In the previous PART-I we saw about A) tool steel performance requirements in the work.
In the current PART-II we are going to see about :-
B) die steel in the process performance requirements
C) mold steel in metallurgical quality requirements
B) die steel in the process performance requirements
(1)machinability:-
Including steel machinability by cutting both hot forging and cold, depending on the chemical composition of steel after heat treatment of internal organization and the quality of metallurgical production, in recent years, in order to improve the machinability of steel in add some steel in the steel cutting element or change in the distribution of the inclusions to improve the surface quality of die steel and reduce the die wear. In thermal processing, a number of high-carbon high-alloy tool steel, in particular, to improve the carbide morphology and distribution, grain size and degree of austenitic alloy is very important.
In addition should have good processability, but also has good electrical turning model of processing and processing of such impression.
(2) hardenability and hardenability:-
Die under these two performance requirements are different emphases in different working conditions, and for the requirements of the hardness of the uniformity of the high cross-section of the mold, such as hammer forging die steel, its high hardenability more important, while only requires a small die with high hardness, such as blanking blanking die steel, even more emphasis on high hardenability.
(3) heat deformation:-
Mold parts in the heat, require little deformation in all directions to have similar changes, and organizational stability. Quenching distortion is small, except with the quenching temperature] time and cooling medium and other factors, but it mainly depends on the composition of the steel uniform, metallurgical quality and organizational stability.
(4) decarburization sensitivity:-
Die steel forging, annealing or quenching, in the absence of heated under protective atmosphere, its surface will have defects such as oxidation and decarbonization, so that die down in durability. In addition to decarburization and heat treatment process, equipment related, in respect of material itself, depending on the chemical composition of steel, especially carbon, in the presence of high silicon, molybdenum and other elements, it will also increase decarburization.
In addition, the conditions should be based on the use of molds should be considered mirror polishing of the mold making, and so grinding and electrochemical properties.
C) mold steel in metallurgical quality requirements
It can play a high metallurgical quality of the properties of the steel substrate, die within the metallurgical quality of steel and its basic performance with the same importance in the study of performance, we must study the quality of metallurgical factors. More frequently encountered in general internal and external quality of die steel in the following areas:
(1)the uniformity of chemical composition:-
Die steel usually contains many elements of the alloy steel, steel ingot mold from the liquid during solidification, crystallization of the separation were the reason, various elements in liquid steel solidification structure in the formation of uneven distribution of segregation, the chemical composition segregation will result in differences in microstructure and properties, which affect the quality of steel is one important factor. Reduce the segregation of steel, can effectively improve the performance of steel. In recent years, many of metallurgical plant and abroad to study in the production of uniform, grain refinement of steel.
(2) the content of harmful elements:-
Sulfur and phosphorus in steel during solidification and the formation of phosphide and sulfide precipitation in the grain boundary, resulting in the intergranular brittleness of the plastic reduction of the steel, high S, P content, easy to make the ingot cracks in the rolling and may significantly reduce the mechanical properties of steel. Fortunately, one studies in Japan said that S, P content on the W (Cr) 5% hot work die steel (H13) of the impact toughness and thermal fatigue performance results show that, as the W (S, P) content of 0.025% from and 0.010% to W (P) 0.005%, and W (S) 0.001%, the thermal fatigue crack length and number will be reduced by half. Hitachi Metals will SKD61 steel in W (P) content from 0.03% to 0.001%, while steel can be 45HRC toughness increased by the 39.2J/cm2 to 127.5J/cm2. In addition, the reduction of steel in the S, P content also can increase the isotropic steel.
(3) non-metallic inclusions in steel:-
Good quality steel chemical composition not only to comply with technical standards and non-metallic inclusions in steel content should be kept as small as non-metallic inclusions in steel volume occupied by the small, but for steel Performance is great. Reduce non-metallic inclusions in steel is the steel of the main tasks. Commonly referred to as non-metallic inclusions in steel, mainly refers to the iron and other alloying elements with oxygen, sulfur and nitrogen compounds formed by the role, such as FeO, MnO, Al2O3, SiO2, FeS, MnS, AlN, VN, etc. , as well as steel and pouring into the refractory, which elements are mainly Si, Al, Fe, Cr, Ca, Mg and other oxides.
Non-metallic inclusions in steel on its source, can be divided into internal and external inclusions , the inclusions cents in the liquid and the solidification of steel in the process of formation of compounds.
