The grades in the Chinese public norm (GB9440-88) are fundamentally as per the global norm (ISO5922-1981).
Graphitization strengthening mostly includes the strong state graphitization system, the impact of the graphitization toughening process and the impact of different components on strong state graphitization.
(1) Solid-state graphitising system. The carburized body in the white cast iron billet is a temperamental stage, which can be disintegrated into stable stages – ferrite and graphite as long as the circumstances are accessible, which is the strong state graphitization process. The important condition is that the strong graphitization of white cast iron can be done relying upon the thermodynamic and dynamic states of carburization and graphite development. The thermodynamic perspective is that the carburized body from underneath the iron-carbon stage chart A, a great deal of temperature conditions to keep warm, yet additionally happen in the strong graphitization process. In any case, regardless of whether the disintegration of the carburized body can be done consistently, and whether the graphitization interaction can be at last finished, depends generally on the capacity and plausibility of the dispersion of carbon particles after the deterioration of the carburized body, so the old stage vanishes and the new stage is shaped by different opposition factors and other dynamic circumstances.
On account of carburized body and lattice multi-stage presence, graphite cores are probably going to be delivered at the point of interaction between the carburized body and the encompassing strong arrangement; assuming that there are different sulfides, oxides and different incorporations particles inside the cast iron, the development of graphite cores is simpler. To make the presence of graphite cores in white cast iron keep on developing, should have the states of solid dissemination of carbon nuclear energy. Unadulterated iron-carbon amalgams are more challenging to graphitize, and the presence of components that advance graphitization can speed up the graphitization interaction. Numerous thoughts regarding the instrument of strong graphitization of solid metal depend for the most part on the conventional two-stage toughening process. At the high temperature stage, when warmed to the austenite temperature district, after four connections: in the austenite – carburite interface nucleation; carburite disintegrated in the encompassing austenite; carbon iotas in the austenite by the austenite carburite point of interaction to the austenite-graphite interface dispersion; carbon particles in the graphite center on the precipitation bringing about graphite development. During this phase of the toughening system. The carburite is continually dissolving and the graphite is developing until the carburite is totally broken down. Now the harmony association of solid metal is austenite in addition to graphite. In the low-temperature stage, the eutectic change into ferrite happens, lastly the balance association of ferrite in addition to graphite is shaped. Because of the presentation of the low temperature graphitization toughening process, the strong graphitization system has advanced. Warming temperature isn’t higher than A, temperature, however just 720 ~ 750 ℃ holding stage, cast iron association from the first pearlite in addition to Leylandite straightforwardly changed into ferrite in addition to graphite. The key is to further develop the lower temperature of graphitization power conditions, as well as reinforce the cast iron innate graphitization factors. For example, refining the carburized body, refining the grain to expand the connection point and expanding the disengagement thickness, consequently expanding the underlying graphite center number to decrease the dispersion distance.
(2) The impact of graphitization toughening process. The principal stage regularly utilized temperature 920 ~ 980 ℃ protection, mysterious Leyland eutectic carburite in austenite keep on dissolving into the austenite and progressively vanish, the gathering of hairy stone zero continuously framed. The second phase of usually utilized temperature 710 ~ 730 ℃ protection, or from 750 ℃ gradually (3 ~ 5 ℃/h) cooled to 700 ℃. Pre-treatment ordinarily utilized temperature partitioned into high-temperature pretreatment that is around 750 ℃ protection 1 ~ 2h, and low-temperature pretreatment that is 350 ~ 450 ℃ protection 3 ~ 5h. Its job is to build the quantity of stone get particles, diminish the dissemination of carbon iotas distance, abbreviate the tempering cycle, further develop graphite morphology.
(3) The impact of different components on strong graphitization. Carbon can advance graphitization, increment the quantity malleable cast iron pipe fittings of toughened graphite centers, abbreviate the hour of stone most graphitization, particularly abbreviate the time phase of graphitization. Silicon firmly advance graphitization, can advance the deterioration of the carburized body, so inside as far as possible to expand how much silicon in the ferrofluid, can emphatically abbreviate the first – , the second phase of tempering time. In the heater before the expansion of ferrosilicon or silicon containing compound inoculant can cause a huge fixation vacillations, helpful for the acknowledgment of low temperature graphitization. Manganese can produce MnS with sulfur, so in the fitting substance reach can abbreviate the graphitization time. Nonetheless, when how much free (manganese and sulfide consolidated to create overabundance manganese other than MnS) surpasses a specific worth (>0.15% to 0.25%) or is deficient (negative worth), graphitization is obstructed, particularly the second phase of graphitization. Sulfur emphatically prevents graphitisation. At the point when the sulfur content isn’t extremely high (<0.25%), its destructive impacts can be killed by manganese. At the point when the sulfur content is high, it makes strengthening of graphitisation troublesome. Phosphorus pitifully advances graphitisation during cementing and has little impact on the strong graphitisation during toughening. Over a specific sum on the second phase of graphitization marginally frustrate the job. Others, for example, chromium, molybdenum, vanadium and tellurium play a solid part in blocking graphitization; aluminum, zirconium and calcium play a solid part in advancing graphitization.