Carbon steel sheets is an iron-carbon alloy with a carbon content of 0.028% to 2.11%. Also called carbon steel sheets. Also contains some silicon, manganese, sulfur, phosphorus. Strength is also ok, but the lower the plasticity.
Iron-carbon alloys with a mass fraction of less than 2.11%
Brand: Example Q235-A·F, indicating σs=235MPa.
Note on the grade: Q is the quality grade of high-quality strength A (there are four grades of ABCD), and F is boiling.
Features: Price, process performance (such as weldability and coldness) are excellent.
Application: General engineering structure and general mechanical parts. For example, Q235 can be used to make bolts, bolts, pins, hooks and threads, carbon steel sheets, metal bars, etc. of important types of mechanical parts structures.
Brand: Example 45, 65Mn, 08F.
Note on grades: It directly indicates the ten thousand percent of the carbon content of the metal.
Application: Non-alloy carbon steel sheets for manufacturing important mechanical parts are generally used after heat treatment.
Common carbon steel sheets numbers and uses:
08F, low mass fraction of carbon, good plasticity, low strength, used for stamping parts such as automobile and instrument housing;
20. Good plasticity and weldability, used for parts with low strength requirements and carburized parts, such as hoods, welding containers, small shafts, nuts, washers and carburized gears, etc.;
45, 40Mn, after quenching and tempering, the comprehensive mechanical properties are good, and it is used for mechanical parts with large force, such as gears, connecting rods, machine tool spindles, etc.;
60, 65Mn carbon steel sheet has high strength; used to manufacture various springs, locomotive wheel flanges, and low-speed wheels.
Grade: For example, T12 steel sheet means carbon tool steel sheet with Wc=1.2%.
Note for grades: T plus the thousandths of the carbon content of the metal.
Features: It belongs to eutectoid carbon steel sheet and hypereutectoid carbon steel sheets, with high strength, hardness and good wear resistance. It is suitable for manufacturing various low-speed cutting tools.
Common carbon steel sheets numbers and uses:
T7, T8: Make parts that withstand a certain impact and require toughness. Such as sledgehammers, punches, chisels, woodworking tools, scissors.
T9, T10, T11: Manufacturing tools that require high hardness and high wear resistance with low impact. Such as taps, small drills, dies, hand saw blades.
T12, T13: Make tools that are immune to impact. Such as files, scrapers, razors, measuring tools.
Brand: For example, ZG200-400, which means the cast carbon steel sheet with σs=200MPa and σb=400MPa.
Performance: The casting performance is worse than that of cast iron, but the mechanical properties are better than that of cast iron.
Application: It is mainly used to manufacture relatively important mechanical parts with complex shapes and high mechanical performance requirements, but it is difficult to form by forging and other methods in the process, such as gearbox casings of automobiles, couplers and couplings of locomotives and vehicles.
manganese
About 0.25%~0.80%. Solid solution strengthening; removing FeO, reducing the brittleness of the carbon steel sheet; synthesizing MnS with vulcanization, which can reduce the harmful effect of sulfur. beneficial.
silicon
It is about 0.10%~0.40%, solid solution strengthening; in addition to the adverse effect of FeO on the quality of the carbon steel sheet, it is beneficial.
sulfur
FeS and Fe form a low-melting eutectic (melting point is 985°C), which causes the carbon steel sheet to become brittle and crack during hot working at 1000~1250°C, which is called “hot brittleness”. harmful.
phosphorus
The strength and hardness are increased, but the plasticity and toughness are reduced, and it is “cold and brittle”. harmful.
Heat treatment is an important metal processing method, the purpose is to improve the performance of the carbon steel plate (use performance and process performance). The process characteristic of heat treatment of carbon steel plate is that the carbon steel plate is heated to a certain temperature, kept for a certain period of time, and then cooled at a certain cooling rate. Through this process, the properties of the steel plate are changed.
Quenching heat treatment is to heat the carbon steel sheets to 30-50°C above AC3 or AC1, and then put it into a different cooling medium for rapid cooling (the cooling rate is greater than the critical cooling rate) to obtain the martensitic structure (M). The microstructure after quenching is martensite and retained austenite.
1. Determination of quenching temperature
Depending on the material, find its critical temperature AC3 or AC1 in Table 1, and then add 40°C to get its heating temperature.
Hypo-eutectoid carbon steel sheets (45 carbon steel sheets, 30 carbon steel sheets):
Heating temperature = AC3 + 40°C
Hypereutectoid carbon steel sheets (T10 carbon steel sheets):
Heating temperature = AC1 + 40°C
So the heating temperature of the final 30 carbon steel sheets = °C + 40°C=
45 Heating temperature of carbon steel sheets = °C + 40°C=
45 Heating temperature of carbon steel sheets = °C + 40°C=
2. Determination of holding time
After the parts are heated to the required heating temperature with the furnace, they should be kept for a period of time to ensure that the entire part reaches the required temperature evenly and fully. Obviously the holding time is related to the size and shape of the workpiece.
Calculate the holding time of the test piece by measuring the size of the part and then looking up Table2.
The size of the part is a cylindrical part with a diameter of 20 mm, so the holding time of 30 carbon steel plate, 45 carbon steel sheets and T10 carbon steel sheets are:
3.Selection of cooling medium
Cooling is a key process in quenching. It directly affects the properties of the quenched steel plate. The cooling rate of quenching should be greater than the critical cooling rate to obtain the supercooled martensite structure. At the same time, in the cooling process, it is necessary to control the generation of internal stress during the crystallization process to prevent deformation and cracking.
In order to ensure the quenching effect, appropriate cooling medium and cooling method should be selected. In this experiment, we choose water at room temperature as the cooling medium.