Non-metallic inclusions in steel in the basic kinds of sense to stay a certain size as a crack, it destroys the continuity of the metal, causing stress concentration, the role of stress in the outside world, the crack extension is easy to develop and expand the lead to performance reduced. The presence of plastic inclusions, with the extension of forging deformation rolling process, resulting in anisotropy of steel produced. While inclusion of peeling polishing process to improve the surface roughness of the mold. Therefore, the mold is large and important to improve the purity of steel is very important.
(4)white dot:-
Hot rolled steel billet and white point is more common in large forging defects, is a breakdown of internal steel mold making. The presence of white steel with a very negative impact on performance, which mainly affects the mechanical properties of the steel mold design decreases when the forging hardening heat treatment cracking, or use to develop into more serious accident damage, so in any case Next, we can not use a white point of the forgings. White point of the different sensitivity of steel is different, generally considered prone to white spots are chrome steel, steel, chrome molybdenum steel, manganese steel, manganese steel, molybdenum, chromium nickel molybdenum steel, chromium tungsten steel. Which contains W (C) greater than 0.30%, W (Cr) greater than 1%, W (Ni) 2.5% of the earth martensitic chrome-nickel steel and chrome-nickel molybdenum steel, the sensitivity of the biggest white spot. The reason is the formation of white steel, precipitation of hydrogen in the precipitation accumulation, vertical section of the steel to form crystalline silver bright white thick round or oval spots. It tends to make forgings and billet material internal cracks. Die steel 5CrNiMo, 5CrMnMo white as the most likely to occur if the increase in carbon elements Cr, Mo, and V can reduce the white point after the sensitivity. In the production of such steel degassing must pay attention to and strengthen the great relief after forging or cold forging dehydrogenation annealing.
(5)the oxygen content:-
Generally we did not provide for die steel in steel gas content allowed. With the increase of oxygen content, oxide particles and volume increased, decreased fatigue properties of steel, are also prone to hot cracking. Some people have been tested 4Cr5MoSiV1 steel, the oxygen content of no more than 1.5 * 10-5, which provides Japan's Sanyo Special Steel Company of high purity oxygen content of steel is not greater than 1.0 * 10-5. Therefore, in recent years, in order to improve the quality of the mold making supplier. Gradually die steel at home and abroad to the low oxygen content in the direction of development.
(6) the carbide inhomogeneity:-
Carbide is the most essential components of die steel, in addition to the carbide can be dissolved in austenite, there will be some residual carbon is not soluble in austenite. Carbide size, shape, distribution of properties such as the use of die steel has a very important influence. On the carbide size, shape and distribution methods and steel smelting, steel ingot solidification conditions and heat processing of deformation conditions and so on. Eutectoid carbon steel may be formed at the grain boundaries or in the processing of the wind-shaped deformation of carbide carbide carbide is elongated to form zonal or both, ledeburite die steel, there is a carbide and secondary carbides in the hot deformation process, the mesh can be broken most of eutectic carbide, carbide be extended along the deformation direction, resulting in ribbon, with the increase of deformation, the carbide becomes uniform, fine . Carbide heterogeneity on quenching deformation, cracking, mechanical properties of steel greater.
(7) segregation:-
Segregation of the steel composition and organization of the performance of non-uniformity, which is in the mold steel macrostructure often test the existence of a defect. Is the ingot formed in the solidification process, and steel, chemical composition and pouring temperature and so on. Generally divided into dendritic segregation, square segregation, dotted segregation. Because the presence of dendritic segregation, so that all negative then the mechanical properties in different directions showed significant differences. Square ingot segregation is due to crystallization, the end of the columnar crystals and equiaxed ingot heart interval, bringing together more impurities and pores formed. Square severe segregation, the impact on the quality of steel is significant, especially cutting the amount of large parts or the force of the Department of heart mold parts. Segregation in addition to the mechanical properties of die steel isotropic, the polishing of the mold have an impact on performance. Therefore, foreign-related standards have strict requirements.
(8) loose:-
Loose density of steel is not the performance. Most loose in the upper and central parts of ingots, because in these places more focus on the result of impurities and gases. Because osteoporosis defects, reducing the strength and toughness of steel, but also seriously affected the surface roughness after processing, in general the impact of mold steel is not particularly large, but if cold roll, a large block, punch and mold and others have more stringent requirements. Such as deep cavity of the forging die and punch requires loose no more than 1 or 2, for the dial or light pieces of plastic mold steel, requires no more than one loose.
