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Heat Treatment Of Marine Casting
Sep 06, 2017

Heat Treatment of Marine Casting
At present, in the production of marine steel Casting, the largest carbon steel ship Casting single weight of 180t, the maximum heat treatment furnace size of 13mXllmX5.5m. High-strength (tensile strength up to 480Mpa) and high impact toughness (0 ° C 27J) for high-strength (high tensile strength) and high impact toughness (0 ° C 27J) for high-strength (high tensile strength) , And even the user requirements to reach 0 ° C 55J above) requirements, compliance is more difficult, and the performance is not stable enough. The traditional heat treatment process is shown in Fig. This kind of heat treatment process, does not apply to large Casting, especially marine carbon and manganese steel Casting, the reason, nothing more than the following three (1) due to large Casting thick wall thickness, need a long time insulation will lead to grain Grow up; (2) due to the normalization cooling speed is insufficient, prone to grain original position to retain the show. (3) when the need to 480W level of products but also to ensure that the chemical composition of low-carbon, the traditional process requires a long time to temper the tempering, the performance of the performance of the product is not stable, Processing, in which case it is more prone to reduce the intensity so as not to meet the standard requirements. In the use of traditional technology, to meet the high strength requirements, the impact toughness success rate of only 30%. Therefore, the use of appropriate heat treatment process, so that carbon and manganese steel Casting can meet both high strength, but also to meet the high impact toughness, especially low temperature impact toughness is the industry in the marine steel Casting on a bottleneck. The development of a new type of marine carbon and manganese steel Casting heat treatment process, breaking the use of large-scale heat treatment furnace, dealing with large quantities, large tonnage of marine carbon and manganese steel Casting heat treatment bottlenecks, industry is an urgent need to solve one of the key issues.
 It is an object of the present invention to develop a new heat treatment process which aims at solving the problem of unstable performance in the treatment of large-thickness carbon steel Casting in large-scale heat treatment furnaces so that the large-sized marine Casting after heat treatment satisfy both high strength and high To meet the high impact toughness, especially low temperature impact toughness aspects of the performance requirements. The technical solution of the present invention is a heat treatment process for a marine carbon-manganese steel Casting which is characterized in that it comprises the following steps (1. 1) containing C 彡 0.23%, Si 彡 0.60%, MnO. 7 1.60% and Cu 彡 0.30%, Ni 彡 0.40%, Mo 彡 0. 15% of the marine carbon and manganese steel Casting into the 13mX llmX5m large-scale heat treatment furnace for the first normalizing treatment to The heating rate of 750C / h is heated to 920 ° C ± 20 ° C for 8 36 hours, so that the organization of the Casting is completely austenitized and then air cooled and cooled to 700 ° C in one hour; 2) The second normalizing treatment of the Casting in step (1. 1) is carried out and heated to a temperature of 830 ° C ± 20 ° C at a heating rate of 750 ° C / h for 8 16 hours, Cooled to 600 ° C to obtain sorbite tissue and then baked. The holding time at the time of the first normalizing treatment is calculated according to the maximum thickness of the Casting of 25 mm / h. The holding time at the time of the second normalizing treatment is calculated according to the maximum thickness of the Casting 50 mm / h. Compared with the prior art, the advantages of the present invention are mainly manifested in the present invention
1. The invention has wide application range and can cover the large wall thickness Casting of most carbon and manganese steel, which is beneficial to the furnace of large heat treatment furnace and can improve the utilization efficiency and production efficiency of the equipment. 2. The invention can meet the requirements of the existing ship regulations for the impact toughness at different temperatures while ensuring high strength. 3, can save a lot of heat treatment time, and reduce the heat treatment costs (1) in the first normalizing, cooling to 700 ° C can be a second normalizing, from 700 ° C and then heated to 830 ° C temperature difference At 130 ° C, less than the traditional process from 200 ° C to 600 ° C 400 ° C temperature difference, the heating rate is roughly the same circumstances can save a lot of heating time. (2) The second normalizing and holding time is calculated according to the wall thickness of 50mm / h, and the tempering time of the traditional process is calculated according to the wall thickness of 25mm / h, which can save nearly 50% of the holding time. (3) after the second normalizing the cooling, for the furnace down to 600 V can be baked, about 4 hours, while the traditional process of tempering furnace after the cold time of 10 hours, can save 6 hours. 4. The process of the present invention is fairly stable, facilitates mass production, has a very high success rate, reduces the cost of repeated heat treatment, and reduces the cost of shipping by the classification societies.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A heat treatment process for a marine carbon-manganese steel Casting as shown in Fig. 1 is characterized by comprising the following steps consisting essentially of C 彡 0.23%, Si 彡 0.60%, MnO.71. 60% and Cu 彡 0.30%, Ni 彡 0.40%, Mo 彡 0. 15% of the marine carbon and manganese steel Casting into the 13mXllmX5m large-scale heat treatment furnace for the first normalizing treatment to not more than 75 ° C / h Heating rate to 920 ° C 20 ° C, insulation 8 36 hours, the insulation time in accordance with the maximum wall thickness of 25mm / h calculation, so that the organization is completely austenitized, complete the first normalizing, and then The first normalizing baked ventilated cooling, reduced to below 700 ° C in one hour, and then heated to 8300C 20 ° C at a temperature not higher than 75 ° C / h, 8 16 hours for insulation, The maximum wall thickness of 50mm / h calculation, and then in the furnace naturally cooled to 600 ° C below, you can baked, into the room to cool to room temperature, complete the heat treatment process. Large marine Casting riser diameter mostly in more than 600mm, the maximum riser diameter of 2. 9m. Thickness of the carbon steel Casting as-cast segregation serious, columnar crystal structure thick.