sharpness and local organizations, the chemical composition changes to the edge part of the crack or scratch off adhesive metal mold, so that the surface rough. So good anti-adhesion is also very important.
(6)polishing and etching performance:-
With the mold, in particular the widespread use of plastic mold, low surface roughness values (sometimes even the extent of the mirror) has been very nature of the necessary, low surface roughness effects to mold the life and production efficiency and product quality. High surface quality can reduce corrosion (especially local pitting); reduce the risk of cracking, polished steel, chemical composition, structure, hardness and carbide distribution must be uniform. Large carbides and in particular their segregation into the strip, the polishing of the surface is extremely harmful. Particularly important that the steel can not contain no large deformation of oxide inclusions, or segregation, and thus must be strictly controlled, and oxygen smelting process. Vacuum arc remelting, electroslag remelting good effect, this process has become the main advanced plastic mold steel production. Even the simple vacuum degassing will also help eliminate a large oxide inclusions, the smelting process can not only reduce the oxide content, and oxides can be more fine, uniform, while controlling the process of smelting and oxygen, can also change the inclusions type, so that the plastic softening and has good toughness and improve the polishing performance.
Steel, the hole is not closed for any would affect the polishing performance, so hot lamination process in the metallurgical defects such as loose and tight to keep the organization is necessary, which can be formed by the modern processing technologies. For example, repeatedly upsetting and stretching techniques, rotating forging technology, high temperature static and repression can be refined the original cast, dendrites in the gap. Remelting, vacuum arc remelting refining process, the uniformity of the steel is also very beneficial. Hardened by the heat treatment or surface defects caused should avoid decarburization causes uneven hardness. Composition of these measures with a reasonable design and control, we can produce steel mirror finish are excellent.
In addition, the mold should be based on differences in working conditions and environment, consider the use of tool steel should have good thermal conductivity, corrosion resistance, oxidation resistance and permeability and so on.
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