In the current PART-II we are going to see about :-
B) die steel in the process performance requirements
C) mold steel in metallurgical quality requirements
B) die steel in the process performance requirements
(1)machinability:-
Including steel machinability by cutting both hot forging and cold, depending on the chemical composition of steel after heat treatment of internal organization and the quality of metallurgical production, in recent years, in order to improve the machinability of steel in add some steel in the steel cutting element or change in the distribution of the inclusions to improve the surface quality of die steel and reduce the die wear. In thermal processing, a number of high-carbon high-alloy tool steel, in particular, to improve the carbide morphology and distribution, grain size and degree of austenitic alloy is very important.
In addition should have good processability, but also has good electrical turning model of processing and processing of such impression.
(2) hardenability and hardenability:-
Die under these two performance requirements are different emphases in different working conditions, and for the requirements of the hardness of the uniformity of the high cross-section of the mold, such as hammer forging die steel, its high hardenability more important, while only requires a small die with high hardness, such as blanking blanking die steel, even more emphasis on high hardenability.
(3) heat deformation:-
Mold parts in the heat, require little deformation in all directions to have similar changes, and organizational stability. Quenching distortion is small, except with the quenching temperature] time and cooling medium and other factors, but it mainly depends on the composition of the steel uniform, metallurgical quality and organizational stability.
(4) decarburization sensitivity:-
Die steel forging, annealing or quenching, in the absence of heated under protective atmosphere, its surface will have defects such as oxidation and decarbonization, so that die down in durability. In addition to decarburization and heat treatment process, equipment related, in respect of material itself, depending on the chemical composition of steel, especially carbon, in the presence of high silicon, molybdenum and other elements, it will also increase decarburization.
In addition, the conditions should be based on the use of molds should be considered mirror polishing of the mold making, and so grinding and electrochemical properties.
C) mold steel in metallurgical quality requirements
It can play a high metallurgical quality of the properties of the steel substrate, die within the metallurgical quality of steel and its basic performance with the same importance in the study of performance, we must study the quality of metallurgical factors. More frequently encountered in general internal and external quality of die steel in the following areas:
(1)the uniformity of chemical composition:-
Die steel usually contains many elements of the alloy steel, steel ingot mold from the liquid during solidification, crystallization of the separation were the reason, various elements in liquid steel solidification structure in the formation of uneven distribution of segregation, the chemical composition segregation will result in differences in microstructure and properties, which affect the quality of steel is one important factor. Reduce the segregation of steel, can effectively improve the performance of steel. In recent years, many of metallurgical plant and abroad to study in the production of uniform, grain refinement of steel.
(2) the content of harmful elements:-
Sulfur and phosphorus in steel during solidification and the formation of phosphide and sulfide precipitation in the grain boundary, resulting in the intergranular brittleness of the plastic reduction of the steel, high S, P content, easy to make the ingot cracks in the rolling and may significantly reduce the mechanical properties of steel. Fortunately, one studies in Japan said that S, P content on the W (Cr) 5% hot work die steel (H13) of the impact toughness and thermal fatigue performance results show that, as the W (S, P) content of 0.025% from and 0.010% to W (P) 0.005%, and W (S) 0.001%, the thermal fatigue crack length and number will be reduced by half. Hitachi Metals will SKD61 steel in W (P) content from 0.03% to 0.001%, while steel can be 45HRC toughness increased by the 39.2J/cm2 to 127.5J/cm2. In addition, the reduction of steel in the S, P content also can increase the isotropic steel.
(3) non-metallic inclusions in steel:-
Good quality steel chemical composition not only to comply with technical standards and non-metallic inclusions in steel content should be kept as small as non-metallic inclusions in steel volume occupied by the small, but for steel Performance is great. Reduce non-metallic inclusions in steel is the steel of the main tasks. Commonly referred to as non-metallic inclusions in steel, mainly refers to the iron and other alloying elements with oxygen, sulfur and nitrogen compounds formed by the role, such as FeO, MnO, Al2O3, SiO2, FeS, MnS, AlN, VN, etc. , as well as steel and pouring into the refractory, which elements are mainly Si, Al, Fe, Cr, Ca, Mg and other oxides.
Non-metallic inclusions in steel on its source, can be divided into internal and external inclusions , the inclusions cents in the liquid and the solidification of steel in the process of formation of compounds.
