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The casting process of high manganese steel
Scope of application of the high manganese steel casting, high manganese steel under high energy impact working conditions and is broad. Many foundry, producing such steel castings for lack of the necessary understanding. Now on the specific operation do briefly, producer for reference.
1 chemical composition
High manganese steel in accordance with national standards are divided into five grades, the main difference is the content of carbon and its scope is 0.75% - 1.45%. By the impact of a large, low carbon content. Manganese content between 14.0% and 11.0%, the general should not be less than 13%. There is no high manganese steel GB, but manganese content should be more than 18%. The content of silicon in high and low, on impact toughness of influence is big, therefore should take the lower end, to no more than 0.5% is appropriate. Low phosphorus and sulfur is the most basic requirements, due to the high manganese content in a natural desulfurization effect, so the reduction of phosphorus is the most important, and managed to make phosphorus is to improve the abrasion resistance of less than 0.07%. Chromium, generally in the 2.0% the left and right.
2 charge
The material into the furnace is determined by the chemical composition. The main burden is high quality carbon steel or steel ingot, high carbon ferromanganese, medium carbon ferromanganese, high carbon ferrochrome and high manganese steel back to burden. Here special remind is considered by the people as long as a suitable chemical composition, can use recycled scrap. This person is harmful. Some factory is the poor quality of products, all for this. Not only high manganese steel, high manganese steel, usually metal castings, should not be too much use of recycled scrap, scrap should not more than 25%. So, recycled material to the excess? As long as the waste to a minimum, recycled material will not excess.
3 smelting
This paper focuses on the speak sequence, regardless of frequency furnace or electric furnace, always first melting carbon steel, and all kinds of ferromanganese and other precious alloy materials, to several points, each time a small amount of valuable elements into the furnace, in the end, in order to reduce the loss of material. The piece should be as small as possible, with 50 - 80mm melt is appropriate. After cleaning, the temperature reaches 1580 to 1600 DEG C, to deoxidation, dehydrogenation, nitrogen, available aluminum wire, can also be used Si-Ca or SiC alloy material. The deoxidizing agent must close to deep in the furnace. When the metal surface covering agent tightly covered, partition outside air. To calm a period of time, the oxide. Inclusion has enough time to rise. However, many companies will only wire even aluminum powder, and again on the liquid metal, and without cover, not wasted! During this period, timely use of medium carbon ferromanganese to adjust the content of manganese and carbon.
Before tapping of molten steel, the ladle baking to 400 DEG C is very necessary. In the baked with v-during Ti Fe, rare earth and trace elements do modification. It is a refinement of crystallization in the necessary means and its impact on the performance of the product is crucial.
4 charge and other materials
To prolong furnace life, when distinguish the attributes of the lining and steel. The steel lining is alkaline, of course choose magnesia ramming lining material. Turns to cycle transposition operation. Add lining material can not be too thick, every time is about 80 cm, bishop long time beaten to low temperature baking. Such as improving the production efficiency, the author recommended molding crucible (Shenyang power plant and to the factory and finished products are sold), from the open furnace with thee, not 1 hours, can be put into production at the same time, forming the crucible of the wear furnace great benefit. Of course, the length of the furnace to fix big relationship. Many operators like shot athletes like to the charge from three or four meters away into the furnace, neither safety and injury to furnace, should be placed near the furnace charge preheating, then use the clip will slowly along the burden on the burden of the next warm-up, and then use the clip will slowly burden into the furnace wall.
Moulding materials and coating should also be consistent with the liquid metal attributes, or by ZTE materials (such as chromite sand, corundum, etc.). If you want to get a collective recrystallization. The storage of large amount of chromite sand is correct, especially EPC production plant, it will overcome loose the disadvantage of the heat slowly.
5 casting process design
The steel is characterized by solidification shrinkage, poor heat dissipation, accordingly, shrinkage rate from 2.5% to 2.7% in the process of casting design, casting more grown up, should take the upper limit. The retreat must be sand and sand core. The open gating system. Multiple dispersed ingate from thin wall casting. Introduced, and flat and wide horn shape, cross-sectional area near the casting is larger than the cross-sectional area and the runner is connected, so that the liquid metal quickly into a mold, prevent the temperature difference of the whole mold is too large. The riser diameter greater than the hot section diameter, height is close to the hot section, diameter 2.5 3 times, must use the heat riser riser even one, get plenty of high temperature liquid metal to the casting in solidification contraction of the room. The sprue, riser in high (sand box has 5 - 8 slope) is correct. The pouring temperature fast water as much as possible. Once the coagulation, to and When loose sand box. Clever designers have always been good at using cold iron, including the cold iron in cold iron. It is refined a crystallization, eliminate shrinkage, shrinkage porosity, and improve the yield of the process, of course, the suitable dosage and specifications is should be considered. In cold iron to clean, fusible, amount to less suitable. Three dimensions of external iron chill the dimensional and cooling material for 0.6 0.7 times the function relationship. Don't work too small, casting cracking caused by excessive. Casting in type to long time heat preservation until less than 200 DEG C and then out of the box.
6 heat treatment
Heat treatment is the low temperature cracking stage caused by heating up too fast. So the correct operation is 350 DEG C, heating rate <80 /h DEG, 750 DEG C, <100 C /h, and insulation in different period. >750 Deg. C, casting in a plastic state, can quickly heat up to 1050 degrees C according to. The casting thickness determine the holding time, and then rose to more than 1100 DEG. Released into the water then cooling to room temperature as soon as possible. When the temperature is too slow, the holding time is too short, released into the water time interval is too long (not >0.5min), all of which affect the quality of castings. The water temperature should be <30 degrees, quenching after the temperature of <50 DEG C, the water should be not less than 8 times the weight of castings. The cold water from the bottom into the warm water pool, top of the outflow from the pool. Casting in the pond to constantly move in three directions.
7 cutting and welding
Because of poor heat conduction performance of the manganese steel, so in riser cutting should pay great attention to. Best castings is placed in the water, was cut partially exposed outside the water, cutting leave a certain amount of stubble, heat treatment after wear off.
Many plants, welding and welding repair become inevitable. Selection of austenitic manganese nickel electrode (D256 or D266 type), specifications slender, phi of 3.2mm x 350mm and outer coating is alkaline. When operating with small current, weak arc, small bead welding layer, and always maintain a low temperature less degree of the operating method of the heat. While welding side struck, eliminate stress. Important castings must detection.
Producers to consider, is not only to reduce the production cost, but more important is a waste and maximize the quality product, and the most to limit expand capture market share. It seems to be slow and fees, in fact, is fast and province, this concept is not only to recognize, more important is to do.