4. Put the workpiece into the furnace, set the heating control temperature of the electric furnace temperature controller, and start heating.
5. After the electric furnace reaches the set temperature, the time of keeping warm starts.
6. The workpiece is out of the oven and quickly put into water to cool.
The martensitic structure of the carbon steel sheets after quenching is hard and brittle, and there is a large internal stress inside the workpiece. The purpose of tempering is to eliminate internal stress, appropriately reduce hardness and improve processability. According to different process requirements, tempering is divided into three process methods: high temperature tempering, medium temperature tempering and low temperature tempering.
The cooling method of tempering is air cooling, that is, the workpiece is slowly cooled at room temperature after being released from the furnace.
1. Put the workpiece into the furnace, set the heating control temperature of the electric furnace temperature controller, and start heating;
2. After the electric furnace reaches the set temperature, the timing of the heat preservation starts, and the heat preservation time is 30 minutes;
3. The workpiece is released from the oven and slowly cooled at room temperature.
(1)The output reached the highest level in history. From January to June 2013, the country produced a total of 390 million tons of crude carbon steel plates, a year-on-year increase of 7.4% and an increase of 5.6 percentage points over the same period a year ago. In the first six months, the average daily output of crude carbon steel sheets was 2.154 million tons, equivalent to an annual output of 786 million tons of crude carbon steel sheets. Among them, it reached a record high of 2.208 million tons in February. Although it fell from March to June, it still remained at a high level of more than 2.1 million tons. From January to June, the output of crude carbon steel plates in Hebei and Jiangsu provinces increased by 6.8% and 13.2% year-on-year respectively. The total new output of the two provinces accounted for 42.4% of the national increase of 26.94 million tons. Provinces such as Henan and Yunnan also increased production by more than 1 million tons. In terms of enterprise types, from January to June, the crude carbon steel plate output of key large and medium-sized iron and steel enterprises increased by 5.5% year-on-year, which was 2 percentage points lower than the national average. However, 60% of the increase in production came from key large and medium-sized iron and steel enterprises.
(2)The price of steel plate is running at a low level. From January to June 2013, the overall performance of the domestic steel plate market was sluggish. With the substantial release of crude carbon steel plate production capacity, the market supply and demand has fallen into an imbalance, and the price of carbon steel plates has entered a downward channel, which has been in a weak decline for more than 4 months. As of July 26, 2013, the carbon steel plate price index dropped to 100.48 points, which was lower than 6.6 points at the beginning of the year. The prices of the eight types of carbon steel plates that were counted by the carbon steel plate Industry Association decreased to varying degrees compared with the beginning of the year, with an average drop of 5.7%. In terms of varieties, the prices of construction wire rods and threaded carbon steel plates, which account for a large proportion of my country’s carbon steel plate production, fell by 4.9% and 6.7%, respectively, and the prices of medium and heavy plates and hot-rolled coils fell by 5.7% and 9.7%, respectively.
(3) The export of carbon steel plates has grown rapidly. The imbalance of supply and demand in the domestic carbon steel plate market stimulates the export of enterprises. From January to June, my country exported a total of 30.69 million tons of steel plates, a year-on-year increase of 12.6%; imported steel plates of 6.83 million tons, a decrease of 1.8%, and imported steel billets and ingots of 320,000 tons, an increase of 50%. Converting billets into crude carbon steel plates, the cumulative net export was 25.06 million tons, a year-on-year increase of 17.3%, accounting for 6.4% of my country’s crude carbon steel plate output. In terms of export prices, the average export price of bars and wires from January to June was US$624.3/ton, down 18% year-on-year; plates were US$835.2/ton, down 2.8% year-on-year.
(4) carbon steel plate plants and social inventories are operating at a high level. The contradiction between market supply and demand spread to the circulation field, and the domestic carbon steel plate inventory continued to increase at the end of the previous year. On March 15, it reached a record high of 22.52 million tons, an increase of 3.51 million tons over the previous year’s highest point, of which construction steel plate inventory was 14.32 million tons, accounting for 63.6% of the total inventory. After that, as seasonal consumption increased, inventories gradually fell, falling to 15.4 million tons on July 26. The oversupply in the market has also pushed up the inventory of carbon steel plate factories. In mid-March, the inventory of carbon steel plates in key enterprises hit a record, reaching 14.51 million tons, a year-on-year increase of 29.7%. In the same period in 2012, it increased by 11.4%.
(5) The profit level of carbon steel plate mills has been declining month by month. In the first half of 2013, the metallurgical industry realized a profit of 73.69 billion yuan, a year-on-year increase of 13.7%, of which the ferrous metal smelting and rolling processing industry realized a profit of 45.44 billion yuan, a year-on-year increase of 22.7%. From January to May, the profitability of key large and medium-sized steel and iron enterprises was far below the overall level of the industry, and showed a downward trend month by month. Although the profit increased by 34%, it was only 2.8 billion yuan, and the sales profit margin was 0.19%. In the month of May, 86 key large and medium-sized steel and iron enterprises only achieved a profit of 150 million yuan, a month-on-month decline for 5 consecutive months, of which 34 suffered losses, with a loss of 40%.
(6) The growth rate of investment in fixed assets in the steel and iron industry dropped significantly. From January to June 2013, the investment in fixed assets of the steel and iron industry was 303.5 billion yuan, a year-on-year increase of 4.3%, of which the investment in ferrous metal smelting and rolling was 235.6 billion yuan, a year-on-year increase of 3.3%, a decrease of 6.1 percentage points compared with the same period in 2012; The investment in mining and selection was 67.9 billion yuan, a year-on-year increase of 7.8%, and the growth rate dropped sharply by 15 percentage points.