Non-metallic inclusions in steel in the basic kinds of sense to stay a certain size as a crack, it destroys the continuity of the metal, causing stress concentration, the role of stress in the outside world, the crack extension is easy to develop and expand the lead to performance reduced. The presence of plastic inclusions, with the extension of forging deformation rolling process, resulting in anisotropy of steel produced. While inclusion of peeling polishing process to improve the surface roughness of the mold. Therefore, the mold is large and important to improve the purity of steel is very important.
(4)white dot:-
Hot rolled steel billet and white point is more common in large forging defects, is a breakdown of internal steel mold making. The presence of white steel with a very negative impact on performance, which mainly affects the mechanical properties of the steel mold design decreases when the forging hardening heat treatment cracking, or use to develop into more serious accident damage, so in any case Next, we can not use a white point of the forgings. White point of the different sensitivity of steel is different, generally considered prone to white spots are chrome steel, steel, chrome molybdenum steel, manganese steel, manganese steel, molybdenum, chromium nickel molybdenum steel, chromium tungsten steel. Which contains W (C) greater than 0.30%, W (Cr) greater than 1%, W (Ni) 2.5% of the earth martensitic chrome-nickel steel and chrome-nickel molybdenum steel, the sensitivity of the biggest white spot. The reason is the formation of white steel, precipitation of hydrogen in the precipitation accumulation, vertical section of the steel to form crystalline silver bright white thick round or oval spots. It tends to make forgings and billet material internal cracks. Die steel 5CrNiMo, 5CrMnMo white as the most likely to occur if the increase in carbon elements Cr, Mo, and V can reduce the white point after the sensitivity. In the production of such steel degassing must pay attention to and strengthen the great relief after forging or cold forging dehydrogenation annealing.
(5)the oxygen content:-
Generally we did not provide for die steel in steel gas content allowed. With the increase of oxygen content, oxide particles and volume increased, decreased fatigue properties of steel, are also prone to hot cracking. Some people have been tested 4Cr5MoSiV1 steel, the oxygen content of no more than 1.5 * 10-5, which provides Japan's Sanyo Special Steel Company of high purity oxygen content of steel is not greater than 1.0 * 10-5. Therefore, in recent years, in order to improve the quality of the mold making supplier. Gradually die steel at home and abroad to the low oxygen content in the direction of development.
(6) the carbide inhomogeneity:-
Carbide is the most essential components of die steel, in addition to the carbide can be dissolved in austenite, there will be some residual carbon is not soluble in austenite. Carbide size, shape, distribution of properties such as the use of die steel has a very important influence. On the carbide size, shape and distribution methods and steel smelting, steel ingot solidification conditions and heat processing of deformation conditions and so on. Eutectoid carbon steel may be formed at the grain boundaries or in the processing of the wind-shaped deformation of carbide carbide carbide is elongated to form zonal or both, ledeburite die steel, there is a carbide and secondary carbides in the hot deformation process, the mesh can be broken most of eutectic carbide, carbide be extended along the deformation direction, resulting in ribbon, with the increase of deformation, the carbide becomes uniform, fine . Carbide heterogeneity on quenching deformation, cracking, mechanical properties of steel greater.
(7) segregation:-
Segregation of the steel composition and organization of the performance of non-uniformity, which is in the mold steel macrostructure often test the existence of a defect. Is the ingot formed in the solidification process, and steel, chemical composition and pouring temperature and so on. Generally divided into dendritic segregation, square segregation, dotted segregation. Because the presence of dendritic segregation, so that all negative then the mechanical properties in different directions showed significant differences. Square ingot segregation is due to crystallization, the end of the columnar crystals and equiaxed ingot heart interval, bringing together more impurities and pores formed. Square severe segregation, the impact on the quality of steel is significant, especially cutting the amount of large parts or the force of the Department of heart mold parts. Segregation in addition to the mechanical properties of die steel isotropic, the polishing of the mold have an impact on performance. Therefore, foreign-related standards have strict requirements.
(8) loose:-
Loose density of steel is not the performance. Most loose in the upper and central parts of ingots, because in these places more focus on the result of impurities and gases. Because osteoporosis defects, reducing the strength and toughness of steel, but also seriously affected the surface roughness after processing, in general the impact of mold steel is not particularly large, but if cold roll, a large block, punch and mold and others have more stringent requirements. Such as deep cavity of the forging die and punch requires loose no more than 1 or 2, for the dial or light pieces of plastic mold steel, requires no more than one loose.
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